The most typical applications of ICMP: PING and traceroute

ICMP,Internet Control Message Protocol, Internet control message protocol is mainly used to detect network connectivity and achieve link tracking. The most typical applications are PING and traceroute.

PING:

Send echo request message (echo request) and echo reply message (echo reply) to detect whether there is a problem with the link from the source host to the destination host, whether the destination is reachable, and the delay of the communication.

Traceroute:

The link address information is obtained by sending a probe message. The first probe message TTL is 1. When it arrives at the first router, TTL minus 1 to 0, so drop the probe packet. At the same time, the source host sends back the ICMP time exceeded message to the source host. Then the source host gets the IP address of the first router. Then the source host sends a second probe message, TTL increases by 1 to 2, arrives at the first router TTL minus 1 to 1, and forwards the probe packet to the second router. When TTL minus 1 is 0, the source host gets the IP address of the second router by dropping the probe packet and sending the ICMP time-lapse message back to the source host. And so on, until the probe message reaches the destination of the traceroute, the source host gets the IP address of each hop route to the destination.