Network Working Group R. Hinden
Request for Comments: 4291 Nokia
Obsoletes: 3513 S. Deering
Category: Standards Track Cisco Systems
 February 2006
 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.
Copyright Notice
 Copyright (C) The Internet Society (2006).
Abstract
 This specification defines the addressing architecture of the IP
 Version 6 (IPv6) protocol. 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 node's required addresses.
 This document obsoletes RFC 3513, "IP Version 6 Addressing
 Architecture".
Table of Contents
 1. Introduction ....................................................2
 2. IPv6 Addressing .................................................2
 2.1. Addressing Model ...........................................3
 2.2. Text Representation of Addresses ...........................4
 2.3. Text Representation of Address Prefixes ....................5
 2.4. Address Type Identification ................................6
 2.5. Unicast Addresses ..........................................6
 2.5.1. Interface Identifiers ...............................7
 2.5.2. The Unspecified Address .............................9
 2.5.3. The Loopback Address ................................9
 2.5.4. Global Unicast Addresses ............................9
 2.5.5. IPv6 Addresses with Embedded IPv4 Addresses ........10
 2.5.6. Link-Local IPv6 Unicast Addresses ..................11
 2.5.7. Site-Local IPv6 Unicast Addresses ..................11
 2.6. Anycast Addresses .........................................12
 2.6.1. Required Anycast Address ...........................12
 2.7. Multicast Addresses .......................................13
 2.7.1. Pre-Defined Multicast Addresses ....................15
 2.8. A Node's Required Addresses ...............................17
 3. Security Considerations ........................................18
 4. IANA Considerations ............................................18
 5. Acknowledgements ...............................................18
 6. References .....................................................18
 6.1. Normative References ......................................18
 6.2. Informative References ....................................18
 Appendix A: Creating Modified EUI-64 Format Interface Identifiers .20
 Appendix B: Changes from RFC 3513 .................................22
1. Introduction
 This specification defines the addressing architecture of the IP
 Version 6 protocol. It includes the basic formats for the various
 types of IPv6 addresses (unicast, anycast, and multicast).
2. IPv6 Addressing
 IPv6 addresses are 128-bit identifiers for interfaces and sets of
 interfaces (where "interface" is as defined in Section 2 of [IPV6]).
 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, "subnet". When this name is used with the term "ID" for
 identifier after the name (e.g., "subnet ID"), it refers to the
 contents of the named field. When it is used with the term "prefix"
 (e.g., "subnet prefix"), it refers to all of the address from the
 left 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, or
 end with, zero-valued fields.
2.1. Addressing Model
 IPv6 addresses of all types are assigned to interfaces, not nodes.
 An IPv6 unicast address refers to a single interface. 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.
 All interfaces are required to have at least one Link-Local unicast
 address (see Section 2.8 for additional required addresses). A
 single interface may also have multiple IPv6 addresses of any type
 (unicast, anycast, and multicast) or scope. Unicast addresses with a
 scope greater than link-scope are not needed for interfaces that are
 not used as the origin or destination of any IPv6 packets to or from
 non-neighbors. This is sometimes convenient for point-to-point
 interfaces. There is one exception to this addressing model:
 A unicast address or a set of unicast addresses 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.
 Currently, IPv6 continues the IPv4 model in that a subnet prefix is
 associated with one link. Multiple subnet prefixes 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 one to
 four hexadecimal digits of the eight 16-bit pieces of the address.
 Examples:
 ABCD:EF01:2345:6789:ABCD:EF01:2345:6789
 2001:DB8:0:0:8:800:200C: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 some methods 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 one or more groups of 16 bits of zeros.
 The "::" can only appear once in an address. The "::" can also be
 used to compress leading or trailing zeros in an address.
 For example, the following addresses
 2001:DB8:0:0:8:800:200C:417A a unicast address
 FF01:0:0:0:0:0:0:101 a multicast address
 0:0:0:0:0:0:0:1 the loopback address
 0:0:0:0:0:0:0:0 the unspecified address
 may be represented as
 2001:DB8::8:800:200C:417A a unicast address
 FF01::101 a multicast address
 ::1 the loopback address
 :: the unspecified address
 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. Text Representation of Address Prefixes
 The text representation of IPv6 address prefixes is similar to the
 way IPv4 address prefixes are written in Classless Inter-Domain
 Routing (CIDR) notation [CIDR]. An IPv6 address prefix is
 represented by the notation:
 ipv6-address/prefix-length
 where
 ipv6-address is an IPv6 address in any of the notations listed
 in Section 2.2.
 prefix-length is a decimal value specifying how many of the
 leftmost contiguous bits of the address comprise
 the prefix.
 For example, the following are legal representations of the 60-bit
 prefix 20010DB80000CD3 (hexadecimal):
 2001:0DB8:0000:CD30:0000:0000:0000:0000/60
 2001:0DB8::CD30:0:0:0:0/60
 2001:0DB8:0:CD30::/60
 The following are NOT legal representations of the above prefix:
 2001:0DB8:0:CD3/60 may drop leading zeros, but not trailing
 zeros, within any 16-bit chunk of the address
 2001:0DB8::CD30/60 address to left of "/" expands to
 2001:0DB8:0000:0000:0000:0000:0000:CD30
 2001:0DB8::CD3/60 address to left of "/" expands to
 2001:0DB8:0000:0000:0000:0000:0000:0CD3
 When writing both a node address and a prefix of that node address
 (e.g., the node's subnet prefix), the two can be combined as follows:
 the node address 2001:0DB8:0:CD30:123:4567:89AB:CDEF
 and its subnet number 2001:0DB8:0:CD30::/60
 can be abbreviated as 2001:0DB8:0:CD30:123:4567:89AB:CDEF/60
2.4. Address Type Identification
 The type of an IPv6 address is identified by the high-order bits of
 the address, as follows:
 Address type Binary prefix IPv6 notation Section
 ------------ ------------- ------------- -------
 Unspecified 00...0 (128 bits) ::/128 2.5.2
 Loopback 00...1 (128 bits) ::1/128 2.5.3
 Multicast 11111111 FF00::/8 2.7
 Link-Local unicast 1111111010 FE80::/10 2.5.6
 Global Unicast (everything else)
 Anycast addresses are taken from the unicast address spaces (of any
 scope) and are not syntactically distinguishable from unicast
 addresses.
 The general format of Global Unicast addresses is described in
 Section 2.5.4. Some special-purpose subtypes of Global Unicast
 addresses that contain embedded IPv4 addresses (for the purposes of
 IPv4-IPv6 interoperation) are described in Section 2.5.5.
 Future specifications may redefine one or more sub-ranges of the
 Global Unicast space for other purposes, but unless and until that
 happens, implementations must treat all addresses that do not start
 with any of the above-listed prefixes as Global Unicast addresses.
2.5. Unicast Addresses
 IPv6 unicast addresses are aggregatable with prefixes of arbitrary
 bit-length, similar to IPv4 addresses under Classless Inter-Domain
 Routing.
 There are several types of unicast addresses in IPv6, in particular,
 Global Unicast, site-local unicast (deprecated, see Section 2.5.7),
 and Link-Local unicast. There are also some special-purpose subtypes
 of Global Unicast, such as IPv6 addresses with embedded IPv4
 addresses. Additional address types or subtypes 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 |
 +-------------------------------+---------------------------------+
 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.
 Except for the knowledge of the subnet boundary discussed in the
 previous paragraphs, nodes should not make any assumptions about the
 structure of an IPv6 address.
2.5.1. Interface Identifiers
 Interface identifiers in IPv6 unicast addresses are used to identify
 interfaces on a link. They are required to be unique within a subnet
 prefix. It is recommended that the same interface identifier not be
 assigned to different nodes on a link. They may also be unique over
 a broader scope. In some cases, an interface's identifier will be
 derived directly from that interface's link-layer address. The same
 interface identifier may be used on multiple interfaces on a single
 node, as long as they are attached to different subnets.
 Note that the uniqueness of interface identifiers is independent of
 the uniqueness of IPv6 addresses. For example, a Global Unicast
 address may be created with a local scope interface identifier and a
 Link-Local address may be created with a universal scope interface
 identifier.
 For all unicast addresses, except those that start with the binary
 value 000, Interface IDs are required to be 64 bits long and to be
 constructed in Modified EUI-64 format.
 Modified EUI-64 format-based interface identifiers may have universal
 scope when derived from a universal token (e.g., IEEE 802 48-bit MAC
 or IEEE EUI-64 identifiers [EUI64]) or may have local scope where a
 global token is not available (e.g., serial links, tunnel end-points)
 or where global tokens are undesirable (e.g., temporary tokens for
 privacy [PRIV]).
 Modified EUI-64 format interface identifiers are formed by inverting
 the "u" bit (universal/local bit in IEEE EUI-64 terminology) when
 forming the interface identifier from IEEE EUI-64 identifiers. In
 the resulting Modified EUI-64 format, the "u" bit is set to one (1)
 to indicate universal scope, and it is set to zero (0) to indicate
 local scope. The first three octets in binary of an IEEE EUI-64
 identifier are as follows:
 0 0 0 1 1 2
 |0 7 8 5 6 3|
 +----+----+----+----+----+----+
 |cccc|ccug|cccc|cccc|cccc|cccc|
 +----+----+----+----+----+----+
 written in Internet standard bit-order, where "u" is the
 universal/local bit, "g" is the individual/group bit, and "c" is the
 bits of the company_id. Appendix A, "Creating Modified EUI-64 Format
 Interface Identifiers", provides examples on the creation of Modified
 EUI-64 format-based interface identifiers.
 The motivation for inverting the "u" bit when forming an interface
 identifier is to make it easy for system administrators to hand
 configure non-global identifiers when hardware tokens are not
 available. This is expected to be the case for serial links and
 tunnel end-points, for example. The alternative would have been for
 these to be of the form .&checktime(0200,0,0,':'):1, .&checktime(0200,0,0,':'):2, etc., instead of the
 much simpler 0:0:0:1, 0:0:0:2, etc.
 IPv6 nodes are not required to validate that interface identifiers
 created with modified EUI-64 tokens with the "u" bit set to universal
 are unique.
 The use of the universal/local bit in the Modified EUI-64 format
 identifier is to allow development of future technology that can take
 advantage of interface identifiers with universal scope.
 The details of forming interface identifiers are defined in the
 appropriate "IPv6 over <link>" specification, such as "IPv6 over
 Ethernet" [ETHER], and "IPv6 over FDDI" [FDDI].
2.5.2. 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 packets 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 packets or in IPv6 Routing headers. An IPv6 packet with a
 source address of unspecified must never be forwarded by an IPv6
 router.
2.5.3. 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 packet to itself. It must
 not be assigned to any physical interface. It is treated as having
 Link-Local scope, and may be thought of as the Link-Local unicast
 address of a virtual interface (typically called the "loopback
 interface") to an imaginary link that goes nowhere.
 The loopback address must not be used as the source address in IPv6
 packets that are sent outside of a single node. An IPv6 packet with
 a destination address of loopback must never be sent outside of a
 single node and must never be forwarded by an IPv6 router. A packet
 received on an interface with a destination address of loopback must
 be dropped.
2.5.4. Global Unicast Addresses
 The general format for IPv6 Global Unicast addresses is as follows:
 | n bits | m bits | 128-n-m bits |
 +------------------------+-----------+----------------------------+
 | global routing prefix | subnet ID | interface ID |
 +------------------------+-----------+----------------------------+
 where the global routing prefix is a (typically hierarchically-
 structured) value assigned to a site (a cluster of subnets/links),
 the subnet ID is an identifier of a link within the site, and the
 interface ID is as defined in Section 2.5.1.
 All Global Unicast addresses other than those that start with binary
 000 have a 64-bit interface ID field (i.e., n + m = 64), formatted as
 described in Section 2.5.1. Global Unicast addresses that start with
 binary 000 have no such constraint on the size or structure of the
 interface ID field.
 Examples of Global Unicast addresses that start with binary 000 are
 the IPv6 address with embedded IPv4 addresses described in Section
 2.5.5. An example of global addresses starting with a binary value
 other than 000 (and therefore having a 64-bit interface ID field) can
 be found in [GLOBAL].
2.5.5. IPv6 Addresses with Embedded IPv4 Addresses
 Two types of IPv6 addresses are defined that carry an IPv4 address in
 the low-order 32 bits of the address. These are the "IPv4-Compatible
 IPv6 address" and the "IPv4-mapped IPv6 address".
2.5.5.1. IPv4-Compatible IPv6 Address
 The "IPv4-Compatible IPv6 address" was defined to assist in the IPv6
 transition. The format of the "IPv4-Compatible IPv6 address" is as
 follows:
 | 80 bits | 16 | 32 bits |
 +--------------------------------------+--------------------------+
 |0000..............................0000|0000| IPv4 address |
 +--------------------------------------+----+---------------------+
 Note: The IPv4 address used in the "IPv4-Compatible IPv6 address"
 must be a globally-unique IPv4 unicast address.
 The "IPv4-Compatible IPv6 address" is now deprecated because the
 current IPv6 transition mechanisms no longer use these addresses.
 New or updated implementations are not required to support this
 address type.
2.5.5.2. IPv4-Mapped IPv6 Address
 A second type of IPv6 address that holds an embedded IPv4 address is
 defined. This address type is used to represent the addresses of
 IPv4 nodes as IPv6 addresses. The format of the "IPv4-mapped IPv6
 address" is as follows:
 | 80 bits | 16 | 32 bits |
 +--------------------------------------+--------------------------+
 |0000..............................0000|FFFF| IPv4 address |
 +--------------------------------------+----+---------------------+
 See [RFC4038] for background on the usage of the "IPv4-mapped IPv6
 address".
2.5.6. Link-Local IPv6 Unicast Addresses
 Link-Local addresses are for use on a single link. Link-Local
 addresses have the following format:
 | 10 |
 | bits | 54 bits | 64 bits |
 +----------+-------------------------+----------------------------+
 |1111111010| 0 | interface ID |
 +----------+-------------------------+----------------------------+
 Link-Local addresses are designed to be used for addressing on a
 single link for purposes such as automatic address configuration,
 neighbor discovery, or when no routers are present.
 Routers must not forward any packets with Link-Local source or
 destination addresses to other links.
2.5.7. Site-Local IPv6 Unicast Addresses
 Site-Local addresses were originally designed to be used for
 addressing inside of a site without the need for a global prefix.
 Site-local addresses are now deprecated as defined in [SLDEP].
 Site-Local addresses have the following format:
 | 10 |
 | bits | 54 bits | 64 bits |
 +----------+-------------------------+----------------------------+
 |1111111011| subnet ID | interface ID |
 +----------+-------------------------+----------------------------+
 The special behavior of this prefix defined in [RFC3513] must no
 longer be supported in new implementations (i.e., new implementations
 must treat this prefix as Global Unicast).
 Existing implementations and deployments may continue to use this
 prefix.
2.6. 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 prefix P of that
 address that identifies the topological region in which all
 interfaces belonging to that anycast address reside. Within the
 region identified by P, the anycast address must be maintained 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 entry 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 maintained 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 organization providing Internet service.
 Such addresses could be used as intermediate addresses in an IPv6
 Routing header, to cause a packet to be delivered via a particular
 service provider or sequence of service 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.
2.6.1. Required Anycast Address
 The Subnet-Router anycast address is predefined. Its format is as
 follows:
 | n bits | 128-n bits |
 +------------------------------------------------+----------------+
 | subnet prefix | 00000000000000 |
 +------------------------------------------------+----------------+
 The "subnet prefix" in an anycast address is the prefix that
 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 to which they have
 interfaces.
 The Subnet-Router anycast address is intended to be used for
 applications where a node needs to communicate with any one of the
 set of routers.
2.7. Multicast Addresses
 An IPv6 multicast address is an identifier for a group of interfaces
 (typically on different nodes). An interface may belong to any
 number of multicast groups. Multicast addresses have the following
 format:
 | 8 | 4 | 4 | 112 bits |
 +------ -+----+----+---------------------------------------------+
 |11111111|flgs|scop| group ID |
 +--------+----+----+---------------------------------------------+
 binary 11111111 at the start of the address identifies the address
 as being a multicast address.
 +-+-+-+-+
 flgs is a set of 4 flags: |0|R|P|T|
 +-+-+-+-+
 The high-order flag is reserved, and must be initialized to 0.
 T = 0 indicates a permanently-assigned ("well-known") multicast
 address, assigned by the Internet Assigned Numbers Authority
 (IANA).
 T = 1 indicates a non-permanently-assigned ("transient" or
 "dynamically" assigned) multicast address.
 The P flag's definition and usage can be found in [RFC3306].
 The R flag's definition and usage can be found in [RFC3956].
 scop is a 4-bit multicast scope value used to limit the scope of
 the multicast group. The values are as follows:
 0 reserved
 1 Interface-Local scope
 2 Link-Local scope
 3 reserved
 4 Admin-Local scope
 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
 Interface-Local scope spans only a single interface on a node
 and is useful only for loopback transmission of multicast.
 Link-Local multicast scope spans the same topological region as
 the corresponding unicast scope.
 Admin-Local scope is the smallest scope that must be
 administratively configured, i.e., not automatically derived
 from physical connectivity or other, non-multicast-related
 configuration.
 Site-Local scope is intended to span a single site.
 Organization-Local scope is intended to span multiple sites
 belonging to a single organization.
 scopes labeled "(unassigned)" are available for administrators
 to define additional multicast regions.
 group ID identifies the multicast group, either permanent or
 transient, within the given scope. Additional definitions of the
 multicast group ID field structure are provided in [RFC3306].
 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
 101 (hex), then
 FF01:0:0:0:0:0:0:101 means all NTP servers on the same interface
 (i.e., the same node) as the sender.
 FF02:0:0:0:0:0:0:101 means all NTP servers on the same link as the
 sender.
 FF05:0:0:0:0:0:0:101 means all NTP servers in the same site as the
 sender.
 FF0E:0:0:0:0:0:0:101 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 FF15:0:0:0:0:0:0:101 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 a different scope, nor to a permanent group with the same group
 ID.
 Multicast addresses must not be used as source addresses in IPv6
 packets or appear in any Routing header.
 Routers must not forward any multicast packets beyond of the scope
 indicated by the scop field in the destination multicast address.
 Nodes must not originate a packet to a multicast address whose scop
 field contains the reserved value 0; if such a packet is received, it
 must be silently dropped. Nodes should not originate a packet to a
 multicast address whose scop field contains the reserved value F; if
 such a packet is sent or received, it must be treated the same as
 packets destined to a global (scop E) multicast address.
2.7.1. Pre-Defined Multicast Addresses
 The following well-known multicast addresses are pre-defined. The
 group IDs defined in this section are defined for explicit scope
 values.
 Use of these group IDs for any other scope values, with the T flag
 equal to 0, is not allowed.
 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 (interface-local) or 2 (link-local).
 All Routers Addresses: FF01:0:0:0:0:0:0:2
 FF02:0:0:0:0:0:0:2
 FF05:0:0:0:0:0:0:2
 The above multicast addresses identify the group of all IPv6 routers,
 within scope 1 (interface-local), 2 (link-local), or 5 (site-local).
 Solicited-Node Address: FF02:0:0:0:0:1:FFXX:XXXX
 Solicited-Node multicast address are computed as a function of a
 node's unicast and anycast addresses. A Solicited-Node multicast
 address is formed by taking the low-order 24 bits of an address
 (unicast or anycast) and appending those bits to the prefix
 FF02:0:0:0:0:1:FF00::/104 resulting in a multicast address in the
 range
 FF02:0:0:0:0:1:FF00:0000
 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:FF0E:8C6C. IPv6
 addresses that differ only in the high-order bits (e.g., due to
 multiple high-order prefixes associated with different aggregations)
 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 join (on the appropriate interface)
 the associated Solicited-Node multicast addresses for all unicast and
 anycast addresses that have been configured for the node's interfaces
 (manually or automatically).
2.8. A Node's Required Addresses
 A host is required to recognize the following addresses as
 identifying itself:
 o Its required Link-Local address for each interface.
 o Any additional Unicast and Anycast addresses that have been
 configured for the node's interfaces (manually or
 automatically).
 o The loopback address.
 o The All-Nodes multicast addresses defined in Section 2.7.1.
 o The Solicited-Node multicast address for each of its unicast and
 anycast addresses.
 o Multicast addresses of all other groups to which the node
 belongs.
 A router is required to recognize all addresses that a host is
 required to recognize, plus the following addresses as identifying
 itself:
 o The Subnet-Router Anycast addresses for all interfaces for which
 it is configured to act as a router.
 o All other Anycast addresses with which the router has been
 configured.
 o The All-Routers multicast addresses defined in Section 2.7.1.
3. Security Considerations
 IPv6 addressing documents do not have any direct impact on Internet
 infrastructure security. Authentication of IPv6 packets is defined
 in [AUTH].
4. IANA Considerations
 The "IPv4-Compatible IPv6 address" is deprecated by this document.
 The IANA should continue to list the address block containing these
 addresses at http://www.iana.org/assignments/ipv6-address-space as
 "Reserved by IETF" and not reassign it for any other purpose. For
 example:
 0000::/8 Reserved by IETF [RFC3513] [1]
 The IANA has added the following note and link to this address block.
 [5] 0000::/96 was previously defined as the "IPv4-Compatible IPv6
 address" prefix. This definition has been deprecated by RFC
 4291.
 The IANA has updated the references for the IPv6 Address Architecture
 in the IANA registries accordingly.
5. Acknowledgements
 The authors would like to acknowledge the contributions of Paul
 Francis, Scott Bradner, Jim Bound, Brian Carpenter, Matt Crawford,
 Deborah Estrin, Roger Fajman, Bob Fink, Peter Ford, Bob Gilligan,
 Dimitry Haskin, Tom Harsch, Christian Huitema, Tony Li, Greg
 Minshall, Thomas Narten, Erik Nordmark, Yakov Rekhter, Bill Simpson,
 Sue Thomson, Markku Savela, Larry Masinter, Jun-ichiro Itojun Hagino,
 Tatuya Jinmei, Suresh Krishnan, and Mahmood Ali.
6. References
6.1. Normative References
 [IPV6] Deering, S. and R. Hinden, "Internet Protocol, Version 6
 (IPv6) Specification", RFC 2460, December 1998.
6.2. Informative References
 [AUTH] Kent, S. and R. Atkinson, "IP Authentication Header", RFC
 2402, November 1998.
 [CIDR] Fuller, V., Li, T., Yu, J., and K. Varadhan, "Classless
 Inter-Domain Routing (CIDR): an Address Assignment and
 Aggregation Strategy", RFC 1519, September 1993.
 [ETHER] Crawford, M., "Transmission of IPv6 Packets over Ethernet
 Networks", RFC 2464, December 1998.
 [EUI64] IEEE, "Guidelines for 64-bit Global Identifier (EUI-64)
 Registration Authority",
 http://standards.ieee.org/regauth/oui/tutorials/EUI64.html,
 March 1997.
 [FDDI] Crawford, M., "Transmission of IPv6 Packets over FDDI
 Networks", RFC 2467, December 1998.
 [GLOBAL] Hinden, R., Deering, S., and E. Nordmark, "IPv6 Global
 Unicast Address Format", RFC 3587, August 2003.
 [PRIV] Narten, T. and R. Draves, "Privacy Extensions for Stateless
 Address Autoconfiguration in IPv6", RFC 3041, January 2001.
 [RFC3513] Hinden, R. and S. Deering, "Internet Protocol Version 6
 (IPv6) Addressing Architecture", RFC 3513, April 2005.
 [RFC3306] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6
 Multicast Addresses", RFC 3306, August 2002.
 [RFC3956] Savola, P. and B. Haberman, "Embedding the Rendezvous Point
 (RP) Address in an IPv6 Multicast Address", RFC 3956,
 November 2004.
 [RFC4038] Shin, M-K., Hong, Y-G., Hagino, J., Savola, P., and E.
 Castro, "Application Aspects of IPv6 Transition", RFC 4038,
 March 2005.
 [SLDEP] Huitema, C. and B. Carpenter, "Deprecating Site Local
 Addresses", RFC 3879, September 2004.
Appendix A: Creating Modified EUI-64 Format Interface Identifiers
 Depending on the characteristics of a specific link or node, there
 are a number of approaches for creating Modified EUI-64 format
 interface identifiers. This appendix describes some of these
 approaches.
 Links or Nodes with IEEE EUI-64 Identifiers
 The only change needed to transform an IEEE EUI-64 identifier to an
 interface identifier is to invert the "u" (universal/local) bit. An
 example is a globally unique IEEE EUI-64 identifier of the form:
 |0 1|1 3|3 4|4 6|
 |0 5|6 1|2 7|8 3|
 +----------------+----------------+----------------+----------------+
 |cccccc0gcccccccc|ccccccccmmmmmmmm|mmmmmmmmmmmmmmmm|mmmmmmmmmmmmmmmm|
 +----------------+----------------+----------------+----------------+
 where "c" is the bits of the assigned company_id, "0" is the value of
 the universal/local bit to indicate universal scope, "g" is
 individual/group bit, and "m" is the bits of the manufacturer-
 selected extension identifier. The IPv6 interface identifier would
 be of the form:
 |0 1|1 3|3 4|4 6|
 |0 5|6 1|2 7|8 3|
 +----------------+----------------+----------------+----------------+
 |cccccc1gcccccccc|ccccccccmmmmmmmm|mmmmmmmmmmmmmmmm|mmmmmmmmmmmmmmmm|
 +----------------+----------------+----------------+----------------+
 The only change is inverting the value of the universal/local bit.
 Links or Nodes with IEEE 802 48-bit MACs
 [EUI64] defines a method to create an IEEE EUI-64 identifier from an
 IEEE 48-bit MAC identifier. This is to insert two octets, with
 hexadecimal values of 0xFF and 0xFE (see the Note at the end of
 appendix), in the middle of the 48-bit MAC (between the company_id
 and vendor-supplied id). An example is the 48-bit IEEE MAC with
 Global scope:
 |0 1|1 3|3 4|
 |0 5|6 1|2 7|
 +----------------+----------------+----------------+
 |cccccc0gcccccccc|ccccccccmmmmmmmm|mmmmmmmmmmmmmmmm|
 +----------------+----------------+----------------+
 where "c" is the bits of the assigned company_id, "0" is the value of
 the universal/local bit to indicate Global scope, "g" is
 individual/group bit, and "m" is the bits of the manufacturer-
 selected extension identifier. The interface identifier would be of
 the form:
 |0 1|1 3|3 4|4 6|
 |0 5|6 1|2 7|8 3|
 +----------------+----------------+----------------+----------------+
 |cccccc1gcccccccc|cccccccc11111111|11111110mmmmmmmm|mmmmmmmmmmmmmmmm|
 +----------------+----------------+----------------+----------------+
 When IEEE 802 48-bit MAC addresses are available (on an interface or
 a node), an implementation may use them to create interface
 identifiers due to their availability and uniqueness properties.
 Links with Other Kinds of Identifiers
 There are a number of types of links that have link-layer interface
 identifiers other than IEEE EUI-64 or IEEE 802 48-bit MACs. Examples
 include LocalTalk and Arcnet. The method to create a Modified EUI-64
 format identifier is to take the link identifier (e.g., the LocalTalk
 8-bit node identifier) and zero fill it to the left. For example, a
 LocalTalk 8-bit node identifier of hexadecimal value 0x4F results in
 the following interface identifier:
 |0 1|1 3|3 4|4 6|
 |0 5|6 1|2 7|8 3|
 +----------------+----------------+----------------+----------------+
 |0000000000000000|0000000000000000|0000000000000000|0000000001001111|
 +----------------+----------------+----------------+----------------+
 Note that this results in the universal/local bit set to "0" to
 indicate local scope.
 Links without Identifiers
 There are a number of links that do not have any type of built-in
 identifier. The most common of these are serial links and configured
 tunnels. Interface identifiers that are unique within a subnet
 prefix must be chosen.
 When no built-in identifier is available on a link, the preferred
 approach is to use a universal interface identifier from another
 interface or one that is assigned to the node itself. When using
 this approach, no other interface connecting the same node to the
 same subnet prefix may use the same identifier.
 If there is no universal interface identifier available for use on
 the link, the implementation needs to create a local-scope interface
 identifier. The only requirement is that it be unique within a
 subnet prefix. There are many possible approaches to select a
 subnet-prefix-unique interface identifier. These include the
 following:
 Manual Configuration
 Node Serial Number
 Other Node-Specific Token
 The subnet-prefix-unique interface identifier should be generated in
 a manner such that it does not change after a reboot of a node or if
 interfaces are added or deleted from the node.
 The selection of the appropriate algorithm is link and implementation
 dependent. The details on forming interface identifiers are defined
 in the appropriate "IPv6 over <link>" specification. It is strongly
 recommended that a collision detection algorithm be implemented as
 part of any automatic algorithm.
 Note: [EUI-64] actually defines 0xFF and 0xFF as the bits to be
 inserted to create an IEEE EUI-64 identifier from an IEEE MAC-
 48 identifier. The 0xFF and 0xFE values are used when starting
 with an IEEE EUI-48 identifier. The incorrect value was used
 in earlier versions of the specification due to a
 misunderstanding about the differences between IEEE MAC-48 and
 EUI-48 identifiers.
 This document purposely continues the use of 0xFF and 0xFE
 because it meets the requirements for IPv6 interface
 identifiers (i.e., that they must be unique on the link), IEEE
 EUI-48 and MAC-48 identifiers are syntactically equivalent, and
 that it doesn't cause any problems in practice.
Appendix B: Changes from RFC 3513
 The following changes were made from RFC 3513, "IP Version 6
 Addressing Architecture":
 o The restrictions on using IPv6 anycast addresses were removed
 because there is now sufficient experience with the use of anycast
 addresses, the issues are not specific to IPv6, and the GROW
 working group is working in this area.
 o Deprecated the Site-Local unicast prefix. Changes include the
 following:
 - Removed Site-Local from special list of prefixes in Section
 2.4.
 - Split section titled "Local-use IPv6 Unicast Addresses" into
 two sections, "Link-Local IPv6 Unicast Addresses" and "Site-
 Local IPv6 Unicast Addresses".
 - Added text to new section describing Site-Local deprecation.
 o Changes to resolve issues raised in IAB response to Robert Elz
 appeal. Changes include the following:
 - Added clarification to Section 2.5 that nodes should make no
 assumptions about the structure of an IPv6 address.
 - Changed the text in Section 2.5.1 and Appendix A to refer to
 the Modified EUI-64 format interface identifiers with the "u"
 bit set to one (1) as universal.
 - Added clarification to Section 2.5.1 that IPv6 nodes are not
 required to validate that interface identifiers created in
 Modified EUI-64 format with the "u" bit set to one are unique.
 o Changed the reference indicated in Section 2.5.4 "Global Unicast
 Addresses" to RFC 3587.
 o Removed mention of NSAP addresses in examples.
 o Clarified that the "x" in the textual representation can be one to
 four digits.
 o Deprecated the "IPv6 Compatible Address" because it is not being
 used in the IPv6 transition mechanisms.
 o Added the "R" and "P" flags to Section 2.7 on multicast addresses,
 and pointers to the documents that define them.
 o Editorial changes.
Authors' Addresses
 Robert M. Hinden
 Nokia
 313 Fairchild Drive
 Mountain View, CA 94043
 USA
 Phone: +1 650 625-2004
 EMail: bob.hinden@nokia.com
 Stephen E. Deering
 Cisco Systems, Inc.
 170 West Tasman Drive
 San Jose, CA 95134-1706
 USA
Full Copyright Statement
 Copyright (C) The Internet Society (2006).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
 The IETF takes no position regarding the validity or scope of any
 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights. Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
 assurances of licenses to be made available, or the result of an
 attempt made to obtain a general license or permission for the use of
 such proprietary rights by implementers or users of this
 specification can be obtained from the IETF on-line IPR repository at
 http://www.ietf.org/ipr.
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
 rights that may cover technology that may be required to implement
 this standard. Please address the information to the IETF at
 ietf-ipr@ietf.org.
Acknowledgement
 Funding for the RFC Editor function is provided by the IETF
 Administrative Support Activity (IASA).