ICMP is the Internet Control Message Protocol
You can read RFC 792 for a full explanation.
The well-known ping command is a type of ICMP request.
Packet Layout:
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-------------------------------+-------------------------------+ | Type | Code | Checksum | +-------------------------------+-------------------------------+ | Identifier | Sequence Number | +-------------------------------+-------------------------------+ | Data ... +--------------------------------------------- Type 8 = echo request. Type 0 = echo reply.
Links:
Using ICMP tunneling to steal Internet
ICMP-Meldungstypen
Nummer | Meldung |
---|---|
0 | Echo-Antwort |
3 | Ziel nicht erreichbar |
4 | Quellreduktion |
5 | Umleitung / Änderungsanfrage |
8 | Echo-Anfrage |
9 | Router-Angebot |
10 | Router-Auswahl |
11 | Zeitüberschreitung |
12 | Parameterproblem |
13 | Zeitangabeanfrage |
14 | Zeitangabeantwort |
15 | Informationsanfrage |
16 | Informationsantwort |
17 | Adressmaskenanfrage |
18 | Adressmaskenantwort |