Systems Engineering and RDBMS

Archive for the ‘Load Balancing’ Category

SQL Server 2005 P2P Replication

Posted by decipherinfosys on August 20, 2008

We had covered P2P replication before in one of our posts over here.  Here is a link to the technet post which talks about how MSFT has implemented it in house:

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Microsoft Load Balancing in a Switched Environment

Posted by decipherinfosys on January 30, 2007

Here is some information on how to configure two or more Windows servers running Microsoft Load Balancing Services (WLBS) in a switched environment.

For WLBS to work properly, every packet directed to the virtual IP (VIP) address must be able to reach all WLBS hosts in the cluster. The hosts then decide which packets to accept.

When the cluster network adapter of each WLBS host is connected to a port on a Layer 2 switch instead of a hub, the switch attempts to learn the MAC (hardware) address of the computer connected to each port so that it can associate a port to a MAC address. Ethernet switches send frames to a MAC address by referencing the port associated with that address.

If a switch associates the cluster’s virtual MAC address to a port, WLBS will be unable to correctly load balance the traffic. Below are some steps to prevent a switch from associating the cluster’s virtual MAC address with a port:

1. Use Unicast Mode – This will ensure that requests to the cluster will be routed through the cluster’s network adapter only, and the appropriate host will reply through its dedicated network adapter, which connects to a dedicated port on the switch.  Unicast Mode is configured within the Properties of Network Load Balancing.

Note: Unicast mode requires multiple network interface cards (NICs).

Note: For best results, do notconfigure a default gateway on the NIC assigned to the WLBS cluster.

2. Mask the WLBS Cluster MAC Address – When you use Unicast Mode, make sure the MaskSourceMAC registry value is set to its default value of 1. This forces the cluster to use a virtual MAC address when sending packets through the switch. The switch then maps this virtual MAC address to a port, but sends traffic to the real cluster MAC address to all ports on the switch.

If a switch cannot associate a MAC address to a port it will send the frames to all of its ports, which results in ‘flooding’.

The MaskSourceMAC registry key is located at:


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