v6ops Working Group                                     E. Levy-Abegnoli
Internet-Draft                                           G. Van de Velde
Internet-Draft                                          E. Levy-Abegnoli
Expires: January 2, March 14, 2009                                     C. Popoviciu
                                                           Cisco Systems
                                                              J. Mohacsi
                                                            July 1,
                                                      September 10, 2008

                             IPv6 RA-Guard

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   It is particularly easy to experience "rogue" routers on an unsecured
   link.  Devices acting as a rougue router may send illegitimate RAs.
   Section 6 of SeND [RFC3971] provides a full solution to this problem,
   by enabling routers certification.  This solution does, however,
   require all nodes on an L2 network segment to support SeND, as well
   as it carries some deployment challenges.  End-nodes must be
   provisioned with certificate anchors.  The solution works better when
   end-nodes have access to a Certificate Revocation List server, and to
   a Network Time Protocol server, both typically off-link, which brings
   some bootstrap issues.

   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 and
   sometimes desirable to use SeND
   [RFC3971] a rogue Router Advertisement (RA) [RFC4861] could be sent
   by accident due enable layer 2 devices to misconfiguraton or ill intended.  Simple solutions
   for protecting against drop rogue RAs are beneficial in complementing SeND
   in securing
   before they reach end-nodes.  In order to distinguish valid from
   rogue RAs, the L2 domain for ceratin types of devices can use a spectrum of criterias, from a
   static scheme that blocks RAs received on un-trusted ports, or in certain
   transitional situations. from
   un-trusted sources, to a more dynamic scheme that uses SeND to
   challenge RA sources.

   This document proposes a solution reviews various techniques applicable on the L2 devices
   to reduce the threat of rogue RAs
   by enabling layer 2 devices to forward only RAs received over
   designated ports. RAs.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  RA-guard as a deployment complement to SEND  Model and Applicability  . . . . . . . . . . 3
   3.  RA-Guard state-machine . . . . . . . . .  3
   3.  Stateless RA-Guard . . . . . . . . . . . 4
     3.1.  RA-Guard state: OFF . . . . . . . . . . .  5
   4.  Stateful RA-Guard  . . . . . . . . . 4
     3.2.  RA-Guard state: LEARNING . . . . . . . . . . . . .  5
     4.1.  State Machine  . . . . 4
     3.3.  RA-Guard state: ACTIVE . . . . . . . . . . . . . . . . . .  5
     4.2.  SeND-based RA-Guard interface states . . . . . .  . . . . . . . . . . . . . 5
     4.1.  RA-Blocking interface . . . . . . . . . . . . .  6
   5.  RA-Guard Use Considerations  . . . . . . 5
     4.2.  RA-Forwarding interface . . . . . . . . . . .  7
   6.  IANA Considerations  . . . . . . . 5
     4.3.  RA-Learning interface . . . . . . . . . . . . . .  7
   7.  Security Considerations  . . . . . 5
     4.4.  RA-Guard interface state transition . . . . . . . . . . . . 5
   5.  RA-Guard Use Considerations . .  7
   8.  Acknowledgements . . . . . . . . . . . . . . . . 6
   6.  IANA Considerations . . . . . . .  7
   9.  Normative References . . . . . . . . . . . . . . . 6
   7.  Security Considerations . . . . . .  7
   Authors' Addresses . . . . . . . . . . . . . . 6
   8.  Acknowledgements . . . . . . . . . .  8
   Intellectual Property and Copyright Statements . . . . . . . . . . . . . 6
   9.  Normative References  . . . . . . . . . . . . . . . . . . . . . 6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7
   Intellectual Property and Copyright Statements  . . . . . . . . . . 9 10

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 necessary to support SeND, there is always the
   risk of facing operational problems due to rogue Router
   Advertisements generated malliciously maliciously or unintentionaly unintentionally 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 for 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  Model and Applicability

   RA-Guard applies to an environment where all messages between IPv6
   end-devices traverse the controlled L2 networking devices.  It does
   not apply to a shared media such as an Ethernet hub, when devices can
   communicate directly without going through an RA-Guard capable L2
   networking device.

   Figure 1 illustrates a deployment complement to SEND

   RA-guard scenario for RA-Guard.

                      Block                Allow
      +------+        incoming +---------+ incoming      +--------+
      |Host  |        RA       |    L2   | RA            | Router |
      |      |--------\--------|  device |--------/------|        |
      +------+         \       +----+----+       /       +--------+
                        \           |           /
                         \          |Block     /
                          \         |incoming /
                           \        |RA      /
                                |  Host |
                                |       |

   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 until 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  An RA-Guard
   implementation which SeND-validates RAs 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 Advertisements based
   on a set of criterias, from a simplistic "RA dis-allowed disallowed on a given
   interface" to "RA allowed from pre-defined sources" and up to full
   SEND fledge
   fladge SeND "RA allowed from authorized sources only".

   In addition to this granularity on the criteria for filtering out
   Router Advertizements, RA-guard Advertisements, RA-Guard introduces the concept of router
   authorization proxy.  Instead of each node on the link analysing analyzing 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
   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 an
   context environment consisting of with a mix of SeND capable devices
   (L2 switches and routers) and devices that do not consistently use
   SeND.  Futhermore, RA-guard  Furthermore, RA-Guard is useful to simplify SeND deployments,
   as only the L2 switch and the routers are required to carry
   certificates -their (their own and the trust anchor certificates-. certificates).

3.  Stateless RA-Guard state-machine

   Stateless RA-Guard runs on devices that provide connectivity between hosts examines incoming RAs and
   other hosts decide whether to
   forward or networking devices.  An example block them based solely on information found in the
   message or in the L2-device configuration.  Typical information
   available in the frames received, useful for RA validation is:

   o  Link-layer address of such RA-Guard
   capable device would be an OSI Layer-2 switch. the sender
   o  Port on which the frame was received
   o  IP source address
   o  Prefix list

   The capability following configuration information created on the L2-device can
   enabled globally at device level or at interface level.

   When RA-Guard is SEND-based, the timing of made available to RA-Guard, to validate against the learning phase, as
   well as information
   found in the overall behavior received RA frame:

   o  Allowed/Disallowed link-layer address of RA-sender
   o  Allowed/Disallowed ports for receiving RAs
   o  Allowed/Disallowed IP source addresses of RA-sender
   o  Allowed Prefix list and Prefix ranges
   o  Router Priority

   Once the L2 device doing RA-guard is as-
   defined in [RFC3971].

   When RA-guard is using more static criterias, has validated the state-machine content of the RA-Guard capability consists of three different states:
      State 1: OFF
      State 2: LEARNING RA frame against
   the configuration, it forwards the RA to destination, whether unicast
   or multicast.  Otherwise, the RA is dropped.

4.  Stateful RA-Guard

4.1.  State 3: ACTIVE Machine

   Stateful RA-Guard learns dynamically about legitimate RA senders, and
   store this information for allowing subsequent RAs.  A simple
   stateful scheme would be for the L2-device to listen to RAs during a
   certain period of time, then to allow subsequent RAs only on those
   ports on which valid RAs were received during this period.  A more
   sophisticated stateful scheme is based on SeND, and is described in
   Section 4.2.

   The transition between these states state machine for stateful RA-Guard can be triggered by manual
   configuration global, per-interface,
   or by meeting per-peer, depending on the scheme used for authorizing RAs.

   When RA-Guard is SEND-based, the state machine is per-peer and
   defined in [RFC3971].

   When RA-Guard is using a pre-defined criteria.

3.1. discovery method, the state-machine of the
   RA-Guard state: capability consists of four different states:

   o  State 1: OFF
         A device or interface in RA-Guard "OFF" state, operates as if
         the RA-
   Guard RA-Guard capability is not available.

3.2.  RA-Guard state:
   o  State 2: 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 pre-
         defined period of time by capturing router advertisments advertisements or it
         can be event triggered.  The information gathered is compared
         against pre-defined criteria which qualify the validity of the

         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
   o  State 3: BLOCKING
         A device or interface running RA-Guard and in Active Blocking 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 RA-messages.
   o  State 4: FORWARDING
         A device or interface in the RA Blocking state blocks all ingress RA messages
   when running RA-Guard capability is activated on a device.

4.2.  RA-Forwarding interface

   An interface and in the RA Forwarding state forwards all
         will accept 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 forward them against the criteria identifying valid RAs.  While in
   this state, the RAs to their destination/

   The transition between these states can be blocked triggered by manual
   configuration or forwarded until by meeting a decission is
   taken regarding their validity.

4.4. pre-defined criteria.

4.2.  SeND-based RA-Guard interface state transition

   In this scenario, the simplest cases, an RA-Guard enabled interface can be manually
   set in an RA-Blocking L2 device is blocking or RA-Forwarding state.  By default, forwarding RAs based
   on SeND considerations.  Upon capturing an RA on the
   interfaces interface, the
   L2-device will first verify the CGA address and the RSA signature, as
   specified in section 5 of a legitimate node-in-the-middle could [RFC3971].  RA should be set dropped in RA-
   Blocking mode and enabled case of
   failure of this verification.  It will then apply host behavior as
   described in section 6.4.6 of [RFC3971].  In particular, the L2
   device will attempt to retrieve a valid certificate from its cache
   for forwarding by the network
   administrator.  In public key referred to in the more general case, RA.  If such certificate is
   found, the L2 device will forward the interface acquires RA
   information during to destination.  If not, the
   L2 device will generate a CPS, sourced with UNSPECIFIED address, to
   query the router certificate(s).  It will then capture the CPA(s),
   and attempt to validate the certificate chain.  Failure to validate
   the chain will result in dropping the RA.  Upon validation success,
   the L2 device will forward the RA Learning state to destination and by using a pre-defined
   validity criteria (see section 2) decides whether and store the analyzed RAs
   router certificate in its cache.

   In order to operate in this scenario, the L2-device should be forwarded or blocked.  Based on
   provisioned with a trust anchor certificate, as specified in section
   6 of [RFC3971].  It may also establish a layer-3 connectivity with a
   CRL server and/or with and NTP server.  Bootstrapping issue in this decission, the
   interface transitions into the RA Blocking or
   case can be resolved by using the RA Forwarding

   Upon detecting new RAs, configuration method to specify a
   trusted port to a first router, and send-based-ra-guard method on all
   other ports.  The first router can transition back into an RA-Guard
   Learning state. then be used for NTP and CRL

5.  RA-Guard Use Considerations

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

   RA-Guard mecahnism does mechanisms do not protect against tunneled offer protection in environments where
   IPv6 traffic. traffic is tunneled.

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.

              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

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

   Phone: +32 2704 5473
   Email: gunter@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

   Janos Mohacsi
   18-22 Victor Hugo
   Budapest  H-1132

   Phone: tbc
   Email: mohacsi@niif.hu

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