Q. Which network is used for intra-cluster communication in Windows Server 2008?

A. Two types of networks operate within a Server 2008 failover cluster. One is the network that clients use to reach services hosted on the cluster. The other network is used only within the cluster and is controlled via the network properties within the cluster, as shown here. Note that you can prohibit a cluster from using a network at all.

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Every network that's enabled for use by the cluster has a heartbeat going across it. One of the networks is picked for intra-cluster communications, the same network that's used for Cluster Shared Volume data and the Live Migration memory copy in Windows Server 2008 R2 (with some additional configuration available for Live Migration). By default, networks that are for internal use only with no client communication are used ahead of networks that host client communications.

In Server 2008 R2, you'll be able to set metrics for each network, similar to routes with TCP/IP, and the network with the lowest metric is used for the intra-cluster communication. Networks enabled for client communication (public networks) start at a metric value of 10000 and cluster-only communication networks start at 1000. Both can be adjusted manually.

The following PowerShell commands and output will function in Server 2008 R2. The AutoMetric value in the table shows whether the metric was set by default (a value of TRUE) or if the user configured a value (FALSE).

PS C:\Users\savadmin> Add-Module FailoverClusters
PS C:\Users\savadmin> Get-ClusterNetwork | ft Name, Metric, AutoMetric

Name Metric AutoMetric
---- ------ ----------
Cluster Network 1 10000 TRUE
Cluster Network 2 1000 TRUE

In this example, Cluster Network 1 is enabled for client communication, so it has a value of 10000, while Cluster Network 2 is internal only, so it has a value of 1000.

The Network Fault Tolerant (NetFT) driver is responsible for picking the network and for selecting an alternate network if the current intra-cluster network becomes unavailable.

See also:
How do I create a failover cluster in Windows Server 2008?
Is a Windows Server 2003 and Windows Server 2008 mixed-cluster possible?
How can I add disk resources to a Windows Server 2008 cluster from the command line?
How do cluster shared volumes work in Windows Server 2008 R2?

How to Manage Failover Clusters in Windows Server 2008
Configure Windows Server 2008 Failover Clustering from the Command Line

Check out hundreds more useful Q&As like this in John Savill's FAQ for Windows. Also, watch instructional videos made by John at ITTV.net.
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