We have a problem where a server will seem to drop off the network. It will still answer to a ping, but not to a NetBIOS session request. Upon looking closer with a protocol analyzer, we found that the server was sending a NBT Reset_Connection packet, and thus it appeared that it was off the network. The real problem is that some of the servers experiencing this problem are domain controllers, one of which is the Primary. The only work-around (besides rebooting) is to restart the server service and the computer browser service. We tried different network cards, re-applying service packs, re-installing TCP/IP, and finally installing a whole new system. After putting in two new servers, they have now started the same thing all over again.
Any ideas?