Review the protocol used for unreachable and TTL-exceeded notifications and connectivity diagnostics in an IP network.
Which description is correct?
ICMP carries IP-layer control, error, and diagnostic messages. It does not use application TCP or UDP port numbers.
Detailed explanation
Incorrect. A reliable byte stream is TCP's service.
Incorrect. A reliable byte stream is TCP's service.
Incorrect. This describes UDP transport and its port fields.
Incorrect. This describes UDP transport and its port fields.
Correct. ICMP carries IP control and diagnostic messages such as echo requests and replies.
Correct. ICMP carries IP control and diagnostic messages such as echo requests and replies.
Incorrect. Time synchronization is NTP's role.
Incorrect. Time synchronization is NTP's role.
Try it yourself
An example you can run in a temporary verification environment.
python3 -c "import socket; print(socket.getprotobyname('icmp'))"Expected result
1（IPv4 ICMPのプロトコル番号）Key points
- IP control and error messages
- Echo request and reply
- No TCP/UDP ports
Notes
- Environment: Python 3 socket / 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.