Trying to get an Adtran 3200 and Cisco 2811 to play nice VPN together. Getting "Received Vendor ID not registered with IKE" in debug output during IKE negotiation on Adtran. The Adtran VPN config works successfully with another Adtran unit, so thinking my Cisco config is a tad off or a compatibility issue. Insight welcome.

Response from Adtran was "Received Vendor ID not registered with IKE usually indicates an option or feature the remote vendor is using that the local router does not support. In nearly every instance, this is not a critical error that would keep the VPN from negotiating."

They were correct. Turned out the problem was an incorrect IP address on the public interface of the initiating router resulting in messages from the remote router never making their way back to the initiating router. Yet, despite the incorrect address, the router has functioned as an Internet gateway for over six years.