SIP Traffic is Handled by the SIP ALG by Default
Previous versions of FortiOS used the SIP session helper for all SIP sessions. You had to remove the SIP session helper from the configuration for SIP traffic to use the SIP ALG.
In FortiOS 5.2, all SIP traffic is now processed by the SIP ALG by default. You can change the default setting using the following command:
config system settings
set default-voip-alg-mode {proxy-based | kernel-helper-based}
end
The default is proxy-based, which means the SIP ALG is used. If set to kernel-helper-based, the SIP session helper is used. If a SIP session is accepted by a firewall policy with a VoIP profile, the session is processed using the SIP ALG even if default-voip-alg-mode is set to kernel-helper-based.
If a SIP session is accepted by a firewall policy that does not include a VoIP profile:
• If default-voip-alg-mode is set to proxy-based, SIP traffic is processed by the SIP ALG using the default VoIP profile.
• If default-voip-alg-mode is set to kernel-helper-based, SIP traffic is processed by the SIP session helper. If the SIP session help has been removed, then no SIP processing takes place.