Background

• ICMP provides simple error reporting, diagnostics, and limited configuration for IP hosts

• • It is required on all IP hosts

• It is logically on the IP layer (part of layer 3)

• • But ICMP packets are encapsulated by IP

• Like IP, it is connectionless and unreliable

• The error reporting messages copy the offending packet’s

• • IP header and the first 8 bytes of its TCP or UDP header
  • Or, the entire packet so that the ICMP message is < 576 bytes (RFC1812)