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New Member

One Way Voice - H323 call + NAT


I have the following issue:

The calling part is a phone directly connected to a Voip GW. The Voip GW is in a LAN having private IP. The call is sent to an AS5xxx series. It is authenticated by the public IP of that LAN, the call is connected and there is one way voice.

On As5xxx I see the call connected (with "show call active voice brief" command), but the IP from where the call is coming is the private IP of the Voip GW, and not the public IP of the LAN where the GW is. So - i think the cisco don't know where to send the RTP packets, and the voice back is lost.

There is a command on cisco for this h323 calls issue (like "nat symmetric check-media-src" for sip calls) ?

Any help will be appreciated

Thank you



Re: One Way Voice - H323 call + NAT


You said that your natting this through a firewall. What kind of firewall are you using. If you using a Cisco ASA, PIX turn on the h323 fixup.

Your problem is when h323 calls it uses H225 for call control. Inside that call control is the ip address's that each side is using. If you firewall doesn't support h323 inspection it won't change the h323 messages to actually specify your public ip address.

Let me know if this helps.

Patrick Laidlaw

New Member

Re: One Way Voice - H323 call + NAT

The router is a Fritzbox fone ADSL Modem/Router/SIP gateway all in one.

My client told me that the call was sent to another VoIP carrier's cisco box and it was working. So, I presume is some config in the AS5xxx. Any idea ?



New Member

Re: One Way Voice - H323 call + NAT

well - this is a shame, but the problem was fixed by enabling the feature "IP sharing" on H323 GW behind the NAT. This is what my customer told me after I was searching half a day for a cisco command to fix this.

Anyway I think there is a command on cisco - you can choose where to send the call back - to the VoIP protocol IP or IP protocol IP ... i don't quite remember. I just remember that is very hard to find the command.

If someone know something about please let me know - for future issues...

Thanks alot


New Member

Re: One Way Voice - H323 call + NAT

just be sure you open all ports used by RTP stream

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