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Understanding virtual clusters

Updated: January 21, 2005

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

Understanding virtual clusters

It is becoming increasingly common to host multiple applications or Web sites on a single Network Load Balancing (NLB) cluster. When doing so, you may require independent load balancing policies, defined through port rules, applied to each of these applications or sites.

In the Windows Server 2003 family of products you can configure multiple Network Load Balancing clusters on the same network adapter and then apply specific port rules to each of those IP addresses. These are referred to as "virtual clusters."

You can also use virtual clusters to block network traffic to a specific host for a specific application, without affecting traffic for other applications on that host. You can also use virtual clusters to limit each application, Web site, or virtual IP address to a specific subset of computers within your primary cluster. See the diagram below for an example of this use of virtual clusters.

A four host cluster with two virtual clusters

This diagram depicts a four host Network Load Balancing cluster. Through the use of virtual clusters and IP address-specific load weight, Network Load Balancing directs network traffic as follows:

  • Users accessing Web Site A (IP address nnn.nnn.nnn.1) are directed to any of the four hosts

  • Users accessing Web site B (IP address nnn.nnn.nnn.2), which is a virtual cluster, are directed to hosts 1 and 2

  • Users accessing Web site C (IP address nnn.nnn.nnn.3), which is a virtual cluster, are directed to hosts 3 and 4

For more information on how this is configured, see Virtual clusters and Create a new port rule.

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