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NBMA Next Hop Resolution Protocol (NHRP)
RFC 2332

Document type: RFC - Proposed Standard (April 1998; No errata)
Document stream: IETF
Last updated: 2013-03-02
Other versions: plain text, pdf, html

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IESG State: RFC 2332 (Proposed Standard)
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Network Working Group                                         J. Luciani
Request for Comments: 2332                                  Bay Networks
Category: Standards Track                                        D. Katz
                                                           cisco Systems
                                                           D. Piscitello
                                                   Core Competence, Inc.
                                                                 B. Cole
                                                        Juniper Networks
                                                            N. Doraswamy
                                                            Bay Networks
                                                              April 1998

                NBMA Next Hop Resolution Protocol (NHRP)

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

Abstract

   This document describes the NBMA Next Hop Resolution Protocol (NHRP).
   NHRP can be used by a source station (host or router) connected to a
   Non-Broadcast, Multi-Access (NBMA) subnetwork to determine the
   internetworking layer address and NBMA subnetwork addresses of the
   "NBMA next hop" towards a destination station.  If the destination is
   connected to the NBMA subnetwork, then the NBMA next hop is the
   destination station itself.  Otherwise, the NBMA next hop is the
   egress router from the NBMA subnetwork that is "nearest" to the
   destination station.  NHRP is intended for use in a multiprotocol
   internetworking layer environment over NBMA subnetworks.

   Note that while this protocol was developed for use with NBMA
   subnetworks, it is possible, if not likely, that it will be applied
   to BMA subnetworks as well.  However, this usage of NHRP is for
   further study.

   This document is intended to be a functional superset of the NBMA
   Address Resolution Protocol (NARP) documented in [1].

Luciani, et. al.            Standards Track                     [Page 1]
RFC 2332                       NBMA NHRP                      April 1998

   Operation of NHRP as a means of establishing a transit path across an
   NBMA subnetwork between two routers will be addressed in a separate
   document (see [13]).

1. Introduction

   The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
   SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
   document, are to be interpreted as described in [15].

   The NBMA Next Hop Resolution Protocol (NHRP) allows a source station
   (a host or router), wishing to communicate over a Non-Broadcast,
   Multi-Access (NBMA) subnetwork, to determine the internetworking
   layer addresses and NBMA addresses of suitable "NBMA next hops"
   toward a destination station.  A subnetwork can be non-broadcast
   either because it technically doesn't support broadcasting (e.g., an
   X.25 subnetwork) or because broadcasting is not feasible for one
   reason or another (e.g., an SMDS multicast group or an extended
   Ethernet would be too large).  If the destination is connected to the
   NBMA subnetwork, then the NBMA next hop is the destination station
   itself.  Otherwise, the NBMA next hop is the egress router from the
   NBMA subnetwork that is "nearest" to the destination station.

   One way to model an NBMA network is by using the notion of logically
   independent IP subnets (LISs). LISs, as defined in [3] and [4], have
   the following properties:

      1)  All members of a LIS have the same IP network/subnet number
          and address mask.

      2)  All members of a LIS are directly connected to the same
          NBMA subnetwork.

      3)  All hosts and routers outside of the LIS are accessed via
          a router.

      4)  All members of a LIS access each other directly (without
          routers).

   Address resolution as described in [3] and [4] only resolves the next
   hop address if the destination station is a member of the same LIS as
   the source station; otherwise, the source station must forward
   packets to a router that is a member of multiple LIS's.  In multi-LIS

Luciani, et. al.            Standards Track                     [Page 2]
RFC 2332                       NBMA NHRP                      April 1998

   configurations, hop-by-hop address resolution may not be sufficient

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