Hub-and-spoke configurations

This section describes how to set up hub-and-spoke IPsec VPNs. The following topics are included in this section:

Configuration overview

Configure the hub

Configure the spokes

Dynamic spokes configuration example

Configuration overview

In a hub-and-spoke configuration, VPN connections radiate from a central FortiGate unit (the hub) to a number of remote peers (the spokes). Traffic can pass between private networks behind the hub and private networks behind the remote peers. Traffic can also pass between remote peer private networks through the hub.

Example hub-and-spoke configuration

The actual implementation varies in complexity depending on:

 

Configuration overview

• Whether the spokes are statically or dynamically addressed
• The addressing scheme of the protected subnets
• How peers are authenticated

This guide discusses the issues involved in configuring a hub-and-spoke VPN and provides some basic configuration examples.

Hub-and-spoke infrastructure requirements

• The FortiGate hub must be operating in NAT mode and have a static public IP address.
• Spokes may have static IP addresses, dynamic IP addresses (see FortiGate dialup-client configurations on page 1), or static domain names and dynamic IP addresses (see Dynamic DNS configuration on page 1).

Spoke gateway addressing

The public IP address of the spoke is the VPN remote gateway as seen from the hub. Statically addressed spokes each require a separate VPN Phase 1 configuration on the hub. When there are many spokes, this becomes rather cumbersome.

Using dynamic addressing for spokes simplifies the VPN configuration because then the hub requires only a single Phase 1 configuration with “dialup user” as the remote gateway. You can use this configuration even if the remote peers have static IP addresses. A remote peer can establish a VPN connection regardless of its IP address if its traffic selectors match and it can authenticate to the hub. See Configuration overview on page 100 for an example of this configuration.

Protected networks addressing

The addresses of the protected networks are needed to configure destination selectors and sometimes for security policies and static routes. The larger the number of spokes, the more addresses there are to manage. You can

• Assign spoke subnets as part of a larger subnet, usually on a new network or
• Create address groups that contain all of the needed addresses

Using aggregated subnets

If you are creating a new network, where subnet IP addresses are not already assigned, you can simplify the VPN configuration by assigning spoke subnets that are part of a large subnet.

Aggregated subnets

All spokes use the large subnet address, 10.1.0.0/16 for example, as:

• The IPsec destination selector
• The destination of the security policy from the private subnet to the VPN (required for policy-based VPN, optional for route-based VPN)
• The destination of the static route to the VPN (route-based)

Each spoke uses the address of its own protected subnet as the IPsec source selector and as the source address in its VPN security policy. The remote gateway is the public IP address of the hub FortiGate unit.

Using an address group

If you want to create a hub-and-spoke VPN between existing private networks, the subnet addressing usually does not fit the aggregated subnet model discussed earlier. All of the spokes and the hub will need to include the addresses of all the protected networks in their configuration.

On FortiGate units, you can define a named firewall address for each of the remote protected networks and add these addresses to a firewall address group. For a policy-based VPN, you can then use this address group as the destination of the VPN security policy.

For a route-based VPN, the destination of the VPN security policy can be set to All. You need to specify appropriate routes for each of the remote subnets.

Authentication

Authentication is by a common pre-shared key or by certificates. For simplicity, the examples in this chapter assume that all spokes use the same pre-shared key.

Configure the hub

At the FortiGate unit that acts as the hub, you need to:

hub

• Configure the VPN to each spoke
• Configure communication between spokes

You configure communication between spokes differently for a policy-based VPN than for a route-based VPN. For a policy-based VPN, you configure a VPN concentrator. For a route-based VPN, you must either define security policies or group the IPsec interfaces into a zone.

Define the hub-spoke VPNs

Perform these steps at the FortiGate unit that will act as the hub. Although this procedure assumes that the spokes are all FortiGate units, a spoke could also be VPN client software, such as FortiClient Endpoint Security.

Configuring the VPN hub

1. At the hub, define the Phase 1 configuration for each spoke. See Phase 1 parameters on page 52. Enter these settings in particular:

Name	Enter a name to identify the VPN in Phase 2 configurations, security policies and the VPN monitor.
Remote Gateway	The remote gateway is the other end of the VPN tunnel. There are three options: Static IP Address  — Enter the spoke’s public IP Address. You will need to create a Phase 1 configuration for each spoke. Either the hub or the spoke can establish the VPN connection. Dialup User — No additional information is needed. The hub accepts connections from peers with appropriate encryption and authentication settings. Only one Phase 1 configuration is needed for multiple dialup spokes. Only the spoke can establish the VPN tunnel. Dynamic DNS — If the spoke subscribes to a dynamic DNS service, enter the spoke’s Dynamic DNS domain name. Either the hub or the spoke can establish the VPN connection. For more information, see Dynamic DNS configuration on page 1.
Local Interface	Select the FortiGate interface that connects to the remote gateway. This is usually the FortiGate unit’s public interface.

2. Define the Phase 2 parameters needed to create a VPN tunnel with each spoke. See Phase 2 parameters on page
3. 72. Enter these settings in particular:

Name	Enter a name to identify this spoke Phase 2 configuration.
Phase 1	Select the name of the Phase 1 configuration that you defined for this spoke.

IPsec VPN in ADVPN hub-and-spoke

IPsec VPN traffic is allowed through a tunnel between an ADVPN hub-and-spoke.

CLI Syntax:

config vpn ipsec phase1-interface edit “int-fgtb” … set auto-discovery-sender [enable | disable] set auto-discovery-receiver [enable | disable] set auto-discovery-forwarder [enable | disable] …

next

end

config vpn ipsec phase2-interface edit “int-fgtb” …

set auto-discovery-sender phase1 [enable | disable] …

next

end

Define the hub-spoke security policies

1. Define a name for the address of the private network behind the hub. For more information, see Defining policy addresses on page 1.
2. Define names for the addresses or address ranges of the private networks behind the spokes. For more information, see Defining policy addresses on page 1.
3. Define the VPN concentrator. See To define the VPN concentrator on page 105.
4. Define security policies to permit communication between the hub and the spokes. For more information, see Defining VPN security policies on page 1.

Route-based VPN security policies

Define ACCEPT security policies to permit communications between the hub and the spoke. You need one policy for each direction.

Adding policies

1. Go to Policy & Objects > IPv4 Policy and select Create New.
2. Leave the Policy Type as Firewall and leave the Policy Subtype as Address.
3. Enter these settings in particular:

Incoming Interface	Select the VPN Tunnel (IPsec Interface) you configured in Step 1.
Source Address	Select the address name you defined in Step 2 for the private network behind the spoke FortiGate unit.
Outgoing Interface	Select the hub’s interface to the internal (private) network.
Destination Address	Select the source address that you defined in Step 1.
Action	Select ACCEPT.
Enable NAT	Enable.

 

hub

Incoming Interface	Select the VPN Tunnel (IPsec Interface) you configured inStep 1.
Source Address	Select the address name you defined in Step 2 for the private network behind the spoke FortiGate units.
Outgoing Interface	Select the source address that you defined in Step 1.
Destination Address	Select the hub’s interface to the internal (private) network.
Action	Select ACCEPT.
Enable NAT	Enable.

Policy-based VPN security policy

Define an IPsec security policy to permit communications between the hub and the spoke.

Adding policies

1. Go to Policy & Objects > IPv4 Policy and select Create New.
2. Enter these settings in particular:

Incoming Interface	Select the hub’s interface to the internal (private) network.
Source Address	Select the source address that you defined in Step 1.
Outgoing Interface	Select the hub’s public network interface.
Destination Address	Select the address name you defined in Step 2 for the private network behind the spoke FortiGate unit.
VPN Tunnel	Select Use Existing and select the name of the Phase 1 configuration that you created for the spoke in Step 1. Select Allow traffic to be initiated from the remote site to enable traffic from the remote network to initiate the tunnel.

In the policy list, arrange the policies in the following order:

l IPsec policies that control traffic between the hub and the spokes first  l The default security policy last

Configuring communication between spokes (policy-based VPN)

For a policy-based hub-and-spoke VPN, you define a concentrator to enable communication between the spokes.

To define the VPN concentrator

1. At the hub, go to VPN > IPsec Concentrator and select Create New.
2. In the Concentrator Name field, type a name to identify the concentrator.
3. From the Available Tunnels list, select a VPN tunnel and then select the right-pointing arrow.
4. Repeat Step 3 until all of the tunnels associated with the spokes are included in the concentrator.
5. Select OK.

Configuring communication between spokes (route-based VPN)

For a route-based hub-and-spoke VPN, there are several ways you can enable communication between the spokes:

• Put all of the IPsec interfaces into a zone and enable intra-zone traffic. This eliminates the need for any security policy for the VPN, but you cannot apply UTM features to scan the traffic for security threats.
• Put all of the IPsec interfaces into a zone and create a single zone-to-zone security policy
• Create a security policy for each pair of spokes that are allowed to communicate with each other. The number of policies required increases rapidly as the number of spokes increases.

Using a zone as a concentrator

A simple way to provide communication among all of the spokes is to create a zone and allow intra-zone communication. You cannot apply UTM features using this method.

1. Go to Network > Interfaces.
2. Select the down-arrow on the Create New button and select Zone.
3. In the Zone Name field, enter a name, such as Our_VPN_zone.
4. Clear Block intra-zone traffic.
5. In the Interface Members list, select the IPsec interfaces that are part of your VPN.
6. Select OK.

Using a zone with a policy as a concentrator

If you put all of the hub IPsec interfaces involved in the VPN into a zone, you can enable communication among all of the spokes and apply UTM features with just one security policy.

Creating a zone for the VPN

1. Go to Network > Interfaces.
2. Select the down-arrow on the Create New button and select Zone.
3. In the Zone Name field, enter a name, such as Our_VPN_zone.
4. Select Block intra-zone traffic.
5. In the Interface Members list, select the IPsec interfaces that are part of your VPN.
6. Select OK.

Creating a security policy for the zone

1. Go to Policy & Objects > IPv4 Policy and select Create New.
2. Leave the Policy Type as Firewall and leave the Policy Subtype as Address.
3. Enter the settings: and select OK.

Incoming Interface

Select the zone you created for your VPN.

spokes

Source Address	Select All.
Outgoing Interface	Select the zone you created for your VPN.
Destination Address	Select All.
Action	Select ACCEPT.
Enable NAT	Enable.

Using security policies as a concentrator

To enable communication between two spokes, you need to define an ACCEPT security policy for them. To allow either spoke to initiate communication, you must create a policy for each direction. This procedure describes a security policy for communication from Spoke 1 to Spoke 2. Others are similar.

1. Define names for the addresses or address ranges of the private networks behind each spoke. For more information, see Defining policy addresses on page 1.
2. Go to Policy & Objects > IPv4 Policy and select Create New.
3. Leave the Policy Type as Firewall and leave the Policy Subtype as Address.
4. Enter the settings and select OK.

Incoming Interface	Select the IPsec interface that connects to Spoke 1.
Source Address	Select the address of the private network behind Spoke 1.
Outgoing Interface	Select the IPsec interface that connects to Spoke 2.
Destination Address	Select the address of the private network behind Spoke 2.
Action	Select ACCEPT.
Enable NAT	Enable.

Configure the spokes

Although this procedure assumes that the spokes are all FortiGate units, a spoke could also be VPN client software, such as FortiClient Endpoint Security.

Perform these steps at each FortiGate unit that will act as a spoke.

Creating the Phase 1 and phase_2 configurations

1. At the spoke, define the Phase 1 parameters that the spoke will use to establish a secure connection with the hub. See Phase 1 parameters on page 52. Enter these settings:

Remote Gateway	Select Static IP Address.
IP Address	Type the IP address of the interface that connects to the hub.

 

Configure the spokes

2. Create the Phase 2 tunnel definition. See Phase 2 parameters on page 72. Select the set of Phase 1 parameters that you defined for the hub. You can select the name of the hub from the Static IP Address part of the list.

Configuring security policies for hub-to-spoke communication

1. Create an address for this spoke. See Defining policy addresses on page 1. Enter the IP address and netmask of the private network behind the spoke.
2. Create an address to represent the hub. See Defining policy addresses on page 1. Enter the IP address and netmask of the private network behind the hub.
3. Define the security policy to enable communication with the hub.

Route-based VPN security policy

Define two security policies to permit communications to and from the hub.

1. Go to Policy & Objects > IPv4 Policy and select Create New.
2. Leave the Policy Type as Firewall and leave the Policy Subtype as Address.
3. Enter these settings:

Incoming Interface	Select the virtual IPsec interface you created.
Source Address	Select the hub address you defined in Step 1.
Outgoing Interface	Select the spoke’s interface to the internal (private) network.
Destination Address	Select the spoke addresses you defined in Step 2.
Action	Select ACCEPT.
Enable NAT	Enable

 

Incoming Interface	Select the spoke’s interface to the internal (private) network.
Source Address	Select the spoke address you defined in Step 1.
Outgoing Interface	Select the virtual IPsec interface you created.
Destination Address	Select the hub destination addresses you defined in Step 2.
Action	Select ACCEPT.
Enable NAT	Enable

Policy-based VPN security policy

Define an IPsec security policy to permit communications with the hub. See Defining VPN security policies on page 1.

1. Go to Policy & Objects > IPv4 Policy and select Create New.
2. Enter these settings in particular:

spokes

Incoming Interface	Select the spoke’s interface to the internal (private) network.
Source Address	Select the spoke address you defined in Step 1.
Outgoing Interface	Select the spoke’s interface to the external (public) network.
Destination Address	Select the hub address you defined in Step 2.
VPN Tunnel	Select Use Existing and select the name of the Phase 1 configuration you defined. Select Allow traffic to be initiated from the remote site to enable traffic from the remote network to initiate the tunnel.

Configuring security policies for spoke-to-spoke communication

Each spoke requires security policies to enable communication with the other spokes. Instead of creating separate security policies for each spoke, you can create an address group that contains the addresses of the networks behind the other spokes. The security policy then applies to all of the spokes in the group.

1. Define destination addresses to represent the networks behind each of the other spokes. Add these addresses to an address group.
2. Define the security policy to enable communication between this spoke and the spokes in the address group you created.

Policy-based VPN security policy

Define an IPsec security policy to permit communications with the other spokes. See Defining VPN security policies on page 1. Enter these settings in particular:

Route-based VPN security policy

Define two security policies to permit communications to and from the other spokes.

1. Go to Policy & Objects > IPv4 Policy and select Create New.
2. Leave the Policy Type as Firewall and leave the Policy Subtype as Address. Enter these settings in particular:

Incoming Interface	Select the virtual IPsec interface you created.
Source Address	Select the spoke address group you defined in Step “Configure the spokes ” on page 107.
Outgoing Interface	Select the spoke’s interface to the internal (private) network.
Destination Address	Select this spoke’s address name.
Action	Select ACCEPT.
Enable NAT	Enable

4. Select Create New, leave the Policy Type as Firewall and leave the Policy Subtype as Address, and enter these settings:

Incoming Interface	Select the spoke’s interface to the internal (private) network.
Source Address	Select this spoke’s address name.
Outgoing Interface	Select the virtual IPsec interface you created.
Destination Address	Select the spoke address group you defined in Step 1.
Action	Select ACCEPT.
Enable NAT	Enable

Policy-based VPN security policy

1. Go to Policy & Objects > IPv4 Policy and select Create New.
2. Enter the following:

Incoming Interface	Select this spoke’s internal (private) network interface.
Source Address	Select this spoke’s source address.
Outgoing Interface	Select the spoke’s interface to the external (public) network.
Destination Address	Select the spoke address group you defined in Step 1.
VPN Tunnel	Select Use Existing and select the name of the Phase 1 configuration you defined. Select Allow traffic to be initiated from the remote site to enable traffic from the remote network to initiate the tunnel.

Place this policy or policies in the policy list above any other policies having similar source and destination addresses.

Dynamic spokes configuration example

This example demonstrates how to set up a basic route-based hub-and-spoke IPsec VPN that uses preshared keys to authenticate VPN peers.

 

Example hub-and-spoke configuration

In the example configuration, the protected networks 10.1.0.0/24, 10.1.1.0/24 and 10.1.2.0/24 are all part of the larger subnet 10.1.0.0/16. The steps for setting up the example hub-and-spoke configuration create a VPN among Site 1, Site 2, and the HR Network.

The spokes are dialup. Their addresses are not part of the configuration on the hub, so only one spoke definition is required no matter the number of spokes. For simplicity, only two spokes are shown.

In an ADVPN topology, any two pair of peers can create a shortcut, as long as one of the devices is not behind NAT.

The on-the-wire format of the ADVPN messages  use TLV encoding.  Because of this, this feature is not compatible with any previous ADVPN builds.

Configure the hub (FortiGate_1)

The Phase 1 configuration defines the parameters that FortiGate_1 will use to authenticate spokes and establish secure connections.

For the purposes of this example, one preshared key will be used to authenticate all of the spokes. Each key must contain at least 6 printable characters and best practices dictates that it only be known by network administrators. For optimum protection against currently known attacks, each key must consist of a minimum of 16 randomly chosen alphanumeric characters.

Define the IPsec configuration

1. At FortiGate_1, go to VPN > IPsec Tunnels and create the new custom tunnel or edit an existing tunnel.
2. Edit the Phase 1 Proposal (if it is not available, you may need to click the Convert to Custom Tunnel button).

Define the Phase 1 parameters that the hub will use to establish a secure connection to the spokes.

Name	Enter a name (for example, toSpokes).
Remote Gateway	Dialup user
Local Interface	External
Mode	Main
Authentication Method	Preshared Key
Pre-shared Key	Enter the preshared key.
Peer Options	Any peer ID

The basic Phase 2 settings associate IPsec Phase 2 parameters with the Phase 1 configuration and specify the remote end points of the VPN tunnels.

3. Open the Phase 2 Selectors panel (if it is not available, you may need to click the Convert to Custom Tunnel button).
4. Enter the following information, and select OK:

Name	Enter a name for the Phase 2 definition (for example, toSpokes_ph2).
Phase 1	Select the Phase 1 configuration that you defined previously (for example, toSpokes).

Define the security policies

security policies control all IP traffic passing between a source address and a destination address. For a routebased VPN, the policies are simpler than for a policy-based VPN. Instead of an IPSEC policy, you use an ACCEPT policy with the virtual IPsec interface as the external interface.

Before you define security policies, you must first define firewall addresses to use in those policies. You need addresses for:

• The HR network behind FortiGate_1
• The aggregate subnet address for the protected networks

Defining the IP address of the HR network behind FortiGate_1

1. Go to Policy & Objects > Addresses.
2. Select Create New, enter the following information, and select OK:

	Name		Enter an address name (for example, HR_Network).
	Type		Subnet
Subnet/IP Range				Enter the IP address of the HR network behind FortiGate_1 (for example, 10.1.0.0/24).

Specifying the IP address the aggregate protected subnet

1. Go to Policy & Objects > Addresses.
2. Select Create New, enter the following information, and select OK:

Address Name	Enter an address name (for example, Spoke_net).
Type	Subnet
Subnet/IP Range	Enter the IP address of the aggregate protected network, 10.1.0.0/16

Defining the security policy for traffic from the hub to the spokes  1. Go to Policy & Objects > IPv4 Policy and select Create New,

2. Leave the Policy Type as Firewall and leave the Policy Subtype as Address. 3. Enter the following information, and select OK:

Incoming Interface	Select the interface to the HR network, port 1.
Source Address	Select HR_Network.
Outgoing Interface	Select the virtual IPsec interface that connects to the spokes, toSpokes.
Destination Address	Select Spoke_net.
Action	Select ACCEPT.

Place the policy in the policy list above any other policies having similar source and destination addresses.

Configure communication between spokes

Spokes communicate with each other through the hub. You need to configure the hub to allow this

communication. An easy way to do this is to create a zone containing the virtual IPsec interfaces even if there is only one, and create a zone-to-zone security policy.

1. Go to Network > Interfaces.
2. Select the down-arrow on the Create New button and select Zone.
3. In the Zone Name field, enter a name, such as Our_VPN_zone.
4. Select Block intra-zone traffic.

You could enable intra-zone traffic and then you would not need to create a security policy. But, you would not be able to apply UTM features.

5. In Interface Members, select the virtual IPsec interface, toSpokes.
6. Select OK.

Creating a security policy for the zone

1. Go to Policy & Objects > IPv4 Policy and select Create New.
2. Leave the Policy Type as Firewall and leave the Policy Subtype as Address.
3. Enter these settings:

Incoming Interface	Select Our_VPN_zone.
Source Address	Select All.
Outgoing Interface	Select Our_VPN_zone.
Destination Address	Select All.
Action	Select ACCEPT.
Enable NAT	Enable.

4. Select OK.

Configure the spokes

In this example, all spokes have nearly identical configuration, requiring the following:

• Phase 1 authentication parameters to initiate a connection with the hub.
• Phase 2 tunnel creation parameters to establish a VPN tunnel with the hub.
• A source address that represents the network behind the spoke. This is the only part of the configuration that is different for each spoke.
• A destination address that represents the aggregate protected network.
• A security policy to ena.ble communications between the spoke and the aggregate protected network Define the IPsec configuration

At each spoke, create the following configuration.

1. At the spoke, go to VPN > IPsec Tunnels and create the new custom tunnel or edit an existing tunnel.
2. Edit the Phase 1 Proposal (if it is not available, you may need to click the Convert to Custom Tunnel button). Enter the following information:

Name	Type a name, for example, toHub.
Remote Gateway	Select Static IP Address.
IP Address	Enter 172.16.10.1.
Local Interface	Select Port2.
Mode	Main
Authentication Method	Preshared Key
Pre-shared Key	Enter the preshared key. The value must be identical to the preshared key that you specified previously in the FortiGate_1 configuration
Peer Options	Select Any peer ID.

1. Open the Phase 2 Selectors panel (if it is not available, you may need to click the Convert to Custom Tunnel button).
2. Enter the following information and select OK:

Name	Enter a name for the tunnel, for example, toHub_ph2.
Phase 1	Select the name of the Phase 1 configuration that you defined previously, for example, toHub.
Advanced	Select to show the following Quick Mode Selector settings.
Source	Enter the address of the protected network at this spoke. For spoke_1, this is 10.1.1.0/24. For spoke_2, this is 10.1.2.0/24.
Destination	Enter the aggregate protected subnet address, 10.1.0.0/16.

Define the security policies

You need to define firewall addresses for the spokes and the aggregate protected network and then create a security policy to enable communication between them.

Defining the IP address of the network behind the spoke

1. Go to Policy & Objects > Addresses.
2. Select Create New and enter the following information:

Address Name	Enter an address name, for example LocalNet.
Type	Subnet
Subnet/IP Range	Enter the IP address of the private network behind the spoke. For spoke_1, this is 10.1.1.0/24. For spoke_2, this is 10.1.2.0/24.

Specifying the IP address of the aggregate protected network

1. Go to Policy & Objects > Addresses.
2. Select Create New and enter the following information:

Address Name	Enter an address name, for example,  Spoke_net.
Type	Subnet
Subnet/IP Range	Enter the IP address of the aggregate protected network, 10.1.0.0/16.

Defining the security policy

1. Go to Policy & Objects > IPv4 Policy and select Create New.
2. Leave the Policy Type as Firewall and leave the Policy Subtype as Address.
3. Enter the following information:

Incoming Interface	Select the virtual IPsec interface, toHub.
Source Address	Select the aggregate protected network address Spoke_net.
Outgoing Interface	Select the interface to the internal (private) network, port1.
Destination Address	Select the address for this spoke’s protected network LocalNet.
Action	Select ACCEPT.

4. Select Create New.
5. Leave the Policy Type as Firewall and leave the Policy Subtype as Address. Enter the following information, and select OK:

Incoming Interface	Select the interface to the internal private network, port1.
Source Address	Select the address for this spoke’s protected network, LocalNet.
Outgoing Interface	Select the virtual IPsec interface, toHub.
Destination Address	Select the aggregate protected network address, Spoke_net.
Action	Select ACCEPT.

Place these policies in the policy list above any other policies having similar source and destination addresses.

 

Gateway-to-gateway

This section explains how to set up a basic gateway-to-gateway (site-to-site) IPsec VPN.

The following topics are included in this section:

Configuration overview

Gateway-to-gateway configuration

How to work with overlapping subnets Testing

Configuration overview

In a gateway-to-gateway configuration, two FortiGate units create a VPN tunnel between two separate private networks. All traffic between the two networks is encrypted and protected by FortiGate security policies.

Example gateway-to-gateway configuration

In some cases, computers on the private network behind one VPN peer may (by co-incidence) have IP addresses that are already used by computers on the network behind the other VPN peer. In this type of situation

(ambiguous routing), conflicts may occur in one or both of the FortiGate routing tables and traffic destined for the remote network through the tunnel may not be sent. To resolve issues related to ambiguous routing, see Configuration overview on page 84.

Configuration overview

In other cases, computers on the private network behind one VPN peer may obtain IP addresses from a local DHCP server. However, unless the local and remote networks use different private network address spaces, unintended ambiguous routing and/or IP-address overlap issues may arise. For a discussion of the related issues, see FortiGate dialup-client configurations  on page 1.

Configuration overview

You can set up a fully meshed or partially meshed configuration (see below).

Fully meshed configuration

In a fully meshed network, all VPN peers are connected to each other, with one hop between peers. This topology is the most fault-tolerant: if one peer goes down, the rest of the network is not affected. This topology is difficult to scale because it requires connections between all peers. In addition, unnecessary communication can occur between peers. Best practices dictates a hub-and-spoke configuration instead (see Hub-and-spoke configurations on page 1).

 

Partially meshed configuration

A partially meshed network is similar to a fully meshed network, but instead of having tunnels between all peers, tunnels are only configured between peers that communicate with each other regularly.

Gateway-to-gateway configuration

The FortiGate units at both ends of the tunnel must be operating in NAT mode and have static public IP addresses.

When a FortiGate unit receives a connection request from a remote VPN peer, it uses IPsec Phase 1 parameters to establish a secure connection and authenticate that VPN peer. Then, if the security policy permits the connection, the FortiGate unit establishes the tunnel using IPsec Phase 2 parameters and applies the IPsec security policy. Key management, authentication, and security services are negotiated dynamically through the IKE protocol.

To support these functions, the following general configuration steps must be performed by both FortiGate units:

• Define the Phase 1 parameters that the FortiGate unit needs to authenticate the remote peer and establish a secure connection.
• Define the Phase 2 parameters that the FortiGate unit needs to create a VPN tunnel with the remote peer.
• Create security policies to control the permitted services and permitted direction of traffic between the IP source and destination addresses.

Gateway-to-gateway configuration

Configuring Phase 1 and Phase 2 for both peers

This procedure applies to both peers. Repeat the procedure on each FortiGate unit, using the correct IP address for each. You may wish to vary the Phase 1 names but this is optional. Otherwise all steps are the same for each peer.

The Phase 1 configuration defines the parameters that FortiGate_1 will use to authenticate FortiGate_2 and establish a secure connection. For the purposes of this example, a preshared key will be used to authenticate FortiGate_2. The same preshared key must be specified at both FortiGate units. Before you define the Phase 1 parameters, you need to:

• Reserve a name for the remote gateway.
• Obtain the IP address of the public interface to the remote peer. l Reserve a unique value for the preshared key.

The key must contain at least 6 printable characters and best practices dictate that it only be known by network administrators. For optimum protection against currently known attacks, the key must have a minimum of 16 randomly chosen alphanumeric characters.

At the local FortiGate unit, define the Phase 1 configuration needed to establish a secure connection with the remote peer. See IPsec VPN in the web-based manager on page 38.

1. Go to VPN > IPsec Tunnels and create the new custom tunnel or edit an existing tunnel.
2. Edit the Phase 1 Proposal (if it is not available, you may need to click the Convert to Custom Tunnel button). Enter the following information, and select OK.

Name	Enter peer_1. A name to identify the VPN tunnel. This name appears in Phase 2 configurations, security policies and the VPN monitor.
Remote Gateway	Select Static IP Address.
IP Address	Enter 172.20.0.2 when configuring FortiGate_1. Enter 172.18.0.2 when configuring FortiGate_2. The IP address of the remote peer public interface.
Local Interface	Select wan1.

The basic Phase 2 settings associate IPsec Phase 2 parameters with the Phase 1 configuration and specify the remote end point of the VPN tunnel. Before you define the Phase 2 parameters, you need to reserve a name for the tunnel. See IPsec VPN in the web-based manager on page 38.

1. Open the Phase 2 Selectors panel (if it is not available, you may need to click the Convert to Custom Tunnel button).
2. Enter a Name of peer_1_p2.
3. Select peer_1 from the Phase 1 drop-down menu.

Creating security policies

Security policies control all IP traffic passing between a source address and a destination address.

An IPsec security policy is needed to allow the transmission of encrypted packets, specify the permitted direction of VPN traffic, and select the VPN tunnel that will be subject to the policy. A single policy is needed to control both inbound and outbound IP traffic through a VPN tunnel.

Before you define security policies, you must first specify the IP source and destination addresses. In a gatewayto-gateway configuration:

• The IP source address corresponds to the private network behind the local FortiGate unit. l The IP destination address refers to the private network behind the remote VPN peer.

When you are creating security policies, choose one of either route-based or policy-based methods and follow it for both VPN peers. DO NOT configure both route-based and policy-based policies on the same FortiGate unit for the same VPN tunnel.

The configuration of FortiGate_2 is similar to that of FortiGate_1. You must:

• Define the Phase 1 parameters that FortiGate_2 needs to authenticate FortiGate_1 and establish a secure connection.
• Define the Phase 2 parameters that FortiGate_2 needs to create a VPN tunnel with FortiGate_1.
• Create the security policy and define the scope of permitted services between the IP source and destination addresses.

When creating security policies it is good practice to include a comment describing what the policy does.

Creating firewall addresses

Define names for the addresses or address ranges of the private networks that the VPN links. These addresses are used in the security policies that permit communication between the networks.

To define the IP address of the network behind FortiGate_1

1. Go to Policy & Objects > Addresses and select Create New.
2. Enter the Name of Finance_network. Select a Type of Subnet.
3. Enter the Subnet of 21.101.0/24.
4. Select OK.

To specify the address of the network behind FortiGate_2

1. Go to Policy & Objects > Addresses and select Create New.
2. Enter the Name of HR_network.
3. Select a Type of Subnet.
4. Enter the Subnet/IP Range of 31.101.0/24. 5. Select OK.

Creating route-based VPN security policies

Define an ACCEPT security policy to permit communications between the source and destination addresses.

To create route-based VPN security policies  1. Go to Policy & Objects > IPv4 Policy and select Create New

2. Leave the Policy Type as Firewall and leave the Policy Subtype as Address.

Gateway-to-gateway configuration

3. Enter the following, and select OK.

Incoming Interface	Select internal. The interface that connects to the private network behind this FortiGate unit.
Source Address	Select Finance_network when configuring FortiGate_1. Select HR_network when configuring FortiGate_2. The address name for the private network behind this FortiGate unit.
Outgoing Interface	Select peer_1. The VPN Tunnel (IPsec Interface) you configured earlier.
Destination Address	Select HR_network when configuring FortiGate_1. Select Finance_network when configuring FortiGate_2. The address name that you defined for the private network behind the remote peer.
Action	Select ACCEPT.
Enable NAT	Disable.
Comments	Allow Internal to remote VPN network traffic.

4. Optionally, configure any additional features you may want, such as UTM or traffic shaping.
5. Select Create New to create another policy for the other direction.
6. Leave the Policy Type as Firewall and leave the Policy Subtype as Address.
7. Enter the following information, and select OK.

Incoming Interface	Select peer_1. The VPN Tunnel (IPsec Interface) you configured.
Source Address	Select HR_network when configuring FortiGate_1. Select Finance_Network when configuring FortiGate_2. The address name defined for the private network behind the remote peer.
Outgoing Interface	Select internal. The interface that connects to the private network behind this FortiGate unit.
Destination Address		Select Finance_Network when configuring FortiGate_1. Select HR_network when configuring FortiGate_2. The address name defined for the private network behind this FortiGate unit.
Action		Select ACCEPT.
Enable NAT		Disable.
Comments		Allow remote VPN network traffic to Internal.

8. Configure any additional features such as UTM or traffic shaping you may want. (optional).

All network traffic must have a static route to direct its traffic to the proper destination. Without a route, traffic will not flow even if the security policies are configured properly. You may need to create a static route entry for both directions of VPN traffic if your security policies allow bi-directional tunnel initiation.

To configure the route for a route-based VPN:

1. On FortiGate_2, go to Network > Static Routes and select Create New.
2. Enter the following information, and then select OK:

Destination IP / Mask	10.21.101.0/24
Device	FGT2_to_FGT1_Tunnel
Gateway	Leave as default: 0.0.0.0.
Distance (Advanced)	Leave this at its default. If there are other routes on this FortiGate unit, you may need to set the distance on this route so the VPN traffic will use it as the default route. However, this normally happens by default because this route is typically a better match than the generic default route.

Creating policy-based VPN security policy

Define an IPsec security policy to permit communications between the source and destination addresses.

1. Go to Policy & Objects > IPv4 Policy.
2. Complete the following:

Incoming Interface

Select internal. The interface that connects to the private network behind this FortiGate unit.

 

Source Address	Select Finance_network when configuring FortiGate_1. Select HR_network when configuring FortiGate_2. The address name defined for the private network behind this FortiGate unit.
Outgoing Interface	Select wan1. The FortiGate unit’s public interface.
Destination Address	Select HR_network when configuring FortiGate_1. Select Finance_network when configuring FortiGate_2.
VPN Tunnel	Select Use Existing and select peer_1 from the VPN Tunnel drop-down list. Select Allow traffic to be initiated from the remote site to enable traffic from the remote network to initiate the tunnel.
Comments	Bidirectional policy-based VPN policy.

Place VPN policies in the policy list above any other policies having similar source and destination addresses.

How to work with overlapping subnets

A site-to-site VPN configuration sometimes has the problem that the private subnet addresses at each end are the same. You can resolve this problem by remapping the private addresses using virtual IP addresses (VIP).

VIPs allow computers on those overlapping private subnets to each have another set of IP addresses that can be used without confusion. The FortiGate unit maps the VIP addresses to the original addresses. This means if PC1 starts a session with PC2 at 10.31.101.10, FortiGate_2 directs that session to 10.11.101.10 — the actual IP address of PC2.The figure below demonstrates this — Finance network VIP is 10.21.101.0/24 and the HR network is 10.31.101.0/24.

How to work with overlapping subnets

Overlapped subnets example

Solution for route-based VPN

You need to:

• Configure IPsec Phase 1 and Phase 2 as you usually would for a route-based VPN. In this example, the resulting IPsec interface is named FGT1_to_FGT2.
• Configure virtual IP (VIP) mapping:
• the 10.21.101.0/24 network mapped to the 10.11.101.0/24 network on FortiGate_1
• the 10.31.101.0/24 network mapped to the 10.11.101.0/24 network on FortiGate_2 l Configure an outgoing security policy with ordinary source NAT on both FortiGates.
• Configure an incoming security policy with the VIP as the destination on both FortiGates.
• Configure a route to the remote private network over the IPsec interface on both FortiGates.

To configure VIP mapping on both FortiGates

1. Go to Policy & Objects > Virtual IPs and create a new Virtual IP.
2. Enter the following information, and select OK:

	Name		Enter a name, for example, my_vip.
	External Interface		Select FGT1_to_FGT2. The IPsec interface.
VIP Type		Depending on both FortiGates, select one of the following options: l    IPv4: If both FortiGates use IPv4 (Static NAT). l    IPv6: If both FortiGates use IPv6 (Static NAT). l    NAT46: Maps the IPv4 address into an IPv6 prefix. l    NAT64: Maps the IPv6 address into an IPv4 prefix.
External IP Address/Range		For the External IP Address field enter: 10.21.101.1  when configuring FortiGate_1, or 10.31.101.1  when configuring FortiGate_2.
Mapped IP Address/Range		For the Mapped IP Address enter 10.11.101.1. For the Range enter 10.11.101.254.
Port Forwarding		Disable

3. Repeat this procedure on both FortiGate_1 and FortiGate_2.

To configure the outbound security policy on both FortiGates

1. Go to Policy & Objects > IPv4 Policy and select Create New.
2. Enter the following information, and select OK:

Incoming Interface	Select Port 1.
Outgoing Interface	Select FGT1_to_FGT2. The IPsec interface.
Source	Select all.
Destination Address	Select all.
Action	Select ACCEPT
NAT	Enable NAT.

3. Repeat this procedure on both FortiGate_1 and FortiGate_2.

To configure the inbound security policy on both FortiGates

1. Go to Policy & Objects > IPv4 Policy and select Create New.
2. Enter the following information, and then select OK:

Incoming Interface

Select FGT1_to_FGT2.

How to work with overlapping subnets

Outgoing Interface	Select Port 1. The IPsec interface.
Source	Select all.
Destination Address	Select my-vip.
Action	Select ACCEPT
NAT	Disable NAT.

3. Repeat this procedure on both FortiGate_1 and FortiGate_2.

To configure the static route for both FortiGates

1. Go to Network > Static Routes and create a new Route (or IPv6 Route as necessary).
2. Enter the following information, and then select OK:

Destination	Enter a subnet of 10.31.101.0/24 when configuring FortiGate_1. Enter a subnet of 10.21.101.0/24 when configuring FortiGate_2.
Device	Select FGT1_to_FGT2.
Gateway	Leave as default: 0.0.0.0.
Administrative Distance	Leave at default (10). If you have advanced routing on your network, you may have to change this value.
Advanced Options	If you have advanced routing on your network, enable Advanced Options and enter a Priority.

Solution for policy-based VPN

As with the route-based solution, users contact hosts at the other end of the VPN using an alternate subnet address. PC1 communicates with PC2 using IP address 10.31.101.10, and PC2 communicates with PC1 using IP address 10.21.101.10.

In this solution however, outbound NAT is used to translate the source address of packets from the

10.11.101.0/24 network to the alternate subnet address that hosts at the other end of the VPN use to reply. Inbound packets from the remote end have their destination addresses translated back to the 10.11.101.0/24 network.

For example, PC1 uses the destination address 10.31.101.10 to contact PC2. Outbound NAT on FortiGate_1 translates the PC1 source address to 10.21.101.10. At the FortiGate_2 end of the tunnel, the outbound NAT configuration translates the destination address to the actual PC2 address of 10.11.101.10. Similarly, PC2 replies to PC1 using destination address 10.21.101.10, with the PC2 source address translated to 10.31.101.10. PC1 and PC2 can communicate over the VPN even though they both have the same IP address.

You need to:

• Configure IPsec Phase 1 as you usually would for a policy-based VPN. l Configure IPsec Phase 2 with the use-natip disable CLI option.  l Define a firewall address for the local private network, 10.11.101.0/24.
• Define a firewall address for the remote private network:
• Define a firewall address for 10.31.101.0/24 on FortiGate_1
• Define a firewall address for 10.21.101.0/24 on FortiGate_2
• Configure an outgoing IPsec security policy with outbound NAT to map 10.11.101.0/24 source addresses:
• To the 10.21.101.0/24 network on FortiGate_1
• To the 10.31.101.0/24 network on FortiGate_2

To configure IPsec Phase 2 – CLI

config vpn ipsec phase2 edit “FGT1_FGT2_p2” set keepalive enable set pfs enable set phase1name FGT1_to_FGT2 set proposal 3des-sha1 3des-md5 set replay enable set use-natip disable

end

In this example, your Phase 1 definition is named FGT1_to_FGT2. use-natip is set to disable, so you can specify the source selector using the src-addr-type, src-start-ip / src-end-ip or src-subnet keywords. This example leaves these keywords at their default values, which specify the subnet 0.0.0.0/0.

The pfs keyword ensures that perfect forward secrecy (PFS) is used. This ensures that each Phase 2 key created is unrelated to any other keys in use.

To define the local private network firewall address

1. Go to Policy & Objects > Addresses and create a new Address. 2. Enter the following information and select OK.

Category	Set to Address.
Name	Enter vpn-local. A meaningful name for the local private network.
Type	Set to IP/Netmask.
Subnet / IP Range	10.11.101.0 255.255.255.0
Interface	Set to any.

To define the remote private network firewall address

1. Go to Policy & Objects > Addresses and create a new Address.
2. Enter the following information, and select OK:

Category

Set to Address.

Testing

Name	Enter vpn-remote. A meaningful name for the remote private network.
Type	Set to IP/Netmask.
Subnet / IP Range	10.31.101.0 255.255.255.0 on FortiGate_1. 10.21.101.0 255.255.255.0 on FortiGate_2.
Interface	Any

To configure the IPsec security policy

In the CLI on FortiGate_1, enter the commands:

config firewall policy edit 1 set srcintf “port1” set dstintf “port2” set srcaddr “vpn-local” set dstaddr “vpn-remote” set action ipsec set schedule “always” set service “ANY” set inbound enable set outbound enable set vpntunnel “FGT1_to_FGT2” set natoutbound enable

set natip 10.31.101.0 255.255.255.0

end

Optionally, you can set everything except natip in the web-based manager and then use the CLI to set natip.

Enter the same commands on FortiGate_2, but set natip be 10.21.101.0 255.255.255.0.

Testing

The best testing is to look at the packets both as the VPN tunnel is negotiated, and when the tunnel is up.

Determining what the other end of the VPN tunnel is proposing

1. Start a terminal program such as PuTTY and set it to log all output.

When necessary refer to the logs to locate information when output is verbose.

2. Logon to the FortiGate unit using a super_admin account.
3. Enter the following CLI commands.
4. Display all the possible IKE error types and the number of times they have occurred:

 

diag vpn ike errors

 

5. Check for existing debug sessions:

 

diag debug info

 

 

Testing

If a debug session is running, to halt it enter:

diag debug disable

 

6. Confirm your proposal settings:

 

diag vpn ike config list

 

7. If your proposal settings do not match what you expect, make a change to it and save it to force an update in memory. If that fixes the problem, stop here.
8. List the current vpn filter:

 

diag vpn ike filter

 

9. If all fields are set to any, there are no filters set and all VPN IKE packets will be displayed in the debug output. If your system has only a few VPNs, skip setting the filter.

If your system has many VPN connections this will result in very verbose output and make it very difficult to locate the correct connection attempt.

10. Set the VPN filter to display only information from the destination IP address for example 10.10.10.10:

 

diag vpn ike log-filter dst-addr4 10.10.10.10

To add more filter options, enter them one per line as above. Other filter options are:

clear	erase the current filter
dst-addr6	the IPv6 destination address range to filter by
dst-port	the destination port range to filter by
interface	interface that IKE connection is negotiated over
list	display the current filter
name	the phase1 name to filter by
negate	negate the specified filter parameter
src-addr4	the IPv4 source address range to filter by
src-addr6	the IPv6 source address range to filter by
src-port	the source port range to filter by
vd	index of virtual domain. 0 matches all

11. Start debugging:

diag debug app ike 255 diag debug enable

 

12. Have the remote end attempt a VPN connection.

If the remote end attempts the connection they become the initiator. This situation makes it easier to debug VPN tunnels because then you have the remote information and all of your local information. by initiate the connection, Testing

you will not see the other end’s information.

13. If possible go to the web-based manager on your FortiGate unit, go to the VPN monitor and try to bring the tunnel up.
14. Stop the debug output:

 

diag debug disable

 

15. Go back through the output to determine what proposal information the initiator is using, and how it is different from your VPN P1 proposal settings.

Things to look for in the debug output of attempted VPN connections are shown below.

Important terms to look for in VPN debug output

initiator	Starts the VPN attempt, in the above procedure that is the remote end
responder	Answers the initiator’s request
local ID	In aggressive mode, this is not encrypted
error no SA proposal chosen	There was no proposal match — there was no encryption-authentication pair in common, usually occurs after a long list of proposal attempts
R U THERE and R U THERE ack	dead peer detection (dpd), also known as dead gateway detection — after three failed attempts to contact the remote end it will be declared dead, no farther attempts will be made to contact it
negotiation result	lists the proposal settings that were agreed on
SA_life_soft and SA_life_ hard	negotiating a new key, and the key life
R U THERE	If you see this, it means Phase 1 was successful
tunnel up	the negotiation was successful, the VPN tunnel is operational

Defining VPN security policies

This section explains how to specify the source and destination IP addresses of traffic transmitted through an IPsec VPN, and how to define appropriate security policies.

The following topics are included in this section:

Defining policy addresses

Defining security policies for policy-based and route-based VPNs

Defining policy addresses

A VPN tunnel has two end points. These end points may be VPN peers such as two FortiGate gateways. Encrypted packets are transmitted between the end points. At each end of the VPN tunnel, a VPN peer intercepts encrypted packets, decrypts the packets, and forwards the decrypted IP packets to the intended destination.

You need to define firewall addresses for the private networks behind each peer. You will use these addresses as the source or destination address depending on the security policy.

policy addresses

Example topology for the following policies

In general:

• In a gateway-to-gateway, hub-and-spoke, dynamic DNS, redundant-tunnel, or transparent configuration, you need to define a policy address for the private IP address of the network behind the remote VPN peer (for example,

192.168.10.0/255.255.255.0 or 192.168.10.0/24).

• In a peer-to-peer configuration, you need to define a policy address for the private IP address of a server or host behind the remote VPN peer (for example, 16.5.1/255.255.255.255 or 172.16.5.1/32 or 172.16.5.1).

For a FortiGate dialup server in a dialup-client or Internet-browsing configuration:

• If you are not using VIP addresses, or if the FortiGate dialup server assigns VIP addresses to FortiClient dialup clients through FortiGate DHCP relay, select the predefined destination address “all” in the security policy to refer to the dialup clients.
• If you assign VIP addresses to FortiClient dialup clients manually, you need to define a policy address for the VIP address assigned to the dialup client (for example, 254.254.1/32), or a subnet address from which the VIP addresses are assigned (for example, 10.254.254.0/24 or 10.254.254.0/255.255.255.0).
• For a FortiGate dialup client in a dialup-client or Internet-browsing configuration, you need to define a policy address for the private IP address of a host, server, or network behind the FortiGate dialup server.

VPN security policies                                  Defining security policies for policy-based and route-based VPNs

Defining a security IP address

1. Go to Policy & Objects > Addresses and select Create New.
2. In the Name field, type a descriptive name that represents the network, server(s), or host(s).
3. In Type, select Subnet.
4. In the Subnet/IP Range field, type the corresponding IP address and subnet mask.

For a subnet you could use the format 172.16.5.0/24 or its equivalent 172.16.5.0/255.255.255.0. For a server or host it would likely be 172.16.5.1/32. Alternately you can use an IP address range such as

192.168.10.[80-100] or 192.168.10.80-192.168.10.100.

5. Select OK.

Defining security policies for policy-based and route-based VPNs

Security policies allow IP traffic to pass between interfaces on a FortiGate unit. You can limit communication to particular traffic by specifying source address and destination addresses. Then only traffic from those addresses will be allowed.

Policy-based and route-based VPNs require different security policies.

• A policy-based VPN requires an IPsec security policy. You specify the interface to the private network, the interface to the remote peer and the VPN tunnel. A single policy can enable traffic inbound, outbound, or in both directions.
• A route-based VPN requires an Accept security policy for each direction. As source and destination interfaces, you specify the interface to the private network and the virtual IPsec interface (Phase 1 configuration) of the VPN. The IPsec interface is the destination interface for the outbound policy and the source interface for the inbound policy. One security policy must be configured for each direction of each VPN interface.

There are examples of security policies for both policy-based and route-based VPNs throughout this guide. See Route-based or policy-based VPN on page 119.

If the security policy, which grants the VPN Connection is limited to certain services,

DHCP must be included, otherwise the client won’t be able to retrieve a lease from the FortiGate’s (IPsec) DHCP server, because the DHCP Request (coming out of the tunnel) will be blocked.

Policy-based VPN

An IPsec security policy enables the transmission and reception of encrypted packets, specifies the permitted direction of VPN traffic, and selects the VPN tunnel. In most cases, a single policy is needed to control both inbound and outbound IP traffic through a VPN tunnel. Be aware of the following considerations below before creating an IPsec security policy.

Allow traffic to be initiated from the remote site

Security policies specify which IP addresses can initiate a tunnel. By default, traffic from the local private network initiates the tunnel. When the Allow traffic to be initiated form the remote site option is selected, traffic from a dialup client, or a computer on a remote network, initiates the tunnel. Both can be enabled at the same time for bi-directional initiation of the tunnel.

security policies for policy-based and route-based VPNs

Outbound and inbound NAT

When a FortiGate unit operates in NAT mode, you can also enable inbound or outbound NAT. Outbound NAT may be performed on outbound encrypted packets or IP packets in order to change their source address before they are sent through the tunnel. Inbound NAT is performed to intercept and decrypt emerging IP packets from the tunnel.

By default, these options are not selected in security policies and can only be set through the CLI. For more information on this, see the “config firewall” chapter of the FortiGate CLI Reference.

Source and destination addresses

Most security policies control outbound IP traffic. A VPN outbound policy usually has a source address originating on the private network behind the local FortiGate unit, and a destination address belonging to a dialup VPN client or a network behind the remote VPN peer. The source address that you choose for the security policy identifies from where outbound cleartext IP packets may originate, and also defines the local IP address or addresses that a remote server or client will be allowed to access through the VPN tunnel. The destination address that you choose identifies where IP packets must be forwarded after they are decrypted at the far end of the tunnel, and determines the IP address or addresses that the local network will be able to access at the far end of the tunnel.

Enabling other policy features

You can fine-tune a policy for services such as HTTP, FTP, and POP3, enable logging, traffic shaping, antivirus protection, web filtering, email filtering, file transfer, email services, and optionally allow connections according to a predefined schedule.

As an option, differentiated services (diffserv or DSCP) for the security policy can be enabled through the CLI. For more information on this feature, see the Traffic Shaping handbook chapter,  or the “firewall” chapter of the FortiGate CLI Reference.

Before you begin

Before you define the IPsec policy, you must:

• Define the IP source and destination addresses. See Defining policy addresses on page 78.
• Specify the Phase 1 authentication parameters. See Phase 1 parameters on page 52.
• Specify the Phase 2 parameters. See Phase 2 parameters on page 72.

Defining an IPsec security policy

1. Go to Policy & Objects > IPv4 Policy.
2. Select Create New and set the following options:

Name	Enter a name for the security policy.
Incoming Interface	Select the local interface to the internal (private) network.
Outgoing Interface	Select the local interface to the external (public) network.
Source	Select the name that corresponds to the local network, server(s), or host(s) from which IP packets may originate.

VPN security policies                                  Defining security policies for policy-based and route-based VPNs

Destination Address	Select the name that corresponds to the remote network, server(s), or host (s) to which IP packets may be delivered.
Schedule	Keep the default setting (always) unless changes are needed to meet specific requirements.
Service	Keep the default setting (ANY) unless changes are needed to meet your specific requirements.
Action	For the purpose of this configuration, set Action to IPsec. Doing this will close Firewall / Network Options and open VPN Tunnel options. Select the VPN tunnel of your choice, and select Allow traffic to be initiated from the remote site, which will allow traffic from the remote network to initiate the tunnel.

3. You may enable UTM features, and/or event logging, or select advanced settings to authenticate a user group, or shape traffic. For more information, see the Firewall handbook chapter.
4. Select OK.
5. Place the policy in the policy list above any other policies having similar source and destination addresses.

Defining multiple IPsec policies for the same tunnel

You must define at least one IPsec policy for each VPN tunnel. If the same remote server or client requires access to more than one network behind a local FortiGate unit, the FortiGate unit must be configured with an IPsec policy for each network. Multiple policies may be required to configure redundant connections to a remote destination or control access to different services at different times.

To ensure a secure connection, the FortiGate unit must evaluate policies with Action set to IPsec  before

ACCEPT and DENY. Because the FortiGate unit reads policies starting at the top of the list, you must move all IPsec policies to the top of the list, and be sure to  reorder your multiple IPsec policies that apply to the tunnel so that specific constraints can be evaluated before general constraints.

Adding multiple IPsec policies for the same VPN tunnel can cause conflicts if the policies specify similar source and destination addresses, but have different settings for the same service. When policies overlap in this manner, the system may apply the wrong IPsec policy or the tunnel may fail.

For example, if you create two equivalent IPsec policies for two different tunnels, it does not matter which one comes first in the list of IPsec policies — the system will select the correct policy based on the specified source and destination addresses. If you create two different IPsec policies for the same tunnel (that is, the two policies treat traffic differently depending on the nature of the connection request), you might have to reorder the IPsec policies to ensure that the system selects the correct IPsec policy.

Route-based VPN

When you define a route-based VPN, you create a virtual IPsec interface on the physical interface that connects to the remote peer. You create ordinary Accept security policies to enable traffic between the IPsec interface and the interface that connects to the private network. This makes configuration simpler than for policy-based VPNs, which require IPsec security policies.

security policies for policy-based and route-based VPNs

Defining security policies for a route-based VPN

1. Go to Policy & Objects > IPv4 Policy.
2. Select Create New and define an ACCEPT security policy to permit communication between the local private network and the private network behind the remote peer. Enter these settings in particular:

Name	Enter a name for the security policy.
Incoming Interface	Select the interface that connects to the private network behind this FortiGate unit.
Outgoing Interface	Select the IPsec Interface you configured.
Source	Select the address name that you defined for the private network behind this FortiGate unit.
Destination Address	Select the address name that you defined for the private network behind the remote peer.
Action	Select ACCEPT.
NAT	Disable NAT.

To permit the remote client to initiate communication, you need to define a security policy for communication in that direction.

3. Select Create New and enter these settings in particular:

Name		Enter a name for the security policy.
Incoming Interface		Select the IPsec Interface you configured.
Outgoing Interface		Select the interface that connects to the private network behind this FortiGate unit.
Source		Select the address name that you defined for the private network behind the remote peer.
Destination Address		Select the address name that you defined for the private network behind this FortiGate unit.
Action		Select ACCEPT.
NAT		Disable NAT.

 

Phase 2 parameters

This section describes the Phase 2 parameters that are required to establish communication through a VPN. The following topics are included in this section:

Phase 2 settings

Configuring the Phase 2 parameters

Phase 2 settings

After IPsec VPN Phase 1 negotiations complete successfully, Phase 2 negotiation begins. Phase 2 parameters define the algorithms that the FortiGate unit can use to encrypt and transfer data for the remainder of the session. The basic Phase 2 settings associate IPsec Phase 2 parameters with a Phase 1 configuration.

When defining Phase 2 parameters, you can choose any set of Phase 1 parameters to set up a secure connection and authenticate the remote peer.

For more information on Phase 2 settings in the web-based manager, see IPsec VPN in the web-based manager on page 38.

The information and procedures in this section do not apply to VPN peers that perform negotiations using manual keys.

Phase 2 Proposals

In Phase 2, the VPN peer or client and the FortiGate unit exchange keys again to establish a secure communication channel. The Phase 2 Proposal parameters select the encryption and authentication algorithms needed to generate keys for protecting the implementation details of Security Associations (SAs). The keys are generated automatically using a Diffie-Hellman algorithm.

Replay Detection

IPsec tunnels can be vulnerable to replay attacks. Replay Detection enables the FortiGate unit to check all IPsec packets to see if they have been received before. If any encrypted packets arrive out of order, the FortiGate unit discards them.

IKE/IPsec Extended Sequence Number (ESN) support

64-bit Extended Sequence numbers (as described in RFC 4303, RFC 4304 as an addition to IKEv1, and RFC 5996 for IKEv2.) are supported for IPsec when Replay Detection is enabled.

Perfect Forward Secrecy (PFS)

By default, Phase 2 keys are derived from the session key created in Phase 1. Perfect Forward Secrecy (PFS) forces a new Diffie-Hellman exchange when the tunnel starts and whenever the Phase 2 keylife expires, causing a new key to be generated each time. This exchange ensures that the keys created in Phase 2 are unrelated to the Phase 1 keys or any other keys generated automatically in Phase 2.

Phase 2 settings

Keylife

The Keylife setting sets a limit on the length of time that a Phase 2 key can be used. The default units are seconds. Alternatively, you can set a limit on the number of kilobytes (KB) of processed data, or both. If you select both, the key expires when either the time has passed or the number of KB have been processed. When the Phase 2 key expires, a new key is generated without interrupting service.

Quick mode selectors

Quick mode selectors determine which IP addresses can perform IKE negotiations to establish a tunnel. By only allowing authorized IP addresses access to the VPN tunnel, the network is more secure.

The default settings are as broad as possible: any IP address or configured address object, using any protocol, on any port.

While the drop down menus for specifying an address also show address groups, the use of address groups may not be supported on a remote endpoint device that is not a FortiGate.

The address groups are at the bottom of the list to make it easy to distinguish between addresses and address groups.

When configuring Quick Mode selector Source address and Destination address, valid options include IPv4 and IPv6 single addresses, IPv4 subnet, or IPv6 subnet. For more information on IPv6 IPsec VPN, see Overview of IPv6 IPsec support on page 1.

There are some configurations that require specific selectors:

• The VPN peer is a third-party device that uses specific phase2 selectors.
• The FortiGate unit connects as a dialup client to another FortiGate unit, in which case (usually) you must specify a source IP address, IP address range, or subnet. However, this is not required if you are using dynamic routing and mode-cfg.

With FortiOS VPNs, your network has multiple layers of security, with quick mode selectors being an important line of defence.

• Routes guide traffic from one IP address to another.
• Phase 1 and Phase 2 connection settings ensure there is a valid remote end point for the VPN tunnel that agrees on the encryption and parameters.
• Quick mode selectors allow IKE negotiations only for allowed peers. l Security policies control which IP addresses can connect to the VPN.
• Security policies also control what protocols are allowed over the VPN along with any bandwidth limiting.

FortiOS is limited with IKEv2 selector matching. When using IKEv2 with a named traffic selector, no more than 32 subnets per traffic selector are added, since FortiOS doesn’t fully implement the IKEv2 selector matching rules.

The workaround is to use multiple Phase 2s. If the configuration is FGT <-> FGT, then the better alternative is to just use 0.0.0.0 <-> 0.0.0.0 and use the firewall policy for enforcement.

Phase 2 parameters                                                                                          Configuring the

Using the add-route option

Consider using the add-route option to add a route to a peer destination selector. Phase 2 includes the option of allowing the add-route to automatically match the settings in Phase 1. For more information, refer to Phase 1 parameters on page 52.

Syntax

Phase 2

config vpn ipsec {phase2 | phase2-interface} edit <name> set add-route {phase1 | enable | disable}

end

end

Configuring the Phase 2 parameters

If you are creating a hub-and-spoke configuration or an Internet-browsing configuration, you may have already started defining some of the required Phase 2 parameters. If so, edit the existing definition to complete the configuration.

Specifying the Phase 2 parameters

1. Go to VPN > IPsec Tunnels and create the new custom tunnel or edit an existing tunnel.
2. Open the Phase 2 Selectors panel (if it is not available, you may need to click the Convert to Custom Tunnel button).
3. Enter a Name for the Phase 2 configuration, and select a Phase 1 configuration from the drop-down list.
4. Select Advanced.
5. Include the appropriate entries as follows:

Phase 2 Proposal

Select the encryption and authentication algorithms that will be used to change data into encrypted code. Add or delete encryption and authentication algorithms as required. Select a minimum of one and a maximum of three combinations. The remote peer must be configured to use at least one of the proposals that you define. It is invalid to set both Encryption and Authentication to null.

Configuring the Phase 2 parameters

Encryption	Select a symmetric-key algorithms: NULL — Do not use an encryption algorithm. DES — Digital Encryption Standard, a 64-bit block algorithm that uses a 56-bit key. 3DES — Triple-DES; plain text is encrypted three times by three keys. AES128 — A 128-bit block algorithm that uses a 128-bit key. AES192 — A 128-bit block algorithm that uses a 192-bit key. AES256 — A 128-bit block algorithm that uses a 256-bit key.
Authentication	You can select either of the following message digests to check the authenticity of messages during an encrypted session: NULL — Do not use a message digest. MD5 — Message Digest 5. SHA1 — Secure Hash Algorithm 1 – a 160-bit message digest. To specify one combination only, set the Encryption and Authentication options of the second combination to NULL. To specify a third combination, use the Add button beside the fields for the second combination. For information regarding NP accelerated offloading of IPsec VPN authentication algorithms, please refer to the Hardware Acceleration handbook chapter.
Enable replay detection	Optionally enable or disable replay detection. Replay attacks occur when an unauthorized party intercepts a series of IPsec packets and replays them back into the tunnel.
Enable perfect forward secrecy (PFS)	Enable or disable PFS. Perfect forward secrecy (PFS) improves security by forcing a new Diffie-Hellman exchange whenever keylife expires.
Diffie-Hellman Group	Select one Diffie-Hellman group (1, 2, 5, 14 through 21, or 27 through 30). The remote peer or dialup client must be configured to use the same group.
Keylife	Select the method for determining when the Phase 2 key expires: Seconds, KBytes, or Both. If you select Both, the key expires when either the time has passed or the number of KB have been processed. The range is from 120 to 172800 seconds, or from 5120 to 2147483648 KB.
Autokey Keep Alive	Enable the option if you want the tunnel to remain active when no data is being processed.
Auto-negotiate	Enable the option if you want the tunnel to be automatically renegotiated when the tunnel expires.

Phase 2 parameters                                                                                          Configuring the

DHCP-IPsec

Select Enable if the FortiGate unit acts as a dialup server and FortiGate DHCP server or relay will be used to assign VIP addresses to FortiClient dialup clients. The DHCP server or relay parameters must be configured separately. If the FortiGate unit acts as a dialup server and the FortiClient dialup client VIP addresses match the network behind the dialup server, select Enable to cause the FortiGate unit to act as a proxy for the dialup clients. This is available only for Phase 2 configurations associated with a dialup Phase 1 configuration. It works only on policy-based VPNs.

Autokey Keep Alive

The Phase 2 SA has a fixed duration. If there is traffic on the VPN as the SA nears expiry, a new SA is negotiated and the VPN switches to the new SA without interruption. If there is no traffic, however, the SA expires (by default) and the VPN tunnel goes down. A new SA will not be generated until there is traffic.

The Autokey Keep Alive option ensures that a new Phase 2 SA is negotiated, even if there is no traffic, so that the VPN tunnel stays up.

Auto-negotiate

By default, the Phase 2 security association (SA) is not negotiated until a peer attempts to send data. The triggering packet and some subsequent packets are dropped until the SA is established. Applications normally resend this data, so there is no loss, but there might be a noticeable delay in response to the user.

If the tunnel goes down, the auto-negotiate feature (when enabled) attempts to re-establish the tunnel. Autonegotiate initiates the Phase 2 SA negotiation automatically, repeating every five seconds until the SA is established.

Automatically establishing the SA can be important for a dialup peer. It ensures that the VPN tunnel is available for peers at the server end to initiate traffic to the dialup peer. Otherwise, the VPN tunnel does not exist until the dialup peer initiates traffic.

The auto-negotiate feature is available through the Command Line Interface (CLI) via the following commands:

config vpn ipsec phase2 edit <phase2_name> set auto-negotiate enable

end

Installing dynamic selectors via auto-negotiate

The IPsec SA connect message generated is used to install dynamic selectors. These selectors can now be installed via the auto-negotiate mechanism. When phase 2 has auto-negotiate enabled, and phase 1 has meshselector-type set to subnet, a new dynamic selector will be installed for each combination of source and destination subnets. Each dynamic selector will inherit the auto-negotiate option from the template selector and begin SA negotiation. Phase 2 selector sources from dial-up clients will all establish SAs without traffic being initiated from the client subnets to the hub.

Configuring the Phase 2 parameters

DHCP-IPsec

Select this option if the FortiGate unit assigns VIP addresses to FortiClient dialup clients through a DHCP server or relay. This option is available only if the Remote Gateway in the Phase 1 configuration is set to Dialup User and it works only on policy-based VPNs.

With the DHCP-IPsec option, the FortiGate dialup server acts as a proxy for FortiClient dialup clients that have VIP addresses on the subnet of the private network behind the FortiGate unit. In this case, the FortiGate dialup server acts as a proxy on the local private network for the FortiClient dialup client. When a host on the network behind the dialup server issues an ARP request that corresponds to the device MAC address of the FortiClient host (when a remote server sends an ARP to the local FortiClient dialup client), the FortiGate unit answers the ARP request on behalf of the FortiClient host and forwards the associated traffic to the FortiClient host through the tunnel.

This feature prevents the VIP address assigned to the FortiClient dialup client from causing possible arp broadcast problems — the normal and VIP addresses can confuse some network switches by two addresses having the same MAC address.

 

Phase 1 parameters

This chapter provides detailed step-by-step procedures for configuring a FortiGate unit to accept a connection from a remote peer or dialup client. The Phase 1 parameters identify the remote peer or clients and supports authentication through preshared keys or digital certificates. You can increase access security further using peer identifiers, certificate distinguished names, group names, or the FortiGate extended authentication (XAuth) option for authentication purposes.

For more information on Phase 1 parameters in the web-based manager, see IPsec VPN in the web-based manager on page 38.

The information and procedures in this section do not apply to VPN peers that perform negotiations using manual keys.

The following topics are included in this section:

Overview

Defining the tunnel ends

Choosing Main mode or Aggressive mode

Choosing the IKE version

Authenticating the FortiGate unit

Authenticating remote peers and clients

Defining IKE negotiation parameters

Using XAuth authentication

Dynamic IPsec route control

Overview

To configure IPsec Phase 1 settings, go to VPN > IPsec Tunnels and edit the Phase 1 Proposal (if it is not available, you may need to click the Convert to Custom Tunnel button).

IPsec Phase 1 settings define:

• The remote and local ends of the IPsec tunnel
• If Phase 1 parameters are exchanged in multiple rounds with encrypted authentication information (main mode) or in a single message with authentication information that is not encrypted (aggressive mode)
• If a preshared key or digital certificates will be used to authenticate the FortiGate unit to the VPN peer or dialup client
• If the VPN peer or dialup client is required to authenticate to the FortiGate unit. A remote peer or dialup client can authenticate by peer ID or, if the FortiGate unit authenticates by certificate, it can authenticate by peer certificate.
• The IKE negotiation proposals for encryption and authentication
• Optional XAuth authentication, which requires the remote user to enter a user name and password. A FortiGate VPN server can act as an XAuth server to authenticate dialup users. A FortiGate unit that is a dialup client can also be configured as an XAuth client to authenticate itself to the VPN server.

For all the Phase 1 web-based manager fields, see IPsec VPN in the web-based manager on page 38.

 

Defining the tunnel ends

If you want to control how IKE is negotiated when there is no traffic, as well as the length of time the unit waits for negotiations to occur, use the negotiation-timeout and auto-negotiate commands in the CLI.

Defining the tunnel ends

To begin defining the Phase 1 configuration, go to VPN > IPsec Tunnels and select Create New. Enter a unique descriptive name for the VPN tunnel and follow the instructions in the VPN Creation Wizard.

The Phase 1 configuration mainly defines the ends of the IPsec tunnel. The remote end is the remote gateway with which the FortiGate unit exchanges IPsec packets. The local end is the FortiGate interface that sends and receives IPsec packets.

The remote gateway can be:

• A static IP address
• A domain name with a dynamic IP address
• A dialup client

A statically addressed remote gateway is the simplest to configure. You specify the IP address. Unless restricted in the security policy, either the remote peer or a peer on the network behind the FortiGate unit can bring up the tunnel.

If the remote peer has a domain name and subscribes to a dynamic DNS service, you need to specify only the domain name. The FortiGate unit performs a DNS query to determine the appropriate IP address. Unless restricted in the security policy, either the remote peer or a peer on the network behind the FortiGate unit can bring up the tunnel.

If the remote peer is a dialup client, only the dialup client can bring up the tunnel. The IP address of the client is not known until it connects to the FortiGate unit. This configuration is a typical way to provide a VPN for client PCs running VPN client software such as the FortiClient Endpoint Security application.

The local end of the VPN tunnel, the Local Interface, is the FortiGate interface that sends and receives the IPsec packets. This is usually the public interface of the FortiGate unit that is connected to the Internet (typically the WAN1 port). Packets from this interface pass to the private network through a security policy.

By default, the local VPN gateway is the IP address of the selected Local Interface. If you are configuring an interface mode VPN, you can optionally use a secondary IP address of the Local Interface as the local gateway.

Choosing Main mode or Aggressive mode

The FortiGate unit and the remote peer or dialup client exchange Phase 1 parameters in either Main mode or Aggressive mode. This choice does not apply if you use IKE version 2, which is available only for route-based configurations.

• In Main mode, the Phase 1 parameters are exchanged in multiple rounds with encrypted authentication information
• In Aggressive mode, the Phase 1 parameters are exchanged in a single message with unencrypted authentication information.

Although Main mode is more secure, you must select Aggressive mode if there is more than one dialup Phase 1 configuration for the interface IP address, and the remote VPN peer or client is authenticated using an identifier local ID. Aggressive mode might not be as secure as Main mode, but the advantage to Aggressive mode is that it Choosing the IKE version

is faster than Main mode (since fewer packets are exchanged). Aggressive mode is typically used for remote access VPNs. But you would also use aggressive mode if one or both peers have dynamic external IP addresses. Descriptions of the peer options in this guide indicate whether Main or Aggressive mode is required.

Choosing the IKE version

If you create a route-based VPN, you have the option of selecting IKE version 2. Otherwise, IKE version 1 is used. IKEv2, defined in RFC 4306, simplifies the negotiation process that creates the security association (SA). If you select IKEv2:

• There is no choice in Phase 1 of Aggressive or Main mode. l FortiOS does not support Peer Options or Local ID.
• Extended Authentication (XAUTH) is not available. l You can select only one Diffie-Hellman Group.  l You can utilize EAP and MOBIKE.

Repeated authentication in IKEv2

This feature provides the option to control whether a device requires its peer to re-authenticate or whether re-key is sufficient. It does not influence the re-authentication or re-key behavior of the device itself, which is controlled by the peer (with the default being to re-key). This solution is in response to RFC 4478. As described by the IETF, “the purpose of this is to limit the time that security associations (SAs) can be used by a third party who has gained control of the IPsec peer”.

Syntax

config vpn ipsec phase1-interface edit p1 set reauth [enable | disable]

next

end

IKEv2 cookie notification for IKE_SA_INIT

IKEv2 offers an optional exchange within IKE_SA_INIT (the initial exchange between peers when establishing a secure tunnel) as a result of an inherent vulnerability in IPsec implementations, as described in RFC 5996.

Two expected attacks against IKE are state and CPU exhaustion, where the target is flooded with session initiation requests from forged IP addresses. These attacks can be made less effective if a responder uses minimal CPU and commits no state to an SA until it knows the initiator can receive packets at the address from which it claims to be sending them.

If the IKE_SA_INIT response includes the cookie notification, the initiator MUST then retry the IKE_SA_INIT request, and include the cookie notification containing the received data as the first payload, and all other payloads unchanged.

Upon detecting that the number of half-open IKEv2 SAs is above the threshold value, the VPN dialup server requires all future SA_INIT requests to include a valid cookie notification payload that the server sends back, in order to preserve CPU and memory resources.

the FortiGate unit

For most devices, the threshold value is set to 500, half of the maximum 1,000 connections.

This feature is enabled by default in FortiOS 5.4.

IKEv2 Quick Crash Detection

There is support for IKEv2 Quick Crash Detection (QCD) as described in RFC 6290.

RFC 6290 describes a method in which an IKE peer can quickly detect that the gateway peer that it has and established an IKE session with has rebooted, crashed, or otherwise lost IKE state. When the gateway receives IKE messages or ESP packets with unknown IKE or IPsec SPIs, the IKEv2 protocol allows the gateway to send the peer an unprotected IKE message containing INVALID_IKE_SPI or INVALID_SPI notification payloads.

RFC 6290 introduces the concept of a QCD token, which is generated from the IKE SPIs and a private QCD secret, and exchanged between peers during the protected IKE AUTH exchange.

Adding Quick Crash Detection – CLI Syntax

config system settings set ike-quick-crash-detect [enable | disable]

end

IKEv1 Quick Crash Detection

Based on the IKEv2 QCD feature described above, IKEv1 QCD is implemented using a new IKE vendor ID,

“Fortinet Quick Crash Detection”, and so both endpoints must be FortiGate devices. The QCD token is sent in the Phase 1 exchange and must be encrypted, so this is only implemented for IKEv1 in Main mode (Aggressive mode is not supported as there is no available AUTH message in which to include the token).

Otherwise, the feature works the same as in IKEv2 (RFC 6290).

Authenticating the FortiGate unit

The FortiGate unit can authenticate itself to remote peers or dialup clients using either a pre-shared key or an RSA Signature (certificate).

Authenticating the FortiGate unit with digital certificates

To authenticate the FortiGate unit using digital certificates, you must have the required certificates installed on the remote peer and on the FortiGate unit. The signed server certificate on one peer is validated by the presence of the root certificate installed on the other peer. If you use certificates to authenticate the FortiGate unit, you can also require the remote peers or dialup clients to authenticate using certificates.

For more information about obtaining and installing certificates, see the FortiOS User Authentication guide.

Authenticating the FortiGate unit using digital certificates

1. Go to VPN > IPsec Tunnels and create the new custom tunnel or edit an existing tunnel.
2. Edit the Phase 1 Proposal (if it is not available, you may need to click the Convert to Custom Tunnel button):

Authenticating the FortiGate unit

Name	Enter a name that reflects the origination of the remote connection. For interface mode, the name can be up to 15 characters long.
Remote Gateway	Select the nature of the remote connection. Each option changes the available fields you must configure. For more information, see Authenticating the FortiGate unit on page 55.
Local Interface	Select the interface that is the local end of the IPsec tunnel. For more information, see Authenticating the FortiGate unit on page 55. The local interface is typically the WAN1 port.
Mode	Select a mode. It is easier to use Aggressive mode. In Main mode, parameters are exchanged in multiple encrypted rounds. In Aggressive mode, parameters are exchanged in a single unencrypted message. Aggressive mode must be used when the remote VPN peer or client has a dynamic IP address, or the remote VPN peer or client will be authenticated using an identifier (local ID). For more information, see Authenticating the FortiGate unit on page 55.
Authentication Method	Select Signature.
Certificate Name	Select the name of the server certificate that the FortiGate unit will use to authenticate itself to the remote peer or dialup client during Phase 1 negotiations. You must obtain and load the required server certificate before this selection. See the FortiOS User Authentication guide. If you have not loaded any certificates, use the certificate named Fortinet_Factory.
Peer Options	Peer options define the authentication requirements for remote peers or dialup clients. They are not for your FortiGate unit itself. See Authenticating the FortiGate unit on page 55.
Advanced	You can use the default settings for most Phase 1 configurations. Changes are required only if your network requires them. These settings includes IKE version, DNS server, P1 proposal encryption and authentication settings, and XAuth settings. See Authenticating the FortiGate unit on page 55.

3. If you are configuring authentication parameters for a dialup user group, optionally define extended authentication (XAuth) parameters in the Advanced section. See Authenticating the FortiGate unit on page 55. Select OK.

the FortiGate unit

Authenticating the FortiGate unit with a pre-shared key

The simplest way to authenticate a FortiGate unit to its remote peers or dialup clients is by means of a pre-shared

key. This is less secure than using certificates, especially if it is used alone, without requiring peer IDs or extended authentication (XAuth). Also, you need to have a secure way to distribute the pre-shared key to the peers.

If you use pre-shared key authentication alone, all remote peers and dialup clients must be configured with the same pre-shared key. Optionally, you can configure remote peers and dialup clients with unique pre-shared keys. On the FortiGate unit, these are configured in user accounts, not in the phase_1 settings. For more information, see Authenticating the FortiGate unit on page 55.

The pre-shared key must contain at least 6 printable characters and best practices dictate that it be known only to network administrators. For optimum protection against currently known attacks, the key must consist of a minimum of 16 randomly chosen alphanumeric characters.

If you authenticate the FortiGate unit using a pre-shared key, you can require remote peers or dialup clients to authenticate using peer IDs, but not client certificates.

Authenticating the FortiGate unit with a pre-shared key

1. Go to VPN > IPsec Tunnels and create the new custom tunnel or edit an existing tunnel.
2. Edit the Phase 1 Proposal (if it is not available, you may need to click the Convert to Custom Tunnel button):

Name	Enter a name that reflects the origination of the remote connection.
Remote Gateway	Select the nature of the remote connection. For more information, see Authenticating the FortiGate unit on page 55.
Local Interface	Select the interface that is the local end of the IPsec tunnel. For more information, see Authenticating the FortiGate unit on page 55. The local interface is typically the WAN1 port.
Mode	Select Main or Aggressive mode. In Main mode, the Phase 1 parameters are exchanged in multiple rounds with encrypted authentication information. In Aggressive mode, the Phase 1 parameters are exchanged in single message with authentication information that is not encrypted. When the remote VPN peer or client has a dynamic IP address, or the remote VPN peer or client will be authenticated using an identifier (local ID), you must select Aggressive mode if there is more than one dialup Phase 1 configuration for the interface IP address. For more information, see Authenticating the FortiGate unit on page 55.
Authentication Method	Select Pre-shared Key.

 

Pre-shared Key	Enter the preshared key that the FortiGate unit will use to authenticate itself to the remote peer or dialup client during Phase 1 negotiations. You must define the same value at the remote peer or client. The key must contain at least 6 printable characters and best practices dictate that it only be known by network administrators. For optimum protection against currently known attacks, the key must consist of a minimum of 16 randomly chosen alphanumeric characters.
Peer options	Peer options define the authentication requirements for remote peers or dialup clients, not for the FortiGate unit itself. You can require the use of peer IDs, but not client certificates. For more information, see Authenticating the FortiGate unit on page 55.
Advanced	You can retain the default settings unless changes are needed to meet your specific requirements. See Authenticating the FortiGate unit on page 55.

3. If you are configuring authentication parameters for a dialup user group, optionally define extended authentication (XAuth) parameters. See Authenticating the FortiGate unit on page 55.
4. Select OK.

Authenticating remote peers and clients

Certificates or pre-shared keys restrict who can access the VPN tunnel, but they do not identify or authenticate the remote peers or dialup clients. You have the following options for authentication:

Methods of authenticating remote VPN peers

Certificates or Pre-shared key	Local ID	User account pre-shared keys	Reference
Certificates			See Enabling VPN access for specific certificate holders  on page 59.
Either	X		See Enabling VPN access by peer identifier on page 61.
Pre-shared key		X	See Enabling VPN access with user accounts and pre-shared keys on page 62.
Pre-shared key	X	X	See Enabling VPN access with user accounts and pre-shared keys on page 62.

remote peers and clients

Repeated Authentication in Internet Key Exchange (IKEv2) Protocol

This feature provides the option to control whether a device requires its peer to re-authenticate or whether re-key is sufficient. It does not influence the re-authentication or re-key behavior of the device itself, which is controlled by the peer (with the default being to re-key).

This solution is in response to RFC 4478. This solution is intended to limit the time that security associations (SAs) can be used by a third party who has gained control of the IPsec peer.

CLI Syntax:

config vpn ipsec phase1-interface edit p1 set reauth [enable | disable]

next

end

 

disable: Disable IKE SA re-authentication. enable: Enable IKE SA re-authentication.

Enabling VPN access for specific certificate holders

When a VPN peer or dialup client is configured to authenticate using digital certificates, it sends the Distinguished Name (DN) of its certificate to the FortiGate unit. This DN can be used to allow VPN access for the certificate holder. That is, a FortiGate unit can be configured to deny connections to all remote peers and dialup clients except the one having the specified DN.

Before you begin

The following procedures assume that you already have an existing Phase 1 configuration (see Authenticating remote peers and clients on page 58). Follow the procedures below to add certificate-based authentication parameters to the existing configuration.

Before you begin, you must obtain the certificate DN of the remote peer or dialup client. If you are using the FortiClient application as a dialup client, refer to FortiClient online help for information about how to view the certificate DN. To view the certificate DN of a FortiGate unit, see Viewing server  certificate information and obtaining the local DN  on page 60.

Use the config user peer CLI command to load the DN value into the FortiGate configuration. For example, if a remote VPN peer uses server certificates issued by your own organization, you would enter information similar to the following:

config user peer edit DN_FG1000 set cn 192.168.2.160 set cn-type ipv4

end

The value that you specify to identify the entry (for example, DN_FG1000) is displayed in the Accept this peer certificate only list in the IPsec Phase 1 configuration when you return to the web-based manager.

If the remote VPN peer has a CA-issued certificate to support a higher level of credibility, you would enter information similar to the following in the CLI:

config user peer edit CA_FG1000 set ca CA_Cert_1 set subject FG1000_at_site1

end

The value that you specify to identify the entry (for example, CA_FG1000) is displayed in the Accept this peer certificate only list in the IPsec Phase 1 configuration when you return to the web-based manager. For more information about these CLI commands, see the “user” chapter of the FortiGate CLI Reference.

A group of certificate holders can be created based on existing user accounts for dialup clients. To create the user accounts for dialup clients, see the “User” chapter of the FortiGate Administration Guide. To create the certificate group afterward, use the config user peergrp CLI command. See the “user” chapter of the FortiGate CLI Reference.

Viewing server  certificate information and obtaining the local DN

1. Go to System > Certificates.
2. Note the CN value in the Subject field (for example, CN = 172.16.10.125, CN = info@fortinet.com, or CN = www.example.com).

Viewing CA root certificate information and obtaining the CA certificate name

1. Go to System > Certificates > CA Certificates.
2. Note the value in the Name column (for example, CA_Cert_1).

Configuring certificate authentication for a VPN

With peer certificates loaded, peer users and peer groups defined, you can configure your VPN to authenticate users by certificate.

Enabling access for a specific certificate holder or a group of certificate holders

1. At the FortiGate VPN server, go to VPN > IPsec Tunnels and create the new custom tunnel or edit an existing tunnel.
2. Edit the Phase 1 Proposal (if it is not available, you may need to click the Convert to Custom Tunnel button).
3. From the Authentication Method list, select RSA Signature.
4. From the Certificate Name list, select the name of the server certificate that the FortiGate unit will use to authenticate itself to the remote peer or dialup client Under Peer Options, select one of these options:
   • To accept a specific certificate holder, select Accept this peer certificate only and select the name of the certificate that belongs to the remote peer or dialup client. The certificate DN must be added to the FortiGate configuration through CLI commands before it can be selected here. See Before you begin on page 59.
   • To accept dialup clients who are members of a certificate group, select Accept this peer certificate group only and select the name of the group. The group must be added to the FortiGate configuration through CLI commands before it can be selected here. See Before you begin on page 59.
5. If you want the FortiGate VPN server to supply the DN of a local server certificate for authentication purposes, select Advanced and then from the Local ID list, select the DN of the certificate that the FortiGate VPN server is to use.
6. Select OK.

remote peers and clients

Enabling VPN access by peer identifier

Whether you use certificates or pre-shared keys to authenticate the FortiGate unit, you can require that remote peers or clients have a particular peer ID. This adds another piece of information that is required to gain access to the VPN. More than one FortiGate/FortiClient dialup client may connect through the same VPN tunnel when the dialup clients share a preshared key and assume the same identifier.

A peer ID, also called local ID, can be up to 63 characters long containing standard regular expression characters. Local ID is set in phase1 Aggressive Mode configuration.

You cannot require a peer ID for a remote peer or client that uses a pre-shared key and has a static IP address.

Authenticating remote peers or dialup clients using one peer ID

1. At the FortiGate VPN server, go to VPN > IPsec Tunnels and create the new custom tunnel or edit an existing tunnel.
2. Edit the Phase 1 Proposal (if it is not available, you may need to click the Convert to Custom Tunnel button).
3. Select Aggressive mode in any of the following cases:
   • The FortiGate VPN server authenticates a FortiGate dialup client that uses a dedicated tunnel
   • A FortiGate unit has a dynamic IP address and subscribes to a dynamic DNS service
   • FortiGate/FortiClient dialup clients sharing the same preshared key and local ID connect through the same VPN tunnel
4. For the Peer Options, select This peer ID and type the identifier into the corresponding field.
5. Select OK.

Assigning an identifier (local ID) to a FortiGate unit

Use this procedure to assign a peer ID to a FortiGate unit that acts as a remote peer or dialup client.

1. Go to VPN > IPsec Tunnels and create the new custom tunnel or edit an existing tunnel.
2. Edit the Phase 1 Proposal (if it is not available, you may need to click the Convert to Custom Tunnel button).
3. Select Advanced.
4. In the Local ID field, type the identifier that the FortiGate unit will use to identify itself.
5. Set Mode to Aggressive if any of the following conditions apply:
   • The FortiGate unit is a dialup client that will use a unique ID to connect to a FortiGate dialup server through a dedicated tunnel.
   • The FortiGate unit has a dynamic IP address, subscribes to a dynamic DNS service, and will use a unique ID to connect to the remote VPN peer through a dedicated tunnel.
   • The FortiGate unit is a dialup client that shares the specified ID with multiple dialup clients to connect to a FortiGate dialup server through the same tunnel.
6. Select OK.

Configuring the FortiClient application

Follow this procedure to add a peer ID to an existing FortiClient configuration:

1. Start the FortiClient application.
2. Go to VPN > Connections, select the existing configuration.
3. Select Advanced > Edit > Advanced.
4. Under Policy, select Config.
5. In the Local ID field, type the identifier that will be shared by all dialup clients. This value must match the This peer ID value that you specified previously in the Phase 1 gateway configuration on the FortiGate unit.
6. Select OK to close all dialog boxes.
7. Configure all dialup clients the same way using the same preshared key and local ID.

Enabling VPN access with user accounts and pre-shared keys

You can permit access only to remote peers or dialup clients that have pre-shared keys and/or peer IDs configured in user accounts on the FortiGate unit.

If you want two VPN peers (or a FortiGate unit and a dialup client) to accept reciprocal connections based on peer IDs, you must enable the exchange of their identifiers when you define the Phase 1 parameters.

The following procedures assume that you already have an existing Phase 1 configuration (see Authenticating remote peers and clients on page 58). Follow the procedures below to add ID checking to the existing configuration.

Before you begin, you must obtain the identifier (local ID) of the remote peer or dialup client. If you are using the

FortiClient Endpoint Security application as a dialup client, refer to the Authenticating FortiClient Dialup Clients Technical Note to view or assign an identifier. To assign an identifier to a FortiGate dialup client or a FortiGate unit that has a dynamic IP address and subscribes to a dynamic DNS service, see Assigning an identifier (local ID) to a FortiGate unit  on page 61.

If required, a dialup user group can be created from existing user accounts for dialup clients. To create the user accounts and user groups, see the User Authentication handbook chapter.

The following procedure supports FortiGate/FortiClient dialup clients that use unique preshared keys and/or peer IDs. The client must have an account on the FortiGate unit and be a member of the dialup user group.

The dialup user group must be added to the FortiGate configuration before it can be selected. For more information, see the User Authentication handbook chapter.

The FortiGate dialup server compares the local ID that you specify at each dialup client to the FortiGate useraccount user name. The dialup-client preshared key is compared to a FortiGate user-account password.

Authenticating dialup clients using unique preshared keys and/or peer IDs

1. At the FortiGate VPN server, go to VPN > IPsec Tunnels and create the new custom tunnel or edit an existing tunnel.
2. Edit the Phase 1 Proposal (if it is not available, you may need to click the Convert to Custom Tunnel button).
3. If the clients have unique peer IDs, set Mode to Aggressive.
4. Clear the Pre-shared Key

The user account password will be used as the preshared key.

5. Select Peer ID from dialup group and then select the group name from the list of user groups. Select OK.

 

Follow this procedure to add a unique pre-shared key and unique peer ID to an existing FortiClient configuration.

Configuring FortiClient – pre-shared key and peer ID

1. Start the FortiClient Endpoint Security application.
2. Go to VPN > Connections, select the existing configuration. Select Advanced > Edit.
3. In the Preshared Key field, type the FortiGate password that belongs to the dialup client (for example,

1234546).

The user account password will be used as the preshared key.  5. Select Advanced.

6. Under Policy, select Config.
7. In the Local ID field, type the FortiGate user name that you assigned previously to the dialup client (for example, FortiC1ient1).
8. Select OK to close all dialog boxes.

Configure all FortiClient dialup clients this way using unique preshared keys and local IDs.

Follow this procedure to add a unique pre-shared key to an existing FortiClient configuration.

Configuring FortiClient – preshared key only

1. Start the FortiClient Endpoint Security application.
2. Go to VPN > Connections, select the existing configuration Select Advanced > Edit.
3. In the Preshared Key field, type the user name, followed by a “+” sign, followed by the password that you specified previously in the user account settings on the FortiGate unit (for example, FC2+1FG6LK) 5. Select OK to close all dialog boxes.

Configure all the FortiClient dialup clients this way using their unique peer ID and pre-shared key values.

Defining IKE negotiation parameters

In Phase 1, the two peers exchange keys to establish a secure communication channel between them. As part of the Phase 1 process, the two peers authenticate each other and negotiate a way to encrypt further communications for the duration of the session. For more information see Defining IKE negotiation parameters on page 63. The Phase 1 Proposal parameters select the encryption and authentication algorithms that are used to generate keys for protecting negotiations. The IKE negotiation parameters determine:

• Which encryption algorithms may be applied for converting messages into a form that only the intended recipient can read
• Which authentication hash may be used for creating a keyed hash from a preshared or private key
• Which Diffie-Hellman group (DH Group) will be used to generate a secret session key

Phase 1 negotiations (in main mode or aggressive mode) begin as soon as a remote VPN peer or client attempts to establish a connection with the FortiGate unit. Initially, the remote peer or dialup client sends the FortiGate unit a list of potential cryptographic parameters along with a session ID. The FortiGate unit compares those parameters to its own list of advanced Phase 1 parameters and responds with its choice of matching parameters 63

Defining IKE negotiation

to use for authenticating and encrypting packets. The two peers handle the exchange of encryption keys between them, and authenticate the exchange through a preshared key or a digital signature.

Generating keys to authenticate an exchange

The FortiGate unit supports the generation of secret session keys automatically using a Diffie-Hellman algorithm. These algorithms are defined in RFC 2409. The Keylife setting in the Phase 1 Proposal area determines the amount of time before the Phase 1 key expires. Phase 1 negotiations are re-keyed automatically when there is an active security association. See Dead Peer Detection  on page 67.

You can enable or disable automatic re-keying between IKE peers through the phase1-rekey attribute of the config system global CLI command. For more information, see the “System” chapter of the FortiGate CLI Reference.

When in FIPS-CC mode, the FortiGate unit requires DH key exchange to use values at least 3072 bits long. However most browsers need the key size set to 1024. You can set the minimum size of the DH keys in the CLI.

config system global    set dh-params 3072 end

When you use a preshared key (shared secret) to set up two-party authentication, the remote VPN peer or client and the FortiGate unit must both be configured with the same preshared key. Each party uses a session key derived from the Diffie-Hellman exchange to create an authentication key, which is used to sign a known combination of inputs using an authentication algorithm (such as HMAC-MD5, HMAC-SHA-1, or HMAC-SHA256). Hash-based Message Authentication Code (HMAC) is a method for calculating an authentication code using a hash function plus a secret key, and is defined in RFC 2104. Each party signs a different combination of inputs and the other party verifies that the same result can be computed.

When you use preshared keys to authenticate VPN peers or clients, you must distribute matching information to all VPN peers and/or clients whenever the preshared key changes.

As an alternative, the remote peer or dialup client and FortiGate unit can exchange digital signatures to validate each other’s identity with respect to their public keys. In this case, the required digital certificates must be installed on the remote peer and on the FortiGate unit. By exchanging certificate DNs, the signed server certificate on one peer is validated by the presence of the root certificate installed on the other peer.

The following procedure assumes that you already have a Phase 1 definition that describes how remote VPN peers and clients will be authenticated when they attempt to connect to a local FortiGate unit. For information about the Local ID and XAuth options, see Defining IKE negotiation parameters on page 63 and Defining IKE negotiation parameters on page 63. Follow this procedure to add IKE negotiation parameters to the existing definition.

Defining IKE negotiation parameters

1. Go to VPN > IPsec Tunnels and create the new custom tunnel or edit an existing tunnel.
2. Edit the Phase 1 Proposal (if it is not available, you may need to click the Convert to Custom Tunnel button).
3. Select Phase 1 Proposal and include the appropriate entries as follows:

Phase 1 Proposal		Select the encryption and authentication algorithms that will be used to generate keys for protecting negotiations. Add or delete encryption and authentication algorithms as required. Select a minimum of one and a maximum of three combinations. The remote peer must be configured to use at least one of the proposals that you define. It is invalid to set both Encryption and Authentication to null.
Encryption		Select a symmetric-key algorithms: NULL — Do not use an encryption algorithm. DES — Digital Encryption Standard, a 64-bit block algorithm that uses a 56-bit key. 3DES — Triple-DES; plain text is encrypted three times by three keys. AES128 — A 128-bit block algorithm that uses a 128-bit key. AES192 — A 128-bit block algorithm that uses a 192-bit key. AES256 — A 128-bit block algorithm that uses a 256-bit key.
Authentication		You can select either of the following message digests to check the authenticity of messages during an encrypted session: NULL — Do not use a message digest. MD5 — Message Digest 5. SHA1 — Secure Hash Algorithm 1 – a 160-bit message digest. To specify one combination only, set the Encryption and Authentication options of the second combination to NULL. To specify a third combination, use the Add button beside the fields for the second combination. For information regarding NP accelerated offloading of IPsec VPN authentication algorithms, please refer to the Hardware Acceleration handbook chapter.

Defining IKE negotiation

Diffie-Hellman Group	Select one or more Diffie-Hellman groups from DH groups 1, 2, 5, 14 through 21, and 27 through 30. When using aggressive mode, DH groups cannot be negotiated. By default, DH group 14 is selected, to provide sufficient protection for stronger cipher suites that include AES and SHA2. If you select multiple DH groups, the order they appear in the configuration is the order in which they are negotiates. If both VPN peers (or a VPN server and its client) have static IP addresses and use aggressive mode, select a single DH group. The setting on the FortiGate unit must be identical to the setting on the remote peer or dialup client. When the remote VPN peer or client has a dynamic IP address and uses aggressive mode, select up to three DH groups on the FortiGate unit and one DH group on the remote peer or dialup client. The setting on the remote peer or dialup client must be identical to one of the selections on the FortiGate unit. If the VPN peer or client employs main mode, you can select multiple DH groups. At least one of the settings on the remote peer or dialup client must be identical to the selections on the FortiGate unit.
Keylife	Type the amount of time (in seconds) that will be allowed to pass before the IKE encryption key expires. When the key expires, a new key is generated without interrupting service. The keylife can be from 120 to 172800 seconds.
Nat-traversal	Enable this option if a NAT device exists between the local FortiGate unit and the VPN peer or client. The local FortiGate unit and the VPN peer or client must have the same NAT traversal setting (both selected or both cleared). When in doubt, enable NAT-traversal. See NAT traversal  on page 66.
Keepalive Frequency	If you enabled NAT traversal, enter a keepalive frequency setting. The value represents an interval from 0 to 900 seconds where the connection will be maintained with no activity. For additional security this value must be as low as possible. See NAT keepalive frequency  on page 67.
Dead Peer Detection	Enable this option to reestablish VPN tunnels on idle connections and clean up dead IKE peers if required. This feature minimizes the traffic required to check if a VPN peer is available or unavailable (dead). See Dead Peer Detection  on page 67.

NAT traversal

Network Address Translation (NAT) is a way to convert private IP addresses to publicly routable Internet addresses and vise versa. When an IP packet passes through a NAT device, the source or destination address in the IP header is modified. FortiGate units support NAT version 1 (encapsulate on port 500 with non-IKE marker), version 3 (encapsulate on port 4500 with non-ESP marker), and compatible versions.

NAT cannot be performed on IPsec packets in ESP tunnel mode because the packets do not contain a port number. As a result, the packets cannot be demultiplexed. To work around this, the FortiGate unit provides a way to protect IPsec packet headers from NAT modifications. When the Nat-traversal option is enabled, outbound encrypted packets are wrapped inside a UDP IP header that contains a port number. This extra encapsulation allows NAT devices to change the port number without modifying the IPsec packet directly.

To provide the extra layer of encapsulation on IPsec packets, the Nat-traversal option must be enabled whenever a NAT device exists between two FortiGate VPN peers or a FortiGate unit and a dialup client such as FortiClient. On the receiving end, the FortiGate unit or FortiClient removes the extra layer of encapsulation before decrypting the packet.

Additionally, you can force IPsec to use NAT traversal. If NAT is set to Forced, the FortiGate will use a port value of zero when constructing the NAT discovery hash for the peer. This causes the peer to think it is behind a NAT device, and it will use UDP encapsulation for IPsec, even if no NAT is present. This approach maintains interoperability with any IPsec implementation that supports the NAT-T RFC.

NAT keepalive frequency

When a NAT device performs network address translation on a flow of packets, the NAT device determines how long the new address will remain valid if the flow of traffic stops (for example, the connected VPN peer may be idle). The device may reclaim and reuse a NAT address when a connection remains idle for too long.

To work around this, when you enable NAT traversal specify how often the FortiGate unit sends periodic keepalive packets through the NAT device in order to ensure that the NAT address mapping does not change during the lifetime of a session. To be effective, the keepalive interval must be smaller than the session lifetime value used by the NAT device.

The keepalive packet is a 138-byte ISAKMP exchange.

Dead Peer Detection

Sometimes, due to routing issues or other difficulties, the communication link between a FortiGate unit and a

VPN peer or client may go down. Packets could be lost if the connection is left to time out on its own. The FortiGate unit provides a mechanism called Dead Peer Detection (DPD), sometimes referred to as gateway detection or ping server, to prevent this situation and reestablish IKE negotiations automatically before a connection times out: the active Phase 1 security associations are caught and renegotiated (rekeyed) before the Phase 1 encryption key expires.

By default, Dead Peer Detection sends probe messages every five seconds by default (see dpdretryinterval in the FortiGate CLI Reference). If you are experiencing high network traffic, you can experiment with increasing the ping interval. However longer intervals will require more traffic to detect dead peers which will result in more traffic.

In the web-based manager, the Dead Peer Detection option can be enabled when you define advanced Phase 1 options. The config vpn ipsec phase1 CLI command supports additional options for specifying a retry count and a retry interval.

For more information about these commands and the related config router gwdetect CLI command, see the FortiGate CLI Reference.

For example, enter the following CLI commands to configure dead peer detection on the existing IPsec Phase 1 configuration called test to use 15 second intervals and to wait for 3 missed attempts before declaring the peer dead and taking action.

config vpn ipsec phase1-interface edit <value> set dpd [disable | on-idle | on-demand] set dpd-retryinveral 15 set dpd-retrycount 3

 

Using XAuth authentication

next

end

DPD Scalability

On a dial-up server, if a multitude of VPN connections are idle, the increased DPD exchange could negatively impact the performance/load of the daemon. For this reason, an option is available in the CLI to send DPD passively in a mode called “on-demand”.

• When there is no traffic and the last DPD-ACK had been received, IKE will not send DPDs periodically.
• IKE will only send out DPDs if there are outgoing packets to send but no inbound packets had since been received.

Syntax

Set DPD to on-demand to trigger DPD when IPsec traffic is sent but no reply is received from the peer.

config vpn ipsec phase1-interface edit <value> set dpd [disable | on-idle | on-demand]

next

end

Certificate key size control

Proxy will choose the same SSL key size as the HTTPS server. If the key size from the server is 512, the proxy will choose 1024. If the key size is bigger than 1024, the proxy will choose 2048.

As a result, the firewall ssl-ssh-profile commands certname-rsa, certname-dsa, and certname-ecdsa have been replaced with more specific key size control commands under vpn certificate setting.

CLI syntax

config vpn certificate setting set certname-rsa1024 <name> set certname-rsa2048 <name> set certname-dsa1024 <name> set certname-dsa2048 <name> set certname-ecdsa256 <name> set certname-ecdsa384 <name>

end

Using XAuth authentication

Extended authentication (XAuth) increases security by requiring the remote dialup client user to authenticate in a separate exchange at the end of Phase 1. XAuth draws on existing FortiGate user group definitions and uses established authentication mechanisms such as PAP, CHAP, RADIUS, and LDAP to authenticate dialup clients. You can configure a FortiGate unit to function either as an XAuth server or an XAuth client.If the server or client is Using XAuth authentication

attempting a connection using XAuth and the other end is not using XAuth, the failed connection attempts that are logged will not specify XAuth as the reason.

Using the FortiGate unit as an XAuth server

A FortiGate unit can act as an XAuth server for dialup clients. When the Phase 1 negotiation completes, the FortiGate unit challenges the user for a user name and password. It then forwards the user’s credentials to an external RADIUS or LDAP server for verification.

If the user records on the RADIUS server have suitably configured Framed-IP-Address fields, you can assign client virtual IP addresses by XAuth instead of from a DHCP address range. See Assigning VIPs by RADIUS user group on page 1.

The authentication protocol to use for XAuth depends on the capabilities of the authentication server and the XAuth client:

• Select PAP Server whenever possible.
• You must select PAP Server for all implementations of LDAP and some implementations of Microsoft RADIUS.
• Select Auto Server when the authentication server supports CHAP Server but the XAuth client does not. The FortiGate unit will use PAP to communicate with the XAuth client and CHAP to communicate with the authentication server. You can also use Auto Server to allows multiple source interfaces to be defined in an IPsec/IKE policy

Before you begin, create user accounts and user groups to identify the dialup clients that need to access the network behind the FortiGate dialup server. If password protection will be provided through an external RADIUS or LDAP server, you must configure the FortiGate dialup server to forward authentication requests to the authentication server. For information about these topics, see the FortiGate User Authentication Guide.

Authenticating a dialup user group using XAuth settings

1. At the FortiGate dialup server, go to VPN > IPsec Tunnels and create the new custom tunnel or edit an existing tunnel.
2. Select Convert To Custom Tunnel.
3. Edit XAUTH, select the Type setting, which determines the type of encryption method to use between the XAuth client, the FortiGate unit and the authentication server. Select one of the following options:
   • Disabled — Disables XAuth settings.
   • PAP Server — Password Authentication Protocol.
   • CHAP Server — Challenge-Handshake Authentication Protocol.
   • Auto Server — Use PAP between the XAuth client and the FortiGate unit, and CHAP between the FortiGate unit and the authentication server.
4. From the User Group list, select the user group that needs to access the private network behind the FortiGate unit. The group must be added to the FortiGate configuration before it can be selected here. For multiple user groups to be defined in the IPsec/IKE policy, select Inherit from policy.
5. Select OK.
6. Create as many policies as needed, specifying Source User(s) and Destination Address.

For example, one policy could have user1 have access to test_local_subnet_1, while user2 has access to test_ local_subnet_2.

Dynamic IPsec route control

As of FortiOS 5.4.1, when XAuth settings are enabled, Inherit from policy is only available under PAP Server and CHAP Server, not Auto Server. Because of this, only one user group may be defined for Auto Server.

Using the FortiGate unit as an XAuth client

If the FortiGate unit acts as a dialup client, the remote peer, acting as an XAuth server, might require a username and password. You can configure the FortiGate unit as an XAuth client, with its own username and password, which it provides when challenged.

Configuring the FortiGate dialup client as an XAuth client

1. At the FortiGate dialup client, go to VPN > IPsec Tunnels and create the new custom tunnel or edit an existing tunnel.
2. Edit the Phase 1 Proposal (if it is not available, you may need to click the Convert to Custom Tunnel button).
3. Under XAuth, select Enable as Client.
4. In the Username field, type the FortiGate PAP, CHAP, RADIUS, or LDAP user name that the FortiGate XAuth server will compare to its records when the FortiGate XAuth client attempts to connect.
5. In the Password field, type the password to associate with the user name.
6. Select OK.

Dynamic IPsec route control

You can add a route to a peer destination selector by using the add-route option, which is available for all dynamic IPsec Phases 1 and 2, for both policy-based and route-based IPsec VPNs. This option was previously only available when mode-cfg was enabled in Phase 1.

The add-route option adds a route to the FortiGate unit’s routing information base when the dynamic tunnel is negotiated. You can use the distance and priority options to set the distance and priority of this route. If this results in a route with the lowest distance, it is added to the FortiGate unit’s forwarding information base.

You can also enable add-route in any policy-based or route-based Phase 2 configuration that is associated with a dynamic (dialup) Phase 1. In Phase 2, add-route can be enabled, disabled, or set to use the same route as Phase 1.

The add-route feature is enabled by default and is configured in the CLI.

Syntax

Phase 1

config vpn ipsec edit <name> set type dynamic

set add-route {enable | disable}

end

end

 

Phase 2

Dynamic IPsec route control

config vpn ipsec {phase2 | phase2-interface} edit <name> set add-route {phase1 | enable | disable}

end

end

Blocking IPsec SA Negotiation

For interface-based IPsec, IPsec SA negotiation blocking can only be removed if the peer offers a wildcard selector. If a wildcard selector is offered then the wildcard route will be added to the routing table with the distance/priority value configured in Phase 1 and, if that is the route with the lowest distance, it is installed into the forwarding information base.

In cases where this occurs, it is important to ensure that the distance value configured on Phase 1 is set appropriately.

 

IPsec VPN in the web-based manager

To configure an IPsec VPN, use the general procedure below. With these steps, your FortiGate unit will automatically generate unique IPsec encryption and authentication keys. If a remote VPN peer or client requires a specific IPsec encryption or authentication key, you must configure your FortiGate unit to use manual keys instead.

1. Define Phase 1 parameters to authenticate remote peers and clients for a secure connection. See IPsec VPN in the web-based manager on page 38.
2. Define Phase 2 parameters to create a VPN tunnel with a remote peer or dialup client. See IPsec VPN in the webbased manager on page 38.
3. Create a security policy to permit communication between your private network and the VPN. Policy-based VPNs have an action of IPSEC, where for interface-based VPNs the security policy action is ACCEPT. See Defining VPN security policies on page 1.

The FortiGate unit implements the Encapsulated Security Payload (ESP) protocol. Internet Key Exchange (IKE) is performed automatically based on pre-shared keys or X.509 digital certificates. Interface mode, supported in NAT mode only, creates a virtual interface for the local end of a VPN tunnel.

This chapter contains the following sections:

Phase 1 configuration

Phase 2 configuration

Concentrator

IPsec Monitor

Phase 1 configuration

To begin defining the Phase 1 configuration, go to VPN > IPsec Tunnels and select Create New. Enter a unique descriptive name for the VPN tunnel and follow the instructions in the VPN Creation Wizard.

The Phase 1 configuration mainly defines the ends of the IPsec tunnel. The remote end is the remote gateway with which the FortiGate unit exchanges IPsec packets. The local end is the FortiGate interface that sends and receives IPsec packets.

If you want to control how the IKE negotiation is processed when there is no traffic, as well as the length of time the FortiGate unit waits for negotiations to occur, you can use the negotiation-timeout and autonegotiate commands in the CLI.

For more information, refer to  Phase 2 parameters on page 72 and Phase 2 parameters on page 72.

 

Name	Type a name for the Phase 1 definition. The maximum name length is 15 characters for an interface mode VPN, 35 characters for a policy-based VPN. If Remote Gateway is Dialup User, the maximum name length is further reduced depending on the number of dialup tunnels that can be established: by 2 for up to 9 tunnels, by 3 for up to 99 tunnels, 4 for up to 999 tunnels, and so on. For a tunnel mode VPN, the name normally reflects where the remote connection originates. For a route-based tunnel, the FortiGate unit also uses the name for the virtual IPsec interface that it creates automatically.
Remote Gateway	Select the category of the remote connection: Static IP Address — If the remote peer has a static IP address. Dialup User — If one or more FortiClient or FortiGate dialup clients with dynamic IP addresses will connect to the FortiGate unit. Dynamic DNS — If a remote peer that has a domain name and subscribes to a dynamic DNS service will connect to the FortiGate unit.
IP Address	If you selected Static IP Address, enter the IP address of the remote peer.
Dynamic DNS	If you selected Dynamic DNS, enter the domain name of the remote peer.
Local Interface	This option is available in NAT mode only. Select the name of the interface through which remote peers or dialup clients connect to the FortiGate unit. By default, the local VPN gateway IP address is the IP address of the interface that you selected.
Mode	Main mode — the Phase 1 parameters are exchanged in multiple rounds with encrypted authentication information. Aggressive mode — the Phase 1 parameters are exchanged in single message with authentication information that is not encrypted. When the remote VPN peer has a dynamic IP address and is authenticated by a pre-shared key, you must select Aggressive mode if there is more than one dialup phase1 configuration for the interface IP address. When the remote VPN peer has a dynamic IP address and is authenticated by a certificate, you must select Aggressive mode if there is more than one Phase 1 configuration for the interface IP address and these Phase 1 configurations use different proposals.
Authentication Method	Select Preshared Key or RSA Signature.

 

Pre-shared Key	If you selected Pre-shared Key, enter the pre-shared key that the FortiGate unit will use to authenticate itself to the remote peer or dialup client during Phase 1 negotiations. You must define the same key at the remote peer or client. The key must contain at least 6 printable characters. For optimum protection against currently known attacks, the key must consist of a minimum of 16 randomly chosen alphanumeric characters. The limit is 128 characters.
Certificate Name	If you selected RSA Signature, select the name of the server certificate that the FortiGate unit will use to authenticate itself to the remote peer or dialup client during Phase 1 negotiations. For information about obtaining and loading the required server certificate, see the FortiOS User Authentication guide.
Peer Options	Peer options are available to authenticate VPN peers or clients, depending on the Remote Gateway and Authentication Method settings.
Any peer ID	Accept the local ID of any remote VPN peer or client. The FortiGate unit does not check identifiers (local IDs). You can set Mode to Aggressive or Main. You can use this option with RSA Signature authentication. But, for highest security, configure a PKI user/group for the peer and set Peer Options to Accept this peer certificate only.
This peer ID	This option is available when Aggressive Mode is enabled. Enter the identifier that is used to authenticate the remote peer. This identifier must match the Local ID that the remote peer’s administrator has configured. If the remote peer is a FortiGate unit, the identifier is specified in the Local ID field of the Advanced Phase 1 configuration. If the remote peer is a FortiClient user, the identifier is specified in the Local ID field, accessed by selecting Config in the Policy section of the VPN connection’s Advanced Settings. In circumstances where multiple remote dialup VPN tunnels exist, each tunnel must have a peer ID set.
Peer ID from dialup group	Authenticate multiple FortiGate or FortiClient dialup clients that use unique identifiers and unique pre-shared keys (or unique pre-shared keys only) through the same VPN tunnel. You must create a dialup user group for authentication purposes. Select the group from the list next to the Peer ID from dialup group option. You must set Mode to Aggressive when the dialup clients use unique identifiers and unique pre-shared keys. If the dialup clients use unique preshared keys only, you can set Mode to Main if there is only one dialup Phase 1 configuration for this interface IP address.

Phase 1 advanced configuration settings

You can use the following advanced parameters to select the encryption and authentication algorithms that the FortiGate unit uses to generate keys for the IKE exchange. You can also use the following advanced parameters to ensure the smooth operation of Phase 1 negotiations.

These settings are mainly configured in the CLI, although some options are available after the tunnel is created using the VPN Creation Wizard (using the Convert to Custom Tunnel option).

If the FortiGate unit will act as a VPN client, and you are using security certificates for authentication, set the Local ID to the distinguished name (DN) of the local server certificate that the FortiGate unit will use for authentication purposes.

Note that, since FortiOS 5.4, an exact match is required to optimize IKE’s gateway search utilizing binary trees. However, it is also possible to have partial matching of ‘user.peer:cn’ to match peers to gateways by performing a secondary match. When IKE receives IDi of type ASN1.DN, the first search is done with the whole DN string. If none is found, IKE will extract just the CN attribute value and perform a second search.

VXLAN over IPsec

Packets with VXLAN header are encapsulated within IPsec tunnel mode. To configure VXLAN over IPsec – CLI: config vpn ipsec phase1-interface/phase1 edit ipsec set interface <name> set encapsulation vxlan/gre set encapsulation-address ike/ipv4/ipv6 set encap-local-gw4 xxx.xxx.xxx.xxx  set encap-remote-gw xxx.xxx.xxx.xxx next end

 

IPsec tunnel idle timer	You can define an idle timer for IPsec tunnels. When no traffic has passed through the tunnel for the configured idle-timeout value, the IPsec tunnel will be flushed. To configure IPsec tunnel idle timeout – CLI: config vpn ipsec phase1-interface edit p1 set idle-timeout [enable | disable] set idle-timeoutinterval <integer> //IPsec tunnel idle timeout in minutes (10 – 43200). end end
IPv6 Version	Select if you want to use IPv6 addresses for the remote gateway and interface IP addresses.
Local Gateway IP	Specify an IP address for the local end of the VPN tunnel. Select one of the following: Main Interface IP — The FortiGate unit obtains the IP address of the interface from the network interface settings. Specify — Enter a secondary address of the interface selected in the Phase 1 Local Interface field. You cannot configure Interface mode in a transparent mode VDOM.
Phase 1 Proposal	Select the encryption and authentication algorithms used to generate keys for protecting negotiations and add encryption and authentication algorithms as required. You need to select a minimum of one and a maximum of three combinations. The remote peer or client must be configured to use at least one of the proposals that you define. Select one of the following symmetric-key encryption algorithms: DES — Digital Encryption Standard, a 64-bit block algorithm that uses a 56-bit key. 3DES — Triple-DES; plain text is encrypted three times by three keys. AES128 — A 128-bit block algorithm that uses a 128-bit key. AES192 — A 128-bit block algorithm that uses a 192-bit key. AES256 — A 128-bit block algorithm that uses a 256-bit key.

 

	You can select either of the following message digests to check the authenticity of messages during an encrypted session: MD5 — Message Digest 5. SHA1 — Secure Hash Algorithm 1 – a 160-bit message digest. To specify one combination only, set the Encryption and Authentication options of the second combination to NULL. To specify a third combination, use the Add button beside the fields for the second combination.
Diffie-Hellman Group	Select one or more Diffie-Hellman groups from DH groups 1, 2, 5, and 14 through 21. At least one of the Diffie-Hellman Group settings on the remote peer or client must match one the selections on the FortiGate unit. Failure to match one or more DH groups will result in failed negotiations.
Keylife	Enter the time (in seconds) that must pass before the IKE encryption key expires. When the key expires, a new key is generated without interrupting service. The keylife can be from 120 to 172 800 seconds.
Local ID	If the FortiGate unit will act as a VPN client and you are using peer IDs for authentication purposes, enter the identifier that the FortiGate unit will supply to the VPN server during the Phase 1 exchange. If the FortiGate unit will act as a VPN client, and you are using security certificates for authentication, select the distinguished name (DN) of the local server certificate that the FortiGate unit will use for authentication purposes. If the FortiGate unit is a dialup client and will not be sharing a tunnel with other dialup clients (that is, the tunnel will be dedicated to this Fortinet dialup client), set Mode to Aggressive. Note that this Local ID value must match the peer ID value given for the remote VPN peer’s Peer Options.

 

XAuth	This option supports the authentication of dialup clients. It is available for IKE v1 only. Disable — Select if you do not use XAuth. Enable as Client — If the FortiGate unit is a dialup client, enter the user name and password that the FortiGate unit will need to authenticate itself to the remote XAuth server. Enable as Server — This is available only if Remote Gateway is set to Dialup User. Dialup clients authenticate as members of a dialup user group. You must first create a user group for the dialup clients that need access to the network behind the FortiGate unit. You must also configure the FortiGate unit to forward authentication requests to an external RADIUS or LDAP authentication server. Select a Server Type setting to determine the type of encryption method to use between the FortiGate unit, the XAuth client and the external authentication server, and then select the user group from the User Group list.
Username	Enter the user name that is used for authentication.
Password	Enter the password that is used for authentication.
NAT Traversal	Select the check box if a NAT device exists between the local FortiGate unit and the VPN peer or client. The local FortiGate unit and the VPN peer or client must have the same NAT traversal setting (both selected or both cleared) to connect reliably. Additionally, you can force IPsec to use NAT traversal. If NAT is set to Forced, the FortiGate will use a port value of zero when constructing the NAT discovery hash for the peer. This causes the peer to think it is behind a NAT device, and it will use UDP encapsulation for IPsec, even if no NAT is present. This approach maintains interoperability with any IPsec implementation that supports the NAT-T RFC.
Keepalive Frequency	If you enabled NAT-traversal, enter a keepalive frequency setting.
Dead Peer Detection	Select this check box to reestablish VPN tunnels on idle connections and clean up dead IKE peers if required. You can use this option to receive notification whenever a tunnel goes up or down, or to keep the tunnel connection open when no traffic is being generated inside the tunnel. For example, in scenarios where a dialup client or dynamic DNS peer connects from an IP address that changes periodically, traffic may be suspended while the IP address changes. With Dead Peer Detection selected, you can use the config vpn ipsec phase1 (tunnel mode) or config vpn ipsec phase1- interface (interface mode) CLI command to optionally specify a retry count and a retry interval.

 

IKEv1 fragmentation

UDP fragmentation can cause issues in IPsec when either the ISP or perimeter firewall(s) cannot pass or fragment the oversized UDP packets that occur when using a very large public security key (PSK). The result is that IPsec tunnels do not come up. The solution is IKE fragmentation.

For most configurations, enabling IKE fragmentation allows connections to automatically establish when they otherwise might have failed due to intermediate nodes dropping IKE messages containing large certificates, which typically push the packet size over 1500 bytes.

FortiOS will fragment a packet on sending if, and only if, all the following are true:

• Phase 1 contains “set fragmentation enable”.
• The packet is larger than the minimum MTU (576 for IPv4, 1280 for IPv6). l The packet is being re-transmitted.

By default, IKE fragmentation is enabled, but upon upgrading, any existing phase1-interface may have have “set fragmentation disable” added in order to preserve the existing behaviour of not supporting fragmentation.

Enabling or disabling IKE fragmentation – CLI

config vpn ipsec phase1-interface edit 1 set fragmentation [enable | disable]

next

end

IKEv2 fragmentation

With IKEv2, because RFC 7383 requires each fragment to be individually encrypted and authenticated, we would have to keep a copy of the unencrypted payloads around for each outgoing packet, in case the original single packet was never answered and we wanted to retry with fragments. With the following implementation, if the IKE payloads are greater than a configured threshold, the IKE packets are preemptively fragmented and encrypted.

CLI syntax

config vpn ipsec phase1-interface edit ike set ike-version 2

set fragmentation [enable|disable] set fragmentation-mtu [500-16000]

next

end

Phase 2 configuration

After IPsec Phase 1 negotiations end successfully, you begin Phase 2. You can configure the Phase 2 parameters to define the algorithms that the FortiGate unit may use to encrypt and transfer data for the remainder of the session. During Phase 2, you select specific IPsec security associations needed to implement security services and establish a tunnel.

The basic Phase 2 settings associate IPsec Phase 2 parameters with the Phase 1 configuration that specifies the remote end point of the VPN tunnel. In most cases, you need to configure only basic Phase 2 settings.

2

These settings are mainly configured in the CLI, although some options are available after the tunnel is created using the VPN Creation Wizard (using the Convert to Custom Tunnel option).

Name	Type a name to identify the Phase 2 configuration.
Phase 1	Select the Phase 1 tunnel configuration. For more information on configuring Phase 1, see Phase 1 configuration on page 38. The Phase 1 configuration describes how remote VPN peers or clients will be authenticated on this tunnel, and how the connection to the remote peer or client will be secured.
Advanced	Define advanced Phase 2 parameters. For more information, see Phase 2 advanced configuration settings below.

Phase 2 advanced configuration settings

In Phase 2, the FortiGate unit and the VPN peer or client exchange keys again to establish a secure communication channel between them. You select the encryption and authentication algorithms needed to generate keys for protecting the implementation details of Security Associations (SAs). These are called Phase 2 Proposal parameters. The keys are generated automatically using a Diffie-Hellman algorithm.

You can use a number of additional advanced Phase 2 settings to enhance the operation of the tunnel.

Phase 2 Proposal

Select the encryption and authentication algorithms that will be proposed to the remote VPN peer. You can specify up to three proposals. To establish a VPN connection, at least one of the proposals that you specify must match configuration on the remote peer. Initially there are two proposals. Add and Delete icons are next to the second Authentication field. It is invalid to set both Encryption and Authentication to NULL.

Encryption

Select a symmetric-key algorithms: NULL — Do not use an encryption algorithm. DES — Digital Encryption Standard, a 64-bit block algorithm that uses a 56-bit key. 3DES — Triple-DES; plain text is encrypted three times by three keys. AES128 — A 128-bit block algorithm that uses a 128-bit key. AES192 — A 128-bit block algorithm that uses a 192-bit key. AES256 — A 128-bit block algorithm that uses a 256-bit key.

 

Authentication	You can select either of the following message digests to check the authenticity of messages during an encrypted session: NULL — Do not use a message digest. MD5 — Message Digest 5. SHA1 — Secure Hash Algorithm 1 – a 160-bit message digest. To specify one combination only, set the Encryption and Authentication options of the second combination to NULL. To specify a third combination, use the Add button beside the fields for the second combination.
Enable replay detection	Replay attacks occur when an unauthorized party intercepts a series of IPsec packets and replays them back into the tunnel.
Enable perfect forward secrecy (PFS)	Perfect forward secrecy (PFS) improves security by forcing a new Diffie-Hellman exchange whenever keylife expires.
Diffie-Hellman Group	Select one Diffie-Hellman group (1, 2, 5, or 14 through 21). This must match the DH Group that the remote peer or dialup client uses.
Keylife	Select the method for determining when the Phase 2 key expires: Seconds, KBytes, or Both. If you select Both, the key expires when either the time has passed or the number of KB have been processed.
Autokey Keep Alive	Select the check box if you want the tunnel to remain active when no data is being processed.
Auto-negotiate	Enable the option if you want the tunnel to be automatically renegotiated when the tunnel expires.
DHCP-IPsec	Provide IP addresses dynamically to VPN clients. This is available for Phase 2 configurations associated with a dialup Phase 1 configuration. You also need configure a DHCP server or relay on the private network interface. You must configure the DHCP parameters separately. If you configure the DHCP server to assign IP addresses based on RADIUS user group attributes, you must also set the Phase 1 Peer Options to Peer ID from dialup group and select the appropriate user group. See Phase 1 configuration on page 38. If the FortiGate unit acts as a dialup server and you manually assigned FortiClient dialup clients VIP addresses that match the network behind the dialup server, selecting the check box will cause the FortiGate unit to act as a proxy for the dialup clients.

2

Quick Mode Selector	Specify the source and destination IP addresses to be used as selectors for IKE negotiations. If the FortiGate unit is a dialup server, keep the default value of 0.0.0.0/0 unless you need to circumvent problems caused by ambiguous IP addresses between one or more of the private networks making up the VPN. You can specify a single host IP address, an IP address range, or a network address. You may optionally specify source and destination port numbers and a protocol number. If you are editing an existing Phase 2 configuration, the Source address and Destination address fields are unavailable if the tunnel has been configured to use firewall addresses as selectors. This option exists only in the CLI.
Source address	If the FortiGate unit is a dialup server, enter the source IP address that corresponds to the local senders or network behind the local VPN peer (for example, 172.16.5.0/24 or 172.16.5.0/255.255.255.0 for a subnet, or 172.16.5.1/32 or 172.16.5.1/255.255.255.255 for a server or host, or 192.168.10.[80-100] or 192.168.10.80192.168.10.100 for an address range). A value of 0.0.0.0/0 means all IP addresses behind the local VPN peer. If the FortiGate unit is a dialup client, source address must refer to the private network behind the Fortinet dialup client.
Source port	Enter the port number that the local VPN peer uses to transport traffic related to the specified service (protocol number). The range is from 0 to 65535. To specify all ports, type 0.
Destination address	Enter the destination IP address that corresponds to the recipients or network behind the remote VPN peer (for example, 192.168.20.0/24 for a subnet, or 172.16.5.1/32 for a server or host, or 192.168.10. [80-100] for an address range). A value of 0.0.0.0/0 means all IP addresses behind the remote VPN peer.
Destination port	Enter the port number that the remote VPN peer uses to transport traffic related to the specified service (protocol number). To specify all ports, enter 0.
Protocol	Enter the IP protocol number of the service. To specify all services, enter 0.

FortiClient VPN

Use the FortiClient VPN for OS X, Windows, and Android VPN Wizard option when configuring an IPsec VPN for remote users to connect to the VPN tunnel using FortiClient.

When configuring a FortiClient VPN connection, the settings for Phase 1 and Phase 2 settings are automatically configured by the FortiGate unit. They are set to:

• Remote Gateway — Dialup User
• Mode — Aggressive
• Default settings for Phase 1 and 2 Proposals
• XAUTH Enable as Server (Auto)
• IKE mode-config will be enabled
• Peer Option — “Any peer ID”

The remainder of the settings use the current FortiGate defaults. Note that FortiClient settings need to match these FortiGate defaults. If you need to configure advanced settings for the FortiClient VPN, you must do so using the CLI.

Name		Enter a name for the FortiClient VPN.
Local Outgoing Interface		Select the local outgoing interface for the VPN.
Authentication Method		Select the type of authentication used when logging in to the VPN.
Preshared Key		If Pre-shared Key was selected in Authentication Method, enter the pre-shared key in the field provided.
User Group		Select a user group. You can also create a user group from the drop-down list by selecting Create New.
Address Range Start IP		Enter the start IP address for the DHCP address range for the client.
Address Range End IP		Enter the end IP address for the address range.
Subnet Mask		Enter the subnet mask.
Enable IPv4 Split Tunnel		Enabled by default, this option enables the FortiClient user to use the VPN to access internal resources while other Internet access is not sent over the VPN, alleviating potential traffic bottlenecks in the VPN connection. Disable this option to have all traffic sent through the VPN tunnel.
Accessible Networks		Select from a list of internal networks that the FortiClient user can access.
Client Options		These options affect how the FortiClient application behaves when connected to the FortiGate VPN tunnel. When enabled, a check box for the corresponding option appears on the VPN login screen in FortiClient, and is not enabled by default. Save Password – When enabled, if the user selects this option, their password is stored on the user’s computer and will automatically populate each time they connect to the VPN. Auto Connect – When enabled, if the user selects this option, when the FortiClient application is launched, for example after a reboot or system startup, FortiClient will automatically attempt to connect to the VPN tunnel. Always Up (Keep Alive) – When enabled, if the user selects this option, the FortiClient connection will not shut down. When not selected, during periods of inactivity, FortiClient will attempt to stay connected every three minutes for a maximum of 10 minutes.

 

Concentrator

Endpoint Registration	When selected, the FortiGate unit requests a registration key from FortiClient before a connection can be established. A registration key is defined by going to System > Advanced. For more information on FortiClient VPN connections to a FortiGate unit, see the FortiClient Administration Guide.
DNS Server	Select which DNS server to use for this VPN: Use System DNS — Use the same DNS servers as the FortiGate unit. These are configured at Network > DNS. This is the default option. Specify — Specify the IP address of a different DNS server.

Concentrator

In a hub-and-spoke configuration, policy-based VPN connections to a number of remote peers radiate from a single, central FortiGate unit. Site-to-site connections between the remote peers do not exist; however, you can establish VPN tunnels between any two of the remote peers through the FortiGate unit’s “hub”.

In a hub-and-spoke network, all VPN tunnels terminate at the hub. The peers that connect to the hub are known as “spokes”. The hub functions as a concentrator on the network, managing all VPN connections between the spokes. VPN traffic passes from one tunnel to the other through the hub.

You define a concentrator to include spokes in the hub-and-spoke configuration. You create the concentrator in VPN > IPsec Concentrator and select Create New. A concentrator configuration specifies which spokes to include in an IPsec hub-and-spoke configuration.

Concentrator Name	Type a name for the concentrator.
Available Tunnels	A list of defined IPsec VPN tunnels. Select a tunnel from the list and then select the right arrow.
Members	A list of tunnels that are members of the concentrator. To remove a tunnel from the concentrator, select the tunnel and select the left arrow.

IPsec Monitor

You can use the IPsec Monitor to view activity on IPsec VPN tunnels and start or stop those tunnels. The display provides a list of addresses, proxy IDs, and timeout information for all active tunnels, including tunnel mode and route-based (interface mode) tunnels.

To view the IPsec monitor, go to Monitor > IPsec Monitor.

Tunnels are considered as “up” if at least one phase 2 selector is active. To avoid confusion, when a tunnel is down, IPsec Monitor will keep the Phase 2 Selectors column, but hide it by default and be replaced with Phase 1 status column.

IPsec Monitor

For dialup VPNs, the list provides status information about the VPN tunnels established by dialup clients, and their IP addresses.

For static IP or dynamic DNS VPNs, the list provides status and IP addressing information about VPN tunnels, active or not, to remote peers that have static IP addresses or domain names. You can also start and stop individual tunnels from the list.

IPsec VPN overview

This section provides a brief overview of IPsec technology and includes general information about how to configure IPsec VPNs using this guide.

The following topics are included in this section:

Types of VPNs

Planning your VPN

General preparation steps

How to use this guide to configure an IPsec VPN

 

VPN configurations interact with the firewall component of the FortiGate unit. There must be a security policy in place to permit traffic to pass between the private network and the VPN tunnel.

Security policies for VPNs specify:

• The FortiGate interface that provides the physical connection to the remote VPN gateway, usually an interface connected to the Internet
• The FortiGate interface that connects to the private network
• IP addresses associated with data that has to be encrypted and decrypted
• Optionally, a schedule that restricts when the VPN can operate
• Optionally, the services (types of data) that can be sent

When the first packet of data that meets all of the conditions of the security policy arrives at the FortiGate unit, a VPN tunnel may be initiated and the encryption or decryption of data is performed automatically afterward. For more information, see Defining VPN security policies on page 1.

Where possible, you should create route-based VPNs. Generally, route-based VPNs are more flexible and easier to configure than policy-based VPNs — by default they are treated as interfaces. However, these two VPN types have different requirements that limit where they can be used.

Types of VPNs

FortiGate unit VPNs can be policy-based or route-based. There is little difference between the two types. In both cases, you specify Phase 1 and Phase 2 settings. However there is a difference in implementation. A route-based VPN creates a virtual IPsec network interface that applies encryption or decryption as needed to any traffic that it carries. That is why route-based VPNs are also known as interface-based VPNs. A policy-based VPN is implemented through a special security policy that applies the encryption you specified in the Phase 1 and Phase 2 settings.

Route-based VPNs

For a route-based VPN, you create two security policies between the virtual IPsec interface and the interface that connects to the private network. In one policy, the virtual interface is the source. In the other policy, the virtual interface is the destination.  This creates bidirectional policies that ensure traffic will flow in both directions over the VPN.

A route-based VPN is also known as an interface-based VPN.

overview                                                                                                                       Types of VPNs

Each route-based IPsec VPN tunnel requires a virtual IPsec interface. As such, the amount of possible route-based IPsec VPNs is limited by the system.interface table size. The system.interface table size for most devices is 8192.

For a complete list of table sizes for all devices, refer to the Maximum Values table.

Policy-based VPNs

For a policy-based VPN, one security policy enables communication in both directions.  You enable inbound and outbound traffic as needed within that policy, or create multiple policies of this type to handle different types of traffic differently. For example HTTPS traffic may not require the same level of scanning as FTP traffic.

A policy-based VPN is also known as a tunnel-mode VPN.

Comparing policy-based or route-based VPNs

For both VPN types you create Phase 1 and Phase 2 configurations. Both types are handled in the stateful inspection security layer, assuming there is no IPS or AV. For more information on the three security layers, see the FortiOS Troubleshooting guide.

The main difference is in the security policy.

You create a policy-based VPN by defining an IPSEC security policy between two network interfaces and associating it with the VPN tunnel (Phase 1) configuration.

You create a route-based VPN by creating a virtual IPsec interface. You then define a regular ACCEPT security policy to permit traffic to flow between the virtual IPsec interface and another network interface. And lastly, configure a static route to allow traffic over the VPN.

Where possible, you should create route-based VPNs. Generally, route-based VPNs are more flexible and easier to configure than policy-based VPNs — by default they are treated as interfaces. However, these two VPN types have different requirements that limit where they can be used.

Comparison of policy-based and route-based VPNs

Features	Policy-based	Route-based
Both NAT and transparent modes available	Yes	NAT mode only
L2TP-over-IPsec supported	Yes	Yes
GRE-over-IPsec supported	No	Yes
security policy requirements	Requires a security policy with IPSEC action that specifies the VPN tunnel	Requires only a simple security policy with ACCEPT action
Number of policies per VPN	One policy controls connections in both directions	A separate policy is required for connections in each direction

Planning your VPN                                                                                                                   IPsec VPN overview

Planning your VPN

It is a good idea to plan the VPN configuration ahead of time. This will save time later and help you configure your VPN correctly.

All VPN configurations are comprised of numerous required and optional parameters. Before you begin, you need to determine:

• Where the IP traffic originates and where it needs to be delivered
• Which hosts, servers, or networks to include in the VPN
• Which VPN devices to include in the configuration
• Through which interfaces the VPN devices communicate
• Through which interfaces do private networks access the VPN gateways

Once you have this information, you can select a VPN topology that suits the network environment.

Network topologies

The topology of your network will determine how remote peers and clients connect to the VPN and how VPN traffic is routed.

VPN network topologies and brief descriptions

Topology	Description
Gateway-to-gateway configurations	Standard one-to-one VPN between two FortiGate units. See Gateway-togateway configurations  on page 1.
Hub-and-spoke configurations	One central FortiGate unit has multiple VPNs to other remote FortiGate units. See Hub-and-spoke configurations on page 1.
Dynamic DNS configuration	One end of the VPN tunnel has a changing IP address and the other end must go to a dynamic DNS server for the current IP address before establishing a tunnel. See Dynamic DNS configuration on page 1.
FortiClient dialup-client configurations	Typically remote FortiClient dialup-clients use dynamic IP addresses through NAT devices. The FortiGate unit acts as a dialup server allowing dialup VPN connections from multiple sources. See FortiClient dialup-client configurations on page 1.
FortiGate dialup-client configurations	Similar to FortiClient dialup-client configurations but with more gateway-togateway settings such as unique user authentication for multiple users on a single VPN tunnel. See FortiGate dialup-client configurations  on page 1.
Internet-browsing configuration	Secure web browsing performed by dialup VPN clients, and/or hosts behind a remote VPN peer. See Internet-browsing configuration on page 1.

overview                                                                                                       General preparation steps

Topology	Description
Redundant VPN configurations	Options for supporting redundant and partially redundant IPsec VPNs, using route-based approaches. See Redundant VPN configurations on page 1.
Transparent mode VPNs	In transparent mode, the FortiGate acts as a bridge with all incoming traffic being broadcast back out on all other interfaces. Routing and NAT must be performed on external routers. See Transparent mode VPNs on page 1.
L2TP and IPsec (Microsoft VPN)	Configure VPN for Microsoft Windows dialup clients using the built in L2TP software. Users do not have to install any See L2TP and IPsec (Microsoft VPN) on page 1.

These sections contain high-level configuration guidelines with cross-references to detailed configuration procedures. If you need more detail to complete a step, select the cross-reference in the step to drill-down to more detail. Return to the original procedure to complete the procedure. For a general overview of how to configure a VPN, see Planning your VPN .

General preparation steps

A VPN configuration defines relationships between the VPN devices and the private hosts, servers, or networks making up the VPN. Configuring a VPN involves gathering and recording the following information. You will need this information to configure the VPN.

• The private IP addresses of participating hosts, servers, and/or networks. These IP addresses represent the source addresses of traffic that is permitted to pass through the VPN. A IP source address can be an individual IP address, an address range, or a subnet address.
• The public IP addresses of the VPN end-point interfaces. The VPN devices establish tunnels with each other through these interfaces.
• The private IP addresses associated with the VPN-device interfaces to the private networks. Computers on the private networks behind the VPN gateways will connect to their VPN gateways through these interfaces.

How to use this guide to configure an IPsec VPN

This guide uses a task-based approach to provide all of the procedures needed to create different types of VPN configurations. Follow the step-by-step configuration procedures in this guide to set up the VPN. The following configuration procedures are common to all IPsec VPNs:

1. Define the Phase 1 parameters that the FortiGate unit needs to authenticate remote peers or clients and establish a secure a connection. See Phase 1 parameters on page 52.
2. Define the Phase 2 parameters that the FortiGate unit needs to create a VPN tunnel with a remote peer or dialup client. See Phase 2 parameters on page 72.
3. Specify the source and destination addresses of IP packets that are to be transported through the VPN tunnel. See Defining policy addresses on page 1.

How to use this guide to configure an IPsec VPN                                                                         IPsec VPN overview

4. Create an IPsec security policy to define the scope of permitted services between the IP source and destination addresses. See Defining VPN security policies on page 1.

These steps assume you configure the FortiGate unit to generate unique IPsec encryption and authentication keys automatically. In situations where a remote VPN peer or client requires a specific IPsec encryption and authentication key, you must configure the FortiGate unit to use manual keys instead of performing Steps 1 and 2.

 

IPsec VPN concepts

Virtual Private Network (VPN) technology enables remote users to connect to private computer networks to gain access to their resources in a secure way. For example, an employee traveling or working from home can use a VPN to securely access the office network through the Internet.

Instead of remotely logging on to a private network using an unencrypted and unsecure Internet connection, the use of a VPN ensures that unauthorized parties cannot access the office network and cannot intercept any of the information that is exchanged between the employee and the office. It is also common to use a VPN to connect the private networks of two or more offices.

Fortinet offers VPN capabilities in the FortiGate Unified Threat Management (UTM) appliance and in the

FortiClient Endpoint Security suite of applications. A FortiGate unit can be installed on a private network, and FortiClient software can be installed on the user’s computer. It is also possible to use a FortiGate unit to connect to the private network instead of using FortiClient software.

This chapter discusses VPN terms and concepts including:

VPN tunnels

VPN gateways

Clients, servers, and peers

Encryption

Authentication

Phase 1 and Phase 2 settings

IKE and IPsec packet processing

VPN tunnels

The data path between a user’s computer and a private network through a VPN is referred to as a tunnel. Like a physical tunnel, the data path is accessible only at both ends. In the telecommuting scenario, the tunnel runs between the FortiClient application on the user’s PC, or a FortiGate unit or other network device and the FortiGate unit on the office private network.

Encapsulation makes this possible. IPsec packets pass from one end of the tunnel to the other and contain data packets that are exchanged between the local user and the remote private network. Encryption of the data packets ensures that any third-party who intercepts the IPsec packets can not access the data.

VPN tunnels Encoded data going through a VPN tunnel

You can create a VPN tunnel between:

• A PC equipped with the FortiClient application and a FortiGate unit
• Two FortiGate units
• Third-party VPN software and a FortiGate unit

For more information on third-party VPN software, refer to the Fortinet Knowledge Base for more information.

Tunnel templates

Several tunnel templates are available in the IPsec VPN Wizard that cover a variety of different types of IPsec VPN. A list of these templates appear on the first page of the Wizard, located at VPN > IPsec Wizard. The tunnel template list follows.

IPsec VPN Wizard options

VPN Type	Remote Device Type	NAT Options	Description
Site to Site	FortiGate	l   No NAT between sites l   This site is behind NAT l   The remote site is behind NAT	Static tunnel between this FortiGate and a remote FortiGate.
	Cisco	l   No NAT between sites l   This site is behind NAT l   The remote site is behind NAT	Static tunnel between this FortiGate and a remote Cisco firewall.

VPN gateways

VPN Type	Remote Device Type	NAT Options	Description
Remote Access	FortiClient VPN for OS X, Windows, and Android	N/A	On-demand tunnel for users using the FortiClient software.
	iOS Native	N/A	On-demand tunnel for iPhone/iPad users using the native iOS IPsec client.
	Android Native	N/A	On-demand tunnel for Android users using the native L2TP/IPsec client.
	Windows Native	N/A	On-demand tunnel for Android users using the native L2TP/IPsec client.
	Cisco AnyConnect	N/A	On-demand tunnel for users using the Cisco IPsec client.
Custom	N/A	N/A	No Template.

VPN tunnel list

Once you create an IPsec VPN tunnel, it appears in the VPN tunnel list at VPN > IPsec Tunnels. By default, the tunnel list indicates the name of the tunnel, its interface binding, the tunnel template used, and the tunnel status. If you right-click on the table header row, you can include columns for comments, IKE version, mode (aggressive vs main), phase 2 proposals, and reference number. The tunnel list page also includes the option to create a new tunnel, as well as the options to edit or delete a highlighted tunnel.

FortiView VPN tunnel map

A geospatial map can be found under FortiView > VPN Map to help visualize IPsec (and SSL) VPN connections to a FortiGate using Google Maps. This feature adds a geographical-IP API service for resolving spatial locations from IP addresses.

VPN gateways

A gateway is a router that connects the local network to other networks. The default gateway setting in your computer’s TCP/IP properties specifies the gateway for your local network.

VPN gateways

A VPN gateway functions as one end of a VPN tunnel. It receives incoming IPsec packets, decrypts the encapsulated data packets and passes the data packets to the local network. Also, it encrypts data packets destined for the other end of the VPN tunnel, encapsulates them, and sends the IPsec packets to the other VPN gateway. The VPN gateway is a FortiGate unit because the private network behind it is protected, ensuring the security of the unencrypted VPN data. The gateway can also be FortiClient software running on a PC since the unencrypted data is secure on the PC.

The IP address of a VPN gateway is usually the IP address of the network interface that connects to the Internet. Optionally, you can define a secondary IP address for the interface and use that address as the local VPN gateway address. The benefit of doing this is that your existing setup is not affected by the VPN settings.

The following diagram shows a VPN connection between two private networks with FortiGate units acting as the VPN gateways. This configuration is commonly referred to as Gateway-to-Gateway IPsec VPN.

VPN tunnel between two private networks

Although the IPsec traffic may actually pass through many Internet routers, you can visualize the VPN tunnel as a simple secure connection between the two FortiGate units.

Users on the two private networks do not need to be aware of the VPN tunnel. The applications on their computers generate packets with the appropriate source and destination addresses, as they normally do. The FortiGate units manage all the details of encrypting, encapsulating, and sending the packets to the remote VPN gateway.

The data is encapsulated in IPsec packets only in the VPN tunnel between the two VPN gateways. Between the user’s computer and the gateway, the data is on the secure private network and it is in regular IP packets.

For example User1 on the Site  A network, at IP address 10.10.1.7, sends packets with destination IP address 192.168.10.8, the address of User2 on the Site B network. The Site A FortiGate unit is configured to send packets with destinations on the 192.168.10.0 network through the VPN, encrypted and encapsulated. Similarly, the Site Clients, servers, and peers

B FortiGate unit is configured to send packets with destinations on the 10.10.1.0 network through the VPN tunnel to the Site A VPN gateway.

In the site-to-site, or gateway-to-gateway VPN shown below, the FortiGate units have static (fixed) IP addresses and either unit can initiate communication.

You can also create a VPN tunnel between an individual PC running FortiClient and a FortiGate unit, as shown below. This is commonly referred to as Client-to-Gateway IPsec VPN.

VPN tunnel between a FortiClient PC and a FortiGate unit

On the PC, the FortiClient application acts as the local VPN gateway. Packets destined for the office network are encrypted, encapsulated into IPsec packets, and sent through the VPN tunnel to the FortiGate unit. Packets for other destinations are routed to the Internet as usual. IPsec packets arriving through the tunnel are decrypted to recover the original IP packets.

Clients, servers, and peers

A FortiGate unit in a VPN can have one of the following roles:

• Server — responds to a request to establish a VPN tunnel.
• Client — contacts a remote VPN gateway and requests a VPN tunnel. l Peer — brings up a VPN tunnel or responds to a request to do so.

The site-to-site VPN shown above is a peer-to-peer relationship. Either FortiGate unit VPN gateway can establish the tunnel and initiate communications. The FortiClient-to-FortiGate VPN shown below is a client-server relationship. The FortiGate unit establishes a tunnel when the FortiClient PC requests one.

Encryption

A FortiGate unit cannot be a VPN server if it has a dynamically-assigned IP address. VPN clients need to be configured with a static IP address for the server. A FortiGate unit acts as a server only when the remote VPN gateway has a dynamic IP address or is a client-only device or application, such as FortiClient.

As a VPN server, a FortiGate unit can also offer automatic configuration for FortiClient PCs. The user needs to know only the IP address of the FortiGate VPN server and a valid user name/password. FortiClient downloads the VPN configuration settings from the FortiGate VPN server. For information about configuring a FortiGate unit as a VPN server, see the FortiClient Administration Guide.

Encryption

Encryption mathematically transforms data to appear as meaningless random numbers. The original data is called plaintext and the encrypted data is called ciphertext. The opposite process, called decryption, performs the inverse operation to recover the original plaintext from the ciphertext.

The process by which the plaintext is transformed to ciphertext and back again is called an algorithm. All algorithms use a small piece of information, a key, in the arithmetic process of converted plaintext to ciphertext, or vice-versa. IPsec uses symmetrical algorithms, in which the same key is used to both encrypt and decrypt the data. The security of an encryption algorithm is determined by the length of the key that it uses. FortiGate IPsec VPNs offer the following encryption algorithms, in descending order of security:

Encryption	Description
AES-GCM	Galois/Counter Mode (GCM), a block cipher mode of operation providing both confidentiality and data origin authentication.
AES256	A 128-bit block algorithm that uses a 256-bit key.
AES192	A 128-bit block algorithm that uses a 192-bit key.
AES128	A 128-bit block algorithm that uses a 128-bit key.
3DES	Triple-DES, in which plain text is DES-encrypted three times by three keys.
DES	Digital Encryption Standard, a 64-bit block algorithm that uses a 56-bit key

The default encryption algorithms provided on FortiGate units make recovery of encrypted data almost impossible without the proper encryption keys.

There is a human factor in the security of encryption. The key must be kept secret, known only to the sender and receiver of the messages. Also, the key must not be something that unauthorized parties might easily guess, such as the sender’s name, birthday or simple sequence such as 123456.

Diffie-Hellman groups

FortiOS IPsec VPN supports the following Diffie-Hellman (DH) asymmetric key algorithms for public key cryptography.

Encryption

DH Group	Description
1	More Modular Exponential (MODP) DH Group with a 768-bit modulus.
2	MODP with a 1024-bit modulus.
5	MODP with a 1536-bit modulus.
14	MODP with a 2048-bit modulus.
15	MODP with a 3027-bit modulus.
16	MODP with a 4096-bit modulus.
17	MODP with a 6144-bit modulus.
18	MODP with a 8192-bit modulus.
19	256-bit random elliptic curve group.
20	384-bit random elliptic curve group.
21	521-bit random elliptic curve group.
27	Brainpool 224-bit elliptic curve group.
28	Brainpool 256-bit elliptic curve group.
29	Brainpool 384-bit elliptic curve group.
30	Brainpool 512-bit elliptic curve group.

* When using aggressive mode, DH groups cannot be negotiated.

By default, DH group 14 is selected, to provide sufficient protection for stronger cipher suites that include AES and SHA2. If you select multiple DH groups, the order they appear in the configuration is the order in which they are negotiates.

If both VPN peers (or a VPN server and its client) have static IP addresses and use aggressive mode, select a single DH group. The setting on the FortiGate unit must be identical to the setting on the remote peer or dialup client.

When the remote VPN peer or client has a dynamic IP address and uses aggressive mode, select up to three DH groups on the FortiGate unit and one DH group on the remote peer or dialup client. The setting on the remote peer or dialup client must be identical to one of the selections on the FortiGate unit.

If the VPN peer or client employs main mode, you can select multiple DH groups. At least one of the settings on the remote peer or dialup client must be identical to the selections on the FortiGate unit.

Authentication

IPsec overheads

The FortiGate sets an IPsec tunnel Maximum Transmission Unit (MTU) of 1436 for 3DES/SHA1 and an MTU of 1412 for AES128/SHA1, as seen with diag vpn tunnel list. This indicates that the FortiGate allocates 64 bytes of overhead for 3DES/SHA1 and 88 bytes for AES128/SHA1, which is the difference if you subtract this MTU from a typical ethernet MTU of 1500 bytes.

During the encryption process, AES/DES operates using a specific size of data which is block size. If data is smaller than that, it will be padded for the operation. MD5/SHA-1 HMAC also operates using a specific block size.

The following table describes the potential maximum overhead for each IPsec encryption:

IPsec Transform Set	IPsec Overhead (Max. bytes)
ESP-AES (256, 192, or 128),ESP-SHA-HMAC, or MD5	73
ESP-AES (256, 192, or 128)	61
ESP-3DES, ESP-DES	45
ESP-(DES or 3DES), ESP-SHA-HMAC, or MD5	57
ESP-Null, ESP-SHA-HMAC, or MD5	45
AH-SHA-HMAC or MD5	44

Authentication

To protect data via encryption, a VPN must ensure that only authorized users can access the private network. You must use either a preshared key on both VPN gateways or RSA X.509 security certificates. The examples in this guide use only preshared key authentication. Refer to the Fortinet Knowledge Base for articles on RSA X.509 security certificates.

Preshared keys

A preshared key contains at least six random alphanumeric characters. Users of the VPN must obtain the preshared key from the person who manages the VPN server and add the preshared key to their VPN client configuration.

Although it looks like a password, the preshared key, also known as a shared secret, is never sent by either gateway. The preshared key is used in the calculations at each end that generate the encryption keys. As soon as the VPN peers attempt to exchange encrypted data, preshared keys that do not match will cause the process to fail.

Additional authentication

To increase security, you can require additional means of authentication from users, such as:

Phase 1 and Phase 2 settings

• An identifier, called a peer ID or a local ID.
• Extended authentication (XAUTH) which imposes an additional user name/password requirement.

A Local ID is an alphanumeric value assigned in the Phase 1 configuration. The Local ID of a peer is called a Peer

ID.

In FortiOS 5.2, new authentication methods have been implemented for IKE: ECDSA-256, ECDSA-384, and ECDSA-521. However, AES-XCBC is not supported.

Phase 1 and Phase 2 settings

A VPN tunnel is established in two phases: Phase 1 and Phase 2. Several parameters determine how this is done. Except for IP addresses, the settings simply need to match at both VPN gateways. There are defaults that are appropriate for most cases.

FortiClient distinguishes between Phase 1 and Phase 2 only in the VPN Advanced settings and uses different terms. Phase 1 is called the IKE Policy. Phase 2 is called the IPsec Policy.

Phase 1

In Phase 1, the two VPN gateways exchange information about the encryption algorithms that they support and then establish a temporary secure connection to exchange authentication information.

When you configure your FortiGate unit or FortiClient application, you must specify the following settings for Phase 1:

Remote gateway	The remote VPN gateway’s address. FortiGate units also have the option of operating only as a server by selecting the “Dialup User” option.
Preshared key	This must be the same at both ends. It is used to encrypt Phase 1 authentication information.
Local interface	The network interface that connects to the other VPN gateway. This applies on a FortiGate unit only.

All other Phase 1 settings have default values. These settings mainly configure the types of encryption to be used. The default settings on FortiGate units and in the FortiClient application are compatible. The examples in this guide use these defaults.

For more detailed information about Phase 1 settings, see Phase 1 parameters on page 52.

Phase 2

Similar to the Phase 1 process, the two VPN gateways exchange information about the encryption algorithms that they support for Phase 2. You may choose different encryption for Phase 1 and Phase 2. If both gateways have at least one encryption algorithm in common, a VPN tunnel can be established. Keep in mind that more algorithms each phase does not share with the other gateway, the longer negotiations will take. In extreme cases this may cause timeouts during negotiations.

 

To configure default Phase 2 settings on a FortiGate unit, you need only select the name of the corresponding Phase 1 configuration. In FortiClient, no action is required to enable default Phase 2 settings.

For more detailed information about Phase 2 settings, see Phase 2 parameters on page 72.

Security Association

The establishment of a Security Association (SA) is the successful outcome of Phase 1 negotiations. Each peer maintains a database of information about VPN connections. The information in each SA can include cryptographic algorithms and keys, keylife, and the current packet sequence number. This information is kept synchronized as the VPN operates. Each SA has a Security Parameter Index (SPI) that is provided to the remote peer at the time the SA is established. Subsequent IPsec packets from the peer always reference the relevant SPI. It is possible for peers to have multiple VPNs active simultaneously, and correspondingly multiple SPIs.

The IPsec SA connect message generated is used to install dynamic selectors. These selectors can be installed via the auto-negotiate mechanism. When phase 2 has auto-negotiate enabled, and phase 1 has mesh selectortype set to subnet, a new dynamic selector will be installed for each combination of source and destination subnets. Each dynamic selector will inherit the auto-negotiate option from the template selector and begin SA negotiation. Phase 2 selector sources from dial-up clients will all establish SAs without traffic being initiated from the client subnets to the hub.

Remote IP address change detection

SAs are stored in a hash table when keyed off the IPsec SA SPI value. This enables the FortiGate, for each inbound ESP packet received, to immediately look up the SA and compare the stored IP address against the one in the incoming packet. If the incoming and stored IP addresses differ, an IP address change can be made in the kernel SA, and an update event can be triggered for IKE.

IKE and IPsec packet processing

Internet Key Exchange (IKE) is the protocol used to set up SAs in IPsec negotiation. As described in Phase 1 parameters on page 52, you can optionally choose IKEv2 over IKEv1 if you configure a route-based IPsec VPN. IKEv2 simplifies the negotiation process, in that it provides no choice of Aggressive or Main mode in Phase 1. IKEv2 also uses less bandwidth.

The following sections identify how IKE versions 1 and 2 operate and differentiate.

IKEv1

Phase 1

A peer, identified in the IPsec policy configuration, begins the IKE negotiation process. This IKE Security Association (SA) agreement is known as Phase 1. The Phase 1 parameters identify the remote peer or clients and supports authentication through pre-shared key (PSK) or digital certificate. You can increase access security further using peer identifiers, certificate distinguished names, group names, or the FortiGate extended authentication (XAuth) option for authentication purposes. Basically, Phase 1 authenticates a remote peer and sets up a secure communication channel for establishing Phase 2, which negotiates the IPsec SA.

IKE and IPsec packet processing

IKE Phase 1 can occur in either Main mode or Aggressive mode. For more information, see  Phase 1 parameters on page 52.

IKE Phase 1 is successful only when the following are true:

• Each peer negotiates a matching IKE SA policy.
• Each peer is authenticated and their identities protected.
• The Diffie-Hellman exchange is authenticated (the pre-shared secret keys match).

For more information on Phase 1, see Phase 1 parameters on page 52.

Phase 2

Phase 2 parameters define the algorithms that the FortiGate unit can use to encrypt and transfer data for the remainder of the session in an IPsec SA. The basic Phase 2 settings associate IPsec Phase 2 parameters with a Phase 1 configuration.

In Phase 2, the VPN peer or client and the FortiGate unit exchange keys again to establish a more secure communication channel. The Phase 2 Proposal parameters select the encryption and authentication algorithms needed to generate keys for protecting the implementation details of the SA. The keys are generated automatically using a Diffie-Hellman algorithm.

In Phase 2, Quick mode selectors determine which IP addresses can perform IKE negotiations to establish a tunnel. By only allowing authorized IP addresses access to the VPN tunnel, the network is more secure. For more information, see Phase 2 parameters on page 72.

IKE Phase 2 is successful only when the following are true:

• The IPsec SA is established and protected by the IKE SA.
• The IPsec SA is configured to renegotiate after set durations (see Phase 2 parameters on page 72 and Phase 2 parameters on page 72).
• Optional: Replay Detection is enabled. Replay attacks occur when an unauthorized party intercepts a series of IPsec packets and replays them back into the tunnel. See Phase 2 parameters on page 72.
• Optional: Perfect Forward Secrecy (PFS) is enabled. PFS improves security by forcing a new Diffie-Hellman exchange whenever keylife expires. See Phase 2 parameters on page 72.

For more information on Phase 2, see Phase 2 parameters on page 72.

With Phase 2 established, the IPsec tunnel is fully negotiated and traffic between the peers is allowed until the SA terminates (for any number of reasons; time-out, interruption, disconnection, etc).

The entire IKEv1 process is demonstrated in the following diagram:

IKEv2

Phase 1

Unlike Phase 1 of IKEv1, IKEv2 does not provide options for Aggressive or Main mode. Furthermore, Phase 1 of IKEv2 begins immediately with an IKE SA initiation, consisting of only two packets (containing all the information typically contained in four packets for IKEv1), securing the channel such that all following transactions are encrypted (see Phase 1 parameters on page 52).

The encrypted transactions contain the IKE authentication, since remote peers have yet to be authenticated. This stage of IKE authentication in IKEv2 can loosely be called Phase 1.5.

Phase 1.5

As part of this phase, IKE authentication must occur. IKE authentication consists of the following:

• The authentication payloads and Internet Security Association and Key Management Protocol (ISAKMP) identifier.
• The authentication method (RSA, PSK, ECDSA, or EAP). l The IPsec SA parameters.

Due to the number of authentication methods potentially used, and SAs established, the overall IKEv2 negotiation can range from 4 packets (no EAP exchange at all) to many more.

At this point, both peers have a security association complete and ready to encrypt traffic.

IKE and IPsec packet processing

Phase 2

In IKEv1, Phase 2 uses Quick mode to negotiate an IPsec SA between peers. In IKEv2, since the IPsec SA is already established, Phase 2 is essentially only used to negotiate “child” SAs, or to re-key an IPsec SA. That said, there are only two packets for each exchange of this type, similar to the exchange at the outset of Phase 1.5.

The entire IKEv2 process is demonstrated in the following diagram:

Support for IKEv2 session resumption

If a gateway loses connectivity to the network, clients can attempt to re-establish the lost session by presenting the ticket to the gateway (as described in RFC 5723). As a result, sessions can be resumed much faster, as DH exchange that is necessary to establish a brand new connection is skipped. This feature implements “ticket-byvalue”, whereby all information necessary to restore the state of a particular IKE SA is stored in the ticket and sent to the client.

IKEv2 asymmetric authentication

Asymmetric authentication allows both sides of an authentication exchange to use different authentication methods, for example the initiator may be using a shared key, while the responder may have a public signature key and certificate.

The command authmethod-remote is avilable under config vpn ipsec phase1-interface.

For more detailed information on authentication of the IKE SA, see RFC 5996 – Internet Key Exchange Protocol Version 2 (IKEv2).

IKEv2 Digital Signature Authentication support

FortiOS supports the use of Digital Signature authentication, which changes the format of the Authentication Data payload in order to support different signature methods.

Instead of just  containing a raw signature value calculated as defined in the original IKE RFCs,  the Auth Data now includes an ASN.1 formatted object that provides  details on how the signature was calculated, such as the signature type, hash algorithm, and signature padding method.

For more detailed information on IKEv2 Digital Signature authentication, see RFC 7427 – Signature Authentication in the Internet Key Exchange Version 2 (IKEv2).

Unique IKE identifiers

When enabled, the following phase1 CLI command (enforce-unique-id) requires all IPsec VPN clients to use a unique identifer when connecting.

CLI syntax

config vpn ipsec phase1 edit <name> set enforce-unique-id {keep-new | keep-old | disable} Default is disable. next

end

 

Use keep-new to replace the old connnection if an ID collision is detected on the gateway. Use keep-old to reject the new connection if an ID collision is detected.

IKEv2 ancillary RADIUS group authentication

This feature provides for the IDi information to be extracted from the IKEv2 AUTH exchange and sent to a RADIUS server, along with a fixed password (configurable via CLI only), to perform an additional group authentication step prior to tunnel establishment. The RADIUS server may return framed-IP-address, framed-ipnetmask, and dns-server attributes, which are then applied to the tunnel.

It should be noted, unlike Xauth or EAP, this feature does not perform individual user authentication, but rather treats all users on the gateway as a single group, and authenticates that group with RADIUS using a fixed password. This feature also works with RADIUS accounting, including the phase1 acct-verify option.

Syntax

config vpn ipsec phase1-interface edit <name> set mode-cfg enable set type dynamic set ike-version 2

set group-authentication {enable | disable} set group-authentication-secret <password>

next end