Internet Control Messaging Protocol (ICMP) is used by ping and traceroute utilities. Packet Internet Groper (ping) allows you to validate that an IP address exists and can accept requests.
- Ping is an echo and the response is an echo response.
- Routers send Destination Unreachable messages when they can’t reach the destination network and they are forced to drop the packet. The router that drops the packet sends the ICMP DU message.
A traceroute traces the route or path taken from a client to a remote host. Traceroute also reports the IP addresses of the routers at each next hop on the way to the destination. This is especially useful when you suspect that a router on the route to an unreachable network is responsible for dropping the packet.