3268
Active Directory Global Catalog over LDAP
Microsoft Global Catalog LDAP
What is port 3268?
Port 3268 provides LDAP access to the Microsoft Active Directory Global Catalog, which contains a partial replica of all objects in an AD forest. It is used for cross-domain authentication, universal group lookups, and queries that must span multiple domains. Access is unencrypted — use port 3269 for the TLS-secured equivalent.
Quick checks
$
nc -zv example.com 3268
$
nmap -p 3268 example.com
$
telnet example.com 3268