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Local NetBIOS Name Query Broadcast Not Forwarded by Router
Article ID: 150881 - View products that this article applies to.
This article was previously published under Q150881
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.
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:
(http://support.microsoft.com/kb/136403/EN-US/ )Description 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.
Article ID: 150881 - Last Review: February 21, 2007 - Revision: 3.2