SIP TRUNK - no audio

[freihd]

I have a sip trunk configured with a sip provider in IP Office v2 R11.1 behind a Meraki firewall

No signal issues for incoming and outgoing calls, but no audio in both directions when answering call, and system status shows 100% packet loss with media IP even though there is a ping from IPO

I set and run a STUN address for Google in the LAN1 network topology which provides the full cone NAT & public, and fixes the audio issue for only a few hours

Firewall engineer advised me that the Meraki doesnt do sip alg inspection.
and I should use either :
Using the STUN server,
Is there a free STUN server that runs permanently without any restrictions or does it require a subscription?

Or

configure IPO to correctly send the public address in its header, how is it done?

Any advice appreciated.

[thiel2]

On the SIP Line > Transport tab: Use Network Topology info > LAN1 (or 2)

In System > LAN1 (or 2) > Network Topology tab: CLEAR the field for IP Office STUN Server, set Firewall Type to Unknown, Binding Refresh Time to 60, Public IP Address to your Public IP, SIP Registar Public Ports USP & TCP to 5060

Now the IPO will send SIP messages that include the Public IP so that the SIP Provider will know where to return traffic