ICMP

CMP (Internet Control Message Protocol) is a fundamental protocol used in computer networking, operating at the network layer (Layer 3 of the OSI model). Its primary role is to facilitate error reporting and diagnostics between network devices, such as routers, switches, and hosts.

ICMP is used to notify the sender when issues arise during data transmission, such as when a destination is unreachable, a packet’s time-to-live (TTL) expires, or fragmentation is required but not permitted. For example, if a router cannot forward a packet to its next hop, it sends an ICMP message back to the source device indicating the problem.