1.07.1Basic
Specify the standard port for DNS queries and responses.
The same port number is used with UDP and TCP.
Which port is used?
× Incorrect
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
Correct53
Correct. DNS uses port 53 for both UDP and TCP.
Incorrect67
Incorrect. 67/udp is used by DHCP servers.
Incorrect80
Incorrect. 80/tcp is HTTP.
Incorrect123
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
Network prefix
The part of an IP address that identifies the network rather than a host.
Transport protocol
TCP and UDP provide different delivery, reliability, and connection semantics.
Service port
A numbered endpoint used to deliver traffic to a network service.
Question IDKL-102-949
EnvironmentLinux NSS servicesデータベース / 外部通信なし
Last technical review2026-08-13
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