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VoIP / NAT Problem with single IP address

I have a 3620 setup as a H.323 VoIP gateway, It's on a 10.0.0.0 LAN and has a loopback port with the real world public IP address, I have bound this with the H.323 voip bind command. I am connected to the outside world through a 1750 router with an Adsl connection with one real IP address, I'm NAT overloading onto this.

When the 3620 sends out its first setup message to port 1720 it is sent correctly out over the net to my remote gateway, but when the reply is received , which is addressed to the Public address, the dialer 0 (ATM/ADSL) interface sends a RESET back to the Internet gateway, presumably because it thinks the packet is for itself and it doesnt have a port 1720 open?, I really wanted to relay this back to the 10.0.0.0 3620 router.

If i remove the H323 BIND statement from the loopback interfaceon the 3620 then the call is setup fine, however I have one way voice due to the internal 10.0.0.0 address being sent out in the body of the message

My question, is, is there a way around this. I can see how having some more IP address might help.

Thanks in Advance, Paul C.

IOS Version is

C1700 Software (C1700-Y7-M), Version 12.2(15)T9

3600 Software (C3620-IS-M), Version 12.2(19a)

IP NAT Settings on 1750 are:

ip nat inside source list WK_LOCAL_IPS interface Dialer0 overload

ip nat inside source static tcp 10.0.1.220 1720 81.86.69.5 1720 extendable

1 ACCEPTED SOLUTION

Accepted Solutions
Bronze

Re: VoIP / NAT Problem with single IP address

I think I see the problem.

You are running c1700-y7-mz, which is IP/ADSL feature set.

You need a PLUS feature set, so download IP/ADSL PLUS (c1700-sy7-mz) and you should be set.

4 REPLIES
Bronze

Re: VoIP / NAT Problem with single IP address

Configuring the loopback IP the way you tried definately wont work.

But, IOS NAT should be looking into the H.323 packets and translating the IP's for you. I suspect that the problem isnt that the remote gateway is transmitting to 10.0.0.x.

You can verify what IP it is transmitting to by doing a "show call active voice brief" on the remote gateway. If the remote gateway is not a cisco router, then you will have to get a sniffer trace.

Bronze
Anonymous
N/A

Re: VoIP / NAT Problem with single IP address

Thanks for the comments, i have traced the h.225/245 messages at the remote gateway (3640) and they are seeing the 10.0.1.220 address as the return address for rtp, so I don't think the addresses are being translated. I don't think my IOS is fixing up the embedded addresses in the VoIP packets, looking at the Cisco documents i notice the NAT enhancements are not suported on 1750 routers, however the commands are there in my IOS. http://www.cisco.com/en/US/partner/products/sw/iosswrel/ps1834/products_feature_guide09186a0080080535.html

If I can find a way to make the embedded addresses get translated, then I wont need the Bind staement and everything should work fine.

Paul C.

Bronze

Re: VoIP / NAT Problem with single IP address

I think I see the problem.

You are running c1700-y7-mz, which is IP/ADSL feature set.

You need a PLUS feature set, so download IP/ADSL PLUS (c1700-sy7-mz) and you should be set.

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