CREST Practitioner Security Analyst (CPSA) Practice

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Which port is used by DNS services traditionally?

The correct answer is: 53

DNS (Domain Name System) services traditionally use port 53 for both UDP and TCP protocols. This port is essential for resolving domain names into IP addresses, which is a fundamental function of the DNS. The choice of port 53 is standardized across all DNS implementations, ensuring that DNS queries and responses are consistently directed to this port by clients and servers alike. The other ports listed—67, 69, and 70—are associated with different network services. Port 67 is used for the DHCP server, enabling dynamic host configuration protocol services. Port 69 is associated with Trivial File Transfer Protocol (TFTP), which facilitates simple file transfers, often used in scenarios like network booting. Port 70, on the other hand, was used by Gopher, an early method for distributing content on the internet before the wider adoption of the web. Hence, these ports do not correspond to DNS functions and highlight the specificity of port 53’s role in the DNS hierarchy.