wdiff rfc7872.original rfc7872.txt

IPv6 Operations Working Group (v6ops)
Internet Engineering Task Force (IETF) F. Gont
Internet-Draft
Request for Comments: 7872 SI6 Networks / UTN-FRH
Intended status:
Category: Informational J. Linkova
Expires: June 12, 2016
ISSN: 2070-1721 Google
T. Chown
University of Southampton
Jisc
W. Liu
Huawei Technologies
December 10, 2015
May 2016

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 Extension Headers (EHs) are dropped in the Internet
(as originally measured in August 2014 and later in June 2015, with
similar results), 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, EHs 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. EHs.

Status of This Memo

This Internet-Draft document is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents not an Internet Standards Track specification; it is
published for informational purposes.

This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a maximum candidate for any level of Internet
Standard; see Section 2 of RFC 5741.

Information about the current status of six months this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained 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 June 12, 2016.
http://www.rfc-editor.org/info/rfc7872.

This document is subject to BCP 78 and the IETF Trust's Legal
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(http://trustee.ietf.org/license-info) in effect on the date of
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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.
4. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1.
4.1. Normative References . . . . . . . . . . . . . . . . . . 6
6.2.
4.2. Informative References . . . . . . . . . . . . . . . . . 7 6
Appendix A. Reproducing Our Experiment . . . . . . . . . . . . . 8 7
A.1. Obtaining the List of Domain Names . . . . . . . . . . . 8 7
A.2. Obtaining AAAA Resource Records . . . . . . . . . . . . . 9 8
A.3. Filtering the IPv6 Address Datasets . . . . . . . . . . . 9 8
A.4. Performing Measurements with Each IPv6 Address Dataset . 10 8
A.5. Obtaining Statistics from our Our Measurements . . . . . . . 11 10
Appendix B. Measurements Caveats . . . . . . . . . . . . . . . . 12 11
B.1. Isolating the Dropping Node . . . . . . . . . . . . . . . 12 11
B.2. Obtaining the Responsible Organization for the Packet
Drops . . . . . . . . . . . . . . . . . . . . . . . . . . 13 12
Appendix C. Troubleshooting Packet Drops due Due to IPv6 Extension
Headers . . . . . . . . . . . . . . . . . . . . . . 14 13
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14

1. Introduction

IPv6 Extension Headers (EHs) allow for the extension of the IPv6
protocol,
protocol and provide support for core functionality such as IPv6
fragmentation. While packets employing IPv6 Extension Headers EHs 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] [Gont-IEPG88], and [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 EHs 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 EHs 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 EHs 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" Launch" site
(http://www.worldipv6launch.org/)
<http://www.worldipv6launch.org> and Alexa's top 1M web sites
(http://www.alexa.com). list of the Top
1-Million 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 records of the aforementioned list)

o Name servers (NS -> AAAA records 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 bytes;

o IPv6 packets resulting in two IPv6 fragments of 512 bytes each
(approximately)
(approximately); and

o IPv6 packets with a Hop-by-Hop Options header of 8 bytes bytes.

In the case of packets with a Destination Options Header header and the case
of packets with a 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
Destination Port set to 80.

Besides obtaining the packet drop rate when employing the
aforementioned IPv6 extension headers, EHs, we tried to identify whether the Autonomous
System (AS) dropping the packets was the same as the
Autonomous System AS 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, 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, concern since they
affect the deployability and usability of IPv6 extension headers EHs (including IPv6
fragmentation) by a third-party 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 EHs get dropped, the packet drops are the result of
an explicit and intended policy, 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 AS 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",
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).

+-------------+-----------------+-----------------+-----------------+

+----------+------------------+------------------+------------------+
| Dataset | DO8 | HBH8 | FH512 |
+-------------+-----------------+-----------------+-----------------+
+----------+------------------+------------------+------------------+
| Webservers Web | 11.88% | 40.70% | 30.51% |
| servers | (17.60%/20.80%) | (31.43%/40.00%) | (5.08%/6.78%) |
+-------------+-----------------+-----------------+-----------------+
+----------+------------------+------------------+------------------+
| Mailservers Mail | 17.07% | 48.86% | 39.17% |
| servers | (6.35%/26.98%) | (40.50%/65.42%) | (2.91%/12.73%) |
+-------------+-----------------+-----------------+-----------------+
+----------+------------------+------------------+------------------+
| Nameservers Name | 15.37% | 43.25% | 38.55% |
| servers | (14.29%/33.46%) | (42.49%/72.07%) | (3.90%/13.96%) |
+-------------+-----------------+-----------------+-----------------+
+----------+------------------+------------------+------------------+

Table 1: WIPv6LD dataset: Dataset: Packet drop rate Drop Rate for different destination
types, Different Destination
Types, and estimated percentage Estimated (Best-Case / Worst-Case) Percentage of dropped packets that were deemed
to be dropped Packets
That Were Dropped in a different Different AS (lower, in parentheses)

NOTE: In the tables above and below, "HBH8" stands for "packets
with a Hop-By-Hop Options extension header of 8 bytes", "DO8"
stands for "packets with a Destination Options extension header of
8 bytes", and "FH512" stands for "IPv6 packets with a Fragment
Header of 512 bytes".

NOTE: As an example, we note that the cell describing the support
of IPv6 packets with DO8 for webservers web servers (containing the value
"11.88% (17.60%/20.80%)") should be read as: "when sending IPv6
packets with DO8 to public webservers, web servers, 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 Web | 10.91% | 39.03% | 28.26% |
| servers | (46.52%/53.23%) | (36.90%/46.35%) | (53.64%/61.43%) |
+-------------+-----------------+-----------------+-----------------+
+----------+------------------+------------------+------------------+
| Mailservers Mail | 11.54% | 45.45% | 35.68% |
| servers | (2.41%/21.08%) | (41.27%/61.13%) | (3.15%/10.92%) |
+-------------+-----------------+-----------------+-----------------+
+----------+------------------+------------------+------------------+
| Nameservers Name | 21.33% | 54.12% | 55.23% |
| servers | (10.27%/56.80%) | (50.64%/81.00%) | (5.66%/32.23%) |
+-------------+-----------------+-----------------+-----------------+
+----------+------------------+------------------+------------------+

Table 2: Alexa's top Top 1M sites dataset: Sites Dataset: Packet drop rate Drop Rate for different
destination types, Different
Destination Types, and estimated percentage Estimated (Best-Case / Worst-Case) Percentage
of dropped packets that
were deemed to be dropped Packets That Were Dropped in a different 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 EHs in general that result in packet drops.
Secondly, our results indicate that a significant percentage of such
packet drops occurs in transit Autonomous Systems; ASes; 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 EHs 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.

4. References

6.1.

4.1. 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>.

[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.

4.2. 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. meeting before IETF 89, 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 Header Support in
the IPv6 Internet", IEPG 88. Vancouver, BC, Canada. meeting before IETF 88, 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>.
service-names-port-numbers>.

[IPv6-Toolkit]
SI6 Networks, "SI6 Networks' IPv6 Toolkit", Toolkit v2.0 (Guille)",
<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. Meeting before IETF 90, July 20, 2014,
<http://www.iepg.org/2014-07-20-ietf90/
iepg-ietf90-ipv6-ehs-in-the-real-world-v2.0.pdf>.

[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), gunzip)
and the SI6 Networks' IPv6 Toolkit v2.0 (Guille) [IPv6-Toolkit].

Throughout this appendix, "#" denotes the command-line prompt for
commands that require superuser privileges, whereas "$" denotes the
prompt for commands that do not require superuser privileges.

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 Comma-Separated Value (CSV) format. The aforementioned
file can be extracted with
"gunzip

$ gunzip < top-1m.csv.zip > top-1m.csv". top-1m.csv

A list of domain names (i.e., with other data stripped) can be
obtained with the following command of [IPv6-Toolkit]: "cat

$ cat top-1m.csv | script6 get-alexa-domains > top-1m.txt". top-1m.txt

This command will create a "top-1m.txt" file, 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>. 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 dataset should be processed in the same
way as the Alexa Dataset, 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 mail servers 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
top-1m-mail-aaaa.txt

The AAAA records corresponding to the nameservers name servers 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
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., (e.g., 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

$ 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 Web Servers

In order to measure DO8 with the list of webservers: web servers:

# cat top-1m-web-aaaa-unique.txt | script6 trace6 do8 tcp 80 > top-
1m-web-aaaa-do8-m.txt
top-1m-web-aaaa-do8-m.txt

In order to measure HBH8 with the list of webservers: web servers:

# cat top-1m-web-aaaa-unique.txt | script6 trace6 hbh8 tcp 80 > top-
1m-web-aaaa-hbh8-m.txt
top-1m-web-aaaa-hbh8-m.txt

In order to measure FH512 with the list of webservers: web servers:

# cat top-1m-web-aaaa-unique.txt | script6 trace6 fh512 tcp 80 > top-
1m-web-aaaa-fh512-m.txt
top-1m-web-aaaa-fh512-m.txt

A.4.2. Measurements with mail servers Mail Servers

In order to measure DO8 with the list of mailservers: mail servers:

# cat top-1m-mail-aaaa-unique.txt | script6 trace6 do8 tcp 25 > top-
1m-mail-aaaa-do8-m.txt
top-1m-mail-aaaa-do8-m.txt

In order to measure HBH8 with the list of webservers: mail servers:

# cat top-1m-mail-aaaa-unique.txt | script6 trace6 hbh8 tcp 25 > top-
1m-mail-aaaa-hbh8-m.txt
top-1m-mail-aaaa-hbh8-m.txt

In order to measure FH512 with the list of webservers: mail servers:

# 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 Name Servers

In order to measure DO8 with the list of mameservers: name servers:

# cat top-1m-dns-aaaa-unique.txt | script6 trace6 do8 tcp 53 > top-
1m-dns-aaaa-do8-m.txt
top-1m-dns-aaaa-do8-m.txt

In order to measure HBH8 with the list of webservers: name servers:

# cat top-1m-dns-aaaa-unique.txt | script6 trace6 hbh8 tcp 53 > top-
1m-dns-aaaa-hbh8-m.txt
top-1m-dns-aaaa-hbh8-m.txt

In order to measure FH512 with the list of webservers: name servers:

# cat top-1m-dns-aaaa-unique.txt | script6 trace6 fh512 tcp 53 > top-
1m-dns-aaaa-fh512-m.txt
top-1m-dns-aaaa-fh512-m.txt

A.5. Obtaining Statistics from our 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: web servers:

$ cat top-1m-web-aaaa-do8-m.txt | script6 get-trace6-stats > top-1m-
web-aaaa-do8-stats.txt
top-1m-web-aaaa-do8-stats.txt

In order to compute the statistics corresponding to our measurements
of HBH8 with the list of webservers: web servers:

$ cat top-1m-web-aaaa-hbh8-m.txt | script6 get-trace6-stats > top-1m-
web-aaaa-hbh8-stats.txt
top-1m-web-aaaa-hbh8-stats.txt

In order to compute the statistics corresponding to our measurements
of FH512 with the list of webservers: web servers:

$ cat top-1m-web-aaaa-fh512-m.txt | script6 get-trace6-stats > top-
1m-web-aaaa-fh512-stats.txt
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: mail servers:

$ cat top-1m-mail-aaaa-do8-m.txt | script6 get-trace6-stats > top-1m-
mail-aaaa-do8-stats.txt
top-1m-mail-aaaa-do8-stats.txt

In order to compute the statistics corresponding to our measurements
of HBH8 with the list of mailservers: mail servers:

$ cat top-1m-mail-aaaa-hbh8-m.txt | script6 get-trace6-stats > top-
1m-mail-aaaa-hbh8-stats.txt
top-1m-mail-aaaa-hbh8-stats.txt

In order to compute the statistics corresponding to our measurements
of FH512 with the list of mailservers: mail servers:

$ cat top-1m-mail-aaaa-fh512-m.txt | script6 get-trace6-stats > top-
1m-mail-aaaa-fh512-stats.txt
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: name servers:

$ cat top-1m-dns-aaaa-do8-m.txt | script6 get-trace6-stats > top-1m-
dns-aaaa-do8-stats.txt
top-1m-dns-aaaa-do8-stats.txt

In order to compute the statistics corresponding to our measurements
of HBH8 with the list of mailservers: mail servers:

$ cat top-1m-dns-aaaa-hbh8-m.txt | script6 get-trace6-stats > top-1m-
dns-aaaa-hbh8-stats.txt
top-1m-dns-aaaa-hbh8-stats.txt

In order to compute the statistics corresponding to our measurements
of FH512 with the list of mailservers: mail servers:

$ cat top-1m-dns-aaaa-fh512-m.txt | script6 get-trace6-stats > top-
1m-dns-aaaa-fh512-stats.txt
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. EHs.

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, 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:

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, 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 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 Autonomous System Numbers (ASNs)
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 Exchange Point (IXP), the address space could
correspond to the IXP AS, 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 do 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,
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 a different
AS than the destination AS.

We note that the aforementioned ambiguity should also be considered
when troubleshooting and reporting IPv6 packet drops, drops since
identifying the organization responsible for the packet drops might
probe
prove to be a non-trivial task.

Finally, we note that a specific organization might be operating more
than one Autonomous System. AS. However, our measurements assume that different Autonomous System Numbers ASNs
imply different organizations.

Appendix C. Troubleshooting Packet Drops due Due to IPv6 Extension Headers

Isolating IPv6 blackholes essentially involves performing IPv6
traceroute for a destination system with and without IPv6 extension
headers. EHs. The
EH-free traceroute would provide the full working path towards a destination,
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 looking-up "M" in
the EH-free traceroute, 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. EHs. 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,
AS, etc.

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 draft 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 of Go6 Lab
<http://go6lab.si/> and Jared Mauch of 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.

Fernando Gont would like to thank Nelida Garcia and Guillermo Gont
for their love and support.

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
United States

Email: furry@google.com

Tim Chown
University of Southampton
Highfield
Southampton , Hampshire SO17 1BJ
Jisc
Lumen House, Library Avenue
Harwell Oxford, Didcot OX11 0SG
United Kingdom

Email: tjc@ecs.soton.ac.uk

Will(Shucheng) tim.chown@jisc.ac.uk

Will (Shucheng) Liu
Huawei Technologies
Bantian, Longgang District
Shenzhen 518129
P.R.
China

Email: liushucheng@huawei.com