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voip rtp nat problem

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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
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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