Reference Guide

show arp retries
ICMP
For diagnostics, the internet control message protocol (ICMP) provides 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 Tasks for ICMP
The following lists the configuration tasks for ICMP.
● Enabling ICMP Unreachable Messages
For a complete listing of all commands related to ICMP, refer to the Dell Networking OS Command Line Reference Guide.
Enabling ICMP Unreachable Messages
By default, ICMP unreachable messages are disabled.
When enabled, ICMP unreachable messages are created and sent out all interfaces.
To disable and re-enable ICMP unreachable messages, use the following commands.
● To disable ICMP unreachable messages.
INTERFACE mode
no ip unreachable
● Set the system to create and send ICMP unreachable messages on the interface.
INTERFACE mode
ip unreachable
To view if ICMP unreachable messages are sent on the interface, use the show config command in INTERFACE mode. If it is
not listed in the show config command output, it is enabled. Only non-default information is displayed in the show config
command output.
UDP Helper
User datagram protocol (UDP) helper allows you to direct the forwarding IP/UDP broadcast traffic by creating special
broadcast addresses and rewriting the destination IP address of packets to match those addresses.
Configure UDP Helper
Configuring the system to direct UDP broadcast is a two-step process:
1. Enable UDP helper and specify the UDP ports for which traffic is forwarded. Refer to Enabling UDP Helper.
2. Configure a broadcast address on interfaces that will receive UDP broadcast traffic. Refer to Configuring a Broadcast
Address.
Important Points to Remember
● The existing ip directed broadcast command is rendered meaningless if you enable UDP helper on the same
interface.
● The broadcast traffic rate should not exceed 200 packets per second when you enable UDP helper.
● You may specify a maximum of 16 UDP ports.
● UDP helper is compatible with IP helper (ip helper-address):
IPv4 Routing
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