The "NLB troubleshooting overview for Windows Server 2003" article is available

This article lists common scenarios that have solutions that are described in the NLB troubleshooting overview for Windows Server 2003 document. To download this document, visit the following Microsoft Web site:

Network Load Balancing (NLB) is a clustering technology that is included in Microsoft Windows Server 2003. NLB uses a distributed algorithm to balance network traffic across a number of hosts. Network load balancing helps enhance the scalability and the availability of Internet Protocol-based services, such as virtual private networking, streaming media, Terminal Services, the Proxy service, and more. Network load balancing also provides high levels of host availability by detecting host failures and by automatically redistributing traffic to hosts that are still in operation.

When you use NLB, you may find that you have to troubleshoot issues to identify the cause before you can resolve the issue. The NLB troubleshooting overview for Windows Server 2003 document provides guidelines and information about the following scenarios.

Problems occur when you perform a configuration operation or a management operation

A configuration operation or a management operation is not successful. For example, you might experience this problem when you try to bind NLB, add a port rule, or stop a cluster.

No connectivity to virtual Internet protocols

You have set up a cluster on one or more computers, but the cluster is unresponsive. Requests from clients that are addressed to the virtual IP addresses or to the cluster IP address are not answered by the cluster. Or, requests that are addressed to the virtual IP addresses or to the cluster IP address and that are sent across one or more routers are not answered by the cluster. This issue occurs with requests from clients on the same local area network (LAN).

Periodic connectivity to virtual IP addresses

Client computers experience periodic connection problems with the virtual IP addresses. Any client computer may experience periodic connectivity problems. The problem may not be caused by the client computers.

Some client computers can connect to virtual IP addresses but other client computers cannot

Specific client computers experience connection problems with the cluster. The problem may be specific to the location of the client computers relative to the cluster.

Cannot connect to or from a dedicated IP address

Network traffic experiences connectivity problems. This issue occurs with network traffic that is addressed to a dedicated IP address or that originates from the dedicated IP address.

Irregular load balancing or poor performance occurs

All client computers can connect to the cluster, but the network load is not balanced evenly among the nodes in the cluster. Additionally, there are other performance problems, such as slow response or low throughput.

Problems that are related to client authentication occur

Client computers cannot be authenticated to the virtual service through a Secure Sockets Layer (SSL) connection or through a Kerberos connection.

Problems that are related to session persistence occur

A session experiences problems because the application or the protocol that the session uses requires some form of session persistence that is not being preserved.

Problems that are related to convergence occur

You may experience problems where cluster nodes converge into separate clusters or where one or more nodes remain in the converging state.

Problems that are specific to the application or the protocol that you are using occur

You may experience a problem that is specific to a particular application or protocol. For example, you may experience problems when you try to access read-only file shares or when you use SSL.