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. You can use proxy ARP 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 and a mask of The switch is configured with the IP address and a mask of The switch is also configured with a proxy ARP entry of IP address and mask, without the always parameter.

When the IP host tries to communicate with the host at address, the IP host 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, using its own MAC address. All subsequent data packets from are sent to the switch, and the switch routes the packets to