IPv6 Operations T. Chown
Internet-Draft University of Southampton
Intended status: Informational S. Venaas
Expires: January 15, 2009 UNINETT
July 14, 2008
Rogue IPv6 Router Advertisement Problem Statement
draft-chown-v6ops-rogue-ra-01
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on January 15, 2009.
Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract
When deploying IPv6 networks, whether IPv6-only or dual-stack,
routers are configured to use IPv6 Router Advertisements to convey
information to on link nodes that enable them to autoconfigure on the
network. This information includes the implied default router
address taken from the observed source address of the Router
Advertisement (RA) message. However, in some networks 'bogus' RAs
are observed, which may be present due to misconfigurations or
Chown & Venaas Expires January 15, 2009 [Page 1]
Internet-Draft Rogue IPv6 Router Advertisements July 2008
possibly malicious attacks on the network. In this draft we
summarise the scenarios in which rogue RAs may be observed, and we
present a list of possible solutions to the problem. The goal of
this draft is to present a framework around which solutions can be
proposed and discussed.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Bogus RA Scenarios . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Administrator misconfiguration . . . . . . . . . . . . . . 3
2.2. User misconfiguration . . . . . . . . . . . . . . . . . . 4
2.3. Malicious misconfiguration . . . . . . . . . . . . . . . . 4
3. Methods to Mitigate against Rogue RAs . . . . . . . . . . . . 4
3.1. Manual configuration . . . . . . . . . . . . . . . . . . . 4
3.2. Secure Neighbor Discovery . . . . . . . . . . . . . . . . 4
3.3. Introduce RA snooping . . . . . . . . . . . . . . . . . . 5
3.4. Use the Router Preference Option . . . . . . . . . . . . . 5
3.5. Rely on Layer 2 admission control . . . . . . . . . . . . 5
3.6. Use host-based packet filters . . . . . . . . . . . . . . 5
3.7. Use an 'intelligent' deprecation tool . . . . . . . . . . 6
3.8. Wait before using new advertisements . . . . . . . . . . . 6
3.9. Add a Default Gateway Option to DHCPv6 . . . . . . . . . . 6
4. Other considerations . . . . . . . . . . . . . . . . . . . . . 7
5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
9. Informative References . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
Intellectual Property and Copyright Statements . . . . . . . . . . 10
Chown & Venaas Expires January 15, 2009 [Page 2]
Internet-Draft Rogue IPv6 Router Advertisements July 2008
1. Introduction
The Neighbor Discovery protocol [6] describes the operation of IPv6
Router Advertisements (RAs), which are used during the IPv6
autoconfiguration process, whether stateful (via DHCPv6 [1] or DHCPv6
Light [2]) or stateless (as per RFC4862 [7]). In either case, the
default router address is drawn directly from the source address of
the RA message. In contrast to IPv4, there is no DHCPv6 option to
configure a default gateway address.
In observing the operation of deployed IPv6 networks, it is apparent
that there is a problem with undesired or 'bogus' IPv6 Router
Advertisements (RAs) appearing on network links or subnets. By
'bogus' we mean RAs that were not the intended configured RAs, rather
RAs that have appeared for some other reason.
The problem with rogue RAs is that they can cause partial or complete
failure of operation on an IPv6 link. As such they are an
operational issue for which solution(s) are required, and for which
best practice needs to be conveyed.
In the next section, we discuss the scenarios that may give rise to
rogue RAs being present. In the following section we present some
candidate solutions for the problem, some of which may be more
practical to deploy than others.
2. Bogus RA Scenarios
There are three broad classes of scenario in which bogus RAs may be
introduced to an IPv6 network.
2.1. Administrator misconfiguration
Here an administrator incorrectly configures RAs on a router
interface, causing incorrect RAs to appear on links and hosts to
generate incorrect IPv6 address or other information. In this case
the default gateway may be correct, but a host might for example
become multi-addressed, possibly with a correct and incorrect address
based on a correct and incorrect prefix. There is also the
possibility of bad lifetime information being configured.
In the case of a Layer 2 VLAN misconfiguration, RAs may 'flood' to
unintended links, causing hosts or more than one link to potentially
become incorrectly multiaddressed, with possibly two different
default routers available.
Chown & Venaas Expires January 15, 2009 [Page 3]
Internet-Draft Rogue IPv6 Router Advertisements July 2008
2.2. User misconfiguration
In this case a user's device 'accidentally' transmits RAs onto the
local link, adding an addition default gateway and prefix
information. This is typically seen on wireless (though sometimes
wired) networks where a laptop has been used as a home gateway (e.g.
a 6to4 gateway) and has then been attached to another network with
the gateway configuration still active. A not infrequent cause here
is the Windows Internet Connection Sharing service (ICS) which turns
a host into a 6to4 gateway; this can be a useful feature, unless it
is run when not intended. We have had reports that hosts may not see
the genuine RAs on link due to host firewalls, and then turning on a
connection sharing service and 6to4 as a result.
There are also reported incidents in enterprise networks of users
physically plugging Ethernet cables into the wrong sockets and
bridging two subnets together, causing an problem similar to VLAN
flooding.
2.3. Malicious misconfiguration
Here an attacker is deliberately generating RAs on the local network
in an attempt to perform some form of denial of service or man-in-
the-middle attack.
3. Methods to Mitigate against Rogue RAs
In this section we present a summary of methods suggested to date for
reducing or removing the possibility of rogue RAs being seen on a
network.
3.1. Manual configuration
The default gateway can usually be manually configured on a device.
This is of course a resource intensive solution, and also prone to
mistakes in itself.
3.2. Secure Neighbor Discovery
The SEND [3] protocol provides a method for hosts and routers to
perform secure Neighbor Discovery. At present there are very few
SEND implementations available, and SEND is perceived as a complex
protocol to deploy. It is also likely that not all scenarios will be
able to use SeND, for various reasons.
Chown & Venaas Expires January 15, 2009 [Page 4]
Internet-Draft Rogue IPv6 Router Advertisements July 2008
3.3. Introduce RA snooping
It should be possible to implement 'RA snooping' in Layer 2 switches
in a similar way to DHCP snooping, such that RAs observed from
incorrect sources are blocked or dropped, and not propagated through
a subnet. One candidate solution in this space called RA-Guard [8]
has recently been proposed. This type of solution has appeal because
it is a familiar model for enterprise network managers, but it can
also be used to complement SeND.
It is interesting to note that the Windows ICS that runs a 6to4
gateway also starts an IPv4 DHCP service, so any snooping solution is
mitigating against both these issues.
This type of solution may not be applicable everywhere, e.g. in
environments where there are not centrally controlled switches.
3.4. Use the Router Preference Option
RFC4191 [4] introduced router preference options, such that an RA
could carry one of three router preference values: High, Medium
(default) or Low. Thus an administrator could use High settings for
managed RAs, and hope that 'accidental' RAs would be medium priority,
and that hosts implemented this optional protocol.
3.5. Rely on Layer 2 admission control
In principle, if a technology such as IEEE 802.1x is used, devices
would first need to authenticate to the network before being able to
send or receive IPv6 traffic. Ideally authentication would be
mutual. This may mitigate against a malicious attacker, but doesn't
address the misconfiguration issues.
3.6. Use host-based packet filters
In a managed environment hosts could be configured via their
'personal firewall' to only accept RAs from trusted sources.
However, the problem is then pushed to keeping this configuration
maintained and correct. If a router fails and is replaced, possibly
with a new Layer 2 interface address, the link local source address
in the filter may be incorrect and no network exists to push the new
information to the host.
Also, hosts could potentially be configured to discard 6to4-based RAs
in a managed enterprise environment.
Chown & Venaas Expires January 15, 2009 [Page 5]
Internet-Draft Rogue IPv6 Router Advertisements July 2008
3.7. Use an 'intelligent' deprecation tool
It could be possible to run a daemon on a link (perhaps on the router
on the link) to watch for incorrect RAs and to send a deprecating RA
with router lifetime of zero when such an RA is observed. The KAME
rafixd is an example of such a tool, which has been used at IETF
meetings with some success. Whether or not such a tool is the
preferred method, monitoring a link for observed RAs seems prudent
from a network management perspective. Some such tools exist
already, e.g. ndpmon.
3.8. Wait before using new advertisements
It might be possible, in generally static networks, to configure an
option such that any new RAs that are seen are not acted upon for a
certain period, e.g. 2 hours. This might allow time for a
misconfiguration or accidental RA to be detected and stopped, before
hosts use the data in the RA. Of course this would add delays where
genuine new RAs are required, while new hosts appearing on a network
would still be vulnerable (or be unable to configure at all).
3.9. Add a Default Gateway Option to DHCPv6
It may be possible to define a new Default Gateway Option for DHCPv6
that would allow network administrators to only have hosts use DHCPv6
for default gateway configuration in managed networks. While such an
option could be defined, its ramifications remain unclear. In the
absence of RAs, other configuration information would also be
missing, e.g. on-link prefix information. Of course, it may be that
an RA is still required to inform the host to use DHCPv6, and that
may introduce a Catch-22 unless hosts are configured directly to only
use DHCPv6.
An advantage of DHCPv6 is that should an error be introduced, only
hosts that have refreshed their DHCP information since that time are
affected, while a rogue RA will most likely affect all hosts
immediately. DHCPv6 also allows different answers to be given to
different hosts.
One objection to introducing such an option is that DHCPv6 in itself
is not a secure protocol, and it is also of course subject to
misconfigurations, accidental or otherwise. Comparing the threat
model for rogue RAs and rogue DHCPv6 servers is an interesting
exercise in itself. Use of Authenticated DHCP is currently minimal
and thus the (lack of) security is just pushed to another place,
albeit one that site administrators are more familiar and (rightly or
wrongly) comfortable with.
Chown & Venaas Expires January 15, 2009 [Page 6]
Internet-Draft Rogue IPv6 Router Advertisements July 2008
4. Other considerations
There are other general observations that have been made.
One is that it would generally be prudent for network monitoring or
management platforms to be able to observe and report on observed
RAs, and whether unintended RAs (possibly from unintended sources)
are present on a network. Further, it may be useful for individual
hosts to be able to report their address status, e.g. this could be
useful during an IPv6 renumbering phased process as described in
RFC4192 [5].
The second is how readily a host can recover from bad configuration
information, e.g. considering the '2 hour rule' of Section 5.5.3 of
RFC4862 (though this applies to the prefix lifetime not the router
lifetime). We should ensure that methods exist for a network
administrator to correct bad configuration information on a link or
subnet, and that OS platforms support these methods. At least if the
problem can be detected, and corrected promptly, the impact is
minimised.
A comment has been made that in the case of 6to4 being run by a host
on a subnet that is not administratively configured with IPv6, some
OSes or applications may begin using IPv6 to the 6to4 host (router)
rather than IPv4 to the intended default IPv4 router. Mitigating
against this condition can also be seen to be important.
5. Conclusions
In this text we have described scenarios via which rogue Router
Advertisements (RAs) may appear on a network, and some measures that
could be used to mitigate against these.
While SEND perhaps offers the most robust solution, implementations
are not widely available, and the solution is perceived as complex
(parallels can possibly be drawn with Authenticated DHCP in terms of
likely deployment). Adding a new DHCPv6 Default Gateway Option would
allow configuration by DHCP, and be a method that IPv4 administrators
are comfortable with (for better or worse), but such an option would
have significant impacts elsewhere, and in any event one must
recognise that the security risk is then simply shifted elsewhere.
Further feedback on the solutions is certainly welcome. In the
meantime, perhaps the simplest initial step would be for RA snooping
to be defined and deployed for Layer 2 devices, in such a way that
can address (shared) wireless as well as wired networks. One draft
proposal in this space, RA-Guard, has recently been published [8].
Chown & Venaas Expires January 15, 2009 [Page 7]
Internet-Draft Rogue IPv6 Router Advertisements July 2008
Alternatively, certain switch platforms can already implement a form
of snooping by the administrator configuring Access Control Lists
(ACLs) that block RA ICMP messages that might be inbound on 'user'
ports. A cleaner solution is desirable though.
This topic has also highlighted that some DHCPv6 on-link prefix
option may be useful for some scenarios, caused in part by the change
of the 'default on-link' rule. This should be seen as independent of
whether DHCPv6 is extended to add a Default Gateway Option, which is
another open question at this time.
The material presented here is relevant to the IETF dhc and v6ops
working groups, but the text is labeled as v6ops due to its
operational issue focus. Should new DHCP features be defined as a
result, we assume these would be presented within the dhc working
group.
6. Security Considerations
There are no extra Security consideration for this document.
7. IANA Considerations
There are no extra IANA consideration for this document.
8. Acknowledgments
Thanks are due to members of the IETF IPv6 Operations and DHCP WGs
for their inputs on this topic, including but not limited to Iljitsch
van Beijnum, David Malone, Tony Hain, Christian Huitema, Remi Denis-
Courmant, Chip Popoviciu, Dave Thaler and Tatuya Jinmei.
9. Informative References
[1] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M.
Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 3315, July 2003.
[2] Droms, R., "Stateless Dynamic Host Configuration Protocol (DHCP)
Service for IPv6", RFC 3736, April 2004.
[3] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.
Chown & Venaas Expires January 15, 2009 [Page 8]
Internet-Draft Rogue IPv6 Router Advertisements July 2008
[4] Draves, R. and D. Thaler, "Default Router Preferences and More-
Specific Routes", RFC 4191, November 2005.
[5] Baker, F., Lear, E., and R. Droms, "Procedures for Renumbering
an IPv6 Network without a Flag Day", RFC 4192, September 2005.
[6] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor
Discovery for IP version 6 (IPv6)", RFC 4861, September 2007.
[7] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless Address
Autoconfiguration", RFC 4862, September 2007.
[8] Van de Velde, G., Levy-Abegnoli, E., Popoviciu, C., and J.
Mohacsi, "IPv6 RA-Guard (draft-ietf-v6ops-ra-guard-00)",
July 2008.
Authors' Addresses
Tim Chown
University of Southampton
Southampton, Hampshire SO17 1BJ
United Kingdom
Email: tjc@ecs.soton.ac.uk
Stig Venaas
UNINETT
Trondheim NO 7465
Norway
Email: venaas@uninett.no
Chown & Venaas Expires January 15, 2009 [Page 9]
Internet-Draft Rogue IPv6 Router Advertisements July 2008
Full Copyright Statement
Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Acknowledgment
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
Chown & Venaas Expires January 15, 2009 [Page 10]