88
Centralized ticket-based authentication (Kerberos)
Kerberos Authentication
What is port 88?
Kerberos on port 88 is the authentication protocol used by Microsoft Active Directory and many Unix/Linux systems. It relies on encrypted tickets issued by a Key Distribution Center (KDC), avoiding the transmission of passwords over the network. A server with port 88 open is most likely an Active Directory Domain Controller. Well-known attack techniques include Pass-the-Ticket, Golden Ticket forgery, and Kerberoasting.
Quick checks
$
nc -zv example.com 88
$
nmap -p 88 example.com