Load Balancing PPTP with WLBS (203597)

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Two network interface cards (NICs) must be used on each Windows NT Load Balancing Service (WLBS) host for this deployment. One NIC must be set to respond to the WLBS virtual IP address, while the other is set to respond to the dedicated IP address unique to each system. Because of a current limitation of VPN, these two addresses must be in different Class C address spaces.

For additional information about how to configure WLBS using multiple NICs, please see the following article in the Microsoft Knowledge Base:
To use WLBS to provide simple failover:

Do not create any port rules. The host with the highest host priority (that is, "1") set in the WLBS Setup screen will handle all incoming connections by default. Upon node failure, all connections will then be handled by the node with the second highest host priority (that is, "2").

To use WLBS to provide load balancing between PPTP servers:

Set one port rule on all cluster hosts. The port rule should be for port range 0 to 65,535 (that is, all ports), with Single Affinity set. This is the default port rule for WLBS.

For additional information about how to configure WLBS port rules, please see the following article in the Microsoft Knowledge Base:
NOTE: Client sessions handled by a particular cluster host will break if the host becomes unavailable. Clients will then be prompted to log on again, with their new session then being handled by the appropriate remaining host.