ICMP-type values

ICMP協定
Using the ping and traceroute commands, we obtain the round-trip time (RTT). This is the time required to send an echo packet, and get an answer back. This can be useful to have a rough idea of the delay on the link. However, these figures are not precise enough to be used for performance evaluation.

When a packet destination is the router itself, this packet has to be process-switched. The processor has to handle the information from this packet, and send an answer back. This is not the main goal of a router. By definition, a router is built to route packets. Answering a ping is offered as a best-effort service.

ICMP Type	Literal
0	echo-reply
3	destination unreachable code 0 = net unreachable 1 = host unreachable 2 = protocol unreachable 3 = port unreachable 4 = fragmentation needed and DF set 5 = source route failed
4	source-quench
5	redirect code 0 = redirect datagrams for the network 1 = redirect datagrams for the host 2 = redirect datagrams for the type of service and network 3 = redirect datagrams for the type of service and host
6	alternate-address
8	echo
9	router-advertisement
10	router-solicitation
11	time-exceeded code 0 = time to live exceeded in transit 1 = fragment reassembly time exceeded
12	parameter-problem
13	timestamp-request
14	timestamp-reply
15	information-request
16	information-reply
17	mask-request
18	mask-reply
31	conversion-error
32	mobile-redirect

The table below lists the possible output characters from the ping facility:

Character	Description
!	Each exclamation point indicates receipt of a reply.
.	Each period indicates the network server timed out while waiting for a reply.
U	A destination unreachable error PDU was received.
Q	Source quench (destination too busy).
M	Could not fragment.
?	Unknown packet type.
&	Packet lifetime exceeded.