Which protocol uses port 53 for communication?

The correct answer is DNS, which stands for Domain Name System. DNS is a critical protocol in networking that resolves human-readable domain names, like www.example.com, into IP addresses that computers use to communicate with each other over the internet. This process is essential for routing traffic on the internet. DNS servers listen for requests on port 53, which is designated for both TCP and UDP traffic.

When a user's device needs to access a website, it typically sends a query to a DNS server using this port. The DNS server then translates the domain name into an IP address and sends the response back to the user's device, allowing it to establish a connection with the server hosting the desired website. This functionality is a foundational component of how the internet operates, facilitating user-friendly navigation.

In contrast, the other protocols mentioned serve different purposes: FTP (File Transfer Protocol) is used for transferring files, typically using ports 20 and 21; SMTP (Simple Mail Transfer Protocol) is used for sending emails over the internet, primarily using port 25; and SSH (Secure Shell) is a protocol used for securely accessing network devices over an unsecured network, usually operating on port 22.