IPv6 over Non-Broadcast Multiple Access (NBMA) networks
RFC 2491

Document Type RFC - Proposed Standard (January 1999; No errata)
Updated by RFC 8064
Last updated 2013-03-02
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Network Working Group                                       G. Armitage
Request for Comments: 2491                          Lucent Technologies
Category: Standards Track                                   P. Schulter
                                              Bright Tiger Technologies
                                                                M. Jork
                                                 Digital Equipment GmbH
                                                              G. Harter
                                                                 Compaq
                                                           January 1999

        IPv6 over Non-Broadcast Multiple Access (NBMA) networks

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 (1999).  All Rights Reserved.

Abstract

   This document describes a general architecture for IPv6 over NBMA
   networks. It forms the basis for subsidiary companion documents that
   describe details for various specific NBMA technologies (such as ATM
   or Frame Relay). The IPv6 over NBMA architecture allows conventional
   host-side operation of the IPv6 Neighbor Discovery protocol, while
   also supporting the establishment of 'shortcut' NBMA forwarding paths
   when dynamically signaled NBMA links are available. Operations over
   administratively configured Point to Point NBMA links are also
   described.

   Dynamic NBMA shortcuts are achieved through the use of IPv6 Neighbor
   Discovery protocol operation within Logical Links, and inter-router
   NHRP for the discovery of off-Link NBMA destinations. Both flow-
   triggered and explicitly source-triggered shortcuts are supported.

1. Introduction.

   Non Broadcast Multiple Access (NBMA) networks may be utilized in a
   variety of ways. At one extreme, they can be used to simply provide
   administratively configurable point to point service, sufficient to
   interconnect IPv6 routers (and even IPv6 hosts, in certain

Armitage, et. al.           Standards Track                     [Page 1]
RFC 2491                IPv6 over NBMA networks             January 1999

   situations). At the other extreme, NBMA networks that support dynamic
   establishment and teardown of Virtual Circuits (or functional
   equivalents) may be used to emulate the service provided to the IPv6
   layer by conventional broadcast media such as Ethernet.  Typically
   this emulation requires complex convergence protocols, particularly
   to support IPv6 multicast.

   This document describes a general architecture for IPv6 over NBMA
   networks. It forms the basis for companion documents that provide
   details specific to various NBMA technologies (for example, ATM [17]
   or Frame Relay). The IPv6 over NBMA architecture allows conventional
   host-side operation of the IPv6 Neighbor Discovery protocol, while
   also supporting the establishment of 'shortcut' NBMA forwarding paths
   (when dynamically signaled NBMA links are available).

   The majority of this document focuses on the use of dynamically
   managed point to point and point to multipoint calls between
   interfaces on an NBMA network. These will be generically referred to
   as "SVCs" in the rest of the document. The use of administratively
   configured point to point calls will also be discussed. Such calls
   will be generically referred to as "PVCs". Depending on context,
   either may be shortened to "VC".

   Certain NBMA networks may provide a form of connectionless service
   (e.g. SMDS). In these cases, a "call" or "VC" shall be considered to
   implicitly exist if the sender has an NBMA destination address to
   which it can transmit packets whenever it desires.

1.1 Neighbor Discovery.

   A key difference between this architecture and previous IP over NBMA
   protocols is its mechanism for supporting IPv6 Neighbor Discovery.

   The IPv4 world evolved an approach to address resolution that
   depended on the operation of an auxiliary protocol operating at the
   'link layer' - starting with Ethernet ARP (RFC 826 [14]). In the
   world of NBMA (Non Broadcast, Multiple Access) networks ARP has been
   applied to IPv4 over SMDS (RFC 1209 [13]) and IPv4 over ATM (RFC 1577
   [3]). More recently the ION working group has developed NHRP (Next
   Hop Resolution Protocol [8]), a general protocol for performing
   intra-subnet and inter-subnet address resolution applicable to a
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