SIP and HA–session failover and geographic redundancy

FortiGate high availability supports SIP session failover (also called stateful failover) for active-passive HA. To support SIP session failover, create a standard HA configuration and select the 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.

In some cases, failover during call teardown can result in hanging RTP connections which can accumulate over time and use up system memory. If this becomes a problem, you can set a time for the call-keepalive SIP VoIP profile setting. The FortiGate will then terminate calls with no activity after the time limit is exceeded.

Range is 1 to 10,080 seconds. This options should be used with caution because it results in extra FortiGate CPU overhead and can cause delay/jitter for the VoIP call. Also, the FortiGate unit terminates the call without sending SIP messages to end the call. And if the SIP endpoints send SIP messages to terminate the call they will be blocked by the FortiGate unit if they are sent after the FortiGate unit terminates the call.

 

SIP geographic redundancy

Maintains a active-standby SIP server configuration, which even supports geographical distribution. If the active SIP server fails (missing SIP heartbeat messages or SIP traffic) FortiOS will redirect the SIP traffic to a secondary SIP server. SIP geographic redundancy

Geographic redundancy
Primary Server	Secondary Server	Primary Server Fa	Secondary Server ilover
SSIPIP SSeervrveer r	SIPSIP SeSrveervrer	SIP Server	SIP Server

 

SIP

SIP Heartbeat (SIP OPTION)

SIP Heartbeat

SIP Heartbeat

Failover

SIP

 

SIP is forwarded to primary SIP Server, as long as it’s successfully sending heartbeats

 

SIP Signaling Firewall

In the case of SIP heartbeat absence, the SFW will forward the SIP traffic to the secondary SIP Server.

 

SIP Signaling Firewall

Supporting geographic redundancy when blocking OPTIONS messages

For some geographic redundant SIP configurations, the SIP servers may use SIP OPTIONS messages as heartbeats to notify the FortiGate unit that they are still operating (or alive). This is a kind of passive SIP monitoring mechanism where the FortiGate unit isn’t actively monitoring the SIP servers and instead the FortiGate unit passively receives and analyzes OPTIONS messages from the SIP servers.

If FortiGate units block SIP OPTIONS messages because block-options is enabled, the configuration may fail to operate correctly because the OPTIONS messages are blocked by one or more FortiGate units.

However, you can work around this problem by enabling the block-geo-red-options application control list option. This option causes the FortiGate unit to refresh the local SIP server status when it receives an OPTIONS message before dropping the message. The end result is the heartbeat signals between geographically redundant SIP servers are maintained but OPTIONS messages do not pass through the FortiGate unit.

 

Use the following command to block OPTIONS messages while still supporting geographic redundancy:

 

config voip profile edit VoIP_Pro_Name

config sip

set block-options disable

set block-geo-red-options enable end

end

 

The block-options option setting overrides the block-geo-red-options option. If block-options is enabled the FortiGate unit only blocks SIP OPTIONS messages and does not refresh local SIP server status.

 

 

Support for RFC 2543-compliant branch parameters

RFC 3261 is the most recent SIP RFC, it obsoletes RFC 2543. However, some SIP implementations may use RFC 2543-compliant SIP calls.

The rfc2543-branch VoIP profile option allows the FortiGate unit to support SIP calls that include an RFC 2543-compliant branch parameter in the SIP Via header. This option also allows FortiGate units to support SIP calls that include Via headers that are missing the branch parameter.

 

config voip profile edit VoIP_Pro_Name

config sip

set rfc2543-branch enable end

end