I’ve been facing a weird issue with my UCM 6510 which is preventing me from making calls from fixed remote extensions.
We have +80 extensions, most are locals and some remotes. Local extensions works fine but remote extensions different than GS Wave or Zoiper can not make calls. They can get inbound calls just fine but they can not make outbound.
The UCM is behing a Fortigate with SIP ALG disabled, I also tried moving it outside the firewall and the issue remains.
The following packet sniffer shows the issue clearly when calling from the ATA or GXP1625:
If you place the call from GS Wave, connected to the same natted LAN it goes without any issue at all:
I am out of ideas right now, it was working fine until suddendly it stopped working. I’ve played with many differents NAT types (STUN, uPnP, Keep-Alive) with no success.