Specify the standard port for DNS queries and responses.
The same port number is used with UDP and TCP.
Which port is used?
DNS uses port 53 with both UDP and TCP. UDP is common for ordinary queries, while TCP is used for cases such as large responses and zone transfers.
Detailed explanation
Correct. DNS uses port 53 for both UDP and TCP.
Correct. DNS uses port 53 for both UDP and TCP.
Incorrect. 67/udp is used by DHCP servers.
Incorrect. 67/udp is used by DHCP servers.
Incorrect. 80/tcp is HTTP.
Incorrect. 80/tcp is HTTP.
Incorrect. 123/udp is NTP.
Incorrect. 123/udp is NTP.
Try it yourself
An example you can run in a temporary verification environment.
getent services domain | sed -n '1,2p'Expected result
domain 53/tcpまたは53/udpを示す行Key points
- DNS is port 53
- Both UDP and TCP use it
- Transport depends on the operation
Notes
- Environment: Linux NSS servicesデータベース / 外部通信なし
- Command output formatting can vary slightly by distribution or tool version.
- Run the example in a temporary directory or process when possible.
Foundation review
Read the scope first
Check whether the command acts on the current shell, a new process, an existing process, or a file.
Verify the observable result
Use the supplied command and compare the output with the expected result.