V6OPS B. Liu
Internet-Draft S. Jiang
Intended status: Informational Huawei Technologies
Expires: February 18, 2017 X. Gong
W. Wang
BUPT University
E. Rey
ERNW GmbH
August 17, 2016
DHCPv6/SLAAC Interaction Problems on Address and DNS Configuration
draft-ietf-v6ops-dhcpv6-slaac-problem-07
Abstract
The IPv6 Neighbor Discovery (ND) Protocol includes an ICMPv6 Router
Advertisement (RA) message. The RA message contains three flags,
indicating the availability of address auto-configuration mechanisms
and other configuration such as DNS-related configuration. These are
the M, O, and A flags, which by definition are advisory, not
prescriptive.
This document describes divergent host behaviors observed in popular
operating systems. It also discusses operational problems that the
divergent behaviors might cause.
Status of This Memo
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 18, 2017.
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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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. The M, O and A Flags . . . . . . . . . . . . . . . . . . . . 3
2.1. Flags Definition . . . . . . . . . . . . . . . . . . . . 4
2.2. Flags Relationship . . . . . . . . . . . . . . . . . . . 4
3. Behavior Ambiguity Analysis . . . . . . . . . . . . . . . . . 4
4. Observed Divergent Host Behaviors . . . . . . . . . . . . . . 6
4.1. Divergent Behavior on Address Auto-Configuration . . . . 6
4.2. Divergent Behavior on DNS Configuration . . . . . . . . . 7
5. Operational Problems . . . . . . . . . . . . . . . . . . . . 9
5.1. Standalone Stateless DHCPv6 Configuration not available . 9
5.2. Renumbering Issues . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. Test Results . . . . . . . . . . . . . . . . . . . . 12
A.1. Test Set 1 . . . . . . . . . . . . . . . . . . . . . . . 12
A.1.1. Test Environment . . . . . . . . . . . . . . . . . . 12
A.1.2. Address Auto-configuration Behavior in the Initial
State . . . . . . . . . . . . . . . . . . . . . . . . 12
A.1.3. Address Auto-configuration Behavior in State
Transitions . . . . . . . . . . . . . . . . . . . . . 13
A.2. Test Set 2 . . . . . . . . . . . . . . . . . . . . . . . 15
A.2.1. Test Environment . . . . . . . . . . . . . . . . . . 15
A.2.2. Address/DNS Auto-configuration Behavior of Using Only
One IPv6 Router and a DHCPv6 Server . . . . . . . . . 15
A.2.3. Address/DNS Auto-configuration Behavior of Using Two
IPv6 Router and a DHCPv6 Server . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
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1. Introduction
IPv6 [RFC2460] hosts could invoke Neighbor Discovery (ND) [RFC4861]
to to discover which auto-configuration mechanisms are available to
them. There are two auto-configuration mechanisms in IPv6:
o DHCPv6 [RFC3315]
o Stateless Address Autoconfiguration (SLAAC) [RFC4862]
ND specifies an ICMPv6-based [RFC4443] Router Advertisement (RA)
message. Routers periodically multicast the RA messages to all on-
link nodes. They also unicast RA messages in response to
solicitations. The RA message contains (but not limited to):
o an M (Managed) flag, indicating that addresses are available from
DHCPv6 or not
o an O (OtherConfig) flag, indicating that other configuration
information (e.g., DNS-related information) is available from
DHCPv6 or not
o zero or more Prefix Information (PI) Options
an A (Autonomous) flag is included, indicating that the prefix
can be used for SLAAC or not
The M and O flags are advisory, not prescriptive. For example, the M
flag indicates that addresses are available from DHCPv6, but It does
not indicate that hosts are required to acquire addresses from
DHCPv6. Similar statements can be made about the O flag. (A flag is
also advisory by definition in standard, but it is quite prescriptive
in implementations according to the test results in the appendix.)
Because of the advisory definition of the flags, in some cases
different operating systems appear divergent behaviors. This
document analyzes possible divergent host behaviors might happen
(most of the possible divergent behaviors are already observed in
popular operating systems) and the operational problems might caused
by divergent behaviors.
2. The M, O and A Flags
This section briefly reviews how the M, O and A flags are defined in
ND[RFC4861] and SLAAC[RFC4862].
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2.1. Flags Definition
o M (Managed) Flag
As decribed in [RFC4861], "When set, it indicates that
addresses are available via Dynamic Host Configuration
Protocol".
o O (Otherconfig) Flag
"When set, it indicates that other configuration information is
available via DHCPv6. Examples of such information are DNS-
related information or information on other servers within the
network." [RFC4861]
"If neither M nor O flags are set, this indicates that no
information is available via DHCPv6" . [RFC4861]
o A (Autonomous) Flag
A flag is defined in the PIO, "When set indicates that this
prefix can be used for stateless address configuration as
specified in [RFC4862].".
2.2. Flags Relationship
Per [RFC4861], "If the M flag is set, the O flag is redundant and can
be ignored because DHCPv6 will return all available configuration
information.".
There is no explicit description of the relationship between A flag
and the M/O flags.
3. Behavior Ambiguity Analysis
The ambiguity of the flags definition means that when interpreting
the same messages, different hosts might behave differently. The
ambiguity space is analyzed as the following aspects.
1) Dependency between DHCPv6 and RA
In standards, behavior of DHCPv6 and Neighbor Discovery protocols
is specified respectively. But it is not clear that whether there
should be any dependency between them. More specifically, it is
unclear whether RA (with M=1) is required to trigger DHCPv6; in
other words, It is unclear whether hosts should initiate DHCPv6 by
themselves if there are no RAs at all.
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2) Overlapping configuration between DHCPv6 and RA
When address and DNS configuration are both available from DHCPv6
and RA, it is not clear how to deal with the overlapping
information. Should the hosts accept all the information? If the
information conflicts, which one should take higher priority?
For DNS configuration, [RFC6106] clearly specifies "In the case
where the DNS options of RDNSS and DNSSL can be obtained from
multiple sources, such as RA and DHCP, the IPv6 host SHOULD keep
some DNS options from all sources" and "the DNS information from
DHCP takes precedence over that from RA for DNS queries"
(Section 5.3.1 of [RFC6106]). But for address configuration,
there's no such guidance.
3) Interpretation on Flags Transition
- Impact on SLAAC/DHCPv6 on and off
When flags are in transition, e.g. the host is already SLAAC-
configured, then M flag changes from FALSE to TRUE, it is not
clear whether the host should start DHCPv6 or not; or vise
versa, the host is already configured by both SLAAC and DHCPv6,
then M flag change from TRUE to FALSE, it is also not clear
whether the host should turn DHCPv6 off or not.
- Impact on address lifetime
When one address configuration method is off, that is, the A
flag or M flag changes from TRUE to FALSE, it is not clear
whether one host should immediately release the corresponding
address or just retain it until the lifetime expires.
4) Relationship between the Flags
As described above, the relationship between A flag and M/O flags
is unspecified.
It could be reasonably deduced that M flag should be independent
from A flag. In other words, the M flag only cares DHCPv6 address
configuration, while the A flag only cares SLAAC.
But for A flag and O flag, ambiguity could possibly happen. For
example, when A is FALSE (when M is also FALSE) and O is TRUE, it
is not clear whether the host should initiate a stand-alone
stateless DHCPv6 session.
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Divergent behaviors on all these aspects have been observed among
some popular operating systems as described in Section 4 below.
4. Observed Divergent Host Behaviors
The authors tested several popular operating systems in order to
determine what behaviors the M, O and A flag elicit. In some cases,
the M, O and A flags elicit divergent behaviors. The table below
characterizes those cases. For test details, please refer to
Appendix A.
Operation diverges in two ways: one is regarding to address auto-
configuration; the other is regarding to DNS configuration.
4.1. Divergent Behavior on Address Auto-Configuration
Divergence 1-1
o Host state: has not acquired any addresses.
o Input: no RA.
o Divergent Behavior
1) Acquiring addresses from DHCPv6.
2) No DHCPv6 action.
Divergence 1-2
o Host state: has acquired addresses from DHCPv6 only (M = 1).
o Input: RA with M =0.
o Divergent Behavior
1) Releasing DHCPv6 addresses immediately.
2) Releasing DHCPv6 addresses when they expire.
Divergence 1-3
o Host state: has acquired addresses from SLAAC only (A=1).
o Input: RA with M =1.
o Divergent Behavior
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1) Acquiring DHCPv6 addresses immediately.
2) Acquiring DHCPv6 addresses only if their SLAAC addresses
expire and cannot be refreshed.
4.2. Divergent Behavior on DNS Configuration
Divergence 2-1
o Host state: has not acquired any addresses or information.
o Input: RA with M=0, O=1, no RDNSS; and a DHCPv6 server on the same
link providing RDNSS (regardless of address provisioning).
o Divergent Behavior
1) Acquiring RDNNS from DHCPv6, regardless of the A flag
setting.
2) Acquiring RDNNS from DHCPv6 only if A=1.
Divergence 2-2
(This divergence is only for those operations systems which
support[RFC6106].)
o Host state: has not acquired any addresses or information.
o Input: RA with M=0/1, A=1, O=1 and an RDNSS is advertised; and a
DHCPv6 server on the same link providing IPv6 addresses and RDNSS.
o Divergent Behavior
1) Getting RDNSS from both the RAs and the DHCPv6 server, and
the RDNSS obtained from the router has a higher priority.
2) Getting RDNSS from both the RAs and the DHCPv6 server, but
the RDNSS obtained from the DHCPv6 server has a higher
priority.
3) Getting RDNSS from the router, and a "domain search list"
information only from the DHCPv6 server(no RDNSS).
Divergence 2-3
(This divergence is only for those operations systems which
support[RFC6106].)
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o Host state: has acquired address and RDNSS from the first router's
RAs (M=0, O=0, PIO with A=1, and RDNSS advertised).
o Input: another router advertising M=1, O=1, no prefix information;
and a DHCPv6 server on the same link providing IPv6 addresses and
RDNSS.
o Divergent Behavior
1) Never getting any information (neither IPv6 address nor
RDNSS) from the DHCPv6 server.
2) Getting an IPv6 address and RDNSS from the DHCPv6 server
while retaining the address and RDNSS obtained from the RAs of
the first router.
(More details: the RDNSS obtained from the first router has
a higher priority; when they receive again RAs from the
first router, they lose/forget the information (IPv6 address
and RDNSS) obtained from the DHCPv6 server.)
Divergence 2-4
(This divergence is only for those operations systems which
support[RFC6106].)
o Host state: has acquired address and RDNSS from the DHCPv6 server
indicated by the first router (M=1, O=1, no PIO or RDNSS
advertised).
o Input: another router advertising M=0, O=0, PIO with A=1, and
RNDSS.
o Divergent Behavior
1) Getting address and RDNSS from the second router's RAs, and
releasing the IPv6 address and the RDNSS obtained from the
DHCPv6 server.
(More details: when receiving RAs from the first router
again, it performs the DHCPv6 Confirm/Reply procedure and
gets an IPv6 address and RDNSS from the DHCPv6 server while
retaining the ones obtained from the RAs of the second
router. Moreover, the RDNSS from router 1 has higher
priority than the one from DHCPv6.)
2) Getting address and RDNSS from the second router's RAs, and
retaining the IPv6 address and the "Domain Search list"
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obtained from the DHCPv6 server. (It did not get the RDNSS
from the DHCPv6 server, as described in Divergence 2-2.)
(More details: when receiving RAs from the first router
again, there is no change; all the obtained information is
retained.)
3) Getting address but no RDNSS from the second router's RAs,
and also retaining the IPv6 address and the RDNSS obtained from
the DHCPv6 server.
(More details: when receiving RAs from the first router
again, there is no change; all the obtained information is
retained.)
5. Operational Problems
This section is not a full collection of the potential problems. It
is some operational issues that the authors could see at current
stage.
5.1. Standalone Stateless DHCPv6 Configuration not available
It is impossible for some hosts to acquire stateless DHCPv6
configuration unless addresses are acquired from either DHCPv6 or
SLAAC (Which requires M flag or A flag is TURE).
5.2. Renumbering Issues
According to [RFC6879] a renumbering exercise can include the
following steps:
o Causing a host to
release the SLAAC address and acquire a new address from
DHCPv6; or vice-versa.
release the current SLAAC address and acquire another new SLAAC
address (might comes from different source).
retain current SLAAC or DHCPv6 address and acquire another new
address from DHCPv6 or SLAAC.
Ideally, these steps could be initiated by multicasting RA messages
onto the link that is being renumbered. Sadly, this is not possible,
because the RA messages may elicit a different behavior from each
host.
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6. Security Considerations
An attacker, without having to install a rogue router, can install a
rogue DHCPv6 server and provide IPv6 addresses to Windows 8.1
systems. This can allow her to interact with these systems in a
different scope, which, for instance, is not monitored by an IDPS
system.
If an attacker wants to perform MiTM (Man in The Middle) using a
rogue DNS while legitimates RAs with the O flag set are sent to
enforce the use of a DHCPv6 server, the attacker can spoof RAs with
the same settings with the legitimate prefix (in order to remain
undetectable) but advertising the attacker's DNS using RDNSS. In
this case, Fedora 21, Centos 7 and Ubuntu 14.04 will use the rogue
RDNSS (advertised by the RAs) as a first option.
Fedora 21 and Centos 7 behaviour cannot be explored for a MiTM attack
using a rogue DNS information either, since the one obtained by the
RAs of the first router has a higher priority.
The behaviour of Fedora 21, Centos 7 and Windows 7 can be exploited
for DoS purposes. A rogue IPv6 router not only provides its own
information to the clients, but it also removes the previous obtained
(legitimate) information. The Fedora and Centos behaviour can also
be exploited for MiTM purposes by advertising rogue RDNSS by RAs
which include RDNSS information.
(Note: the security considerations for specific operating systems are
based on the detailed test results as described in Appendix A.)
7. IANA Considerations
This draft does not request any IANA action.
8. Acknowledgements
The authors wish to acknowledge BNRC-BUPT (Broad Network Research
Centre in Beijing University of Posts and Telecommunications) for
their testing efforts. Special thanks to Xudong Shi, Longyun Yuan
and Xiaojian Xue for their extraordinary effort.
Special thanks to Ron Bonica who made a lot of significant
contribution to this draft, including draft editing and presentations
which dramatically improved this work.
The authors also wish to acknowledge Brian E Carpenter, Ran Atkinson,
Mikael Abrahamsson, Tatuya Jinmei, Mark Andrews and Mark Smith for
their helpful comments.
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9. References
9.1. Normative References
[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>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<http://www.rfc-editor.org/info/rfc4862>.
[RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
"IPv6 Router Advertisement Options for DNS Configuration",
RFC 6106, DOI 10.17487/RFC6106, November 2010,
<http://www.rfc-editor.org/info/rfc6106>.
9.2. Informative References
[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
2003, <http://www.rfc-editor.org/info/rfc3315>.
[RFC3736] Droms, R., "Stateless Dynamic Host Configuration Protocol
(DHCP) Service for IPv6", RFC 3736, DOI 10.17487/RFC3736,
April 2004, <http://www.rfc-editor.org/info/rfc3736>.
[RFC6879] Jiang, S., Liu, B., and B. Carpenter, "IPv6 Enterprise
Network Renumbering Scenarios, Considerations, and
Methods", RFC 6879, DOI 10.17487/RFC6879, February 2013,
<http://www.rfc-editor.org/info/rfc6879>.
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Appendix A. Test Results
The authors from two orgnizations tested different scenarios
independent of each other. The following text decribes the two test
sets respectively.
A.1. Test Set 1
A.1.1. Test Environment
The test environment was replicated on a single server using VMware.
For simplicity of operation, only one host was run at a time.
Network elements were as follows:
o Router: Quagga 0.99-19 soft router installed on Ubuntu 11.04
virtual host
o DHCPv6 Server: Dibbler-server installed on Ubuntu 11.04 virtual
host
o Host 1: Window 7 / Window 8.1 Virtual Host
o Host 2: Ubuntu 14.04 (Linux Kernel 3.12.0) Virtual Host
o Host 3: Mac OS X v10.9 Virtual Host
o Host 4: IOS 8.0 (model: Apple iPhone 5S, connected via wifi)
A.1.2. Address Auto-configuration Behavior in the Initial State
The bullet list below describes host behavior in the initial state,
when the host has not yet acquired any auto-configuration
information. Each bullet item represents an input and the behavior
elicited by that input.
o A=0, M=0, O=0
* Windows 8.1 acquired addresses and other information from
DHCPv6.
* All other hosts acquired no configuration information.
o A=0, M=0, O=1
* Windows 8.1 acquired addresses and other information from
DHCPv6.
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* Windows 7, OSX 10.9 and IOS 8.0 acquired other information from
DHCPv6.
* Ubuntu 14.04 acquired no configuration information.
o A=0, M=1, O=0
* All hosts acquired addresses and other information from DHCPv6.
o A=0, M=1, O=1
* All hosts acquired addresses and other information from DHCPv6.
o A=1, M=0, O=0
* Windows 8.1 acquired addresses from SLAAC and DHCPv6. It also
acquired non-address information from DHCPv6.
* All the other host acquired addresses from SLAAC
o A=1, M=0, O=1
* Windows 8.1 acquired addresses from SLAAC and DHCPv6. It also
acquired other information from DHCPv6.
* All the other hosts acquired addresses from SLAAC and other
information from DHCPv6.
o A=1, M=1, O=0
* All hosts acquired addresses from SLAAC and DHCPv6. They also
acquired other information from DHCPv6.
o A=1, M=1, O=1
* All hosts acquired addresses from SLAAC and DHCPv6. They also
acquired other information from DHCPv6.
As showed above, four inputs result in divergent behaviors.
A.1.3. Address Auto-configuration Behavior in State Transitions
The bullet list below describes behavior elicited during state
transitions. The value x can represents both 0 and 1.
o Old state (M = x, O = x, A = 1) , New state (M = x, O = x, A = 0)
(This means a SLAAC-configured host, which is regardless of DHCPv6
configured or not, receiving A in transition from 1 to 0. )
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* All the hosts retain SLAAC addresses until they expire
o Old state (M = 0, O = x, A = 1), New state (M = 1, O = x, A = 1)
(This means a SLAAC-only host receiving M in transition from 0 to
1.)
* Windows 7 acquires addresses from DHCPv6, immediately.
* Ubuntu 14.04/OSX 10.9/IOS 8.0 acquires addresses from DHCPv6
only if the SLAAC addresses are allowed to expire
* Windows 8.1 was not tested because it always acquire addresses
from DHCPv6 regardless of the M flag setting.
o Old state (M = 1, O = x, A = x), New state (M = 0, O = x, A = x)
(This means a DHCPv6-configured host receiving M in transition
from 1 to 0.)
* Windows 7 immediately released the DHCPv6 address
* Windows 8.1/Ubuntu 14.04/OSX 10.9/IOS 8.0 keep the DHCPv6
addresses until they expire
o Old state (M = 1, O = x, A = 0), New state (M = 1, O = x, A = 1)
(This means a DHCPv6-only host receiving A in transition from 0 to
1.)
* All host acquire addresses from SLAAC
o Old state (M = 0, O = 1, A = x), New state (M = 1, O = 1, A = x)
(This means a Stateless DHCPv6-configured host [RFC3736], which is
regardless of SLAAC configured or not, receiving M in transition
from 0 to 1 with keeping O=1 )
* Windows 7 acquires addresses and refreshes other information
from DHCPv6
* Ubuntu 14.04/OSX 10.9/IOS 8.0 does nothing
* Windows 8.1 was not tested because it always acquire addresses
from DHCPv6 regardless of the M flag setting.
o Old state (M = 1, O = 1, A = x), New state (M = 0, O = 1, A = x)
(This means a Stateful DHCPv6-configured host, which is regardless
of SLAAC configured or not, receiving M in transition from 0 to 1
with keeping O=1 )
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* Windows 7 released all DHCPv6 addresses and refreshes all
DHCPv6 other information.
* Windows 8.1/Ubuntu 14.04/OSX 10.9/IOS 8.0 does nothing
A.2. Test Set 2
A.2.1. Test Environment
This test was built on real devices. All the devices are located on
the same link.
o A DHCPv6 Server and specifically, a DHCP ISC Version 4.3.1
installed in CentOs 6.6. The DHCPv6 server is configured to
provide both IPv6 addresses and RDNSS information.
o Two routers Cisco 4321 using Cisco IOS Software version 15.5(1)S.
o The following OS as clients:
* Fedora 21, kernel version 3.18.3-201 x64
* Ubuntu 14.04.1 LTS, kernel version 3.13.0-44-generic (rdnssd
packet installed)
* CentOS 7, kernel version 3.10.0-123.13.2.el7
* Mac OS-X 10.10.2 Yosemite 14.0.0 Darwin
* Windows 7
* Windows 8.1
A.2.2. Address/DNS Auto-configuration Behavior of Using Only One IPv6
Router and a DHCPv6 Server
In these scenarios there is two one router and, unless otherwise
specified, one DHCPv6 server on the same link. The behaviour of the
router and of the DHCPv6 server remain unchanged during the tests.
Case 1: One Router with the Management Flag not Set and a DHCPv6
Server
o Set up
* One IPv6 Router with M=0, A=1, O=0 and an RDNSS is advertised
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* A DHCPv6 server on the same link advertising IPv6 addresses and
RDNSS
o Results
* Fedora 21, MAC OS-X, CentOS 7 and Ubuntu 14.04 get an IPv6
address and an RDNSS from the IPv6 router only.
* Windows 7 get an IPv6 address from the router only, but they do
not get any DNS information, neither from the router nor from
the DHCPv6 server. They also do not get IPv6 address from the
DHCPv6 server.
* Windows 8.1 get an IPv6 address from both the IPv6 router and
the DHCPv6 server, despite the fact that the Management flag
(M) is not set. They get RDNSS information from the DHCPv6
only.
Case 2: One Router with Conflicting Parameters and a DHCPv6 Server
o Set up
* One IPv6 Router with M=0, A=1, O=1 and an RDNSS is advertised
* A DHCPv6 server on the same link advertising IPv6 addresses and
RDNSS
o Results
* Fedora 21, Centos 7 and Ubuntu 14.04 get IPv6 address using
SLAAC only (no address from the DHCPv6 server).
+ Fedora 21, Centos 7 get RDNSS from both the RAs and the
DHCPv6 server. The RDNSS obtained from the router has a
higher priority though.
+ Ubuntu 14.04 gets an RDNSS from the router, and a "domain
search list" information from the DHCPv6 server - but not
RDNSS information.
* MAC OS-X also gets RDNSS from both, IPv6 address using SLAAC
(no IPv6 address from the DHCPv6 server) but the RDNSS obtained
from the DHCPv6 server is first (it has a higher priority).
However, the other obtained from the RAs is also present.
* Windows 7 and Windows 8.1 obtain IPv6 addresses using SLAAC and
RDNSS from the DHCPv6 server. They do not get IPv6 address
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from the DHCPv6 server. Compare the Windows 8.1 behaviour with
the previous case.
Case 3: Same as Case 2 but Without a DHCPv6 Server
o Set up
* One IPv6 Router with M=0, A=1, O=1 and an RDNSS is advertised
* no DHCPv6 present
o Results
* Windows 7 and Windows 8.1 get an IPv6 address using SLAAC but
they do not get RDNSS information.
* MAC OS-X, Fedora 21, Centos 7 and Ubuntu 14.04 get an IPv6
address using SLAAC and RDNSS from the RAs.
Case 4: All Flags are Set and a DHCPv6 Server is Present
o Set up
* One IPv6 Router with M=1, A=1, O=1 and an RDNSS is advertised
* A DHCPv6 server on the same link advertising IPv6 addresses and
RDNSS
o Results
* Fedora 21 and Centos 7:
+ They get IPv6 address both from SLAAC and DHCPv6 server.
+ They get RDNSS both from RAs and DHCPv6 server.
+ The DNS of the RAs has higher priority.
* Ubuntu 14.04:
+ It gets IPv6 address both using SLAAC and from the DHCPv6
server.
+ It gets RDNSS from RAs only.
+ From the DHCPv6 server it only gets "Domain Search List"
information, no RDNSS.
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* MAC OS-X:
+ It gets IPv6 addresses both using SLAAC and from the DHCPv6
server.
+ It also gets RDNSS both from RAs and the DHCPv6 server.
+ The DNS server of the DHCPv6 has higher priority.
* Windows 7 and Windows 8.1:
+ They get IPv6 address both from SLAAC and DHCPv6 server.
+ They get RDNSS only from the DHCPv6 server.
Case 5: All Flags are Set and There is No DHCPv6 Server is Present
o Set up
* One IPv6 Router with M=1, A=1, O=1 and an RDNSS is advertised
* no DHCPv6 is present
o Results
* Windows 7 and Windows 8.1 get an IPv6 address using SLAAC but
no RDNSS information.
* MAC OS-X, Fedora 21, Centos 7, Ubuntu 14.04 get an IPv6 address
using SLAAC and RDNSS from the RAs.
Case 6: A Prefix is Advertised by RAs but the 'A' flag is not Set
o Set up
* An IPv6 Router with M=0, A=0 (while a prefix information is
advertised), O=0 and an RDNSS is advertised.
* DHCPv6 is present
o Results
* Fedora 21, Centos 7, Ubuntu 14.04 and MAC OS-X:
+ They do not get any IPv6 address (neither from the RAs, nor
from the DHCPv6).
+ They get a RDNSS from the router only (not from DHCPv6).
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* Windows 8.1
+ They get IPv6 address and RDNSS from the DHCPv6 server
("last resort" behaviour).
+ They do not get any information (neither IPv6 address not
RDNSS) from the router.
* Windows 7:
+ They get nothing (neither IPv6 address nor RDNSS) from any
source (RA or DHCPv6).
A.2.3. Address/DNS Auto-configuration Behavior of Using Two IPv6 Router
and a DHCPv6 Server
these scenarios there are two routers on the same link. At first,
only one router is present (resembling the "legitimate router)",
while the second one joins the link after the clients first
configured by the RAs of the first router. Our goal is to examine
the behaviour of the clients during the interchange of the RAs from
the two different routers.
Case 7: Router 1 Advertising M=0, O=0 and RDNSS, and then Router 2
advertising M=1, O=1 while DHCPv6 is Present
o Set up
* Initially:
+ One IPv6 router with M=0, O=0, A=1 and RDNSS advertised and
15 seconds time interval of the RAs
* After a while (when clients are configured by the RAs of the
above router):
+ Another IPv6 router with M=1, O=1, no advertised prefix
information, and 30 seconds time interval of the RAs.
+ A DHCPv6 server on the same link providing IPv6 addresses
and RDNSS.
o Results
* MAC OS-X and Ubuntu 14.04:
+ Initially they get address and RDNSS from the first router.
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+ When they receive RAs from the second router, they never get
any information (IPv6 address or RDNSS) from the DHCPv6
server.
* Windows 7:
+ Initially they get address from the first router - no RDNSS.
+ When they receive RAs from the second router, they never get
any information (IPv6 address or RDNSS) from the DHCPv6
server.
* Fedora 21 and Centos 7:
+ Initially they get IPv6 address and RDNSS from the RAs of
the first router. o
+ When they receive an RA from router 2, they also get an IPv6
address and RDNSS from the DHCPv6 server while retaining the
ones (IPv6 address and RDNSS) obtained from the RAs of the
first router. The RDNSS obtained from the first router has
a higher priority than the one obtained from the DHCPv6
server (probably because it was received first). o
+ When they receive again RAs from the first router, they
lose/forget the information (IPv6 address and RDNSS)
obtained from the DHCPv6 server.
* Windows 8.1:
+ Initially, they get just an IPv6 address from the first
router 1 - no RDNSS information (since they do not implement
RFC 6106).
+ When they receive RAs from the second router, then they also
get an IPv6 address from the DHCPv6 server, as well as RDNSS
from it. They do not lose the IPv6 address obtained by the
first router using SLAAC.
+ When they receive RA from the first router, they retain all
the obtained so far information (there isn't any change).
Case 8: (Router 2) Initially M=1, O=1 and DHCPv6, then 2nd Router
(Router 1) Rogue RAs Using M=0, O=0 and RDNSS Provided
o Set up
* Initially:
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+ One IPv6 router with M=1, O=1, no advertised prefix
information, and 30 seconds time interval of the RAs.
+ A DHCPv6 server on the same link advertising IPv6 addresses
and RDNSS.
* After a while (when clients are configured by the RAs of the
above router):
+ Another IPv6 router with M=0, O=0, A=1, RDNSS advertised and
15 seconds time interval of the RAs.
o Results
* Fedora 21 and Centos 7:
+ At first, they get information (IPv6 address and RDNSS) from
the DHCPv6 server.
+ When they receive RAs from the second router, they get
address(es) and RDNSS from these RAs. At the same time, the
IPv6 address and the RDNSS obtained from the DHCPv6 server
are gone.
+ When they receives again an RA from the first router, they
perform the DHCPv6 Confirm/Reply procedure and they get an
IPv6 address and RDNSS from the DHCPv6 server while
retaining the ones obtained from the RAs of the second
router. Moreover, the RDNSS from router 1 has higher
priority than the one from DHCPv6.
* Ubuntu 14.04:
+ At first, it gets information (IPv6 address and RDNSS) from
the DHCPv6 server.
+ When it receives RAs from the second router, it also gets
information from it, but it does not lose the information
obtained from the DHCPv6 server. It retains both. It only
gets "Domain Search list" from the DHCPv6 server-no RDNSS
information.
+ When it receives RAs from the first router, there is no
change; it retains all the obtained information.
* Windows 7:
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+ Initially they get IPv6 address and RDNSS from the DHCPv6
server.
+ When they get RAs from the second router, they lose this
information (IPv6 address and RDNSS obtained from the DHCPv6
server) and they get only SLAAC addresses using the RAs of
the second router-no RDNSS.
+ When they receive RAs from the first router again, they get
RDNSS and IPv6 address from the DHCPv6 server, but they also
keep the SLAAC addresses.
* Windows 8.1:
+ Initially they get information (IPv6 address and RDNSS) from
the DHCPv6 server.
+ When they receive RAs from the second router, they never get
any information from them.
* MAC OS-X:
+ Initially it gets information (IPv6 address and RDNSS) from
the DHCPv6 server.
+ When it gets RAs from the second router, it also gets a
SLAAC IPv6 address but no RDNSS information from the RAs of
this router. It also does not lose any information obtained
from DHCPv6.
+ When it gets RAs from the first router again, the situation
does not change (IPv6 addresses from both the DHCPv6 and
SLAAC process are retained, but RDNSS information only from
the DHCPv6 server).
Authors' Addresses
Bing Liu
Huawei Technologies
Q14, Huawei Campus, No.156 Beiqing Road
Hai-Dian District, Beijing, 100095
P.R. China
Email: leo.liubing@huawei.com
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Sheng Jiang
Huawei Technologies
Q14, Huawei Campus, No.156 Beiqing Road
Hai-Dian District, Beijing, 100095
P.R. China
Email: jiangsheng@huawei.com
Xiangyang Gong
BUPT University
No.3 Teaching Building
Beijing University of Posts and Telecommunications (BUPT)
No.10 Xi-Tu-Cheng Rd.
Hai-Dian District, Beijing
P.R. China
Email: xygong@bupt.edu.cn
Wendong Wang
BUPT University
No.3 Teaching Building
Beijing University of Posts and Telecommunications (BUPT)
No.10 Xi-Tu-Cheng Rd.
Hai-Dian District, Beijing
P.R. China
Email: wdwang@bupt.edu.cn
Enno Rey
ERNW GmbH
Email: erey@ernw.de
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