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Community Member

one way audio and IOS Zone Based FIrewall

Interesting problem. I am running CME 4.2 on a 2801 router. I have a 7960 phone that can register no problem to the 2801. I have an FXO port that connects the router to the PSTN. I am also using IOS Zone Based Firewall for the firewall.

When I try to place a call, it goes through however I get one way audio. The PSTN end can hear me, however I cannot hear them. If I disable zone security (remove zone membership) on that interface it works fine.

The thing is, what zone pair would I have to define to enable this to work? It should just be a self zone which is fully enabled by default.

Any ideas??


Re: one way audio and IOS Zone Based FIrewall

One-way or no-way voice occurs when a call is connected but one or both ends are unable to receive audio or Dual Tone Multifrequency (DTMF) digits. Unlike the call setup procedure, audio is sent directly between end points within Real-Time Protocol (RTP) packets.

To resolve these issues, locate the point at which RTP packets are not being transmitted in both directions. One-way or no-way voice can begin at a number of points in a packet voice network, as shown:

IP phone

Default gateway

Routing network

Voice gateway

Network Address Translation (NAT) or PIX Firewall

Telco interaction, in particular with audio cut-through

Community Member

Re: one way audio and IOS Zone Based FIrewall

thanks for the reply. Both the IP phone and the CME router are in the same VLAN. Each can ping each other without difficulty. When I disable zone based firewall it works just fine which is strange.

Community Member

Re: one way audio and IOS Zone Based FIrewall

we had the same issue. cisco tac determined its a bug. we tried their ios bugfix but this caused other issues. we had to remove zbf.

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