Network Working Group R. Hinden Request for Comments: 3513 Nokia Obsoletes: 2373 S. Deering Category: Standards Track Cisco Systems April 2003 Internet Protocol Version 6 (IPv6) 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 (2003). All Rights Reserved.
AbstractThis 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.
1. Introduction.................................................3 2. IPv6 Addressing..............................................3 2.1 Addressing Model.........................................4 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........................................7 2.5.1 Interface Identifiers..............................8 2.5.2 The Unspecified Address............................9 2.5.3 The Loopback Address...............................9 2.5.4 Global Unicast Addresses..........................10 2.5.5 IPv6 Addresses with Embedded IPv4 Addresses.......10 2.5.6 Local-use IPv6 Unicast Addresses..................11 2.6 Anycast Addresses.......................................12 2.6.1 Required Anycast Address..........................13 2.7 Multicast Addresses.....................................13 2.7.1 Pre-Defined Multicast Addresses...................15 2.8 A Node's Required Addresses.............................17 3. Security Considerations.....................................17 4. IANA Considerations.........................................18 5. References..................................................19 5.1 Normative References....................................19 5.2 Informative References..................................19 Appendix A. Creating Modified EUI-64 format Interface IDs......21 Appendix B. Changes from RFC-2373..............................24 Authors' Addresses.............................................25 Full Copyright Statement.......................................26
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.
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: 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: 0:0:0:0:0:0:188.8.131.52 0:0:0:0:0:FFFF:184.108.40.206 or in compressed form: ::220.127.116.11 ::FFFF:18.104.22.168 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 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
The general format of global unicast addresses is described in section 2.5.4. Some special-purpose subtypes of global unicast addresses which 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.
from router to router, depending on what positions the router holds in the routing hierarchy. EUI64]) or may have local scope where a global token is not available (e.g., serial links, tunnel end-points, etc.) 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 global 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" are 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 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 Modified EUI-64 format 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.
NSAP]. 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 [AGGR]. TRAN] include a technique for hosts and routers to dynamically tunnel IPv6 packets over IPv4 routing infrastructure. IPv6 nodes that use this technique are assigned special IPv6 unicast addresses that carry a global 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 | +--------------------------------------+----+---------------------+ Note: The IPv4 address used in the "IPv4-compatible IPv6 address" must be a globally-unique IPv4 unicast address. A second type of IPv6 address which holds an embedded IPv4 address is also defined. This address type is used to represent the addresses of IPv4 nodes 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 | +--------------------------------------+----+---------------------+
ANYCST]. Until more experience has been gained and solutions are specified, 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.
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 Internet Assigned Number Authority (IANA). 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 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 and site-local multicast scopes span the same topological regions as the corresponding unicast scopes. 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. 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. 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 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.
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 every unicast and anycast address it is assigned. AUTH].
RFC1888] Unassigned 0000 01 1/64 Unassigned 0000 1 1/32 Unassigned 0001 1/16 Global Unicast 001 1/8 [RFC2374] 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", the "loopback address", and the IPv6 Addresses with Embedded IPv4 Addresses are assigned out of the 0000 0000 binary prefix space. 2. For now, IANA should limit its allocation of IPv6 unicast address space to the range of addresses that start with binary value 001. The rest of the global unicast address space (approximately 85% of the IPv6 address space) is reserved for future definition and use, and is not to be assigned by IANA at this time.
[IPV6] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. [RFC2026] Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9 , RFC 2026, October 1996. [ANYCST] Partridge, C., Mendez, T. and W. Milliken, "Host Anycasting Service", RFC 1546, November 1993. [AUTH] Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402, November 1998. [AGGR] Hinden, R., O'Dell, M. and S. Deering, "An Aggregatable Global Unicast Address Format", RFC 2374, July 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. [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. [PRIV] Narten, T. and R. Draves, "Privacy Extensions for Stateless Address Autoconfiguration in IPv6", RFC 3041, January 2001. [TOKEN] Crawford, M., Narten, T. and S. Thomas, "Transmission of IPv6 Packets over Token Ring Networks", RFC 2470, December 1998.
EUI64] defines a method to create a IEEE 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 IEEE MAC with global scope:
|0 1|1 3|3 4| |0 5|6 1|2 7| +----------------+----------------+----------------+ |cccccc0gcccccccc|ccccccccmmmmmmmm|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 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 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 EIU-64 or IEEE 802 48-bit MACs. Examples include LocalTalk and Arcnet. The method to create an 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 must be chosen that are unique within a subnet-prefix.
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. 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 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 within a subnet prefix. There are many possible approaches to select a subnet-prefix-unique interface identifier. These include: Manual Configuration Node Serial Number Other node-specific token The subnet-prefix-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.
RFC-2373 "IP Version 6 Addressing Architecture": - Clarified text in section 2.2 to allow "::" to represent one or more groups of 16 bits of zeros. - Changed uniqueness requirement of Interface Identifiers from unique on a link to unique within a subnet prefix. Also added a recommendation that the same interface identifier not be assigned to different machines on a link. - Change site-local format to make the subnet ID field 54-bit long and remove the 38-bit zero's field. - Added description of multicast scop values and rules to handle the reserved scop value 0. - Revised sections 2.4 and 2.5.6 to simplify and clarify how different address types are identified. This was done to insure that implementations do not build in any knowledge about global unicast format prefixes. Changes include: o Removed Format Prefix (FP) terminology o Revised list of address types to only include exceptions to global unicast and a singe entry that identifies everything else as Global Unicast. o Removed list of defined prefix exceptions from section 2.5.6 as it is now the main part of section 2.4. - Clarified text relating to EUI-64 identifiers to distinguish between IPv6's "Modified EUI-64 format" identifiers and IEEE EUI- 64 identifiers. - Combined the sections on the Global Unicast Addresses and NSAP Addresses into a single section on Global Unicast Addresses, generalized the Global Unicast format, and cited [AGGR] and [NSAP] as examples. - Reordered sections 2.5.4 and 2.5.5. - Removed section 2.7.2 Assignment of New IPv6 Multicast Addresses because this is being redefined elsewhere. - Added an IANA considerations section that updates the IANA IPv6 address allocations and documents the NSAP and AGGR allocations. - Added clarification that the "IPv4-compatible IPv6 address" must use global IPv4 unicast addresses. - Divided references in to normative and non-normative sections. - Added reference to [PRIV] in section 2.5.1 - Added clarification that routers must not forward multicast packets outside of the scope indicated in the multicast address. - Added clarification that routers must not forward packets with source address of the unspecified address. - Added clarification that routers must drop packets received on an interface with destination address of loopback. - Clarified the definition of IPv4-mapped addresses.
- Removed the ABNF Description of Text Representations Appendix. - Removed the address block reserved for IPX addresses. - Multicast scope changes: o Changed name of scope value 1 from "node-local" to "interface-local" o Defined scope value 4 as "admin-local" - Corrected reference to RFC1933 and updated references. - Many small changes to clarify and make the text more consistent.
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