RFC 1868 (rfc1868) - Page 1 of 4

ARP Extension - UNARP

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Network Working Group                                          G. Malkin
Request For Comments: 1868                                Xylogics, Inc.
Category: Experimental                                     November 1995

                         ARP Extension - UNARP

Status of this Memo

   This memo defines an Experimental Protocol for the Internet
   community.  This memo does not specify an Internet standard of any
   kind.  Discussion and suggestions for improvement are requested.
   Distribution of this memo is unlimited.


   The Address Resolution Protocol allows an IP node to determine the
   hardware (datalink) address of a neighboring node on a broadcast
   network.  The protocol depends on timers to age away old ARP entries.
   This document specifies a trivial modification to the ARP mechanism,
   not the packet format, which allows a node to announce that it is
   leaving the network and that all other nodes should modify their ARP
   tables accordingly.


   Thanks to James Carlson/Xylogics for reviewing this document and
   proposing the backwards compatibility mechanism.

1. Introduction

   The primary purpose of the Address Resolution Protocol, as defined in
   [1], is to determine a node's hardware address based on its network
   address (protocol address in ARPspeak).  The ARP protocol
   specifically states that nodes should not periodically advertise
   their existence for two reasons: first, this would generate a lot of
   network traffic and table maintenance overhead; second, it is highly
   unlikely that all nodes will need to communicate to all other nodes.
   Since a node does not advertise its existence, neither does it
   advertise its imminent departure.  This is not a serious problem
   since most ARP implementations maintain timers to age away old
   entries, and departing nodes seldom depart gracefully in any case.

   Over time, an additional use has been found for ARP: Proxy ARP.
   While there are those who believe Proxy ARP is an evil thing, it does
   serve a purpose; that is, it allows for communication in ways never
   considered in the original IP architecture.  For example, allows
   dial-in hosts to connect to a network without consuming a large

Malkin                        Experimental

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