voip rtp nat problem

Discussion in 'Cisco' started by Michelangelo, Aug 18, 2007.

  1. Michelangelo

    Michelangelo Guest

    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
    Michelangelo, Aug 18, 2007
    #1
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