Internet Control Message Protocol (ICMP)
Internet Control Message Protocol (ICMP) is a required TCP/IP standard defined in RFC 792, "Internet Control Message Protocol (ICMP)." With ICMP, hosts and routers that use IP communication can report errors and exchange limited control and status information.
ICMP messages are usually sent automatically in one of the following situations:
ICMP messages are encapsulated and sent within IP datagrams, as shown in the following illustration.
Different types of ICMP messages are identified in the ICMP header. Because ICMP messages are carried in IP datagrams, they are unreliable.
The most common ICMP messages are listed and described in the following table.
You can use the ping command to send ICMP echo request messages and record the receipt of ICMP echo reply messages. With these messages, you can detect network or host communication failures and troubleshoot common TCP/IP connectivity problems.
For more information about ICMP, see RFC 792, "Internet Control Message Protocol (ICMP)." For more information about obtaining RFCs, see Obtaining RFCs