To confirm the LDAP port when AD Sync is not working, which port should you use with telnet?

The correct choice is based on the standard port used for LDAP (Lightweight Directory Access Protocol), which is 389. When troubleshooting issues with Active Directory synchronization, confirming connectivity over this specific port is crucial. LDAP is essential for querying and modifying items in directory services, and it typically operates over port 389 for unencrypted traffic.

Using telnet to test the connection to port 389 allows you to verify whether the server is reachable and responding on that specific port, which can help pinpoint whether network issues or misconfigurations are contributing to the sync failure with Active Directory.

The other ports listed serve different purposes: port 80 is used for HTTP traffic, port 443 is designated for HTTPS secure web traffic, and port 25 is primarily used for SMTP email transmission. None of these ports would be useful for confirming LDAP connectivity in the context of Active Directory synchronization.