Intel 480T, User Manual

Page: 171 / 367

C H A P T E R 1 0 IP Unicast Routing
169
Proxy ARP
Proxy Address Resolution Protocol (ARP) was first invented so that
ARP-capable devices could respond to ARP Request packets on
behalf of ARP-incapable devices. Proxy ARP can also be used to
achieve router redundancy and simplify IP client configuration. The
switch supports proxy ARP for this type of network configuration.
The section describes some example of how to use proxy ARP with
the switch.
ARP-Incapable Devices
To configure the switch to respond to ARP Requests on behalf of
devices that are incapable of doing so, you must configure the IP
address and MAC address of the ARP-incapable device using the
use the following command:
config iparp add proxy <ipaddress> {<mask>}
<mac_address> {always}
Once configured, the system responds to ARP Requests on behalf
of the device as long as the following conditions are satisfied:
• The valid IP ARP Request is received on a router interface.
• The target IP address matches the IP address configured in the
proxy ARP table.
• The proxy ARP table entry indicates that the system always
answers this ARP Request, regardless of the ingress VLAN (the
always
parameter must be applied).
Once all the proxy ARP conditions are met, the switch formulates
an ARP response using the configured MAC address in the packet.
Proxy ARP Between Subnets
In some networks, it is desirable to configure the IP host with a
wider subnet than the actual subnet mask of the segment. Proxy
ARP can be used so that the router answers ARP Requests for
devices outside of the subnet. As a result, the host communicates as
if all devices are local. In reality, communication with devices
outside of the subnet are proxied by the router.