Administrator Guide

1. Enable UDP helper and specify the UDP ports for which trac is forwarded. Refer to Enabling UDP Helper.
Important Points to Remember
• The existing ip directed broadcast command is rendered meaningless if you enable UDP helper on the same interface.
• The broadcast trac 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):
– UDP broadcast trac with port number 67 or 68 are unicast to the dynamic host conguration protocol (DHCP) server per
the ip helper-address conguration whether or not the UDP port list contains those ports.
– If the UDP port list contains ports 67 or 68, UDP broadcast trac is forwarded on those ports.
Enabling UDP Helper
To enable UDP helper, use the following command.
• Enable UPD helper.
ip udp-helper udp-ports
Example of Enabling UDP Helper
Example of the show ip udp-helper Command
Dell(conf-if-te-1/1)#ip udp-helper udp-port 1000
Dell(conf-if-te-1/1)#show config
!
interface TenGigabitEthernet 1/1
ip address 2.1.1.1/24
ip udp-helper udp-port 1000
no shutdown
To view the interfaces and ports on which you enabled UDP helper, use the show ip udp-helper command from EXEC
Privilege mode.
Dell#show ip udp-helper
---------------------------
Port UDP port list
--------------------------
TenGig 1/1 1000
Congurations Using UDP Helper
When you enable UDP helper and the destination IP address of an incoming packet is a broadcast address, the system suppresses
the destination address of the packet.
The following sections describe various congurations that employ UDP helper to direct broadcasts.
• UDP Helper with Broadcast-All Addresses
• UDP Helper with Subnet Broadcast Addresses
• UDP Helper with Congured Broadcast Addresses
• UDP Helper with No Congured Broadcast Addresses
UDP Helper with Broadcast-All Addresses
When the destination IP address of an incoming packet is the IP broadcast address, the system rewrites the address to match the
congured broadcast address.
In the following illustration:
IPv4 Routing
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