Proxy ARP


Proxy ARP is a technique by which a proxy device on a given network answers the ARP queries for an IP address that is not on that network. The proxy is aware of the location of the traffic's destination, and offers its own MAC address as the destination. The traffic directed to the proxy address is then typically routed by the proxy to the intended destination via another interface or via a tunnel.
The process, which results in the node responding with its own MAC address to an ARP request for a different IP address for proxying purposes, is sometimes referred to as publishing.

Uses

Below are some typical uses for proxy ARP:
;Joining a broadcast LAN with serial links.
;Taking multiple addresses from a LAN
;On a firewall
;Mobile-IP
;Transparent subnet gatewaying
;Redundancy
ARP manipulation techniques are the basis for protocols providing redundancy on broadcast networks, most notably Common Address Redundancy Protocol and Virtual Router Redundancy Protocol.

Disadvantages

Disadvantage of Proxy ARP include scalability as ARP resolution by a proxy is required for every device routed in this manner, and reliability as no fallback mechanism is present, and masquerading can be confusing in some environments.
Proxy ARP can create DoS attacks on networks if misconfigured. For example, a misconfigured router with proxy ARP has the ability to receive packets destined for other hosts, but may not have the ability to correctly forward these packets on to their final destination, thus blackholing the traffic.
Proxy ARP can hide device misconfigurations, such as a missing or incorrect default gateway.

Implementations

implements Proxy ARP.