rfc1884.txt

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Network Working Group                       R. Hinden, Ipsilon Networks
Request for Comments: 1884                       S. Deering, Xerox PARC
Category: Standards Track                                       Editors
                                                          December 1995


                  IP Version 6 Addressing Architecture




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 specification defines the addressing architecture of the IP
   Version 6 protocol [IPV6].  The document includes the IPv6 addressing
   model, text representations of IPv6 addresses, definition of IPv6
   unicast addresses, anycast addresses, and multicast addresses, and an
   IPv6 nodes required addresses.
























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Table of Contents

   1. Introduction................................................3

   2. IPv6 Addressing.............................................3
      2.1 Addressing Model........................................4
      2.2 Text Representation of Addresses........................4
      2.3 Address Type Representation.............................5
      2.4 Unicast Addresses.......................................7
        2.4.1 Unicast Address Example.............................8
        2.4.2 The Unspecified Address.............................9
        2.4.3 The Loopback Address................................9
        2.4.4 IPv6 Addresses with Embedded IPv4 Addresses.........9
        2.4.5 NSAP Addresses......................................10
        2.4.6 IPX Addresses.......................................10
        2.4.7 Provider-Based Global Unicast Addresses.............10
        2.4.8 Local-use IPv6 Unicast Addresses....................11
      2.5 Anycast Addresses.......................................12
        2.5.1 Required Anycast Address............................13
      2.6 Multicast Addresses.....................................14
        2.6.1 Pre-Defined Multicast Addresses.....................15
      2.7 A Node's Required Addresses.............................17

   REFERENCES.....................................................18

   SECURITY CONSIDERATIONS........................................18

   DOCUMENT EDITOR'S ADDRESSES....................................18























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1.0 INTRODUCTION

   This specification defines the addressing architecture of the IP
   Version 6 protocol.  It includes a detailed description of the
   currently defined address formats for IPv6 [IPV6].

   The editors would like to acknowledge the contributions of Paul
   Francis, Jim Bound, Brian Carpenter, Deborah Estrin, Peter Ford, Bob
   Gilligan, Christian Huitema, Tony Li, Greg Minshall, Erik Nordmark,
   Yakov Rekhter, Bill Simpson, and Sue Thomson.

2.0 IPv6 ADDRESSING

   IPv6 addresses are 128-bit identifiers for interfaces and sets of
   interfaces.  There are three types of addresses:


       Unicast:   An identifier for a single interface.  A packet sent
                  to a unicast address is delivered to the interface
                  identified by that address.

       Anycast:   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 protocols' measure of
                  distance).

       Multicast: An identifier for a set of interfaces (typically
                  belonging to different nodes).  A packet sent to a
                  multicast address is delivered to all interfaces
                  identified by that address.

   There are no broadcast addresses in IPv6, their function being
   superseded by multicast addresses.

   In this document, fields in addresses are given a specific name, for
   example "subscriber".  When this name is used with the term "ID" for
   identifier after the name (e.g., "subscriber ID"), it refers to the
   contents of the named field.  When it is used with the term "prefix"
   (e.g., "subscriber prefix") it refers to all of the address up to and
   including this field.

   In IPv6, all zeros and all ones are legal values for any field,
   unless specifically excluded.  Specifically, prefixes may contain
   zero-valued fields or end in zeros.





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   2.1 Addressing Model

   IPv6 Addresses of all types are assigned to interfaces, not nodes.
   Since each interface belongs to a single node, any of that node's
   interfaces' unicast addresses may be used as an identifier for the
   node.

   An IPv6 unicast address refers to a single interface.  A single
   interface may be assigned multiple IPv6 addresses of any type
   (unicast, anycast, and multicast).  There are two exceptions to this
   model.  These are:

     1) A single address may be assigned to multiple physical interfaces
        if the implementation treats the multiple physical interfaces as
        one interface when presenting it to the internet layer.  This is
        useful for load-sharing over multiple physical interfaces.

     2) Routers may have unnumbered interfaces (i.e., no IPv6 address
        assigned to the interface) on point-to-point links to eliminate
        the necessity to manually configure and advertise the addresses.
        Addresses are not needed for point-to-point interfaces on
        routers if those interfaces are not to be used as the origins or
        destinations of any IPv6 datagrams.

   IPv6 continues the IPv4 model that a subnet is associated with one
   link.  Multiple subnets may be assigned to the same link.


   2.2 Text Representation of Addresses

   There are three conventional forms for representing IPv6 addresses as
   text strings:

     1. The preferred form is x:x:x:x:x:x:x:x, where the 'x's are the
        hexadecimal values of the eight 16-bit pieces of the address.
        Examples:

                   FEDC:BA98:7654:3210:FEDC:BA98:7654:3210

                   1080:0:0:0:8:800:200C:417A

        Note that it is not necessary to write the leading zeros in an
        individual field, but there must be at least one numeral in
        every field (except for the case described in 2.).

     2. Due to the method of allocating certain styles of IPv6
        addresses, it will be common for addresses to contain long
        strings of zero bits.  In order to make writing addresses



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        containing zero bits easier a special syntax is available to
        compress the zeros.  The use of "::" indicates multiple groups
        of 16-bits of zeros.  The "::" can only appear once in an
        address.  The "::" can also be used to compress the leading
        and/or trailing zeros in an address.

        For example the following addresses:

             1080:0:0:0:8:800:200C:417A  a unicast address
             FF01:0:0:0:0:0:0:43         a multicast address
             0:0:0:0:0:0:0:1             the loopback address
             0:0:0:0:0:0:0:0             the unspecified addresses

        may be represented as:

             1080::8:800:200C:417A       a unicast address
             FF01::43                    a multicast address
             ::1                         the loopback address
             ::                          the unspecified addresses

     3. An alternative form that is sometimes more convenient when
        dealing with a mixed environment of IPv4 and IPv6 nodes is
        x:x:x:x:x:x:d.d.d.d, where the 'x's are the hexadecimal values
        of the six high-order 16-bit pieces of the address, and the 'd's
        are the decimal values of the four low-order 8-bit pieces of the
        address (standard IPv4 representation).  Examples:

             0:0:0:0:0:0:13.1.68.3

             0:0:0:0:0:FFFF:129.144.52.38

        or in compressed form:

             ::13.1.68.3

             ::FFFF:129.144.52.38


   2.3 Address Type Representation

   The specific type of an IPv6 address is indicated by the leading bits
   in the address.  The variable-length field comprising these leading
   bits is called the Format Prefix (FP).  The initial allocation of
   these prefixes is as follows:







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        Allocation                         Prefix         Fraction of
                                           (binary)       Address Space
        -------------------------------    --------       -------------
        Reserved                           0000 0000      1/256
        Unassigned                         0000 0001      1/256

        Reserved for NSAP Allocation       0000 001       1/128
        Reserved for IPX Allocation        0000 010       1/128

        Unassigned                         0000 011       1/128
        Unassigned                         0000 1         1/32
        Unassigned                         0001           1/16
        Unassigned                         001            1/8

        Provider-Based Unicast Address     010            1/8

        Unassigned                         011            1/8

        Reserved for Geographic-
        Based Unicast Addresses            100            1/8

        Unassigned                         101            1/8
        Unassigned                         110            1/8
        Unassigned                         1110           1/16
        Unassigned                         1111 0         1/32
        Unassigned                         1111 10        1/64
        Unassigned                         1111 110       1/128

        Unassigned                         1111 1110 0    1/512

        Link Local Use Addresses           1111 1110 10   1/1024
        Site Local Use Addresses           1111 1110 11   1/1024

        Multicast Addresses                1111 1111      1/256

        Note: The "unspecified address" (see section 2.4.2), the
        loopback address (see section 2.4.3), and the IPv6 Addresses
        with Embedded IPv4 Addresses (see section 2.4.4), are assigned
        out of the 0000 0000 format prefix space.


   This allocation supports the direct allocation of provider addresses,
   local use addresses, and multicast addresses.  Space is reserved for
   NSAP addresses, IPX addresses, and geographic addresses.  The
   remainder of the address space is unassigned for future use.  This
   can be used for expansion of existing use (e.g., additional provider
   addresses, etc.) or new uses (e.g., separate locators and
   identifiers).  Fifteen percent of the address space is initially



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