SIP-ALG (RTP)

[morphxyz]

Dear Community

I have read many threads regarding similar issues. But not quite exactly ours.

FW: DEC2685 OPNsense.
WAN: PPPoE
Telephony: Mitel MiVoice Office 400

So far normal calls work without any specific Rules or NAT settings.

The only Problem we have is if people want to redirect calls automatically to their cell phones. The cell phone rings and the connection is stable. BUT we just can't hear each other.

The technician of the Mitel Box told us to disable SIP-ALG, which, as found in other threads, isn't available in OPNsense anyway.

We have tried Port-Forwardings.. Outbound with static port. nothing seems to fix it.
Do you guys think the issue is even Firewall related?
Or is it more likely to be an issue with the Mitel installation?
After all, regular calls in/out do work properly.

PS: In the Mitel GUI, where the SIP and RTP Ports and configured, I could also define a value for "public NAT-Gateway-Adress".. Is it possible I have to use the OPNsense as value? right now the field is NULL. (See attachment)

Kind regards!
Ben

[Monviech (Cedrik)]

You have to packet capture the SDP (Session Description Protocol) package and analyze it in Wireshark. There is an exchange of sockets (ip+port) inside, that the following RTP multimedia packets will use.

With the sockets, you can see where the RTP stream is sent. Then you can e.g. know if it is a STUN issue, or a Firewall/Routing issue.