Client Connections to Multihomed Server Not Load Balanced

• Microsoft Windows NT Workstation version 4.0
• Microsoft Windows NT Server version 4.0

SYMPTOMS

You have a number of clients that are using TCP/IP to connect to a multihomed server that has no IP addresses on the same subnet as the client and the clients are always connecting to the same address on the server, even though the paths to more than one of the addresses are equal.

CAUSE

When the client’s NetBT layer attempts to resolve the NetBIOS name to an IP address, it queries the WINS server for the address of a multihomed server and receives a list of addresses that are always in the same order. NetBT then takes that list and sorts it, putting addresses on the same subnet (if any) at the top, followed by addresses in the same network class, and then any remaining addresses. It then starts at the top of this list and pings the first address to make sure it is valid. If it does not get a reply, it will go on to the next address; if it does get a reply, it will use the first address.

The problem is that, within these three categories, the order of addresses is left unchanged from the list provided by the WINS server. This means that, as long as the first address in the list is online, it will be the one that is always used by every client, which does not provide for load balancing.

For additional information, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q161425
   TITLE     : WinNT 4.0 SP2 Multi-Homed Computer Connection Enhancement

RESOLUTION

To resolve this problem, obtain the following fix or wait for the next Windows NT service pack.

This fix should have the following time stamp:

   03/18/98  11:34a               120,176 Netbt.sys (Intel)
   03/18/98  11:36a               220,304 Netbt.sys (Alpha)

STATUS

Microsoft has confirmed this to be a problem in Windows NT version 4.0. A supported fix is now available, but has not been fully regression tested and should be applied only to systems experiencing this specific problem. Unless you are severely impacted by this specific problem, Microsoft recommends that you wait for the next Service Pack that contains this fix. Contact Microsoft Technical Support for more information.

Keywords          : kbbug4.00 kbfix4.00 NTSrvWkst
Version           : WinNT;4.0
Issue type        : kbbug
Solution Type     : kbfix