My Aastra 6730i is behind NAT. Aastra documentation says configuring the Rport parameter is recommened for clients behind a Network Address Translation (NAT) or firewall. Connections to VOIP.MS and Callwithus can register with Rport enabled.
“Rport” in RFC 3581, allows a client to request that the server send the response back to the source IP address and the port from which the request came.
How can I trouble shoot this registration failure?