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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force Thomas Narten 3 Internet-Draft IBM 4 Intended Status: BCP Geoff Huston 5 Expires: July 3, 2011 APNIC 6 Obsoletes: 3177 Lea Roberts 7 Stanford University 8 January 3, 2011 10 IPv6 Address Assignment to End Sites 12 14 Status of this Memo 16 This Internet-Draft is submitted to IETF in full conformance with the 17 provisions of BCP 78 and BCP 79. 19 Internet-Drafts are working documents of the Internet Engineering 20 Task Force (IETF), its areas, and its working groups. Note that 21 other groups may also distribute working documents as Internet- 22 Drafts. 24 Internet-Drafts are draft documents valid for a maximum of six months 25 and may be updated, replaced, or obsoleted by other documents at any 26 time. It is inappropriate to use Internet-Drafts as reference 27 material or to cite them other than as "work in progress." 29 The list of current Internet-Drafts can be accessed at 30 http://www.ietf.org/ietf/1id-abstracts.txt. 32 The list of Internet-Draft Shadow Directories can be accessed at 33 http://www.ietf.org/shadow.html. 35 This Internet-Draft will expire on July 3, 2011. 37 Copyright Notice 39 Copyright (c) 2010 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (http://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 This document may contain material from IETF Documents or IETF 53 Contributions published or made publicly available before November 54 10, 2008. The person(s) controlling the copyright in some of this 55 material may not have granted the IETF Trust the right to allow 56 modifications of such material outside the IETF Standards Process. 57 Without obtaining an adequate license from the person(s) controlling 58 the copyright in such materials, this document may not be modified 59 outside the IETF Standards Process, and derivative works of it may 60 not be created outside the IETF Standards Process, except to format 61 it for publication as an RFC or to translate it into languages other 62 than English. 64 Abstract 66 RFC 3177 argued that in IPv6, end sites should be assigned /48 blocks 67 in most cases. The Regional Internet Registries (RIRs) adopted that 68 recommendation in 2002, but began reconsidering the policy in 2005. 69 This document obsoletes the RFC 3177 recommendations on the 70 assignment of IPv6 address space to end sites. The exact choice of 71 how much address space to assign end sites is an issue for the 72 operational community. The IETF's role in this case is limited to 73 providing guidance on IPv6 architectural and operational 74 considerations. This document reviews the architectural and 75 operational considerations of end site assignments as well as the 76 motivations behind the original 3177 recommendations. Moreover, the 77 document clarifies that a one-size-fits-all recommendation of /48 is 78 not nuanced enough for the broad range of end sites and is no longer 79 recommended as a single default. 81 This document obsoletes RFC 3177. 82 Contents 84 Status of this Memo.......................................... 1 86 1. Introduction............................................. 3 88 2. On /48 Assignments to End Sites.......................... 4 90 3. Other RFC 3177 considerations............................ 6 92 4. Impact on IPv6 Standards................................. 7 93 4.1. RFC3056: Connection of IPv6 Domains via IPv4 Clouds. 7 94 4.2. IPv6 Multicast Addressing........................... 7 96 5. Summary.................................................. 7 98 6. Security Considerations.................................. 8 100 7. IANA Considerations...................................... 8 102 8. Acknowledgments.......................................... 8 104 9. Normative References..................................... 8 106 10. Informative References.................................. 8 108 11. Author's Address........................................ 9 110 1. Introduction 112 There are a number of considerations that factor into address 113 assignment policies. For example, to provide for the long-term health 114 and scalability of the public routing infrastructure, it is important 115 that addresses aggregate well [ROUTE-SCALING]. Likewise, giving out 116 an excessive amount of address space could result in premature 117 depletion of the address space. This document focuses on the (more 118 narrow) question of what is an appropriate IPv6 address assignment 119 size for end sites. That is, when end sites request IPv6 address 120 space from ISPs, what is an appropriate assignment size. 122 RFC 3177 [RFC3177] called for a default end site IPv6 assignment size 123 of /48. Subsequently, the Regional Internet Registries (RIRs) 124 developed and adopted IPv6 address assignment and allocation policies 125 consistent with the RFC 3177 recommendations [RIR-IPV6]. In 2005, the 126 RIRs began discussing IPv6 address assignment policy again. Since 127 then, APNIC [APNIC-ENDSITE], ARIN [ARIN-ENDSITE] and RIPE [RIPE- 128 ENDSITE] have revised the end site assignment policy to encourage the 129 assignment of smaller (i.e., /56) blocks to end sites. 131 This document obsoletes RFC 3177, updating its recommendations in the 132 following ways: 134 1) It is no longer recommended that /128s be given out. While there 135 may be some cases where assigning only a single address may be 136 justified, a site by definition implies multiple subnets and 137 multiple devices. 139 2) RFC 3177 specifically recommended using prefix lengths of /48, 140 /64 and /128. Specifying a small number of fixed boundaries has 141 raised concerns that implementations and operational practices 142 might become "hard-coded" to recognize only those fixed 143 boundaries (i.e., a return to "classful addressing"). The actual 144 intention has always been that there be no hard-coded boundaries 145 within addresses, and that CIDR continues to apply to all bits 146 of the routing prefixes. 148 3) This document moves away from the previous recommendation that a 149 single default assignment size (e.g., a /48) makes sense for all 150 end sites in the general case. End sites come in different 151 shapes and sizes, and a one-size-fits-all approach is not 152 necessary or appropriate. 154 This document does, however, reaffirm an important assumption behind 155 RFC 3177: 157 A key principle for address management is that end sites always 158 be able to obtain a reasonable amount of address space for their 159 actual and planned usage, and over time ranges specified in 160 years rather than just months. In practice, that means at least 161 one /64, and in most cases significantly more. One particular 162 situation that must be avoided is having an end site feel 163 compelled to use IPv6-to-IPv6 Network Address Translation or 164 other burdensome address conservation techniques because it 165 could not get sufficient address space. 167 This document does not make a formal recommendation on what the exact 168 assignment size should be. The exact choice of how much address 169 space to assign end sites is an issue for the operational community. 170 The IETF's role in this case is limited to providing guidance on IPv6 171 architectural and operational considerations. This document provides 172 input into those discussions. The focus of this document is to 173 examine the architectural issues and some of the operational 174 considerations relating to the size of the end site assignment. 176 2. On /48 Assignments to End Sites 178 Looking back at some of the original motivations behind the /48 179 recommendation [RFC3177], there were three main concerns. The first 180 motivation was to ensure that end sites could easily obtain 181 sufficient address space without having to "jump through hoops" to do 182 so. For example, if someone felt they needed more space, just the act 183 of asking would at some level be sufficient justification. As a 184 comparison point, in IPv4, typical home users are given a single 185 public IP address (though even this is not always assured), but 186 getting any more than one address is often difficult or even 187 impossible -- unless one is willing to pay a (significantly) 188 increased fee for what is often considered to be a "higher grade" of 189 service. (It should be noted that increased ISP charges to obtain a 190 small number of additional addresses cannot usually be justified by 191 the real per-address cost levied by RIRs, but additional addresses 192 are frequently only available to end users as part of a different 193 type or "higher grade" of service, for which an additional charge is 194 levied. The point here is that the additional cost is not due to the 195 RIR fee structures, but to business choices ISPs make.) An important 196 goal in IPv6 is to significantly change the default and minimal end 197 site assignment, from "a single address" to "multiple networks" and 198 to ensure that end sites can easily obtain address space. 200 A second motivation behind the original /48 recommendation was to 201 simplify the management of an end site's addressing plan in the 202 presence of renumbering (e.g., when switching ISPs). In IPv6, a site 203 may simultaneously use multiple prefixes, including one or more 204 public prefixes from ISPs as well as Unique Local Addresses [ULA- 205 ADDRESSES]. In the presence of multiple prefixes, it is significantly 206 less complex to manage a numbering plan if the same subnet numbering 207 plan can be used for all prefixes. That is, for a link that has (say) 208 three different prefixes assigned to it, the subnet portion of those 209 prefixes would be identical for all assigned addresses. In contrast, 210 renumbering from a larger set of "subnet bits" into a smaller set is 211 often painful, as it it can require making changes to the network 212 itself (e.g., collapsing subnets). Hence renumbering a site into a 213 prefix that has (at least) the same number of subnet bits is more 214 straightforward, because only the top-level bits of the address need 215 to change. A key goal of the RFC 3177 recommendations is to ensure 216 that upon renumbering, one does not have to deal with renumbering 217 into a smaller subnet size. 219 It should be noted that similar arguments apply to the management of 220 zone files in the DNS. In particular, managing the reverse (ip6.arpa) 221 tree is simplified when all links are numbered using the same subnet 222 ids. 224 A third motivation behind the /48 recommendation was to better 225 support network growth common at many sites. In IPv4, it is usually 226 difficult (or impossible) to obtain public address space for more 227 than a few months worth of projected growth. Thus, even slow growth 228 over several years can lead to the need to renumber into a larger 229 address blocks. With IPv6's vast address space, end sites can easily 230 be given more address space (compared with IPv4) to support expected 231 growth over multi-year time periods. 233 While the /48 recommendation does simplify address space management 234 for end sites, it has also been widely criticized as being wasteful. 235 For example, a large business (which may have thousands of employees) 236 would by default receive the same amount of address space as a home 237 user, who today typically has a single (or small number of) LANs and 238 a small number of devices (dozens or less). While it seems likely 239 that the size of a typical home network will grow over the next few 240 decades, it is hard to argue that home sites will make use of 65K 241 subnets within the foreseeable future. At the same time, it might be 242 tempting to give home sites a single /64, since that is already 243 significantly more address space compared with today's IPv4 practice. 244 However, this precludes the expectation that even home sites will 245 grow to support multiple subnets going forward. Hence, it is strongly 246 intended that even home sites be given multiple subnets worth of 247 space by default. Hence, this document still recommends giving home 248 sites significantly more than a single /64, but does not recommend 249 that every home site be given a /48 either. 251 A change in policy (such as above) would have a significant impact on 252 address consumption projections and the expected longevity for IPv6. 253 For example, changing the default assignment from a /48 to /56 (for 254 the vast majority of end sites, e.g, home sites) would result in a 255 savings of up to 8 bits, reducing the "total projected address 256 consumption" by (up to) 8 bits or two orders of magnitude. (The exact 257 amount of savings depends on the relative number of home users 258 compared with the number of larger sites.) 260 The above-mentioned RFC3177 goals can easily be met by giving home 261 users a default assignment of less than /48, such as a /56. 263 3. Other RFC 3177 considerations 265 RFC3177 suggested that some multihoming approaches (e.g., GSE) might 266 benefit from having a fixed /48 boundary. This no longer appears to 267 be a consideration. 269 RFC3177 argued that having a "one size fits all" default assignment 270 size reduced the need for customers to continually or repeatedly 271 justify usage of existing address space in order to get "a little 272 more". Likewise, it also reduces the need for ISPs to evaluate such 273 requests. Given the large amount of address space in IPv6, there is 274 plenty of space to grant end sites enough space to be consistent with 275 reasonable growth projections over multi-year time frames. Thus, it 276 remains highly desirable to provide end sites with enough space (on 277 both initial and subsequent assignments) to last several years. 278 Fortunately, this goal can be achieved in a number of ways and does 279 not require that all end sites receive the same default size 280 assignment. 282 4. Impact on IPv6 Standards 284 4.1. RFC3056: Connection of IPv6 Domains via IPv4 Clouds 286 RFC3056 [RFC3056] describes a way of generating IPv6 addresses from 287 an existing public IPv4 address. That document describes an address 288 format in which the first 48 bits concatenate a well-known prefix 289 with a globally unique public IPv4 address. The "SLA ID" field is 290 assumed to be 16 bits, consistent with a 16-bit "subnet id" field. To 291 facilitate transitioning from an RFC3056 address numbering scheme to 292 one based on a prefix obtained from an ISP, an end site would be 293 advised to number out of the right most bits first, using the left 294 most bits only if the size of the site made that necessary. 296 Similar considerations apply to other documents that allow for a 297 subnet id of 16 bits, including [ULA-ADDRESSES]. 299 4.2. IPv6 Multicast Addressing 301 Some IPv6 multicast address assignment schemes embed a unicast IPv6 302 prefix into the multicast address itself [RFC3306]. Such documents do 303 not assume a particular size for the subnet id per se, but do assume 304 that the IPv6 prefix is a /64. Thus, the relative size of the subnet 305 id has no direct impact on multicast address schemes. 307 5. Summary 309 The exact choice of how much address space to assign end sites is an 310 issue for the operational community. The RFC 3177 [RFC3177] 311 recommendation to assign /48s as a default is not a requirement of 312 the IPv6 architecture; anything of length /64 or shorter works from a 313 standards perspective. However, there are important operational 314 considerations as well, some of which are important if users are to 315 share in the key benefit of IPv6: expanding the usable address space 316 of the Internet. The IETF recommends that any policy on IPv6 address 317 assignment policy to end sites take into consideration: 319 - it should be easy for an end site to obtain address space to 320 number multiple subnets (i.e., a block larger than a single /64) 321 and to support reasonable growth projections over long time 322 periods (e.g., a decade or more). 324 - the default assignment size should take into consideration the 325 likelihood that an end site will have need for multiple subnets 326 in the future and avoid the IPv4 practice of having frequent and 327 continual justification for obtaining small amounts of 328 additional space 330 - Although a /64 can (in theory) address an almost unlimited 331 number of devices, sites should be given sufficient address 332 space to be able to lay out subnets as appropriate, and not be 333 forced to use address conservation techniques such as using 334 bridging. Whether or not bridging is an appropriate choice is an 335 end site matter. 337 - assigning a longer prefix to an end site, compared with the 338 existing prefixes the end site already has assigned to it, is 339 likely to increase operational costs and complexity for the end 340 site, with insufficient benefit to anyone. 342 - the operational considerations of managing and delegating the 343 reverse DNS tree under ip6.arpa on nibble vs. non-nibble 344 boundaries should be given adequate consideration 346 6. Security Considerations 348 This document has no known security implications. 350 7. IANA Considerations 352 This document makes no requests to IANA. 354 8. Acknowledgments 356 This document was motivated by and benefited from numerous 357 conversations held during the ARIN XV and RIPE 50 meetings in April- 358 May, 2005. 360 9. Normative References 362 10. Informative References 364 [APNIC-ENDSITE] "prop-031: Proposal to amend APNIC IPv6 assignment 365 and utilisation requirement policy," 366 http://www.apnic.net/policy/proposals/prop-031 368 [ARIN-ENDSITE] "2005-8: Proposal to amend ARIN IPv6 assignment and 369 utilisation requirement", 370 http://www.arin.net/policy/proposals/2005_8.html 372 [RIR-IPV6] ARIN: http://www.arin.net/policy/nrpm.html#ipv6; RIPE 373 Document ID: ripe-267, Date: 22 January 2003 374 http://www.ripe.net/ripe/docs/ipv6policy.html; 375 APNIC: 376 http://www.apnic.net/docs/policy/ipv6-address- 377 policy.html 379 [RFC3056] "Connection of IPv6 Domains via IPv4 Clouds," B. Carpenter, 380 K. Moore, RFC 3056, February 2001. 382 [RFC3306] "Unicast-Prefix-based IPv6 Multicast Addresses," B. 383 Haberman, D. Thaler, RFC 3306, August 2002. 385 [RFC3177] IAB/IESG Recommendations on IPv6 Address Allocations to 386 Sites. IAB, IESG. September 2001. 388 [RIPE-ENDSITE] "Proposal to Amend the IPv6 Assignment and Utilisation 389 Requirement Policy", 2005-8, 390 http://ripe.net/ripe/policies/proposals/2005-08.html 392 [ROUTE-SCALING] "Routing and Addressing Problem Statement", draft- 393 narten-radir-problem-statement-05.txt 395 [ULA-ADDRESSES] RFC 4193 "Unique Local IPv6 Unicast Addresses," R. 396 Hinden, B. Haberman, RFC 4193, October 2005. 398 11. Author's Address 400 Thomas Narten 401 IBM Corporation 402 3039 Cornwallis Ave. 403 PO Box 12195 404 Research Triangle Park, NC 27709-2195 406 Phone: 919-254-7798 407 EMail: narten@us.ibm.com 409 Geoff Huston 410 APNIC 412 EMail: gih@apnic.net 413 Rosalea G Roberts 414 Stanford University, Networking Systems 415 P.O. Box 19131 416 Stanford, CA 94309-9131 418 Email: lea.roberts@stanford.edu 419 Phone: +1-650-723-3352