Services and TCP ports

There are a number of different services and protocols in use on the Internet. The most commonly known is HTTP which is used by web servers to transmit requests and responses for unencrypted web pages. These services are set up to listen for requests on a numbered port. These services and protocols can use any port from 1 to 65,535. To keep things simple for everyone a large number of the more commonly used services started using a standardized list of ports. For instance, though it is not required, by default, most web servers listen for HTTP requests on port 80 and by default, web browsers will send HTTP traffic to port 80. If you wish to use another port such as 8080 you would put “:8080” at the end of the URL to indicate that you want the browser to use 8080 instead of the default port.

Example

Default URL for HTTP traffic when the web server is listening on the standard HTTP port:

http://fortinet.com

URL to the same address when the web server is listening for HTTP traffic on port 8080 http://fortinet.com:8080

Services represent typical traffic types and application packets that pass through the FortiGate unit. Firewall services define one or more protocols and port numbers associated with each service. Security policies use service definitions to match session types. You can organize related services into service groups to simplify your security policy list.

Many well-known traffic types have been predefined on the FortiGate unit. If there is a service that does not appear on the list you can create a service or edit an existing one. You need to know the ports, IP addresses or protocols of that particular service or application uses, to create a service.

Best Practices

While you can edit a predefined service it is best to leave those ones alone and create a new service and name it something similar such as the same service name with a descriptive identifier appended.

Based on the previous example, instead of the name “HTTP” you could name the ser- vice “HTTP8080” or use the application that is using that port, “HTTP-Application”.

NAT

NAT or Network Address Translation is the process that enables a single device such as a router or firewall to act as an agent between the Internet or Public Network and a local or private network. This “agent”, in real time, translates the source IP address of a device on one network interface, usually the Internal, to a different IP address as it leaves another interface, usually the interface connected to the ISP and the Internet. This enables a single public address to represent a significantly larger number of private addresses.

The Origins of NAT

In order to understand NAT it helps to know why it was created. At one time, every computer that was part of a network had to have it’s own addresses so that the other computers could talk to it. There were a few protocols in use at the time, some of which were only for use on a single network, but of those that were routable, the one that had become the standard for the Internet was IP (Internet Protocol) version 4.

When IP version 4 addressing was created nobody had any idea how many addresses would be needed. The total address range was based on the concept of 2 to the 32nd power, which works out to be 4 294 967 296 potential addresses. Once you eliminate some of those for reserved addresses, broadcast addresses, network addresses, multicasting, etc., you end up with a workable scope of about 3.2 million addressees. This was thought to be more than enough at the time. The designers were not expecting the explosion of personal computing, the World Wide Web or smart phones. As of the beginning of 2012, some estimate the number of computers in the world in the neighborhood of 1 billion, and most of those computer users are going to want to be on the Internet or Search the World Wide Web. In short, we ran out of addresses.

This problem of an address shortage was realized before we actually ran out, and in the mid 1990s 2 technical papers called RFCs numbered 1631 (http://www.ietf.org/rfc/rfc1631.txt) and 1918 (http://tools.ietf.org/html/rfc1918), proposed components of a method that would be used as a solution until a new addressing methodology could be implemented across the Internet infrastructure. For more information on this you can look up IP version 6.

RFC 1631 described a process that would allow networking devices to translate a single public address to multiple private IP addresses and RFC 1918 laid out the use of the private addresses. The addresses that were on the Internet (Public IP addresses) could not be duplicated for them to work as unique addresses, but behind a firewall, which most large institutions had, they could use their own Private IP addresses for internal use and the internal computers could share the external or Public IP address.

To give an idea on a small scale how this works, image that a company has a need for 200 computer addresses. Before Private IP addresses and NAT the company would have purchased a full Class C address range which would have been 254 usable IP addresses; wasting about 50 addresses. Now with NAT, that company only needs 1 IP address for its 200 computers and this leaves the rest of the IP addresses in that range available for other companies to do the same thing.

NAT gives better value than it would first appear because it is not 253 companies that can use 254 addresses but each of those 254 companies could set up their networking infrastructures to use up to thousands of Private IP addresses, more if they don’t all have to talk to the Internet at the same time. This process enabled the Internet to keep growing even though we technically have many more computers networked than we have addresses.

IPv6

Internet Protocol version 6 (IPv6) will succeed IPv4 as the standard networking protocol of the Internet. IPv6 provides a number of advances over IPv4 but the primary reason for its replacing IPv4 is its limitation in addresses. IPv4 uses 32 bit addresses which means there is a theoretical limit of 2 to the power of 32. The IPv6 address scheme is based on a 128 bit address or a theoretical limit of 2 to the power of 128.

Possible Addresses:

• IPv4 = 4,294,967,296 (over 4 billion)
• IPv6 = 340,282,366,920,938,463,463,374,607,431,768,211,456 (over 340 undecillion – We had to look that term up. We didn’t know what a number followed by 36 digits was either)

Assuming a world population of approximately 8 billion people, IPv6 would allow for each individual to have approximately 42,535,295,865,117,200,000,000,000,000 devices with an IP address. That’s 42 quintillion devices.

There is little likelihood that you will ever need to worry about these numbers as any kind of serious limitation in addressing but they do give an idea of the scope of the difference in the available addressing.

Aside from the difference of possible addresses there is also the different formatting of the addresses that will need to be addressed.

A computer would view an IPv4 address as a 32 bit string of binary digits made up of 1s and 0s, broken up into 4 octets of 8 digits separated by a period “.”

Example:

10101100.00010000.11111110.00000001

To make number more user friendly for humans we translate this into decimal, again 4 octets separated by a period “.”which works out to: 172.16.254.1

A computer would view an IPv6 address as a 128 bit string of binary digits made up of 1s and 0s, broken up into 8 octets of 16 digits separated by a colon “:”

1000000000000001:0000110110111000:101011000001000:1111111000000001:000000000000000

0:0000000000000000:0000000000000000:0000000000000000

To make number a little more user friendly for humans we translate this into hexadecimal, again 8 octets separated by a colon “:” which works out to:

8001:0DB8:AC10:FE01:0000:0000:0000:0000:

Because any four-digit group of zeros within an IPv6 address may be reduced to a single zero or altogether omitted, this address can be shortened further to:

8001:0DB8:AC10:FE01:0:0:0:0 or

8001:0DB8:AC10:FE01::

Some of the other benefits of IPv6 include:

• More efficient routing
• Reduced management requirement
• Stateless auto-reconfiguration of hosts
• Improved methods to change Internet Service Providers
• Better mobility support
• Multi-homing
• Security
• Scoped address: link-local, site-local and global address space

IPv6 in FortiOS

From an administrative point of view IPv6 works almost the same as IPv4 in FortiOS. The primary difference is the use IPv6 format for addresses. There is also no need for NAT if the FortiGate firewall is the interface between IPv6 networks. If the subnets attached to the FortiGate firewall are IPv6 and IPv4 NAT can be configured between the 2 different formats. This will involve either configuring a dual stack routing or IPv4 tunneling configuration. The reason for this is simple. NAT was developed primarily for the purpose of extending the number of usable IPv4 addresses. IPv6’s addressing allows for enough available addresses so the NAT is no longer necessary.

When configuring IPv6 in FortiOS, you can create a dual stack route or IPv4-IPv6 tunnel. A dual stack routing configuration implements dual IP layers, supporting both IPv4 and IPv6, in both hosts and routers. An IPv4-IPv6 tunnel is essentially similar, creating a tunnel that encapsulates IPv6 packets within IPv4 headers that carry these IPv6 packets over IPv4 tunnels. The FortiGate unit can also be easily integrated into an IPv6 network. Connecting the FortiGate unit to an IPv6 network is exactly the same as connecting it to an IPv4 network, the only difference is that you are using IPv6 addresses.

By default the IPv6 settings are not displayed in the Web-based Manager. It is just a matter of enabling the display of these feature to use them through the web interface. To enable them just go to System > Admin > Settings and select IPv6 Support on GUI. Once enabled, you will be able to use IPv6 addresses as well as the IPv4 addressing for the following FortiGate firewall features:

• Static routing
• Policy Routing
• Packet and network sniffing
• Dynamic routing (RIPv6, BGP4+, and OSPFv3)
• IPsec VPN
• DNS
• DHCP
• SSL VPN
• Network interface addressing
• Security Profiles protection
• Routing access lists and prefix lists l  NAT/Route and Transparent mode l  NAT 64 and NAT 66
• IPv6 tunnel over IPv4 and IPv4 tunnel over IPv6
• Logging and reporting
• Security policies
• SNMP
• Authentication
• Virtual IPs and groups
• IPv6 over SCTP
• IPv6-specific troubleshooting, such as ping6

Dual Stack routing configuration

Dual stack routing implements dual IP layers in hosts and routers, supporting both IPv6 and IPv4. A dual stack architecture supports both IPv4 and IPv6 traffic and routes the appropriate traffic as required to any device on the network. Administrators can update network components and applications to IPv6 on their own schedule, and even maintain some IPv4 support indefinitely if that is necessary. Devices that are on this type of network, and connect to the Internet, can query Internet DNS servers for both IPv4 and IPv6 addresses. If the Internet site supports IPv6, the device can easily connect using the IPv6 address. If the Internet site does not support IPv6, then the device can connect using the IPv4 addresses. In the FortiOS dual stack architecture it is not just the basic addressing functions that operate in both versions of IP. The other features of the appliance such as Security Profiles and routing can also use both IP stacks.

If an organization with a mixed network uses an Internet service provider that does not support IPv6, they can use an IPv6 tunnel broker to connect to IPv6 addresses that are on the Internet. FortiOS supports IPv6 tunneling over IPv4 networks to tunnel brokers. The tunnel broker extracts the IPv6 packets from the tunnel and routes them to their destinations.

IPv6 Tunneling

IPv6 Tunneling is the act of tunneling IPv6 packets from an IPv6 network through an IPv4 network to another IPv6 network. This is different than Network Address Translation (NAT) because once the packet reaches its final destination the true originating address of the sender will still be readable. The IPv6 packets are encapsulated within packets with IPv4 headers, which carry their IPv6 payload through the IPv4 network. This type of configuration is more appropriate for those who have completely transitional over to IPv6, but need an Internet connection, which is still mostly IPv4 addresses.

The key to IPv6 tunneling is the ability of the 2 devices, whether they are a host or a network device, to be dual stack compatible. They have to be able to work with both IPv4 and IPv6 at the same time. In the process the entry node of the tunnel portion of the path will create an encapsulating IPv4 header and transmit the encapsulated packet. The exit node at the end of the tunnel receives the encapsulated packet. The IPv4 header is removed.

The IPv6 header is updated and the IPv6 packet is processed.

There are two types of tunnels in IPv6:

Automatic tun- nels

Configured tun- nels

Automatic tunnels are configured by using IPv4 address information embedded in an IPv6 address – the IPv6 address of the destination host includes information about which IPv4 address the packet should be tunneled to.

Configured tunnels must be configured manually. These tunnels are used when using IPv6 addresses that do not have any embedded IPv4 information. The IPv6 and IPv4 addresses of the endpoints of the tunnel must be specified.

Tunnel Configurations

There are a few ways in which the tunneling can be performed depending on which segment of the path between the end points of the session the encapsulation takes place.

Network Device to Network Device

Host to Network

Device

Dual stack capable devices connected by an IPv4 infrastructure can tunnel IPv6 pack- ets between themselves. In this case, the tunnel spans one segment of the path taken by the IPv6 packets.

Dual stack capable hosts can tunnel IPv6 packets to an intermediary IPv6 or IPv4 net- work device that is reachable through an IPv4 infrastructure. This type of tunnel spans the first segment of the path taken by the IPv6 packets.

Host to Host             Dual stack capable hosts that are interconnected by an IPv4 infrastructure can tunnel IPv6 packets between themselves. In this case, the tunnel spans the entire path taken by the IPv6 packets.

Network Device to Host

Dual stack capable network devices can tunnel IPv6 packets to their final destination IPv6 or IPv4 host. This tunnel spans only the last segment of the path taken by the IPv6 packets.

Regardless of whether the tunnel starts at a host or a network device, the node that does the encapsulation needs to maintain soft state information, such as the maximum transmission unit (MTU), about each tunnel in order to process the IPv6 packets.

Tunneling IPv6 through IPsec VPN

A variation on the tunneling IPv6 through IPv4 is using an IPsec VPN tunnel between to FortiGate devices. FortiOS supports IPv6 over IPsec. In this sort of scenario, 2 networks using IPv6 behind FortiGate units are separated by the Internet, which uses IPv4. An IPsec VPN tunnel is created between the 2 FortiGate units and a tunnel is created over the IPv4 based Internet but the traffic in the tunnel is IPv6. This has the additional advantage of make the traffic secure as well.

Interfaces and Zones

A Firewall is a gateway device that may be the nexus point for more than 2 networks. The interface that the traffic is coming in on and should be going out on is a fundamental concern for the purposes of routing as well as security. Routing, policies and addresses are all associated with interfaces. The interface is essentially the connection point of a subnet to the FortiGate unit and once connected can be connected to other subnets.

Physical interfaces or not the only ones that need to be considered. There are also virtual interfaces that can be applied to security policies. VLANs are one such virtual interface. Interfaces if certain VPN tunnels are another.

Policies are the foundation of the traffic control in a firewall and the Interfaces and addressing is the foundation that policies are based upon. Using the identity of the interface that the traffic connects to the FortiGate unit tells the firewall the initial direction of the traffic. The direction of the traffic is one of the determining factors in deciding how the traffic should be dealt with. You can tell that interfaces are a fundamental part of the policies because, by default, this is the criteria that the policies are sorted by.

Zones are a mechanism that was created to help in the administration of the firewalls. If you have a FortiGate unit with a large number of ports and a large number of nodes in you network the chances are high that there is going to be some duplication of policies. Zones provide the option of logically grouping multiple virtual and physical FortiGate firewall interfaces. The zones can then be used to apply security policies to control the incoming and outgoing traffic on those interfaces. This helps to keep the administration of the firewall simple and maintain consistency.

For example you may have several floors of people and each of the port interfaces could go to a separate floor where it connects to a switch controlling a different subnet. The people may be on different subnets but in terms of security they have the same requirements. If there were 4 floors and 4 interfaces a separate policy would have to be written for each floor to be allowed out on to the Internet off the WAN1 interface. This is not too bad if that is all that is being done, but now start adding the use of more complicated policy scenarios with Security Profiles, then throw in a number of Identity based issues and then add the complication that people in that organization tend to move around in that building between floors with their notebook computers.

Each time a policy is created for each of those floors there is a chance of an inconsistency cropping up. Rather than make up an additional duplicate set of policies for each floor, a zone can be created that combines multiple interfaces. And then a single policy can created that uses that zone as one side of the traffic connection.

How Packets are handled by FortiOS

To give you idea of what happens to a packet as it makes its way through the FortiGate unit here is a brief overview. This particular trip of the packet is starting on the Internet side of the FortiGate firewall and ends with the packet exiting to the Internal network. An outbound trip would be similar. At any point in the path if the packet is going through what would be considered a filtering process and if fails the filter check the packet is dropped and does not continue any further down the path.

This information is covered in more detail in other in the Troubleshooting chapter of the FortiOS Handbook in the Life of a Packet section.

The incoming packet arrives at the external interface. This process of entering the device is referred to as ingress.

Step #1 – Ingress

1. Denial of Service Sensor

2. IP integrity header checking

3. IPsec connection check

4. Destination NAT

5. Routing

Step #2 – Stateful Inspection Engine

1. Session Helpers

2. Management Traffic

3. SSL VPN

4. User Authentication

5. Traffic Shaping

6. Session Tracking

7. Policy lookup

Step #3 – Security Profiles scanning process

1. Flow-based Inspection Engine

2. IPS

3. Application Control

4. Data Leak Prevention

5. Email Filter

6. Web Filter

7. Anti-virus

8. Proxy-based Inspection Engine

9. VoIP Inspection

10. Data Leak Prevention

11. Email Filter

12. Web Filter

13. Anti-virus

14. ICAP

Step #4 – Egress

1. IPsec

2. Source NAT

3. Routing