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SIP ALG / SIP NAT Traversal

I have a 2900 series router running IOS version 15.1(4).  I am trying to connect 3rd party sip softphones to a 3rd party SIP Call controller on the inside.  With low-cost firewall/gateways, I normally enable the SIP ALG feature and it will dynamically open the UDP ports for a SIP conversation for the duration of it and then close them.  Does cisco IOS firewall have a SIP ALG feature and how do I configure it?  Any guidance is much appreciated. 

Eddie

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Hall of Fame Community Legend

Cisco routers have ALG enabled by default.

You need to talk to your voice service provider if they support NAT and/or ALG. 

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Im trying to connect a SIP softphone (on the outside) to a IP PBX on the inside.  I am seeing postings that say that "ip nat service sip" is the command that enables that feature, and others say that it breaks it.  So far my testings shows that it does break it.  Ultimately I want my outside softphone to register to the Phone system as an external IP address.  It seems like SIP normally relays the internal IP address and the ALG router will make the translation on outbound and send it to the right source. 

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Based on what I have read, I think Im looking for: 

Hosted NAT Traversal for Session Border Controller

Is this a NAT traversal solution that is available on ISR routers like the 2900 series running 15.1 IOS? 

Any Input is much appreciated. 

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