Overview
Internet Control Message Protocol (ICMP) is not used to exchange user data but rather to provide feedback about problems in the network environment. It is a core part of the Network Layer.
Common Uses
- Ping: Uses 'Echo Request' and 'Echo Reply' to test connectivity and latency.
- Traceroute: Uses ICMP 'Time Exceeded' messages to map the path to a destination.
- Destination Unreachable: Sent by a router when it cannot deliver a packet.
Security
ICMP can be used in attacks like the 'Ping of Death' or ICMP floods, leading many administrators to block certain types of ICMP traffic at the firewall.