IPv6 Operations Working Group (v6ops) F. Gont
Internet-Draft SI6 Networks / UTN-FRH
Intended status: Informational J. Linkova
Expires: March 14, 2015 Google
T. Chown
University of Southampton
W. Liu
Huawei Technologies
September 10, 2014
IPv6 Extension Headers in the Real World
draft-gont-v6ops-ipv6-ehs-in-real-world-01
Abstract
This document summarizes the operational implications of IPv6
extension headers, and presents real-world data regarding the extent
to which packets with IPv6 extension headers are filtered in the
public Internet, and where in the network such filtering occurs.
Additionally, this document provides guidance to operators in
troubleshooting IPv6 blackholes resulting from the use of IPv6
extension headers, advice to protocol designers regarding the use of
IPv6 extension headers, and a discussion of areas where further work
might be needed.
Status of This Memo
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This Internet-Draft will expire on March 14, 2015.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Previous Work on IPv6 Extension Headers . . . . . . . . . . . 3
3. Operational Implications . . . . . . . . . . . . . . . . . . 4
3.1. Performance Issues . . . . . . . . . . . . . . . . . . . 4
3.2. Security Implications . . . . . . . . . . . . . . . . . . 4
4. Support of IPv6 Extension Headers in the Public Internet . . 5
5. Implications of Widespread IPv6 Extension Header Filtering . 8
5.1. Advice to Protocol Designers . . . . . . . . . . . . . . 8
5.2. A possible attack vector . . . . . . . . . . . . . . . . 8
5.3. Possible Future Work . . . . . . . . . . . . . . . . . . 10
6. Troubleshooting Packet Drops due to IPv6 Extension Headers . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. Security Considerations . . . . . . . . . . . . . . . . . . . 10
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
10.1. Normative References . . . . . . . . . . . . . . . . . . 11
10.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. Measurements Caveats . . . . . . . . . . . . . . . . 14
A.1. Isolating the Dropping Node . . . . . . . . . . . . . . . 14
A.2. Obtaining the Responsible Organization for the Packet
Drops . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
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, IPv6 Extension Headers have been deemed to
present a challenge to IPv6 implementations and networks, and have
been assumed/known to be intentionally filtered in some existing IPv6
deployments.
Discussions over the operational implications of IPv6 extension
headers and their usability in the public Internet come up over and
over again at both in IETF circles and other venues, and not
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infrequently some key aspects involving IPv6 extension headers are
overlooked.
This document tries raise awareness about the operational
implications of IPv6 Extension Headers, and their usability in the
public Internet. Additionally, it provides some guidance in
troubleshooting IPv6 blackholes resulting from the filtering of
packets that employ IPv6 extension headers. Finally, it aims to
raise awareness about the operational reality of IPv6 extension
headers to protocol designers, and trigger discussion within the IETF
community regarding areas where future work might be required.
Section 2 of this document summarizes the work that has been done in
the area of IPv6 extension headers. Section 3 discusses the
operational implications of IPv6 Extension Headers. Section 4
presents real-world data regarding the extent to which IPv6 Extension
Headers are usable in the public Internet. Section 5 provides advise
to protocol designers regarding the use of IPv6 extension headers,
and aims to raise awareness about the possible interoperability
implications on existing protocols. Finally, Section 6 provides some
guidance in troubleshooting of problems that may arise as a result of
filtering packets that employ 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 filter 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 case where the IPv6 header chain is
fragmented into two or more fragments (and formally forbids such
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 a 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.
While packets employing IPv6 Extension Headers have been "known" to
be dropped in some IPv6 deployments, there was not much concrete data
on the topic. Some preliminary measurements have been presented in
[PMTUD-Blackholes], [Gont-IEPG88] and [Gont-Chown-IEPG89], whereas
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[Linkova-Gont-IEPG90] presents more comprehensive results on which
Section 4 of this document is based.
3. Operational Implications
3.1. Performance Issues
Many IPv6 router implementations suffer from a negative performance
impact when IPv6 Extension Headers are employed.
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 case is 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). In such case, the router will need to process the entire IPv6
header chain in order to find the required information, and this may
cause the packet to be processed in the slow path [Cisco-EH-Cons].
Processing a large amounts of traffic in the slow path may cause the
router to be unable to handle the same traffic loads when compared to
normal packets, and may result in Denial of Service (DoS) scenarios.
We note that, for obvious reasons, the aforementioned performance
issues may also affect other devices such as firewalls, Network
Intrusion Detection Systems (NIDS), etc. [Zack-FW-Benchmark].
3.2. 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
Different from IPv4, where the upper-layer protocol can be found
after the variable-length IPv4 header, the structure of IPv6 packets
is both more flexible and complex. Namely, finding the upper-layer
information may imply processing the (daisy-chain like) entire IPv6
header chain. This has been often overlooked, and a number of
security devices have been found to be trivially evasible by
inserting one or more IPv6 Extension Headers between the main IPv6
header and the upper layer protocol. [RFC7113] describes this issue
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for the RA-Guard case, but the same techniques can be employed for
circumventing e.g. some IPv6 firewalls. Additionally,
inconsistencies in how some packets may be processed may result in
evasion of security controls [I-D.kampanakis-6man-ipv6-eh-parsing]
[Atlasis2014].
As noted in Section 3.1, packets that employ IPv6 Extension Headers
may have a negative performance impact on the handling devices.
Unless appropriate mitigations are put in place (e.g., packet
filtering 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.
IPv6 implementations, as virtually every piece of software, tend to
mature over time. While the IPv6 protocol itself (and many
implementations) have been around for a long time already, bugs in
IPv6 Extension Header processing have been recently found in a number
of implementations. Because there is currently almost no 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.
Besides the general implications of IPv6 Extension Headers, each
Extension Header tends to its own specific implications. One
particular case is that of the Fragment Header, which is employed to
provide the fragmentation function in IPv6. While many of the
security implications of the fragmentation/reassembly mechanism are
known from the IPv4 world, many of the related issues have creeped
into IPv6 implementations. They range from Denial of Service attacks
to information leakage (see e.g.
[I-D.ietf-6man-predictable-fragment-id], [Bonica-NANOG58],
[Atlasis2012]).
4. Support of IPv6 Extension Headers in the Public Internet
This section summarizes the results obtained when measuring the
support of IPv6 Extension Headers on the path towards different types
of public IPv6 servers. Two sources were employed for the list of
public IPv6 servers: the "World IPv6 Launch Day" site
(http://www.worldipv6launch.org/) and Alexa's top 1M web sites
(http://www.alexa.com). For each list of domain names, the following
datasets were obtained:
o Web servers (AAAA records of the aforementioned list)
o Mail servers (MX -> AAAA of such list)
o Name servers (NS -> AAAA of such list)
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Duplicate and unreachable addresses were eliminated from each of
those lists prior to obtaining the results below. Additionally,
addresses that were found to be unreachable were discarded from the
dataset (please see Appendix A for further details).
For each of the aforementioned address sets, three different types of
probes were performed:
o IPv6 packets with a Destination Options header of 8 bytes
o IPv6 packets resulting in two IPv6 fragments of 512 bytes each
(approximately)
o IPv6 packets with a Hop-by-Hop Options header of 8 bytes
In the case of packets with Destination Options Header and Hop-by-Hop
Options header, the desired EH size was achieved by means of PadN
options [RFC2460]. The upper-layer protocol of the probe packets
was, in all cases, TCP [RFC0793] segments with the Destination Port
set to the service port [IANA-PORT-NUMBERS] of the corresponding
dataset. For example, the probe packets for all the measurements
involving web servers were TCP segments with the destination port set
to 80.
Besides obtaining the packet drop rate when employing the
aforementioned IPv6 extension headers, we tried to identify whether
the Autonomous System (AS) dropping the packets was the same as the
Autonomous System of the destination/target address. This is of
particular interest since it essentially reveals whether the packet
drops are under the control of the intended destination of the
packets. Packets dropped by the destination AS are less of a
concern, since the device dropping the packets is under the control
of the same organization as that to which the packets are destined
(hence, it is probably easier to update the filtering policy if
deemed necessary). On the other hand, packets dropped by transit
ASes are more of a concern, since they affect the deployability and
usability of IPv6 extension headers (including IPv6 fragmentation) by
a third-party (the destination AS). In any case, we note that it is
impossible to tell whether, in those cases where IPv6 packets with
extension headers get dropped, the packet drops are the result of an
explicit and intended policy, or the result of improper device
configuration defaults, buggy devices, etc. Thus, packet drops that
occur at the destination AS might still prove to be problematic.
Since there is some ambiguity when identifying the autonomous system
to which a specific router belongs, our measurements result in a
percentage *range* (see Appendix A.2). In the following tables, the
values shown within parentheses represent the estimated range of
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possibility that when a packet is dropped, the packet drop occurs in
an AS other than the destination AS.
+-------------+-----------------+-----------------+-----------------+
| Dataset | DO8 | HBH8 | FH512 |
+-------------+-----------------+-----------------+-----------------+
| Webservers | 11.88% | 40.70% | 30.51% |
| | (17.60%-20.80%) | (31.43%-40.00%) | (5.08%-6.78%) |
+-------------+-----------------+-----------------+-----------------+
| Mailservers | 17.07% | 48.86% | 39.17% |
| | (6.35%-26.98%) | (40.50%-65.42%) | (2.91%-12.73%) |
+-------------+-----------------+-----------------+-----------------+
| Nameservers | 15.37% | 43.25% | 38.55% |
| | (14.29%-33.46%) | (42.49%-72.07%) | (3.90%-13.96%) |
+-------------+-----------------+-----------------+-----------------+
Table 1: WIPv6LD dataset: Packet drop rate for different destination
types, and estimated percentage of dropped packets that were deemed
to be dropped in a different AS (lower, in parentheses)
NOTE: As an example, we note that the cell describing the support
of IPv6 packets with DO8 for webservers (containing the value
"11.88% (17.60%-20.80%)") should be read as: "When sending IPv6
packets with DO8 to public webservers, 11.88% of such packets get
dropped. Among those packets that get dropped, between 17.60%-
20.80% of them get dropped at an AS other than the destination
AS".
+-------------+-----------------+-----------------+-----------------+
| Dataset | DO8 | HBH8 | FH512 |
+-------------+-----------------+-----------------+-----------------+
| Webservers | 10.91% | 39.03% | 28.26% |
| | (46.52%-53.23%) | (36.90%-46.35%) | (53.64%-61.43%) |
+-------------+-----------------+-----------------+-----------------+
| Mailservers | 11.54% | 45.45% | 35.68% |
| | (2.41%-21.08%) | (41.27%-61.13%) | (3.15%-10.92%) |
+-------------+-----------------+-----------------+-----------------+
| Nameservers | 21.33% | 54.12% | 55.23% |
| | (10.27%-56.80%) | (50.64%-81.00%) | (5.66%-32.23%) |
+-------------+-----------------+-----------------+-----------------+
Table 2: Alexa's top 1M sites dataset: Packet drop rate for different
destination types, and estimated percentage of dropped packets that
were deemed to be dropped in a different AS (lower, in parentheses)
There are a number of observations to be made based on the results
presented above. Firstly, while it has been generally assumed that
it is IPv6 fragments that are dropped by operators, our results
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indicate that it is IPv6 extension headers in general that are
dropped. Secondly, our results indicate that a significant
percentage of such packet drops occur in transit Autonomous Systems;
that is, the packet drops are not under the control of the same
organization as the final destination.
5. Implications of Widespread IPv6 Extension Header Filtering
The results presented in Section 4 indicate that at least for part of
the public Internet, communication employing IPv6 extension headers
is unreliable. The following subsections discuss specific
implications arising from this conclusion.
5.1. Advice to Protocol Designers
New protocols that are to operate in the public Internet should
consider the effect of widespread filtering of IPv6 extension headers
in the public Internet. If IPv6 extension headers are at all
employed, a fall-back mechanism that does not rely on IPv6 extension
headers should be considered.
5.2. A possible attack vector
The widespread filtering 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 filtered on the path
from one system (say, "A") to another (say, "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 (with a
Next-Hop 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 to public network
(e.g., client from/to server or server from/to server), where
packets with IPv6 extension headers are filtered 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:
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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 (by the attacker) could make this difficult, if
at all possible.
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 node cannot simply "just filter/drop all incoming ICMPv6 Packet
Too Big error messages", or else it would create a PMTUD
blackhole.
Possible mitigations for this issue include:
o Filtering incoming ICMPv6 Packet Too Big error messages that
advertise a Next-Hop MTU smaller than 1280 bytes.
o Artificially reducing the MTU to 1280 bytes and filter incoming
ICMPv6 PTB error messages.
Both of these mitigations come at the expense of possibly preventing
communication through SIIT [RFC6145] that rely on IPv6 atomic
fragments (see [I-D.gont-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.gont-6man-deprecate-atomfrag-generation] has recently proposed
to deprecate the generation of IPv6 atomic fragments, and update the
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SIIT [RFC6145] such that it does not rely on ICMPv6 atomic fragments.
Thus, any of the above mitigations would eliminate the attack vector
without any interoperability implications.
5.3. Possible Future Work
The impact of widespread filtering of IPv6 EHs on existing protocols
should be considered. In particular, the effect of widespread
filtering of IPv6 fragments on the Domain Name System (DNS) [RFC1034]
should be evaluated (particularly when it is expected that reliance
on IPv6 transport will increase over time).
6. Troubleshooting Packet Drops due to IPv6 Extension Headers
Isolating IPv6 blackholes essentially involves performing IPv6
traceroute for a destination system with and without IPv6 extension
headers. The (EH-free) traceroute would provide the full working
path towards a destination, while the EH-enabled traceroute would
provide the address of the last-responding node for EH-enabled
packets (say, "M"). In principle, one could isolate the dropping
node by looking-up "M" in the EH-free traceroute, with the dropping
node being "M+1" (see Appendix A.1 for caveats).
At the time of this writing, most traceroute implementations do not
support IPv6 extension headers. However, the path6 tool [path6] and
RIPE Atlas [RIPE-Atlas] provide such support. Additionally, the
blackhole6 tool [blackhole6] automates the troubleshooting process
and can readily provide information such as: dropping node's IPv6
address, dropping node's Autonomous System, etc.
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 3.2. A specific attack vector that would leverage the
widespread filtering of packets with IPv6 EHs (along with possible
countermeasures) is discussed in Section 5.2. This document does not
introduce any new security issues.
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9. Acknowledgements
The authors would like to thank (in alphabetical order) Mark Andrews,
Brian Carpenter and Tatuya Jinmei for providing valuable comments on
earlier versions of this document. Additionally, the authors would
like to thank participants of the v6ops and opsec working groups for
their valuable input on the topics discussed in this document.
Fernando Gont would like to thank Jan Zorz and Go6 Lab
for providing access to systems and networks that
were employed to produce some of the measurement results presented in
this document. Additionally, he would like to thank SixXS
for providing IPv6 connectivity.
10. References
10.1. Normative References
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC
793, September 1981.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control
Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) Specification", RFC 4443, March 2006.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
Algorithm", RFC 6145, April 2011.
[RFC6946] Gont, F., "Processing of IPv6 "Atomic" Fragments", RFC
6946, May 2013.
10.2. Informative References
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[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,
.
[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, .
[I-D.gont-6man-deprecate-atomfrag-generation]
Gont, F., Will, W., and T. Anderson, "Deprecating the
Generation of IPv6 Atomic Fragments", draft-gont-6man-
deprecate-atomfrag-generation-01 (work in progress),
August 2014.
[I-D.ietf-6man-predictable-fragment-id]
Gont, F., "Security Implications of Predictable Fragment
Identification Values", draft-ietf-6man-predictable-
fragment-id-01 (work in progress), April 2014.
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[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., and R. Bonica, "Operational
Issues Associated With Long IPv6 Header Chains", draft-
wkumari-long-headers-02 (work in progress), October 2013.
[IANA-PORT-NUMBERS]
IANA, "Service Name and Transport Protocol Port Number
Registry", .
[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,
.
[RFC5927] Gont, F., "ICMP Attacks against TCP", RFC 5927, July 2010.
[RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation
with IPv6 Neighbor Discovery", RFC 6980, August 2013.
[RFC7045] Carpenter, B. and S. Jiang, "Transmission and Processing
of IPv6 Extension Headers", RFC 7045, December 2013.
[RFC7112] Gont, F., Manral, V., and R. Bonica, "Implications of
Oversized IPv6 Header Chains", RFC 7112, January 2014.
[RFC7113] Gont, F., "Implementation Advice for IPv6 Router
Advertisement Guard (RA-Guard)", RFC 7113, February 2014.
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[RFC7123] Gont, F. and W. Liu, "Security Implications of IPv6 on
IPv4 Networks", RFC 7123, 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,
.
[blackhole6]
blackhole6, , "blackhole6 tool manual page",
, 2014.
[path6] path6, , "path6 tool manual page",
, 2014.
Appendix A. Measurements Caveats
A number of issues have needed some consideration when producing the
results presented in Section 4. These same issues should be
considered when troubleshooting connectivity problems resulting from
the use of IPv6 Extension headers.
A.1. Isolating the Dropping Node
Let us assume that we find that IPv6 packets with EHs are being
dropped on their way to the destination system 2001:db8:d::1, and
that the output of running traceroute towards such destination is:
1. 2001:db8:1:1000::1
2. 2001:db8:2:2000::4
3. 2001:db8:2:4000::1
4. 2001:db8:3:4000::1
5. 2001:db8:3:1000::1
6. 2001:db8:4:4000::1
7. 2001:db8:4:1000::1
8. 2001:db8:5:5000::1
9. 2001:db8:5:6000::1
10. 2001:db8:d::1
Additionally, let us assume that the output of EH-enabled traceroute
to the same destination is:
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1. 2001:db8:1:1000::1
2. 2001:db8:2:2000::4
3. 2001:db8:2:4000::1
4. 2001:db8:3:4000::1
5. 2001:db8:3:1000::1
6. 2001:db8:4:4000::1
For the sake of brevity, let us refer to the last-responding node in
the EH-enabled traceroute ("2001:db8:4:4000::1" in this case) as "M".
Assuming both packets in both traceroutes employ the same path, we'll
refer to "the node following the last responding node in the EH-
enabled traceroute" ("2001:db8:4:1000::1" in our case), as "M+1",
etc.
Based on traceroute information above, which node is the one actually
dropping the EH-enabled packets will depend on whether the dropping
node filters packets on ingress or the egress. If the former, the
dropping node will be M+1. If the latter, the dropping node will be
"M".
Throughout this document (and our measurements), we assume that nodes
perform ingress-filtering. Thus, in our example above the last
responding node to the EH-enabled traceroute ("M") is
"2001:db8:4:4000::1", and therefore we assume the "node" dropping
node to be "2001:db8:4:1000::1" ("M+1").
Additionally, we note that when isolating the dropping node we assume
that both the EH-enabled and the EH-free traceroutes result in the
same paths. However, this might not be the case.
A.2. Obtaining the Responsible Organization for the Packet Drops
In order to identify the organization operating the dropping node,
one would be tempted to lookup the ASN corresponding to the dropping
node. However, assuming that M and M+1 are two peering routers, any
of these two organizations could be providing the address space
employed for such peering. Or, in the case of an Internet eXchange
Point (IXP), the address space could correspond to the IXP AS, rather
than to any of the participating ASes. Thus, the organization
operating the dropping node (M+1) could be the AS for M+1, but it
might as well be the AS for M+2. Only when the ASN for M+1 is the
same as the ASN for M+2 we have certainty about who the responsible
organization for the packet drops is (see slides 21-23 of
[Linkova-Gont-IEPG90]).
In the measurement results presented in Section 4, the aforementioned
ambiguity results in "percentage ranges" (rather than a specific
ratio): the lowest percentage value means that, when in doubt, we
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assume the packet drops occur in the same AS as the destination; on
the other hand, the highest percentage value means that, when in
doubt, we assume the packet drops occur at different AS than the
destination AS.
We note that the aforementioned ambiguity should also be considered
when troubleshooting and reporting IPv6 packet drops, since
identifying the organization responsible for the packet drops might
probe to be a non-trivial task.
Finally, we note that a specific organization might be operating more
than one Autonomous System. However, our measurements assume that
different Autonomous System Numbers imply different organizations.
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
J. Linkova
Google
1600 Amphitheatre Parkway
Mountain View, CA 94043
USA
Email: furry@google.com
Tim Chown
University of Southampton
Highfield
Southampton , Hampshire SO17 1BJ
United Kingdom
Email: tjc@ecs.soton.ac.uk
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Will(Shucheng) Liu
Huawei Technologies
Bantian, Longgang District
Shenzhen 518129
P.R. China
Email: liushucheng@huawei.com
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