SIP 871 firewall

Unanswered Question
Jul 13th, 2008


I have a 871w 12.4 (11)T1. I am trying to setup a linksys spa942 phone with Trixbox v1.2. Calls last for 30 seconds then I get one way audio out. When I disable the firewall it works just fine.

I've been through 4 cisco engineers and it's still not working. Any sugestions would be greatly appreciated.



I have this problem too.
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jseneca64 Mon, 07/14/2008 - 12:03

Finally resolved by the firewall team. We upgraded to the latest ios, 12.4(15)T5. There was a bug in 12.4(11)T1, See this: CSCsi84069, CBAC blocks RTP traffic even if pre-generated session exists

Under some very specific circumstances with IP inspect, NAT and ip phones located in different VRF's, it might be that SIP inspection is not allowing through the RTP session of called SIP phone.

No known workaround

Thank you,



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