Deploying Servers - network load balancing
Configure high availability.
Network Load Balancing
Windows Server 2008 also provides network load balancing (NLB) clustering, in which all incoming connection requests are distributed among the various members of the NLB cluster. In addition, using NLB to provide fault tolerance enables it to provide better performance because all members of the NLB cluster are servicing requests.
An NLB cluster uses a virtual IP address and a virtual media access control (MAC) address for network communication. All NLB nodes use the same virtual IP address and virtual MAC address. When an incoming packet is addressed to the virtual IP address and virtual MAC address, all NLB nodes receive it, but only the appropriate node responds.
In addition, all NLB nodes must have the same data to ensure that all nodes respond identically to requests. To ensure that this is the case, you can synchronize data between nodes or store the data in a common location. The option you select depends on the type of application the NLB cluster is hosting. Because any server in a network load balancing cluster can respond to a client request, the application files and data on all servers must be exactly the same.
Traditional NLB clustering is used to connect to any server in the cluster, such as web and FTP servers. To accomplish this with web servers, you would install and configure identical websites on each NLB member and use a separate backend server (such as a SQL server or SQL failover cluster) that stores and provides data to the front-end servers. This way, when a user makes a change such as to their user account or to place an order, it is written to the SQL server. When the same user connects to the NLB cluster (although the connection may be to a different member within the NLB cluster), the user can still access the same data because it is centrally stored with the SQL server or cluster. You can also use NLB clusters as firewall, proxy, and virtual private network (VPN) services. With Windows Server 2008, NLB can also integrate with terminal services to create a terminal service farm so that users can reconnect back to their existing sessions.
You cannot use both types of clustering-fail-over clusters and network load balancing clusters-on the same servers. In earlier versions of Windows Server, you could perform NLB by using IPv4 only. With Windows Server 2008, you can configure NLB by using IPv6.