Sometimes called promiscuous ARP and described in RFCs 925 and 1027, proxy ARP is a method by
which routers may make themselves available to hosts. For example, a host 192.168.12.5/24 needs to
send a packet to 192.168.20.101/24, but it is not configured with default gateway information and
therefore does not know how to reach a router. It may issue an ARP Request for 192.168.20.101; the local
router, receiving the request and knowing how to reach network 192.168.20.0, will issue an ARP Reply
with its own data link identifier in the hardware address field. In effect, the router has tricked the local
host into thinking that the router's interface is the interface of 192.168.20.101. All packets destined for
that address will be sent to the router.