Administrator Guide

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:
1 Packet 1 is dropped at ingress if you did not congure UDP helper address.
2 If you enable UDP helper (using the ip udp-helper udp-port command), and the UDP destination port of the packet matches
the UDP port congured, the system changes the destination address to the congured broadcast 1.1.255.255 and routes the packet
to VLANs 100 and 101. If you do not congure an IP broadcast address (using the
ip udp-broadcast-address command) on
VLANs 100 or 101, the packet is forwarded using the original destination IP address 255.255.255.255.
Packet 2, sent from a host on VLAN 101 has a broadcast MAC address and IP address. In this case:
1 It is ooded on VLAN 101 without changing the destination address because the forwarding process is Layer 2.
2 If you enabled UDP helper, the system changes the destination IP address to the congured broadcast address 1.1.255.255 and
forwards the packet to VLAN 100.
IPv4 Routing
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