Remote softphone cannot register to LAN PBX via VPN

Posted on 2013-05-23
Medium Priority
Last Modified: 2013-06-04
Hi all,
Appreciate in advance if anyone can help me this problem.
My office has one Juniper SSG5 firewall.
For remote users, I install Shrew soft VPN client for their remote access.
Users have no problem use VPN access LAN share drive or RDP to office desktop.
However users' softphone cannot register to LAN PBX through VPN.
I use wireshark and get attached result. is VPN client. is IP PBX.
From the capture, it shows Destination port: vat
I don't know what does that mean. Can somebody please give me a hint or direction for troubleshooting?

Question by:generait

Assisted Solution

Eikroman earned 750 total points
ID: 39193779

vat, in Wireshark is probably port 3456 (examine the packet to make sure). It may be used in SIP.

Anyway, if there is no restrictions on VPN clients communication, the problem is most likely in the SIP client software/configuration.

I have seen a situation where SIP client couldn't correctly handle VPN connection.
SIP client erroneously binded itself to the regular internet connection interface and tried to contact internal VPN IP over Internet, which of course didn't work. In our case, it was a software bug.

It's easily detectable on client side using Wireshark by checking on which interface SIP client tries to communicate. On server side, there will be no or partial handshake.
LVL 24

Accepted Solution

Mohammed Hamada earned 750 total points
ID: 39199208
VAT on 3456 (default port) is a Video/Audio (tool == vat) conferencing protocol but I don't think you need it in this case.

In your PBX network settings, have you configured the gateway IP to be pointing to the firewall Local IP so your users can register to the PBX through the firewall ? Because when the phone registration request is sent through the VPN it will first go to the firewall while holding the registrar IP address and if your PBX doesn't have the Gateway IP address set as your Firewall's Local IP then the firewall will not be able to route the registration request there.

Where did you use wireshark btw? On the PBX or on the client PC? U have to use it on both and check for SIP requests. what does the invite looks like.
please attach the log here so we can see but after you make sure that PBX's gateway is pointing to the firewall's Local IP.

Author Closing Comment

ID: 39220384
Thanks for your reponse.
Finally the PBX vendor modified system parameters then solved the issue.
The networking has no problem in this situation.
Again thanks for all inputs.

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