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Q232997: Convergence in Windows NT Load Balancing Service

Article: Q232997
Product(s): Microsoft Windows NT
Version(s): winnt:1.0,4.0
Operating System(s): 
Keyword(s): kbnetwork
Last Modified: 10-AUG-2001

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The information in this article applies to:

- Microsoft Windows NT Server, Enterprise Edition version 4.0 
- Microsoft Windows NT Load Balancing Service 1.0 
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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.

REFERENCES
==========

For more information about Cluster Server and WLBS, please see the following
Microsoft Knowledge Base article:

  Q232711 How Cluster Integrity is Monitored in WLBS

Additional query words:

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Keywords          : kbnetwork 
Technology        : kbWinNTsearch kbWinNT400search kbWinNTSsearch kbWinNTSEntSearch kbWinNTSEnt400 kbWinNTS400search kbWinNTLBS100 kbWinNTLBSSearch
Version           : winnt:1.0,4.0
Issue type        : kbinfo

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