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> Chapter 33 - VoIP Solutions: SIP > How the SIP ALG performs NAT > Controlling how the SIP ALG NATs SIP contact header line addresses

Controlling how the SIP ALG NATs SIP contact header line addresses

You can enable contact-fixup so that the SIP ALG performs normal SIP NAT translation to SIP contact headers as SIP messages pass through the FortiGate.

Disable contact-fixup if you do not want the SIP ALG to perform normal NAT translation of the SIP contact header if a Record-Route header is also available. If contact-fixup is disabled, the FortiGate ALG does the following with contact headers:

  • For Contact in Requests, if a Record-Route header is present and the request comes from the external network, the SIP Contact header is not translated.
  • For Contact in Responses, if a Record-Route header is present and the response comes from the external network, the SIP Contact header is not translated.

If contact-fixup is disabled, the SIP ALG must be able to identify the external network. To identify the external network, you must use the config system interface command to set the external keyword to enable for the interface that is connected to the external network.

Enter the following command to perform normal NAT translation of the SIP contact header:

config voip profile

edit VoIP_Pro_1

config sip

set contact-fixup enable

end

end