FTP Server and Port Numbers

FTP (File Transfer Protocol) is a standard network protocol used for transferring files between a client and a server on a computer network. In order for the FTP client to connect to the FTP server, the server needs to listen for incoming connections on a specific port number.

The Port Number for FTP Server

The correct answer to the question is option 'B', which is port number 21. Port numbers are used to identify specific services or applications running on a computer network. In the case of FTP, port number 21 is designated as the default control connection port.

Understanding Port Numbers

Port numbers range from 0 to 65535 and are divided into three categories:

1. Well-known ports: These ports range from 0 to 1023 and are assigned to specific services or applications. Examples include HTTP (port 80), FTP (port 21), SSH (port 22), and Telnet (port 23).

2. Registered ports: These ports range from 1024 to 49151 and are assigned by the Internet Assigned Numbers Authority (IANA) to specific services or applications.

3. Dynamic or private ports: These ports range from 49152 to 65535 and can be used by any service or application on an ad-hoc basis.

The Role of Port 21 in FTP

Port number 21 is reserved for FTP control connections. When an FTP client initiates a connection to an FTP server, it sends a request to the server's IP address on port 21. The server listens for incoming connections on this port and responds to the client's request.

The control connection is responsible for sending commands from the client to the server and receiving responses from the server. It handles tasks such as authentication, file system navigation, and file transfer control.

Conclusion

In summary, the FTP server listens for connections on port number 21. This port is reserved for FTP control connections, which handle commands and responses between the client and server. Understanding port numbers is essential for establishing successful network connections and ensuring the proper functioning of specific services and applications.