FGSP – FortiGate Session Life Support Protocol

FortiGate Session Life Support Protocol (FGSP) distributes sessions between two FortiGate units and the FGSP performs session synchronization. If one of the peers fails, session failover occurs and active sessions fail over to the peer that is still operating. This failover occurs without any loss of data. Also, the external routers or load balancers will detect the failover and re-distribute all sessions to the peer that is still operating. The two FortiGate units must be the same model and must be running the same firmware.

You can also use the config system cluster-sync command to configure FGSP between two FortiGate units.

The FortiGate’s HA Heartbeat listens on ports TCP/703, TCP/23, or ETH Layer 2/8890.

In previous versions of FortiOS, FGSP was called TCP session synchronization or standalone session synchronization. However, FGSP has been expanded to include both IPv4 and IPv6 TCP, UDP, ICMP, expectation, NAT sessions, and IPsec tunnels.

FGSP – FortiGate Session Life Support

Configuration synchronization

Configuration synchronization can also be performed, allowing you to make configuration changes once for both FortiGate units instead of requiring multiple configuration changes on each FortiGate unit. However interface IP addresses, BGP neighbor settings, and other settings that identify the FortiGate unit on the network are not synchronized. You can enable configuration synchronization by entering the following command:

config system ha set standalone-config-sync enable

end

UDP and ICMP (connectionless) session synchronization

In many configurations, due to their non-stateful nature, UDP and ICMP sessions don’t need to be synchronized to naturally failover. However, if it is required, you can configure the FGSP to also synchronize UDP and ICMP sessions by entering the following command:

config system ha set session-pickup enable

set session-pickup-connectionless enable

end

Expectation (asymmetric) session synchronization

Synchronizing asymmetric traffic can be very useful in situations where multiple Internet connections from different ISPs are spread across two FortiGates.

The FGSP enforces firewall policies for asymmetric traffic, including cases where the TCP 3-way handshake is split between two FortiGates. For example, FGT-A receives the TCP-SYN, FGT-B receives the TCP-SYN-ACK, and FGT-A receives the TCP-ACK. Under normal conditions a firewall will drop this connection since the 3-way handshake was not seen by the same firewall. However two FortiGates with FGSP configured will be able to properly pass this traffic since the firewall sessions are synchronized.

If traffic will be highly asymmetric, as described above, the following command must be enabled on both FortiGates:

config system ha set session-pickup enable set session-pickup-expectation enable

end

Security profile inspection with asymmetric and symmetric traffic

Security profile inspection, flow or proxy based, is not expected to work properly if the traffic in the session is load balanced across more than one FortiGate in either direction. However, flow-based inspection should be used in FGSP deployments.

For symmetric traffic, security profile inspection can be used but with the following limitations:

• No session synchronization for the sessions inspected using proxy-based inspection. Sessions will drop and need to be reestablished after data path failover.
• Sessions with flow-based inspection will failover, and inspection of sessions after a failover may not work.

FGSP                  Session Life Support Protocol

Improving session synchronization performance

Two HA configuration options are available to reduce the performance impact of enabling session failover (also known as session pickup): 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

If session pickup is enabled, as soon as new sessions are added to the primary unit session table they are synchronized to the other cluster units. 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.

FGSP – FortiGate Session Life Support

NAT session synchronization

NAT sessions are not synchronized by default. You can enable NAT session synchronization by entering the following command:

config system ha set session-pickup enable set session-pickup-nat enable

end

Note that, after a failover with this configuration, all sessions that include the IP addresses of interfaces on the failed FortiGate unit will have nowhere to go since the IP addresses of the failed FortiGate unit will no longer be on the network. If you want NAT sessions to resume after a failover you should not configure NAT to use the destination interface IP address, since the FGSP FortiGate units have different IP addresses. To avoid this issue, you should use IP pools with the type set to overload (which is the default IP pool type), as shown in the example below:

config firewall ippool edit FGSP-pool set type overload set startip 172.20.120.10 set endip 172.20.120.20

end

In NAT/Route mode, only sessions for route mode security policies are synchronized. FGSP HA is also available for FortiGate units or virtual domains operating in Transparent mode. Only sessions for normal Transparent mode policies are synchronized.

IPsec tunnel synchronization

When you use the config system cluster-sync command to enable FGSP, IPsec keys and other runtime data are synchronized between cluster units. This means that if one of the cluster units goes down the cluster unit that is still operating can quickly get IPsec tunnels re-established without re-negotiating them. However, after a failover, all existing tunnel sessions on the failed FortiGate have to be restarted on the still operating FortiGate.

IPsec tunnel sync only supports dialup IPsec. The interfaces on both FortiGates that are tunnel endpoints must have the same IP addresses and external routers must be configured to load balance IPsec tunnel sessions to the FortiGates in the cluster.

Standalone configuration synchronization uses a very similar process as FGCP. There is a similar relationship between the two FortiGates but only in regards to configuration synchronization, not session information. The primary unit is selected by using priority/override. The heartbeat is used to check the primary unit’s health. Once heartbeat loss is detected, a new primary unit is selected.

FGSP                  Session Life Support Protocol

Automatic session synchronization after peer reboot

The following command allows you to configure an automatic session synchronization after a peer FGSP unit has rebooted. FGSP will send out heartbeat signals (every 1 – 10 seconds, as shown below) if one FortiGate is rebooting and the other FortiGate fails.

To configure automatic session synchronization:

config system session-sync edit 1

set down-intfs-before-sess-sync <interfaces> – List of interfaces to be turned down before session synchronization is complete.

set-hb-interval <integer> – (1 – 10 seconds) set hb-lost-threshold <integer> – (1 – 10)

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