Internet Protocols - CCIE Routing and Switching Exam Certification Guide - page 293

ICMP Message Types Table 6-16

ICMP Type Number Type Name Description

0 Echo Reply Used by the ping application to test connectivity. The

station receiving each message replies with an echo
reply message.

3 Destination

Unreachable

The following codes are used:
0—Destination network unreachable.
1—Destination host unreachable.
2 —Destination protocol unreachable.
3—Destination port unreachable.
4—Fragmentation needed and DF set.
5—Source route failed.
Codes 0, 1, 4, and 5 are received from a router. Codes
2 and 3 are received from the destination host.

4 Source Quench Used if a router discards a packet because it does not

have the buffer space needed to queue the packets for
output. A source quench message is sent, which is a
request to the host to cut back the rate at which it is
sending traffic to the destination.

5 Redirect Tells the sending host to send its traffic for the

destination network directly to another gateway.

8 Echo Used by the ping application to test connectivity. The

station testing connectivity sends the echo message.

11 Time Exceeded The following codes are used:

0—Time to live exceeded in transit
1—Fragment reassembly time exceeded
Code 0 can be received from a router. Code 1 is
received from the destination host.

12 Parameter Problem Used if problems are in the header of the IP packet.

13 Timestamp Contains the original timestamp in the ICMP message.

14 Timestamp Reply Adds the received timestamp and transmit timestamp

in the ICMP message.

15 Information Request Used by a host to find out what network it is on.

16 Information Reply Received by the host with information on which

network it is on.