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.

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

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.

   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

        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:

        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

   allocated.  The remaining 85% is reserved for future use.

   Unicast addresses are distinguished from multicast addresses by the
   value of the high-order octet of the addresses: a value of FF
   (11111111) identifies an address as a multicast address; any other
   value identifies an address as a unicast address.  Anycast addresses
   are taken from the unicast address space, and are not syntactically
   distinguishable from unicast addresses.

   2.4 Unicast Addresses

   The IPv6 unicast address is contiguous bit-wise maskable, similar to
   IPv4 addresses under Class-less Interdomain Routing [CIDR].

   There are several forms of unicast address assignment in IPv6,
   including the global provider based unicast address, the geographic
   based unicast address, the NSAP address, the IPX hierarchical
   address, the site-local-use address, the link-local-use address, and
   the IPv4-capable host address.  Additional address types can be
   defined in the future.

   IPv6 nodes may have considerable or little knowledge of the internal
   structure of the IPv6 address, depending on the role the node plays
   (for instance, host versus router).  At a minimum, a node may
   consider that unicast addresses (including its own) have no internal
   structure:

    |                           128 bits                              |
    +-----------------------------------------------------------------+
    |                          node address                           |
    +-----------------------------------------------------------------+

   A slightly sophisticated host (but still rather simple) may
   additionally be aware of subnet prefix(es) for the link(s) it is
   attached to, where different addresses may have different values for
   n:

    |                         n bits                 |   128-n bits   |
    +------------------------------------------------+----------------+
    |                   subnet prefix                | interface ID   |
    +------------------------------------------------+----------------+

   Still more sophisticated hosts may be aware of other hierarchical
   boundaries in the unicast address.  Though a very simple router may
   have no knowledge of the internal structure of IPv6 unicast

   addresses, routers will more generally have knowledge of one or more
   of the hierarchical boundaries for the operation of routing
   protocols.  The known boundaries will differ from router to router,
   depending on what positions the router holds in the routing
   hierarchy.

   2.4.1 Unicast Address Examples

   An example of a Unicast address format which will likely be common on
   LANs and other environments where IEEE 802 MAC addresses are
   available is:

    |              n bits            | 80-n bits |     48 bits        |
    +--------------------------------+-----------+--------------------+
    |        subscriber prefix       | subnet ID |   interface ID     |
    +--------------------------------+-----------+--------------------+

   Where the 48-bit Interface ID is an IEEE-802 MAC address.  The use of
   IEEE 802 MAC addresses as a interface ID is expected to be very
   common in environments where nodes have an IEEE 802 MAC address.  In
   other environments, where IEEE 802 MAC addresses are not available,
   other types of link layer addresses can be used, such as E.164
   addresses, for the interface ID.

   The inclusion of a unique global interface identifier, such as an
   IEEE MAC address, makes possible a very simple form of auto-
   configuration of addresses.  A node may discover a subnet ID by
   listening to Router Advertisement messages sent by a router on its
   attached link(s), and then fabricating an IPv6 address for itself by
   using its IEEE MAC address as the interface ID on that subnet.

   Another unicast address format example is where a site or
   organization requires additional layers of internal hierarchy.  In
   this example the subnet ID is divided into an area ID and a subnet
   ID.  Its format is:

    |         s bits       | n bits  |   m bits     | 128-s-n-m bits  |
    +----------------------+---------+--------------+-----------------+
    |   subscriber prefix  | area ID |  subnet ID   |  interface ID   |
    +----------------------+---------+--------------+-----------------+

   This technique can be continued to allow a site or organization to
   add additional layers of internal hierarchy.  It may be desirable to
   use an interface ID smaller than a 48-bit IEEE 802 MAC address to
   allow more space for the additional layers of internal hierarchy.
   These could be interface IDs which are administratively created by

   the site or organization.

   2.4.2 The Unspecified Address

   The address 0:0:0:0:0:0:0:0 is called the unspecified address.  It
   must never be assigned to any node.  It indicates the absence of an
   address.  One example of its use is in the Source Address field of
   any IPv6 datagrams sent by an initializing host before it has learned
   its own address.

   The unspecified address must not be used as the destination address
   of IPv6 datagrams or in IPv6 Routing Headers.

   2.4.3 The Loopback Address

   The unicast address 0:0:0:0:0:0:0:1 is called the loopback address.
   It may be used by a node to send an IPv6 datagram to itself.  It may
   never be assigned to any interface.

   The loopback address must not be used as the source address in IPv6
   datagrams that are sent outside of a single node.  An IPv6 datagram
   with a destination address of loopback must never be sent outside of
   a single node.

   2.4.4 IPv6 Addresses with Embedded IPv4 Addresses

   The IPv6 transition mechanisms include a technique for hosts and
   routers to dynamically tunnel IPv6 packets over IPv4 routing
   infrastructure.  IPv6 nodes that utilize this technique are assigned
   special IPv6 unicast addresses that carry an IPv4 address in the
   low-order 32-bits.  This type of address is termed an "IPv4-
   compatible IPv6 address" and has the format:

    |                80 bits               | 16 |      32 bits        |
    +--------------------------------------+--------------------------+
    |0000..............................0000|0000|    IPv4 address     |
    +--------------------------------------+----+---------------------+

   A second type of IPv6 address which holds an embedded IPv4 address is
   also defined.  This address is used to represent the addresses of
   IPv4-only nodes (those that *do not* support IPv6) as IPv6 addresses.
   This type of address is termed an "IPv4-mapped IPv6 address" and has
   the format:

    |                80 bits               | 16 |      32 bits        |
    +--------------------------------------+--------------------------+
    |0000..............................0000|FFFF|    IPv4 address     |
    +--------------------------------------+----+---------------------+

   2.4.5 NSAP Addresses

   This mapping of NSAP address into IPv6 addresses is as follows:

    |   7   |                   121 bits                              |
    +-------+---------------------------------------------------------+
    |0000001|                 to be defined                           |
    +-------+---------------------------------------------------------+

   The draft definition, motivation, and usage are under study [NSAP].

   2.4.6 IPX Addresses

   This mapping of IPX address into IPv6 addresses is as follows:

    |   7   |                   121 bits                              |
    +-------+---------------------------------------------------------+
    |0000010|                 to be defined                           |
    +-------+---------------------------------------------------------+

   The draft definition, motivation, and usage are under study.

   2.4.7 Provider-Based Global Unicast Addresses

   The global provider-based unicast address is assigned as described in
   [ALLOC].  This initial assignment plan for these unicast addresses is
   similar to assignment of IPv4 addresses under the CIDR scheme [CIDR].
   The IPv6 global provider-based unicast address format is as follows:

    | 3 |  n bits   |  m bits   |   o bits    |   125-n-m-o bits   |
    +---+-----------+-----------+-------------+--------------------+
    |010|registry ID|provider ID|subscriber ID|  intra-subscriber  |
    +---+-----------+-----------+-------------+--------------------+

   The high-order part of the address is assigned to registries, who
   then assign portions of the address space to providers, who then
   assign portions of the address space to subscribers, etc.

   The registry ID identifies the registry which assigns the provider
   portion of the address.  The term "registry prefix" refers to the
   high-order part of the address up to and including the registry ID.

   The provider ID identifies a specific provider which assigns the
   subscriber portion of the address.  The term "provider prefix" refers
   to the high-order part of the address up to and including the
   provider ID.

   The subscriber ID distinguishes among multiple subscribers attached
   to the provider identified by the provider ID.  The term "subscriber
   prefix" refers to the high-order part of the address up to and
   including the subscriber ID.

   The intra-subscriber portion of the address is defined by an
   individual subscriber and is organized according to the subscribers
   local internet topology.  It is likely that many subscribers will
   choose to divide the intra-subscriber portion of the address into a
   subnet ID and an interface ID.  In this case the subnet ID identifies
   a specific physical link and the interface ID identifies a single
   interface on that subnet.

   2.4.8 Local-use IPv6 Unicast Addresses

   There are two types of local-use unicast addresses defined.  These
   are Link-Local and Site-Local.  The Link-Local is for use on a single
   link and the Site-Local is for use in a single site.  Link-Local
   addresses have the following format:

    |   10     |
    |  bits    |        n bits           |       118-n bits           |
    +----------+-------------------------+----------------------------+
    |1111111010|           0             |       interface ID         |
    +----------+-------------------------+----------------------------+

   Link-Local addresses are designed to be used for addressing on a
   single link for purposes such as auto-address configuration, neighbor
   discovery, or when no routers are present.

   Routers MUST not forward any packets with link-local source
   addresses.

   Site-Local addresses have the following format:

    |   10     |
    |  bits    | n bits  |    m bits     |       118-n-m bits         |
    +----------+---------+---------------+----------------------------+
    |1111111011|    0    |   subnet ID   |       interface ID         |
    +----------+---------+---------------+----------------------------+

   Site-Local addresses may be used for sites or organizations that are
   not (yet) connected to the global Internet.  They do not need to
   request or "steal" an address prefix from the global Internet address
   space.  IPv6 site-local addresses can be used instead.  When the
   organization connects to the global Internet, it can then form global
   addresses by replacing the site-local prefix with a subscriber
   prefix.

   Routers MUST not forward any packets with site-local source addresses
   outside of the site.

   2.5 Anycast Addresses

   An IPv6 anycast address is an address that is assigned to more than
   one interface (typically belonging to different nodes), with the
   property that a packet sent to an anycast address is routed to the
   "nearest" interface having that address, according to the routing
   protocols' measure of distance.

   Anycast addresses are allocated from the unicast address space, using
   any of the defined unicast address formats.  Thus, anycast addresses
   are syntactically indistinguishable from unicast addresses.  When a
   unicast address is assigned to more than one interface, thus turning
   it into an anycast address, the nodes to which the address is
   assigned must be explicitly configured to know that it is an anycast
   address.

   For any assigned anycast address, there is a longest address prefix P
   that identifies the topological region in which all interfaces
   belonging to that anycast address reside.  Within the region
   identified by P, each member of the anycast set must be advertised as
   a separate entry in the routing system (commonly referred to as a
   "host route"); outside the region identified by P, the anycast
   address may be aggregated into the routing advertisement for prefix
   P.

   Note that in, the worst case, the prefix P of an anycast set may be
   the null prefix, i.e., the members of the set may have no topological
   locality.  In that case, the anycast address must be advertised as a

   separate routing entry throughout the entire internet, which presents
   a severe scaling limit on how many such "global" anycast sets may be
   supported.  Therefore, it is expected that support for global anycast
   sets may be unavailable or very restricted.

   One expected use of anycast addresses is to identify the set of
   routers belonging to an internet service provider.  Such addresses
   could be used as intermediate addresses in an IPv6 Routing header, to
   cause a packet to be delivered via a particular provider or sequence
   of providers.  Some other possible uses are to identify the set of
   routers attached to a particular subnet, or the set of routers
   providing entry into a particular routing domain.

   There is little experience with widespread, arbitrary use of internet
   anycast addresses, and some known complications and hazards when
   using them in their full generality [ANYCST].  Until more experience
   has been gained and solutions agreed upon for those problems, the
   following restrictions are imposed on IPv6 anycast addresses:

      o An anycast address MUST NOT be used as the source address of an
        IPv6 packet.

      o An anycast address MUST NOT be assigned to an IPv6 host, that
        is, it may be assigned to an IPv6 router only.

   2.5.1 Required Anycast Address

   The Subnet-Router anycast address is predefined.  It's format is as
   follows:

    |                         n bits                 |   128-n bits   |
    +------------------------------------------------+----------------+
    |                   subnet prefix                | 00000000000000 |
    +------------------------------------------------+----------------+

   The "subnet prefix" in an anycast address is the prefix which
   identifies a specific link.  This anycast address is syntactically
   the same as a unicast address for an interface on the link with the
   interface identifier set to zero.

   Packets sent to the Subnet-Router anycast address will be delivered
   to one router on the subnet.  All routers are required to support the
   Subnet-Router anycast addresses for the subnets which they have
   interfaces.

   The subnet-router anycast address is intended to be used for
   applications where a node needs to communicate with one of a set of
   routers on a remote subnet.  For example when a mobile host needs to
   communicate with one of the mobile agents on it's "home" subnet.

   2.6 Multicast Addresses

   An IPv6 multicast address is an identifier for a group of nodes.  A
   node may belong to any number of multicast groups.  Multicast
   addresses have the following format:

    |   8    |  4 |  4 |                  112 bits                   |
    +------ -+----+----+---------------------------------------------+
    |11111111|flgs|scop|                  group ID                   |
    +--------+----+----+---------------------------------------------+

        11111111 at the start of the address identifies the address as
        being a multicast address.

                                      +-+-+-+-+
        flgs is a set of 4 flags:     |0|0|0|T|
                                      +-+-+-+-+

             The high-order 3 flags are reserved, and must be
             initialized to 0.

             T = 0 indicates a permanently-assigned ("well-known")
             multicast address, assigned by the global internet
             numbering authority.

             T = 1 indicates a non-permanently-assigned ("transient")
             multicast address.

        scop is a 4-bit multicast scope value used to limit the scope of
        the multicast group.  The values are:

             0  reserved
             1  node-local scope
             2  link-local scope
             3  (unassigned)
             4  (unassigned)
             5  site-local scope
             6  (unassigned)
             7  (unassigned)
             8  organization-local scope
             9  (unassigned)
             A  (unassigned)

             B  (unassigned)
             C  (unassigned)
             D  (unassigned)
             E  global scope
             F  reserved

        group ID identifies the multicast group, either permanent or
        transient, within the given scope.

   The "meaning" of a permanently-assigned multicast address is
   independent of the scope value.  For example, if the "NTP servers
   group" is assigned a permanent multicast address with a group ID of
   43 (hex), then:

        FF01:0:0:0:0:0:0:43 means all NTP servers on the same node as
        the sender.

        FF02:0:0:0:0:0:0:43 means all NTP servers on the same link as
        the sender.

        FF05:0:0:0:0:0:0:43 means all NTP servers at the same site as
        the sender.

        FF0E:0:0:0:0:0:0:43 means all NTP servers in the internet.

   Non-permanently-assigned multicast addresses are meaningful only
   within a given scope.  For example, a group identified by the non-
   permanent, site-local multicast address FF15:0:0:0:0:0:0:43 at one
   site bears no relationship to a group using the same address at a
   different site, nor to a non-permanent group using the same group ID
   with different scope, nor to a permanent group with the same group
   ID.

   Multicast addresses must not be used as source addresses in IPv6
   datagrams or appear in any routing header.

   2.6.1 Pre-Defined Multicast Addresses

   The following well-known multicast addresses are pre-defined:

        Reserved Multicast Addresses:   FF00:0:0:0:0:0:0:0
                                        FF01:0:0:0:0:0:0:0
                                        FF02:0:0:0:0:0:0:0
                                        FF03:0:0:0:0:0:0:0
                                        FF04:0:0:0:0:0:0:0
                                        FF05:0:0:0:0:0:0:0
                                        FF06:0:0:0:0:0:0:0

                                        FF07:0:0:0:0:0:0:0
                                        FF08:0:0:0:0:0:0:0
                                        FF09:0:0:0:0:0:0:0
                                        FF0A:0:0:0:0:0:0:0
                                        FF0B:0:0:0:0:0:0:0
                                        FF0C:0:0:0:0:0:0:0
                                        FF0D:0:0:0:0:0:0:0
                                        FF0E:0:0:0:0:0:0:0
                                        FF0F:0:0:0:0:0:0:0

   The above multicast addresses are reserved and shall never be
   assigned to any multicast group.

        All Nodes Addresses:    FF01:0:0:0:0:0:0:1
                                FF02:0:0:0:0:0:0:1

   The above multicast addresses identify the group of all IPv6 nodes,
   within scope 1 (node-local) or 2 (link-local).

        All Routers Addresses:   FF01:0:0:0:0:0:0:2
                                 FF02:0:0:0:0:0:0:2

   The above multicast addresses identify the group of all IPv6 routers,
   within scope 1 (node-local) or 2 (link-local).

        DHCP Server/Relay-Agent: FF02:0:0:0:0:0:0:C

   The above multicast addresses identify the group of all IPv6 DHCP
   Servers and Relay Agents within scope 2 (link-local).

        Solicited-Node Address:  FF02:0:0:0:0:1:XXXX:XXXX

   The above multicast address is computed as a function of a node's
   unicast and anycast addresses.  The solicited-node multicast address
   is formed by taking the low-order 32 bits of the address (unicast or
   anycast) and appending those bits to the 96-bit prefix FF02:0:0:0:0:1
   resulting in a multicast address in the range

           FF02:0:0:0:0:1:0000:0000

   to

           FF02:0:0:0:0:1:FFFF:FFFF

   For example, the solicited node multicast address corresponding to
   the IPv6 address 4037::01:800:200E:8C6C is FF02::1:200E:8C6C.  IPv6
   addresses that differ only in the high-order bits, e.g., due to
   multiple high-order prefixes associated with different providers,

   will map to the same solicited-node address thereby reducing the
   number of multicast addresses a node must join.

   A node is required to compute and support a Solicited-Node multicast
   addresses for every unicast and anycast address it is assigned.

   2.7 A Node's Required Addresses

   A host is required to recognize the following addresses as
   identifying itself:

      o Its Link-Local Address for each interface
      o Assigned Unicast Addresses
      o Loopback Address
      o All-Nodes Multicast Address
      o Solicited-Node Multicast Address for each of its assigned
        unicast and anycast addresses
      o Multicast Addresses of all other groups which the host belongs.

   A router is required to recognize the following addresses as
   identifying itself:

      o Its Link-Local Address for each interface
      o Assigned Unicast Addresses
      o Loopback Address
      o The Subnet-Router anycast addresses for the links it has
        interfaces.
      o All other Anycast addresses with which the router has been
        configured.
      o All-Nodes Multicast Address
      o All-Router Multicast Address
      o Solicited-Node Multicast Address for each of its assigned
        unicast and anycast addresses
      o Multicast Addresses of all other groups which the router
        belongs.

   The only address prefixes which should be predefined in an
   implementation are the:

      o Unspecified Address
      o Loopback Address
      o Multicast Prefix (FF)
      o Local-Use Prefixes (Link-Local and Site-Local)
      o Pre-Defined Multicast Addresses
      o IPv4-Compatible Prefixes

   Implementations should assume all other addresses are unicast unless
   specifically configured (e.g., anycast addresses).

REFERENCES

     [ALLOC] Rekhter, Y., and T. Li, "An Architecture for IPv6 Unicast
             Address Allocation", RFC 1887, cisco Systems, December
             1995.

     [ANYCST] Partridge, C., Mendez, T., and W. Milliken, "Host
             Anycasting Service", RFC 1546, BBN, November 1993.

     [CIDR] Fuller, V., Li, T., Varadhan, K., and J. Yu, "Supernetting:
             an Address Assignment and Aggregation Strategy", RFC 1338,
             BARRNet, cisco, Merit, OARnet, June 1992.

     [IPV6] Deering, S., and R. Hinden, Editors, "Internet Protocol,
             Version 6 (IPv6) Specification", RFC 1883, Xerox PARC,
             Ipsilon Networks, December 1995.

     [MULT] Deering, S., "Host Extensions for IP multicasting", STD 5,
             RFC 1112, Stanford University, August 1989.

     [NSAP] Carpenter, B., Editor, "Mechanisms for OSIN SAPs, CLNP and
             TP over IPv6", Work in Progress.

SECURITY CONSIDERATIONS

   Security issues are not discussed in this document.

DOCUMENT EDITOR'S ADDRESSES

   Robert M. Hinden                     Stephen E. Deering
   Ipsilon Networks, Inc.               Xerox Palo Alto Research Center
   2191 E. Bayshore Road, Suite 100     3333 Coyote Hill Road
   Palo Alto, CA 94303                  Palo Alto, CA 94304
   USA                                  USA

   Phone: +1 415 846 4604               Phone: +1 415 812 4839
   Fax:   +1 415 855 1414               Fax:   +1 415 812 4471
   EMail: hinden@ipsilon.com            EMail: deering@parc.xerox.com
