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Network Working Group                                      R. HindenRequest for Comments: 2450                                     NokiaCategory: Informational                                December 1998Proposed TLA and NLA Assignment RulesStatus of this Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (1998).  All Rights Reserved.1.0 Introduction   This document proposes rules for Top-Level Aggregation Identifiers   (TLA ID) and Next-Level Aggregation Identifiers (NLA ID) as defined   in [AGGR].  These proposed rules apply to registries allocating TLA   ID's and to organizations receiving TLA ID's.   This proposal is intended as input from the IPng working group to the   IANA and Registries.  It is not intended for any official IETF   status.  Its content represents the result of extensive discussion   between the IPng working group, IANA, and Registries.   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 Scope   The proposed TLA and NLA assignment rules described in this document   are intended for the first two years of IPv6 TLA address assignments.   As routing technology evolves and we gain additional experience with   allocating IPv6 addresses the procedures proposed in this document   may change.Hinden                       Informational                      [Page 1]

RFC 2450         Proposed TLA and NLA Assignment Rules     December 19983.0 IPv6 Aggregatable Global Unicast Address Format   This document proposes assignment rules for the TLA ID and NLA ID   fields in the IPv6 Aggregatable Global Unicast Address Format.  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.   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 its overall route aggregation   properties.  It will provide efficient route aggregation with only   provider-based aggregation.   The aggregatable global unicast address format as defined in [AGGR]   is as follows:      | 3|  13 | 8 |   24   |   16   |          64 bits               |      +--+-----+---+--------+--------+--------------------------------+      |FP| TLA |RES|  NLA   |  SLA   |         Interface ID           |      |  | ID  |   |  ID    |  ID    |                                |      +--+-----+---+--------+--------+--------------------------------+      <--Public Topology--->   Site                            <-------->                             Topology                                      <------Interface Identifier----->   Where      FP           Format Prefix (001)      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 Identifier4.0 Technical Motivation   The design choices for the size of the fields in the aggregatable   address format were based on the need to meet a number of technical   requirements that are described in [AGGR].  An extract of the   technical requirements from [AGGR] is as follows:Hinden                       Informational                      [Page 2]

RFC 2450         Proposed TLA and NLA Assignment Rules     December 1998      The size of the Top-Level Aggregation Identifier is 13 bits.  This      allows for 8,192 TLA ID's.  This size was chosen to insure that      the default-free routing table in top level routers in the      Internet is kept within the limits, with a reasonable margin, of      the current routing technology.  The margin is important because      default-free routers will also carry a significant number of      longer (i.e., more-specific) prefixes for optimizing paths      internal to a TLA and between TLAs.      The important issue is not only the size of the default-free      routing table, but the complexity of the topology that determines      the number of copies of the default-free routes that a router must      examine while computing a forwarding table.  In current practice      with IPv4, it is common to see a prefix announced fifteen times      via different paths.  The complexity of Internet topology is very      likely to increase in the future.  It is important that IPv6      default-free routing support additional complexity as well as a      considerably larger internet.      It should be noted for comparison that the current IPv4 default-      free routing table is approximately 50,000 prefixes.  While this      shows that it is possible to support more routes than 8,192 it is      matter of debate if the number of prefixes supported today in IPv4      is already too high for current routing technology.  There are      serious issues of route stability as well as cases of providers      not supporting all top level prefixes.  The technical requirement      was to pick a TLA ID size that was below, with a reasonable      margin, what was being done with IPv4.      The choice of 13 bits for the TLA field was an engineering      compromise.  Fewer bits would have been too small by not      supporting enough top level organizations.  More bits would have      exceeded what can be reasonably accommodated, with a reasonable      margin, with current routing technology in order to deal with the      issues described in the previous paragraphs.      If in the future, routing technology improves to support a larger      number of top level routes in the default-free routing tables      there are two choices on how to increase the number TLA      identifiers.  The first is to expand the TLA ID field into the      reserved field.  This would increase the number of TLA ID's to      approximately 2 million.  The second approach is to allocate      another format prefix (FP) for use with this address format.      Either or a combination of these approaches allows the number of      TLA ID's to increase significantly.Hinden                       Informational                      [Page 3]

RFC 2450         Proposed TLA and NLA Assignment Rules     December 1998      The size of the Reserved field is 8 bits.  This size was chosen to      allow significant growth of either the TLA ID and/or the NLA ID      fields.      The size of the Next-Level Aggregation Identifier field is 24      bits.  This allows for approximately sixteen million NLA ID's if      used in a flat manner.  Used hierarchically it allows for a      complexity roughly equivalent to the IPv4 address space (assuming      an average network size of 254 interfaces).  If in the future      additional room for complexity is needed in the NLA ID, this may      be accommodated by extending the NLA ID into the Reserved field.      The size of the Site-Level Aggregation Identifier field is 16      bits.  This supports 65,535 individual subnets per site.  The      design goal for the size of this field was to 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.      The Site-Level Aggregation Identifier field was given a fixed size      in order to force the length of all prefixes identifying a      particular site to be the same length (i.e., 48 bits).  This      facilitates movement of sites in the topology (e.g., changing      service providers and multi-homing to multiple service providers).      The Interface ID Interface Identifier field is 64 bits.  This size      was chosen to meet the requirement specified in [ARCH] to support      EUI-64 based Interface Identifiers.   The proposed TLA/NLA assignment rules described in this document are   consistent with these technical requirements.   The specific technical motivation for the proposed TLA/NLA assignment   rules described in this document is as follows:    - Limit the number of top level prefixes in the Internet to a      manageable size.  This is important to insure that the default-      free routing table in the top level routers in the Internet is      kept within the limits, with a reasonable margin, of current      routing technology.    - Only assign top level prefixes to transit providers, not to leaf      sites even if they are multiply homed.  The aggregation address      format is designed to have a clear separation between transit      providers and leaf sites.  Sites which wish to be multihomed to      multiple transit providers have in IPv6 a number of alternatives      to having a top level prefix.Hinden                       Informational                      [Page 4]

RFC 2450         Proposed TLA and NLA Assignment Rules     December 1998    - Only assign top level prefixes to organizations who are capable      and intend to provide operational IPv6 transit services within      three months of assignment.  The goal is to not assign top level      prefixes to organizations who only want a prefix in case they      might provide service sometime in the future.  The assignment of      prefixes is intended to closely match the operational IPv6      Internet and to be consistent with the current practice of      registries making assignments when addresses are actually used.    - Organizations assigned TLA ID's are required to make all the      assignments publically available.  This is necessary in order for      the registries to have accurate information on assignments and to      enable trouble shooting Internet problems.    - Allocation of prefixes that are consistent with the address format      in [AGGR].  Specifically the allocation prefixes that are not      longer than 48 bits as to not infringe into the SLA and Interface      Identifier fields.  This is to facilitate movement of sites in the      topology (e.g., changing service providers and multi-homing to      multiple service providers).5.0 Proposed Rules for Assignment of Top-Level Aggregation ID's   TLA ID's are assigned to organizations providing transit topology.   They are specifically not assigned to organizations only providing   leaf topology.  TLA ID assignment does not imply ownership.  It does   imply stewardship over a valuable Internet resource.   The IAB and IESG have authorized the Internet Assigned Numbers   Authority (IANA) as the appropriate entity to have the responsibility   for the management of the IPv6 address space as defined in [ALLOC].   The IANA will assign small blocks (e.g., few hundred) of TLA ID's to   registries.  The registries will assign the TLA ID's to organizations   meeting the requirements for TLA ID assignment.  When the registries   have assigned all of their TLA ID's they can request that the IANA   give them another block.  The blocks do not have to be contiguous.   The IANA may also assign TLA ID's to organizations directly.  This   includes the temporary TLA assignment for testing and experimental   usage for activities such as the 6bone or new approaches like   exchanges.Hinden                       Informational                      [Page 5]

RFC 2450         Proposed TLA and NLA Assignment Rules     December 19985.1 Proposed TLA Allocation Stages   TLA allocations will be done in two stages.  The first stage is to   allocate a Sub-TLA ID.  When the recipient has demonstrated that they   have assigned more than 90% of the NLA ID for their Sub-TLA ID, they   will be allocated a TLA ID.  The Sub-TLA ID does not have to be   returned.   Sub-TLA ID's are assigned out of TLA ID 0x0001 as follows.  Note that   use of the Reserved field to create the Sub-TLA field is specific to   TLA ID 0x0001.  It does not affect any other TLA.      | 3  |    13    |    13   |       19      |      +----+----------+---------+---------------+      | FP |   TLA    | Sub-TLA |       NLA     |      |    |   ID     |         |       ID      |      +----+----------+---------+---------------+   where:    FP = 001 = Format Prefix       This is the Format Prefix used to identify aggregatable global       unicast addresses.    TLA ID = 0x0001 = Top-Level Aggregation Identifier       This is the TLA ID assigned by the IANA for Sub-TLA allocation.    Sub-TLA ID = Sub-TLA Aggregation Identifier       The Sub-TLA ID field is used by the registries for initial       allocations to organizations meeting the requirements inSection5.2 of this document.  The IANA will assign small blocks (e.g.,       few hundred) of Sub-TLA ID's to registries.  The registries will       assign the Sub-TLA ID's to organizations meeting the requirements       specified inSection 5.2.  When the registries have assigned all       of their Sub-TLA ID's they can request that the IANA give them       another block.  The blocks do not have to be contiguous.  The       IANA may also assign Sub-TLA ID's to organizations directly.       This includes the temporary TLA assignment for testing and       experimental usage for activities such as the 6bone or new       approaches like exchanges.Hinden                       Informational                      [Page 6]

RFC 2450         Proposed TLA and NLA Assignment Rules     December 1998    NLA ID = Next-Level Aggregation Identifier       Next-Level Aggregation ID'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.  SeeSection 6.0 for more detail.   Sub-TLA allocations are interim until the organization receiving the   Sub-TLA can show evidence of IPv6 Internet transit service.  If   transit service can not be demonstrated by three months from the date   of allocation the Sub-TLA allocation will be revoked.   As part of assigning a TLA ID to an organization, the IANA or   Registries may initially only assign a fraction of the NLA ID space   for a particular TLA ID to the organization receiving the TLA ID   assignment.  When the organization has assigned more than 90% of the   NLA ID space it may request additional NLA ID space in its TLA ID.5.2 Proposed Assignment Requirements   The proposed assignment requirements are intended as input from the   IPng working group to the IANA and Registries.  It is not intended   for any official IETF status.   Registries enforce the following requirements for organizations   assigned Sub-TLA and TLA ID's:   1) Must have a plan to offer native IPv6 service within 3 months from      assignment.  The plan must include NLA ID allocation and      registration procedures.  NLA ID allocation and registration may      be subcontracted to other organizations such as a registry.      Native IPv6 service is defined as providing IPv6 service as      defined in the appropriate "IPv6 over <link>" specification such      as "IPv6 over Ethernet" [ETHER], "IPv6 over FDDI" [FDDI], etc.,      for the link at the boundary of the organization.  This should      include running Neighbor Discovery (as appropriate) and exchanging      IPv6 routing information.  The method the organization uses to      carry IPv6 traffic across its network is independent of this      definition and is a local issue for the organization.   2) Must have a verifiable track record of providing Internet transit      to other organizations.  Sub-TLA and/or TLA ID's must not be      assigned to organizations that are only providing leaf service      even if multihomed.Hinden                       Informational                      [Page 7]

RFC 2450         Proposed TLA and NLA Assignment Rules     December 1998      Verification of an organization's track record in providing      Internet transit service must be verified by techniques such as      traceroute, BGP advertisements, etc.   3) Payment of a registration fee to the Internet Assigned Numbers      Authority (IANA).  Registries may also charge some fee for      services rendered, generally in relation to the cost of providing      those services.  All payment of registration and service fees must      be made prior to the actual Sub-TLA ID and/or TLA ID assignment.   4) Must provide registry services for the NLA ID address space it is      responsible for under its Sub-TLA ID and/or TLA ID.  This must      include both sites and next level providers.  The database of NLA      assignments must be public and made available to the registries.   5) Periodically (interval set by registry) provide to registry      utilization statistics of the Sub-TLA ID and/or TLA ID it has      custody of.  The organization must also show evidence of carrying      TLA routing and transit traffic.  This can be in the form of      traffic statistics, traceroutes, routing table dumps, or similar      means.   6) Organizations requesting another Sub-TLA and/or TLA ID must show      evidence to the registries that they have assigned more than 90%      of the NLA ID space in their previous allocations.   Organizations which are given custody of a Sub-TLA ID and/or TLA ID,   and fail to continue to meet all the above requirements may have the   Sub-TLA ID and/or TLA ID custody revoked.6.0 Proposed Rules Assignment of Next-Level Aggregation ID's   Next-Level Aggregation ID's are used by organizations assigned a   Sub-TLA ID and/or 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.   Registries may initially only assign a fraction of the NLA ID space   for a particular Sub-TLA ID and/or TLA ID to the organization   receiving the Sub-TLA ID and/or TLA ID assignment.  When the   organization has assigned more than 90% of the NLA ID space it may   request additional NLA ID space in its Sub-TLA ID and/or TLA ID.   Organizations assigned Sub-TLA ID and/or TLA ID's are required to   assume (directly or indirectly) registry duties for the NLA ID's they   assign.  Each organization assigned a NLA ID is required to assume   registry duties for the next level NLA ID's it assigns and followHinden                       Informational                      [Page 8]

RFC 2450         Proposed TLA and NLA Assignment Rules     December 1998   Registry guidelines.  This responsibility includes passing this   information back to the registry that assigned the TLA and/or   Sub-TLA.  The TLA ID and/or Sub-TLA ID holder collects this   information from the next level, the next level holder collects this   information from the level below, etc.   The design of the bit layout of the NLA ID space for a specific   Sub-TLA ID and/or TLA ID is left to the organization responsible for   that Sub-TLA ID and/or TLA ID.  Likewise the design of the bit layout   of the next level NLA ID is the responsibility of the organization   assigned 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 [CIDR].   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.7.0 Acknowledgments   The author would like to express his thanks to Thomas Narten, Steve   Deering, Bob Fink, Matt Crawford, Rebecca Nitzan, Allison Mankin, Jim   Bound, Christian Huitema, Scott Bradner, Brian Carpenter, John   Stewart, Eric Hoffman, Jon Postel, Daniel Karrenberg, Kim Hubbard,   Mirjam Kuehne, Paula Caslav, David Conrad, and David Kessens for   their review and constructive comments.8.0 Security Considerations   IPv6 addressing documents do not have any direct impact on Internet   infrastructure security.  Authentication of IPv6 packets is defined   in [AUTH].  Authentication of the ownership of prefixes to avoid   "prefix stealing" is a related security issue but is beyond the scope   of this document.9.0 References   [AGGR]    Hinden, R., Deering, S. and M. O'Dell, "An Aggregatable             Global Unicast Address Format",RFC 2374, July 1998.   [ALLOC]   IAB and IESG, "IPv6 Address Allocation Management",RFC1881, December 1995.   [ARCH]    Hinden, R., "IP Version 6 Addressing Architecture",RFC2373, July 1998.Hinden                       Informational                      [Page 9]

RFC 2450         Proposed TLA and NLA Assignment Rules     December 1998   [AUTH]    Atkinson, R. and  S. Kent, "IP Authentication Header",RFC2402, November 1998.   [CIDR]    Fuller, V., Li, T., Varadhan, K. and J. Yu, "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.   [FDDI]    Crawford, M., "Transmission of IPv6 Packets over FDDI             Networks",RFC 2467, December 1998.   [IPV6]    Deering, S. and R. Hinden, Editors, "Internet Protocol,             Version 6 (IPv6) Specification",RFC 2460, December 1998.   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate             Requirement Levels",BCP 14,RFC 2119, March 1997.10.0 Author's Address   Robert M. Hinden   Nokia   232 Java Drive   Sunnyvale, CA 94089   USA   Phone: +1 408 990-2004   EMail: hinden@iprg.nokia.comHinden                       Informational                     [Page 10]

RFC 2450         Proposed TLA and NLA Assignment Rules     December 199811.0  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.Hinden                       Informational                     [Page 11]