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voip rtp nat problem

 
 
Michelangelo
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      08-17-2007
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 10.10.10.128:5060 147.135.4.129:5060
147.135.4.129:5060
udp AAA.BBB.CCC.DDD:0 10.10.10.128:16426 147.135.4.247:38192
147.135.4.247:38192
tcp AAA.BBB.CCC.DDD:60011 10.10.10.128:60011 147.135.0.32:8080
147.135.0.32:8080
udp AAA.BBB.CCC.DDD:60203 10.10.10.128:60203 147.135.0.6:53
147.135.0.6:53
udp AAA.BBB.CCC.DDD:60203 10.10.10.128:60203 147.135.8.6:53
147.135.8.6:53
udp AAA.BBB.CCC.DDD:60203 10.10.10.128:60203 195.110.128.1:53
195.110.128.1:53
icmp AAA.BBB.CCC.DDD:28976 10.10.10.128:2188210480 147.135.8.6:2188210312
147.135.8.6:28976
icmp AAA.BBB.CCC.DDD:28976 10.10.10.128:2188210480 195.110.128.1:2188210312
195.110.128.1:28976

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?

TIA,

Mike


 
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