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rfc:rfc1884

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]

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