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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 2460 (Obsoleted by RFC 8200) == Outdated reference: A later version (-09) exists of draft-ietf-6man-oversized-header-chain-07 == Outdated reference: A later version (-02) exists of draft-taylor-v6ops-fragdrop-01 -- Obsolete informational reference (is this intentional?): RFC 2629 (Obsoleted by RFC 7749) -- Obsolete informational reference (is this intentional?): RFC 5201 (Obsoleted by RFC 7401) Summary: 1 error (**), 0 flaws (~~), 3 warnings (==), 5 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 6man B. Carpenter 3 Internet-Draft Univ. of Auckland 4 Updates: 2460, 2780 (if approved) S. Jiang 5 Intended status: Standards Track Huawei Technologies Co., Ltd 6 Expires: March 30, 2014 September 26, 2013 8 Transmission and Processing of IPv6 Extension Headers 9 draft-ietf-6man-ext-transmit-04 11 Abstract 13 Various IPv6 extension headers have been standardised since the IPv6 14 standard was first published. This document updates RFC 2460 to 15 clarify how intermediate nodes should deal with such extension 16 headers and with any that are defined in future. It also specifies 17 how extension headers should be registered by IANA, with a 18 corresponding minor update to RFC 2780. 20 Status of This Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at http://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on March 30, 2014. 37 Copyright Notice 39 Copyright (c) 2013 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 Table of Contents 54 1. Introduction and Problem Statement . . . . . . . . . . . . . 2 55 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 56 2. Requirement to Transmit Extension Headers . . . . . . . . . . 5 57 2.1. All Extension Headers . . . . . . . . . . . . . . . . . . 5 58 2.2. Hop-by-Hop Options . . . . . . . . . . . . . . . . . . . 6 59 3. Security Considerations . . . . . . . . . . . . . . . . . . . 6 60 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 61 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 62 6. Change log [RFC Editor: Please remove] . . . . . . . . . . . 8 63 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 64 7.1. Normative References . . . . . . . . . . . . . . . . . . 9 65 7.2. Informative References . . . . . . . . . . . . . . . . . 9 66 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 68 1. Introduction and Problem Statement 70 In IPv6, an extension header is any header that follows the initial 71 40 bytes of the packet and precedes the upper layer header (which 72 might be a transport header, an ICMPv6 header, or a notional "No Next 73 Header"). 75 An initial set of IPv6 extension headers was defined by [RFC2460], 76 which also described how they should be handled by intermediate 77 nodes, with the exception of the hop-by-hop options header: 79 "...extension headers are not examined or processed 80 by any node along a packet's delivery path, until the packet reaches 81 the node (or each of the set of nodes, in the case of multicast) 82 identified in the Destination Address field of the IPv6 header." 84 This provision meant that forwarding nodes should be completely 85 transparent to extension headers. There was no provision for 86 forwarding nodes to modify them, remove them, insert them, or use 87 them to affect forwarding behaviour. Thus, new extension headers 88 could be introduced progressively, used only by hosts that have been 89 updated to create and interpret them [RFC6564]. The extension header 90 mechanism is an important part of the IPv6 architecture, and several 91 new extension headers have been standardised since RFC 2460. 93 Today, packets are often forwarded not only by straightforward IP 94 routers, but also by a variety of intermediate nodes, often referred 95 to as middleboxes, such as firewalls, load balancers, or packet 96 classifiers. However, experience has shown that as a result, the 97 network is not transparent to IPv6 extension headers. Contrary to 98 Section 4 of RFC 2460, middleboxes sometimes examine and process the 99 entire IPv6 packet before making a decision to either forward or 100 discard the packet. This means that they need to traverse the chain 101 of extension headers, if present, until they find the transport 102 header (or an encrypted payload). Unfortunately, because not all 103 IPv6 extension headers follow a uniform TLV format, this process is 104 clumsy and requires knowledge of each extension header's format. A 105 separate problem is that the header chain may even be fragmented 106 [I-D.ietf-6man-oversized-header-chain]. 108 The process is potentially slow as well as clumsy, possibly 109 precluding its use in nodes attempting to process packets at line 110 speed. The present document does not intend to solve this problem, 111 which is caused by the fundamental architecture of IPv6 extension 112 headers. This document focuses on clarifying how the header chain 113 should be handled in the current IPv6 architecture. 115 If they encounter an unrecognised extension header type, some 116 firewalls treat the packet as suspect and drop it. Unfortunately, it 117 is an established fact that several widely used firewalls do not 118 recognise some or all of the extension headers standardised since RFC 119 2460. It has also been observed that certain firewalls do not even 120 handle all the extension headers standardised in RFC 2460, including 121 the fragment header [I-D.taylor-v6ops-fragdrop], causing fundamental 122 problems of end-to-end connectivity. This applies in particular to 123 firewalls that attempt to inspect packets at very high speed, since 124 they cannot take the time to reassemble fragmented packets, 125 especially when under a denial of service attack. 127 Other types of middlebox, such as load balancers or packet 128 classifiers, might also fail in the presence of extension headers 129 that they do not recognise. 131 A contributory factor to this problem is that, because extension 132 headers are numbered out of the existing IP Protocol Number space, 133 there is no collected list of them. For this reason, it is hard for 134 an implementor to quickly identify the full set of standard extension 135 headers. An implementor who consults only RFC 2460 will miss all 136 extension headers defined subsequently. 138 This combination of circumstances creates a "Catch-22" situation 139 [Heller] for the deployment of any newly standardised extension 140 header except for local use. It cannot be widely deployed, because 141 existing middleboxes will drop it on many paths through the Internet. 142 However, most middleboxes will not be updated to allow the new header 143 to pass until it has been proved safe and useful on the open 144 Internet, which is impossible until the middleboxes have been 145 updated. 147 The uniform TLV format now defined for extension headers [RFC6564] 148 will improve the situation, but only for future extensions. Some 149 tricky and potentially malicious cases will be avoided by forbidding 150 very long chains of extension headers that need to be fragmented 151 [I-D.ietf-6man-oversized-header-chain]. This will alleviate concerns 152 that stateless firewalls cannot locate a complete header chain as 153 required by the present document. 155 However, these changes are insufficient to correct the underlying 156 problem. The present document clarifies that the above requirement 157 from RFC 2460 applies to all types of nodes that forward IPv6 packets 158 and to all extension headers standardised now and in the future. It 159 also requests IANA to create a subsidiary registry that clearly 160 identifies extension header types, and updates RFC 2780 accordingly. 161 Fundamental changes to the IPv6 extension header architecture are out 162 of scope for this document. 164 Also, Hop-by-Hop options are not handled by many high speed routers, 165 or are processed only on a slow path. This document also updates the 166 requirements for processing the Hop-by-Hop options header to make 167 them more realistic. 169 1.1. Terminology 171 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 172 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 173 document are to be interpreted as described in [RFC2119]. 175 In the remainder of this document, the term "forwarding node" refers 176 to any router, firewall, load balancer, prefix translator, or any 177 other device or middlebox that forwards IPv6 packets with or without 178 examining the packet in any way. 180 In this document "standard" IPv6 extension headers are those 181 specified in detail by IETF standards actions. "Experimental" 182 extension headers are those defined by any Experimental RFC, and the 183 experimental extension header values 253 and 254 defined by [RFC3692] 184 and [RFC4727]. "Defined" extension headers are the "standard" 185 extension headers plus the "experimental" ones. 187 2. Requirement to Transmit Extension Headers 189 2.1. All Extension Headers 191 As mentioned above, forwarding nodes that discard packets containing 192 extension headers are known to cause connectivity failures and 193 deployment problems. Therefore, it is important that forwarding 194 nodes that inspect IPv6 headers can parse all defined extension 195 headers and deal with them appropriately, as specified in this 196 section. 198 Any forwarding node along an IPv6 packet's path, which forwards the 199 packet for any reason, SHOULD do so regardless of any extension 200 headers that are present, as required by RFC 2460. Exceptionally, if 201 a forwarding node is designed to examine extension headers for any 202 reason, such as firewalling, it MUST recognise and deal appropriately 203 with all standard IPv6 extension header types and SHOULD recognise 204 and deal appropriately with experimental IPv6 extension header types. 205 The list of standard and experimental extension header types is 206 maintained by IANA (see Section 4) and implementors are advised to 207 check this list regularly for updates. 209 RFC 2460 requires destination hosts to discard packets containing 210 unrecognised extension headers. However, intermediate forwarding 211 nodes SHOULD NOT do this, since that might cause them to 212 inadvertently discard traffic using a recently standardised extension 213 header, not yet recognised by the intermediate node. The exceptions 214 to this rule are discussed next. 216 If a forwarding node discards a packet containing a standard IPv6 217 extension header, it MUST be the result of a configurable policy, and 218 not just the result of a failure to recognise such a header. This 219 means that the discard policy for each standard type of extension 220 header MUST be individually configurable. The default configuration 221 SHOULD allow all standard extension headers. 223 Experimental IPv6 extension headers SHOULD be treated in the same way 224 as standard extension headers, including an individually configurable 225 discard policy. However, the default configuration MAY drop 226 experimental extension headers. 228 Forwarding nodes MUST be configurable to allow packets containing 229 unrecognised extension headers, but the default configuration MAY 230 drop such packets. 232 The IPv6 Routing Header Types 0 and 1 have been deprecated [RFC5095]. 233 However, this does not mean that the IPv6 Routing Header can be 234 unconditionally dropped by forwarding nodes. Packets containing 235 standardised and undeprecated Routing Headers SHOULD be forwarded by 236 default. At the time of writing, these include Type 2 [RFC6275], 237 Type 3 [RFC6554], and the experimental Routing Header Types 253 and 238 254 [RFC4727]. Others may be defined in future. 240 2.2. Hop-by-Hop Options 242 The IPv6 Hop-by-Hop Options header SHOULD be processed by 243 intermediate forwarding nodes as described in [RFC2460]. However, it 244 is to be expected that high performance routers will either ignore 245 it, or assign packets containing it to a slow processing path. 246 Designers planning to use a Hop-by-Hop option need to be aware of 247 this likely behaviour. 249 As a reminder, in RFC 2460, it is stated that the Hop-by-Hop Options 250 header, if present, must be first. 252 3. Security Considerations 254 Forwarding nodes that operate as firewalls MUST conform to the 255 requirements in the previous section in order to respect the IPv6 256 extension header architecture. In particular, packets containing 257 standard extension headers are only to be discarded as a result of an 258 intentionally configured policy. 260 These changes do not affect a firewall's ability to filter out 261 traffic containing unwanted or suspect extension headers, if 262 configured to do so. However, the changes do require firewalls to be 263 capable of permitting any or all extension headers, if configured to 264 do so. The default configurations are intended to allow normal use 265 of any standard extension header, avoiding the connectivity issues 266 described in Section 1 and Section 2.1. 268 When new extension headers are standardised in the future, those 269 implementing and configuring forwarding nodes, including firewalls, 270 will need to take them into account. A newly defined header will 271 exercise new code paths in a host that does recognise it, so caution 272 may be required. Additional security issues with experimental values 273 or new extension headers are to be found in [RFC4727] and [RFC6564]. 274 As a result, it is to be expected that the deployment process will be 275 slow and will depend on satisfactory operational experience. Until 276 deployment is complete, the new extension will fail in some parts of 277 the Internet. This aspect needs to be considered when deciding to 278 standardise a new extension. Specific security considerations for 279 each new extension should be documented in the document that defines 280 it. 282 4. IANA Considerations 284 IANA is requested to clearly mark in the Assigned Internet Protocol 285 Numbers registry those values which are also IPv6 Extension Header 286 types defined by an IETF Standards Action or IESG Approval (see list 287 below), for example by adding an extra column title "IPv6 Extension 288 Header" to indicate this. This will also apply to any IPv6 Extension 289 Header types defined in the future. 291 Additionally, IANA is requested to make the existing empty IPv6 Next 292 Header Types registry redirect users to a new IPv6 Extension Header 293 Types registry. It will contain only those protocol numbers which 294 are also marked as IPv6 Extension Header types in the Assigned 295 Internet Protocol Numbers registry. Experimental values will be 296 marked as such. The initial list will be as follows: 298 o 0, Hop-by-Hop Options, [RFC2460] 300 o 43, Routing, [RFC2460], [RFC5095] 302 o 44, Fragment, [RFC2460] 304 o 50, Encapsulating Security Payload, [RFC4303] 306 o 51, Authentication, [RFC4302] 308 o 60, Destination Options, [RFC2460] 310 o 135, MIPv6, [RFC6275] 312 o 139, experimental use, HIP, [RFC5201] 314 o 140, shim6, [RFC5533] 316 o 253, experimental use, [RFC3692], [RFC4727] 318 o 254, experimental use, [RFC3692], [RFC4727] 320 This list excludes type 59, No Next Header, [RFC2460], which is not 321 an extension header as such. 323 The references to the IPv6 Next Header field in [RFC2780] are to be 324 interpreted as also applying to the IPv6 Extension Header field and 325 the IPv6 Extension Header Types registry will be managed accordingly. 327 5. Acknowledgements 328 This document was triggered by mailing list discussions including 329 John Leslie, Stefan Marksteiner and others. Valuable comments and 330 contributions were made by Dominique Barthel, Tim Chown, Lorenzo 331 Colitti, Fernando Gont, C. M. Heard, Bob Hinden, Ray Hunter, Suresh 332 Krishnan, Marc Lampo, Sandra Murphy, Michael Richardson, Dan 333 Romascanu, Dave Thaler, Joe Touch, Bjoern Zeeb, and others. 335 Brian Carpenter was a visitor at the Computer Laboratory, Cambridge 336 University during part of this work. 338 This document was produced using the xml2rfc tool [RFC2629]. 340 6. Change log [RFC Editor: Please remove] 342 draft-ietf-6man-ext-transmit-04: updates following IETF Last Call, 343 normative requirements clarified, IANA considerations clarified, 344 security consuderations expanded, 2013-09-26. 346 draft-ietf-6man-ext-transmit-03: added details for experimental 347 values, various clarifications and minor corrections, 2013-08-22. 349 draft-ietf-6man-ext-transmit-02: explicit mention of header types 253 350 and 254, editorial fixes, 2013-08-06. 352 draft-ietf-6man-ext-transmit-01: tuned use of normative language, 353 clarified that only standardised extensions are covered (hence 354 excluding HIP), 2013-05-29. 356 draft-ietf-6man-ext-transmit-00: first WG version, more 357 clarifications, 2013-03-26. 359 draft-carpenter-6man-ext-transmit-02: clarifications following WG 360 comments, recalibrated firewall requirements, 2013-02-22. 362 draft-carpenter-6man-ext-transmit-01: feedback at IETF85: clarify 363 scope and impact on firewalls, discuss line-speed processing and lack 364 of uniform TLV format, added references, restructured IANA 365 considerations, 2012-11-13. 367 draft-carpenter-6man-ext-transmit-00: original version, 2012-08-14. 369 7. References 370 7.1. Normative References 372 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 373 Requirement Levels", BCP 14, RFC 2119, March 1997. 375 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 376 (IPv6) Specification", RFC 2460, December 1998. 378 [RFC2780] Bradner, S. and V. Paxson, "IANA Allocation Guidelines For 379 Values In the Internet Protocol and Related Headers", BCP 380 37, RFC 2780, March 2000. 382 [RFC3692] Narten, T., "Assigning Experimental and Testing Numbers 383 Considered Useful", BCP 82, RFC 3692, January 2004. 385 [RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4, 386 ICMPv6, UDP, and TCP Headers", RFC 4727, November 2006. 388 [RFC6564] Krishnan, S., Woodyatt, J., Kline, E., Hoagland, J., and 389 M. Bhatia, "A Uniform Format for IPv6 Extension Headers", 390 RFC 6564, April 2012. 392 7.2. Informative References 394 [Heller] Heller, J., "Catch-22", Simon and Schuster , 1961. 396 [I-D.ietf-6man-oversized-header-chain] 397 Gont, F., Manral, V., and R. Bonica, "Implications of 398 Oversized IPv6 Header Chains", draft-ietf-6man-oversized- 399 header-chain-07 (work in progress), September 2013. 401 [I-D.taylor-v6ops-fragdrop] 402 Jaeggli, J., Colitti, L., Kumari, W., Vyncke, E., Kaeo, 403 M., and T. Taylor, "Why Operators Filter Fragments and 404 What It Implies", draft-taylor-v6ops-fragdrop-01 (work in 405 progress), June 2013. 407 [RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629, 408 June 1999. 410 [RFC4302] Kent, S., "IP Authentication Header", RFC 4302, December 411 2005. 413 [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 414 4303, December 2005. 416 [RFC5095] Abley, J., Savola, P., and G. Neville-Neil, "Deprecation 417 of Type 0 Routing Headers in IPv6", RFC 5095, December 418 2007. 420 [RFC5201] Moskowitz, R., Nikander, P., Jokela, P., and T. Henderson, 421 "Host Identity Protocol", RFC 5201, April 2008. 423 [RFC5533] Nordmark, E. and M. Bagnulo, "Shim6: Level 3 Multihoming 424 Shim Protocol for IPv6", RFC 5533, June 2009. 426 [RFC6275] Perkins, C., Johnson, D., and J. Arkko, "Mobility Support 427 in IPv6", RFC 6275, July 2011. 429 [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6 430 Routing Header for Source Routes with the Routing Protocol 431 for Low-Power and Lossy Networks (RPL)", RFC 6554, March 432 2012. 434 Authors' Addresses 436 Brian Carpenter 437 Department of Computer Science 438 University of Auckland 439 PB 92019 440 Auckland 1142 441 New Zealand 443 Email: brian.e.carpenter@gmail.com 445 Sheng Jiang 446 Huawei Technologies Co., Ltd 447 Q14, Huawei Campus 448 No.156 Beiqing Road 449 Hai-Dian District, Beijing 100095 450 P.R. China 452 Email: jiangsheng@huawei.com