Knowledge Base

Local NetBIOS Name Query Broadcast Not Forwarded by Router

Article ID: 150881

Article Last Modified on 2/21/2007

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

This article was previously published under Q150881

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:

136403Description 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: kbinfo kbnetwork KB150881