voip rtp nat problem

Hi all,

I have a Cisco 857W as router (with 1 fixed public address). NAT is in use and behind it there are some servers (mail, www, dns).

Everything works fine except my voip box (Linksys/SPA2100-3.3.7). It is able to register with VoIP provider (BroadVoice). It can also dial, but nothing is heard on my side (so I suspect a problem with NAT on the rtp side.

I did a debug ip nat and found something strange (look at second line, there is a port with 0 - zero value in the inside global):

Pro Inside global Inside local Outside local Outside global udp AAA.BBB.CCC.DDD:1042 udp AAA.BBB.CCC.DDD:0 tcp AAA.BBB.CCC.DDD:60011 udp AAA.BBB.CCC.DDD:60203 udp AAA.BBB.CCC.DDD:60203 udp AAA.BBB.CCC.DDD:60203 icmp AAA.BBB.CCC.DDD:28976 icmp AAA.BBB.CCC.DDD:28976

Did a capture with Wireshark (on the inside side) and found many RTP packets going out but none coming in.

I am very disappointed since before the Cisco 857W I was using a very basic Home router and the voip box was working well (behind a NAT).

Please help !!!

Is this a configuration problem or a bug on the IOS sw?



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