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| Proxy ARP | |
|---|---|
| Name | Proxy ARP |
| Type | Networking technique |
| Introduced | 1980s |
| Protocol | ARP |
| Usage | Legacy routing, NAT scenarios |
Proxy ARP Proxy ARP is a network technique that allows a router or host to answer Address Resolution Protocol requests on behalf of another node, enabling interoperability between disparate Internet Protocol subnets, legacy LAN segments, and certain Virtual Private Network topologies. Developed contemporaneously with early TCP/IP deployments during the 1980s, Proxy ARP has been discussed in standards and operational documents by organizations such as the Internet Engineering Task Force, used in implementations from vendors like Cisco Systems, and referenced in academic work from institutions including Massachusetts Institute of Technology and Stanford University.
Proxy ARP operates within the suite of protocols surrounding IPv4 and interacts with mechanisms defined in Address Resolution Protocol specifications and related Request for Comments documents from the Internet Engineering Task Force. Historically it facilitated connectivity across heterogeneous media such as Ethernet, Token Ring, and early FDDI deployments when routing or tunneling options from vendors like Juniper Networks or Hewlett-Packard were limited. Network operators at enterprises like IBM and universities such as University of California, Berkeley used Proxy ARP alongside tools from projects like BSD and Linux to enable host-to-host reachability without reconfiguring client stacks.
When a client sends an ARP request for a target IP, a device performing Proxy ARP inspects its routing table, neighbor cache, or Network Address Translation mappings and replies with its own MAC address, appearing to be the target to the requester. This behavior relies on interaction with Internet Protocol Version 4 addressing, ARP packet format, and link-layer characteristics of technologies such as IEEE 802.3 and IEEE 802.11. Implementations consult forwarding tables similar to those in routers from Cisco Systems, Juniper Networks, or software routers like Quagga and Bird, and may be influenced by control-plane components from platforms like OpenStack, VMware ESXi, and Kubernetes network plugins.
Proxy ARP has been employed to support scenarios such as host mobility in environments managed by systems like Mobile IP pilots, multi-homed hosts in deployments by organizations such as AT&T and Verizon Business, and simplified traffic engineering for Network Address Translation use in consumer devices from vendors like Netgear and Linksys. It can enable transparent bridging for virtual machine migrations in platforms such as Xen and KVM, and facilitate address conservation strategies used in some legacy Internet Service Provider configurations. Network designers referencing guidance from entities like the Internet Engineering Task Force and textbooks from authors affiliated with Princeton University and Carnegie Mellon University have noted operational simplicity as a benefit in constrained scenarios.
Proxy ARP can introduce security and scalability concerns when compared to routing, tunneling, or modern overlay solutions promoted by companies like Google and Amazon Web Services. It may complicate access control schemes employed by devices from Fortinet and Palo Alto Networks, interfere with authentication systems in deployments by Cisco Systems and Juniper Networks, and be susceptible to malicious ARP spoofing techniques analyzed in research from institutions such as ETH Zurich and University of Cambridge. Operational limits include increased ARP traffic on segments like those found in carrier networks operated by Deutsche Telekom and NTT, and management challenges in large-scale data centers designed by teams from Facebook and Microsoft Azure.
Configuration of Proxy ARP appears in operating systems and network products including Linux, FreeBSD, OpenBSD, and commercial routers from Cisco Systems and Juniper Networks, typically via system sysctl parameters, interface commands, or neighbor proxy tables. Instructions and best practices are found in vendor documentation from Cisco Systems, examples in community resources maintained by groups such as IETF and USENIX, and operational discussions in forums tied to projects like Netfilter and iptables. Administrators at enterprises like Goldman Sachs and research labs at Lawrence Berkeley National Laboratory often disable Proxy ARP in favor of explicit routing and ARP filtering to maintain predictable behavior.
Alternatives and related techniques include classical IPv4 routing, Network Address Translation, overlay networking solutions advocated by Cloudflare and HashiCorp, tunneling protocols such as GRE and IPsec, and virtual networking abstractions found in Open vSwitch and VXLAN implementations from vendors like Arista Networks. Other related protocols and concepts with overlapping use cases include Neighbor Discovery Protocol for IPv6, link-layer discovery protocols used in equipment by Dell EMC and HPE, and service-oriented solutions in platforms developed by Red Hat and Canonical.
Category:Internet protocols