DNS uses which port and transport protocols?

DNS uses which port and transport protocols?

• A. DNS uses TCP port 53 and UDP port 53
• B. DNS uses only UDP port 53
• C. DNS uses TCP port 53 only
• D. DNS uses port 67 for servers

Answer: (A)

DNS relies on port 53 and uses both UDP and TCP as transport protocols. For typical queries, UDP to port 53 is used because it’s fast and lightweight. If a response is too large to fit in a UDP packet or a zone transfer between DNS servers is required, DNS switches to a TCP connection on port 53 to ensure reliable delivery. That combination—port 53 with both UDP and TCP—best reflects how DNS operates. The notion of using only UDP or only TCP misses important cases (UDP for standard queries, TCP for large responses and zone transfers). Port 67 belongs to DHCP servers, not DNS.

DNS relies on port 53 and uses both UDP and TCP as transport protocols. For typical queries, UDP to port 53 is used because it’s fast and lightweight. If a response is too large to fit in a UDP packet or a zone transfer between DNS servers is required, DNS switches to a TCP connection on port 53 to ensure reliable delivery. That combination—port 53 with both UDP and TCP—best reflects how DNS operates. The notion of using only UDP or only TCP misses important cases (UDP for standard queries, TCP for large responses and zone transfers). Port 67 belongs to DHCP servers, not DNS.