On 6/8/11 11:36 PM, Ujjval Karihaloo wrote:
Hi All:
We have seen many PBX NAT?ed behind a Firewall that does not do the Sip ALG correctly. Most cases putting the Private IP in the Contact header and the ACME responds back to the Private IP.
Example call inbound to the PBX, the PBX sends a 200 OK (as call is answered) with a Private IP in the contact header. ACME sends the ACK back to the Private IP blackholing it.
I have seen SBC?s that do adjust to the Layer 3 IP:port if they notice Private IPs in the SIP signaling. Is there a setting on ACME to do that?
Read up on nat-traversal always in the sip interface section of the config. I will note, however, that that looks for the Contact-URI and topmost VIA to match and to be different than the source address in layer 3 (IP), rather than looking for RFC 1918 addresses. Of course, given that there are umpteen hundred knobs to twist on an Acme, there's probably some way of getting it to do this only for RFC 1918 addresses, but I'm not sure there's value in doing that and certainly couldn't tell you how to do it. My understanding is that "nat-traversal always" is the "normal" way of doing what you appear to need. As an operational note, we've had more problems with various customer firewalls doing pretty bad jobs with SIP, such as the one that worked fine until somebody transferred a call at which point the firewall just dropped all sorts of vital packets on the floor, than we've ever had just letting our Acmes do NAT traversal. Our standard recommendation is to turn all SIP aware proxies, fix-up, etc. off. --Jon Radel