Configuring an IP helper address

To forward a client broadcast request for a UDP application when the client and server are on different networks, you must configure a helper address on the interface connected to the client.

Specify the server IP address or the subnet directed broadcast address of the IP subnet the server is in as the helper address. You can configure up to 16 helper addresses on each interface. You can configure a helper address on an Ethernet port or a virtual interface.

By default, IP helper does not forward client broadcast request to a server within the network. To forward a client broadcast request when the client and server are on the same network, configure an IP helper with the unicast option on the interface connected to the client.

To configure a helper address on unit 1, slot 1, port 2, enter the following commands.

  1. Enter global configuration mode. 
    device# configure terminal
  2. Enter interface configuration mode. 
    device(config)# interface ethernet 1/1/2
  3. Configure an IP helper address. 
    device(config-if-e1000-1/1/2)# ip helper-address 10.95.7.6
    In this example, a help address is configured for server 10.95.7.6 to the port. If the port receives a client request for any of the applications that the Layer 3 switch is enabled to forward, the Layer 3 switch forwards the client request to the server.

In the following example, a unicast IP helper address is configured. 

device(mode)# configure terminal
device(config)# interface ethernet 1/1/2
device(config-if-e1000-1/1/2)# ip helper-address 10.98.5.7 unicast
Parent topic: UDP broadcast and IP helper