Help with communication between IP Communicators

Unanswered Question
Apr 3rd, 2009

Hi All,

I have the following situation...

About 50 remote VPN clients connecting to a 2821, but each computer is an IP Communicator...

The problem is that each computer establishes the VPN tunnel to the router and get an IP address from the pool (192.168.3.x) and when they try to reach another IP Communicator through the VPN tunnel, there's no voice passing through...

The telephone rings, but nothing is heard...

I think the problem is the following...

Since all the 50 remote IP Communicators get an IP address on the same subnet (192.168.3.x), when they try to talk to each other, they never send the traffic through the tunnel to the router since the destination is on the same subnet....

The reason why the telephone rings is because the IP Communicator is able to reach the Call Manager and the Call Manager is able to ring the called telephone, but then the RTP session between the two IP Communicators, is when the traffic is never sent through the tunnel since both source and destination are on the same subnet...

I am attaching a simple diagram representing the situation, and any comments are appreciated...

How do I get this to work?

For example, I can assign a different pool to every remote IP communicator so they can be on a different subnet and therefore establish a call through the tunnel, but that's not going to be scalable....

Thank you all!

I have this problem too.
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fedecotof Tue, 04/14/2009 - 10:27

Thank you but I don't quite understand what you mean with using the VPN IP address instead than the interface IP address...

Do you mean in the VPN client software or in the IP Communicator or where?

I just did a route print in one of the computers that connect through VPN and I do get all traffic to the pool should be sent through the tunnel.... 20 20 20

So, could you please clarify what do you mean with using the VPN address instead of using the interface address? I will appreciate it!!

Thank you!

CHRIS CHARLEBOIS Tue, 04/14/2009 - 11:59

It isn't a routing issue, at least not in the data sense of the word. When the voice traffic gets set up, each client advertises an IP address which should be the target for the other side's voice stream. The problem comes when a client has two IP addresses, as in the case when a PC has a physical IP address and a virtual VPN IP address. IP Communicator will typically bind the physical address, and so will advertise that physical address to the other end to use as the target. The problem is that the other side usually has no route to get to that physical address because that physical address is a RFC1918 addressed subnet behind a NAT firewall. Therefore the configuration change needs to be made on the IP Communicator.

But that may not be your problem. Can you ping the other computers on the VPN using the 192.168.3.x address? Is your VPN blocking any traffic?

fedecotof Wed, 04/15/2009 - 09:30


I am going to test and see if I can PING the other IP Communicators from the IP Communicator I'm using and let you know.

I guess my question now is...

How do you force the IP Communicator to use the VPN IP address and not the physical address? I mean, there's not a command like on a router to do that, so how do you do it?

Thank you again!

fedecotof Mon, 04/20/2009 - 11:54


I am able to PING from one IP Communicator to another through the VPN tunnel, so there's no routing issue as you said...

My question is then.... how do I force the IP Communicator to establish the call using the VPN address instead than the physical address?

Thank you!


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