Cisco Certified Network Associate (CCNA) Practice Exam

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Which TCP port number corresponds to DNS?

TCP 20
TCP 25
TCP 53
TCP 80

The correct answer is: TCP 53

The correct answer is TCP 53, as this port number is specifically designated for Domain Name System (DNS) services. DNS is a protocol used for resolving hostnames to IP addresses and vice versa, enabling users to access websites using easily memorable domain names rather than numerical IP addresses. While other port numbers listed correspond to different protocols and services—TCP 20 is used for FTP data transfer, TCP 25 is typically used for sending emails via Simple Mail Transfer Protocol (SMTP), and TCP 80 is associated with HTTP for web traffic—TCP 53 is exclusively reserved for DNS. This clear designation makes it crucial for network communication and management, especially in resolving domain names when users attempt to connect to servers or services on the internet or local networks.