Reference Guide

468 | IPv4 Addressing
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ICMP
For diagnostics, Internet Control Message Protocol (ICMP) provide routing information to end stations by
choosing the best route (ICMP redirect messages) or determining if a router is reachable (ICMP Echo or
Echo Reply). ICMP Error messages inform the router of problems in a particular packet. These messages
are sent only on unicast traffic
Configuration Task List for ICMP
Use the following steps to configure ICMP:
• Enable ICMP unreachable messages
• Enable ICMP redirects
Enable ICMP unreachable messages
By default, ICMP unreachable messages are disabled. When enabled ICMP unreachable messages are
created and sent out all interfaces. To disable ICMP unreachable messages, use the
no ip unreachable
command.
To reenable the creation of ICMP unreachable messages on the interface, use the following command in
the INTERFACE mode:
To view if ICMP unreachable messages are sent on the interface, use the
show config command in the
INTERFACE mode. If it is not listed in the
show config command output, it is enabled. Only nondefault
information is displayed in the
show config command output.
Enable ICMP redirects
Enable ICMP redirects is supported on e platform
By default, ICMP redirect messages are disabled. When enabled, ICMP redirect messages are created and
sent out all interfaces. To disable ICMP redirect messages, use the
no ip redirect command.
To reenable the creation of ICMP redirect messages on the interface, use the following command in the
INTERFACE mode:
Command Syntax Command Mode Purpose
ip unreachable
INTERFACE Set FTOS to create and send ICMP unreachable messages on the interface.
Command Syntax Command Mode Purpose
ip redirect
INTERFACE Set FTOS to create and send ICMP redirect messages on the interface.