v6ops Working Group                                      G. Van de Velde
Internet-Draft                                          E. Levy-Abegnoli
Expires: January 2, 2009                                    C. Popoviciu
                                                           Cisco Systems
                                                              J. Mohacsi
                                                            July 1, 2008

                             IPv6 RA-Guard

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   When using IPv6 within a single L2 network segment it is neccesary to
   ensure that all routers advertising their services within it are
   valid.  In cases where it is not convinient or possible to use SeND
   [RFC3971] a rogue Router Advertisement (RA) [RFC4861] could be sent
   by accident due to misconfiguraton or ill intended.  Simple solutions
   for protecting against rogue RAs are beneficial in complementing SeND
   in securing the L2 domain for ceratin types of devices or in certain
   transitional situations.

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   This document proposes a solution to reduce the threat of rogue RAs
   by enabling layer 2 devices to forward only RAs received over
   designated ports.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  RA-guard as a deployment complement to SEND . . . . . . . . . . 3
   3.  RA-Guard state-machine  . . . . . . . . . . . . . . . . . . . . 4
     3.1.  RA-Guard state: OFF . . . . . . . . . . . . . . . . . . . . 4
     3.2.  RA-Guard state: LEARNING  . . . . . . . . . . . . . . . . . 4
     3.3.  RA-Guard state: ACTIVE  . . . . . . . . . . . . . . . . . . 5
   4.  RA-Guard interface states . . . . . . . . . . . . . . . . . . . 5
     4.1.  RA-Blocking interface . . . . . . . . . . . . . . . . . . . 5
     4.2.  RA-Forwarding interface . . . . . . . . . . . . . . . . . . 5
     4.3.  RA-Learning interface . . . . . . . . . . . . . . . . . . . 5
     4.4.  RA-Guard interface state transition . . . . . . . . . . . . 5
   5.  RA-Guard Use Considerations . . . . . . . . . . . . . . . . . . 6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 6
   9.  Normative References  . . . . . . . . . . . . . . . . . . . . . 6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7
   Intellectual Property and Copyright Statements  . . . . . . . . . . 9

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1.  Introduction

   When operating IPv6 in a shared L2 network segment without complete
   SeND support by all devices connected or without the availability of
   the infrastructure neccesary to support SeND, there is always the
   risk of facing operational problems due to rogue Router
   Advertisements generated malliciously or unintentionaly by
   unauthorized or improperly configured routers connecting to the

   There are several examples of work done on this topic which resulted
   in several related studies [reference1] [reference2]
   [reference3].This document describes a solution framework to the
   rogue-RA problem where network segments are designed around a single
   or a set of L2-switching devices capable of identifying invalid RAs
   and blocking them.  The solutions developed within this framework can
   span the spectrum from basic (where the port of the L2 device is
   statically instructed to forward or not to forward RAs received from
   the connected device) to advanced (where a criteria is used by the L2
   device to dynamically validate or invalidate a received RA, this
   criteria can even be based on SeND mechanisms).

2.  RA-guard as a deployment complement to SEND

   RA-guard does not intend to provide a substitute for SeND based
   solutions.  It actually intends to provide complementary solutions in
   those environments where SeND might not be suitable or fully
   supported by all devices involved.  It may take time untill SeND is
   ubiquitous in IPv6 networks and some of its large scale deployment
   aspects are sorted out such as provisioning hosts with trust anchors.
   It is also reasonable to expect that some devices might not consider
   implementing SeND at all such as IPv6 enabled sensors.  The RA-guard
   "SeND-validating" RA on behalf of hosts would potentially simplify
   some of these challenges.

   RA-guard can be seen as a superset of SEND with regard to router
   authorization.  Its purpose is to filter Router Advertizements based
   on a set of criterias, from a simplistic "RA dis-allowed on a given
   interface" to "RA allowed from pre-defined sources" and up to full
   SEND fledge "RA allowed from authorized sources only".

   In addition to this granularity on the criteria for filtering out
   Router Advertizements, RA-guard introduces the concept of router
   authorization proxy.  Instead of each node on the link analysing RAs
   and making an individual decision, a legitimate node-in-the-middle
   performs the analysis on behalf of all other nodes on the link.  The
   analysis itself is not different from what each node would do: if

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   SeND is enabled, the RA is checked against X.509 certificates.  If
   any other criteria is in use, such as known L3 (addresses) or L2
   (link-layer address, port number) legitimate sources of RAs, the
   node-in-the middle can use this criteria and filter out any RA that
   does not comply.  If this node-in-the-middle is a L2 device, it will
   not change the content of the validated RA, and avoid any of the nd-
   proxy pitfalls.

   RA-guard intends to provide simple solutions to the rogue-RA problem
   in contexts where simplicity is required while leveraging SeND in
   context with a mix of SeND capable devices (L2 switches and routers)
   and devices that do not consistently use SeND.  Futhermore, RA-guard
   is useful to simplify SeND deployments, as only the L2 switch and the
   routers are required to carry certificates -their own and the trust
   anchor certificates-.

3.  RA-Guard state-machine

   RA-Guard runs on devices that provide connectivity between hosts and
   other hosts or networking devices.  An example of such RA-Guard
   capable device would be an OSI Layer-2 switch.  The capability can be
   enabled globally at device level or at interface level.

   When RA-Guard is SEND-based, the timing of the learning phase, as
   well as the overall behavior of the device doing RA-guard is as-
   defined in [RFC3971].

   When RA-guard is using more static criterias, the state-machine of
   the RA-Guard capability consists of three different states:
      State 1: OFF
      State 2: LEARNING
      State 3: ACTIVE

   The transition between these states can be triggered by manual
   configuration or by meeting a pre-defined criteria.

3.1.  RA-Guard state: OFF

   A device or interface in RA-Guard "OFF" state, operates as if the RA-
   Guard capability is not available.

3.2.  RA-Guard state: LEARNING

   A device or interface in the RA-Guard "Learning" state is actively
   acquiring information about the devices connected to its interfaces.
   The learning process takes place over a pre-defined period of time by
   capturing router advertisments or it can be event triggered.  The

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   information gathered is compared against pre-defined criteria which
   qualify the validity of the RAs.

   In this state, the RA-Guard enabled device or interface is either
   blocking all RAs until their validity is verified or, alternatively
   it can temporarily forward the RAs until the decision is being made.

3.3.  RA-Guard state: ACTIVE

   A device or interface running RA-Guard and in Active state will block
   ingress RA-messages deemed invalid and will forward those deemed
   valid based on a pre-defined criteria defined.

4.  RA-Guard interface states

   The interfaces of devices with the RA-guard capability enabled can be
   in three possible states related to RA handling: Learning, Blocking
   and Forwarding.

4.1.  RA-Blocking interface

   An interface in the RA Blocking state blocks all ingress RA messages
   when RA-Guard capability is activated on a device.

4.2.  RA-Forwarding interface

   An interface in the RA Forwarding state forwards all ingress RA
   messages deemed valid when RA-Guard capability is activated on a

4.3.  RA-Learning interface

   An interface in a RA Learning state snoops all received RAs and
   compares them against the criteria identifying valid RAs.  While in
   this state, the RAs can be blocked or forwarded until a decission is
   taken regarding their validity.

4.4.  RA-Guard interface state transition

   In the simplest cases, an RA-Guard enabled interface can be manually
   set in an RA-Blocking or RA-Forwarding state.  By default, the
   interfaces of a legitimate node-in-the-middle could be set in RA-
   Blocking mode and enabled for forwarding by the network
   administrator.  In the more general case, the interface acquires RA
   information during the RA Learning state and by using a pre-defined
   validity criteria (see section 2) decides whether the analyzed RAs
   should be forwarded or blocked.  Based on this decission, the

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   interface transitions into the RA Blocking or the RA Forwarding

   Upon detecting new RAs, a port can transition back into an RA-Guard
   Learning state.

5.  RA-Guard Use Considerations

   The RA-Guard mechanism is effective only when all mesages between
   IPv6 devices in the target environment traverse the controlled L2
   networking devices.  When on a shared media such as an Ethernet hub,
   devices can communicate directly without going through an RA-Guard
   capable L2 networking device.  In this scenario, the RA- Guard
   feature cannot protect against rogue-RAs.

   RA-Guard mecahnism does not protect against tunneled IPv6 traffic.

6.  IANA Considerations

   There are no extra IANA consideration for this document.

7.  Security Considerations

   There are no extra Security consideration for this document.

8.  Acknowledgements

   The authors dedicate this document to the memory of Jun-ichiro Hagino
   (itojun) for his contributions to the development and deployment of

9.  Normative References

   [RFC3971]  Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
              Neighbor Discovery (SEND)", RFC 3971, March 2005.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

              LORIA/INRIA, "NDPMon - IPv6 Neighbor Discovery Protocol
              Monitor (http://ndpmon.sourceforge.net/)", November 2007.

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              KAME Project, "rafixd - developed at KAME - An active
              rogue RA nullifier (http://www.kame.net/dev/cvsweb2.cgi/
              kame/kame/kame/rafixd/)", November 2007.

              Hagino (itojun), Jun-ichiro., "Discussion of the various
              solutions (http://ipv6samurais.com/ipv6samurais/
              demystified/rogue-RA.html)", 2007.

Authors' Addresses

   Gunter Van de Velde
   Cisco Systems
   De Kleetlaan 6a
   Diegem  1831

   Phone: +32 2704 5473
   Email: gunter@cisco.com

   Eric Levy Abegnoli
   Cisco Systems
   Village d'Entreprises Green Side - 400, Avenue Roumanille
   Biot - Sophia Antipolis, PROVENCE-ALPES-COTE D'AZUR  06410

   Phone: +33 49 723 2620
   Email: elevyabe@cisco.com

   Ciprian Popoviciu
   Cisco Systems
   7025-6 Kit Creek Road
   Research Triangle Park, North Carolina  NC 27709-4987

   Phone: +1 919 392-3723
   Email: cpopovic@cisco.com

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   Janos Mohacsi
   18-22 Victor Hugo
   Budapest  H-1132

   Phone: tbc
   Email: mohacsi@niif.hu

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