101 · Question #685
What does ICMP Time Exceeded'' mean?
The correct answer is D. TTL has reached zero. ICMP Time Exceeded is generated when a packet's TTL field is decremented to zero by a router, indicating the packet was discarded before reaching its destination.
Question
What does ICMP Time Exceeded'' mean?
Options
- AThe ping command exceeded the time limit.
- BThe traceroute command exceeded the time limit
- CRemote host did not respond
- DTTL has reached zero
How the community answered
(38 responses)- A3% (1)
- C8% (3)
- D89% (34)
Why each option
ICMP Time Exceeded is generated when a packet's TTL field is decremented to zero by a router, indicating the packet was discarded before reaching its destination.
The ping command uses ICMP Echo Request and Echo Reply; a timeout in ping produces no reply, not a Time Exceeded message.
Traceroute deliberately causes Time Exceeded messages by sending packets with incrementing TTL values, but the message itself is triggered by TTL reaching zero, not a traceroute time limit.
An unresponsive remote host results in no ICMP reply or an ICMP Host Unreachable message, not a Time Exceeded message.
Each router along a path decrements the IP TTL field by one. When a router decrements TTL to zero, it drops the packet and sends an ICMP Type 11 (Time Exceeded) message back to the source. This mechanism is exploited by traceroute to discover each hop along a path.
Concept tested: ICMP Time Exceeded and TTL expiration
Source: https://www.rfc-editor.org/rfc/rfc792
Topics
Community Discussion
No community discussion yet for this question.