What does it mean when I get a server failure when connecting to a router with DNS protocol
"Server failure" is, according to RFC 1035, an error that means that "The name server was unable to process this query due to a problem with the name server."  That error code doesn't provide enough information to indicate what the problem is; it could be that the router is having a problem, or it could be that the router is talking to some other name server and got an equally mysterious "server failure" error from that server.

What's the host name it's trying to look up?