Microsoft KB Archive/224131

= Network Switch with Full-Duplex Incompatible with Half-Duplex Network Interface Cards (NICs) =

Article ID: 224131

Article Last Modified on 11/1/2006

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APPLIES TO


 * Microsoft Windows NT Server 4.0 Standard Edition

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This article was previously published under Q224131



SYMPTOMS
Clients cannot log on to the domain controllers. Additional NetBIOS traffic problems are:
 * Loss of connectivity between servers resulting in servers being unavailable in Server Manager.
 * Trust relationships failing to work and failing to be created.
 * Other connectivity where sessions for two-way are required.

The primary domain controller (PDC) forces a browsing election every 12 minutes and generates the following event:

Event ID: 8003

Description: The master browser has received a server announcement from the Windows NT client that believes that it is the master browser for the domain on transport (NetBT). The master browser is stopping or an election is being forced.

The client computer is located in a different subnet, and UDP 137 and 138 broadcasts are not being forwarded.



CAUSE
This problem occurs when network logon validation is prevented over a network switch.

The network switch prevents the server from authenticating the client. The two-way communication session necessary for logon validation is prevented. The Windows NT client computer that cannot successfully communicate with the Windows NT server acting as the subnet master browser may cause a browser election, which causes the Event ID 8003 error to be registered on the PDC.



RESOLUTION
Network switches and server network interface cards (NICs) have to have the duplex settings matched for NetBIOS communication to function properly. Both need to be either full-duplex or half-duplex, but they cannot be mismatched.

Browser elections resolution: Some OEM FDDI adapters configured for full-duplex might be incompatible with some network switches. When the OEM FDDI cards were replaced with full-duplex cards, the browsing elections went away.



Troubleshooting Steps

 * 1) Removed any unnecessary protocols besides TCP/IP and attempt to log on.
 * 2) Put the client and the server on a passive hub and attempt to log on. This eliminates the network switch from the logon process; if communication resumes, it points to network switch configuration issues.
 * 3) Reset switch, restart the client, and test the connectivity.
 * 4) Ping across the switch by IP address from client to server or server to client. This may work in spite of connectivity issues; ping is broadcast based and not a session controlled three-way communication.
 * 5) Check the switch configuration settings for duplex settings and also check the server's NIC for duplex settings. If the network switch and server NIC are mismatched with one on full-duplex and the other half-duplex, the three-way communication will be prevented and NetBIOS connectivity will fail.
 * 6) Replaced the half-duplex NIC on the server with a full-duplex and test. This may be required to avoid the mismatch if the network switch and/or the server's NIC are not configurable. It is a more dramatic step than reconfiguring devices, but has proven to be a sound solution. Resetting the server NIC to half-duplex will lose communication again.

Additional query words: hub router connectivity bridging

Keywords: kbhardware kbprb KB224131

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