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.

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

device(config)# interface ethernet 1/1/2
device(config-if-1/1/2)# ip helper-address 1 10.95.7.6

The commands in this example change the CLI to the configuration level for port 1/1/2, then add a helper address 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.

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 unicast option on the interface connected to the client.

To configure an IP helper unicast option on unit 1, slot 1, port 2, enter the following commands:

device(config)# interface 1/1/2
device(config-if-1/1/2)# ip helper-address 1 10.10.10.1 unicast

The IP helper with unicast parameter forwards the client request to the server 10.10.10.1 which is within the network.

Syntax: ip helper-address num ip-addr [unicast]

The num variable specifies the helper address number and can be from 1 through 16.

The ip-addr variable specifies the server IP address or the subnet directed broadcast address of the IP subnet the server is in.

The unicast parameter specifies that the client request must be forwarded to the server that is on the same network.