389
Directory services for users and resources (LDAP / Active Directory)
Lightweight Directory Access Protocol
What is port 389?
LDAP on port 389 provides access to directory services — primarily Microsoft Active Directory and OpenLDAP. It stores information about users, groups, computers, and policies, and is the foundation of single sign-on in enterprise networks. The connection is unencrypted; use LDAPS (port 636) or STARTTLS for encryption. An LDAP server exposed to the internet can leak organizational structure and user details.
Quick checks
$
nc -zv example.com 389
$
nmap -p 389 example.com