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+
+Network Working Group R. Hinden
+Request for Comments: 2373 Nokia
+Obsoletes: 1884 S. Deering
+Category: Standards Track Cisco Systems
+ July 1998
+
+ 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 (1998). All Rights Reserved.
+
+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 node's required addresses.
+
+Table of Contents
+
+ 1. Introduction.................................................2
+ 2. IPv6 Addressing..............................................2
+ 2.1 Addressing Model.........................................3
+ 2.2 Text Representation of Addresses.........................3
+ 2.3 Text Representation of Address Prefixes..................5
+ 2.4 Address Type Representation..............................6
+ 2.5 Unicast Addresses........................................7
+ 2.5.1 Interface Identifiers................................8
+ 2.5.2 The Unspecified Address..............................9
+ 2.5.3 The Loopback Address.................................9
+ 2.5.4 IPv6 Addresses with Embedded IPv4 Addresses.........10
+ 2.5.5 NSAP Addresses......................................10
+ 2.5.6 IPX Addresses.......................................10
+ 2.5.7 Aggregatable Global Unicast Addresses...............11
+ 2.5.8 Local-use IPv6 Unicast Addresses....................11
+ 2.6 Anycast Addresses.......................................12
+ 2.6.1 Required Anycast Address............................13
+ 2.7 Multicast Addresses.....................................14
+
+
+
+Hinden & Deering Standards Track [Page 1]
+
+RFC 2373 IPv6 Addressing Architecture July 1998
+
+
+ 2.7.1 Pre-Defined Multicast Addresses.....................15
+ 2.7.2 Assignment of New IPv6 Multicast Addresses..........17
+ 2.8 A Node's Required Addresses.............................17
+ 3. Security Considerations.....................................18
+ APPENDIX A: Creating EUI-64 based Interface Identifiers........19
+ APPENDIX B: ABNF Description of Text Representations...........22
+ APPENDIX C: CHANGES FROM RFC-1884..............................23
+ REFERENCES.....................................................24
+ AUTHORS' ADDRESSES.............................................25
+ FULL COPYRIGHT STATEMENT.......................................26
+
+
+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 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,
+ and Sue Thomson.
+
+ The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
+ "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
+ document are to be interpreted as described in [RFC 2119].
+
+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.
+
+
+
+Hinden & Deering Standards Track [Page 2]
+
+RFC 2373 IPv6 Addressing Architecture July 1998
+
+
+ There are no broadcast addresses in IPv6, their function being
+ superseded by multicast addresses.
+
+ In this document, fields in addresses are given a specific name, for
+ example "subscriber". When this name is used with the term "ID" for
+ identifier after the name (e.g., "subscriber ID"), it refers to the
+ contents of the named field. When it is used with the term "prefix"
+ (e.g. "subscriber prefix") it refers to all of the address up to and
+ including this field.
+
+ In IPv6, all zeros and all ones are legal values for any field,
+ unless specifically excluded. Specifically, prefixes may contain
+ zero-valued fields or end in zeros.
+
+2.1 Addressing Model
+
+ IPv6 addresses of all types are assigned to interfaces, not nodes.
+ 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 be assigned multiple IPv6 addresses of any
+ type (unicast, anycast, and multicast) or scope. Unicast addresses
+ with 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:
+
+ An 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 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 the
+ hexadecimal values of the eight 16-bit pieces of the address.
+ Examples:
+
+
+
+Hinden & Deering Standards Track [Page 3]
+
+RFC 2373 IPv6 Addressing Architecture July 1998
+
+
+ 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 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 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
+ FF01:0:0:0:0:0:0:101 a multicast address
+ 0:0:0:0:0:0:0:1 the loopback address
+ 0:0:0:0:0:0:0:0 the unspecified addresses
+
+ may be represented as:
+
+ 1080::8:800:200C:417A a unicast address
+ FF01::101 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
+
+
+
+
+
+Hinden & Deering Standards Track [Page 4]
+
+RFC 2373 IPv6 Addressing Architecture July 1998
+
+
+2.3 Text Representation of Address Prefixes
+
+ The text representation of IPv6 address prefixes is similar to the
+ way IPv4 addresses prefixes are written in CIDR notation. 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 12AB00000000CD3 (hexadecimal):
+
+ 12AB:0000:0000:CD30:0000:0000:0000:0000/60
+ 12AB::CD30:0:0:0:0/60
+ 12AB:0:0:CD30::/60
+
+ The following are NOT legal representations of the above prefix:
+
+ 12AB:0:0:CD3/60 may drop leading zeros, but not trailing zeros,
+ within any 16-bit chunk of the address
+
+ 12AB::CD30/60 address to left of "/" expands to
+ 12AB:0000:0000:0000:0000:000:0000:CD30
+
+ 12AB::CD3/60 address to left of "/" expands to
+ 12AB:0000:0000:0000:0000:000:0000:0CD3
+
+ When writing both a node address and a prefix of that node address
+ (e.g., the node's subnet prefix), the two can combined as follows:
+
+ the node address 12AB:0:0:CD30:123:4567:89AB:CDEF
+ and its subnet number 12AB:0:0:CD30::/60
+
+ can be abbreviated as 12AB:0:0:CD30:123:4567:89AB:CDEF/60
+
+
+
+
+
+
+
+
+
+Hinden & Deering Standards Track [Page 5]
+
+RFC 2373 IPv6 Addressing Architecture July 1998
+
+
+2.4 Address Type Representation
+
+ The specific type of an IPv6 address is indicated by the leading bits
+ in the address. The variable-length field comprising these leading
+ bits is called the Format Prefix (FP). The initial allocation of
+ these prefixes is as follows:
+
+ Allocation Prefix Fraction of
+ (binary) Address Space
+ ----------------------------------- -------- -------------
+ Reserved 0000 0000 1/256
+ Unassigned 0000 0001 1/256
+
+ Reserved for NSAP Allocation 0000 001 1/128
+ Reserved for IPX Allocation 0000 010 1/128
+
+ Unassigned 0000 011 1/128
+ Unassigned 0000 1 1/32
+ Unassigned 0001 1/16
+
+ Aggregatable Global Unicast Addresses 001 1/8
+ Unassigned 010 1/8
+ Unassigned 011 1/8
+ Unassigned 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 Unicast Addresses 1111 1110 10 1/1024
+ Site-Local Unicast Addresses 1111 1110 11 1/1024
+
+ Multicast Addresses 1111 1111 1/256
+
+ Notes:
+
+ (1) The "unspecified address" (see section 2.5.2), the loopback
+ address (see section 2.5.3), and the IPv6 Addresses with
+ Embedded IPv4 Addresses (see section 2.5.4), are assigned out
+ of the 0000 0000 format prefix space.
+
+
+
+
+
+
+
+Hinden & Deering Standards Track [Page 6]
+
+RFC 2373 IPv6 Addressing Architecture July 1998
+
+
+ (2) The format prefixes 001 through 111, except for Multicast
+ Addresses (1111 1111), are all required to have to have 64-bit
+ interface identifiers in EUI-64 format. See section 2.5.1 for
+ definitions.
+
+ This allocation supports the direct allocation of aggregation
+ addresses, local use addresses, and multicast addresses. Space is
+ reserved for NSAP addresses and IPX addresses. The remainder of the
+ address space is unassigned for future use. This can be used for
+ expansion of existing use (e.g., additional aggregatable addresses,
+ etc.) or new uses (e.g., separate locators and identifiers). Fifteen
+ percent of the address space is initially allocated. The remaining
+ 85% is reserved for future use.
+
+ Unicast addresses are distinguished from multicast addresses by the
+ value of the high-order octet of the addresses: a value of FF
+ (11111111) identifies an address as a multicast address; any other
+ value identifies an address as a unicast address. Anycast addresses
+ are taken from the unicast address space, and are not syntactically
+ distinguishable from unicast addresses.
+
+2.5 Unicast Addresses
+
+ IPv6 unicast addresses are aggregatable with contiguous bit-wise
+ masks similar to IPv4 addresses under Class-less Interdomain Routing
+ [CIDR].
+
+ There are several forms of unicast address assignment in IPv6,
+ including the global aggregatable global unicast address, the NSAP
+ address, the IPX hierarchical address, the site-local address, the
+ link-local 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:
+
+
+
+Hinden & Deering Standards Track [Page 7]
+
+RFC 2373 IPv6 Addressing Architecture July 1998
+
+
+ | n bits | 128-n bits |
+ +------------------------------------------------+----------------+
+ | subnet prefix | interface ID |
+ +------------------------------------------------+----------------+
+
+ Still more sophisticated hosts may be aware of other hierarchical
+ boundaries in the unicast address. Though a very simple router may
+ have no knowledge of the internal structure of IPv6 unicast
+ addresses, routers will more generally have knowledge of one or more
+ of the hierarchical boundaries for the operation of routing
+ protocols. The known boundaries will differ from router to router,
+ depending on what positions the router holds in the routing
+ hierarchy.
+
+2.5.1 Interface Identifiers
+
+ Interface identifiers in IPv6 unicast addresses are used to identify
+ interfaces on a link. They are required to be unique on that link.
+ They may also be unique over a broader scope. In many cases an
+ interface's identifier will be the same as that interface's link-
+ layer address. The same interface identifier may be used on multiple
+ interfaces on a single node.
+
+ Note that the use of the same interface identifier on multiple
+ interfaces of a single node does not affect the interface
+ identifier's global uniqueness or each IPv6 addresses global
+ uniqueness created using that interface identifier.
+
+ In a number of the format prefixes (see section 2.4) Interface IDs
+ are required to be 64 bits long and to be constructed in IEEE EUI-64
+ format [EUI64]. EUI-64 based Interface identifiers may have global
+ scope when a global token is available (e.g., IEEE 48bit MAC) or may
+ have local scope where a global token is not available (e.g., serial
+ links, tunnel end-points, etc.). It is required that the "u" bit
+ (universal/local bit in IEEE EUI-64 terminology) be inverted when
+ forming the interface identifier from the EUI-64. The "u" bit is set
+ to one (1) to indicate global scope, and it is set to zero (0) to
+ indicate local scope. The first three octets in binary of an EUI-64
+ identifier are as follows:
+
+ 0 0 0 1 1 2
+ |0 7 8 5 6 3|
+ +----+----+----+----+----+----+
+ |cccc|ccug|cccc|cccc|cccc|cccc|
+ +----+----+----+----+----+----+
+
+
+
+
+
+
+Hinden & Deering Standards Track [Page 8]
+
+RFC 2373 IPv6 Addressing Architecture July 1998
+
+
+ written in Internet standard bit-order , where "u" is the
+ universal/local bit, "g" is the individual/group bit, and "c" are the
+ bits of the company_id. Appendix A: "Creating EUI-64 based Interface
+ Identifiers" provides examples on the creation of different EUI-64
+ based interface identifiers.
+
+ The motivation for inverting the "u" bit when forming the interface
+ identifier is to make it easy for system administrators to hand
+ configure local scope identifiers when hardware tokens are not
+ available. This is expected to be case for serial links, tunnel end-
+ points, etc. The alternative would have been for these to be of the
+ form 0200:0:0:1, 0200:0:0:2, etc., instead of the much simpler ::1,
+ ::2, etc.
+
+ The use of the universal/local bit in the IEEE EUI-64 identifier is
+ to allow development of future technology that can take advantage of
+ interface identifiers with global scope.
+
+ The details of forming interface identifiers are defined in the
+ appropriate "IPv6 over <link>" specification such as "IPv6 over
+ Ethernet" [ETHER], "IPv6 over FDDI" [FDDI], etc.
+
+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.
+
+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 may
+ never be assigned to any physical interface. It may be thought of as
+ being associated with a virtual interface (e.g., the loopback
+ interface).
+
+ 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.
+
+
+
+
+
+
+Hinden & Deering Standards Track [Page 9]
+
+RFC 2373 IPv6 Addressing Architecture July 1998
+
+
+2.5.4 IPv6 Addresses with Embedded IPv4 Addresses
+
+ The IPv6 transition mechanisms [TRAN] include a technique for hosts
+ and routers to dynamically tunnel IPv6 packets over IPv4 routing
+ infrastructure. IPv6 nodes that utilize this technique are assigned
+ special IPv6 unicast addresses that carry an IPv4 address in the low-
+ order 32-bits. This type of address is termed an "IPv4-compatible
+ IPv6 address" and has the format:
+
+ | 80 bits | 16 | 32 bits |
+ +--------------------------------------+--------------------------+
+ |0000..............................0000|0000| IPv4 address |
+ +--------------------------------------+----+---------------------+
+
+ A second type of IPv6 address which holds an embedded IPv4 address is
+ also defined. This address is used to represent the addresses of
+ IPv4-only nodes (those that *do not* support IPv6) as IPv6 addresses.
+ This type of address is termed an "IPv4-mapped IPv6 address" and has
+ the format:
+
+ | 80 bits | 16 | 32 bits |
+ +--------------------------------------+--------------------------+
+ |0000..............................0000|FFFF| IPv4 address |
+ +--------------------------------------+----+---------------------+
+
+2.5.5 NSAP Addresses
+
+ This mapping of NSAP address into IPv6 addresses is defined in
+ [NSAP]. This document recommends that network implementors who have
+ planned or deployed an OSI NSAP addressing plan, and who wish to
+ deploy or transition to IPv6, should redesign a native IPv6
+ addressing plan to meet their needs. However, it also defines a set
+ of mechanisms for the support of OSI NSAP addressing in an IPv6
+ network. These mechanisms are the ones that must be used if such
+ support is required. This document also defines a mapping of IPv6
+ addresses within the OSI address format, should this be required.
+
+2.5.6 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.
+
+
+
+
+Hinden & Deering Standards Track [Page 10]
+
+RFC 2373 IPv6 Addressing Architecture July 1998
+
+
+2.5.7 Aggregatable Global Unicast Addresses
+
+ The global aggregatable global unicast address is defined in [AGGR].
+ This address format is designed to support both the current provider
+ based aggregation and a new type of aggregation called exchanges.
+ The combination will allow efficient routing aggregation for both
+ sites which connect directly to providers and who connect to
+ exchanges. Sites will have the choice to connect to either type of
+ aggregation point.
+
+ The IPv6 aggregatable global unicast address format is as follows:
+
+ | 3| 13 | 8 | 24 | 16 | 64 bits |
+ +--+-----+---+--------+--------+--------------------------------+
+ |FP| TLA |RES| NLA | SLA | Interface ID |
+ | | ID | | ID | ID | |
+ +--+-----+---+--------+--------+--------------------------------+
+
+ Where
+
+ 001 Format Prefix (3 bit) for Aggregatable Global
+ Unicast Addresses
+ TLA ID Top-Level Aggregation Identifier
+ RES Reserved for future use
+ NLA ID Next-Level Aggregation Identifier
+ SLA ID Site-Level Aggregation Identifier
+ INTERFACE ID Interface Identifier
+
+ The contents, field sizes, and assignment rules are defined in
+ [AGGR].
+
+2.5.8 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 | 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 auto-address configuration, neighbor
+ discovery, or when no routers are present.
+
+
+
+
+Hinden & Deering Standards Track [Page 11]
+
+RFC 2373 IPv6 Addressing Architecture July 1998
+
+
+ Routers must not forward any packets with link-local source or
+ destination addresses to other links.
+
+ Site-Local addresses have the following format:
+
+ | 10 |
+ | bits | 38 bits | 16 bits | 64 bits |
+ +----------+-------------+-----------+----------------------------+
+ |1111111011| 0 | subnet ID | interface ID |
+ +----------+-------------+-----------+----------------------------+
+
+ Site-Local addresses are designed to be used for addressing inside of
+ a site without the need for a global prefix.
+
+ Routers must not forward any packets with site-local source or
+ destination addresses outside of the site.
+
+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 address prefix P
+ that identifies the topological region in which all interfaces
+ belonging to that anycast address reside. Within the region
+ identified by P, each member of the anycast set must be advertised as
+ a separate entry in the routing system (commonly referred to as a
+ "host route"); outside the region identified by P, the anycast
+ address may be aggregated into the routing advertisement for prefix
+ P.
+
+ Note that in, the worst case, the prefix P of an anycast set may be
+ the null prefix, i.e., the members of the set may have no topological
+ locality. In that case, the anycast address must be advertised as a
+ separate routing entry throughout the entire internet, which presents
+
+
+
+
+
+Hinden & Deering Standards Track [Page 12]
+
+RFC 2373 IPv6 Addressing Architecture July 1998
+
+
+ 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
+ aggregation or sequence of aggregations. 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.
+
+2.6.1 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 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 2373 IPv6 Addressing Architecture July 1998
+
+
+ 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 its "home" subnet.
+
+2.7 Multicast Addresses
+
+ An IPv6 multicast address is an identifier for a group of nodes. A
+ node may belong to any number of multicast groups. Multicast
+ addresses have the following format:
+
+ | 8 | 4 | 4 | 112 bits |
+ +------ -+----+----+---------------------------------------------+
+ |11111111|flgs|scop| group ID |
+ +--------+----+----+---------------------------------------------+
+
+ 11111111 at the start of the address identifies the address as
+ being a multicast address.
+
+ +-+-+-+-+
+ flgs is a set of 4 flags: |0|0|0|T|
+ +-+-+-+-+
+
+ The high-order 3 flags are reserved, and must be initialized to
+ 0.
+
+ T = 0 indicates a permanently-assigned ("well-known") multicast
+ address, assigned by the global internet numbering authority.
+
+ T = 1 indicates a non-permanently-assigned ("transient")
+ multicast address.
+
+ scop is a 4-bit multicast scope value used to limit the scope of
+ the multicast group. The values are:
+
+ 0 reserved
+ 1 node-local scope
+ 2 link-local scope
+ 3 (unassigned)
+ 4 (unassigned)
+ 5 site-local scope
+ 6 (unassigned)
+ 7 (unassigned)
+ 8 organization-local scope
+ 9 (unassigned)
+ A (unassigned)
+ B (unassigned)
+ C (unassigned)
+
+
+
+Hinden & Deering Standards Track [Page 14]
+
+RFC 2373 IPv6 Addressing Architecture July 1998
+
+
+ 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
+ 101 (hex), then:
+
+ FF01:0:0:0:0:0:0:101 means all NTP servers on 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 at 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 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.
+
+2.7.1 Pre-Defined Multicast Addresses
+
+ The following well-known multicast addresses are pre-defined:
+
+ Reserved Multicast Addresses: FF00:0:0:0:0:0:0:0
+ FF01:0:0:0:0:0:0:0
+ FF02:0:0:0:0:0:0:0
+ FF03:0:0:0:0:0:0:0
+ FF04:0:0:0:0:0:0:0
+ FF05:0:0:0:0:0:0:0
+ FF06:0:0:0:0:0:0:0
+ FF07:0:0:0:0:0:0:0
+ FF08:0:0:0:0:0:0:0
+ FF09:0:0:0:0:0:0:0
+
+
+
+Hinden & Deering Standards Track [Page 15]
+
+RFC 2373 IPv6 Addressing Architecture July 1998
+
+
+ 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
+ FF05:0:0:0:0:0:0:2
+
+ The above multicast addresses identify the group of all IPv6 routers,
+ within scope 1 (node-local), 2 (link-local), or 5 (site-local).
+
+ Solicited-Node Address: FF02:0:0:0:0:1:FFXX: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 24 bits of the 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 the associated Solicited-Node
+ multicast addresses for every unicast and anycast address it is
+ assigned.
+
+
+
+Hinden & Deering Standards Track [Page 16]
+
+RFC 2373 IPv6 Addressing Architecture July 1998
+
+
+2.7.2 Assignment of New IPv6 Multicast Addresses
+
+ The current approach [ETHER] to map IPv6 multicast addresses into
+ IEEE 802 MAC addresses takes the low order 32 bits of the IPv6
+ multicast address and uses it to create a MAC address. Note that
+ Token Ring networks are handled differently. This is defined in
+ [TOKEN]. Group ID's less than or equal to 32 bits will generate
+ unique MAC addresses. Due to this new IPv6 multicast addresses
+ should be assigned so that the group identifier is always in the low
+ order 32 bits as shown in the following:
+
+ | 8 | 4 | 4 | 80 bits | 32 bits |
+ +------ -+----+----+---------------------------+-----------------+
+ |11111111|flgs|scop| reserved must be zero | group ID |
+ +--------+----+----+---------------------------+-----------------+
+
+ While this limits the number of permanent IPv6 multicast groups to
+ 2^32 this is unlikely to be a limitation in the future. If it
+ becomes necessary to exceed this limit in the future multicast will
+ still work but the processing will be sightly slower.
+
+ Additional IPv6 multicast addresses are defined and registered by the
+ IANA [MASGN].
+
+2.8 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 Addresses
+ o Solicited-Node Multicast Address for each of its assigned
+ unicast and anycast addresses
+ o Multicast Addresses of all other groups to which the host
+ 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 the interfaces it is
+ configured to act as a router on.
+ o All other Anycast addresses with which the router has been
+ configured.
+ o All-Routers Multicast Addresses
+
+
+
+
+Hinden & Deering Standards Track [Page 17]
+
+RFC 2373 IPv6 Addressing Architecture July 1998
+
+
+ o Multicast Addresses of all other groups to 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).
+
+3. Security Considerations
+
+ IPv6 addressing documents do not have any direct impact on Internet
+ infrastructure security. Authentication of IPv6 packets is defined
+ in [AUTH].
+
+
+
+
+
+
+
+
+
+
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+
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+
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+
+Hinden & Deering Standards Track [Page 18]
+
+RFC 2373 IPv6 Addressing Architecture July 1998
+
+
+APPENDIX A : Creating EUI-64 based Interface Identifiers
+--------------------------------------------------------
+
+ Depending on the characteristics of a specific link or node there are
+ a number of approaches for creating EUI-64 based interface
+ identifiers. This appendix describes some of these approaches.
+
+Links or Nodes with EUI-64 Identifiers
+
+ The only change needed to transform an EUI-64 identifier to an
+ interface identifier is to invert the "u" (universal/local) bit. For
+ example, a globally unique 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" are 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" are 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 MAC's
+
+ [EUI64] defines a method to create a EUI-64 identifier from an IEEE
+ 48bit MAC identifier. This is to insert two octets, with hexadecimal
+ values of 0xFF and 0xFE, in the middle of the 48 bit MAC (between the
+ company_id and vendor supplied id). For example the 48 bit MAC with
+ global scope:
+
+ |0 1|1 3|3 4|
+ |0 5|6 1|2 7|
+ +----------------+----------------+----------------+
+ |cccccc0gcccccccc|ccccccccmmmmmmmm|mmmmmmmmmmmmmmmm|
+ +----------------+----------------+----------------+
+
+
+
+
+
+Hinden & Deering Standards Track [Page 19]
+
+RFC 2373 IPv6 Addressing Architecture July 1998
+
+
+ where "c" are 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" are 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 48bit MAC addresses are available (on an interface or a
+ node), an implementation should use them to create interface
+ identifiers due to their availability and uniqueness properties.
+
+Links with Non-Global Identifiers
+
+ There are a number of types of links that, while multi-access, do not
+ have globally unique link identifiers. Examples include LocalTalk
+ and Arcnet. The method to create an EUI-64 formatted 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 must be chosen that are unique for
+ the link.
+
+ When no built-in identifier is available on a link the preferred
+ approach is to use a global interface identifier from another
+ interface or one which is assigned to the node itself. To use this
+ approach no other interface connecting the same node to the same link
+ may use the same identifier.
+
+
+
+
+Hinden & Deering Standards Track [Page 20]
+
+RFC 2373 IPv6 Addressing Architecture July 1998
+
+
+ If there is no global 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 on the link.
+ There are many possible approaches to select a link-unique interface
+ identifier. They include:
+
+ Manual Configuration
+ Generated Random Number
+ Node Serial Number (or other node-specific token)
+
+ The link-unique interface identifier should be generated in a manner
+ 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.
+
+
+
+
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+Hinden & Deering Standards Track [Page 21]
+
+RFC 2373 IPv6 Addressing Architecture July 1998
+
+
+APPENDIX B: ABNF Description of Text Representations
+----------------------------------------------------
+
+ This appendix defines the text representation of IPv6 addresses and
+ prefixes in Augmented BNF [ABNF] for reference purposes.
+
+ IPv6address = hexpart [ ":" IPv4address ]
+ IPv4address = 1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT
+
+ IPv6prefix = hexpart "/" 1*2DIGIT
+
+ hexpart = hexseq | hexseq "::" [ hexseq ] | "::" [ hexseq ]
+ hexseq = hex4 *( ":" hex4)
+ hex4 = 1*4HEXDIG
+
+
+
+
+
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+Hinden & Deering Standards Track [Page 22]
+
+RFC 2373 IPv6 Addressing Architecture July 1998
+
+
+APPENDIX C: CHANGES FROM RFC-1884
+---------------------------------
+
+ The following changes were made from RFC-1884 "IP Version 6
+ Addressing Architecture":
+
+ - Added an appendix providing a ABNF description of text
+ representations.
+ - Clarification that link unique identifiers not change after
+ reboot or other interface reconfigurations.
+ - Clarification of Address Model based on comments.
+ - Changed aggregation format terminology to be consistent with
+ aggregation draft.
+ - Added text to allow interface identifier to be used on more than
+ one interface on same node.
+ - Added rules for defining new multicast addresses.
+ - Added appendix describing procedures for creating EUI-64 based
+ interface ID's.
+ - Added notation for defining IPv6 prefixes.
+ - Changed solicited node multicast definition to use a longer
+ prefix.
+ - Added site scope all routers multicast address.
+ - Defined Aggregatable Global Unicast Addresses to use "001" Format
+ Prefix.
+ - Changed "010" (Provider-Based Unicast) and "100" (Reserved for
+ Geographic) Format Prefixes to Unassigned.
+ - Added section on Interface ID definition for unicast addresses.
+ Requires use of EUI-64 in range of format prefixes and rules for
+ setting global/local scope bit in EUI-64.
+ - Updated NSAP text to reflect working in RFC1888.
+ - Removed protocol specific IPv6 multicast addresses (e.g., DHCP)
+ and referenced the IANA definitions.
+ - Removed section "Unicast Address Example". Had become OBE.
+ - Added new and updated references.
+ - Minor text clarifications and improvements.
+
+
+
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+Hinden & Deering Standards Track [Page 23]
+
+RFC 2373 IPv6 Addressing Architecture July 1998
+
+
+REFERENCES
+
+ [ABNF] Crocker, D., and P. Overell, "Augmented BNF for
+ Syntax Specifications: ABNF", RFC 2234, November 1997.
+
+ [AGGR] Hinden, R., O'Dell, M., and S. Deering, "An
+ Aggregatable Global Unicast Address Format", RFC 2374, July
+ 1998.
+
+ [AUTH] Atkinson, R., "IP Authentication Header", RFC 1826, August
+ 1995.
+
+ [ANYCST] Partridge, C., Mendez, T., and W. Milliken, "Host
+ Anycasting Service", RFC 1546, November 1993.
+
+ [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 Pacekts over Ethernet
+ Networks", Work in Progress.
+
+ [EUI64] IEEE, "Guidelines for 64-bit Global Identifier (EUI-64)
+ Registration Authority",
+ http://standards.ieee.org/db/oui/tutorials/EUI64.html,
+ March 1997.
+
+ [FDDI] Crawford, M., "Transmission of IPv6 Packets over FDDI
+ Networks", Work in Progress.
+
+ [IPV6] Deering, S., and R. Hinden, Editors, "Internet Protocol,
+ Version 6 (IPv6) Specification", RFC 1883, December 1995.
+
+ [MASGN] Hinden, R., and S. Deering, "IPv6 Multicast Address
+ Assignments", RFC 2375, July 1998.
+
+ [NSAP] Bound, J., Carpenter, B., Harrington, D., Houldsworth, J.,
+ and A. Lloyd, "OSI NSAPs and IPv6", RFC 1888, August 1996.
+
+ [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
+ Requirement Levels", BCP 14, RFC 2119, March 1997.
+
+ [TOKEN] Thomas, S., "Transmission of IPv6 Packets over Token Ring
+ Networks", Work in Progress.
+
+ [TRAN] Gilligan, R., and E. Nordmark, "Transition Mechanisms for
+ IPv6 Hosts and Routers", RFC 1993, April 1996.
+
+
+
+
+Hinden & Deering Standards Track [Page 24]
+
+RFC 2373 IPv6 Addressing Architecture July 1998
+
+
+AUTHORS' ADDRESSES
+
+ Robert M. Hinden
+ Nokia
+ 232 Java Drive
+ Sunnyvale, CA 94089
+ USA
+
+ Phone: +1 408 990-2004
+ Fax: +1 408 743-5677
+ EMail: hinden@iprg.nokia.com
+
+
+ Stephen E. Deering
+ Cisco Systems, Inc.
+ 170 West Tasman Drive
+ San Jose, CA 95134-1706
+ USA
+
+ Phone: +1 408 527-8213
+ Fax: +1 408 527-8254
+ EMail: deering@cisco.com
+
+
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+Hinden & Deering Standards Track [Page 25]
+
+RFC 2373 IPv6 Addressing Architecture July 1998
+
+
+Full Copyright Statement
+
+ Copyright (C) The Internet Society (1998). All Rights Reserved.
+
+ This document and translations of it may be copied and furnished to
+ others, and derivative works that comment on or otherwise explain it
+ or assist in its implementation may be prepared, copied, published
+ and distributed, in whole or in part, without restriction of any
+ kind, provided that the above copyright notice and this paragraph are
+ included on all such copies and derivative works. However, this
+ document itself may not be modified in any way, such as by removing
+ the copyright notice or references to the Internet Society or other
+ Internet organizations, except as needed for the purpose of
+ developing Internet standards in which case the procedures for
+ copyrights defined in the Internet Standards process must be
+ followed, or as required to translate it into languages other than
+ English.
+
+ The limited permissions granted above are perpetual and will not be
+ revoked by the Internet Society or its successors or assigns.
+
+ This document and the information contained herein is provided on an
+ "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
+ TASK FORCE DISCLAIMS 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.
+
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