WEB servers with Microsoft NLB

WEB servers with 
Microsoft Network Load Balancing

NLB is wonderful free component for load balancing available on all Windows server 2K and later. NLB distribute load between two servers or more and server’s farm can be expanded at any point of time without service interruption.

Technically, NLB create a virtual IP that represent all servers behind the NLB, where in which it distributes incoming connections between servers.

Our example will be WEB servers that are identical from WEB/application prospective, and both are connected to the same pool of data into database server, actual WEB can be accessed by VIP using NLB. 

Implementation steps:

• Enable NLB feature from Server Manager

• Open NLB manager from Server Manager and create new cluster 

• Choose the interface that you wish to add it to NLB farm. (the virtual IP need to be configured alongside with the actual IP address in this interface)

• Chose the priority and default status

• Configure the NLB IP address.

• Now you can add as much host as you wish to the same NLB farm by following same steps.

An important parameter is the cluster operation mode options, which are as follow:

-     

            Unicast:
if this option is your choice, another network card has to be used for the application as NLB reserve this interface for load balancing traffic only. Technically, in unicast mode, NLB replaces the actual MAC address of each server in the cluster to a common NLB MAC address. When all the server in the cluster have the same MAC address, all packets forwarded to that address are sent to all members of the cluster

-          Multicast:

In multicast mode one NIC can handle the application (WEB in our example) & NLB traffic simultaneously. This choice instructs the cluster members to respond to ARPs for their virtual address using a multicast MAC address. 

Depends on the operation mode, some configurations should be considered at L2 level, have a look on the following link: http://www.cisco.com/en/US/products/hw/switches/ps708/products_configuration_example09186a0080a07203.shtml

In conclusion, NLB is a very simple cost-effective way to distribute traffic between several servers that are accessing same database and identically same application. In the same time NLB provide kind of service redundancy in case of a hardware failure, maintenance window, … etc