Article ID: 216471 - View products that this article applies to.
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When connecting from a multihomed computer to another multihomed computer, where both computers have two separate networks in common, the optimal route may not be chosen. Additionally, the outbound path may differ from the inbound path.
When a call is placed using NetBIOS over TCP/IP (NetBT), for example, "net use \\mycomputer\myshare" on a multihomed computer, the outbound calls are placed on both interfaces. Each interface should query WINS and then choose the best target IP address for the called computer. Two improvements are now available in this algorithm.
The algorithm used in determining the best target IP address has been changed to include two improvements, available in this new version of Netbt.sys.
Previously, a match was chosen in the order below. For additional information, see the following article or articles in the Microsoft Knowledge Base:
(http://support.microsoft.com/kb/161425/EN-US/ )WinNT 4.0 SP2 Multihomed Computer Connection Enhancement
--------- ------------------| Router1 |---------------- | Net1SubnetA --------- Net1SubnetB | | NIC1 NIC1 | ----------- ----------- | Computer1 | | Computer2 | ----------- ----------- | NIC2 NIC2 | | Net2SubnetA --------- Net2SubnetB | ------------------| Router2 |---------------- ---------
In the scenario shown above, if a NetBT call is placed from Computer1 to Computer2, a call will go out each interface (NIC1 and NIC2). NIC1 will query WINS, and, assuming that WINS returns an IP address for each interface on Computer2, it will choose the IP address associated with Computer2NIC1 as the best IP address to connect to, because both share the same network ID (even though the subnet ID is different). This IP address will be cached for NIC1 in the per-interface name cache. NIC2 will also query WINS, and assuming that WINS returns an IP address for each interface on Computer2, it will choose the IP address associated with NIC2, and this IP address will be cached in the per-interface name cache for NIC2.
Calls are placed on both interfaces (and the WINS server for each interface is queried separately) because the computer cannot assume that the target computer is reachable on both networks in all cases.
This enhancement can improve the path used for connections from a multihomed computer to another multihomed computer, when both have two networks in common. It does not offer any changes for other scenarios.
To resolve this problem, obtain the latest service pack for Windows NT 4.0 or the individual software update. For information on obtaining the latest service pack, please go to:
Microsoft has confirmed that this is a problem in Windows NT 4.0. This problem was first corrected in Windows NT version 4.0 Service Pack 5.