# Address Resolution Protocol

### From Wikipedia, the free encyclopedia.

Internet protocol suite edit (http://en.wikipedia.org/w/index.php?title=Template:IPstack&action=edit)
Application layer | HTTP, SMTP, FTP, SSH, IRC, SNMP, SIP, RTP, ...
Transport layer | TCP, UDP, ICMP, SCTP, DCCP, ...
Network layer | IPv4, IPv6, ARP, ...
Data link layer | Ethernet, Wi-Fi, Token ring, FDDI, ...
Physical layer | RS-232, RS-449, ...

In computer networking using the internet protocol suite, the Address Resolution Protocol is a method for finding a host's Ethernet (MAC) address from its IP address. The sender broadcasts an ARP packet containing the Internet address of another host and waits for it (or some other host) to send back its Ethernet address. Each host maintains a cache of address translations to reduce delay and loading. ARP allows the Internet address to be independent of the Ethernet address but it only works if all hosts support it.

ARP is defined in RFC 826 (http://www.ietf.org/rfc/rfc826.txt).

The alternative for hosts that do not do ARP is to use a pre-configured mapping of IP addresses to MAC addresses.

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## Variants of the ARP protocol

ARP was not originally designed as an IP-only protocol, even though it is in practice used almost exclusively to resolve IP addresses to MAC addresses.

ARP can be used to resolve MAC addresses for many different Layer 3 protocols. ARP has also been adapted to resolve other kinds of Layer 2 addresses: for example, ATMARP is used to resolve ATM NSAP addresses in the Classical IP over ATM protocol.

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## See also

- proxy ARP
- reverse ARP
- serial line ARP
- Zeroconf
- ARP spoofing

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## External links

- RFC 826 (http://www.ietf.org/rfc/rfc0826.txt?number=826)
- ARP Sequence Diagram (http://www.eventhelix.com/RealtimeMantra/Networking/Arp.pdf)

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.

Retrieved from "http://en.wikipedia.org/wiki/Address_Resolution_Protocol"

Categories: Internet protocols | Internet standards

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