v6ops Working Group                                     E. Levy-Abegnoli
Internet-Draft                                           G. Van de Velde
Intended status: Informational                              C. Popoviciu
Expires: November 29, 2009                                 Cisco Systems
                                                              J. Mohacsi
                                                            May 28, 2009

                             IPv6 RA-Guard

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   Copyright (c) 2009 IETF Trust and the persons identified as the

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   document authors.  All rights reserved.

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   It is particularly easy to experience "rogue" routers on an unsecured
   link [reference4].  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 possible and
   sometimes desirable to enable layer 2 devices to drop rogue RAs
   before they reach end-nodes.  In order to distinguish valid from
   rogue RAs, the L2 devices can use a spectrum of criterias, from a
   static scheme that blocks RAs received on un-trusted ports, or from
   un-trusted sources, to a more dynamic scheme that uses SeND to
   challenge RA sources.

   This document reviews various techniques applicable on the L2 devices
   to reduce the threat of rogue RAs.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 4
   2.  Model and Applicability . . . . . . . . . . . . . . . . . . . . 4
   3.  Stateless RA-Guard  . . . . . . . . . . . . . . . . . . . . . . 6
   4.  Stateful RA-Guard . . . . . . . . . . . . . . . . . . . . . . . 6
     4.1.  State Machine . . . . . . . . . . . . . . . . . . . . . . . 6
     4.2.  SeND-based RA-Guard . . . . . . . . . . . . . . . . . . . . 7
   5.  RA-Guard Use Considerations . . . . . . . . . . . . . . . . . . 8
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . . 8
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 9
     9.1.  Normative References  . . . . . . . . . . . . . . . . . . . 9
     9.2.  Informative References  . . . . . . . . . . . . . . . . . . 9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 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 necessary to support SeND, there is always the
   risk of facing operational problems due to rogue Router
   Advertisements generated maliciously or 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 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.  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 scenario for RA-Guard.

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                      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 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.  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 Advertisements based
   on a set of criterias, from a simplistic "RA disallowed on a given
   interface" to "RA allowed from pre-defined sources" and up to full
   fladge SeND "RA allowed from authorized sources only".

   In addition to this granularity on the criteria for filtering out
   Router Advertisements, RA-Guard introduces the concept of router
   authorization proxy.  Instead of each node on the link 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.

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   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.  Furthermore, 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.  Stateless RA-Guard

   Stateless RA-Guard examines incoming RAs and decide whether to
   forward or 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 the sender
   o  Port on which the frame was received
   o  IP source address
   o  Prefix list

   The following configuration information created on the L2-device can
   be made available to RA-Guard, to validate against the information
   found in the 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 has validated the content of the 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 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.

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   The state machine for stateful RA-Guard can be global, per-interface,
   or 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 discovery method, the state-machine of the
   RA-Guard 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 capability is not available.
   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 period of time by capturing router 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.
   o  State 3: BLOCKING
         A device or interface running RA-Guard and in Blocking state
         will block ingress RA-messages.
   o  State 4: FORWARDING
         A device or interface running RA-Guard and in Forwarding state
         will accept ingress RAs and forward them to their destination/

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

4.2.  SeND-based RA-Guard

   In this scenario, the L2 device is blocking or forwarding RAs based
   on SeND considerations.  Upon capturing an RA on the interface, the
   L2-device will first verify the CGA address and the RSA signature, as
   specified in section 5 of [RFC3971].  RA should be dropped in 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 the public key referred to in the RA.  If such certificate is
   found, the L2 device will forward the RA 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),

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   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 to destination and and store the
   router certificate in its cache.

   In order to operate in this scenario, the L2-device should be
   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
   case can be resolved by using the 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 then be used for NTP and CRL

5.  RA-Guard Use Considerations

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

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

6.  IANA Considerations

   There are no extra IANA consideration for this document.

7.  Security Considerations

   Once RA-Guard has setup the proper criterias, for example, it
   identified that a port is allowed to receive RAs, or it identified
   legitimiate sources of RA, or certificate base, then there is no
   possible instances of accidently filtered legitimate RA's assuming
   the RA-Guard filter enforcement follows strictly the RA-Guard

8.  Acknowledgements

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

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9.  References

9.1.  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.

9.2.  Informative References

              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.

              Chown, Tim. and Stig. Venaas, "Rogue IPv6 Router
              Advertisement Problem (draft-ietf-v6ops-rogue-ra-00.txt)",
              May 2009.

Authors' Addresses

   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

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   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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