Issue using multisite interconnect

Hi, I have a quite complex situation than shows strange behaviours we are not understanding.

Here is the scheme of the network:

We have:

- a headquarter (extensions 2xx) with a single phone registered both with a local extension and with a branch office extension (using a second sip line, let's call SIP2) to receive calls from branch trunk directly under certain circumstances, connected to the branch subnet via a VPN

- a branch office (extensions 1xx), connected to the headquarter subnet via a VPN

Both are Yeastar S20 and both are behind a Fortigate (SIP ALG disabled). Both have the Linkus configured and both are accessible via Linkus Mobile through the WAN.

Now, this is the situation:

  • both local networks work fine
  • headquarter can call branch extensions without issues
  • branch office cannot call headquarter extensions, the call drops and it's not registered on the CDR. The headquarter IP is not blocked by autodefense, there are some system logs but are not clear
  • if an external call is passed from branch office to the phone in the headquarter subnet via the local number (SIP2), the communication is one way (I can hear the headquarter extension but my voice cannot be heard)

Every device shows no connection errors (there is the green tick on both branch and headquarter and the SIP2 line is correctly registered).

In order to make the external app working we specified in the NAT settings the external (WAN) public IP. i suspect there is some conflict in the NAT settings, due to the global configuration. I am also sure that initially the multisite calls worked.

Any ideas?

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