MS Teams Direct Routing - Internal call transfer failure

Sims_Krastev 

I can provide later the syslog, just do not want to publish all our IP addresses etc. on forum

Currently if I set our SBC to handle all REFERs locally it simply takes REFER from Teams, SBC accept and sends new Invite to Teams. Teams takes that and create new SIP call where as source IP for media presents public IP of our SBC. This call will come as new SIP call to our SBC and SBC simply tries to connect media between private IP and public IP of our WAN interface. And this is failing basically because SBC sends the traffic to its own public IP through WAN interface out of the SBC. There is then firewall which is dropping that from obvious reason.