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To learn more about conf iguring the Availability service for NLB, consult the following TechNet article: http://technet.microsoft.com/en-us/library/aa997237.aspx.

DNS round-robin is a high availability strategy that is used with Edge Transport servers. DNS round-robin is relatively straightforward. Multiple DNS entries with the

same host name are configured for a DNS zone. Each DNS entry is associated with a different IP address. When a client queries the DNS server for the IP address of the target host, the DNS server responds with a different IP address in a round-robin manner. Figure 13-2 displays four different entries for the host name EdgeTransport. tailspintoys.internal, which the DNS server will pass on to clients in a round-robin fashion.

Figure 13-2

The drawback of using DNS round-robin is that it remains unaware of server failure. For example, Contoso has two identically configured Edge Transport servers. An administrator has configured DNS round-robin for the host name mailhost.contoso.com with the IP addresses 10.10.10.10 and 10.10.10.11. The server associated with IP address 10.10.10.11 fails and becomes nonresponsive. The Contoso DNS server will remain unaware of this failure and will still provide the failed server s IP address to 50 percent of querying clients. In the event that a server using round-robin fails, it is necessary to manually delete the host record associated with that server s IP address from the DNS zone database until the server is completely restored.

To f ind out more about conf iguring round-robin on Windows DNS servers, consult the following TechNet article: http://technet2.microsoft.com/windowsserver/f/ en/library/e0f49958-f290-49fc-adb471ed8deefd621033.mspx.

Once set up, clustered mailbox servers are managed using a set of Exchange Management Shell cmdlets. There are several interrelated cmdlet sets that will be covered over

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the course of the next few pages. The first set of cmdlets, listed below, are used to manage clustered mailbox servers at the server level:

Start-ClusteredMailboxServer This cmdlet is used to start a Microsoft Exchange Server 2007 clustered mailbox server after it has shut down, either through the use of the Stop-ClusteredMailboxServer cmdlet or because of a failure. This cmdlet can be used only if the cluster exists and the data for the clustered mailbox server is available and operational. Stop-ClusteredMailboxServer This cmdlet allows an administrator to shut down clustered mailbox server operations without triggering the failover process. A restart of the server will not bring Exchange back online. The only way to activate a server after issuing this command is to use the Start-ClusteredMailboxServer command. Get-ClusteredMailboxServerStatus This cmdlet is used to get basic operational information about a clustered mailbox server. This includes a list of operational computers in the cluster, a list of offline resources associated with the server, and its current state. Running this command also will return which of the six possible status states the clustered mailbox server is currently in:

Online The server is functioning normally. Partially online One or more server resources are offline. Online pending One or more server resources are coming offline. Offline The server is completely offline. Offline pending One or more server resources are in the process of going offline. Failed The clustered mailbox server has failed.

Move-ClusteredMailboxServer This cmdlet is used to gracefully transfer a Microsoft Exchange Server 2007 clustered mailbox server to an available passive node. This cmdlet is used to initiate a planned outage and is not used in the event that the active node fails. When an active node fails, automatic failover occurs. The Move-ClusteredMailboxServer cmdlet is covered in more detail below.

The Move-ClusteredMailboxServer cmdlet can be used only if a clustered mailbox server is currently not running on the target server and the target server is a member of the same cluster. If any data would be lost by running the Move-ClusteredMailboxServer cmdlet, the move will be prevented, leaving the clustered mailbox server on the