Configuring An Ip Helper Address - Brocade Communications Systems FastIron SX 800 Configuration Manual

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 field). When the server responds to the request, the
server sends the response as a unicast packet to the IP address in the Gateway Address field. (If the client and server are directly
attached, the Gateway ID field is empty and the server replies to the client using a unicast or broadcast packet, depending on
the server.)
By default, the Layer 3 switch uses the lowest-numbered IP address on the interface that receives the request as the Gateway address.
You can override the default by specifying the IP address you want the Layer 3 switch to use.
• Hop count - Each router that forwards a BootP/DHCP packet increments the hop count by 1. Routers also discard a forwarded
BootP/DHCP request instead of forwarding the request if the hop count is greater than the maximum number of BootP/DHCP
hops allows by the router. By default, a Brocade Layer 3 switch forwards a BootP/DHCP request if its hop count is four or less,
but discards the request if the hop count is greater than four. You can change the maximum number of hops the Layer 3 switch
will allow to a value from 1 through 15.
NOTE
The BootP/DHCP hop count is not the TTL parameter.

Configuring an IP helper address

The procedure for configuring a helper address for BootP/DHCP requests is the same as the procedure for configuring a helper address
for other types of UDP broadcasts. Refer to
Configuring the BOOTP and DHCP reply source address
You can configure the Brocade device so that a BOOTP/DHCP reply to a client contains the server IP address as the source address
instead of the router IP address. To do so, enter the following command at the Global CONFIG level of the CLI.
device(config)# ip helper-use-responder-ip
Syntax: [no] ip helper-use-responder-ip
Changing the IP address used for stamping BootP and DHCP requests
When the Layer 3 switch forwards a BootP/DHCP request, the Layer 3 switch "stamps" the Gateway Address field. The default value the
Layer 3 switch uses to stamp the packet is the lowest-numbered IP address configured on the interface that received the request. If you
want the Layer 3 switch to use a different IP address to stamp requests received on the interface, use either of the following methods to
specify the address.
The BootP/DHCP stamp address is an interface parameter. Change the parameter on the interface that is connected to the BootP/
DHCP client.
FastIron Ethernet Switch Layer 3 Routing
53-1003627-04
Configuring an IP helper address
Configuring IP parameters - Layer 3 switches
on page 82.
83