SIP No audio/media between pbx and ATA on different vlans

[GPz1100]

PBX ip = 10.10.1.76 (internal lan)

ATA (obi200) = 10.1.3.102 (vlan 3)

The ata is configured on its own vlan to isolate it from the main lan. The ata is able to connect to external sip provider (on the internet) without any signaling or media issues.

PBX is configured on the local network and it too works well with its configured trunks and local lan clients.

Goal: An extension on the pbx has been configured exclusively for the ATA's use.  Firewall rule has been set up to allow the ATA to register successfully to the PBX. At the moment, firewall rule is set to allow any packets between the pbx and ata in either direction.

Problem:  That's as far as I get.  The signaling sets up correctly but RTP/media is only getting passed inbound.  That is, when a call is made using the extension configured above, I can hear the other party, but they can't hear me. Firewall has been disabled in freepbx to rule that out.

I'm open to suggestions?

Thanks!

[GPz1100]

Through the magic of tcpdump I discovered this:

20:24:58.286320 IP 10.10.1.76.14644 > 10.10.3.102.17000: UDP, length 172
20:24:58.299378 IP 10.10.3.102.17000 > 17.142.160.59.14644: UDP, length 172

17.xxxxx is not my real IP. The RTP stream wasn't going back to the PBX IP, but rather to my public ip. I thought about using a DNAT rule but that would likely cause other problems. Instead, poking around in the obi I found an option to enable symmetric RPT.

It's under ITSP PROVIDER x - SIP - General

Enable X_SymmetricRTPEnable [on/off]

From the obi admin guide:

Enable device to apply symmetric RTP behavior on
every call: That is, send RTP to peer at the address
where incoming RTP packets are received from

Tcpdump output:

Before:

20:24:58.286320 IP 10.10.1.76.14644 > 10.10.3.102.17000: UDP, length 172
20:24:58.299378 IP 10.10.3.102.17000 > 17.142.160.59.14644: UDP, length 172

After:

20:35:13.645291 IP 10.10.1.76.15876 > 10.10.3.102.17006: UDP, length 172
20:35:13.645818 IP 10.10.3.102.17006 > 10.10.1.76.15876: UDP, length 172

Problem resolved!