RFC 2390 (rfc2390) - Page 2 of 10

Inverse Address Resolution Protocol

RFC 2390          Inverse Address Resolution Protocol     September 1998


4.  Introduction

   This document will rely heavily on Frame Relay as an example of how
   the Inverse Address Resolution Protocol (InARP) can be useful. It is
   not, however, intended that InARP be used exclusively with Frame
   Relay.  InARP may be used in any network that provides destination
   hardware addresses without indicating corresponding protocol
   addresses.

5.  Motivation

   The motivation for the development of Inverse ARP is a result of the
   desire to make dynamic address resolution within Frame Relay both
   possible and efficient.  Permanent virtual circuits (PVCs) and
   eventually switched virtual circuits (SVCs) are identified by a Data
   Link Connection Identifier (DLCI).  These DLCIs define a single
   virtual connection through the wide area network (WAN) and may be
   thought of as the Frame Relay equivalent to a hardware address.
   Periodically, through the exchange of signaling messages, a network
   may announce a new virtual circuit with its corresponding DLCI.
   Unfortunately, protocol addressing is not included in the
   announcement.  The station receiving such an indication will learn of
   the new connection, but will not be able to address the other side.
   Without a new configuration or a mechanism for discovering the
   protocol address of the other side, this new virtual circuit is
   unusable.

   Other resolution methods were considered to solve the problems, but
   were rejected.  Reverse ARP [4], for example, seemed like a good
   candidate, but the response to a request is the protocol address of
   the requesting station, not the station receiving the request.  IP
   specific mechanisms were limiting since they would not allow
   resolution of other protocols other than IP. For this reason, the ARP
   protocol was expanded.

   Inverse Address Resolution Protocol (InARP) will allow a Frame Relay
   station to discover the protocol address of a station associated with
   the virtual circuit.  It is more efficient than sending ARP messages
   on every VC for every address the system wants to resolve and it is
   more flexible than relying on static configuration.











Bradley, et. al.            Standards Track