we have axon setup on a firewall at a corp location the firewall has a static IP and forwards all request to axon server with IVR and IMS (using port 606) the following is what the user gets on there router when placing someone on hold.
this is a d-link dsl router
Blocked incoming ICMP error message (ICMP type 3) from X.X.X.237 (Corp static ip on firewall) to X.X.X.X (static IP on users router) as there is no UDP session active between X.X.X.X:5060 (users Static IP on router) and 10.30.32.45:606 (private ip on corp server behind firewall.
X.X.X.X are public static IPs