The Cluster Service (ClusSvc) supports the Failover Clustering feature in nextrefserver_7 that controls server cluster operations and manages the cluster database. A cluster is a collection of independent computers that work together to provide load-balancing and failover support. Applications that can run on a cluster, such as Microsoft Exchange Server and Microsoft SQL Server, use the cluster to present a single virtual computer to users.

The cluster software spreads data and computation tasks among the nodes of the cluster. When a node fails, other nodes provide the services and data that were formerly provided by the missing node. When a node is added or repaired, the cluster software assigns some data and computation tasks to that node.

There are two types of cluster solutions for the Windows operating systems that support different application styles: server clusters and Network Load Balancing (NLB) clusters. Server clusters provide a highly available environment for applications that must run reliably for long periods of time (such as databases or file servers), and they provide failover support with tightly integrated cluster management. NLB clusters provide a highly available and highly scalable environment for other types of applications such as public-facing Web servers, and balance the client requests among a set of identical servers.

The Cluster Service is not installed or enabled by default. If the Cluster Service stops after it is installed, clusters are unavailable.

The Cluster Service it an optional feature on a Server Core installation of Windows Server 2008 R2 in addition to the Standard, Enterprise, and Datacenter editions of Windows Server 2008 and Windows Server 2008 R2.

The following table identifies the application protocol, network protocol, and ports that are used by the Cluster Service:

Application protocol	Network protocol	Ports
Cluster Services	UDP	3343
RPC	TCP	135
Cluster administrator	UDP	137
Randomly allocated high UDP ports	UDP	Random port number between 1024 and 65535