![]() ICMP uses the basic support of IP as if it were a higher-level protocol, however, ICMP is actually an integral part of IP. The related ping utility is implemented using the ICMP echo request and echo reply messages. The traceroute command can be implemented by transmitting IP datagrams with specially set IP TTL header fields, and looking for ICMP time exceeded in transit and Destination unreachable messages generated in response. Many commonly used network utilities are based on ICMP messages. If the resulting TTL is 0, the packet is discarded and an ICMP time exceeded in transit message is sent to the datagram's source address. įor example, every device (such as an intermediate router) forwarding an IP datagram first decrements the time to live (TTL) field in the IP header by one. ICMP errors are directed to the source IP address of the originating packet. ICMP messages are typically used for diagnostic or control purposes or generated in response to errors in IP operations (as specified in RFC 1122). ICMP is part of the Internet protocol suite as defined in RFC 792. A separate ICMPv6, defined by RFC 4443, is used with IPv6. ![]() ICMP differs from transport protocols such as TCP and UDP in that it is not typically used to exchange data between systems, nor is it regularly employed by end-user network applications (with the exception of some diagnostic tools like ping and traceroute). It is used by network devices, including routers, to send error messages and operational information indicating success or failure when communicating with another IP address, for example, an error is indicated when a requested service is not available or that a host or router could not be reached. The Internet Control Message Protocol ( ICMP) is a supporting protocol in the Internet protocol suite.
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