Category Archives: FortiOS 5.4 Handbook

The complete handbook for FortiOS 5.4

HA and load balancing

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HA and load balancing

FGCP active-active (a-a) load balancing distributes network traffic among all of the units in a cluster. Load balancing can improve cluster performance because the processing load is shared among multiple cluster units.

This chapter describes how active-active load balancing works and provides detailed active-active HA NAT/Route and Transparent mode packet flow descriptions.

 

Load balancing overview

FGCP active-active HA uses a technique similar to unicast load balancing in which the primary unit is associated with the cluster HA virtual MAC addresses and cluster IP addresses. The primary unit is the only cluster unit to receive packets sent to the cluster. The primary unit then uses a load balancing schedule to distribute sessions to all of the units in the cluster (including the primary unit). Subordinate unit interfaces retain their actual MAC addresses and the primary unit communicates with the subordinate units using these MAC addresses. Packets exiting the subordinate units proceed directly to their destination and do not pass through the primary unit first.

By default, active-active HA load balancing distributes proxy-based security profile processing to all cluster units. Proxy-based security profile processing is CPU and memory-intensive, so FGCP load balancing may result in higher throughput because resource-intensive processing is distributed among all cluster units.

Proxy-based security profile processing that is load balanced includes proxy-based virus scanning, proxy-based web filtering, proxy-based email filtering, and proxy-based data leak prevention (DLP) of HTTP, FTP, IMAP, IMAPS, POP3, POP3S, SMTP, SMTPS, IM, and NNTP, sessions accepted by security policies.

Other features enabled in security policies such as Endpoint security, traffic shaping and authentication have no effect on active-active load balancing.

You can also enable load-balance-all to have the primary unit load balance all TCP sessions. Load balancing TCP sessions increases overhead and may actually reduce performance so it is disabled by default. You can also enable load-balance-udp to have the primary unit load balance all UDP sessions. Load balancing UDP sessions also increases overhead so it is also disabled by default.

NP4 and NP6 processors can also offload and accelerate load balancing.

During active-active HA load balancing the primary unit uses the configured load balancing schedule to determine the cluster unit that will process a session. The primary unit stores the load balancing information for each load balanced session in the cluster load balancing session table. Using the information in this table, the primary unit can then forward all of the remaining packets in each session to the appropriate cluster unit. The load balancing session table is synchronized among all cluster units.

HTTPS, ICMP, multicast, and broadcast sessions are never load balanced and are always processed by the primary unit. IPS,Application Control, flow-based virus scanning, flow-based web filtering, flow-based DLP, flow- based email filtering, VoIP, IM, P2P, IPsec VPN, HTTPS, SSL VPN, HTTP multiplexing, SSL offloading, WAN optimization, explicit web proxy, and WCCP sessions are also always processed only by the primary unit.

In addition to load balancing, active-active HA also provides the same session, device and link failover protection as active-passive HA. If the primary unit fails, a subordinate unit becomes the primary unit and resumes operating the cluster.

Active-active HA also maintains as many load balanced sessions as possible after a failover by continuing to process the load balanced sessions that were being processed by the cluster units that are still operating. See Active-active HA subordinate units sessions can resume after a failover on page 1544 for more information.

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Failover performance

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Failover performance

This section describes the designed device and link failover times for a FortiGate cluster and also shows results of a failover performance test.

 

Device failover performance

By design FGCP device failover time is 2 seconds for a two-member cluster with ideal network and traffic conditions. If subsecond failover is enabled the failover time can drop below 1 second.

All cluster units regularly receive HA heartbeat packets from all other cluster units over the HA heartbeat link. If any cluster unit does not receive a heartbeat packet from any other cluster unit for 2 seconds, the cluster unit that has not sent heartbeat packets is considered to have failed.

It may take another few seconds for the cluster to negotiate and re-distribute communication sessions. Typically if subsecond failover is not enabled you can expect a failover time of 9 to 15 seconds depending on the cluster and network configuration. The failover time can also be increased by more complex configurations and or configurations with network equipment that is slow to respond.

You can change the hb-lost-threshold to increase or decrease the device failover time. See Modifying heartbeat timing on page 1505 for information about using hb-lost-threshold, and other heartbeat timing settings.

 

Link failover performance

Link failover time is controlled by how long it takes for a cluster to synchronize the cluster link database. When a link failure occurs, the cluster unit that experienced the link failure uses HA heartbeat packets to broadcast the updated link database to all cluster units. When all cluster units have received the updated database the failover is complete.

It may take another few seconds for the cluster to negotiate and re-distribute communication sessions.

 

Reducing failover times

  • Keep the network configuration as simple as possible with as few as possible network connections to the cluster.
  • If possible operate the cluster in Transparent mode.
  • Use high-performance switches to that the switches failover to interfaces connected to the new primary unit as quickly as possible.
  • Use accelerated FortiGate interfaces. In some cases accelerated interfaces will reduce failover times.
  • Make sure the FortiGate unit sends multiple gratuitous arp packets after a failover. In some cases, sending more gratuitous arp packets will cause connected network equipment to recognize the failover sooner.

To send 10 gratuitous arp packets:

config system ha set arps 10

end

 

  • Reduce the time between gratuitous arp packets. This may also caused connected network equipment to recognize the failover sooner. To send 50 gratuitous arp packets with 1 second between each packet:

config system ha set arps 50

set arps-interval 1 end

 

  • Reduce the number of lost heartbeat packets and reduce the heartbeat interval timers to be able to more quickly detect a device failure. To set the lost heartbeat threshold to 3 packets and the heartbeat interval to 100 milliseconds:

config system ha

set hb-interval 1

set hb-lost-threshold 3 end

 

  • Reduce the hello state hold down time to reduce the amount of the time the cluster waits before transitioning from the hello to the work state. To set the hello state hold down time to 5 seconds:

config system ha

set helo-holddown 5 end

 

  • Enable sending a link failed signal after a link failover to make sure that attached network equipment responds a quickly as possible to a link failure. To enable the link failed signal:

config system ha

set link-failed-signal enable end

 

Transparent mode active-passive cluster packet flow

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Transparent mode active-passive cluster packet flow

This section describes how packets are processed and how failover occurs in an active-passive HA cluster running in Transparent mode. The cluster is installed on an internal network in front of a mail server and the client connects to the mail server through the Transparent mode cluster.

In an active-passive cluster operating in Transparent mode, two MAC addresses are involved in the communication between a client and a server when the primary unit processes a connection:

  • Client MAC address (MAC_Client)
  • Server MAC address (MAC_Server)

The HA virtual MAC addresses are not directly involved in communication between the client and the server. The client computer sends packets to the mail server and the mail server sends responses. In both cases the packets are intercepted and processed by the cluster.

The cluster’s presence on the network is transparent to the client and server computers. The primary unit sends gratuitous ARP packets to Switch 1 that associate all MAC addresses on the network segment connected to the cluster external interface with the HA virtual MAC address. The primary unit also sends gratuitous ARP packets to Switch 2 that associate all MAC addresses on the network segment connected to the cluster internal interface with the HA virtual MAC address. In both cases, this results in the switches sending packets to the primary unit interfaces.

 

Transparent mode active-passive packet flow

 

Packet flow from client to mail server

1. The client computer requests a connection from 10.11.101.10 to 110.11.101.200.

2. The client computer issues an ARP request to 10.11.101.200.

3. The primary unit forwards the ARP request to the mail server.

4. The mail server responds with its MAC address (MAC_Server) which corresponds to its IP address of 10.11.101.200. The primary unit returns the ARP response to the client computer.

5. The client’s request packet reaches the primary unit internal interface.

 

  IP address MAC address
Source 10.11.101.10 MAC_Client
Destination 10.11.101.200 MAC_Server

 

6. The primary unit processes the packet.

7. The primary unit forwards the packet from its external interface to the mail server.

 

  IP address MAC address
Source 10.11.101.10 MAC_Client
Destination 10.11.101.200 MAC_Server

 

8. The primary unit continues to process packets in this way unless a failover occurs.

 

Packet flow from mail server to client

1. To respond to the client computer, the mail server issues an ARP request to 10.11.101.10.

2. The primary unit forwards the ARP request to the client computer.

3. The client computer responds with its MAC address (MAC_Client) which corresponds to its IP address of 10.11.101.10. The primary unit returns the ARP response to the mail server.

4. The mail server’s response packet reaches the primary unit external interface.

 

  IP address MAC address
Source 10.11.101.200 MAC_Server
Destination 10.11.101.10 MAC_Client

 

5. The primary unit processes the packet.

6. The primary unit forwards the packet from its internal interface to the client.

 

  IP address MAC address
Source 10.11.101.200 MAC_Server
Destination 10.11.101.10 MAC_Client

 

7. The primary unit continues to process packets in this way unless a failover occurs.

 

When a failover occurs

The following steps are followed after a device or link failure of the primary unit causes a failover.

1. If the primary unit fails, the subordinate unit negotiates to become the primary unit.

2. The new primary unit changes the MAC addresses of all of its interfaces to the HA virtual MAC address.

3. The new primary units sends gratuitous ARP packets to switch 1 to associate its MAC address with the MAC addresses on the network segment connected to the external interface.

4. The new primary units sends gratuitous ARP packets to switch 2 to associate its MAC address with the MAC addresses on the network segment connected to the internal interface.

5. Traffic sent to the cluster is now received and processed by the new primary unit.

If there were more than two cluster units in the original cluster, these remaining units would become subordinate units.

WAN optimization and HA

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WAN optimization and HA

You can configure WAN optimization on a FortiGate HA cluster. The recommended HA configuration for WAN optimization is active-passive mode. Also, when the cluster is operating, all WAN optimization sessions are processed by the primary unit only. Even if the cluster is operating in active-active mode, HA does not load- balance WAN optimization sessions. HA also does not support WAN optimization session failover.

In a cluster, the primary unit only stores web cache and byte cache databases. These databases are not synchronized to the subordinate units. So, after a failover, the new primary unit must rebuild its web and byte caches. As well, the new primary unit cannot connect to a SAS partition that the failed primary unit used.

Rebuilding the byte caches can happen relatively quickly because the new primary unit gets byte cache data from the other FortiGate units that it is participating with in WAN optimization tunnels.

 

Failover and attached network equipment

It normally takes a cluster approximately 6 seconds to complete a failover. However, the actual failover time experienced by your network users may depend on how quickly the switches connected to the cluster interfaces accept the cluster MAC address update from the primary unit. If the switches do not recognize and accept the gratuitous ARP packets and update their MAC forwarding table, the failover time will increase.

Also, individual session failover depends on whether the cluster is operating in active-active or active-passive mode, and whether the content of the traffic is to be virus scanned. Depending on application behavior, it may take a TCP session a longer period of time (up to 30 seconds) to recover completely.

 

Monitoring cluster units for failover

You can use logging and SNMP to monitor cluster units for failover. Both the primary and subordinate units can be configured to write log messages and send SNMP traps if a failover occurs. You can also log into the cluster web-based manager and CLI to determine if a failover has occurred.

 

NAT/Route mode active-passive cluster packet flow

This section describes how packets are processed and how failover occurs in an active-passive HA cluster running in NAT/Route mode. In the example, the NAT/Route mode cluster acts as the internet firewall for a client computer’s internal network. The client computer’s default route points at the IP address of the cluster internal interface. The client connects to a web server on the Internet. Internet routing routes packets from the cluster external interface to the web server, and from the web server to the cluster external interface.

In an active-passive cluster operating in NAT/Route mode, four MAC addresses are involved in communication between the client and the web server when the primary unit processes the connection:

  • Internal virtual MAC address (MAC_V_int) assigned to the primary unit internal interface,
  • External virtual MAC address (MAC_V_ext) assigned to the primary unit external interface,
  • Client MAC address (MAC_Client),
  • Server MAC address (MAC_Server),

In NAT/Route mode, the HA cluster works as a gateway when it responds to ARP requests. Therefore, the client and server only know the gateway MAC addresses. The client only knows the cluster internal virtual MAC address (MAC_V_int) and the server only know the cluster external virtual MAC address (MAC_V_int).

 

NAT/Route mode active-passive packet flow

 

Packet flow from client to web server

1. The client computer requests a connection from 10.11.101.10 to 172.20.120.130.

2. The default route on the client computer recognizes 10.11.101.100 (the cluster IP address) as the gateway to the external network where the web server is located.

3. The client computer issues an ARP request to 10.11.101.100.

4. The primary unit intercepts the ARP request, and responds with the internal virtual MAC address (MAC_V_int) which corresponds to its IP address of 10.11.101.100.

5. The client’s request packet reaches the primary unit internal interface.

 

  IP address MAC address
Source 10.11.101.10 MAC_Client
Destination 172.20.120.130 MAC_V_int

 

6. The primary unit processes the packet.

7. The primary unit forwards the packet from its external interface to the web server.

 

  IP address MAC address
Source 172.20.120.141 MAC_V_ext
Destination 172.20.120.130 MAC_Server

 

8. The primary unit continues to process packets in this way unless a failover occurs.

 

Packet flow from web server to client

1. When the web server responds to the client’s packet, the cluster external interface IP address (172.20.120.141) is recognized as the gateway to the internal network.

2. The web server issues an ARP request to 172.20.120.141.

3. The primary unit intercepts the ARP request, and responds with the external virtual MAC address (MAC_V_ext) which corresponds its IP address of 172.20.120.141.

4. The web server then sends response packets to the primary unit external interface.

 

  IP address MAC address
Source 172.20.120.130 MAC_Server
Destination 172.20.120.141 MAC_V_ext

 

5. The primary unit processes the packet.

6. The primary unit forwards the packet from its internal interface to the client.

 

  IP address MAC address
Source 172.20.120.130 MAC_V_int
Destination 10.11.101.10 MAC_Client

 

7. The primary unit continues to process packets in this way unless a failover occurs.

 

When a failover occurs

The following steps are followed after a device or link failure of the primary unit causes a failover.

1. If the primary unit fails the subordinate unit becomes the primary unit.

2. The new primary unit changes the MAC addresses of all of its interfaces to the HA virtual MAC addresses.

The new primary unit has the same IP addresses and MAC addresses as the failed primary unit.

3. The new primary units sends gratuitous ARP packets from the internal interface to the 10.11.101.0 network to associate its internal IP address with the internal virtual MAC address.

4. The new primary units sends gratuitous ARP packets to the 172.20.120.0 to associate its external IP address with the external virtual MAC address.

5. Traffic sent to the cluster is now received and processed by the new primary unit.

If there were more than two cluster units in the original cluster, these remaining units would become subordinate units.

Session failover (session pick-up)

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Session failover (session pick-up)

Session failover means that a cluster maintains active network TCP and IPsec VPN sessions (including NAT sessions) after a device or link failover. You can also configure session failover to maintain UDP and ICMP sessions. Session failover does not failover multicast, or SSL VPN sessions.

FortiGate HA does not support session failover by default. To enable session failover go to System > HA and select Enable Session Pick-up.

From the CLI enter:

config system ha

set session-pickup enable end

To support session failover, when Enable Session Pick-up is selected, the FGCP maintains an HA session table for most TCP communication sessions being processed by the cluster and synchronizes this session table with all cluster units. If a cluster unit fails, the HA session table information is available to the remaining cluster units and these cluster units use this session table to resume most of the TCP sessions that were being processed by the failed cluster unit without interruption.

 

If session pickup is enabled, you can use the following command to also enable UDP and ICMP session failover:

config system ha

set session-pickup-connectionless enable end

You must enable session pickup for session failover protection. If you do not require session failover protection, leaving session pickup disabled may reduce CPU usage and reduce HA heartbeat network bandwidth usage.

 

If session pickup is not selected

If Enable Session Pick-up is not selected, the FGCP does not maintain an HA session table and most TCP sessions do not resume after a failover. After a device or link failover all sessions are briefly interrupted and must be re-established at the application level after the cluster renegotiates.

Many protocols can successfully restart sessions with little, if any, loss of data. For example, after a failover, users browsing the web can just refresh their browsers to resume browsing. Since most HTTP sessions are very short, in most cases they will not even notice an interruption unless they are downloading large files. Users downloading a large file may have to restart their download after a failover.

Other protocols may experience data loss and some protocols may require sessions to be manually restarted. For example, a user downloading files with FTP may have to either restart downloads or restart their FTP client.

Some sessions may resume after a failover whether or not enable session pick-up is selected:

  • UDP, ICMP, multicast and broadcast packet session failover on page 1543
  • FortiOS Carrier GTP session failover on page 1543
  • Active-active HA subordinate units sessions can resume after a failover on page 1544

 

Improving session synchronization performance

Two HA configuration options are available to reduce the performance impact of enabling session pickup. They include reducing the number of sessions that are synchronized by adding a session pickup delay and using more FortiGate interfaces for session synchronization.

 

Reducing the number of sessions that are synchronized

Enable the session-pickup-delay CLI option to reduce the number of sessions that are synchronized by synchronizing sessions only if they remain active for more than 30 seconds. Enabling this option could greatly reduce the number of sessions that are synchronized if a cluster typically processes very many short duration sessions, which is typical of most HTTP traffic for example.

Use the following command to enable a 30 second session pickup delay:

config system ha

set session-pickup-delay enable end

Enabling session pickup delay means that if a failover occurs more sessions may not be resumed after a failover. In most cases short duration sessions can be restarted with only a minor traffic interruption. However, if you notice too many sessions not resuming after a failover you might want to disable this setting.

 

Using multiple FortiGate interfaces for session synchronization

Using the session-sync-dev option you can select one or more FortiGate interfaces to use for synchronizing sessions as required for session pickup. Normally session synchronization occurs over the HA heartbeat link. Using this HA option means only the selected interfaces are used for session synchronization and not the HA heartbeat link. If you select more than one interface, session synchronization traffic is load balanced among the selected interfaces.

Moving session synchronization from the HA heartbeat interface reduces the bandwidth required for HA heartbeat traffic and may improve the efficiency and performance of the cluster, especially if the cluster is synchronizing a large number of sessions. Load balancing session synchronization among multiple interfaces can further improve performance and efficiency if the cluster is synchronizing a large number of sessions.

Use the following command to perform cluster session synchronization using the port10 and port12 interfaces.

config system ha

set session-sync-dev port10 port12 end

Session synchronization packets use Ethertype 0x8892. The interfaces to use for session synchronization must be connected together either directly using the appropriate cable (possible if there are only two units in the cluster) or using switches. If one of the interfaces becomes disconnected the cluster uses the remaining interfaces for session synchronization. If all of the session synchronization interfaces become disconnected, session synchronization reverts back to using the HA heartbeat link. All session synchronization traffic is between the primary unit and each subordinate unit.

Since large amounts of session synchronization traffic can increase network congestion, it is recommended that you keep this traffic off of your network by using dedicated connections for it.

 

Synchronizing GTP sessions to support GTP tunnel failover

FortiOS Carrier GPRS Tunneling Protocol (GTP) sessions are not normally synchronized by the FGCP, even if you enable session pickup. You can provide GTP session synchronization by using the session-sync-dev command to select one or two session sync interfaces. You must also connect these interfaces together either with direct connections or using switches.

You can also use the command, diagnose firewall gtp hash-stat to display GTP hash stat separately.

 

Session failover not supported for all sessions

Most of the features applied to sessions by FortiGate security profile functionality require the FortiGate unit to maintain very large amounts of internal state information for each session. The FGCP does not synchronize internal state information for the following security profile features, so the following types of sessions will not resume after a failover:

  • Virus scanning of HTTP, HTTPS, FTP, IMAP, IMAPS, POP3, POP3S, SMTP, SMTPS, IM, CIFS, and NNTP sessions,
  • Web filtering and FortiGuard Web Filtering of HTTP and HTTPS sessions,
  • Spam filtering of IMAP, IMAPS, POP3, POP3S, SMTP, and SMTPS sessions,
  • DLP scanning of IMAP, IMAPS, POP3, POP3S, SMTP, SMTPS, SIP, SIMPLE, and SCCP sessions,
  • DLP archiving of HTTP, HTTPS, FTP, IMAP, IMAPS, POP3, SMTP, SMTPS, IM, NNTP, AIM, ICQ, MSN, Yahoo! IM, SIP, SIMPLE, and SCCP signal control sessions, Active-active clusters can resume some of these sessions after a failover. See Active-active HA subordinate units sessions can resume after a failover on page 1544 for details.

 

If you use these features to protect most of the sessions that your cluster processes, enabling session failover may not actually provide significant session failover protection.

TCP sessions that are not being processed by these security profile features resume after a failover even if these sessions are accepted by security policies with security profile options configured. Only TCP sessions that are actually being processed by these security profile features do not resume after a failover.

For example:

  • TCP sessions that are not virus scanned, web filtered, spam filtered, content archived, or are not SIP, SIMPLE, or SCCP signal traffic resume after a failover, even if they are accepted by a security policy with security profile options enabled. For example, SNMP TCP sessions resume after a failover because FortiOS does not apply any security profile options to SNMP sessions.
  • TCP sessions for a protocol for which security profile features have not been enabled resume after a failover even if they are accepted by a security policy with security profile features enabled. For example, if you have not enabled any antivirus or content archiving settings for FTP, FTP sessions resume after a failover.

The following security profile features do not affect TCP session failover:

  • IPS does not affect session failover. Sessions being scanned by IPS resume after a failover. After a failover; however, IPS can only perform packet-based inspection of resumed sessions; reducing the number of vulnerabilities that IPS can detect. This limitation only applies to in-progress resumed sessions.
  • Application control does not affect session failover. Sessions that are being monitored by application control resume after a failover.
  • Logging enabled form security profile features does not affect session failover. security profile logging writes log messages for security profile events; such as when a virus is found by antivirus scanning, when Web Filtering blocks a URL, and so on. Logging does not enable features that would prevent sessions from being failed over, logging just reports on the activities of enabled features.

If more than one security profile feature is applied to a TCP session, that session will not resume after a failover as long as one of the security profile features prevents session failover. For example:

  • Sessions being scanned by IPS and also being virus scanned do not resume after a failover.
  • Sessions that are being monitored by application control and that are being DLP archived or virus scanned will not resume after a failover.

 

IPv6, NAT64, and NAT66 session failover

The FGCP supports IPv6, NAT64, and NAT66 session failover, if session pickup is enabled, these sessions are synchronized between cluster members and after an HA failover the sessions will resume with only minimal interruption.

 

SIP session failover

The FGCP supports SIP session failover (also called stateful failover) for active-passive HA. To support SIP session failover, create a standard HA configuration and select Enable Session Pick-up option.

SIP session failover replicates SIP states to all cluster units. If an HA failover occurs, all in-progress SIP calls (setup complete) and their RTP flows are maintained and the calls will continue after the failover with minimal or no interruption.

SIP calls being set up at the time of a failover may lose signaling messages. In most cases the SIP clients and servers should use message retransmission to complete the call setup after the failover has completed. As a result, SIP users may experience a delay if their calls are being set up when an HA a failover occurs. But in most cases the call setup should be able to continue after the failover.

 

Explicit web proxy, WCCP, and WAN optimization session failover

Similar to security profile sessions, the explicit web proxy, WCCP and WAN optimization features all require the FortiGate unit to maintain very large amounts of internal state information for each session. This information is not maintained and these sessions do not resume after a failover.

 

SSL offloading and HTTP multiplexing session failover

SSL offloading and HTTP multiplexing are both enabled from firewall virtual IPs and firewall load balancing. Similar to the features applied by security profile, SSL offloading and HTTP multiplexing requires the FortiGate unit to maintain very large amounts of internal state information for each session. Sessions accepted by security policies containing virtual IPs or virtual servers with SSL offloading or HTTP multiplexing enabled do not resume after a failover.

 

IPsec VPN session failover

Session failover is supported for all IPsec VPN tunnels. To support IPsec VPN tunnel failover, when an IPsec VPN tunnel starts, the FGCP distributes the SA and related IPsec VPN tunnel data to all cluster units.

 

SSL VPN session failover and SSL VPN authentication failover

Session failover is not supported for SSL VPN tunnels. However, authentication failover is supported for the communication between the SSL VPN client and the FortiGate unit. This means that after a failover, SSL VPN clients can re-establish the SSL VPN session between the SSL VPN client and the FortiGate unit without having to authenticate again.

However, all sessions inside the SSL VPN tunnel that were running before the failover are stopped and have to be restarted. For example, file transfers that were in progress would have to be restarted. As well, any communication sessions with resources behind the FortiGate unit that are started by an SSL VPN session have to be restarted.

To support SSL VPN cookie failover, when an SSL VPN session starts, the FGCP distributes the cookie created to identify the SSL VPN session to all cluster units.

 

PPTP and L2TP VPN sessions

PPTP and L2TP VPNs are supported in HA mode. For a cluster you can configure PPTP and L2TP settings and you can also add security policies to allow PPTP and L2TP pass through. However, the FGCP does not provide session failover for PPTP or L2TP. After a failover, all active PPTP and L2TP sessions are lost and must be restarted.

 

UDP, ICMP, multicast and broadcast packet session failover

By default, even with session pickup enabled, the FGCP does not maintain a session table for UDP, ICMP, multicast, or broadcast packets. So the cluster does not specifically support failover of these packets.

Some UDP traffic can continue to flow through the cluster after a failover. This can happen if, after the failover, a UDP packet that is part of an already established communication stream matches a security policy. Then a new session will be created and traffic will flow. So after a short interruption, UDP sessions can appear to have failed over. However, this may not be reliable for the following reasons:

  • UDP packets in the direction of the security policy must be received before reply packets can be accepted. For example, if a port1 -> port2 policy accepts UDP packets, UDP packets received at port2 destined for the network connected to port1 will not be accepted until the policy accepts UDP packets at port1 that are destined for the network connected to port2. So, if a user connects from an internal network to the Internet and starts receiving UDP packets from the Internet (for example streaming media), after a failover the user will not receive any more UDP packets until the user re-connects to the Internet site.
  • UDP sessions accepted by NAT policies will not resume after a failover because NAT will usually give the new session a different source port. So only traffic for UDP protocols that can handle the source port changing during a session will continue to flow.

 

You can however, enable session pickup for UDP and ICMP packets by enabling session pickup for TCP sessions and then enabling session pickup for connectionless sessions:

config system ha

set session-pickup enable

set session-pickup-connectionless enable end

This configuration causes the cluster units to synchronize UDP and ICMP session tables and if a failover occurs

UDP and ICMP sessions are maintained.

 

FortiOS Carrier GTP session failover

FortiOS Carrier HA supports GTP session failover. The primary unit synchronizes the GTP tunnel state to all cluster units after the GTP tunnel setup is completed. After the tunnel setup is completed, GTP sessions use UDP and HA does not synchronize UDP sessions to all cluster units. However, similar to other UDP sessions, after a failover, since the new primary unit will have the GTP tunnel state information, GTP UDP sessions using the same tunnel can continue to flow with some limitations.

The limitation on packets continuing to flow is that there has to be a security policy to accept the packets. For example, if the FortiOS Carrier unit has an internal to external security policy, GTP UDP sessions using an established tunnel that are received by the internal interface are accepted by the security policy and can continue to flow. However, GTP UDP packets for an established tunnel that are received at the external interface cannot flow until packets from the same tunnel are received at the internal interface.

If you have bi-directional policies that accept GTP UDP sessions then traffic in either direction that uses an established tunnel can continue to flow after a failover without interruption.

 

Active–active HA subordinate units sessions can resume after a failover

In an active-active cluster, subordinate units process sessions. After a failover, all cluster units that are still operating may be able to continue processing the sessions that they were processing before the failover. These sessions are maintained because after the failover the new primary unit uses the HA session table to continue to send session packets to the cluster units that were processing the sessions before the failover. Cluster units maintain their own information about the sessions that they are processing and this information is not affected by the failover. In this way, the cluster units that are still operating can continue processing their own sessions without loss of data.

 

The cluster keeps processing as many sessions as it can. But some sessions can be lost. Depending on what caused the failover, sessions can be lost in the following ways:

  • A cluster unit fails (the primary unit or a subordinate unit). All sessions that were being processed by that cluster unit are lost.
  • A link failure occurs. All sessions that were being processed through the network interface that failed are lost. This mechanism for continuing sessions is not the same as session failover because:
  • Only the sessions that can be maintained are maintained.
  • The sessions are maintained on the same cluster units and not re-distributed.
  • Sessions that cannot be maintained are lost.

Detecting HA remote IP monitoring failovers

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Detecting HA remote IP monitoring failovers

Just as with any HA failover, you can detect HA remote IP monitoring failovers by using SNMP to monitor for HA traps. You can also use alert email to receive notifications of HA status changes and monitor log messages for HA failover log messages. In addition, FortiGate units send the critical log message Ping Server is down when a ping server fails. The log message includes the name of the interface that the ping server has been added to.

 

Flip timeout

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Flip timeout

The HA remote IP monitoring configuration also involves setting a flip timeout. The flip timeout is required to reduce the frequency of failovers if, after a failover, HA remote IP monitoring on the new primary unit also causes a failover. This can happen if the new primary unit cannot connect to one or more of the monitored remote IP addresses. The result could be that until you fix the network problem that blocks connections to the remote IP addresses, the cluster will experience repeated failovers. You can control how often the failovers occur by setting the flip timeout. The flip timeout stops HA remote IP monitoring from causing a failover until the primary unit has been operating for the duration of the flip timeout.

If you set the flip timeout to a relatively high number of minutes you can find and repair the network problem that prevented the cluster from connecting to the remote IP address without the cluster experiencing very many failovers. Even if it takes a while to detect the problem, repeated failovers at relatively long time intervals do not usually disrupt network traffic.

Use the following command to set the flip timeout to 3 hours (360 minutes):

config system ha

set pingserver-flip-timeout 360 end

Monitoring multiple IP addresses from one interface

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Monitoring multiple IP addresses from one interface

You can add multiple IP addresses to a single link monitor to use HA remote IP monitoring to monitor more than one IP address from a single interface. If you add multiple IP addresses, the health checking will be with all of the addresses at the same time. The link monitor only fails when no responses are received from any of the addresses.

config system link-monitor edit port2

set server 192.168.20.20 192.168.20.30 172.20.12.10 end