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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: August 14, 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 February 10, 2021
16 Operational Implications of IPv6 Packets with Extension Headers
17 draft-ietf-v6ops-ipv6-ehs-packet-drops-04
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 August 14, 2021.
43 Copyright Notice
45 Copyright (c) 2021 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 . . . . . . . . . . . . . . . . . . . . . . 13
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 This document has the following goals:
98 o Raise awareness about the operational and security implications of
99 IPv6 Extension Headers specified in [RFC8200], and present reasons
100 why some networks resort to intentionally dropping packets
101 containing IPv6 Extension Headers.
103 o Highlight areas where current IPv6 support by networking devices
104 maybe sub-optimal, such that the aforementioned support is
105 improved.
107 o Highlight operational issues associated with IPv6 extension
108 headers, such that those issues are considered in IETF
109 standardization efforts.
111 Section 3 provides background information about the IPv6 packet
112 structure and associated implications. Section 4 of this document
113 summarizes the previous work that has been carried out in the area of
114 IPv6 extension headers. Section 5 discusses packet forwarding engine
115 constraints in contemporary routers. Section 6 discusses why
116 contemporary routers and middle-boxes may need to access Layer-4
117 information to make a forwarding decision. Finally, Section 7
118 discusses the operational implications of IPv6 EHs.
120 2. Disclaimer
122 This document analyzes the operational challenges represented by
123 packets that employ IPv6 Extension Headers, and documents some of the
124 operational reasons why these packets are often dropped in the public
125 Internet. This document is not a recommendation to drop such
126 packets, but rather an analysis of why they are dropped.
128 3. Background Information
130 It is useful to compare the basic structure of IPv6 packets against
131 that of IPv4 packets, and analyze the implications of the two
132 different packet structures.
134 IPv4 packets have a variable-length header size, that allows for the
135 use of IPv4 "options" -- optional information that may be of use by
136 nodes processing IPv4 packets. The IPv4 header length is specified
137 in the IHL header field of the mandatory IPv4 header, and must be in
138 the range from 20 octets (the minimum IPv4 header size) to 60 octets
139 (accommodating at most 40 octets of options). The upper-layer
140 protocol type is specified via the "Protocol" field of the mandatory
141 IPv4 header.
143 Protocol, IHL
144 +--------+
145 | |
146 | v
147 +------//-----+------------------------+
148 | | |
149 | IPv4 | Upper-Layer |
150 | Header | Protocol |
151 | | |
152 +-----//------+------------------------+
154 variable length
155 <------------->
157 Figure 1: IPv4 Packet Structure
159 IPv6 took a different approach to the IPv6 packet structure. Rather
160 than employing a variable-length header as IPv4 does, IPv6 employs a
161 linked-list-like packet structure, where a mandatory fixed-length
162 IPv6 header is followed by an arbitrary number of optional extension
163 headers, with the upper-layer header being the last header in the
164 IPv6 header chain. Each extension header typically specifies its
165 length (unless it is implicit from the extension header type), and
166 the "next header" type that follows in the IPv6 IPv6 header chain.
168 NH NH, EH-length NH, EH-length
169 +-------+ +------+ +-------+
170 | | | | | |
171 | v | v | v
172 +-------------+-------------+-//-+---------------+--------------+
173 | | | | | |
174 | IPv6 | Ext. | | Ext. | Upper-Layer |
175 | header | Header | | Header | Protocol |
176 | | | | | |
177 +-------------+-------------+-//-+---------------+--------------+
179 fixed length variable number of EHs & length
180 <------------> <-------------------------------->
182 Figure 2: IPv6 Packet Structure
184 This packet structure has the following implications:
186 o [RFC8200] requires the entire IPv6 header chain to be contained in
187 the first fragment of a packet, therefore limiting the IPv6
188 extension header chain to the size of the path MTU.
190 o Other than the path MTU constraints, there are no other limits to
191 the number of IPv6 EHs that may be present in a packet.
192 Therefore, there is no upper-limit regarding "how deep into the
193 IPv6 packet" the upper-layer may be found.
195 o The only way for a node to obtain the upper-layer protocol type or
196 find the upper-layer protocol header is to parse and process the
197 entire IPv6 header chain, in sequence, starting from the mandatory
198 IPv6 header, until the last header in the IPv6 header chain is
199 found.
201 4. Previous Work on IPv6 Extension Headers
203 Some of the operational implications of IPv6 Extension Headers have
204 been discussed at the IETF:
206 o [I-D.taylor-v6ops-fragdrop] discusses a rationale for which
207 operators drop IPv6 fragments.
209 o [I-D.wkumari-long-headers] discusses possible issues arising from
210 "long" IPv6 header chains.
212 o [I-D.kampanakis-6man-ipv6-eh-parsing] describes how
213 inconsistencies in the way IPv6 packets with extension headers are
214 parsed by different implementations could result in evasion of
215 security controls, and presents guidelines for parsing IPv6
216 extension headers with the goal of providing a common and
217 consistent parsing methodology for IPv6 implementations.
219 o [I-D.ietf-opsec-ipv6-eh-filtering] analyzes the security
220 implications of IPv6 EHs, and the operational implications of
221 dropping packets that employ IPv6 EHs and associated options.
223 o [RFC7113] discusses how some popular RA-Guard implementations are
224 subject to evasion by means of IPv6 extension headers.
226 o [RFC8900] analyzes the fragility introduced by IP fragmentation.
228 A number of recent RFCs have discussed issues related to IPv6
229 extension headers, specifying updates to a previous revision of the
230 IPv6 standard ([RFC2460]), many of which have now been incorporated
231 into the current IPv6 core standard ([RFC8200]) or the IPv6 Node
232 Requirements ([RFC8504]). Namely,
234 o [RFC5095] discusses the security implications of Routing Header
235 Type 0 (RTH0), and deprecates it.
237 o [RFC5722] analyzes the security implications of overlapping
238 fragments, and provides recommendations in this area.
240 o [RFC7045] clarifies how intermediate nodes should deal with IPv6
241 extension headers.
243 o [RFC7112] discusses the issues arising in a specific fragmentation
244 case where the IPv6 header chain is fragmented into two or more
245 fragments (and formally forbids such fragmentation case).
247 o [RFC6946] discusses a flawed (but common) processing of the so-
248 called IPv6 "atomic fragments", and specified improved processing
249 of such packets.
251 o [RFC8021] deprecates the generation of IPv6 atomic fragments.
253 o [RFC8504] clarifies processing rules for packets with extension
254 headers, and also allows hosts to enforce limits on the number of
255 options included in IPv6 EHs.
257 o [RFC7739] discusses the security implications of predictable
258 fragment Identification values, and provides recommendations for
259 the generation of these values.
261 o [RFC6980] analyzes the security implications of employing IPv6
262 fragmentation with Neighbor Discovery for IPv6, and formally
263 recommends against such usage.
265 Additionally, [RFC8200] has relaxed the requirement that "all nodes
266 examine and process the Hop-by-Hop Options header" from [RFC2460], by
267 specifying that only nodes that have been explicitly configured to
268 process the Hop-by-Hop Options header are required to do so.
270 A number of studies have measured the extent to which packets
271 employing IPv6 extension headers are dropped in the public Internet:
273 o [PMTUD-Blackholes] and [Linkova-Gont-IEPG90] presented some
274 preliminary measurements regarding the extent to which packet
275 containing IPv6 EHs are dropped in the public Internet.
277 o [RFC7872] presents more comprehensive results and documents the
278 methodology used to obtain these results.
280 o [Huston-2017] and [Huston-2020] measured packet drops resulting
281 from IPv6 fragmentation when communicating with DNS servers.
283 5. Packet Forwarding Engine Constraints
285 Most contemporary routers use dedicated hardware (e.g., ASICs or
286 NPUs) to determine how to forward packets across their internal
287 fabrics (see [IEPG94-Scudder] and [APNIC-Scudder] for details). One
288 of the common methods of handling next-hop lookup is to send a small
289 portion of the ingress packet to a lookup engine with specialised
290 hardware (e.g., ternary CAM or RLDRAM) to determine the packet's
291 next-hop. Technical constraints mean that there is a trade-off
292 between the amount of data sent to the lookup engine and the overall
293 performance of the lookup engine. If more data is sent, the lookup
294 engine can inspect further into the packet, but the overall
295 performance of the system will be reduced. If less data is sent, the
296 overall performance of the router will be increased but the packet
297 lookup engine may not be able to inspect far enough into a packet to
298 determine how it should be handled.
300 NOTE:
301 For example, some contemporary high-end routers are known to use
302 up to 192 bytes or 384 bytes of header.
304 If a hardware forwarding engine on a contemporary router cannot make
305 a forwarding decision about a packet because critical information is
306 not sent to the look-up engine, then the router will normally drop
307 the packet. Section 6 discusses some of the reasons for which a
308 contemporary router might need to access layer-4 information to make
309 a forwarding decision.
311 Historically, some packet forwarding engines punted packets of this
312 form to the control plane for more in-depth analysis, but this is
313 unfeasible on most contemporary router architectures as a result of
314 the vast difference between the hardware forwarding capacity of the
315 router and processing capacity of the control plane and the size of
316 the management link which connects the control plane to the
317 forwarding plane. Other platforms may have a separate software
318 forwarding plane that is distinct both from the hardware forwarding
319 plane and the control plane. However, the limited CPU resources of
320 this software-based forwarding plane, as well as the limited
321 bandwidth of the associated link results in similar throughput
322 constraints.
324 If an IPv6 header chain is sufficiently long that it exceeds the
325 packet look-up capacity of the router, the router might be unable to
326 determine how the packet should be handled, and thus could resort to
327 dropping the packet.
329 5.1. Recirculation
331 Although TLV chains are amenable to iterative processing on
332 architectures that have packet look-up engines with deep inspection
333 capabilities, some packet forwarding engines manage IPv6 Extension
334 Header chains using recirculation. This approach processes Extension
335 Headers one at a time: when processing on one Extension Header is
336 completed, the packet is looped back through the processing engine
337 again. This recirculation process continues repeatedly until there
338 are no more Extension Headers left to be processed.
340 Recirculation is typically used on packet forwarding engines with
341 limited look-up capability, because it allows arbitrarily long header
342 chains to be processed without the complexity and cost associated
343 with packet forwarding engines which have deep look-up capabilities.
344 However, recirculation can impact the forwarding capacity of
345 hardware, as each packet will pass through the processing engine
346 multiple times. Depending on configuration, the type of packets
347 being processed, and the hardware capabilities of the packet
348 forwarding engine, this could impact data-plane throughput
349 performance on the router.
351 6. Requirement to Process Layer-3/layer-4 information in Intermediate
352 Systems
354 The following subsections discuss some of the reasons for which
355 contemporary routers and middle-boxes may need to process Layer-3/
356 layer-4 information to make a forwarding decision.
358 6.1. ECMP and Hash-based Load-Sharing
360 In the case of ECMP (equal cost multi path) load sharing, the router
361 on the sending side of the link needs to make a decision regarding
362 which of the links to use for a given packet. Since round-robin
363 usage of the links is usually avoided to prevent packet reordering,
364 forwarding engines need to use a mechanism that will consistently
365 forward the same data streams down the same forwarding paths. Most
366 forwarding engines achieve this by calculating a simple hash using an
367 n-tuple gleaned from a combination of layer-2 through to layer-4
368 packet header information. This n-tuple will typically use the src/
369 dst MAC address, src/dst IP address, and if possible further layer-4
370 src/dst port information.
372 In the IPv6 world, flows are expected to be identified by means of
373 the IPv6 Flow Label [RFC6437]. Thus, ECMP and Hash-based Load-
374 Sharing should be possible without the need to process the entire
375 IPv6 header chain to obtain upper-layer information to identify
376 flows. Historically, many IPv6 implementations failed to set the
377 Flow Label, and ECMP / hash-based load-sharing devices also did not
378 employ the Flow Label for performing their task. Clearly, widespread
379 support of [RFC6437] would relieve middle-boxes from having to
380 process the entire IPv6 header chain, making Flow Label-based ECMP
381 and Hash-based Load-Sharing [RFC6438] feasible.
383 While support of [RFC6437] is currently widespread for current
384 versions of all popular host implementations, there is still only
385 marginal usage of the IPv6 Flow Label for ECMP and load balancing
386 [Cunha-2020]. A contributing factor could be the issues that have
387 been found in host implementations and middle-boxes [Jaeggli-2018].
389 6.2. Enforcing infrastructure ACLs
391 Infrastructure ACLs (iACLs) drop unwanted packets destined to a
392 network's infrastructure IP addresses. Typically, iACLs are deployed
393 because external direct access to a network's infrastructure
394 addresses is operationally unnecessary, and can be used for attacks
395 of different sorts against router control planes. To this end,
396 traffic usually needs to be differentiated on the basis of layer-3 or
397 layer-4 criteria to achieve a useful balance of protection and
398 functionality. For example, an infrastructure may be configured with
399 the following policy:
401 o Permit some amount of ICMP echo (ping) traffic towards a router's
402 addresses for troubleshooting.
404 o Permit BGP sessions on the shared network of an exchange point
405 (potentially differentiating between the amount of packets/seconds
406 permitted for established sessions and connection establishment),
407 but do not permit other traffic from the same peer IP addresses.
409 6.3. DDoS Management and Customer Requests for Filtering
411 The case of customer DDoS protection and edge-to-core customer
412 protection filters is similar in nature to the iACL protection.
413 Similar to iACL protection, layer-4 ACLs generally need to be applied
414 as close to the edge of the network as possible, even though the
415 intent is usually to protect the customer edge rather than the
416 provider core. Application of layer-4 DDoS protection to a network
417 edge is often automated using Flowspec [RFC5575].
419 For example, a web site that normally only handled traffic on TCP
420 ports 80 and 443 could be subject to a volumetric DDoS attack using
421 NTP and DNS packets with randomised source IP address, thereby
422 rendering traditional [RFC5635] source-based real-time black hole
423 mechanisms useless. In this situation, DDoS protection ACLs could be
424 configured to block all UDP traffic at the network edge without
425 impairing the web server functionality in any way. Thus, being able
426 to block arbitrary protocols at the network edge can avoid DDoS-
427 related problems both in the provider network and on the customer
428 edge link.
430 6.4. Network Intrusion Detection and Prevention
432 Network Intrusion Detection Systems (NIDS) examine network traffic
433 and try to identify traffic patterns that can be correlated to
434 network-based attacks. These systems generally inspect application-
435 layer traffic (if possible), but at the bare minimum inspect layer-4
436 flows. When attack activity is inferred, the operator is notified of
437 the potential intrusion attempt.
439 Network Intrusion Prevention Systems (IPS) operate similarly to
440 NIDS's, but they can also prevent intrusions by reacting to detected
441 attack attempts by e.g., triggering packet filtering policies at
442 firewalls and other devices.
444 Use of extension headers can be problematic for NIDS/IPS, since:
446 o Extension headers increase the complexity of resulting traffic,
447 and the associated work and system requirements to process it.
449 o Use of unknown extension headers can prevent an NIDS/IPS from
450 processing layer-4 information
452 o Use of IPv6 fragmentation requires a stateful fragment-reassembly
453 operation, even for decoy traffic employing forged source
454 addresses (see e.g., [nmap]).
456 As a result, in order to increase the efficiency or effectiveness of
457 these systems, packets employing IPv6 extension headers are often
458 dropped at the network ingress point(s) of networks that deploy these
459 systems.
461 6.5. Firewalling
463 Firewalls enforce security policies by means of packet filtering.
464 These systems usually inspect layer-3 and layer-4 traffic, but can
465 often also examine application-layer traffic flows.
467 As with NIDS/IPS (Section 6.4), use of IPv6 extension headers can
468 represent a challenge to network firewalls, since:
470 o Extension headers increase the complexity of resulting traffic,
471 and the associated work and system requirements to process it (see
472 e.g., [Zack-FW-Benchmark]).
474 o Use of unknown extension headers can prevent firewalls from
475 processing layer-4 information.
477 o Use of IPv6 fragmentation requires a stateful fragment-reassembly
478 operation, even for decoy traffic employing forged source
479 addresses (see e.g., [nmap]).
481 Additionally, a common firewall filtering policy is the so-called
482 "default deny", where all traffic is blocked (by default), and only
483 expected traffic is added to an "allow/accept list".
485 As a result, packets employing IPv6 extension headers are often
486 dropped by network firewalls, either because of the challenges
487 represented by extension headers or because the use of IPv6 extension
488 headers has not been explicitly allowed.
490 7. Operational Implications
492 7.1. Inability to Find Layer-4 Information
494 As discussed in Section 6, routers and middle-boxes that need to find
495 the layer-4 header must process the entire IPv6 extension header
496 chain. When such devices are unable to obtain the required
497 information, the forwarding device has the option to drop the packet
498 unconditionally, forward the packet unconditionally, or process the
499 packet outside the normal forwarding path. Forwarding packets
500 unconditionally will usually allow for the circumvention of security
501 controls (see e.g., Section 6.5), while processing packets outside of
502 the normal forwarding path will usually open the door to DoS attacks
503 (see e.g., Section 5). Thus, in these scenarios, devices often
504 simply resort to dropping such packets unconditionally.
506 7.2. Route-Processor Protection
508 Most contemporary routers have a fast hardware-assisted forwarding
509 plane and a loosely coupled control plane, connected together with a
510 link that has much less capacity than the forwarding plane could
511 handle. Traffic differentiation cannot be performed by the control
512 plane, because this would overload the internal link connecting the
513 forwarding plane to the control plane.
515 The Hop-by-Hop Options header has been particularly challenging since
516 in most circumstances, the corresponding packet is punted to the
517 control plane for processing. As a result, operators usually drop
518 IPv6 packets containing this extension header. [RFC6192] provides
519 advice regarding protection of a router's control plane.
521 7.3. Inability to Perform Fine-grained Filtering
523 Some router implementations do not have support for fine-grained
524 filtering of IPv6 extension headers. For example, an operator that
525 wishes to drop packets containing Routing Header Type 0 (RHT0), may
526 only be able to filter on the extension header type (Routing Header).
527 This could result in an operator enforcing a more coarse filtering
528 policy (e.g., "drop all packets containing a Routing Header" vs.
529 "only drop packets that contain a Routing Header Type 0").
531 7.4. Security Concerns Associated with IPv6 Extension Headers
533 The security implications of IPv6 Extension Headers generally fall
534 into one or more of these categories:
536 o Evasion of security controls
538 o DoS due to processing requirements
540 o DoS due to implementation errors
542 o Extension Header-specific issues
544 Unlike IPv4 packets where the upper-layer protocol can be trivially
545 found by means of the "IHL" ("Internet Header Length") IPv4 header
546 field, the structure of IPv6 packets is more flexible and complex.
547 This can represent a challenge for devices that need to find this
548 information, since locating upper-layer protocol information requires
549 that all IPv6 extension headers be examined. In turn, this presents
550 implementation difficulties, since some packet filtering mechanisms
551 that require upper-layer information (even if just the upper layer
552 protocol type) can be trivially circumvented by inserting IPv6
553 Extension Headers between the main IPv6 header and the upper layer
554 protocol. [RFC7113] describes this issue for the RA-Guard case, but
555 the same techniques could be employed to circumvent other IPv6
556 firewall and packet filtering mechanisms. Additionally,
557 implementation inconsistencies in packet forwarding engines can
558 result in evasion of security controls
559 [I-D.kampanakis-6man-ipv6-eh-parsing] [Atlasis2014] [BH-EU-2014].
561 Sometimes packets with IPv6 Extension Headers can impact throughput
562 performance on routers and middleboxes. Unless appropriate
563 mitigations are put in place (e.g., packet dropping and/or rate-
564 limiting), an attacker could simply send a large amount of IPv6
565 traffic employing IPv6 Extension Headers with the purpose of
566 performing a Denial of Service (DoS) attack (see Section 7 for
567 further details).
569 NOTE:
570 In the most trivial case, a packet that includes a Hop-by-Hop
571 Options header might go through the slow forwarding path, to be
572 processed by the router's CPU. Alternatively, a router configured
573 to enforce an ACL based on upper-layer information (e.g., upper
574 layer protocol or TCP Destination Port) may need to process the
575 entire IPv6 header chain in order to find the required
576 information, thereby causing the packet to be processed in the
577 slow path [Cisco-EH-Cons]. We note that, for obvious reasons, the
578 aforementioned performance issues can affect other devices such as
579 firewalls, Network Intrusion Detection Systems (NIDS), etc.
580 [Zack-FW-Benchmark]. The extent to which performance is affected
581 on these devices is implementation-dependent.
583 IPv6 implementations, like all other software, tend to mature with
584 time and wide-scale deployment. While the IPv6 protocol itself has
585 existed for over 20 years, serious bugs related to IPv6 Extension
586 Header processing continue to be discovered (see e.g., [Cisco-Frag1],
587 [Cisco-Frag2], [Microsoft-SA], and [FreeBSD-SA]). Because there is
588 currently little operational reliance on IPv6 Extension headers, the
589 corresponding code paths are rarely exercised, and there is the
590 potential for bugs that still remain to be discovered in some
591 implementations.
593 IPv6 Fragment Headers are employed to allow fragmentation of IPv6
594 packets. While many of the security implications of the
595 fragmentation / reassembly mechanism are known from the IPv4 world,
596 several related issues have crept into IPv6 implementations. These
597 range from denial of service attacks to information leakage, as
598 discussed in [RFC7739], [Bonica-NANOG58] and [Atlasis2012]).
600 8. IANA Considerations
602 There are no IANA registries within this document. The RFC-Editor
603 can remove this section before publication of this document as an
604 RFC.
606 9. Security Considerations
608 The security implications of IPv6 extension headers are discussed in
609 Section 7.4. This document does not introduce any new security
610 issues.
612 10. Acknowledgements
614 The authors would like to thank (in alphabetical order) Mikael
615 Abrahamsson, Fred Baker, Dale W. Carder, Brian Carpenter, Tim Chown,
616 Owen DeLong, Gorry Fairhurst, Tom Herbert, Lee Howard, Tom Petch,
617 Sander Steffann, Eduard Vasilenko, Eric Vyncke, Rob Wilton, Jingrong
618 Xie, and Andrew Yourtchenko, for providing valuable comments on
619 earlier versions of this document.
621 Fernando Gont would like to thank Jan Zorz / Go6 Lab
622 , Jared Mauch, and Sander Steffann
623 , for providing access to systems and networks
624 that were employed to perform experiments and measurements involving
625 packets with IPv6 Extension Headers.
627 11. References
629 11.1. Normative References
631 [RFC5095] Abley, J., Savola, P., and G. Neville-Neil, "Deprecation
632 of Type 0 Routing Headers in IPv6", RFC 5095,
633 DOI 10.17487/RFC5095, December 2007,
634 .
636 [RFC5722] Krishnan, S., "Handling of Overlapping IPv6 Fragments",
637 RFC 5722, DOI 10.17487/RFC5722, December 2009,
638 .
640 [RFC6946] Gont, F., "Processing of IPv6 "Atomic" Fragments",
641 RFC 6946, DOI 10.17487/RFC6946, May 2013,
642 .
644 [RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation
645 with IPv6 Neighbor Discovery", RFC 6980,
646 DOI 10.17487/RFC6980, August 2013,
647 .
649 [RFC7112] Gont, F., Manral, V., and R. Bonica, "Implications of
650 Oversized IPv6 Header Chains", RFC 7112,
651 DOI 10.17487/RFC7112, January 2014,
652 .
654 [RFC8021] Gont, F., Liu, W., and T. Anderson, "Generation of IPv6
655 Atomic Fragments Considered Harmful", RFC 8021,
656 DOI 10.17487/RFC8021, January 2017,
657 .
659 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
660 (IPv6) Specification", STD 86, RFC 8200,
661 DOI 10.17487/RFC8200, July 2017,
662 .
664 [RFC8504] Chown, T., Loughney, J., and T. Winters, "IPv6 Node
665 Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504,
666 January 2019, .
668 11.2. Informative References
670 [APNIC-Scudder]
671 Scudder, J., "Modern router architecture and IPv6", APNIC
672 Blog, June 4, 2020, .
675 [Atlasis2012]
676 Atlasis, A., "Attacking IPv6 Implementation Using
677 Fragmentation", BlackHat Europe 2012. Amsterdam,
678 Netherlands. March 14-16, 2012,
679 .
682 [Atlasis2014]
683 Atlasis, A., "A Novel Way of Abusing IPv6 Extension
684 Headers to Evade IPv6 Security Devices", May 2014,
685 .
688 [BH-EU-2014]
689 Atlasis, A., Rey, E., and R. Schaefer, "Evasion of High-
690 End IDPS Devices at the IPv6 Era", BlackHat Europe 2014,
691 2014, .
694 [Bonica-NANOG58]
695 Bonica, R., "IPV6 FRAGMENTATION: The Case For
696 Deprecation", NANOG 58. New Orleans, Louisiana, USA. June
697 3-5, 2013, .
700 [Cisco-EH-Cons]
701 Cisco, "IPv6 Extension Headers Review and Considerations",
702 October 2006,
703 .
706 [Cisco-Frag1]
707 Cisco, "Cisco IOS Software IPv6 Virtual Fragmentation
708 Reassembly Denial of Service Vulnerability", September
709 2013, .
712 [Cisco-Frag2]
713 Cisco, "Cisco IOS XR Software Crafted IPv6 Packet Denial
714 of Service Vulnerability", June 2015,
715 .
718 [Cunha-2020]
719 Cunha, I., "IPv4 vs IPv6 load balancing in Internet
720 routes", NPS/CAIDA 2020 Virtual IPv6 Workshop, 2020,
721 .
724 [FreeBSD-SA]
725 FreeBSD, "FreeBSD Security Advisory FreeBSD-SA-20:24.ipv6:
726 IPv6 Hop-by-Hop options use-after-free bug", September
727 2020, .
730 [Huston-2017]
731 Huston, G., "Dealing with IPv6 fragmentation in the
732 DNS", APNIC Blog, 2017,
733 .
736 [Huston-2020]
737 Huston, G., "Measurement of IPv6 Extension Header
738 Support", NPS/CAIDA 2020 Virtual IPv6 Workshop, 2020,
739 .
742 [I-D.ietf-opsec-ipv6-eh-filtering]
743 Gont, F. and W. LIU, "Recommendations on the Filtering of
744 IPv6 Packets Containing IPv6 Extension Headers at Transit
745 Routers", draft-ietf-opsec-ipv6-eh-filtering-07 (work in
746 progress), January 2021.
748 [I-D.kampanakis-6man-ipv6-eh-parsing]
749 Kampanakis, P., "Implementation Guidelines for parsing
750 IPv6 Extension Headers", draft-kampanakis-6man-ipv6-eh-
751 parsing-01 (work in progress), August 2014.
753 [I-D.taylor-v6ops-fragdrop]
754 Jaeggli, J., Colitti, L., Kumari, W., Vyncke, E., Kaeo,
755 M., and T. Taylor, "Why Operators Filter Fragments and
756 What It Implies", draft-taylor-v6ops-fragdrop-02 (work in
757 progress), December 2013.
759 [I-D.wkumari-long-headers]
760 Kumari, W., Jaeggli, J., Bonica, R., and J. Linkova,
761 "Operational Issues Associated With Long IPv6 Header
762 Chains", draft-wkumari-long-headers-03 (work in progress),
763 June 2015.
765 [IEPG94-Scudder]
766 Petersen, B. and J. Scudder, "Modern Router Architecture
767 for Protocol Designers", IEPG 94. Yokohama, Japan.
768 November 1, 2015, .
771 [Jaeggli-2018]
772 Jaeggli, G., "Dealing with IPv6 fragmentation in the
773 DNS", APNIC Blog, 2018,
774 .
777 [Linkova-Gont-IEPG90]
778 Linkova, J. and F. Gont, "IPv6 Extension Headers in the
779 Real World v2.0", IEPG 90. Toronto, ON, Canada. July 20,
780 2014, .
783 [Microsoft-SA]
784 Microsoft, "Windows TCP/IP Remote Code Execution
785 Vulnerability (CVE-2021-24094)", February 2021,
786 .
789 [nmap] Fyodor, "Dealing with IPv6 fragmentation in the
790 DNS", Firewall/IDS Evasion and Spoofing,
791 .
793 [PMTUD-Blackholes]
794 De Boer, M. and J. Bosma, "Discovering Path MTU black
795 holes on the Internet using RIPE Atlas", July 2012,
796 .
799 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
800 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
801 December 1998, .
803 [RFC5575] Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J.,
804 and D. McPherson, "Dissemination of Flow Specification
805 Rules", RFC 5575, DOI 10.17487/RFC5575, August 2009,
806 .
808 [RFC5635] Kumari, W. and D. McPherson, "Remote Triggered Black Hole
809 Filtering with Unicast Reverse Path Forwarding (uRPF)",
810 RFC 5635, DOI 10.17487/RFC5635, August 2009,
811 .
813 [RFC6192] Dugal, D., Pignataro, C., and R. Dunn, "Protecting the
814 Router Control Plane", RFC 6192, DOI 10.17487/RFC6192,
815 March 2011, .
817 [RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
818 "IPv6 Flow Label Specification", RFC 6437,
819 DOI 10.17487/RFC6437, November 2011,
820 .
822 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
823 for Equal Cost Multipath Routing and Link Aggregation in
824 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011,
825 .
827 [RFC7045] Carpenter, B. and S. Jiang, "Transmission and Processing
828 of IPv6 Extension Headers", RFC 7045,
829 DOI 10.17487/RFC7045, December 2013,
830 .
832 [RFC7113] Gont, F., "Implementation Advice for IPv6 Router
833 Advertisement Guard (RA-Guard)", RFC 7113,
834 DOI 10.17487/RFC7113, February 2014,
835 .
837 [RFC7739] Gont, F., "Security Implications of Predictable Fragment
838 Identification Values", RFC 7739, DOI 10.17487/RFC7739,
839 February 2016, .
841 [RFC7872] Gont, F., Linkova, J., Chown, T., and W. Liu,
842 "Observations on the Dropping of Packets with IPv6
843 Extension Headers in the Real World", RFC 7872,
844 DOI 10.17487/RFC7872, June 2016,
845 .
847 [RFC8900] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O.,
848 and F. Gont, "IP Fragmentation Considered Fragile",
849 BCP 230, RFC 8900, DOI 10.17487/RFC8900, September 2020,
850 .
852 [Zack-FW-Benchmark]
853 Zack, E., "Firewall Security Assessment and Benchmarking
854 IPv6 Firewall Load Tests", IPv6 Hackers Meeting #1,
855 Berlin, Germany. June 30, 2013,
856 .
860 Authors' Addresses
862 Fernando Gont
863 SI6 Networks
864 Segurola y Habana 4310, 7mo Piso
865 Villa Devoto, Ciudad Autonoma de Buenos Aires
866 Argentina
868 Email: fgont@si6networks.com
869 URI: https://www.si6networks.com
871 Nick Hilliard
872 INEX
873 4027 Kingswood Road
874 Dublin 24
875 IE
877 Email: nick@inex.ie
879 Gert Doering
880 SpaceNet AG
881 Joseph-Dollinger-Bogen 14
882 Muenchen D-80807
883 Germany
885 Email: gert@space.net
887 Warren Kumari
888 Google
889 1600 Amphitheatre Parkway
890 Mountain View, CA 94043
891 US
893 Email: warren@kumari.net
894 Geoff Huston
896 Email: gih@apnic.net
897 URI: http://www.apnic.net
899 Will (Shucheng) Liu
900 Huawei Technologies
901 Bantian, Longgang District
902 Shenzhen 518129
903 P.R. China
905 Email: liushucheng@huawei.com