Proxy ARP
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Proxy ARP is a technique for using the ARP protocol to provide an ad hoc routing mechanism.
A multi-port networking device (e.g. a router) implementing Proxy ARP will respond to ARP requests on one interface as being responsible for addresses of device addresses on another interface. The device can then receive and forward packets addressed to the other devices.
The advantage of Proxy ARP over other networking schemes is simplicity. A network can be extended using this technique without the knowledge of the upstream router.
As an example, a host A that it wants to contact a B host on an other sottorete will make one demanded ARP for IP address of B; the router it will answer indicating just the MAC address; A it will send the packages to the router, thinking to send them directly to B. the router will forward normally the packages to B. naturally will have to be convinced that B is found on its same one sottorete.
Disadvantages include scalability (ARP resolution is required for every device routed in this manner) and reliability (no fallback mechanism is present, and the masquerading can be confusing in some environments).