Ping response "Request timed out." vs "Destination Host unreachable"

Question

When I ping an IP address, what is the difference between the request and the timeout for the host returned from the command?

Answer 1

End host unreachable

This message indicates one of two problems: either the local system does not have a route to the desired destination, or the remote router reports that it does not have a route to the destination.

If the message is simply “Destination Host Unreachable”, then there is no route from the local system and the packets being sent are never put on the wire.

If the message is "Reply From <IP address>: Destination Host Unreachable", then a routing problem has occurred on the remote router whose address is indicated by the "<IP address" field.

Requested timeout

This message indicates that no echo reply messages were received within the default time of 1 second. This can be caused by many different reasons; the most common are network congestion, ARP request failure, packet filtering, routing error, or silent reset.

More details: http://technet.microsoft.com/en-us/library/cc940095.aspx

Answer 2

The request timeout means that the host did not receive a response from the host, but was able to reach it. An invalid destination host means that there was no valid route to the requested host.

Answer 3

As chaos said, an inaccessible destination can also mean that something is blocking the path from or to your destination. For example, an ACL that filters invalid IP addresses.

Answer 4

As I understand it, "request timeout" means that the ICMP packet received from one host to another host, but the response could not reach the requesting host. There may be more packet loss or some kind of physical problem. “Destination host unreachable” means that there is no proper route between the two hosts.