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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: March 26, 2011 APNIC 6 Updates: 3177 Lea Roberts 7 Stanford University 8 September 26, 2010 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 January 13, 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 revisits and updates the RFC 3177 recommendations on 70 the assignment of IPv6 address space to end sites. The exact choice 71 of how much address space to assign end sites is an issue for the 72 operational community. The role of the IETF is limited to providing 73 guidance on IPv6 architectural and operational considerations. This 74 document reviews the architectural and operational considerations of 75 end site assignments as well as the motivations behind the original 76 3177 recommendations. Moreover, the document clarifies that a one- 77 size-fits-all recommendation of /48 is not nuanced enough for the 78 broad range of end sites and is no longer recommended as a single 79 default. 81 This document updates and replaces RFC 3177. 83 Contents 85 Status of this Memo.......................................... 1 87 1. Introduction............................................. 3 89 2. On /48 Assignments to End Sites.......................... 4 91 3. Other RFC 3177 considerations............................ 6 93 4. Impact on IPv6 Standards................................. 7 94 4.1. RFC3056: Connection of IPv6 Domains via IPv4 Clouds. 7 95 4.2. IPv6 Multicast Addressing........................... 7 97 5. Summary.................................................. 7 99 6. Security Considerations.................................. 8 101 7. IANA Considerations...................................... 8 103 8. Acknowledgments.......................................... 8 105 9. Normative References..................................... 8 107 10. Informative References.................................. 8 109 11. Author's Address........................................ 9 111 1. Introduction 113 There are a number of considerations that factor into address 114 assignment policies. For example, to provide for the long-term health 115 and scalability of the public routing infrastructure, it is important 116 that addresses aggregate well [ROUTE-SCALING]. Likewise, giving out 117 an excessive amount of address space could result in premature 118 depletion of the address space. This document focuses on the (more 119 narrow) question of what is an appropriate IPv6 address assignment 120 size for end sites. That is, when end sites request IPv6 address 121 space from ISPs, what is an appropriate assignment size. 123 RFC 3177 [RFC3177] called for a default end site IPv6 assignment size 124 of /48. Subsequently, the Regional Internet Registries (RIRs) 125 developed and adopted IPv6 address assignment and allocation policies 126 consistent with the RFC 3177 recommendations [RIR-IPV6]. In 2005, the 127 RIRs began discussing IPv6 address assignment policy again. Since 128 then, APNIC [APNIC-ENDSITE], ARIN [ARIN-ENDSITE] and RIPE [RIPE- 129 ENDSITE] have revised the end site assignment policy to encourage the 130 assignment of smaller (i.e., /56) blocks to end sites. 132 This document updates and replaces the RFC 3177 recommendations. 134 Specifically, this document updates RFC 3177 in the following ways: 136 1) It is no longer recommended that /128s be given out. While there 137 may be some cases where assigning only a single address may be 138 justified, a site by definition implies multiple subnets and 139 multiple devices. 141 2) RFC 3177 specifically recommended using prefix lengths of /48, 142 /64 and /128. Specifying a small number of fixed boundaries has 143 raised concerns that implementations and operational practices 144 might become "hard-coded" to recognize only those fixed 145 boundaries (i.e., a return to "classful addressing"). The actual 146 intention has always been that there be no hard-coded boundaries 147 within addresses, and that CIDR continues to apply to all bits 148 of the routing prefixes. 150 3) This document moves away from the previous recommendation that a 151 single default assignment size (e.g., a /48) makes sense for all 152 end sites in the general case. End sites come in different 153 shapes and sizes, and a one-size-fits-all approach is not 154 necessary or appropriate. 156 This document does, however, reaffirm an important assumption behind 157 RFC 3177: 159 A key principle for address management is that end sites always 160 be able to obtain a reasonable amount of address space for their 161 actual and planned usage, and over time ranges specified in 162 years rather than just months. In practice, that means at least 163 one /64, and in most cases significantly more. One particular 164 situation that must be avoided is having an end site feel 165 compelled to use IPv6-to-IPv6 Network Address Translation or 166 other burdensome address conservation techniques because it 167 could not get sufficient address space. 169 This document does not make a formal recommendation on what the exact 170 assignment size should be. The exact choice of how much address 171 space to assign end sites is an issue for the operational community. 172 The role of the IETF is limited to providing guidance on IPv6 173 architectural and operational considerations. This document provides 174 input into those discussions. The focus of this document is to 175 examine the architectural issues and some of the operational 176 considerations relating to the size of the end site assignment. 178 2. On /48 Assignments to End Sites 180 Looking back at some of the original motivations behind the /48 181 recommendation [RFC3177], there were three main concerns. The first 182 motivation was to ensure that end sites could easily obtain 183 sufficient address space without having to "jump through hoops" to do 184 so. For example, if someone felt they needed more space, just the act 185 of asking would at some level be sufficient justification. As a 186 comparison point, in IPv4, typical home users are given a single 187 public IP address (though even this is not always assured), but 188 getting any more than one address is often difficult or even 189 impossible -- unless one is willing to pay a (significantly) 190 increased fee for what is often considered to be a "higher grade" of 191 service. (It should be noted that increased ISP charges to obtain a 192 small number of additional addresses cannot usually be justified by 193 the real per-address cost levied by RIRs, but additional addresses 194 are frequently only available to end users as part of a different 195 type or "higher grade" of service, for which an additional charge is 196 levied. The point here is that the additional cost is not due to the 197 RIR fee structures, but to business choices ISPs make.) An important 198 goal in IPv6 is to significantly change the default and minimal end 199 site assignment, from "a single address" to "multiple networks" and 200 to ensure that end sites can easily obtain address space. 202 A second motivation behind the original /48 recommendation was to 203 simplify the management of an end site's addressing plan in the 204 presence of renumbering (e.g., when switching ISPs). In IPv6, a site 205 may simultaneously use multiple prefixes, including one or more 206 public prefixes from ISPs as well as Unique Local Addresses [ULA- 207 ADDRESSES]. In the presence of multiple prefixes, it is significantly 208 less complex to manage a numbering plan if the same subnet numbering 209 plan can be used for all prefixes. That is, for a link that has (say) 210 three different prefixes assigned to it, the subnet portion of those 211 prefixes would be identical for all assigned addresses. In contrast, 212 renumbering from a larger set of "subnet bits" into a smaller set is 213 often painful, as it it can require making changes to the network 214 itself (e.g., collapsing subnets). Hence renumbering a site into a 215 prefix that has (at least) the same number of subnet bits is more 216 straightforward, because only the top-level bits of the address need 217 to change. A key goal of the RFC 3177 recommendations is to ensure 218 that upon renumbering, one does not have to deal with renumbering 219 into a smaller subnet size. 221 It should be noted that similar arguments apply to the management of 222 zone files in the DNS. In particular, managing the reverse (ip6.arpa) 223 tree is simplified when all links are numbered using the same subnet 224 ids. 226 A third motivation behind the /48 recommendation was to better 227 support network growth common at many sites. In IPv4, it is usually 228 difficult (or impossible) to obtain public address space for more 229 than a few months worth of projected growth. Thus, even slow growth 230 over several years can lead to the need to renumber into a larger 231 address blocks. With IPv6's vast address space, end sites can easily 232 be given more address space (compared with IPv4) to support expected 233 growth over multi-year time periods. 235 While the /48 recommendation does simplify address space management 236 for end sites, it has also been widely criticized as being wasteful. 237 For example, a large business (which may have thousands of employees) 238 would by default receive the same amount of address space as a home 239 user, who today typically has a single (or small number of) LANs and 240 a small number of devices (dozens or less). While it seems likely 241 that the size of a typical home network will grow over the next few 242 decades, it is hard to argue that home sites will make use of 65K 243 subnets within the foreseeable future. At the same time, it might be 244 tempting to give home sites a single /64, since that is already 245 significantly more address space compared with today's IPv4 practice. 246 However, this precludes the expectation that even home sites will 247 grow to support multiple subnets going forward. Hence, it is strongly 248 intended that even home sites be given multiple subnets worth of 249 space by default. Hence, this document still recommends giving home 250 sites significantly more than a single /64, but does not recommend 251 that every home site be given a /48 either. 253 A change in policy (such as above) would have a significant impact on 254 address consumption projections and the expected longevity for IPv6. 255 For example, changing the default assignment from a /48 to /56 (for 256 the vast majority of end sites, e.g, home sites) would result in a 257 savings of up to 8 bits, reducing the "total projected address 258 consumption" by (up to) 8 bits or two orders of magnitude. (The exact 259 amount of savings depends on the relative number of home users 260 compared with the number of larger sites.) 262 The above-mentioned RFC3177 goals can easily be met by giving home 263 users a default assignment of less than /48, such as a /56. 265 3. Other RFC 3177 considerations 267 RFC3177 suggested that some multihoming approaches (e.g., GSE) might 268 benefit from having a fixed /48 boundary. This no longer appears to 269 be a consideration. 271 RFC3177 argued that having a "one size fits all" default assignment 272 size reduced the need for customers to continually or repeatedly 273 justify usage of existing address space in order to get "a little 274 more". Likewise, it also reduces the need for ISPs to evaluate such 275 requests. Given the large amount of address space in IPv6, there is 276 plenty of space to grant end sites enough space to be consistent with 277 reasonable growth projections over multi-year time frames. Thus, it 278 remains highly desirable to provide end sites with enough space (on 279 both initial and subsequent assignments) to last several years. 280 Fortunately, this goal can be achieved in a number of ways and does 281 not require that all end sites receive the same default size 282 assignment. 284 4. Impact on IPv6 Standards 286 4.1. RFC3056: Connection of IPv6 Domains via IPv4 Clouds 288 RFC3056 [RFC3056] describes a way of generating IPv6 addresses from 289 an existing public IPv4 address. That document describes an address 290 format in which the first 48 bits concatenate a well-known prefix 291 with a globally unique public IPv4 address. The "SLA ID" field is 292 assumed to be 16 bits, consistent with a 16-bit "subnet id" field. To 293 facilitate transitioning from an RFC3056 address numbering scheme to 294 one based on a prefix obtained from an ISP, an end site would be 295 advised to number out of the right most bits first, using the left 296 most bits only if the size of the site made that necessary. 298 Similar considerations apply to other documents that allow for a 299 subnet id of 16 bits, including [ULA-ADDRESSES]. 301 4.2. IPv6 Multicast Addressing 303 Some IPv6 multicast address assignment schemes embed a unicast IPv6 304 prefix into the multicast address itself [RFC3306]. Such documents do 305 not assume a particular size for the subnet id per se, but do assume 306 that the IPv6 prefix is a /64. Thus, the relative size of the subnet 307 id has no direct impact on multicast address schemes. 309 5. Summary 311 The exact choice of how much address space to assign end sites is an 312 issue for the operational community. The RFC 3177 [RFC3177] 313 recommendation to assign /48s as a default is not a requirement of 314 the IPv6 architecture; anything of length /64 or shorter works from a 315 standards perspective. However, there are important operational 316 considerations as well, some of which are important if users are to 317 share in the key benefit of IPv6: expanding the usable address space 318 of the Internet. The IETF recommends that any policy on IPv6 address 319 assignment policy to end sites take into consideration: 321 - it should be easy for an end site to obtain address space to 322 number multiple subnets (i.e., a block larger than a single /64) 323 and to support reasonable growth projections over long time 324 periods (e.g., a decade or more). 326 - the default assignment size should take into consideration the 327 likelihood that an end site will have need for multiple subnets 328 in the future and avoid the IPv4 practice of having frequent and 329 continual justification for obtaining small amounts of 330 additional space 332 - Although a /64 can (in theory) address an almost unlimited 333 number of devices, sites should be given sufficient address 334 space to be able to lay out subnets as appropriate, and not be 335 forced to use address conservation techniques such as using 336 bridging. Whether or not bridging is an appropriate choice is an 337 end site matter. 339 - assigning a longer prefix to an end site, compared with the 340 existing prefixes the end site already has assigned to it, is 341 likely to increase operational costs and complexity for the end 342 site, with insufficient benefit to anyone. 344 - the operational considerations of managing and delegating the 345 reverse DNS tree under ip6.arpa on nibble vs. non-nibble 346 boundaries should be given adequate consideration 348 6. Security Considerations 350 This document has no known security implications. 352 7. IANA Considerations 354 This document makes no requests to IANA. 356 8. Acknowledgments 358 This document was motivated by and benefited from numerous 359 conversations held during the ARIN XV and RIPE 50 meetings in April- 360 May, 2005. 362 9. Normative References 364 10. Informative References 366 [APNIC-ENDSITE] "prop-031: Proposal to amend APNIC IPv6 assignment 367 and utilisation requirement policy," 368 http://www.apnic.net/policy/proposals/prop-031-v002.html 370 [ARIN-ENDSITE] "2005-8: Proposal to amend ARIN IPv6 assignment and 371 utilisation requirement", 372 http://www.arin.net/policy/proposals/2005_8.html 374 [RIR-IPV6] ARIN: http://www.arin.net/policy/nrpm.html#ipv6; RIPE 375 Document ID: ripe-267, Date: 22 January 2003 376 http://www.ripe.net/ripe/docs/ipv6policy.html; 377 APNIC: 378 http://www.apnic.net/docs/policy/ipv6-address- 379 policy.html 381 [RFC3056] "Connection of IPv6 Domains via IPv4 Clouds," B. Carpenter, 382 K. Moore, RFC 3056, February 2001. 384 [RFC3306] "Unicast-Prefix-based IPv6 Multicast Addresses," B. 385 Haberman, D. Thaler, RFC 3306, August 2002. 387 [RFC3177] IAB/IESG Recommendations on IPv6 Address Allocations to 388 Sites. IAB, IESG. September 2001. 390 [RIPE-ENDSITE] "Proposal to Amend the IPv6 Assignment and Utilisation 391 Requirement Policy", 2005-8, 392 http://ripe.net/ripe/policies/proposals/2005-08.html 394 [ROUTE-SCALING] "Routing and Addressing Problem Statement", draft- 395 narten-radir-problem-statement-05.txt 397 [ULA-ADDRESSES] RFC 4193 "Unique Local IPv6 Unicast Addresses," R. 398 Hinden, B. Haberman, RFC 4193, October 2005. 400 11. Author's Address 402 Thomas Narten 403 IBM Corporation 404 3039 Cornwallis Ave. 405 PO Box 12195 406 Research Triangle Park, NC 27709-2195 408 Phone: 919-254-7798 409 EMail: narten@us.ibm.com 411 Geoff Huston 412 APNIC 414 EMail: gih@apnic.net 415 Rosalea G Roberts 416 Stanford University, Networking Systems 417 P.O. Box 19131 418 Stanford, CA 94309-9131 420 Email: lea.roberts@stanford.edu 421 Phone: +1-650-723-3352