The load balancing service does not detect program or service problems in Windows 2000, in Windows NT, in Windows Server 2003

Windows NT Load Balancing Service (WLBS), Windows 2000 Network Load Balancing (NLB), and Windows Server 2003 NLB do not provide failover at the service, program, or port level because both WLBS and NLB are TCP/IP load balancers and are not designed to detect when a program or service is not working correctly.

For example, if Microsoft Internet Information Server (IIS) does not work on a cluster node and WLBS or NLB is still running on the node, port 80 or Web packets continue to be routed to the WLBS or NLB node. You may receive program error messages on the host because the program is not running there, but the service does not failover to the other hosts because of WLBS and NLB design limitations.

When a program does not work, the cause is usually more complex than the service not responding on a port. WLBS and NLB rely on external monitoring tools for decision-making processes and remote control if a host needs to be removed from the cluster.

Some independent monitoring tools can control cluster membership based on the availability of content. You can use these tools to monitor programs and services and send a command to stop WLBS or NLB on the node with the unsuccessful program or service. The program or service is removed from the WLBS or NLB cluster and does not receive any further traffic until it rejoins the cluster.

Examples of monitoring tools

• Httpmon.exe: You can use Httpmon.exe on a Web server to monitor the status of the Web service. Httpmon.exe is included in the Microsoft Internet Information Server Resource Kit, or you can download it from the following Microsoft Web site:
  ftp://ftp.microsoft.com/bussys/utilities/httpmon (ftp://ftp.microsoft.com/bussys/utilities/httpmon)
• Exception Monitor: For additional information about this tool, including its download location, please contact Microsoft Product Support Services. For a complete list of Microsoft Product Support Services phone numbers and information about support costs, visit the following Microsoft Web site:
  http://support.microsoft.com/default.aspx?scid=fh;[LN];CNTACTMS (http://support.microsoft.com/default.aspx?scid=fh;%5Bln%5D;cntactms)

Third-party monitoring tools

• SiteScope by Mercury Interactive Corporation (http://www.mercury.com (http://www.mercury.com) )
• AppManager by NetIQ (http://www.netiq.com (http://www.netiq.com) )
• WhatsUp Gold by Ipswitch (http://www.ipswitch.com (http://www.ipswitch.com) )

Microsoft provides third-party contact information to help you find technical support. This contact information may change without notice. Microsoft does not guarantee the accuracy of this third-party contact information.
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