When SIP ALG processes a SIP call, it usually opens pinholes for SIP signaling and RTP/RTCP packets. NAT usually takes place during the process at both the network and SIP application layers. SIP ALG ensures that, with NAT happening, corresponding SIP and RTP/RTCP pinholes are created during the process when it is necessary for call sessions to be established through FortiOS devices.
By default, SIP ALG manages pinholes automatically, but some special configurations can be used to restrict the pinholes if required.
By default, the strict-register attribute is enabled. When enabled, after a SIP endpoint registers to the SIP server through a firewall policy on the FortiOS device, only the SIP messages sent from the same IP address as the SIP server are allowed to pass through the SIP pinhole that is created in the FortiOS device to reach the SIP endpoints. If the attribute is disabled, SIP messages from any IP addresses can pass through the pinhole created after the registration.
SIP pinhole restriction is only supported by SIP ALG and in proxy mode.
config voip profile edit "voip-profile-name" config sip set strict-register [enable|disable] ... end next end