Concept Guide
Important Points to Remember
• The existing ip directed broadcast command is rendered meaningless if you enable UDP helper on the same interface.
• The broadcast trac 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 trac with port number 67 or 68 are unicast to the dynamic host conguration protocol (DHCP) server per the ip
helper-address conguration whether or not the UDP port list contains those ports.
– If the UDP port list contains ports 67 or 68, UDP broadcast trac 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 and Using the UDP Helper show Command
DellEMC(conf-if-gi-1/1)#ip udp-helper udp-port 1000
DellEMC(conf-if-gi-1/1)#show config
!
interface GigabitEthernet 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.
DellEMC#show ip udp-helper
--------------------------------------------------
Port UDP port list
--------------------------------------------------
Gi 1/1 1000
Congurations Using UDP Helper
When you enable UDP helper and the destination IP address of an incoming packet is a broadcast address, Dell EMC Networking OS
suppresses the destination address of the packet.
The following sections describe various congurations that employ UDP helper to direct broadcasts.
• UDP Helper with Broadcast-All Addresses
• UDP Helper with Subnet Broadcast Addresses
• UDP Helper with Congured Broadcast Addresses
• UDP Helper with No Congured Broadcast Addresses
UDP Helper with Broadcast-All Addresses
When the destination IP address of an incoming packet is the IP broadcast address, Dell EMC Networking OS rewrites the address to
match the congured broadcast address.
In the following illustration:
1 Packet 1 is dropped at ingress if you did not congure UDP helper address.
IPv4 Routing
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