Default Ports for Remote Administration

D.

The correct answer is D. TCP 3389.

TCP (Transmission Control Protocol) is a standard communication protocol used by computers to exchange data over a network. In the context of remote administration, a TCP port is a number assigned to a specific process on a server that listens for incoming connections from a remote client.

When a remote administrator connects to a server, they use a client application that communicates with the server over a specific TCP port. By default, different applications and protocols use different ports.

Option A, TCP 25, is the default port for SMTP (Simple Mail Transfer Protocol), which is used for email transmission. It is not used for remote administration.

Option B, TCP 389, is the default port for LDAP (Lightweight Directory Access Protocol), which is used for accessing and managing directory services. It is not used for remote administration.

Option C, TCP 3128, is the default port for the Squid proxy server, which is used for caching web content. It is not used for remote administration.

Option D, TCP 3389, is the default port for Remote Desktop Protocol (RDP), which is used for remote administration of Windows servers. This is the correct answer.

In summary, the default port that should be open on a server for remote administration is TCP 3389, which is used for Remote Desktop Protocol (RDP).