Local NetBIOS Name Query Broadcast Not Forwarded by Router

ID: Q150881

The information in this article applies to:

SUMMARY

Routers do not normally forward b-node broadcasts. NetBIOS over TCP/IP uses b-node broadcasts for name resolution and registration on your local LAN segment. If you want your router to forward b-node broadcasts, you must enable UDP ports 137 and 138.


MORE INFORMATION

A b-node broadcast is a UDP datagram. If these broadcast datagrams pass through your router, it will greatly increase traffic on your internetwork and decrease performance. Not every router can forward b-node broadcasts, and usually this function is disabled on routers that can forward the broadcasts.

By enabling UDP ports 137 and 138 on your router, a name query broadcast with the destination NetBIOS name can be forwarded. RFC 1002 defines UDP ports 137 and 138 as follows: 


Port Number       Key name
137/UDP           #NAME_SERVICE_UDP_PORT

138/UDP           #DGM_SRVC_UDP_PORT


For additional information, please see the following article in the Microsoft Knowledge Base:

Q136403Description of UDP Ports

NOTE: Forwarding UDP broadcasts of ports 137 and 138 may cause browsing problems in some environments. "Inter-Networking with Microsoft TCP/IP Using Microsoft Windows NT, Participant's Workbook," P/N 4271B, pages 144-147. 


Keywords          : kbnetwork nttcp NTSrvWkst 
Version           : WinNT:3.50,3.51
Platform          : winnt 
Issue type        : kbinfo

Last Reviewed: February 18, 1999