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A Service Principle Name (SPN) is the name by which a client uniquely identifies an instance of a service. By default your IIS machine has SPNs for its hostname, such as myServer, and its Fully Qualified Domain Name (FQDN), such as myServer.branch.example.com.
If the proxy machine is accessed by a name other than either of these, such as myServer.example.com, otherName.company.com, or its IP address, then Active Directory authentication will not work. Your choices are:
HOST/ service class for the additional names.
SPNs can be viewed and changed with the setspn.exe tool, which
Microsoft provides as part of the operating system. More information is
available at https://support.microsoft.com/en-us/kb/929650