Microsoft KB Archive/139985

= WINS Client Fails to Reach a Multihomed Server =

Article ID: 139985

Article Last Modified on 12/5/2003

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APPLIES TO


 * Microsoft Windows NT Server 3.5
 * Microsoft Windows NT Server 3.51
 * Microsoft Windows for Workgroups 3.11
 * Microsoft Windows 95

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This article was previously published under Q139985





SYMPTOMS
When the Windows NT Windows Internet Name Service (WINS) resolves a Multi- homed name, it gives an unreachable address to the client.

To reach a multi-homed server, the client sends a request to WINS and gets back a list of IP addresses. From this list, the client chooses an address which is on the same subnet as itself. In some cases (depending on the netid value), the client incorrectly picks an address that is not on its subnet (not local) and depending on the network topology, it may then not be able to reach the multi-homed server.



CAUSE
When a WINS client tries to reach a multi-homed server, the following occurs:  The client requests the WINS server, and gets back a list of IP addresses (for the multi-homed server) From this list, the client tries to choose a "local" IP address (on the same subnet as itself), and builds a sublist containing only those "local" addresses

 If this sublist of "local IP addresses" is not empty (maybe multiple server addresses on the same subnet), the client randomly picks an IP address from this sublist. If this sublist is empty (no address on the same subnet), the client randomly picks an IP address from the original list.  Using this chosen IP address as the destination, the client then tries to establish the TCP connection with the multi-homed server.</li></ol>

The problem is in step 2:

Depending on the netid values, the client may build an incorrect sublist of local addresses by including addresses which are NOT on the same subnet. It then randomly picks an IP address from this sublist. As a result, the chosen IP address may not be on the same subnet.

The problem appears for all the values in which "1" bits in the client's netid appear at the same position in the server netids. For example, suppose the client's IP address is 157.9.5.5 and the subnet mask is 255.255.0.0. The client's netid is 157.9 which is 10011101.00001001 in binary. In this case, all IP addresses with netids in the form 1XX111X1.XXXX1XX1 will be considered as "local". This is the case in particular for addresses like 157.11.x.y, 157.13.x.y, 157.15.x.y....

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RESOLUTION
This problem has been corrected in the latest Service Pack for Windows NT version 3.51.

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STATUS
Microsoft has confirmed this to be a problem in Windows NT versions 3.5 and 3.51, Windows for Workgroups version 3.11, and Windows 95. This problem was corrected in the latest Windows NT 3.51 U.S. Service Pack. For information on obtaining the Service Pack, query on the following word in the Microsoft Knowledge Base (without the spaces):

SERVPACK

Additional query words: Multihomed 3.50 3.51

Keywords: KB139985

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