RFC 1868 (rfc1868) - Page 1 of 4
ARP Extension - UNARP
Alternative Format: Original Text Document
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.
Abstract
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.
Acknowledgements
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