As far as I can tell, the Active Directory Authentication uses LDAP (like most other Softwares do, too) instead of Kerberos.
The difference between LDAP & AD backend is mostly that MS AD uses some different attributes like sAMAccountName for the username, otherwise there should be no noteworthy difference.
You need the LDAP Ports open for authentication to work: 389 (unencrypted) or 636 (TLS encrypted).
Using encrypted LDAP (LDAPS) is recommended, because LDAP transmits the users password unencrypted and without transport encryption (TLS) your credentials could get sniffed.