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/The Internet Control Message Protocol (ICMP)
The Internet Control Message Protocol (ICMP)
In this lesson, we'll study ICMP, the network layer's error reporting protocol.
We'll cover the following...
What Is ICMP?
It’s sometimes necessary for intermediate routers or destination hosts to inform the sender of a packet about any problems that occur while processing it. In the TCP/IP protocol suite, this reporting is done by the Internet Control Message Protocol (ICMP). ICMP is defined in RFC 792.
ICMP Headers
ICMP messages are carried as the payload of IP packets (the protocol value reserved for ICMP is 1). An ICMP message is composed of an 8-byte header and a variable-length payload that usually contains the first bytes of the packet that triggered the transmission of the ICMP message.
In the ICMP header (purple in the diagram above):
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The Type and Code fields indicate the type of problem that was detected by the sender of ...