Internet DRAFT - draft-ietf-v6ops-ipv6-ehs-in-real-world
draft-ietf-v6ops-ipv6-ehs-in-real-world
IPv6 Operations Working Group (v6ops) F. Gont
Internet-Draft SI6 Networks / UTN-FRH
Intended status: Informational J. Linkova
Expires: June 12, 2016 Google
T. Chown
University of Southampton
W. Liu
Huawei Technologies
December 10, 2015
Observations on the Dropping of Packets with IPv6 Extension Headers in
the Real World
draft-ietf-v6ops-ipv6-ehs-in-real-world-02
Abstract
This document presents real-world data regarding the extent to which
packets with IPv6 extension headers are dropped in the Internet (as
originally measured in August 2014 and later in June 2015, with
similar results), and where in the network such dropping occurs. The
aforementioned results serve as a problem statement that is expected
to trigger operational advice on the filtering of IPv6 packets
carrying IPv6 Extension Headers, so that the situation improves over
time. This document also explains how the aforementioned results
were obtained, such that the corresponding measurements can be
reproduced by other members of the community and repeated over time
to observe changes in the handling of packets with IPv6 extension
headers.
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
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 12, 2016.
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Copyright Notice
Copyright (c) 2015 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
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Support of IPv6 Extension Headers in the Internet . . . . . . 3
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . 6
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . 6
6.2. Informative References . . . . . . . . . . . . . . . . . 7
Appendix A. Reproducing Our Experiment . . . . . . . . . . . . . 8
A.1. Obtaining the List of Domain Names . . . . . . . . . . . 8
A.2. Obtaining AAAA Resource Records . . . . . . . . . . . . . 9
A.3. Filtering the IPv6 Address Datasets . . . . . . . . . . . 9
A.4. Performing Measurements with Each IPv6 Address Dataset . 10
A.5. Obtaining Statistics from our Measurements . . . . . . . 11
Appendix B. Measurements Caveats . . . . . . . . . . . . . . . . 12
B.1. Isolating the Dropping Node . . . . . . . . . . . . . . . 12
B.2. Obtaining the Responsible Organization for the Packet
Drops . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Appendix C. Troubleshooting Packet Drops due to IPv6 Extension
Headers . . . . . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
IPv6 Extension Headers (EHs) allow for the extension of the IPv6
protocol, and provide support for core functionality such as IPv6
fragmentation. While packets employing IPv6 Extension Headers have
been suspected 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
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[Gont-Chown-IEPG89], whereas [Linkova-Gont-IEPG90] presents more
comprehensive results on which this document is based.
This document presents real-world data regarding the extent to which
packets containing IPv6 Extension Headers are dropped in the
Internet, as measured in August 2014 and later in June 2015 with
similar results (pending operational advice in this area). The
results presented in this document indicate that in the scenarios
where the corresponding measurements were performed, the use of IPv6
extension headers can lead to packet drops. We note that, in
particular, packet drops occurring at transit networks are
undesirable, and it is hoped and expected that this situation will
improve over time.
2. Support of IPv6 Extension Headers in the 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 of information 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 the aforementioned list)
o Name servers (NS -> AAAA of the aforementioned list)
Duplicate addresses and IPv6 addresses other than global unicast
addresses were eliminated from each of those lists prior to obtaining
the results included in this document. Additionally, addresses that
were found to be unreachable were discarded from the dataset (please
see Appendix B for further details).
For each of the aforementioned address sets, three different types of
probes were employed:
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 a Destination Options Header and the case
of packets with a Hop-by-Hop Options header, the desired EH size was
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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 (see Appendix B.2), each of our
measurements results in two different values: one corresponding to
the "best-case scenario", and one corresponding to the "worst-case
scenario". The "best-case scenario" is that in which, when in doubt,
the packets are assumed to be dropped by the destination AS, whereas
the "worst-case scenario" is that in which, when in doubt, the
packets are assumed to be dropped by a transit AS (please see
Appendix B.2 for details). In the following tables, the values shown
within parentheses represent the possibility that, when a packet is
dropped, the packet drop occurs in an AS other than the destination
AS (considering both the best-case scenario and the worst-case
scenario).
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+-------------+-----------------+-----------------+-----------------+
| 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, 17.60%/20.80%
(best case / worst case) 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
indicate that it is IPv6 extension headers in general that result in
packet drops. Secondly, our results indicate that a significant
percentage of such packet drops occurs in transit Autonomous Systems;
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that is, the packet drops are not under the control of the same
organization as the final destination.
3. 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.
4. Security Considerations
This document presents real-world data regarding the extent to which
IPv6 packets employing extension headers are dropped in the Internet.
As such, this document does not introduce any new security issues.
5. Acknowledgements
The authors would like to thank (in alphabetical order) Mikael
Abrahamsson, Mark Andrews, Fred Baker, Brian Carpenter, Gert Doering,
C. M. Heard, Nick Hilliard, Joel Jaeggli, Tatuya Jinmei, Merike
Kaeo, Warren Kumari, Ted Lemon, Mark Smith, Ole Troan, and Eric
Vyncke, 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.
The authors would like to thank Fred Baker for his guidance in
improving this document.
Fernando Gont would like to thank Jan Zorz / Go6 Lab
<http://go6lab.si/>, and Jared Mauch / NTT America, 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 <https://www.sixxs.net> for providing IPv6
connectivity.
6. References
6.1. Normative References
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<http://www.rfc-editor.org/info/rfc793>.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<http://www.rfc-editor.org/info/rfc1034>.
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[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <http://www.rfc-editor.org/info/rfc2460>.
[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,
<http://www.rfc-editor.org/info/rfc4443>.
[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,
<http://www.rfc-editor.org/info/rfc4861>.
6.2. Informative References
[blackhole6]
blackhole6, , "blackhole6 tool manual page",
<http://www.si6networks.com/tools/ipv6toolkit>, 2014.
[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,
<http://www.iepg.org/2014-03-02-ietf89/
fgont-iepg-ietf89-eh-update.pdf>.
[Gont-IEPG88]
Gont, F., "Fragmentation and Extension header Support in
the IPv6 Internet", IEPG 88. Vancouver, BC, Canada.
November 13, 2013, <http://www.iepg.org/2013-11-ietf88/
fgont-iepg-ietf88-ipv6-frag-and-eh.pdf>.
[IANA-PORT-NUMBERS]
IANA, "Service Name and Transport Protocol Port Number
Registry", <http://www.iana.org/assignments/
service-names-port-numbers/
service-names-port-numbers.txt>.
[IPv6-Toolkit]
"SI6 Networks' IPv6 Toolkit",
<http://www.si6networks.com/tools/ipv6toolkit>.
[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, <http://www.iepg.org/2014-07-20-ietf90/
iepg-ietf90-ipv6-ehs-in-the-real-world-v2.0.pdf>.
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[path6] path6, , "path6 tool manual page",
<http://www.si6networks.com/tools/ipv6toolkit>, 2014.
[PMTUD-Blackholes]
De Boer, M. and J. Bosma, "Discovering Path MTU black
holes on the Internet using RIPE Atlas", July 2012,
<http://www.nlnetlabs.nl/downloads/publications/
pmtu-black-holes-msc-thesis.pdf>.
[RFC5927] Gont, F., "ICMP Attacks against TCP", RFC 5927,
DOI 10.17487/RFC5927, July 2010,
<http://www.rfc-editor.org/info/rfc5927>.
[RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation
with IPv6 Neighbor Discovery", RFC 6980,
DOI 10.17487/RFC6980, August 2013,
<http://www.rfc-editor.org/info/rfc6980>.
[RFC7045] Carpenter, B. and S. Jiang, "Transmission and Processing
of IPv6 Extension Headers", RFC 7045,
DOI 10.17487/RFC7045, December 2013,
<http://www.rfc-editor.org/info/rfc7045>.
[RFC7113] Gont, F., "Implementation Advice for IPv6 Router
Advertisement Guard (RA-Guard)", RFC 7113,
DOI 10.17487/RFC7113, February 2014,
<http://www.rfc-editor.org/info/rfc7113>.
[RFC7123] Gont, F. and W. Liu, "Security Implications of IPv6 on
IPv4 Networks", RFC 7123, DOI 10.17487/RFC7123, February
2014, <http://www.rfc-editor.org/info/rfc7123>.
Appendix A. Reproducing Our Experiment
This section describes, step by step, how to reproduce the experiment
with which we obtained the results presented in this document. Each
subsection represents one step in the experiment. The tools employed
for the experiment are traditional UNIX-like tools (such as gunzip),
and the SI6 Networks' IPv6 Toolkit [IPv6-Toolkit].
A.1. Obtaining the List of Domain Names
The primary data source employed was Alexa's Top 1M web sites,
available at: <http://s3.amazonaws.com/alexa-static/top-1m.csv.zip>.
The file is a zipped file containing the list of the most popular web
sites, in CSV format. The aforementioned file can be extracted with
"gunzip < top-1m.csv.zip > top-1m.csv".
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A list of domain names (i.e., other data stripped) can be obtained
with the following command of [IPv6-Toolkit]: "cat top-1m.csv |
script6 get-alexa-domains > top-1m.txt". This command will create a
"top-1m.txt" file, containing one domain name per line.
NOTE: The domain names corresponding to the WIPv6LD dataset is
available at: <http://www.si6networks.com/datasets/wipv6day-
domains.txt>. Since the corresponding file is a text file
containing one domain name per line, the steps produced in this
subsection need not be performed. The WIPv6LD data set should be
processed in the same way as the Alexa Dataset, starting from
Appendix A.2.
A.2. Obtaining AAAA Resource Records
The file obtained in the previous subsection contains a list of
domain names that correspond to web sites. The AAAA records for such
domain names can be obtained with:
$ cat top-1m.txt | script6 get-aaaa > top-1m-web-aaaa.txt
The AAAA records corresponding to the mailservers of each of the
aforementioned domain names can be obtained with:
$ cat top-1m.txt | script6 get-mx | script6 get-aaaa > top-1m-mail-
aaaa.txt
The AAAA records corresponding to the nameservers of each of the
aforementioned domain names can be obtained with:
$ cat top-1m.txt | script6 get-ns | script6 get-aaaa > top-1m-dns-
aaaa.txt
A.3. Filtering the IPv6 Address Datasets
The lists of IPv6 addresses obtained in the previous step could
possibly contain undesired addresses (i.e., non-global unicast
addresses) and/or duplicate addresses. In order to remove both
undesired and duplicate addresses, each of the three files from the
previous section should be filtered accordingly:
$ cat top-1m-web-aaaa.txt | addr6 -i -q -B multicast -B unspec -k
global > top-1m-web-aaaa-unique.txt
$ cat top-1m-mail-aaaa.txt | addr6 -i -q -B multicast -B unspec -k
global > top-1m-mail-aaaa-unique.txt
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$ cat top-1m-dns-aaaa.txt | addr6 -i -q -B multicast -B unspec -k
global > top-1m-dns-aaaa-unique.txt
A.4. Performing Measurements with Each IPv6 Address Dataset
A.4.1. Measurements with web servers
In order to measure DO8 with the list of webservers:
# cat top-1m-web-aaaa-unique.txt | script6 trace6 do8 tcp 80 > top-
1m-web-aaaa-do8-m.txt
In order to measure HBH8 with the list of webservers:
# cat top-1m-web-aaaa-unique.txt | script6 trace6 hbh8 tcp 80 > top-
1m-web-aaaa-hbh8-m.txt
In order to measure FH512 with the list of webservers:
# cat top-1m-web-aaaa-unique.txt | script6 trace6 fh512 tcp 80 > top-
1m-web-aaaa-fh512-m.txt
A.4.2. Measurements with mail servers
In order to measure DO8 with the list of mailservers:
# cat top-1m-mail-aaaa-unique.txt | script6 trace6 do8 tcp 25 > top-
1m-mail-aaaa-do8-m.txt
In order to measure HBH8 with the list of webservers:
# cat top-1m-mail-aaaa-unique.txt | script6 trace6 hbh8 tcp 25 > top-
1m-mail-aaaa-hbh8-m.txt
In order to measure FH512 with the list of webservers:
# cat top-1m-mail-aaaa-unique.txt | script6 trace6 fh512 tcp 25 >
top-1m-mail-aaaa-fh512-m.txt
A.4.3. Measurements with DNS servers
In order to measure DO8 with the list of mameservers:
# cat top-1m-dns-aaaa-unique.txt | script6 trace6 do8 tcp 53 > top-
1m-dns-aaaa-do8-m.txt
In order to measure HBH8 with the list of webservers:
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# cat top-1m-dns-aaaa-unique.txt | script6 trace6 hbh8 tcp 53 > top-
1m-dns-aaaa-hbh8-m.txt
In order to measure FH512 with the list of webservers:
# cat top-1m-dns-aaaa-unique.txt | script6 trace6 fh512 tcp 53 > top-
1m-dns-aaaa-fh512-m.txt
A.5. Obtaining Statistics from our Measurements
A.5.1. Statistics for Web Servers
In order to compute the statistics corresponding to our measurements
of DO8 with the list of webservers:
$ cat top-1m-web-aaaa-do8-m.txt | script6 get-trace6-stats > top-1m-
web-aaaa-do8-stats.txt
In order to compute the statistics corresponding to our measurements
of HBH8 with the list of webservers:
$ cat top-1m-web-aaaa-hbh8-m.txt | script6 get-trace6-stats > top-1m-
web-aaaa-hbh8-stats.txt
In order to compute the statistics corresponding to our measurements
of FH512 with the list of webservers:
$ cat top-1m-web-aaaa-fh512-m.txt | script6 get-trace6-stats > top-
1m-web-aaaa-fh512-stats.txt
A.5.2. Statistics for Mail Servers
In order to compute the statistics corresponding to our measurements
of DO8 with the list of mailservers:
$ cat top-1m-mail-aaaa-do8-m.txt | script6 get-trace6-stats > top-1m-
mail-aaaa-do8-stats.txt
In order to compute the statistics corresponding to our measurements
of HBH8 with the list of mailservers:
$ cat top-1m-mail-aaaa-hbh8-m.txt | script6 get-trace6-stats > top-
1m-mail-aaaa-hbh8-stats.txt
In order to compute the statistics corresponding to our measurements
of FH512 with the list of mailservers:
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$ cat top-1m-mail-aaaa-fh512-m.txt | script6 get-trace6-stats > top-
1m-mail-aaaa-fh512-stats.txt
A.5.3. Statistics for Name Servers
In order to compute the statistics corresponding to our measurements
of DO8 with the list of nameservers:
$ cat top-1m-dns-aaaa-do8-m.txt | script6 get-trace6-stats > top-1m-
dns-aaaa-do8-stats.txt
In order to compute the statistics corresponding to our measurements
of HBH8 with the list of mailservers:
$ cat top-1m-dns-aaaa-hbh8-m.txt | script6 get-trace6-stats > top-1m-
dns-aaaa-hbh8-stats.txt
In order to compute the statistics corresponding to our measurements
of FH512 with the list of mailservers:
$ cat top-1m-dns-aaaa-fh512-m.txt | script6 get-trace6-stats > top-
1m-dns-aaaa-fh512-stats.txt
Appendix B. Measurements Caveats
A number of issues have needed some consideration when producing the
results presented in this document. These same issues should be
considered when troubleshooting connectivity problems resulting from
the use of IPv6 Extension headers.
B.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:db8:2:4000::1
3. 2001:db8:3:4000::1
4. 2001:db8:3:1000::1
5. 2001:db8:4:4000::1
6. 2001:db8:4:1000::1
7. 2001:db8:5:5000::1
8. 2001:db8:5:6000::1
9. 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:db8:2:4000::1
3. 2001:db8:3:4000::1
4. 2001:db8:3:1000::1
5. 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 that 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 before making the forwarding decision, or after
making the forwarding decision. 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 those
nodes dropping packets that carry IPv6 EHs apply their filtering
policy, and only then, if necessary, forward the packets. 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
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.
B.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 2, the aforementioned
ambiguity results in a "best-case" and a "worst-case" scenario
(rather than a single value): the lowest percentage value means that,
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when in doubt, we 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.
Appendix C. 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 B.1 for caveats).
At the time of this writing, most traceroute implementations do not
support IPv6 extension headers. However, the path6 tool [path6] of
[IPv6-Toolkit] provides such support. Additionally, the blackhole6
tool [blackhole6] of [IPv6-Toolkit] automates the troubleshooting
process and can readily provide information such as: dropping node's
IPv6 address, dropping node's Autonomous System, etc.
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
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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
Will(Shucheng) Liu
Huawei Technologies
Bantian, Longgang District
Shenzhen 518129
P.R. China
Email: liushucheng@huawei.com
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