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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reference: RFC 2460 (Obsoleted by RFC 8200) ** Obsolete normative reference: RFC 5201 (Obsoleted by RFC 7401) == Outdated reference: A later version (-09) exists of draft-ietf-6man-oversized-header-chain-04 == Outdated reference: A later version (-02) exists of draft-taylor-v6ops-fragdrop-01 -- Obsolete informational reference (is this intentional?): RFC 2629 (Obsoleted by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) Summary: 2 errors (**), 0 flaws (~~), 3 warnings (==), 4 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: February 23, 2014 August 22, 2013 8 Transmission and Processing of IPv6 Extension Headers 9 draft-ietf-6man-ext-transmit-03 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 February 23, 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 . . . . . . . . . . 4 57 2.1. All Extension Headers . . . . . . . . . . . . . . . . . . 4 58 2.2. Hop-by-Hop Options . . . . . . . . . . . . . . . . . . . 5 59 3. Security Considerations . . . . . . . . . . . . . . . . . . . 6 60 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 61 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 62 6. Change log [RFC Editor: Please remove] . . . . . . . . . . . 7 63 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 64 7.1. Normative References . . . . . . . . . . . . . . . . . . 8 65 7.2. Informative References . . . . . . . . . . . . . . . . . 9 66 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 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 showed 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 traversed 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 node 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 2. Requirement to Transmit Extension Headers 182 2.1. All Extension Headers 184 Any forwarding node along an IPv6 packet's path, which forwards the 185 packet for any reason, SHOULD do so regardless of any extension 186 headers that are present, as required by RFC 2460. Exceptionally, if 187 this node is designed to examine extension headers for any reason, 188 such as firewalling, it MUST recognise and deal appropriately with 189 all standardised IPv6 extension header types and SHOULD recognise 190 experimental IPv6 extension header types. The list of standardised 191 and experimental extension header types is maintained by IANA (see 192 Section 4) and implementors are advised to check this list regularly 193 for updates. 195 RFC 2460 requires destination hosts to discard packets containing 196 unrecognised extension headers. However, intermediate forwarding 197 nodes SHOULD NOT do this by default, since that might cause them to 198 inadvertently discard traffic using a recently standardised extension 199 header, not yet recognised by the intermediate node. The only 200 exceptions to this rule are discussed below. 202 As mentioned above, forwarding nodes that discard packets containing 203 extension headers are known to cause connectivity failures and 204 deployment problems. Therefore, it is important that forwarding 205 nodes that inspect IPv6 extension headers can parse all standard 206 headers and are able to behave according to the above requirements. 207 If a forwarding node discards a packet containing a standard IPv6 208 extension header, it MUST be the result of a configurable policy, and 209 not just the result of a failure to recognise such a header. This 210 means that the discard policy for each standardised type of extension 211 header MUST be individually configurable. The default configuration 212 SHOULD allow all standardised extension headers. 214 Experimental IPv6 extension headers, including types 253 and 254 215 defined by [RFC3692] and [RFC4727], SHOULD be treated in the same way 216 as standardised extension headers, but they MAY be dropped by 217 default. 219 Forwarding nodes MUST be configurable to allow packets containing 220 unrecognised extension headers, but such packets MAY be dropped by 221 default. 223 The IPv6 Routing Header Types 0 and 1 have been deprecated [RFC5095]. 224 However, this does not mean that the IPv6 Routing Header can be 225 unconditionally dropped by forwarding nodes. Packets containing 226 standardised and undeprecated Routing Headers SHOULD be forwarded by 227 default. At the time of writing, these include Type 2 [RFC6275], 228 Type 3 [RFC6554], and the experimental Routing Header Types 253 and 229 254 [RFC4727]. Others may be defined in future. 231 2.2. Hop-by-Hop Options 233 The IPv6 Hop-by-Hop Options header SHOULD be processed by 234 intermediate forwarding nodes as described in [RFC2460]. However, it 235 is to be expected that high performance routers will either ignore 236 it, or assign packets containing it to a slow processing path. 237 Designers planning to use a Hop-by-Hop option need to be aware of 238 this likely behaviour. 240 As a reminder, in RFC 2460, it is stated that the Hop-by-Hop Options 241 header, if present, must be first. 243 3. Security Considerations 245 Forwarding nodes that operate as firewalls MUST conform to the 246 requirements in the previous section in order to respect the IPv6 247 extension header architecture. In particular, packets containing 248 standard extension headers are only to be discarded as a result of a 249 configurable policy. 251 When new extension headers are standardised in the future, those 252 implementing and configuring forwarding nodes, including firewalls, 253 will need to take account of them. A newly defined header will 254 exercise new code paths in a host that does recognise it, so caution 255 may be required. It is therefore to be expected that the deployment 256 process will be slow and will depend on satisfactory operational 257 experience. Until it is complete, the new extension will fail in 258 some parts of the Internet. This aspect needs to be considered when 259 deciding to standardise a new extension. Specific security 260 considerations for each new extension should be documented in the 261 document that defines it. 263 4. IANA Considerations 265 IANA is requested to clearly mark in the Assigned Internet Protocol 266 Numbers registry those values which are also IPv6 Extension Header 267 types defined by an IETF action, for example by adding an extra 268 column to indicate this. This will also apply to any IPv6 Extension 269 Header types defined in the future. 271 Additionally, IANA is requested to replace the existing empty IPv6 272 Next Header Types registry by an IPv6 Extension Header Types 273 registry. It will contain only those protocol numbers which are also 274 marked as IPv6 Extension Header types in the Assigned Internet 275 Protocol Numbers registry. Experimental values will be marked as 276 such. The initial list will be as follows: 278 o 0, Hop-by-Hop Options, [RFC2460] 280 o 43, Routing, [RFC2460], [RFC5095] 282 o 44, Fragment, [RFC2460] 284 o 50, Encapsulating Security Payload, [RFC4303] 286 o 51, Authentication, [RFC4302] 287 o 60, Destination Options, [RFC2460] 289 o 135, MIPv6, [RFC6275] 291 o 139, experimental use, HIP, [RFC5201] 293 o 140, shim6, [RFC5533] 295 o 253, experimental use, [RFC3692], [RFC4727] 297 o 254, experimental use, [RFC3692], [RFC4727] 299 This list excludes type 59, No Next Header, [RFC2460], which is not 300 an extension header as such. 302 The references to the IPv6 Next Header field in [RFC2780] are to be 303 interpreted as also applying to the IPv6 Extension Header field. 305 5. Acknowledgements 307 This document was triggered by mailing list discussions including 308 John Leslie, Stefan Marksteiner and others. Valuable comments and 309 contributions were made by Dominique Barthel, Tim Chown, Lorenzo 310 Colitti, Fernando Gont, C. M. Heard, Bob Hinden, Ray Hunter, Suresh 311 Krishnan, Marc Lampo, Michael Richardson, Dave Thaler, Joe Touch, 312 Bjoern Zeeb, and others. 314 Brian Carpenter was a visitor at the Computer Laboratory, Cambridge 315 University during part of this work. 317 This document was produced using the xml2rfc tool [RFC2629]. 319 6. Change log [RFC Editor: Please remove] 321 draft-ietf-6man-ext-transmit-03: added details for experimental 322 values, various clarifications and minor corrections, 2013-08-22. 324 draft-ietf-6man-ext-transmit-02: explicit mention of header types 253 325 and 254, editorial fixes, 2013-08-06. 327 draft-ietf-6man-ext-transmit-01: tuned use of normative language, 328 clarified that only standardised extensions are covered (hence 329 excluding HIP), 2013-05-29. 331 draft-ietf-6man-ext-transmit-00: first WG version, more 332 clarifications, 2013-03-26. 334 draft-carpenter-6man-ext-transmit-02: clarifications following WG 335 comments, recalibrated firewall requirements, 2013-02-22. 337 draft-carpenter-6man-ext-transmit-01: feedback at IETF85: clarify 338 scope and impact on firewalls, discuss line-speed processing and lack 339 of uniform TLV format, added references, restructured IANA 340 considerations, 2012-11-13. 342 draft-carpenter-6man-ext-transmit-00: original version, 2012-08-14. 344 7. References 346 7.1. Normative References 348 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 349 Requirement Levels", BCP 14, RFC 2119, March 1997. 351 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 352 (IPv6) Specification", RFC 2460, December 1998. 354 [RFC2780] Bradner, S. and V. Paxson, "IANA Allocation Guidelines For 355 Values In the Internet Protocol and Related Headers", BCP 356 37, RFC 2780, March 2000. 358 [RFC3692] Narten, T., "Assigning Experimental and Testing Numbers 359 Considered Useful", BCP 82, RFC 3692, January 2004. 361 [RFC4302] Kent, S., "IP Authentication Header", RFC 4302, December 362 2005. 364 [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 365 4303, December 2005. 367 [RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4, 368 ICMPv6, UDP, and TCP Headers", RFC 4727, November 2006. 370 [RFC5095] Abley, J., Savola, P., and G. Neville-Neil, "Deprecation 371 of Type 0 Routing Headers in IPv6", RFC 5095, December 372 2007. 374 [RFC5201] Moskowitz, R., Nikander, P., Jokela, P., and T. Henderson, 375 "Host Identity Protocol", RFC 5201, April 2008. 377 [RFC5533] Nordmark, E. and M. Bagnulo, "Shim6: Level 3 Multihoming 378 Shim Protocol for IPv6", RFC 5533, June 2009. 380 [RFC6275] Perkins, C., Johnson, D., and J. Arkko, "Mobility Support 381 in IPv6", RFC 6275, July 2011. 383 [RFC6564] Krishnan, S., Woodyatt, J., Kline, E., Hoagland, J., and 384 M. Bhatia, "A Uniform Format for IPv6 Extension Headers", 385 RFC 6564, April 2012. 387 7.2. Informative References 389 [Heller] Heller, J., "Catch-22", Simon and Schuster , 1961. 391 [I-D.ietf-6man-oversized-header-chain] 392 Gont, F., Manral, V., and R. Bonica, "Implications of 393 Oversized IPv6 Header Chains", draft-ietf-6man-oversized- 394 header-chain-04 (work in progress), August 2013. 396 [I-D.taylor-v6ops-fragdrop] 397 Jaeggli, J., Colitti, L., Kumari, W., Vyncke, E., Kaeo, 398 M., and T. Taylor, "Why Operators Filter Fragments and 399 What It Implies", draft-taylor-v6ops-fragdrop-01 (work in 400 progress), June 2013. 402 [RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629, 403 June 1999. 405 [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6 406 Routing Header for Source Routes with the Routing Protocol 407 for Low-Power and Lossy Networks (RPL)", RFC 6554, March 408 2012. 410 Authors' Addresses 412 Brian Carpenter 413 Department of Computer Science 414 University of Auckland 415 PB 92019 416 Auckland 1142 417 New Zealand 419 Email: brian.e.carpenter@gmail.com 421 Sheng Jiang 422 Huawei Technologies Co., Ltd 423 Q14, Huawei Campus 424 No.156 Beiqing Road 425 Hai-Dian District, Beijing 100095 426 P.R. China 428 Email: jiangsheng@huawei.com