Ping - troubleshooting concepts

When using ping as a troubleshooting tool on a Cisco IOS device, keep in mind that:

  1. If it is not specified, the source address used for the ping is always that of the exit interface indicated by the routing table for the particular destination being pinged.
  2. A ping has two components: The echo request, and the echo reply. A failed ping could be either due to the fact that the echo-request did not reach the destination, or that the echo reply did not reach the source.
  3. A successful ping from a particular source to a particular destination will be successful if performed in the opposite direction. This is the case only if the source and destination IPs remain the same. Simply pinging from a router without specifying the source IP may give different results, since the router chooses the source IP based on the routing table.

For a detailed list of some of the most common reasons for a ping to fail, take a look at Ping - common reasons for failure. In addition, take a look at Ping - debug commands to learn how to more deeply troubleshoot ping responses.