Remote Extension; Inbound Calls Work, Outbound Calls Fail

[brendan.helsham]

We have a situation where a client had a staff member relocate to Papua New Guinea, and they wanted this person to keep working for them. So, we supplied a new PC and a Yealink T-28 to this person in PNG.

The problem is that when we setup the phone to register to the 3CX server, either via the SIP Tunnel Proxy software on the PC (over the Internet or via IPSec VPN to head office), or directly over the Internet to 5060 on the 3CX server, there is no audio on any calls originated by the person in PNG. They hear the ringing sound when they make a call, but as soon as it is answered, no audio is heard at either end. If I call their phone, then there is no problem and we have 2 way audio.

The one hitch in this that I have discovered is that the ISP in PNG (there's not a lot of choice by the way) is actually supplying them a 172.x.x.x "public IP" address that is being translated a second time to a real public IP address (202.1.53.74) that is reported if you open http://www.whatismyip.com

As an aside, I was not able to get the 3CX Soft Phone to work at all, so the Yealink at least worked one way....

So, am I flogging a dead horse trying to get this to work? Why would it only work for inbound calls, not outbound?

Cheers
-Brendan

 

[leejor]

Re: Remote Extension; Inbound Calls Work, Outbound Calls Fai

I've found, in the past, that, as a last resort, either a VPN connection or the tunnel option will usually work. If they are using some sort of a proxy server you may be out of luck. I suppose that you could discuss it with them and see if they have any suggestions.

The one hitch in this that I have discovered is that the ISP in PNG (there's not a lot of choice by the way) is actually supplying them a 172.x.x.x "public IP" address that is being translated a second time to a real public IP address (202.1.53.74) that is reported if you open http://www.whatismyip.com

Is a router then used as well with the 172.x.x.x IP? What does the 3CX log tell you (IP & post), when the set registers?

 

[brendan.helsham]

Re: Remote Extension; Inbound Calls Work, Outbound Calls Fai

I've found, in the past, that, as a last resort, either a VPN connection or the tunnel option will usually work

Yes, my expectation was that if we pointed the SIP Tunnel Proxy client s/w at the LAN IP of the 3CX Server and connected the Cisco IPSec tunnel from the Windows Client, then any routing/NAT issues would disappear. Sadly this was not the case....

Is a router then used as well with the 172.x.x.x IP? What does the 3CX log tell you (IP & post), when the set registers?

Sorry if I wasn't clear....

The internal network at the users home is 192.168.0.0. The ADSL router (Level One WBR-3407A FWIW) status page reports the 172.x.x.x IP address as its WAN/Public IP, and the 202.x.x.x address is reported by whatismyip.com.


From the log when the set registers

13:31:17.557|.\Extension.cpp(358)|Log2||ExtnCfg::updateContact:[CM504001]: Ext.274: new contact is registered. Contact(s): [sip:[email protected]:5062/274]<br>

 

[leejor]

Re: Remote Extension; Inbound Calls Work, Outbound Calls Fai

3:31:17.557|.\Extension.cpp(358)|Log2||ExtnCfg::updateContact:[CM504001]: Ext.274: new contact is registered. Contact(s): [sip:274@192.168.0.3:5062/274]<br>

From the looks of this, you may not have STUN enabled on the set. The registration should show the public IP + port. That said, it sounds like you may have a "double NAT" situation, something that may be very hard to overcome. Be sure that STUN is enabled , then try connecting a PC directly to the modem (if possible), bypassing the users local router (They will pick up a 172.x.x.x IP). Try a call using the 3CX softphone on that PC (normal/VPN/Tunnel)

 

[brendan.helsham]

Re: Remote Extension; Inbound Calls Work, Outbound Calls Fai

I have managed to solve this problem and wanted to post what I discovered after looking for hints in Wireshark traces and various other log files.

The bottom line is that we can't get this to work properly, if connected direct via 5060 to the public IP at the head office, probably due to the double-NAT situation with the dodgy PNG Internet service. I didn't look any further into this option....

We were able to get it to work using the 3CX SIP Proxy Manager when the Cisco IPSec tunnel was in a disconnected state.
The problem of not being able to establish outbound calls, with audio, manifested itself if the IPSec tunnel was connected. This isn't much good long term as the VPN connection needs to be connected so that the user can access information on the head office network whilst she calls customers.

It seems as though the 3CX SIP Proxy Manager was trying to push traffic down the VPN tunnel when it was connected because the SIP Server setting on the phone had the LAN IP address of the 3CX Server.

So, the solution to allow phone calls to be made, irrespective of whether the IPSec tunnel was connected, was to create a persistent route to the internal LAN IP address of the 3CX server, to use the local IP address of the Ethernet Adapter in the PC. This way there was no attempt for the 3CX SIP Proxy Manager to route traffic down the IPSec tunnel.

I hope this workaround helps others who may be trying to achieve the same result at some stage.

Cheers