Allied Telesis AT-S63 - Manual (Page 316)

Chapter 27: Internet Protocol Version 4 Packet Routing
316 Section VII: Routing
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 non-
obsolete ICMP functions listed in Table 24.
Table 24. ICMP Messages Implemented on the AT-9400 Switch
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 out when the
switch drops a packet because it
did not have a route to the
destination.
Source Quench (4) The switch will send a “Source
Quench” if it must drop a packet
due to limited internal resources.
This could be because the source
was sending data too fast to be
forwarded.
Redirect (5) The switch will issue 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).
Ech 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.