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 6.2 lists some of the ICMP messages.
| 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. |