Cisco Certified Network Associate (CCNA) Practice Exam

Which protocol uses port number 53?

1. FTP

2. DNS

3. SMTP

4. HTTP

The correct answer is: DNS

The protocol that uses port number 53 is DNS, which stands for Domain Name System. DNS is fundamental for the functionality of the internet, as it 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 necessary because people find it easier to remember names rather than numerical IP addresses. Port 53 is designated for DNS services, both for TCP and UDP protocols. While DNS primarily uses UDP for queries, it also uses TCP for tasks such as zone transfers and when the response data size exceeds the limit of a UDP packet. This specific port assignment allows DNS servers and clients to communicate effectively across the internet, facilitating the resolution of domain names to their corresponding IP addresses swiftly. In contrast, other options like FTP (File Transfer Protocol), SMTP (Simple Mail Transfer Protocol), and HTTP (Hypertext Transfer Protocol) are associated with different port numbers: FTP uses port 21, SMTP utilizes port 25, and HTTP operates on port 80. Each of these protocols serves distinct functions within network communication, helping to manage file transfers, email delivery, and web traffic, respectively. However, they do not operate on port 53, which is solely allocated for DNS.