Configuration Guide User guide

1012 FastIron Configuration Guide
53-1002494-02
Configuring IP parameters – Layer 3 Switches
• 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
an IP helper address” on page 1011.
Configuring the BOOTP and DHCP reply source address
NOTE
This feature is supported on FastIron X Series and Brocade FCX Series devices. This feature is not
supported on FastIron WS devices.
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.
Brocade(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.
To change the IP address used for stamping BootP/DHCP requests received on interface 1/1, enter
commands such as the following.