INTERNET-DRAFT R. Hinden, Ipsilon Networks July 16, 1997 M. O'Dell, UUNET S. Deering, Cisco An IPv6 Aggregatable Global Unicast Address Format Status of this Memo This document is an Internet Draft. Internet Drafts are working documents of the Internet Engineering Task Force (IETF), its Areas, and its Working Groups. Note that other groups may also distribute working documents as Internet Drafts. Internet Drafts are draft documents valid for a maximum of six months. Internet Drafts may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet Drafts as reference material or to cite them other than as a ``working draft'' or ``work in progress.'' Please check the 1id-abstracts.txt listing contained in the internet- drafts Shadow Directories on nic.ddn.mil, nnsc.nsf.net, nic.nordu.net, ftp.nisc.sri.com, or munnari.oz.au to learn the current status of any Internet Draft. This internet draft expires on January 17, 1998. 1.0 Introduction This document defines an IPv6 aggregatable global unicast address format for use in the Internet. The address format defined in this document is consistent with the IPv6 Protocol [IPV6] and the "IPv6 Addressing Architecture" [ARCH]. It is designed to facilitate scalable Internet routing. This documented replaces RFC 2073, "An IPv6 Provider-Based Unicast Address Format". RFC 2073 will become historic. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this draft-ietf-ipngwg-unicast-aggr-02.txt [Page 1] INTERNET-DRAFT Aggregatable Global Unicast Address Format July 1997 document are to be interpreted as described in [RFC 2119]. 2.0 Overview of the IPv6 Address IPv6 addresses are 128-bit identifiers for interfaces and sets of interfaces. There are three types of addresses: Unicast, Anycast, and Multicast. This document defines a specific type of Unicast address. In this document, fields in addresses are given specific names, 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 addressing bits to the left of and including this field. IPv6 unicast addresses are designed assuming that the Internet routing system makes forwarding decisions based on a "longest prefix match" algorithm on arbitrary bit boundaries and does not have any knowledge of the internal structure of IPv6 addresses. The structure in IPv6 addresses is for assignment and allocation. The only exception to this is the distinction made between unicast and multicast addresses. 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). This document defines an address format for the 001 (binary) Format Prefix for Aggregatable Global Unicast addresses. The same address format could be used for other Format Prefixes, as long as these Format Prefixes also identify IPv6 unicast addresses. Only the "001" Format Prefix is defined here. 3.0 IPv6 Aggregatable Global Unicast Address Format This document defines an address format for the IPv6 aggregatable global unicast address assignment. The authors believe that this address format will be widely used for IPv6 nodes connected to the Internet. This address format is designed to support both the current provider-based aggregation and a new type of exchange-based aggregation. The combination will allow efficient routing aggregation for sites that connect directly to providers and for sites that connect to exchanges. Sites will have the choice to connect to either type of aggregation entity. draft-ietf-ipngwg-unicast-aggr-02.txt [Page 2] INTERNET-DRAFT Aggregatable Global Unicast Address Format July 1997 While this address format is designed to support exchange-based aggregation (in addition to current provider-based aggregation) it is not dependent on exchanges for it's overall route aggregation properties. It will provide efficient route aggregation with only provider-based aggregation. Aggregatable addresses are organized into a three level hierarchy: - Public Topology - Site Topology - Interface Identifier Public topology is the collection of providers and exchanges who provide public Internet transit services. Site topology is local to a specific site or organization which does not provide public transit service to nodes outside of the site. Interface identifiers identify interfaces on links. ______________ ______________ --+/ \+--------------+/ \+---------- ( P1 ) +----+ ( P3 ) +----+ +\______________/ | |----+\______________/+--| |-- | +--| X1 | +| X2 | | ______________ / | |-+ ______________ / | |-- +/ \+ +-+--+ \ / \+ +----+ ( P2 ) / \ +( P4 ) --+\______________/ / \ \______________/ | / \ | | | / | | | | / | | | _|_ _/_ _|_ _|_ _|_ / \ / \ / \ / \ / \ ( S.A ) ( S.B ) ( P5 ) ( P6 )( S.C ) \___/ \___/ \___/ \___/ \___/ | / \ _|_ _/_ \ ___ / \ / \ +-/ \ ( S.D ) ( S.E ) ( S.F ) \___/ \___/ \___/ As shown in the figure above, the aggregatable address format is designed to support long-haul providers (shown as P1, P2, P3, and P4), exchanges [EXCH] (shown as X1 and X2), multiple levels of providers (shown at P5 and P6), and subscribers (shown as S.x) Exchanges (unlike current NAPs, FIXes, etc.) will allocate IPv6 addresses. Organizations who connect to these exchanges will also subscribe (directly, indirectly via the exchange, etc.) for long-haul draft-ietf-ipngwg-unicast-aggr-02.txt [Page 3] INTERNET-DRAFT Aggregatable Global Unicast Address Format July 1997 service from one or more long-haul providers. Doing so, they will achieve addressing independence from long-haul transit providers. They will be able to change long-haul providers without having to renumber their organization. They can also be multihomed via the exchange to more than one long-haul provider without having to have address prefixes from each long-haul provider. Note that the mechanisms used for this type of provider selection and portability are not discussed in the document. 3.1 Aggregatable Global Unicast Address Structure The aggregatable global unicast address format is as follows: | 3 | 13 | 32 | 16 | 64 bits | +---+-----+-----------+--------+--------------------------------+ |FP | TLA | NLA ID | SLA ID | Interface ID | | | ID | | | | +---+-----+-----------+--------+--------------------------------+ <--Public Topology---> Site <--------> Topology <------Interface Identifier-----> Where FP Format Prefix (001) TLA ID Top-Level Aggregation Identifier NLA ID Next-Level Aggregation Identifier SLA ID Site-Level Aggregation Identifier INTERFACE ID Interface Identifier The following sections specify each part of the IPv6 Aggregatable Global Unicast address format. 3.2 Top-Level Aggregation ID Top-Level Aggregation Identifiers (TLA ID) are the top level in the routing hierarchy. Default-free routers must have a routing table entry for every active TLA ID and will probably have additional entries providing routing information for the TLA ID in which they are located. They may have additional entries in order to optimize routing for their specific topology, but the routing topology at all levels must be designed to minimize the number of additional entries fed into the default free routing tables. draft-ietf-ipngwg-unicast-aggr-02.txt [Page 4] INTERNET-DRAFT Aggregatable Global Unicast Address Format July 1997 This addressing format supports 8,192 (2^13) TLA ID's. Additional TLA ID's may be added by using this format for additional format prefixes. The addition of another FP will add another 8,192 TLA ID's. The rules for TLA ID assignment are defined in [TLAASN]. 3.3 Next-Level Aggregation Identifier Next-Level Aggregation Identifier's are used by organizations assigned a TLA ID to create an addressing hierarchy and to identify sites. The organization can assign the top part of the NLA ID in a manner to create an addressing hierarchy appropriate to its network. It can use the remainder of the bits in the field to identify sites it wishes to serve. This is shown as follows: | n | 32-n bits | 16 | 64 bits | +-----+--------------------+--------+-----------------+ |NLA1 | Site ID | SLA ID | Interface ID | +-----+--------------------+--------+-----------------+ Each organization assigned a TLA ID receives 32 bits of NLA ID space. This NLA ID space allows each organization to provide service to approximately as many organizations as the current IPv4 Internet can support total nodes. Organizations assigned TLA ID's may also support NLA ID's in their own Site ID space. This allows the organization assigned a TLA ID to provide service to organizations providing public transit service and to organizations who do not provide public transit service. These organizations receiving an NLA ID may also choose to use their Site ID space to support other NLA ID's. This is shown as follows: draft-ietf-ipngwg-unicast-aggr-02.txt [Page 5] INTERNET-DRAFT Aggregatable Global Unicast Address Format July 1997 | n | 32-n bits | 16 | 64 bits | +-----+--------------------+--------+-----------------+ |NLA1 | Site ID | SLA ID | Interface ID | +-----+--------------------+--------+-----------------+ | m | 32-n-m | 16 | 64 bits | +-----+--------------+--------+-----------------+ |NLA2 | Site ID | SLA ID | Interface ID | +-----+--------------+--------+-----------------+ | o |32-n-m-o| 16 | 64 bits | +-----+--------+--------+-----------------+ |NLA3 | Site ID| SLA ID | Interface ID | +-----+--------+--------+-----------------+ The rules for NLA ID assignment are defined in [TLAASN]. The design of the bit layout of the NLA ID space for a specific TLA ID is left to the organization responsible for that TLA ID. Likewise the design of the bit layout of the next level NLA ID is the responsibility of the previous level NLA ID. It is recommended that organizations assigning NLA address space use "slow start" allocation procedures as is currently done with IPv4 CIDR blocks. The design of an NLA ID allocation plan is a tradeoff between routing aggregation efficiency and flexibility. Creating hierarchies allows for greater amount of aggregation and results in smaller routing tables. Flat NLA ID assignment provides for easier allocation and attachment flexibility, but results in larger routing tables. 3.4 Site-Level Aggregation Identifier The SLA ID field is used by an individual organization to create its own local addressing hierarchy and to identify subnets. This is analogous to subnets in IPv4 except that each organization has a much greater number of subnets. The 16 bit SLA ID field support 65,535 individual subnets. Organizations may choose to either route their SLA ID "flat" (e.g., not create any logical relationship between the SLA identifiers that results in larger routing tables), or to create a two or more level hierarchy (that results in smaller routing tables) in the SLA ID field. The latter is shown as follows: draft-ietf-ipngwg-unicast-aggr-02.txt [Page 6] INTERNET-DRAFT Aggregatable Global Unicast Address Format July 1997 | n | 16-n | 64 bits | +-----+------------+-------------------------------------+ |SLA1 | Subnet | Interface ID | +-----+------------+-------------------------------------+ | m |16-n-m | 64 bits | +----+-------+-------------------------------------+ |SLA2|Subnet | Interface ID | +----+-------+-------------------------------------+ The approach chosen for structuring an SLA ID field is the responsibility of the individual organization. The number of subnets supported in this address format should be sufficient for all but the largest of organizations. Organizations which need additional subnets can arrange with the organization they are obtaining Internet service from to obtain additional site identifiers and use this to create additional subnets. 3.5 Interface ID Interface identifiers 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 or be based on the interface's link-layer address. Interface IDs used in the aggregatable global unicast address format are required to be 64 bits long and to be constructed in IEEE EUI-64 format [EUI-64]. These identifiers may have global scope when a global token (e.g., IEEE 48bit MAC) is available or may have local scope where a global token is not available (e.g., serial links, tunnel end-points, etc.). The "u" bit (universal/local bit in IEEE EUI-64 terminology) in the EUI-64 identifier must be set correctly, as defined in [ARCH], to indicate global or local scope. The procedures for creating EUI-64 based Interface Identifiers is defined in [ARCH]. The details on forming interface identifiers is defined in the appropriate "IPv6 over " specification such as "IPv6 over Ethernet" [ETHER], "IPv6 over FDDI" [FDDI], etc. draft-ietf-ipngwg-unicast-aggr-02.txt [Page 7] INTERNET-DRAFT Aggregatable Global Unicast Address Format July 1997 4.0 Acknowledgments The authors would like to express our thanks to Thomas Narten, Bob Fink, Matt Crawford, Allison Mankin, Jim Bound, Christian Huitema, Scott Bradner, Brian Carpenter, and John Stewart for their review and constructive comments. 5.0 References [ALLOC] IAB and IESG, "IPv6 Address Allocation Management", RFC1881, December 1995. [ARCH] Hinden, R., "IP Version 6 Addressing Architecture", Internet Draft, , July 1997. [AUTH] Atkinson, R., "IP Authentication Header", RFC1826, August 1995. [AUTO] Thompson, S., Narten T., "IPv6 Stateless Address Autoconfiguration", RFC1971, August 1996. [CIDR] Fuller, V., T. Li, K. Varadhan, J. Yu, "Supernetting: an Address Assignment and Aggregation Strategy", RFC1338. [ETHER] Crawford, M., "Transmission of IPv6 Packets over Ethernet Networks", Internet Draft, , March 1997. [EUI64] IEEE, "Guidelines for 64-bit Global Identifier (EUI-64) Registration Authority", http://standards.ieee.org/db/oui/tutorials/EUI64.html, March 1997. [EXCH] Huitema, C., R. Hinden, "Internet Exchanges", document under preparation. [FDDI] Crawford, M., "Transmission of IPv6 Packets over FDDI Networks", Internet Draft, , March 1997. [IPV6] Deering, S., Hinden, R., Editors, "Internet Protocol, Version 6 (IPv6) Specification", RFC1883, December 1995. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC2119, BCP14, March 1997. draft-ietf-ipngwg-unicast-aggr-02.txt [Page 8] INTERNET-DRAFT Aggregatable Global Unicast Address Format July 1997 [TLAASN] Hinden, R., "TLA and NLA Assignment Rules", Internet Draft, , July 1997. 6.0 Security Considerations IPv6 addressing documents do not have any direct impact on Internet infrastructure security. Authentication of IPv6 packets is defined in [AUTH]. 7.0 Authors' Addresses Robert M. Hinden phone: 1 408 990-2004 Ipsilon Networks, Inc. email: hinden@ipsilon.com 232 Java Drive Sunnyvale, CA 94089 USA Mike O'Dell phone: 1 703 206-5890 UUNET Technologies, Inc. email: mo@uunet.uu.net 3060 Williams Drive Fairfax, VA 22030 USA Stephen E. Deering phone: 1 408 527-8213 Cisco Systems, Inc. email: deering@cisco.com 170 West Tasman Drive San Jose, CA 95134-1706 USA draft-ietf-ipngwg-unicast-aggr-02.txt [Page 9]