IPv6 Operations Working Group (v6ops) F. Gont Internet-Draft SI6 Networks / UTN-FRH Intended status: Informational N. Hilliard Expires: September 12, 2016 INEX G. Doering SpaceNet AG W. Liu Huawei Technologies W. Kumari Google March 11, 2016 Operational Implications of IPv6 Packets with Extension Headers draft-gont-v6ops-ipv6-ehs-packet-drops-03 Abstract This document summarizes the security and operational implications of IPv6 extension headers, and attempts to analyze reasons why packets with IPv6 extension headers may be dropped in the public Internet. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on September 12, 2016. Copyright Notice Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents Gont, et al. Expires September 12, 2016 [Page 1] Internet-Draft IPv6 Extension Headers March 2016 carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Previous Work on IPv6 Extension Headers . . . . . . . . . . . 3 3. Security Implications . . . . . . . . . . . . . . . . . . . . 4 4. Operational Implications . . . . . . . . . . . . . . . . . . 5 4.1. Requirement to process required layer-3/layer-4 information . . . . . . . . . . . . . . . . . . . . . . . 5 4.2. Route-Processor Protection . . . . . . . . . . . . . . . 7 4.3. Inability to Perform Fine-grained Filtering . . . . . . . 8 5. A Possible Attack Vector . . . . . . . . . . . . . . . . . . 8 6. Future Work . . . . . . . . . . . . . . . . . . . . . . . . . 10 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 8. Security Considerations . . . . . . . . . . . . . . . . . . . 10 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 10.1. Normative References . . . . . . . . . . . . . . . . . . 11 10.2. Informative References . . . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 1. Introduction IPv6 Extension Headers (EHs) allow for the extension of the IPv6 protocol, and provide support for core functionality such as IPv6 fragmentation. However, common implementation limitations suggest that EHs present a challenge for IPv6 packet routing equipment, and evidence exists to suggest that IPv6 packets with EHs may be intentionally dropped on the public Internet in some network deployments. The authors of this document have been involved in numerous discussions about IPv6 extension headers (both within the IETF and outside of it), and have noticed that a number of security and operational issues were unknown to the larger audience participating in these discussions. This document has the following goals: o Raise awareness about the security and operational implications of IPv6 Extension Headers, and presents reasons why some networks intentionally drop packets containing IPv6 Extension Headers. Gont, et al. Expires September 12, 2016 [Page 2] Internet-Draft IPv6 Extension Headers March 2016 o Highlight areas where current IPv6 support by networking devices maybe sub-optimal, such that the aforementioned support is improved. o Highlight operational issues associated with IPv6 extension headers, such that those issues are considered in IETF standardization efforts. Section 2 of this document summarizes the previous work that has been done in the area of IPv6 extension headers. Section 3 briefly discusses the security implications of IPv6 Extension Headers, while Section 4 discusses their operational implications. Finally, Section 6 proposes an action plan for improving the state of affairs of IPv6 extension headers. 2. Previous Work on IPv6 Extension Headers Some of the implications of IPv6 Extension Headers have been discussed in IETF circles. For example, [I-D.taylor-v6ops-fragdrop] discusses a rationale for which operators drop IPv6 fragments. [I-D.wkumari-long-headers] discusses possible issues arising from "long" IPv6 header chains. [RFC7045] clarifies how intermediate nodes should deal with IPv6 extension headers. [RFC7112] discusses the issues arising in a specific fragmentation case where the IPv6 header chain is fragmented into two or more fragments (and formally forbids such fragmentation case). [I-D.kampanakis-6man-ipv6-eh-parsing] describes how inconsistencies in the way IPv6 packets with extension headers are parsed by different implementations may result in evasion of security controls, and presents guidelines for parsing IPv6 extension headers with the goal of providing a common and consistent parsing methodology for IPv6 implementations. [RFC6980] analyzes the security implications of employing IPv6 fragmentation with Neighbor Discovery for IPv6, and formally recommends against such usage. Finally, [RFC7123] discusses how some popular RA-Guard implementations are subject to evasion by means of IPv6 extension headers. Some preliminary measurements regarding the extent to which packet containing IPv6 EHs are dropped in the public Internet have been presented in [PMTUD-Blackholes], [Gont-IEPG88], [Gont-Chown-IEPG89], and [Linkova-Gont-IEPG90]. [I-D.ietf-v6ops-ipv6-ehs-in-real-world] presents more comprehensive results and documents the methodology for obtaining the presented results. Gont, et al. Expires September 12, 2016 [Page 3] Internet-Draft IPv6 Extension Headers March 2016 3. Security Implications The security implications of IPv6 Extension Headers generally fall into one or more of these categories: o Evasion of security controls o DoS due to processing requirements o DoS due to implementation errors o Extension Header-specific issues Unlike IPv4 packets where the upper-layer protocols can be trivially found by means of the "IHL" ("Internet Header Length") IPv4 header field, the structure of IPv6 packets is more flexible and complex. Locating upper-layer protocol information requires that all IPv6 extension headers be examined. This has presented implementation difficulties, and packet filtering mechanisms that require upper- layer information (even if just the upper layer protocol type) on several security devices can be trivially evaded by inserting IPv6 Extension Headers between the main IPv6 header and the upper layer protocol. [RFC7113] describes this issue for the RA-Guard case, but the same techniques can be employed to circumvent other IPv6 firewall and packet filtering mechanisms. Additionally, implementation inconsistencies in packet forwarding engines may result in evasion of security controls [I-D.kampanakis-6man-ipv6-eh-parsing] [Atlasis2014] [BH-EU-2014]. Packets that use IPv6 Extension Headers may have a negative performance impact on the handling devices. Unless appropriate mitigations are put in place (e.g., packet dropping and/or rate- limiting), an attacker could simply send a large amount of IPv6 traffic employing IPv6 Extension Headers with the purpose of performing a Denial of Service (DoS) attack (see Section 4 for further details). NOTE: In the most trivial case, a packet that includes a Hop-by-Hop Options header will typically go through the slow forwarding path, and be processed by the router's CPU. Another possible case might be that in which a router that has been configured to enforce an ACL based on upper-layer information (e.g., upper layer protocol or TCP Destination Port), needs to process the entire IPv6 header chain (in order to find the required information) and this causes the packet to be processed in the slow path [Cisco-EH-Cons]. We note that, for obvious reasons, the aforementioned performance issues may also affect other devices such as firewalls, Network Gont, et al. Expires September 12, 2016 [Page 4] Internet-Draft IPv6 Extension Headers March 2016 Intrusion Detection Systems (NIDS), etc. [Zack-FW-Benchmark]. The extent to which these devices are affected will typically be implementation-dependent. IPv6 implementations, like all other software, tend to mature with time and wide-scale deployment. While the IPv6 protocol itself has existed for almost 20 years, serious bugs related to IPv6 Extension Header processing continue to be discovered. Because there is currently little operational reliance on IPv6 Extension headers, the corresponding code paths are rarely exercised, and there is the potential that bugs still remain to be discovered in some implementations. IPv6 Fragment Headers are employed to allow fragmentation of IPv6 packets. While many of the security implications of the fragmentation / reassembly mechanism are known from the IPv4 world, several related issues have crept into IPv6 implementations. These range from denial of service attacks to information leakage, for example [I-D.ietf-6man-predictable-fragment-id], [Bonica-NANOG58] and [Atlasis2012]). 4. Operational Implications 4.1. Requirement to process required layer-3/layer-4 information Intermediate systems and middleboxes that need to find the layer-4 header must process the entire IPv6 extension header chain. When such devices are unable to obtain the required information, they may simply drop the corresponding packets. The following subsections discuss some of reasons for which such layer-4 information may be needed by an intermediate systems or middlebox, and why packets containing IPv6 extension headers may represent a challenge in such scenarios. 4.1.1. Packet Forwarding Engine Constraints Most modern routers use dedicated hardware (e.g. ASICs or NPUs) to determine how to forward packets across their internal fabrics (see [IEPG94-Scudder] for details). One of the common methods of handling next-hop lookup is to send a small portion of the ingress packet to a lookup engine with specialised hardware (e.g. ternary CAM or RLDRAM) to determine the packet's next-hop. Technical constraints mean that there is a trade-off between the amount of data sent to the lookup engine and the overall performance of the lookup engine. If more data is sent, the lookup engine can inspect further into the packet, but the overall performance of the system will be reduced. If less data is sent, the overall performance of the router will be increased Gont, et al. Expires September 12, 2016 [Page 5] Internet-Draft IPv6 Extension Headers March 2016 but the packet lookup engine may not be able to inspect far enough into a packet to determine how it should be handled. NOTE: For example, current high-end routers at the time of authorship of this document can use up to 192 bytes of header (Cisco ASR9000 Typhoon) or 384 bytes of header (Juniper MX Trio) If a hardware forwarding engine on a modern router cannot make a forwarding decision about a packet because critical information is not sent to the look-up engine, then the router will normally drop the packet. Historically, some packet forwarding engines punted packets of this form to the control plane for more in-depth analysis, but this is unfeasible on most current router architectures as a result of the vast difference between the hardware forwarding capacity of the router and processing capacity of the control plane and the size of the management link which connects the control plane to the forwarding plane. If an IPv6 header chain is sufficiently long that its header exceeds the packet look-up capacity of the router, then it may be dropped due to hardware inability to determine how it should be handled. 4.1.2. ECMP and Hash-based Load-Sharing In the case of ECMP (equal cost multi path) load sharing, the router on the sending side of the link needs to make a decision regarding which of the links to use for a given packet. Since round-robin usage of the links is usually avoided in order to prevent packet reordering, forwarding engines need to use a mechanism which will consistently forward the same data streams down the same forwarding paths. Most forwarding engines achieve this by calculating a simple hash using an n-tuple gleaned from a combination of layer-2 through to layer-4 packet header information. This n-tuple will typically use the src/dst MAC address, src/dst IP address, and if possible further layer-4 src/dst port information. As layer-4 port information increases the entropy of the hash, it is highly desirable to use it where possible. We note that in the IPv6 world, flows are expected to be identified by means of the IPv6 Flow Label [RFC6437]. Thus, ECMP and Hash-based Load-Sharing would be possible without the need to process the entire IPv6 header chain to obtain upper-layer information to identify flows. However, we note that for a long time many IPv6 implementations failed to set the Flow Label, and ECMP and Hash-based Load-Sharing devices also did not employ the Flow Label for performing their task. Gont, et al. Expires September 12, 2016 [Page 6] Internet-Draft IPv6 Extension Headers March 2016 Clearly, widespread support of [RFC6437] would relieve middle-boxes from having to process the entire IPv6 header chain, making Flow Label-based ECMP and Hash-based Load-Sharing [RFC6438] feasible. 4.1.3. Enforcing infrastructure ACLs Generally speaking, infrastructure ACLs (iACLs) drop unwanted packets destined to parts of a provider's infrastructure, because they are not operationally needed and can be used for attacks of different sorts against the router's control plane. Some traffic needs to be differentiated depending on layer-3 or layer-4 criteria to achieve a useful balance of protection and functionality, for example: o Permit some amount of ICMP echo (ping) traffic towards the router's addresses for troubleshooting. o Permit BGP sessions on the shared network of an exchange point (potentially differentiating between the amount of packets/seconds permitted for established sessions and connection establishment), but do not permit other traffic from the same peer IP addresses. 4.1.4. DDoS Management and Customer Requests for Filtering The case of customer DDoS protection and edge-to-core customer protection filters is similar in nature to the infrastructure ACL protection. Similar to infrastructure ACL protection, layer-4 ACLs generally need to be applied as close to the edge of the network as possible, even though the intent is usually to protect the customer edge rather than the provider core. Application of layer-4 DDoS protection to a network edge is often automated using Flowspec [RFC5575]. For example, a web site which normally only handled traffic on TCP ports 80 and 443 could be subject to a volumetric DDoS attack using NTP and DNS packets with randomised source IP address, thereby rendering useless traditional [RFC5635] source-based real-time black hole mechanisms. In this situation, DDoS protection ACLs could be configured to block all UDP traffic at the network edge without impairing the web server functionality in any way. Thus, being able to block arbitrary protocols at the network edge can avoid DDoS- related problems both in the provider network and on the customer edge link. 4.2. Route-Processor Protection Most modern routers have a fast hardware-assisted forwarding plane and a loosely coupled control plane, connected together with a link that has much less capacity than the forwarding plane could handle. Gont, et al. Expires September 12, 2016 [Page 7] Internet-Draft IPv6 Extension Headers March 2016 Traffic differentiation cannot be done by the control plane side, because this would overload the internal link connecting the forwarding plane to the control plane. The Hop-by-Hop Options header is particularly challenging since, in most (if not all) implementations, it causes the corresponding packet to be punted to a software path. As a result, operators usually drop IPv6 packets containing this extension header. Please see [RFC6192] for advice regarding protection of the router control plane. 4.3. Inability to Perform Fine-grained Filtering Some routers lack of fine-grained filtering of IPv6 extension headers. For example, an operator may want to drop packets containing Routing Header Type 0 (RHT0) but may only be able to filter on the extension header type (Routing Header). As a result, the operator may end up enforcing a more coarse filtering policy (e.g. "drop all packets containing a Routing Header" vs. "only drop packets that contain a Routing Header Type 0"). 5. A Possible Attack Vector The widespread drop of IPv6 packets employing IPv6 Extension Headers can, in some scenarios, be exploited for malicious purposes: if packets employing IPv6 EHs are known to be dropped on the path from system A to system B, an attacker could cause packets sent from A to B to be dropped by sending a forged ICMPv6 Packet Too Big (PTB) [RFC4443] error message to A (advertising an MTU smaller than 1280), such that subsequent packets from A to B include a fragment header (i.e., they result in atomic fragments [RFC6946]). Possible scenarios where this attack vector could be exploited include (but are not limited to): o Communication between any two systems through the public network (e.g., client from/to server or server from/to server), where packets with IPv6 extension headers are dropped by some intermediate router o Communication between two BGP peers employing IPv6 transport, where these BGP peers implement ACLs to drop IPv6 fragments (to avoid control-plane attacks) The aforementioned attack vector is exacerbated by the following factors: Gont, et al. Expires September 12, 2016 [Page 8] Internet-Draft IPv6 Extension Headers March 2016 o The attacker does not need to forge the IPv6 Source Address of his attack packets. Hence, deployment of simple BCP38 filters will not help as a counter-measure. o Only the IPv6 addresses of the IPv6 packet embedded in the ICMPv6 payload need to be forged. While one could envision filtering devices enforcing BCP38-style filters on the ICMPv6 payload, the use of extension headers (by the attacker) could make this difficult, if not impossible. o Many implementations fail to perform validation checks on the received ICMPv6 error messages, as recommended in Section 5.2 of [RFC4443] and documented in [RFC5927]. It should be noted that in some cases, such as when an ICMPv6 error message has (supposedly) been elicited by a connection-less transport protocol (or some other connection-less protocol being encapsulated in IPv6), it may be virtually impossible to perform validation checks on the received ICMPv6 error messages. And, because of IPv6 extension headers, the ICMPv6 payload might not even contain any useful information on which to perform validation checks. o Upon receipt of one of the aforementioned ICMPv6 "Packet Too Big" error messages, the Destination Cache [RFC4861] is usually updated to reflect that any subsequent packets to such destination should include a Fragment Header. This means that a single ICMPv6 "Packet Too Big" error message might affect multiple communication instances (e.g. TCP connections) with such destination. o A router or other middlebox cannot simply drop all incoming ICMPv6 Packet Too Big error messages, as this would create a PMTUD blackhole. Possible mitigations for this issue include: o Dropping incoming ICMPv6 Packet Too Big error messages that advertise an MTU smaller than 1280 bytes. o Artificially reducing the MTU to 1280 bytes and dropping incoming ICMPv6 PTB error messages. Both of these mitigations come at the expense of possibly preventing communication through SIIT [RFC6145], that relies on IPv6 atomic fragments (see [I-D.ietf-6man-deprecate-atomfrag-generation]), and also implies that the filtering device has the ability to filter ICMP PTB messages based on the contents of the MTU field. [I-D.ietf-6man-deprecate-atomfrag-generation] documents while the generation of IPv6 atomic fragments is considered harmful, and Gont, et al. Expires September 12, 2016 [Page 9] Internet-Draft IPv6 Extension Headers March 2016 documents why this functionality is being removed from the upcoming revision of the core IPv6 protocol [I-D.ietf-6man-rfc2460bis]. Thus, any of the above mitigations would eliminate the attack vector without any interoperability implications. 6. Future Work Based on the discussion provided in this document, we recommend the following (*non*-mutually exclusive) actions to improve the state of affairs of IPv6 extension headers: o Vendors must allow for better granularity in the specification of filters for IPv6 extension headers, such that filters for specific EH types and subtypes (e.g. RHT0 vs. RHT2) can be specified wthout affecting other extension header types/subtypes unnecessarily (please see Section 4.3). o Provide advice on the filtering of IPv6 packets that contain IPv6 extension headers (as in [I-D.ietf-opsec-ipv6-eh-filtering]). o The IETF should evaluate the possibility of enforcing a cap on the maximum length of an IPv6 EH chain (e.g., as proposed in [I-D.wkumari-long-headers]). If not at the protocol specification level (i.e., "Standards Track"), such a cap could be recommended as operational advice of the form "IPv6 implementations are expected to support EH chains as long as the they fit in the Path- MTU for the corresponding packets (see [RFC7112]). However, given current technology constraints, we specifically note that all implementations MUST support EH chains of at least X bytes, and MUST be able to process such EH chains (where necessary), without negative performance impact". We explicitly note that the authors of this document do not (in any way) suggest or propose to depracate IPv6 extension headers and that, on the contrary, they propose actions to improve their state of affairs. 7. IANA Considerations There are no IANA registries within this document. The RFC-Editor can remove this section before publication of this document as an RFC. 8. Security Considerations The security implications of IPv6 extension headers are discussed in Section 3. A specific attack vector that could leverage the widespread dropping of packets with IPv6 EHs (along with possible Gont, et al. Expires September 12, 2016 [Page 10] Internet-Draft IPv6 Extension Headers March 2016 countermeasures) is discussed in Section 5. This document does not introduce any new security issues. 9. Acknowledgements The authors would like to thank (in alphabetical order) Mikael Abrahamsson, Fred Baker, Brian Carpenter, Lee Howard, Sander Steffann, Eric Vyncke, and Andrew Yourtchenko, for providing valuable comments on earlier versions of this document. Additionally, the authors would like to thank participants of the v6ops working group for their valuable input on the topics that led to the publication of this document. Fernando Gont would like to thank Sander Steffann, who took the time to meet to discuss this document, even while higher priority events were in place. Fernando Gont would like to thank Jan Zorz / Go6 Lab , and Jared Mauch / NTT America, for providing access to systems and networks that were employed to perform experiments and measurements involving packets with IPv6 Extension Headers. Additionally, he would like to thank SixXS for providing IPv6 connectivity. 10. References 10.1. Normative References [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, December 1998, . [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", RFC 4443, DOI 10.17487/RFC4443, March 2006, . [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, DOI 10.17487/RFC4861, September 2007, . [RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation Algorithm", RFC 6145, DOI 10.17487/RFC6145, April 2011, . Gont, et al. Expires September 12, 2016 [Page 11] Internet-Draft IPv6 Extension Headers March 2016 [RFC6946] Gont, F., "Processing of IPv6 "Atomic" Fragments", RFC 6946, DOI 10.17487/RFC6946, May 2013, . 10.2. Informative References [Atlasis2012] Atlasis, A., "Attacking IPv6 Implementation Using Fragmentation", BlackHat Europe 2012. Amsterdam, Netherlands. March 14-16, 2012, . [Atlasis2014] Atlasis, A., "A Novel Way of Abusing IPv6 Extension Headers to Evade IPv6 Security Devices", May 2014, . [BH-EU-2014] Atlasis, A., Rey, E., and R. Schaefer, "Evasion of High- End IDPS Devices at the IPv6 Era", BlackHat Europe 2014, 2014, . [Bonica-NANOG58] Bonica, R., "IPv6 Extension Headers in the Real World v2.0", NANOG 58. New Orleans, Louisiana, USA. June 3-5, 2013, . [Cisco-EH-Cons] Cisco, , "IPv6 Extension Headers Review and Considerations", October 2006, . [Gont-Chown-IEPG89] Gont, F. and T. Chown, "A Small Update on the Use of IPv6 Extension Headers", IEPG 89. London, UK. March 2, 2014, . [Gont-IEPG88] Gont, F., "Fragmentation and Extension header Support in the IPv6 Internet", IEPG 88. Vancouver, BC, Canada. November 13, 2013, . Gont, et al. Expires September 12, 2016 [Page 12] Internet-Draft IPv6 Extension Headers March 2016 [I-D.ietf-6man-deprecate-atomfrag-generation] Gont, F., LIU, S., and T. Anderson, "Generation of IPv6 Atomic Fragments Considered Harmful", draft-ietf-6man- deprecate-atomfrag-generation-05 (work in progress), January 2016. [I-D.ietf-6man-predictable-fragment-id] Gont, F., "Security Implications of Predictable Fragment Identification Values", draft-ietf-6man-predictable- fragment-id-10 (work in progress), October 2015. [I-D.ietf-6man-rfc2460bis] Deering, S. and B. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", draft-ietf-6man-rfc2460bis-03 (work in progress), January 2016. [I-D.ietf-opsec-ipv6-eh-filtering] Gont, F., LIU, S., and R. Bonica, "Recommendations on Filtering of IPv6 Packets Containing IPv6 Extension Headers", draft-ietf-opsec-ipv6-eh-filtering-00 (work in progress), March 2015. [I-D.ietf-v6ops-ipv6-ehs-in-real-world] Gont, F., Linkova, J., Chown, T., and S. LIU, "Observations on the Dropping of Packets with IPv6 Extension Headers in the Real World", draft-ietf-v6ops- ipv6-ehs-in-real-world-02 (work in progress), December 2015. [I-D.kampanakis-6man-ipv6-eh-parsing] Kampanakis, P., "Implementation Guidelines for parsing IPv6 Extension Headers", draft-kampanakis-6man-ipv6-eh- parsing-01 (work in progress), August 2014. [I-D.taylor-v6ops-fragdrop] Jaeggli, J., Colitti, L., Kumari, W., Vyncke, E., Kaeo, M., and T. Taylor, "Why Operators Filter Fragments and What It Implies", draft-taylor-v6ops-fragdrop-02 (work in progress), December 2013. [I-D.wkumari-long-headers] Kumari, W., Jaeggli, J., Bonica, R., and J. Linkova, "Operational Issues Associated With Long IPv6 Header Chains", draft-wkumari-long-headers-03 (work in progress), June 2015. Gont, et al. Expires September 12, 2016 [Page 13] Internet-Draft IPv6 Extension Headers March 2016 [IEPG94-Scudder] Petersen, B. and J. Scudder, "Modern Router Architecture for Protocol Designers", IEPG 94. Yokohama, Japan. November 1, 2015, . [Linkova-Gont-IEPG90] Linkova, J. and F. Gont, "IPv6 Extension Headers in the Real World v2.0", IEPG 90. Toronto, ON, Canada. July 20, 2014, . [PMTUD-Blackholes] De Boer, M. and J. Bosma, "Discovering Path MTU black holes on the Internet using RIPE Atlas", July 2012, . [RFC5575] Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J., and D. McPherson, "Dissemination of Flow Specification Rules", RFC 5575, DOI 10.17487/RFC5575, August 2009, . [RFC5635] Kumari, W. and D. McPherson, "Remote Triggered Black Hole Filtering with Unicast Reverse Path Forwarding (uRPF)", RFC 5635, DOI 10.17487/RFC5635, August 2009, . [RFC5927] Gont, F., "ICMP Attacks against TCP", RFC 5927, DOI 10.17487/RFC5927, July 2010, . [RFC6192] Dugal, D., Pignataro, C., and R. Dunn, "Protecting the Router Control Plane", RFC 6192, DOI 10.17487/RFC6192, March 2011, . [RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme, "IPv6 Flow Label Specification", RFC 6437, DOI 10.17487/RFC6437, November 2011, . [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label for Equal Cost Multipath Routing and Link Aggregation in Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, . Gont, et al. Expires September 12, 2016 [Page 14] Internet-Draft IPv6 Extension Headers March 2016 [RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation with IPv6 Neighbor Discovery", RFC 6980, DOI 10.17487/RFC6980, August 2013, . [RFC7045] Carpenter, B. and S. Jiang, "Transmission and Processing of IPv6 Extension Headers", RFC 7045, DOI 10.17487/RFC7045, December 2013, . [RFC7112] Gont, F., Manral, V., and R. Bonica, "Implications of Oversized IPv6 Header Chains", RFC 7112, DOI 10.17487/RFC7112, January 2014, . [RFC7113] Gont, F., "Implementation Advice for IPv6 Router Advertisement Guard (RA-Guard)", RFC 7113, DOI 10.17487/RFC7113, February 2014, . [RFC7123] Gont, F. and W. Liu, "Security Implications of IPv6 on IPv4 Networks", RFC 7123, DOI 10.17487/RFC7123, February 2014, . [RIPE-Atlas] RIPE, , "RIPE Atlas", . [Zack-FW-Benchmark] Zack, E., "Firewall Security Assessment and Benchmarking IPv6 Firewall Load Tests", IPv6 Hackers Meeting #1, Berlin, Germany. June 30, 2013, . Authors' Addresses Fernando Gont SI6 Networks / UTN-FRH Evaristo Carriego 2644 Haedo, Provincia de Buenos Aires 1706 Argentina Phone: +54 11 4650 8472 Email: fgont@si6networks.com URI: http://www.si6networks.com Gont, et al. Expires September 12, 2016 [Page 15] Internet-Draft IPv6 Extension Headers March 2016 Nick Hilliard INEX 4027 Kingswood Road Dublin 24 IE Email: nick@inex.ie Gert Doering SpaceNet AG Joseph-Dollinger-Bogen 14 Muenchen D-80807 Germany Email: gert@space.net Will (Shucheng) Liu Huawei Technologies Bantian, Longgang District Shenzhen 518129 P.R. China Email: liushucheng@huawei.com Warren Kumari Google 1600 Amphitheatre Parkway Mountain View, CA 94043 US Email: warren@kumari.net Gont, et al. Expires September 12, 2016 [Page 16]