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:
Access the machine using either its host name or FQDN.
Register an additional SPN for the proxy machine on the domain
controller. Use the 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