Copyright 2003 Error Reporting and Error Correction ICMP is an error-reporting protocol for IP. When datagram delivery errors occur, ICMP is used to report these errors back to the sender of the datagram.
Copyright 2003 ICMP Message Delivery ICMP messages are encapsulated as data in datagrams in the same way any other data is delivered using IP.
Copyright 2003 Detecting Long Routes Whether the actual path includes too many hops or a circular routing path exists, the packet will eventually reach the end of its life, known as its time-to-live (TTL).
Copyright 2003 Echo Messages ICMP message formats start with these same three fields: Type Code Checksum
Copyright 2003 Control Messages They are used to inform hosts of conditions such as network congestion or the existence of a better gateway to a remote network.
Copyright 2003 Redirect/Change Requests All hosts that communicate with multiple IP networks must be configured with a default gateway. This default gateway is the address of a router port connected to the same network as the host.
Copyright 2003 Clock Synchronization and Transit- Time Estimation Hosts on disparate networks who are trying to communicate using software that requires time synchronization. The ICMP time-stamp request message allows a host to ask for a remote hosts current time.
Copyright 2003 Address Mask Requirements When a network administrator uses the process of subnetting to divide a major IP address into multiple subnets, a new subnet mask is created.