What port should be verified as enabled if a network time server is not functioning after port disabling?

The correct answer is 123, which corresponds to the Network Time Protocol (NTP). NTP is a protocol used to synchronize the clocks of computers over a network, ensuring that time is consistent throughout the systems for tasks such as logging, scheduling, and authentication.

If a network time server is not functioning, one of the primary troubleshooting steps is to verify that UDP port 123 is open and accessible. This port is essential for the NTP communications between clients and servers. Without access to this port, clients will not be able to send requests or receive responses from the time server, leading to synchronization issues.

The other ports listed, such as 23 and 110, are not related to time synchronization. Port 23 is typically used for Telnet, which is a protocol for remote control of computers, and port 110 is used for the Post Office Protocol version 3 (POP3), which is for retrieving email from a server. Port 389 is associated with the Lightweight Directory Access Protocol (LDAP), used for accessing directory services. Therefore, verifying port 123 is critical for ensuring the functionality of a network time server.