Allied Telesis AT-FS970M Series - Manual (Page 1800)

Chapter 102: Internet Protocol Version 4 Packet Routing
1800
Internet Control Message Protocol (ICMP)
ICMP allows routers to send error and control messages to other routers
or hosts. It provides the communication between IP software on one
system and IP software on another. The switch implements the ICMP
functions listed in Table 249.
Table 249. ICMP Messages
ICMP Packet (Type) Switch Response
Echo reply (0) This is used to implement the
“ping” command common to most
UNIX and TCP implementations.
The switch sends out an “Echo
reply” packet in response to an
“Echo request.”
Destination unreachable (3) This message is sent when the
switch drops a packet because it
does not have a route to the
destination.
Source Quench (4) The switch sends a “Source
Quench” if it drops a packet due to
insufficient internal resources. This
can happen if the source is
sending data too fast to be
forwarded.
Redirect (5) The switch issues a “redirect”
packet to inform a local host that
its target is located on the same
LAN (no routing is required) or
when it detects a host using a non-
optimal route (usually because a
link has failed or changed its
status).
Echo request (8) This is related to (1) and results in
an “echo reply” packet being sent.
The switch can also generate an
“echo request” packet as a result
of the PING command.