    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.

    Hinden & Deering            Standards Track                     [Page 1]

    RFC 1884              IPv6 Addressing Architecture         December 1995

    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

    Hinden & Deering            Standards Track                     [Page 2]

    RFC 1884              IPv6 Addressing Architecture         December 1995

    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.

    Hinden & Deering            Standards Track                     [Page 3]

    RFC 1884              IPv6 Addressing Architecture         December 1995

       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

    Hinden & Deering            Standards Track                     [Page 4]

    RFC 1884              IPv6 Addressing Architecture         December 1995

            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:

    Hinden & Deering            Standards Track                     [Page 5]

    RFC 1884              IPv6 Addressing Architecture         December 1995

            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

    Hinden & Deering            Standards Track                     [Page 6]

    RFC 1884              IPv6 Addressing Architecture         December 1995

       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

    Hinden & Deering            Standards Track                     [Page 7]

    RFC 1884              IPv6 Addressing Architecture         December 1995

       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

    Hinden & Deering            Standards Track                     [Page 8]

    RFC 1884              IPv6 Addressing Architecture         December 1995

       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:

    Hinden & Deering            Standards Track                     [Page 9]

    RFC 1884              IPv6 Addressing Architecture         December 1995

        |                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  |
        +---+-----------+-----------+-------------+--------------------+

    Hinden & Deering            Standards Track                    [Page 10]

    RFC 1884              IPv6 Addressing Architecture         December 1995

       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.

    Hinden & Deering            Standards Track                    [Page 11]

    RFC 1884              IPv6 Addressing Architecture         December 1995

       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

    Hinden & Deering            Standards Track                    [Page 12]

    RFC 1884              IPv6 Addressing Architecture         December 1995

       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.

    Hinden & Deering            Standards Track                    [Page 13]

    RFC 1884              IPv6 Addressing Architecture         December 1995

       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)

    Hinden & Deering            Standards Track                    [Page 14]

    RFC 1884              IPv6 Addressing Architecture         December 1995

                 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

    Hinden & Deering            Standards Track                    [Page 15]

    RFC 1884              IPv6 Addressing Architecture         December 1995

                                            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,

    Hinden & Deering            Standards Track                    [Page 16]

    RFC 1884              IPv6 Addressing Architecture         December 1995

       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).

    Hinden & Deering            Standards Track                    [Page 17]

    RFC 1884              IPv6 Addressing Architecture         December 1995

    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

    Hinden & Deering            Standards Track                    [Page 18]