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
Configurations 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 configurations that employ UDP helper to direct broadcasts.
UDP Helper with Broadcast-All Addresses
UDP Helper with Subnet Broadcast Addresses
UDP Helper with Configured Broadcast Addresses
UDP Helper with No Configured 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 configured broadcast address.
In the following illustration:
1. Packet 1 is dropped at ingress if you did not configure 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 configured, the system changes the destination
address to the configured broadcast 1.1.255.255 and routes the packet to VLANs 100 and 101. If you
do not configure 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 flooded 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 configured
broadcast address 1.1.255.255 and forwards the packet to VLAN 100.
IPv4 Routing 451