If you do a tell router quit command to shut down the router (to do things like a convert of a mail file) about one in every 10 times the server will hang.
It appears that the server is up, and if you have a console open it accepts commands it’s just that ALL NETWORK ACCESS on all ports is suspended. You need to restart the server for the problem to go away. And by restart I mean “nsd /kill”. A simple quit does not work.
This is easy to reproduce, and needs to be fixed ASAP.