ICMP (Part 3) – Concept Consolidation

Now let’s consolidate the concept of ICMP from what we discussed before. When a gateway on the Internet cannot pass the data packet to the next gateway, it will send a ICMP reply message (according to the error status) back to the sender computer. Consider the situation that shown in the diagram below:

ICMP

More Concept of ICMP:

ICMP was designed as a way to send error and diagnostic messages in an IP inter-network.

  • * ICMP messages are identified by “type” numbers.
  • Each ICMP message also has a “code” number, which specifies a particular error code for that message type.

NOTE:
ICMP messages are carried inside IP packets. And ICMP should be considered as an integral part of IP, not as a higher-layer protocol.

Tomorrow I will discuss briefly how ICMP messages are sent back to sender computer in case a gateway on the Internet cannot pass the data packet to the next gateway.

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