Microsoft KB Archive/232997

= Convergence in Windows NT Load Balancing Service =

Article ID: 232997

Article Last Modified on 11/1/2006

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APPLIES TO


 * Microsoft Windows NT Server 4.0 Enterprise Edition
 * Microsoft Windows NT Load Balancing Service

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This article was previously published under Q232997



SUMMARY
Each server in a Windows NT Load Balancing Service (WLBS) cluster receives all inbound requests to the Virtual IP Address (VIP). Convergence is the process in which the servers (through a proprietary hashing algorithm) agree in advance which server handles a given request. The decision is made based on the packet's source IP address and possibly TCP or UDP port number (if Affinity is not used).



MORE INFORMATION
WLBS balances load in a statistical manner; all of the client IP:port space is mapped to the servers as a consequence of the convergence process. Each server is assigned parts of this space in order to achieve load distribution.

The convergence process is started when servers are added to or removed from a cluster. Cluster integrity is monitored by the periodic exchange of heartbeats between cluster members. When a member misses a user-defined number of heartbeats from a server, it initiates the convergence process to form a new cluster. When a new server is added to the cluster, the existing servers detect the heartbeat from the new server and the convergence process is initiated.

The convergence process takes approximately three seconds, and cluster operations continue during this time. Convergence is complete when all present hosts exchange consistent information and a sufficient number of status messages are exchanged.

