rfc1971.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

Network Working Group                                         S. Thomson
Request for Comments: 1971                                      Bellcore
Category: Standards Track                                      T. Narten
                                                                     IBM
                                                             August 1996


                IPv6 Stateless Address Autoconfiguration

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.

Abstract

   This document specifies the steps a host takes in deciding how to
   autoconfigure its interfaces in IP version 6. The autoconfiguration
   process includes creating a link-local address and verifying its
   uniqueness on a link, determining what information should be
   autoconfigured (addresses, other information, or both), and in the
   case of addresses, whether they should be obtained through the
   stateless mechanism, the stateful mechanism, or both.  This document
   defines the process for generating a link-local address, the process
   for generating site-local and global addresses via stateless address
   autoconfiguration, and the Duplicate Address Detection procedure. The
   details of autoconfiguration using the stateful protocol are
   specified elsewhere.

Table of Contents

   1.  INTRODUCTION.............................................    2
   2.  TERMINOLOGY..............................................    4
      2.1.  Requirements........................................    7
   3.  DESIGN GOALS.............................................    8
   4.  PROTOCOL OVERVIEW........................................    9
      4.1.  Site Renumbering....................................   11
   5.  PROTOCOL SPECIFICATION...................................   11
      5.1.  Node Configuration Variables........................   12
      5.2.  Autoconfiguration-Related Variables.................   12
      5.3.  Creation of Link-Local Addresses....................   13
      5.4.  Duplicate Address Detection.........................   13
         5.4.1.  Message Validation.............................   15
         5.4.2.  Sending Neighbor Solicitation Messages.........   15
         5.4.3.  Receiving Neighbor Solicitation Messages.......   15



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RFC 1971       IPv6 Stateless Address Autoconfiguration      August 1996


         5.4.4.  Receiving Neighbor Advertisement Messages......   16
         5.4.5.  When Duplicate Address Detection Fails.........   16
      5.5.  Creation of Global and Site-Local Addresses.........   17
         5.5.1.  Soliciting Router Advertisements...............   17
         5.5.2.  Absence of Router Advertisements...............   17
         5.5.3.  Router Advertisement Processing................   17
         5.5.4.  Address Lifetime Expiry........................   19
      5.6.  Configuration Consistency...........................   19
   SECURITY CONSIDERATIONS......................................   19
   REFERENCES...................................................   20
   AUTHORS' ADDRESSES...........................................   21
   APPENDIX: LOOPBACK SUPPRESSION & DUPLICATE ADDRESS DETECTION.   22

1.  INTRODUCTION

   This document specifies the steps a host takes in deciding how to
   autoconfigure its interfaces in IP version 6. The autoconfiguration
   process includes creating a link-local address and verifying its
   uniqueness on a link, determining what information should be
   autoconfigured (addresses, other information, or both), and in the
   case of addresses, whether they should be obtained through the
   stateless mechanism, the stateful mechanism, or both.  This document
   defines the process for generating a link-local address, the process
   for generating site-local and global addresses via stateless address
   autoconfiguration, and the Duplicate Address Detection procedure. The
   details of autoconfiguration using the stateful protocol are
   specified elsewhere.

   IPv6 defines both a stateful and stateless address autoconfiguration
   mechanism. Stateless autoconfiguration requires no manual
   configuration of hosts, minimal (if any) configuration of routers,
   and no additional servers.  The stateless mechanism allows a host to
   generate its own addresses using a combination of locally available
   information and information advertised by routers. Routers advertise
   prefixes that identify the subnet(s) associated with a link, while
   hosts generate an "interface token" that uniquely identifies an
   interface on a subnet. An address is formed by combining the two. In
   the absence of routers, a host can only generate link-local
   addresses. However, link-local addresses are sufficient for allowing
   communication among nodes attached to the same link.

   In the stateful autoconfiguration model, hosts obtain interface
   addresses and/or configuration information and parameters from a
   server.  Servers maintain a database that keeps track of which
   addresses have been assigned to which hosts. The stateful
   autoconfiguration protocol allows hosts to obtain addresses, other
   configuration information or both from a server.  Stateless and
   stateful autoconfiguration complement each other. For example, a host



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   can use stateless autoconfiguration to configure its own addresses,
   but use stateful autoconfiguration to obtain other information.
   Stateful autoconfiguration is described in [DHCPv6].

   The stateless approach is used when a site is not particularly
   concerned with the exact addresses hosts use, so long as they are
   unique and properly routable. The stateful approach is used when a
   site requires tighter control over exact address assignments.  Both
   stateful and stateless address autoconfiguration may be used
   simultaneously.  The site administrator specifies which type of
   autoconfiguration to use through the setting of appropriate fields in
   Router Advertisement messages [DISCOVERY].

   IPv6 addresses are leased to an interface for a fixed (possibly
   infinite) length of time. Each address has an associated lifetime
   that indicates how long the address is bound to an interface. When a
   lifetime expires, the binding (and address) become invalid and the
   address may be reassigned to another interface elsewhere in the
   Internet. To handle the expiration of address bindings gracefully, an
   address goes through two distinct phases while assigned to an
   interface. Initially, an address is "preferred", meaning that its use
   in arbitrary communication is unrestricted. Later, an address becomes
   "deprecated" in anticipation that its current interface binding will
   become invalid. While in a deprecated state, the use of an address is
   discouraged, but not strictly forbidden.  New communication (e.g.,
   the opening of a new TCP connection) should use a preferred address
   when possible.  A deprecated address should be used only by
   applications that have been using it and would have difficulty
   switching to another address without a service disruption.

   To insure that all configured addresses are likely to be unique on a
   given link, nodes run a "duplicate address detection" algorithm on
   addresses before assigning them to an interface.  The Duplicate
   Address Detection algorithm is performed on all addresses,
   independent of whether they are obtained via stateless or stateful
   autoconfiguration.  This document defines the Duplicate Address
   Detection algorithm.

   The autoconfiguration process specified in this document applies only
   to hosts and not routers. Since host autoconfiguration uses
   information advertised by routers, routers will need to be configured
   by some other means. However, it is expected that routers will
   generate link-local addresses using the mechanism described in this
   document. In addition, routers are expected to successfully pass the
   Duplicate Address Detection procedure described in this document on
   all addresses prior to assigning them to an interface.





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   Section 2 provides definitions for terminology used throughout this
   document. Section 3 describes the design goals that lead to the
   current autoconfiguration procedure. Section 4 provides an overview
   of the protocol, while Section 5 describes the protocol in detail.

2.  TERMINOLOGY

   IP          - Internet Protocol Version 6.  The terms IPv4 and IPv6
                 are used only in contexts where necessary to avoid
                 ambiguity.

   node        - a device that implements IP.

   router      - a node that forwards IP packets not explicitly
                 addressed to itself.

   host        - any node that is not a router.

   upper layer - a protocol layer immediately above IP.  Examples are
                 transport protocols such as TCP and UDP, control
                 protocols such as ICMP, routing protocols such as OSPF,
                 and internet or lower-layer protocols being "tunneled"
                 over (i.e., encapsulated in) IP such as IPX, AppleTalk,
                 or IP itself.

   link        - a communication facility or medium over which nodes can
                 communicate at the link layer, i.e., the layer
                 immediately below IP.  Examples are Ethernets (simple
                 or bridged); PPP links; X.25, Frame Relay, or ATM
                 networks; and internet (or higher) layer "tunnels",
                 such as tunnels over IPv4 or IPv6 itself.

   interface   - a node's attachment to a link.

   packet      - an IP header plus payload.

   address     - an IP-layer identifier for an interface or a set of
                 interfaces.

   unicast address
               - an identifier for a single interface. A packet sent to
                 a unicast address is delivered to the interface
                 identified by that address.

   multicast address
               - an identifier for a set of interfaces (typically
                 belonging to different nodes). A packet sent to a
                 multicast address is delivered to all interfaces



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RFC 1971       IPv6 Stateless Address Autoconfiguration      August 1996


                 identified by that address.

   anycast address
               - an identifier for a set of interfaces (typically
                 belonging to different nodes).  A packet sent to an
                 anycast address is delivered to one of the interfaces
                 identified by that address (the "nearest" one,
                 according to the routing protocol's measure of
                 distance).  See [ADDR-ARCH].

   solicited-node multicast address
               - a multicast address to which Neighbor Solicitation
                 messages are sent. The algorithm for computing the
                 address is given in [DISCOVERY].

   link-layer address
               - a link-layer identifier for an interface.  Examples
                 include IEEE 802 addresses for Ethernet links and E.164
                 addresses for ISDN links.

   link-local address
               - an address having link-only scope that can be used to
                 reach neighboring nodes attached to the same link.  All
                 interfaces have a link-local unicast address.

   site-local address
               - an address having scope that is limited to the local
                 site.

   global address
               - an address with unlimited scope.

   communication
               - any packet exchange among nodes that requires that the
                 address of each node used in the exchange remain the
                 same for the duration of the packet exchange. Examples
                 are a TCP connection or a UDP request-response.

   tentative address
               - an address whose uniqueness on a link is being
                 verified, prior to its assignment to an interface.  A
                 tentative address is not considered assigned to an
                 interface in the usual sense. An interface discards
                 received packets addressed to a tentative address, but
                 accepts Neighbor Discovery packets related to Duplicate
                 Address Detection for the tentative address.





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   preferred address
               - an address assigned to an interface whose use by upper
                 layer protocols is unrestricted. Preferred addresses
                 may be used as the source (or destination) address of
                 packets sent from (or to) the interface.

   deprecated address
               - An address assigned to an interface whose use is
                 discouraged, but not forbidden.  A deprecated address
                 should no longer be used as a source address in new
                 communications, but packets sent to deprecated
                 addresses are delivered as expected.  A deprecated
                 address may continue to be used as a source address in
                 communications where switching to a preferred address
                 causes hardship to a specific upper-layer activity
                 (e.g., an existing TCP connection).

   valid address
               - a preferred or deprecated address. A valid address may
                 appear as the source or destination address of a
                 packet, and the internet routing system is expected to
                 deliver packets sent to a valid address.

   invalid address
               - an address that is not assigned to any interface. A
                 valid address becomes invalid when its valid lifetime
                 expires.  Invalid addresses should not appear as the
                 destination or source address of a packet. In the
                 former case, the internet routing system will be unable
                 to deliver the packet, in the later case the recipient
                 of the packet will be unable to respond to it.

   preferred lifetime
               - the length of time that a valid address is preferred
                 (i.e., the time until deprecation). When the preferred
                 lifetime expires, the address becomes deprecated.