IOS NAT SIP SUPPORT

[vgioia5090]

i have a ccme behind an ios nat router and when i make calls to the incoming sip trunk the phones ring but when i answer there is no audio and the cell phone im using to caal the sip trunk keeps ringing like i didnt even answer. i can make outgoing calls fine but something is getting blocked coming in. could this be a nat traversal issue, i have implemented the ip inspect sip etc..

[Nicholas Matthews · Accepted solution]

We should be able to support the IOS NAT ALG. There were a few posts about this yesterday. This feature was added in 12.2(8)T.

Compare the SIP message you see on the outside of your NAT router with 'debug ccsip messages'. Check the SDP for the IP address.

To be honest - this problem sounds like more of a firewall problem than pure NAT. Since you have one-way calling abilities, you have problems. On your outgoing dial peer, try adding 'session tranport tcp', or if it's already TCP, try UDP. Sometimes this helps figure out the firewall problem.

[vgioia5090]

thanks, but i dont have a firewall im running a 3660 with ios nat ios ver 12.4(6)T. is there anything else i can try? can you give me a sample config that would pass sip and any other port i would need to do a sip trunk with callcentric? i know the system works because when i use my smoothwall firewall with sip proxy enabled i dint get this problem. any ideas?

[Nicholas Matthews]

if you're using NAT with CBAC ip inspect, you will want to make sure you allow TCP/UDP 5060 in. This will allow incoming calls, and otherwise will not work.

check your ACLs where you're using the inspect, add incoming tcp/udp 5060 to be enabled.

[vgioia5090]

ok i added the config for ALG and it works thanks for all your help

vito

[Chuan Liu]

Hi,

Can you share your configs on the NAT router?

I have c877 and OKI IP-PBX. Outgoing calls are fine. The incoming calls fail, SIP 408 is returned on the SIP server.

Thanks.