CPSA Port Numbers with Services and Protocols Practice Test

DNS queries are typically sent using UDP on port 53. This pairing works well because UDP is a lightweight, connectionless protocol that handles small request–response messages quickly, which suits the fast lookups DNS performs. Historically, DNS messages fit within the UDP size limit, though extensions like EDNS allow larger responses. When a response would be too large or reliability is required (such as certain large zone transfers), DNS can use TCP on port 53 instead. Ports like 80 and 67 belong to HTTP and DHCP, not standard DNS UDP queries.