ipv6 A. White Internet-Draft A. Williams Expires: May 2, 2003 Motorola November 2002 Automatic Globally Unique Site Local Subnet Allocation draft-white-auto-subnet-00 Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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 and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http:// www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on May 2, 2003. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract This memo specifies an automatically generated globally unique site local address format based on IEEE EUI-48 identifiers. White & Williams Expires May 2, 2003 [Page 1] Internet-Draft Auto Globally Unique SL Subnet Alloc November 2002 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Address Format . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1 Existing Site Local Space . . . . . . . . . . . . . . . . . . 4 2.2 New Allocation . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1 Multihomed links . . . . . . . . . . . . . . . . . . . . . . . 5 3.2 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 8 A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9 Full Copyright Statement . . . . . . . . . . . . . . . . . . . 10 White & Williams Expires May 2, 2003 [Page 2] Internet-Draft Auto Globally Unique SL Subnet Alloc November 2002 1. Introduction Site local addresses are specified by the IPv6 addressing architecture [1]. As specified site local addresses are not globally unique and valid only within a "site". If sites freely allocate from the fec0::/48 space, problems can occur when addresses leak outside a sit or when sites merge. Leakage: Even with strong filtering, it is possible for site local addresses to leak outside the site. Because site local addresses are ambiguous (non-unique), multiple devices may share the same address. When a device outside the site attempts to use such an address, it is desirable that communication reliably fails instead of attempting communciation with an incorrect device. Merging: Since site locals are only required to be unique within a site, problems can occur when merging sites. If the sets of site local addresses used between the two sites are not disjoint, renumbering may be required to merge the sites. Manual allocation of site local prefixes by system administrators results in clustering. Many administrators will allocate subnets fec0:0:0:1::/64, fec0:0:0:2::/64, etc, increasing the likelihood of collision during a merge. This memo specifies a mechanism for generating stable globally unique site local subnet addresses (64 bits) without requiring any registration mechanism, based on router interface MAC address. These addresses are not aggregable, but this is not expected to be a problem within a site. 1.1 Definitions 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. Address Format A router generates a unique 64 bit subnet prefix based on a 48 bit device identifier, such as an IEEE EUI-48 identifier (e.g. ethernet MAC address). For each such identifier the router may allocate a number of subnets. Routers with multiple identifiers (e.g. multiple ethernet interfaces) may choose to use a single identifier to address all attached links (and subnets) or to use each interface's identifier to White & Williams Expires May 2, 2003 [Page 3] Internet-Draft Auto Globally Unique SL Subnet Alloc November 2002 address that link, or a combination thereof. Routers using per- interface allocation may set the subnet bits 0 or to an arbitrary value. Two models are available, depending on the prefix used. Inside existing site local space. New allocation 2.1 Existing Site Local Space The first option is to reserve some of the existing fec0::/10 site local address space for globally unique addresses. The proposed prefix is fef0:/12. The 64 bit subnet prefix consists of the 12 bit prefix "1111 1110 1111" (fef0::/12), the 48 bit device identifier and 4 bits of subnet identifier. --------------------------------------------------------------------- | 12 bits | 48 bits | 4 bits | 64 bits | +---------+------------------+----------+----------------------+ | fef | router device ID | sub ID | machine interface ID | +---------+------------------+----------+----------------------+ | <- subnet prefix -> | | Figure 1: Address Format: fef0::/12 --------------------------------------------------------------------- 2.2 New Allocation The second option is to allocate a new non-aggregable non-globally- routable address space. The proposed space is fe00::/10. The 64 bit subnet prefix consists of the 10 bit prefix "1111 1110 00" (fe00::/ 10), the 48 bit device identifier and 6 bits of subnet identifier. White & Williams Expires May 2, 2003 [Page 4] Internet-Draft Auto Globally Unique SL Subnet Alloc November 2002 --------------------------------------------------------------------- | 10 bits | 48 bits | 6 bits | 64 bits | +---------+------------------+----------+----------------------+ | fe0 | router device ID | sub ID | machine interface ID | +---------+------------------+----------+----------------------+ | <- subnet prefix -> | | Figure 2: Address Format: fe00::/10 --------------------------------------------------------------------- 3. Discussion Subnet prefixes allocated by this mechanism are globally unique to the extent that IEEE EUI-48 device identifiers are globally unique. They persist on the link as long as the allocating router is not changed. They can be configured by the router upon startup without any external communication. Subnet prefixes allocated by this mechanism are generally non- aggregable. This is not expected to be a problem for addressing realms small enough to be considered a 'site'. This proposal provides for globally unique site local addresses without requiring any additional registration. Because addresses are globally unique and generated in a predictable manner, merging does not require renumbering. Out of site hosts attempting communication are more likely to fail, since the addresses are unambiguous and will thus be filtered rather than finding an incorrect device. This mechanism also specifies subnet based allocation, as opposed to site based allocation for global or existing site local address. This allows subnet allocation to be zero-configuration, as the subnet address is allocated by the router rather than additional administrative policy. 3.1 Multihomed links In the case where a link contains two (or more) routers, two options are available. Either the link may be multi-homed, with each router providing a generated site local prefix, or one router may be instructed not to use its automatic prefix and be configured with the prefix from the master router on the link. Multihoming is advantageous in a zero-configuration environment, while the administrator may prefer configuration. White & Williams Expires May 2, 2003 [Page 5] Internet-Draft Auto Globally Unique SL Subnet Alloc November 2002 3.2 Limitations Tying the subnet identifier router EUIs has two potential limitations. Routes are unlikely to be aggregable, and changing routers may cause renumbering. It is envisaged that site scoped networks will be small enough (orders of magnitude less than the global internet) that aggregation is unnecessary for effective routing table operation. Site scoped networks with thousands of links / subnets may cause problems. Router change may be dealt with in several ways. Fully zero- configuration systems should be able to reconfigure themselves to compensate for readdressing. In non-zero-configuration systems, the new router could be configured with the old routers addresses. This assumes that the old router is not being re-used (and thus the EUI-48 remains unique). Alternatively, manually configured subnet prefixes could be allocated to subnets attached to critical servers. 4. Example White & Williams Expires May 2, 2003 [Page 6] Internet-Draft Auto Globally Unique SL Subnet Alloc November 2002 --------------------------------------------------------------------- +----------+ | Router | | A | +--+----+--+ 00:80:ab:cd:ef:02| |00:80:ab:cd:ef:01 | | fef0:080a:bcde:f020::/64| |fef0:080a:bcde:f010::/64 +---------------------------+ +-----+ |fef0:0505:566a:abb0::/64 | | | | | fef0:0409:8675 |00:50:55:66:aa:bb +-----+----+ :4231::/64 +-----+----+ | Router +--------------- | Router | 00:40:98:67:54:23| C | | B | +--+----+--+ fef0:0409:8675 +-----+----+ | | :4233::/64 |00:50:55:66:aa:bb | +------------------ | | |fef0:0505:566a:abb0::/64 +----------------------- | fef0:0409:8675:4234::/64 Figure 3: Sample Network --------------------------------------------------------------------- The above diagram shows a sample network. Routers A and B are using the ethernet MAC address (EUI-48) of each interface to generate subnet addresses. Router C is using a single EUI-48 and using the sub ID bits to generate subnet addresses. Note that the link between A and B is multi-homed based on both A and B's interfaces, while C's interface that links to A has been configured not to serve an address. If this had not been done, C would have allocated the prefix fef0:0409:8675:4232::/64 to that link. In the example above, the proposed fef0::/12 prefix has been used as the conversion from EUI-48 to prefix is clearer. 5. IANA Considerations A top level prefix is required for these addresses. There are two options. If this is to be nested within the existing site-local architecture, White & Williams Expires May 2, 2003 [Page 7] Internet-Draft Auto Globally Unique SL Subnet Alloc November 2002 fef0::/12 is suitable. All 54 bits from 13 to 64 are used to define the subnet identifer. This conflicts with [1] (16 bit SLA) but is in accordance with [3]. Alternatively, a new 10 bit prefix could be allocated from within fe00::/9 (e.g. fe00::/10). 6. Security Considerations This proposal reveals the router's device identifier, thus introducing similar concerns to those described in privacy addressing [2]. While the link may be identified from within the site, site based filtering should restrict these identifiers from leaking outside the site. Mechanisms for preventing site local addresses from leaking to the public internet are beyond the scope of this memo. Unless a router is intended to be installed as part of a site local network, automatic allocation of site local subnet addresses SHOULD be disabled by default. References [1] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 2373, July 1998. [2] Narten, T. and R. Draves, "Privacy Extensions for Stateless Address Autoconfiguration in IPv6", RFC 3041, January 2001. [3] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", ID draft-ietf-ipngwg-addr-arch-v3-11, October 2002. Authors' Addresses Andrew White Motorola Australian Research Centre Locked Bag 5028 Botany, NSW 1455 AU Phone: +61 2 9666 0500 EMail: Andrew.E.White@motorola.com URI: http://www.motorola.com.au/marc/ White & Williams Expires May 2, 2003 [Page 8] Internet-Draft Auto Globally Unique SL Subnet Alloc November 2002 Aidan Williams Motorola Australian Research Centre Locked Bag 5028 Botany, NSW 1455 AU Phone: +61 2 9666 0500 EMail: Aidan.Williams@motorola.com URI: http://www.motorola.com.au/marc/ Appendix A. Acknowledgements TBD. White & Williams Expires May 2, 2003 [Page 9] Internet-Draft Auto Globally Unique SL Subnet Alloc November 2002 Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. 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