Reference Guide

IPv4 Routing | 413
The default backoff interval remains at 20 seconds. On the S4810 platform, with FTOS version 8.3.8.0 and
later, the time between ARP resend is configurable. This timer is an exponential backoff timer. Over the
specified period, the time between ARP requests increases. This reduces the potential for the system to
slow down while waiting for a multitude of ARP responses.
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
• UDP Helper
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:
Task Command Syntax Command Mode
Set the number of ARP retries. arp retries number
Default: 5
Range: 1-20
CONFIGURATION
Set the an exponential timer for resending unresolved
ARPs.
arp backoff-time
Default: 30
Range: 1 to 3600
CONFIGURATION
Display all ARP entries learned via gratuitous ARP. show arp retries EXEC Privilege
Command Syntax Command Mode Purpose
ip unreachable
INTERFACE Set FTOS to create and send ICMP unreachable
messages on the interface.