Brocade FastIron Ethernet Switch Layer 3 Routing Configuration Guide - Manual (Page 83)

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 interface 2 on chassis module 1, enter the following commands.
device(config)# interface ethernet 1/2
device(config-if-1/2)# ip helper-address 1 10.95.7.6
The commands in this example change the CLI to the configuration level for port 1/2, 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 interface 2 on chassis module 1, enter the following
commands:
device(config)# interface 1/2
device(config-if-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 parameter specifies the helper address number and can be from 1 through 16.
The ip-addr command 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 which is on the
same network.
BootP and DHCP relay parameter configuration
A host on an IP network can use BootP or DHCP to obtain its IP address from a BootP/DHCP server.
To obtain the address, the client sends a BootP or DHCP request. The request is a subnet directed
broadcast and is addressed to UDP port 67. A limited IP broadcast is addressed to IP address
255.255.255.255 and is not forwarded by the Brocade Layer 3 switch or other IP routers.
When the BootP or DHCP client and server are on the same network, the server receives the broadcast
request and replies to the client. However, when the client and server are on different networks, the
server does not receive the client request, because the Layer 3 switch does not forward the request.
You can configure the Layer 3 switch to forward BootP/DHCP requests. To do so, configure a helper
address on the interface that receives the client requests, and specify the BootP/DHCP server IP
address as the address you are helping the BootP/DHCP requests to reach. Instead of the server IP
address, you can specify the subnet directed broadcast address of the IP subnet the server is in.
BootP and DHCP relay parameters
The following parameters control the Layer 3 switch forwarding of BootP and DHCP requests:
• Helper address - The BootP/DHCP server IP address. You must configure the helper address on
the interface that receives the BootP/DHCP requests from the client. The Layer 3 switch cannot
forward a request to the server unless you configure a helper address for the server.
• Gateway address - The Layer 3 switch places the IP address of the interface that received the
BootP/DHCP request in the request packet Gateway Address field (sometimes called the Router ID
BootP and DHCP relay parameter configuration
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