Identify the standard DNS port and transports for ordinary queries and cases such as zone transfer.
Which pairing is appropriate?
DNS commonly uses UDP 53 and can use TCP 53 for zone transfers or large responses.
Detailed explanation
UDP 53とTCP 53Correct. DNS uses both UDP and TCP port 53.
Correct. DNS uses both UDP and TCP port 53.
UDP 67とUDP 68Incorrect. 67 and 68 are DHCP ports.
Incorrect. 67 and 68 are DHCP ports.
TCP 25だけIncorrect. TCP 25 is SMTP.
Incorrect. TCP 25 is SMTP.
ICMP type 53Incorrect. ICMP does not identify services with ports.
Incorrect. ICMP does not identify services with ports.
Try it yourself
An example you can run in a temporary verification environment.
python3 -c "import socket; print(socket.getservbyname('domain','udp'), socket.getservbyname('domain','tcp'))"Expected result
53 53Key points
- Port 53
- UDP and TCP
- TCP for transfers
Notes
- Environment: Python 3 socket service database
- 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.