Which statement about port 53 is true?

Which statement about port 53 is true?

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

Answer: (B)

Port 53 is the DNS transport port that supports both UDP and TCP. For most DNS queries, UDP on port 53 is used because it’s fast and lightweight. But some operations require reliability or larger data transfers—like zone transfers between DNS servers or responses that exceed UDP’s size limit—so DNS also uses TCP on port 53 to ensure complete, reliable delivery. That’s why the true statement is that DNS uses both TCP and UDP on port 53. The idea that DNS only uses UDP is incorrect, as is the idea that it uses TCP only. Also, port 67 is the DHCP server port, not DNS.

Port 53 is the DNS transport port that supports both UDP and TCP. For most DNS queries, UDP on port 53 is used because it’s fast and lightweight. But some operations require reliability or larger data transfers—like zone transfers between DNS servers or responses that exceed UDP’s size limit—so DNS also uses TCP on port 53 to ensure complete, reliable delivery. That’s why the true statement is that DNS uses both TCP and UDP on port 53. The idea that DNS only uses UDP is incorrect, as is the idea that it uses TCP only. Also, port 67 is the DHCP server port, not DNS.