Which protocol operates on port 53?

The correct answer is that the Domain Name System (DNS) operates on port 53. DNS is a critical service on the internet that translates human-readable domain names (like www.example.com) into IP addresses that computers use to identify each other on the network. This translation is essential because, while humans prefer to remember names, machines rely on numerical addresses to facilitate communication.

When a user enters a URL in their web browser, a DNS query is sent to the DNS server using port 53, whether that query is for specific record types like A records (which map domain names to IPv4 addresses) or AAAA records (which map domain names to IPv6 addresses).

The other protocols mentioned do not utilize port 53. For example, FTP (File Transfer Protocol) typically operates over ports 20 and 21, HTTP (Hypertext Transfer Protocol) primarily uses port 80, and SSH (Secure Shell) commonly uses port 22. Understanding the specific ports on which various protocols operate is essential for network management, security settings, and troubleshooting in networking contexts.