Internet Control Message Protocol (ICMP)

• It is used to send error & control information between ip network devices.
• There are many diffident messages that can be shared, including the following: 

1. Echo request: Determines whether on ip node ( a host or a router is available on network.)
2. Echo Reply: Replies to ICMP echo request.
3. Destination Unreachable: Informs the host that a datagram can't be delivered.
4. Source Quench: Informs the host to lower the rate at which it sends datagram because of congestion.

5. Redirect: Informs the host of a preferred rate.

6. Time Exceeded: Indicate that the TTL of IP datagram has expired.