What happens if I send a ping to a host that is off? Do I get an ICMP message with "host unreachable"? Does ICMP say nothing at all because the packet was correctly delivered even though it was not processed by the destination host? I don't know how ICMP reacts in these cases.
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2 Answers
ICMP doesn't do anything because there is no host to generate ICMP messages back to the source.
The ping application will time out. I think most implementations have a default two-second timeout, but you can probably override that. An implementation of ping is going to have the features that the author of that tool version built in.
answered Feb 18, 2018 at 21:47
With a local ping, the ARP request times out, no ICMP echo request is actually sent.
With a remote ping across one or more routers, the last router (failing local ARP) might return an ICMP error.
