refer:http://technet.microsoft.com/en-us/library/cc772897(WS.10).aspx
SPNs are unique identifiers for services running on servers. Each service that uses Kerberos authentication needs to have an SPN set for it so that clients can identify the service on the network. It is registered in Active Directory under a user account as an attribute calledService-Principal-Name. The SPN is assigned to the account under which the service the SPN identifies is running. Any service can look up the SPN for another service. When a service wants to authenticate to another service, it uses that service’s SPN to differentiate it from other services running on that computer.
In general, only one SPN should be set for each service. Multiple SPNs can cause clients to connect to the wrong system or the ticket may be encrypted with the wrong key.
To add an SPN
Type the following at a command prompt:
setspn -A ServiceClass / Host : Port AccountName
To delete an SPN
Type the following at a command prompt:
setspn -D ServiceClass / Host : Port AccountName
To view the SPNs that are registered for an account
Type the following at a command prompt:
setspn -L AccountName
To reset the default SPN registrations for the host names for an account
Type the following at a command prompt:
setspn -R AccountName
The following section describes the parameters for the Setspn.exe tool:
For more information about using Setspn.exe to manipulate service principal names for accounts, see Setspn.exe: Manipulate Service Principal Names for Accounts on the Microsoft Web site (http://go.microsoft.com/fwlink/?LinkId=43030).