Configuring SIP IP address conservation for the SIP session helper
You can use the following command to enable or disable SIP IP address conservation for the SIP session helper. IP address conservation is enabled by default for the SIP session helper.
config system settings
set sip-nat-trace disable
end
If the SIP message does not include an i= line and if the original source IP address of the traffic (before NAT) was 10.31.101.20 then the FortiGate unit would add the following i= line.
i=(o=IN IP4 10.31.101.20)