Allied Telesis AT-8550 - Manual (Page 134)

Proxy ARP
8-6
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.
For example, an IP host is configured with a class B address of
100.101.102.103 and a mask of 255.255.0.0. The switch is configured
with the IP address 100.101.102.1 and a mask of 255.255.255.0. The
switch is also configured with a proxy ARP entry of IP address
100.101.0.0 and mask 255.255.0.0, without the
always parameter.
When the IP host tries to communicate with the host at address
100.101.45.67, the IP hosts communicates as if the two hosts are on
the same subnet, and sends out an IP ARP Request. The switch
answers on behalf of the device at address 100.101.45.67, using its
own MAC address. All subsequent data packets from
100.101.102.103 are sent to the switch, and the switch routes the
packets to 100.101.45.67.