Internet Control Message Protocol (ICMP)

Internet Control Message Protocol (ICMP) is a network layer protocol and is fundamental to the Internet Protocol (IP) suite. ICMP is used in communication between network devices for reporting errors, exchange operational information, and assist with diagnostics.

It is primarily known for its error reporting role related to network and packet issues. When networked devices encounter errors with IP packets, ICMP can send an error message back to the source, informing it of problems, these can include “Destination Unreachable”, “Time Exceeded”, and “Redirect”

ICMP is vital for network troubleshooting and diagnostics, some command line tools such as Ping and Traceroute utilize ICMP to send ICMP echo requests and Echo Reply messages while testing the reachability of a remote host via Ping. It is used in conjunction with traceroutes to help identify the route packets take to reach their destination.

It’s important to note that ICMP does not establish connections like higher protocols such as TCP or UDP but does play a critical role in providing information about the current stat of the network.