Section 6.3: Internet Control Message Protocol (ICMP)
Internet Control Message Protocol (ICMP) is a TCP/IP protocol designed to help manage and control the operation of a TCP/IP network. The ICMP protocol provides a wide variety of information about a network's status and is considered part of TCP/IP's network layer. ICMP can provide useful information for troubleshooting TCP/IP.
ICMP uses messages to accomplish its tasks. Many of these messages are used in even the smallest IP network. Table 6.1 lists some of the ICMP messages.
Table 6.1: ICMP Messages
| Message | Description |
|---|---|
| Destination Unreachable | Informs the source host that there is a problem delivering a packet. |
| Time Exceeded | Indicates that the time that it takes a packet to be delivered has expired and that the packet has been discarded. |
| Redirect | Indicates that the packet has been redirected to another router that has a better route to the destination address. The message informs the sender to use the better route. |
| Echo | Used by the ping command to verify connectivity. |