Brocade Virtual ADX Switch and Router Guide (Supporting ADX v03.1.00) - Manual (Page 98)

84 Brocade Virtual ADX Switch and Router Guide
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Configuring IP parameters
4
BootP/DHCP forwarding parameters
The following parameters control the forwarding of BootP/DHCP requests for a Virtual ADX:
• Helper address – The BootP/DHCP server’s IP address. You must configure the helper address
on the interface that receives the BootP/DHCP requests from the client. The Virtual ADX
cannot forward a request to the server unless you configure a helper address for the server.
• Gateway address – The Virtual ADX places the IP address of the interface that received the
BootP/DHCP request in the request packet’s 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 Virtual ADX 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 Virtual ADX 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 Virtual ADX 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 Virtual ADX will allow to a value from 1 – 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 83.
Changing the IP address used for stamping BootP/DHCP requests
When the Virtual ADX forwards a BootP/DHCP request, the Virtual ADX “stamps” the Gateway
Address field. The default value the Virtual ADX uses to stamp the packet is the lowest-numbered
IP address configured on the interface that received the request. If you want the Virtual ADX 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.
Virtual ADX(config)# int e 1
Virtual ADX(config-if-1)# ip bootp-gateway 10.157.22.26
These commands change the CLI to the configuration level for port 1/1, then change the
BootP/DHCP stamp address for requests received on port 1/1 to 10.157.22.26. The Layer 3 Switch
will place this IP address in the Gateway Address field of BootP/DHCP requests that the Virtual ADX
receives on port 1/1 and forwards to the BootP/DHCP server.