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Local NetBIOS Name Query Broadcast Not Forwarded by Router

This article was previously published under Q150881
SUMMARY
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.
MORE INFORMATION
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.
Properties

Article ID: 150881 - Last Review: 02/21/2007 01:09:11 - 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
  • kbinfo kbnetwork KB150881
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