This article was previously published under Q150881
Routers do not normally forward b-node broadcasts. NetBIOS over TCP/IP usesb-node broadcasts for name resolution and registration on your local LANsegment. If you want your router to forward b-node broadcasts, you mustenable UDP ports 137 and 138.
A b-node broadcast is a UDP datagram. If these broadcast datagrams passthrough your router, it will greatly increase traffic on your internetworkand decrease performance. Not every router can forward b-node broadcasts,and usually this function is disabled on routers that can forward thebroadcasts.
By enabling UDP ports 137 and 138 on your router, a name query broadcastwith the destination NetBIOS name can be forwarded. RFC 1002 defines UDPports 137 and 138 as follows:
Port Number Key name137/UDP #NAME_SERVICE_UDP_PORT138/UDP #DGM_SRVC_UDP_PORT
For additional information, please see the following article in theMicrosoft Knowledge Base:
NOTE: Forwarding UDP broadcasts of ports 137 and 138 may cause browsingproblems in some environments."Inter-Networking with Microsoft TCP/IP Using Microsoft Windows NT,Participant's Workbook," P/N 4271B, pages 144-147.