Prerequisites for Kerberos Authentication

If you're using Kerberos to authentication captive portal users, keep the following in mind.

Hostname character limit

If you're using Kerberos authentication, the managed device's host name must be less than 15 characters (it's a NetBIOS limitation set by Windows); otherwise, captive portal authentication fails. You set the managed device host name when you set up the device. For more information, see an article like this one on the Microsoft documentation site: Naming conventions in Active Directory for computers, domains, sites, and OUs.

DNS response character limit

DNS must return a response of 64KB or less to the hostname; otherwise, testing the connection the AD connection fails. This limit applies in both directions and is discussed in RFC 6891 section-6.2.5.