STUNned Unnecessarily

It is not often that I hesitate to cover a topic in this blog. I have also not been afraid to name names when necessary. However, a most unusual thing happened yesterday and for the first time, I am reluctant to disclose the full effect. It may have happened only to Broadvox, which would be surprising, but our customers on Avaya platforms had unnecessary service disruptions. It seems that the default Avaya IP PBX configuration points to a public STUN server that is completely unaffiliated with Avaya. This unidentified STUN server began doing something different. Why? No one knows. What? No one knows. Because until yesterday, no one cared since it was just some STUN server sitting out on the Internet doing what STUN servers do. Now if you are like me you have two questions. What the heck is a STUN server and why would Avaya point their product towards a server with which they have no relationship.

First: what is a STUN server?

STUN (Simple Traversal of UDP through NATs (Network Address Translation)) is a protocol for assisting devices behind a NAT firewall or router with their packet routing. This protocol enables a device to find out its public IP address and the type of NAT service its sitting behind and operates on TCP and UDP port 3478. The IP address and the type of NAT service is used to set up UDP communication between the client and a VOIP provider to establish a call. Okay, so far so good but STUN also faces a lack of standardized behaviors and controls in NATs which results in a proliferation of devices whose behavior is highly unpredictable, extremely variable, and uncontrollable (as we saw yesterday).

Second: so why would Avaya by default point to a public server over which they have no control?  My research into the subject shows that the IP community is all over the map on whether to use a STUN server, when to use it and its effect on call set up times. If any of you have some insight into this, I would greatly appreciate your comments.

To STUN or not to STUN? That is the question.

We solved the problem by disabling STUN.

Perhaps a better answer on Friday.