- ICMP => Internet Control Message Protocol
- ICMP is a network layer protocol used for diagnostics and error reporting between routers and end hosts.
- It works directly with IP addresses.
Structure of an ICMP packet
0 8 16 24 32
+--------+--------+--------+--------+
| ICMP Header |
+--------+--------+--------+--------+
| ICMP Data |
+----------------------------+
The ICMP Header contains:
- Type - Echo Request, Echo Reply etc
- Code - Subtype
- Checksum - For error checking
- Identifier - Match request/reply
- Sequence Number - Match request/reply
And most importantly, it contains:
- Source IP address
- Destination IP address