RFC 2390 (rfc2390) - Page 2 of 10
Inverse Address Resolution Protocol
Alternative Format: Original Text Document
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