Free ICMP Resources
Introduction to ICMP
Introduction to ICMP at linux.org.
Examining ICMP Packets
Overview of the ICMP protocol including the fields an ICMP header adds to an IP packet, type codes, and an examinatio of ICMP packets.
Internet Control Message Protocol
The operation of ICMP is illustrated with diagrams including how "ping" works.
ICMP, Internet Control Message Protocol
Includes a description of icmp, message format info, and links to icmp rfc documents.
RFC 792 (ICMP)
ICMP RFC document.
ICMP Type Numbers
A full list (from RFC1700) of icmp type numbers.
Internet Control Message Protocol version 6 tutorial that includes an introduction, message and header formats, message transmission information and more.
Example Packet Decodes
Includes ICMP, IP and TCP sample packet decodes. "Twelve packets are shown from communication between an imaginary remote computer called "client" and a computer known as "server". The client is linked to the server via an Ethernet LAN and a default router (a CISCO router, known as "gateway"). The packets are recorded at the client."