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2 IPv6 Operations Working Group (v6ops) F. Gont
3 Internet-Draft SI6 Networks
4 Intended status: Informational N. Hilliard
5 Expires: June 8, 2021 INEX
6 G. Doering
7 SpaceNet AG
8 W. Kumari
9 Google
10 G. Huston
11 APNIC
12 W. Liu
13 Huawei Technologies
14 December 5, 2020
16 Operational Implications of IPv6 Packets with Extension Headers
17 draft-ietf-v6ops-ipv6-ehs-packet-drops-02
19 Abstract
21 This document summarizes the operational implications of IPv6
22 extension headers specified in the IPv6 protocol specification
23 (RFC8200), and attempts to analyze reasons why packets with IPv6
24 extension headers are often dropped in the public Internet.
26 Status of This Memo
28 This Internet-Draft is submitted in full conformance with the
29 provisions of BCP 78 and BCP 79.
31 Internet-Drafts are working documents of the Internet Engineering
32 Task Force (IETF). Note that other groups may also distribute
33 working documents as Internet-Drafts. The list of current Internet-
34 Drafts is at https://datatracker.ietf.org/drafts/current/.
36 Internet-Drafts are draft documents valid for a maximum of six months
37 and may be updated, replaced, or obsoleted by other documents at any
38 time. It is inappropriate to use Internet-Drafts as reference
39 material or to cite them other than as "work in progress."
41 This Internet-Draft will expire on June 8, 2021.
43 Copyright Notice
45 Copyright (c) 2020 IETF Trust and the persons identified as the
46 document authors. All rights reserved.
48 This document is subject to BCP 78 and the IETF Trust's Legal
49 Provisions Relating to IETF Documents
50 (https://trustee.ietf.org/license-info) in effect on the date of
51 publication of this document. Please review these documents
52 carefully, as they describe your rights and restrictions with respect
53 to this document. Code Components extracted from this document must
54 include Simplified BSD License text as described in Section 4.e of
55 the Trust Legal Provisions and are provided without warranty as
56 described in the Simplified BSD License.
58 Table of Contents
60 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
61 2. Disclaimer . . . . . . . . . . . . . . . . . . . . . . . . . 3
62 3. Background Information . . . . . . . . . . . . . . . . . . . 3
63 4. Previous Work on IPv6 Extension Headers . . . . . . . . . . . 5
64 5. Packet Forwarding Engine Constraints . . . . . . . . . . . . 7
65 5.1. Recirculation . . . . . . . . . . . . . . . . . . . . . . 8
66 6. Requirement to Process Layer-3/layer-4 information in
67 Intermediate Systems . . . . . . . . . . . . . . . . . . . . 8
68 6.1. ECMP and Hash-based Load-Sharing . . . . . . . . . . . . 8
69 6.2. Enforcing infrastructure ACLs . . . . . . . . . . . . . . 9
70 6.3. DDoS Management and Customer Requests for Filtering . . . 9
71 6.4. Network Intrusion Detection and Prevention . . . . . . . 10
72 6.5. Firewalling . . . . . . . . . . . . . . . . . . . . . . . 10
73 7. Operational Implications . . . . . . . . . . . . . . . . . . 11
74 7.1. Inability to Find Layer-4 Information . . . . . . . . . . 11
75 7.2. Route-Processor Protection . . . . . . . . . . . . . . . 11
76 7.3. Inability to Perform Fine-grained Filtering . . . . . . . 12
77 7.4. Security Concerns Associated with IPv6 Extension Headers 12
78 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
79 9. Security Considerations . . . . . . . . . . . . . . . . . . . 13
80 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
81 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
82 11.1. Normative References . . . . . . . . . . . . . . . . . . 14
83 11.2. Informative References . . . . . . . . . . . . . . . . . 15
84 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
86 1. Introduction
88 IPv6 Extension Headers (EHs) allow for the extension of the IPv6
89 protocol, and provide support for core functionality such as IPv6
90 fragmentation. However, common implementation limitations suggest
91 that EHs present a challenge for IPv6 packet routing equipment and
92 middle-boxes, and evidence exists that IPv6 packets with EHs are
93 intentionally dropped in the public Internet in some network
94 deployments.
96 The authors of this document have been involved in numerous
97 discussions about IPv6 extension headers (both within the IETF and in
98 other fora), and have noticed that the security and operational
99 implications associated with IPv6 EHs were unknown to the larger
100 audience participating in these discussions.
102 This document has the following goals:
104 o Raise awareness about the operational and security implications of
105 IPv6 Extension Headers specified in [RFC8200], and present reasons
106 why some networks resort to intentionally dropping packets
107 containing IPv6 Extension Headers.
109 o Highlight areas where current IPv6 support by networking devices
110 maybe sub-optimal, such that the aforementioned support is
111 improved.
113 o Highlight operational issues associated with IPv6 extension
114 headers, such that those issues are considered in IETF
115 standardization efforts.
117 Section 3 provides background information about the IPv6 packet
118 structure and associated implications. Section 4 of this document
119 summarizes the previous work that has been carried out in the area of
120 IPv6 extension headers. Section 5 discusses packet forwarding engine
121 constraints in contemporary routers. Section 6 discusses why
122 contemporary routers and middle-boxes may need to access Layer-4
123 information to make a forwarding decision. Finally, Section 7
124 discusses the operational implications of IPv6 EHs.
126 2. Disclaimer
128 This document analyzes the operational challenges represented by
129 packets that employ IPv6 Extension Headers, and documents some of the
130 operational reasons why these packets are often dropped in the public
131 Internet. This document is not a recommendation to drop such
132 packets, but rather an analysis of why they are dropped.
134 3. Background Information
136 It is useful to compare the basic structure of IPv6 packets against
137 that of IPv4 packets, and analyze the implications of the two
138 different packet structures.
140 IPv4 packets have a variable-length header size, that allows for the
141 use of IPv4 "options" -- optional information that may be of use by
142 nodes processing IPv4 packets. The IPv4 header length is specified
143 in the IHL header field of the mandatory IPv4 header, and must be in
144 the range from 20 octets (the minimum IPv4 header size) to 60 octets
145 (accommodating at most 40 octets of options). The upper-layer
146 protocol type is specified via the "Protocol" field of the mandatory
147 IPv4 header.
149 Protocol, IHL
150 +--------+
151 | |
152 | v
153 +------//-----+------------------------+
154 | | |
155 | IPv4 | Upper-Layer |
156 | Header | Protocol |
157 | | |
158 +-----//------+------------------------+
160 variable length
161 <------------->
163 Figure 1: IPv4 Packet Structure
165 IPv6 took a different approach to the IPv6 packet structure. Rather
166 than employing a variable-length header as IPv4 does, IPv6 employs a
167 linked-list-like packet structure, where a mandatory fixed-length
168 IPv6 header is followed by an arbitrary number of optional extension
169 headers, with the upper-layer header being the last header in the
170 IPv6 header chain. Each extension header typically specifies its
171 length (unless it is implicit from the extension header type), and
172 the "next header" type that follows in the IPv6 IPv6 header chain.
174 NH NH, EH-length NH, EH-length
175 +-------+ +------+ +-------+
176 | | | | | |
177 | v | v | v
178 +-------------+-------------+-//-+---------------+--------------+
179 | | | | | |
180 | IPv6 | Ext. | | Ext. | Upper-Layer |
181 | header | Header | | Header | Protocol |
182 | | | | | |
183 +-------------+-------------+-//-+---------------+--------------+
185 fixed length variable number of EHs & length
186 <------------> <-------------------------------->
188 Figure 2: IPv6 Packet Structure
190 This packet structure has the following implications:
192 o [RFC8200] requires the entire IPv6 header chain to be contained in
193 the first fragment of a packet, therefore limiting the IPv6
194 extension header chain to the size of the Path-MTU.
196 o Other than the Path-MTU constraints, there are no other limits to
197 the number of IPv6 EHs that may be present in a packet.
198 Therefore, there is no upper-limit regarding "how deep into the
199 IPv6 packet" the upper-layer may be found.
201 o The only way for a node to obtain the upper-layer protocol type or
202 find the upper-layer protocol header is to parse and process the
203 entire IPv6 header chain, in sequence, starting from the mandatory
204 IPv6 header, until the last header in the IPv6 header chain is
205 found.
207 4. Previous Work on IPv6 Extension Headers
209 Some of the operational implications of IPv6 Extension Headers have
210 been discussed in IETF circles:
212 o [I-D.taylor-v6ops-fragdrop] discusses a rationale for which
213 operators drop IPv6 fragments.
215 o [I-D.wkumari-long-headers] discusses possible issues arising from
216 "long" IPv6 header chains.
218 o [I-D.kampanakis-6man-ipv6-eh-parsing] describes how
219 inconsistencies in the way IPv6 packets with extension headers are
220 parsed by different implementations could result in evasion of
221 security controls, and presents guidelines for parsing IPv6
222 extension headers with the goal of providing a common and
223 consistent parsing methodology for IPv6 implementations.
225 o [I-D.ietf-opsec-ipv6-eh-filtering] analyzes the security
226 implications of IPv6 EHs, and the operational implications of
227 dropping packets that employ IPv6 EHs and associated options.
229 o [RFC7113] discusses how some popular RA-Guard implementations are
230 subject to evasion by means of IPv6 extension headers.
232 o [RFC8900] analyzes the fragility introduced by IP fragmentation.
234 A number of recent RFCs have discussed issues related to IPv6
235 extension headers, specifying updates to a previous revision of the
236 IPv6 standard ([RFC2460]), many of which have now been incorporated
237 into the current IPv6 core standard ([RFC8200]) or the IPv6 Node
238 Requirements ([RFC8504]). Namely,
239 o [RFC5095] discusses the security implications of Routing Header
240 Type 0 (RTH0), and deprecates it.
242 o [RFC5722] analyzes the security implications of overlapping
243 fragments, and provides recommendations in this area.
245 o [RFC7045] clarifies how intermediate nodes should deal with IPv6
246 extension headers.
248 o [RFC7112] discusses the issues arising in a specific fragmentation
249 case where the IPv6 header chain is fragmented into two or more
250 fragments (and formally forbids such fragmentation case).
252 o [RFC6946] discusses a flawed (but common) processing of the so-
253 called IPv6 "atomic fragments", and specified improved processing
254 of such packets.
256 o [RFC8021] deprecates the generation of IPv6 atomic fragments.
258 o [RFC8504] clarifies processing rules for packets with extension
259 headers, and also allows hosts to enforce limits on the number of
260 options included in IPv6 EHs.
262 o [RFC7739] discusses the security implications of predictable
263 fragment Identification values, and provides recommendations for
264 the generation of these values.
266 o [RFC6980] analyzes the security implications of employing IPv6
267 fragmentation with Neighbor Discovery for IPv6, and formally
268 recommends against such usage.
270 Additionally, [RFC8200] has relaxed the requirement that "all nodes
271 examine and process the Hop-by-Hop Options header" from [RFC2460], by
272 specifying that only nodes that have been explicitly configured to
273 process the Hop-by-Hop Options header are required to do so.
275 A number of studies have measured the extent to which packets
276 employing IPv6 extension headers are dropped in the public Internet:
278 o [PMTUD-Blackholes] and [Linkova-Gont-IEPG90] presented some
279 preliminary measurements regarding the extent to which packet
280 containing IPv6 EHs are dropped in the public Internet.
282 o [RFC7872] presents more comprehensive results and documents the
283 methodology for obtaining the presented results.
285 o [Huston-2017] and [Huston-2020] measured packet drops resulting
286 from IPv6 fragmentation when communicating with DNS servers.
288 5. Packet Forwarding Engine Constraints
290 Most contemporary routers use dedicated hardware (e.g. ASICs or
291 NPUs) to determine how to forward packets across their internal
292 fabrics (see [IEPG94-Scudder] and [APNIC-Scudder] for details). One
293 of the common methods of handling next-hop lookup is to send a small
294 portion of the ingress packet to a lookup engine with specialised
295 hardware (e.g. ternary CAM or RLDRAM) to determine the packet's next-
296 hop. Technical constraints mean that there is a trade-off between
297 the amount of data sent to the lookup engine and the overall
298 performance of the lookup engine. If more data is sent, the lookup
299 engine can inspect further into the packet, but the overall
300 performance of the system will be reduced. If less data is sent, the
301 overall performance of the router will be increased but the packet
302 lookup engine may not be able to inspect far enough into a packet to
303 determine how it should be handled.
305 NOTE:
306 For example, contemporary high-end routers can use up to 192 bytes
307 of header (Cisco ASR9000 Typhoon) or 384 bytes of header (Juniper
308 MX Trio).
310 If a hardware forwarding engine on a contemporary router cannot make
311 a forwarding decision about a packet because critical information is
312 not sent to the look-up engine, then the router will normally drop
313 the packet.
315 NOTE:
316 Section 6 discusses some of the reasons for which a contemporary
317 router might need to access layer-4 information to make a
318 forwarding decision.
320 Historically, some packet forwarding engines punted packets of this
321 form to the control plane for more in-depth analysis, but this is
322 unfeasible on most current router architectures as a result of the
323 vast difference between the hardware forwarding capacity of the
324 router and processing capacity of the control plane and the size of
325 the management link which connects the control plane to the
326 forwarding plane.
328 If an IPv6 header chain is sufficiently long that it exceeds the
329 packet look-up capacity of the router, the router could resort to
330 dropping the packet, as a result of being unable to determine how the
331 packet should be handled.
333 5.1. Recirculation
335 Although TLV chains are amenable to iterative processing on
336 architectures that have packet look-up engines with deep inspection
337 capabilities, some packet forwarding engines manage IPv6 Extension
338 Header chains using recirculation. This approach processes Extension
339 Headers one at a time: when processing on one Extension Header is
340 completed, the packet is looped back through the processing engine
341 again. This recirculation process continues repeatedly until there
342 are no more Extension Headers left to be processed.
344 Recirculation is typically used on packet forwarding engines with
345 limited look-up capability, because it allows arbitrarily long header
346 chains to be processed without the complexity and cost associated
347 with packet forwarding engines which have deep look-up capabilities.
348 However, recirculation can impact the forwarding capacity of
349 hardware, as each packet will pass through the processing engine
350 multiple times. Depending on configuration, the type of packets
351 being processed, and the hardware capabilities of the packet
352 forwarding engine, this could impact data-plane throughput
353 performance on the router.
355 6. Requirement to Process Layer-3/layer-4 information in Intermediate
356 Systems
358 The following subsections discuss some of the reasons for which
359 contemporary routers and middle-boxes may need to process Layer-3/
360 layer-4 information to make a forwarding decision.
362 6.1. ECMP and Hash-based Load-Sharing
364 In the case of ECMP (equal cost multi path) load sharing, the router
365 on the sending side of the link needs to make a decision regarding
366 which of the links to use for a given packet. Since round-robin
367 usage of the links is usually avoided to prevent packet reordering,
368 forwarding engines need to use a mechanism that will consistently
369 forward the same data streams down the same forwarding paths. Most
370 forwarding engines achieve this by calculating a simple hash using an
371 n-tuple gleaned from a combination of layer-2 through to layer-4
372 packet header information. This n-tuple will typically use the src/
373 dst MAC address, src/dst IP address, and if possible further layer-4
374 src/dst port information. Layer-4 port information can increase the
375 entropy of the hash, and it is often thought desirable to use it if
376 available.
378 We note that in the IPv6 world, flows are expected to be identified
379 by means of the IPv6 Flow Label [RFC6437]. Thus, ECMP and Hash-based
380 Load-Sharing would be possible without the need to process the entire
381 IPv6 header chain to obtain upper-layer information to identify
382 flows. However, we note that for a long time many IPv6
383 implementations failed to set the Flow Label, and ECMP and Hash-based
384 Load-Sharing devices also did not employ the Flow Label for
385 performing their task.
387 Clearly, widespread support of [RFC6437] would relieve middle-boxes
388 from having to process the entire IPv6 header chain, making Flow
389 Label-based ECMP and Hash-based Load-Sharing [RFC6438] feasible.
391 While support of [RFC6437] is currently widespread for current
392 versions of all popular host implementations, there is still only
393 marginal usage of the IPv6 Flow Label for ECMP and load balancing
394 [Cunha-2020]. A contributing factor could be the issues that have
395 been found in host implementations and middle-boxes [Jaeggli-2018].
397 6.2. Enforcing infrastructure ACLs
399 Generally speaking, infrastructure ACLs (iACLs) drop unwanted packets
400 destined to parts of a provider's infrastructure, because they are
401 not operationally needed and can be used for attacks of different
402 sorts against router control planes. Some traffic needs to be
403 differentiated depending on layer-3 or layer-4 criteria to achieve a
404 useful balance of protection and functionality, for example:
406 o Permit some amount of ICMP echo (ping) traffic towards a router's
407 addresses for troubleshooting.
409 o Permit BGP sessions on the shared network of an exchange point
410 (potentially differentiating between the amount of packets/seconds
411 permitted for established sessions and connection establishment),
412 but do not permit other traffic from the same peer IP addresses.
414 6.3. DDoS Management and Customer Requests for Filtering
416 The case of customer DDoS protection and edge-to-core customer
417 protection filters is similar in nature to the infrastructure ACL
418 protection. Similar to infrastructure ACL protection, layer-4 ACLs
419 generally need to be applied as close to the edge of the network as
420 possible, even though the intent is usually to protect the customer
421 edge rather than the provider core. Application of layer-4 DDoS
422 protection to a network edge is often automated using Flowspec
423 [RFC5575].
425 For example, a web site that normally only handled traffic on TCP
426 ports 80 and 443 could be subject to a volumetric DDoS attack using
427 NTP and DNS packets with randomised source IP address, thereby
428 rendering traditional [RFC5635] source-based real-time black hole
429 mechanisms useless. In this situation, DDoS protection ACLs could be
430 configured to block all UDP traffic at the network edge without
431 impairing the web server functionality in any way. Thus, being able
432 to block arbitrary protocols at the network edge can avoid DDoS-
433 related problems both in the provider network and on the customer
434 edge link.
436 6.4. Network Intrusion Detection and Prevention
438 Network Intrusion Detection Systems (NIDS) examine network traffic
439 and try to identify traffic patterns that can be correlated to
440 network-based attacks. These systems generally inspect application-
441 layer traffic (if possible), but at the bare minimum inspect layer-4
442 flows. When attack activity is inferred, the operator is signaled of
443 the potential intrusion attempt.
445 Network Intrusion Prevention Systems (IPS) operate similarly to
446 NIDS's, but they can also prevent intrusions by reacting to detected
447 attack attempts by e.g., triggering packet filtering policies at
448 firewalls and other devices.
450 Use of extension headers can result problematic for NIDS/IPS, since:
452 o Extension headers increase the complexity of resulting traffic,
453 and the associated work and system requirements to process it.
455 o Use of unknown extension headers can prevent an NIDS/IPS to
456 process layer-4 information
458 o Use of IPv6 fragmentation requires a stateful fragment-reassembly
459 operation, even for decoy traffic employing forged source
460 addresses (see e.g. [nmap]).
462 As a result, in order to increase the efficiency or effectiveness of
463 these systems, packets employing IPv6 extension headers are often
464 dropped at the network ingress point(s) of networks that deploy these
465 systems.
467 6.5. Firewalling
469 Firewalls enforce security policies by means of packet filtering.
470 These systems generally inspect layer-3 and layer-4 traffic, and can
471 often also examine application-layer traffic flows.
473 As with NIDS/IPS (Section 6.4), use of IPv6 extension headers can
474 represent a challenge to network firewalls, since:
476 o Extension headers increase the complexity of resulting traffic,
477 and the associated work and system requirements to process it (see
478 e.g. [Zack-FW-Benchmark]).
480 o Use of unknown extension headers can prevent firewalls to process
481 layer-4 information
483 o Use of IPv6 fragmentation requires a stateful fragment-reassembly
484 operation, even for decoy traffic employing forged source
485 addresses (see e.g. [nmap]).
487 Additionally, a common firewall filtering policy is the so-called
488 "default deny", where all traffic is blocked (by default), and only
489 expected traffic is added to an "allow/accept list".
491 As a result, whether because of the challenges represented by
492 extension headers or because the use of IPv6 extension headers has
493 not been explicitly allowed, packets employing IPv6 extension headers
494 are often dropped by network firewalls.
496 7. Operational Implications
498 7.1. Inability to Find Layer-4 Information
500 As discussed in Section 6, contemporary routers and middle-boxes that
501 need to find the layer-4 header must process the entire IPv6
502 extension header chain. When such devices are unable to obtain the
503 required information, the forwarding device has the option to drop
504 the packet unconditionally, forward the packet unconditionally, or
505 process the packet outside the normal forwarding path. Forwarding
506 packets unconditionally will usually allow for the circumvention of
507 security controls (see e.g. Section 6.5), while processing packets
508 outside of the normal forwarding path will usually open the door to
509 DoS attacks (see e.g. Section 5). Thus, in these scenarios, devices
510 often simply resort to dropping such packets unconditionally.
512 7.2. Route-Processor Protection
514 Most contemporary routers have a fast hardware-assisted forwarding
515 plane and a loosely coupled control plane, connected together with a
516 link that has much less capacity than the forwarding plane could
517 handle. Traffic differentiation cannot be done by the control plane
518 side, because this would overload the internal link connecting the
519 forwarding plane to the control plane.
521 The Hop-by-Hop Options header has been particularly challenging since
522 in most circumstances, the corresponding packet is punted to the
523 control plane for processing. As a result, operators usually drop
524 IPv6 packets containing this extension header. Please see [RFC6192]
525 for advice regarding protection of the router control plane.
527 7.3. Inability to Perform Fine-grained Filtering
529 Some router implementations do not have support for fine-grained
530 filtering of IPv6 extension headers. For example, an operator that
531 wishes to drop packets containing Routing Header Type 0 (RHT0), may
532 only be able to filter on the extension header type (Routing Header).
533 This could result in an operator enforcing a more coarse filtering
534 policy (e.g. "drop all packets containing a Routing Header" vs. "only
535 drop packets that contain a Routing Header Type 0").
537 7.4. Security Concerns Associated with IPv6 Extension Headers
539 The security implications of IPv6 Extension Headers generally fall
540 into one or more of these categories:
542 o Evasion of security controls
544 o DoS due to processing requirements
546 o DoS due to implementation errors
548 o Extension Header-specific issues
550 Unlike IPv4 packets where the upper-layer protocol can be trivially
551 found by means of the "IHL" ("Internet Header Length") IPv4 header
552 field, the structure of IPv6 packets is more flexible and complex,
553 and can represent a challenge for devices that need to find this
554 information, since locating upper-layer protocol information requires
555 that all IPv6 extension headers be examined. This has presented
556 implementation difficulties, and some packet filtering mechanisms
557 that require upper-layer information (even if just the upper layer
558 protocol type) can be trivially circumvented by inserting IPv6
559 Extension Headers between the main IPv6 header and the upper layer
560 protocol. [RFC7113] describes this issue for the RA-Guard case, but
561 the same techniques could be employed to circumvent other IPv6
562 firewall and packet filtering mechanisms. Additionally,
563 implementation inconsistencies in packet forwarding engines can
564 result in evasion of security controls
565 [I-D.kampanakis-6man-ipv6-eh-parsing] [Atlasis2014] [BH-EU-2014].
567 Packets with attached IPv6 Extension Headers can impact performance
568 on routers that forward them. Unless appropriate mitigations are put
569 in place (e.g., packet dropping and/or rate-limiting), an attacker
570 could simply send a large amount of IPv6 traffic employing IPv6
571 Extension Headers with the purpose of performing a Denial of Service
572 (DoS) attack (see Section 7 for further details).
574 NOTE:
575 In the most trivial case, a packet that includes a Hop-by-Hop
576 Options header might go through the slow forwarding path, and be
577 processed by the router's CPU. Another possible case might be
578 where a router that has been configured to enforce an ACL based on
579 upper-layer information (e.g., upper layer protocol or TCP
580 Destination Port), needs to process the entire IPv6 header chain
581 (in order to find the required information), causing the packet to
582 be processed in the slow path [Cisco-EH-Cons]. We note that, for
583 obvious reasons, the aforementioned performance issues can affect
584 other devices such as firewalls, Network Intrusion Detection
585 Systems (NIDS), etc. [Zack-FW-Benchmark]. The extent to which
586 these devices are affected is typically implementation-dependent.
588 IPv6 implementations, like all other software, tend to mature with
589 time and wide-scale deployment. While the IPv6 protocol itself has
590 existed for over 20 years, serious bugs related to IPv6 Extension
591 Header processing continue to be discovered (see e.g. [Cisco-Frag1],
592 [Cisco-Frag2], and [FreeBSD-SA]). Because there is currently little
593 operational reliance on IPv6 Extension headers, the corresponding
594 code paths are rarely exercised, and there is the potential for bugs
595 that still remain to be discovered in some implementations.
597 IPv6 Fragment Headers are employed to allow fragmentation of IPv6
598 packets. While many of the security implications of the
599 fragmentation / reassembly mechanism are known from the IPv4 world,
600 several related issues have crept into IPv6 implementations. These
601 range from denial of service attacks to information leakage, as
602 discussed in [RFC7739], [Bonica-NANOG58] and [Atlasis2012]).
604 8. IANA Considerations
606 There are no IANA registries within this document. The RFC-Editor
607 can remove this section before publication of this document as an
608 RFC.
610 9. Security Considerations
612 The security implications of IPv6 extension headers are discussed in
613 Section 7.4. This document does not introduce any new security
614 issues.
616 10. Acknowledgements
618 The authors would like to thank (in alphabetical order) Mikael
619 Abrahamsson, Fred Baker, Dale W. Carder, Brian Carpenter, Tim Chown,
620 Owen DeLong, Gorry Fairhurst, Tom Herbert, Lee Howard, Tom Petch,
621 Sander Steffann, Eduard Vasilenko, Eric Vyncke, Jingrong Xie, and
622 Andrew Yourtchenko, for providing valuable comments on earlier
623 versions of this document.
625 Fernando Gont would like to thank Jan Zorz / Go6 Lab
626 , Jared Mauch, and Sander Steffann
627 , for providing access to systems and networks
628 that were employed to perform experiments and measurements involving
629 packets with IPv6 Extension Headers.
631 11. References
633 11.1. Normative References
635 [RFC5095] Abley, J., Savola, P., and G. Neville-Neil, "Deprecation
636 of Type 0 Routing Headers in IPv6", RFC 5095,
637 DOI 10.17487/RFC5095, December 2007,
638 .
640 [RFC5722] Krishnan, S., "Handling of Overlapping IPv6 Fragments",
641 RFC 5722, DOI 10.17487/RFC5722, December 2009,
642 .
644 [RFC6946] Gont, F., "Processing of IPv6 "Atomic" Fragments",
645 RFC 6946, DOI 10.17487/RFC6946, May 2013,
646 .
648 [RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation
649 with IPv6 Neighbor Discovery", RFC 6980,
650 DOI 10.17487/RFC6980, August 2013,
651 .
653 [RFC7112] Gont, F., Manral, V., and R. Bonica, "Implications of
654 Oversized IPv6 Header Chains", RFC 7112,
655 DOI 10.17487/RFC7112, January 2014,
656 .
658 [RFC8021] Gont, F., Liu, W., and T. Anderson, "Generation of IPv6
659 Atomic Fragments Considered Harmful", RFC 8021,
660 DOI 10.17487/RFC8021, January 2017,
661 .
663 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
664 (IPv6) Specification", STD 86, RFC 8200,
665 DOI 10.17487/RFC8200, July 2017,
666 .
668 [RFC8504] Chown, T., Loughney, J., and T. Winters, "IPv6 Node
669 Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504,
670 January 2019, .
672 11.2. Informative References
674 [APNIC-Scudder]
675 Scudder, J., "Modern router architecture and IPv6", APNIC
676 Blog, June 4, 2020, .
679 [Atlasis2012]
680 Atlasis, A., "Attacking IPv6 Implementation Using
681 Fragmentation", BlackHat Europe 2012. Amsterdam,
682 Netherlands. March 14-16, 2012,
683 .
686 [Atlasis2014]
687 Atlasis, A., "A Novel Way of Abusing IPv6 Extension
688 Headers to Evade IPv6 Security Devices", May 2014,
689 .
692 [BH-EU-2014]
693 Atlasis, A., Rey, E., and R. Schaefer, "Evasion of High-
694 End IDPS Devices at the IPv6 Era", BlackHat Europe 2014,
695 2014, .
698 [Bonica-NANOG58]
699 Bonica, R., "IPV6 FRAGMENTATION: The Case For
700 Deprecation", NANOG 58. New Orleans, Louisiana, USA. June
701 3-5, 2013, .
704 [Cisco-EH-Cons]
705 Cisco, "IPv6 Extension Headers Review and Considerations",
706 October 2006,
707 .
710 [Cisco-Frag1]
711 Cisco, "Cisco IOS Software IPv6 Virtual Fragmentation
712 Reassembly Denial of Service Vulnerability", September
713 2013, .
716 [Cisco-Frag2]
717 Cisco, "Cisco IOS XR Software Crafted IPv6 Packet Denial
718 of Service Vulnerability", June 2015,
719 .
722 [Cunha-2020]
723 Cunha, I., "IPv4 vs IPv6 load balancing in Internet
724 routes", NPS/CAIDA 2020 Virtual IPv6 Workshop, 2020,
725 .
728 [FreeBSD-SA]
729 FreeBSD, "FreeBSD Security Advisory FreeBSD-SA-20:24.ipv6:
730 IPv6 Hop-by-Hop options use-after-free bug", September
731 2020, .
734 [Huston-2017]
735 Huston, G., "Dealing with IPv6 fragmentation in the
736 DNS", APNIC Blog, 2017,
737 .
740 [Huston-2020]
741 Huston, G., "Measurement of IPv6 Extension Header
742 Support", NPS/CAIDA 2020 Virtual IPv6 Workshop, 2020,
743 .
746 [I-D.ietf-opsec-ipv6-eh-filtering]
747 Gont, F. and W. LIU, "Recommendations on the Filtering of
748 IPv6 Packets Containing IPv6 Extension Headers", draft-
749 ietf-opsec-ipv6-eh-filtering-06 (work in progress), July
750 2018.
752 [I-D.kampanakis-6man-ipv6-eh-parsing]
753 Kampanakis, P., "Implementation Guidelines for parsing
754 IPv6 Extension Headers", draft-kampanakis-6man-ipv6-eh-
755 parsing-01 (work in progress), August 2014.
757 [I-D.taylor-v6ops-fragdrop]
758 Jaeggli, J., Colitti, L., Kumari, W., Vyncke, E., Kaeo,
759 M., and T. Taylor, "Why Operators Filter Fragments and
760 What It Implies", draft-taylor-v6ops-fragdrop-02 (work in
761 progress), December 2013.
763 [I-D.wkumari-long-headers]
764 Kumari, W., Jaeggli, J., Bonica, R., and J. Linkova,
765 "Operational Issues Associated With Long IPv6 Header
766 Chains", draft-wkumari-long-headers-03 (work in progress),
767 June 2015.
769 [IEPG94-Scudder]
770 Petersen, B. and J. Scudder, "Modern Router Architecture
771 for Protocol Designers", IEPG 94. Yokohama, Japan.
772 November 1, 2015, .
775 [Jaeggli-2018]
776 Jaeggli, G., "Dealing with IPv6 fragmentation in the
777 DNS", APNIC Blog, 2018,
778 .
781 [Linkova-Gont-IEPG90]
782 Linkova, J. and F. Gont, "IPv6 Extension Headers in the
783 Real World v2.0", IEPG 90. Toronto, ON, Canada. July 20,
784 2014, .
787 [nmap] Fyodor, "Dealing with IPv6 fragmentation in the
788 DNS", Firewall/IDS Evasion and Spoofing,
789 .
791 [PMTUD-Blackholes]
792 De Boer, M. and J. Bosma, "Discovering Path MTU black
793 holes on the Internet using RIPE Atlas", July 2012,
794 .
797 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
798 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
799 December 1998, .
801 [RFC5575] Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J.,
802 and D. McPherson, "Dissemination of Flow Specification
803 Rules", RFC 5575, DOI 10.17487/RFC5575, August 2009,
804 .
806 [RFC5635] Kumari, W. and D. McPherson, "Remote Triggered Black Hole
807 Filtering with Unicast Reverse Path Forwarding (uRPF)",
808 RFC 5635, DOI 10.17487/RFC5635, August 2009,
809 .
811 [RFC6192] Dugal, D., Pignataro, C., and R. Dunn, "Protecting the
812 Router Control Plane", RFC 6192, DOI 10.17487/RFC6192,
813 March 2011, .
815 [RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
816 "IPv6 Flow Label Specification", RFC 6437,
817 DOI 10.17487/RFC6437, November 2011,
818 .
820 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
821 for Equal Cost Multipath Routing and Link Aggregation in
822 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011,
823 .
825 [RFC7045] Carpenter, B. and S. Jiang, "Transmission and Processing
826 of IPv6 Extension Headers", RFC 7045,
827 DOI 10.17487/RFC7045, December 2013,
828 .
830 [RFC7113] Gont, F., "Implementation Advice for IPv6 Router
831 Advertisement Guard (RA-Guard)", RFC 7113,
832 DOI 10.17487/RFC7113, February 2014,
833 .
835 [RFC7739] Gont, F., "Security Implications of Predictable Fragment
836 Identification Values", RFC 7739, DOI 10.17487/RFC7739,
837 February 2016, .
839 [RFC7872] Gont, F., Linkova, J., Chown, T., and W. Liu,
840 "Observations on the Dropping of Packets with IPv6
841 Extension Headers in the Real World", RFC 7872,
842 DOI 10.17487/RFC7872, June 2016,
843 .
845 [RFC8900] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O.,
846 and F. Gont, "IP Fragmentation Considered Fragile",
847 BCP 230, RFC 8900, DOI 10.17487/RFC8900, September 2020,
848 .
850 [Zack-FW-Benchmark]
851 Zack, E., "Firewall Security Assessment and Benchmarking
852 IPv6 Firewall Load Tests", IPv6 Hackers Meeting #1,
853 Berlin, Germany. June 30, 2013,
854 .
858 Authors' Addresses
860 Fernando Gont
861 SI6 Networks
862 Segurola y Habana 4310, 7mo Piso
863 Villa Devoto, Ciudad Autonoma de Buenos Aires
864 Argentina
866 Email: fgont@si6networks.com
867 URI: https://www.si6networks.com
869 Nick Hilliard
870 INEX
871 4027 Kingswood Road
872 Dublin 24
873 IE
875 Email: nick@inex.ie
877 Gert Doering
878 SpaceNet AG
879 Joseph-Dollinger-Bogen 14
880 Muenchen D-80807
881 Germany
883 Email: gert@space.net
885 Warren Kumari
886 Google
887 1600 Amphitheatre Parkway
888 Mountain View, CA 94043
889 US
891 Email: warren@kumari.net
892 Geoff Huston
894 Email: gih@apnic.net
895 URI: http://www.apnic.net
897 Will (Shucheng) Liu
898 Huawei Technologies
899 Bantian, Longgang District
900 Shenzhen 518129
901 P.R. China
903 Email: liushucheng@huawei.com