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Main article: "ARP spoofing
Proxy ARP

Because ARP does not provide methods for authenticating ARP replies on a network, ARP replies can come from systems other than the one with the required Layer 2 address. An ARP proxy is a system which answers the ARP request on behalf of another system for which it will forward traffic, normally as a part of the network's design, such as for a dialup internet service. By contrast, in ARP spoofing the answering system, or spoofer, replies to a request for another system's address with the aim of intercepting data bound for that system. A malicious user may use ARP spoofing to perform a "man-in-the-middle or "denial-of-service attack on other users on the network. Various software exists to both detect and perform ARP spoofing attacks, though ARP itself does not provide any methods of protection from such attacks.[19]

Alternatives to ARP[edit]

Each computer maintains its own table of the mapping from "Layer 3 addresses (e.g. "IP addresses) to "Layer 2 addresses (e.g. "ethernet "MAC addresses). In a modern computer this is maintained almost entirely by ARP packets on the local network and is thus often called the 'ARP cache' as opposed to 'Layer 2 address table'. In older computers, where broadcast packets were considered an expensive resource, other methods were used to maintain this table, such as static configuration files,[20] or centrally maintained lists.

Since at least the 1980s,[21] networked computers have had a command called 'arp' for interrogating or manipulating this table, and practically all modern personal operating systems have a variant of this.[22][23][24]

ARP stuffing[edit]

Embedded systems such as networked cameras[25] and networked power distribution devices,[26] which lack a user interface, can use so-called ARP stuffing to make an initial network connection, although this is a misnomer, as ARP is not involved.

This is a solution to an issue in network management of consumer devices, specifically the allocation of IP addresses of ethernet devices where:

  1. the user doesn't have the ability to control "DHCP or similar address allocation protocols
  2. the device doesn't have a user interface to configure it with
  3. the user's computer can't communicate with it because it has no suitable IP address.

The solution adopted is as follows:

Such devices typically have a method to disable this process once the device is operating normally, as it is vulnerable to attack.

Standard documents[edit]

See also[edit]


  1. ^ David C. Plummer (November 1982). "RFC 826, An Ethernet Address Resolution Protocol -- or -- Converting Network Protocol Addresses to 48.bit Ethernet Address for Transmission on Ethernet Hardware". Internet Engineering Task Force, Network Working Group. 
  2. ^ Braden, R. (October 1989). "RFC 1122 - Requirements for Internet Hosts -- Communication Layers". Internet Engineering Task Force. 
  3. ^ IANA ARP - "Protocol Type"
  4. ^ IANA - Ethertype values
  5. ^ "RFC 5342
  6. ^ "IANA ARP parameter assignments". "IANA. 2009-04-24. 
  7. ^ Chappell, Laura A. and Tittel, Ed. Guide to TCP/IP, Third Edition. Thomson Course Technology, 2007, pp. 115-116.
  8. ^ Cheshire, S. (July 2008). "RFC 5227 - IPv4 Address Conflict Detection". Internet Engineering Task Force. 
  9. ^ Perkins, C. (November 2010). "RFC 5944 - IP Mobility Support for IPv4, Revised". Internet Engineering Task Force. A gratuitous ARP MAY use either an ARP Request or an ARP Reply packet. [...] any node receiving any ARP packet (Request or Reply) MUST update its local ARP cache with the Sender Protocol and Hardware Addresses in the ARP packet [...] 
  10. ^ Perkins, C. (October 1996). "RFC 2002 - IP Mobility Support". Internet Engineering Task Force. 
  11. ^ Cheshire, S. (July 2008). "RFC 5227 - IPv4 Address Conflict Detection". Internet Engineering Task Force. Why Are ARP Announcements Performed Using ARP Request Packets and Not ARP Reply Packets? 
  12. ^ "FAQ: The Firewall Does not Update the Address Resolution Protocol Table". "Citrix. 2015-01-16. [...] garpReply enabled [...] generates ARP packets that [...] are of OPCODE type REPLY, rather than REQUEST. 
  13. ^ Gratuitous ARP in DHCP vs. IPv4 ACD Draft Archived October 12, 2007, at the "Wayback Machine.
  14. ^ RFC 2002 Section 4.6
  15. ^ RFC 2131 DHCP – Last lines of Section 4.4.1
  16. ^ Shah, H.; et al. (June 2012). "RFC 6575 Address Resolution Protocol (ARP) Mediation for IP Interworking of Layer 2 VPNs". Internet Engineering Task Force. 
  17. ^ T. Bradley; et al. (September 1998). "RFC 2390 - Inverse Address Resolution Protocol". Internet Engineering Task Force. 
  18. ^ Finlayson, Mann, Mogul, Theimer (June 1984). "RFC 903 - A Reverse Address Resolution Protocol". Internet Engineering Task Force. 
  19. ^ Steve Gibson (2005-12-11). "ARP Cache Poisoning". "GRC. 
  20. ^ Sun Microsystems. "SunOS manual page for ethers(5) file". Retrieved 2011-09-28. 
  21. ^ University of California, Berkeley. "BSD manual page for arp(8C) command". Retrieved 2011-09-28. 
  22. ^ Canonical. "Ubuntu manual page for arp(8) command". Retrieved 2011-09-28. 
  23. ^ Apple Computer. "Mac OS X manual page for arp(8) command". Retrieved 2011-09-28. 
  24. ^ Microsoft. "Windows help for arp command". Retrieved 2011-09-28. 
  25. ^ Axis Communication. "Axis P13 Network Camera Series Installation Guide" (PDF). Retrieved 2011-09-28. 
  26. ^ American Power Corporation. "Switched Rack Power Distribution Unit Installation and Quick Start Manual" (PDF). Retrieved 2011-09-28. 

This article is based on material taken from the "Free On-line Dictionary of Computing prior to 1 November 2008 and incorporated under the "relicensing" terms of the "GFDL, version 1.3 or later.

External links[edit]

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