Local NetBIOS Name Query Broadcast Not Forwarded by Router

This article was previously published under Q150881
This article has been archived. It is offered "as is" and will no longer be updated.
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:

136403Description of UDP Ports

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.

Article ID: 150881 - Last Review: 12/04/2015 14:41:08 - Revision: 3.2

Microsoft Windows 2000 Server, Microsoft Windows 2000 Advanced Server, Microsoft Windows 2000 Professional Edition, Microsoft Windows NT Workstation 3.5, Microsoft Windows NT Workstation 3.51, Microsoft Windows NT Server 3.5, Microsoft Windows NT Server 3.51

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