on the 10.0.0.2 interface (although many operating systems allow direct allocation of multiple addresses to one interface, thus eliminating the need for such workarounds). On a firewall In this scenario a firewall can be configured with a single IP address. One simple example of a use for this would be placing a firewall in front of a single host or group of hosts on a subnetwork. Example: A network (10.0.0.0/8) has a server (10.0.0.20) that should be protected. A proxy ARP firewall can be placed in front of the server. In this way the server is put behind a firewall without having to make any further changes to the network. Mobile-IP In case of Mobile-IP the Home Agent uses proxy ARP in order to receive messages on behalf of the Mobile Node so that it can forward the appropriate message to the actual mobile node's address (Care-of address). Transparent subnet gatewaying A setup that involves two physical segments sharing the same IP subnet and connected together via a router. This use is documented in RFC 1027. Redundancy ARP manipulation techniques are the basis for protocols providing redundancy on broadcast networks (e.g., Ethernet), 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 (as it gives its own MAC address in response to ARP requests for other hosts/routers), 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 OpenBSD implements proxy ARP. Linux implements proxy ARP. References Further reading W. Richard Stevens. The Protocols (TCP/IP Illustrated, Volume 1). Addison-Wesley Professional; 1st edition (December 31, 1993). Internet protocols Internet Standards de:Address Resolution Protocol#Proxy ARP