Connecting phone behind NAT to FreePBX behind NAT

[yois]

I have a Polycom VVX410 with UC 5.7.1 connecting to Asterisk 13.19.1. Both are behind NAT. The FreePBX server has port forwards for SIP and RTP, and they are confirmed working with a Zoiper softphone.

When connecting the Polycom, the phone will REGISTER momentarily with PJSIP, but then the following show up in the Asterisk logs:

[2018-07-18 18:14:54] VERBOSE[20697] res_pjsip/pjsip_configuration.c: Contact 914384/sip:[email protected]:5060 has been created
[2018-07-18 18:14:54] VERBOSE[20697] res_pjsip/pjsip_configuration.c: Endpoint 914384 is now Reachable
[2018-07-18 18:14:57] VERBOSE[20697] res_pjsip/pjsip_configuration.c: Contact 914384/sip:[email protected]:5060 is now Unreachable. RTT: 0.000 msec
[2018-07-18 18:14:57] VERBOSE[20697] res_pjsip/pjsip_configuration.c: Endpoint 914384 is now Unreachable

Doing some tcpdumps on both the PBX and the router on the remote side shows that there’s a conversation taking place between the phone and the PBX, but when the PBX requests OPTIONS from the phone, the Polycom responds twice with an ACK, and another 2 times with “403 Forbidden” but none of the phone responses reach the PBX side. I can’t figure this out, especially since Zioper is working but a Polycom isn’t.

[gdesilva]

Just wondering whether this has got anything to do with NAT on the Polycom device where NAT should be disabled as both Polycom and Asterisk/FreePBX are behind your firewall. Just a thought.

[avayax (Johann Zurner)]

Check which port the Polycom sends the responses to.
It might be your chansip port if you have that enabled.

I have had issues when converting chansip to pjsip or the other way round, options messages would be sent to the wrong port.

[yois]

The problem in the end was using NAT port translation instead of forwarding the actual port 5060. I created a new PJSIP transport on the port I wanted and forwarded that directly, and this solves the problem.