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Versions: 00 01 02 03 04 05                                             
Network Working Group                                        S. Krishnan
Internet-Draft                                                  Ericsson
Intended status: Informational                           N. Steinleitner
Expires: April 11, 2009                         University of Goettingen
                                                                  Y. Qiu
                                         Institute for Infocomm Research
                                                                G. Bajko
                                                                   Nokia
                                                         October 8, 2008


     Guidelines for firewall administrators regarding MIPv6 traffic
                   draft-ietf-mext-firewall-admin-00

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
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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on April 11, 2009.

Abstract

   This document presents some recommendations for firewall
   administrators to help them configure their existing firewalls in a
   way that allows in certain deployment scenarios the Mobile IPv6
   signaling and data messages to pass through.  For other scenarios,
   the support of additional mechanisms to create pinholes required for
   MIPv6 will be necessary.  This document assumes that the firewalls in
   question include some kind of stateful packet filtering capability.



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Table of Contents

   1.  Requirements notation  . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Abbreviations  . . . . . . . . . . . . . . . . . . . . . . . .  3
   4.  Home Agent behind a firewall . . . . . . . . . . . . . . . . .  4
     4.1.  Signaling between the MN and the HA  . . . . . . . . . . .  5
     4.2.  IKEv2 signaling between MN and HA for establishing SAs . .  5
   5.  Correspondent Node behind a firewall . . . . . . . . . . . . .  5
     5.1.  Route optimization signaling between MN and CN through
           HA . . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     5.2.  Route optimization signaling between MN and CN . . . . . .  6
     5.3.  Binding Update from MN to CN . . . . . . . . . . . . . . .  7
     5.4.  Route Optimization data traffic from MN  . . . . . . . . .  7
   6.  Mobile Node behind a firewall  . . . . . . . . . . . . . . . .  7
     6.1.  Signaling between MN and HA  . . . . . . . . . . . . . . .  8
     6.2.  Signaling between MN and CN  . . . . . . . . . . . . . . .  9
     6.3.  IKEv2 signaling between MN and HA for establishing SAs . .  9
   7.  Related documents  . . . . . . . . . . . . . . . . . . . . . .  9
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  9
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 10
     11.2. Informative References . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
   Intellectual Property and Copyright Statements . . . . . . . . . . 12
























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1.  Requirements notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].


2.  Introduction

   Network elements such as firewalls are an integral aspect of a
   majority of IP networks today, given the state of security in the
   Internet, threats, and vulnerabilities to data networks.  MIPv6
   [RFC3775] defines mobility support for IPv6 nodes.  Firewalls will
   interfere with the smooth operation of the MIPv6 protocol unless
   specific steps are taken to allow Mobile IPv6 signaling and data
   messages to pass through the firewall.  The problems caused by
   firewalls to Mobile IPv6 are documented in [RFC4487].

   This document presents some recommendations for firewall
   administrators to help them configure their firewalls in a way that
   allows the Mobile IPv6 signaling and data messages to pass through.
   This document assumes that the firewalls in question include some
   kind of stateful packet filtering capability.  The static rules that
   need to be configured are described in this document.  In some
   scenarios, the support of additional mechanisms to create pinholes
   required for MIPv6 signalling and data traffic to pass through will
   be necessary.  A possible solution, describing the dynamic
   capabilities needed for the firewalls to create pinholes based on
   MIPv6 signalling traffic is described in a companion document
   [MIP6FWVENDOR].  Other solutions may also be possible.

   Some Mobile IPv6 signalling messages require the use of encryption to
   protect the confidentiality of the payload (e.g. the HoTI and HoT
   messages between the MN and the HA).  The other signalling messages
   allow the use of encryption.  If encryption is being used, it is not
   possible to inspect the contents of the signalling packets.  For
   these messages to get through, a generic rule needs to be added in
   the firewall to let ESP packets through without further inspection.


3.  Abbreviations

   This document uses the following abbreviations:

   o  CN: Correspondent Node

   o  CoA: Care of Address




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   o  CoTI: Care of Test Init

   o  HA: Home Agent

   o  HoA: Home Address

   o  HoTI: Home Test Init

   o  HoT: Home Test

   o  MN: Mobile Node

   o  RO: Route Optimization

   o  RRT: Return Routability Test


4.  Home Agent behind a firewall

   This section presents the recommendations for configuring a firewall
   that protects a home agent.

        +----------------+       +---+
        |                |       | A |
        |                |       +---+
        |   +----+       |      External
        |   | HA |    +----+      MN
        |   +----+    | FW |                 +---+
        |  Home Agent +----+                 | B |
        |    of A        |                   +---+
        |                |                  External
        |                |                    Node
        +----------------+
        Network protected
          by a firewall

                      Figure 1: HA behind a firewall

   For each type of traffic that needs to pass through this firewall,
   recommendations are presented on how to identify that traffic.  The
   following types of traffic are considered

   o  Signaling between the MN and the HA

   o  IKEv2 signaling between MN and HA for establishing SAs






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4.1.  Signaling between the MN and the HA

   The signaling between the MN and HA is protected using IPSec ESP.
   These messages are critical to the MIPv6 protocol and if these
   messages are discarded, Mobile IPv6 as specified today will cease to
   work.  In order to permit these messages through, the firewall has to
   detect the messages using the following patterns.

     Destination Address: Address of HA
     Next Header: 50 (ESP)
     Mobility Header Type: 5 (BU)

   This pattern will allow the BU messages from MNs to HA to pass
   through.

4.2.  IKEv2 signaling between MN and HA for establishing SAs

   The MN and HA exchange IKEv2 signaling in order to establish the
   security associations.  The security associations so established will
   later be used for securing the mobility signaling messages.  Hence
   these messages need to be permitted to pass through the firewalls.
   The following pattern will detect these messages.

     Destination Address: Address of HA
     Transport Protocol: UDP
     Destination UDP Port: 500



5.  Correspondent Node behind a firewall

   This section presents the recommendations for configuring a firewall
   if a node behind it should be able to act as Mobile IPv6 CN.

        +----------------+                +----+
        |                |                | HA |
        |                |                +----+
        |                |              Home Agent
        |  +---+      +----+               of B
        |  |CN |      | FW |
        |  | C |      +----+
        |  +---+         |                +---+
        |                |                | B |
        |                |                +---+
        +----------------+           External Mobile
        Network protected                  Node
          by a firewall




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                      Figure 2: CN behind a firewall

   For each type of traffic that needs to pass through this firewall,
   recommendations are presented on how to identify that traffic.  The
   following types of traffic are considered

   o  Route optimization signaling between MN and CN through HA

   o  Route optimization signaling between MN and CN

   o  Binding Update from MN to CN

   o  Route Optimization data traffic from MN

5.1.  Route optimization signaling between MN and CN through HA

   Parts of the initial route optimization signaling has to pass through
   the HA, namely the HoTI and the HoT messages.  Without assistance,
   the HoTI message from the HA to the CN is not able to traverse the
   firewall.  When only a few priviledged nodes (like servers) are
   allowed to be contacted by outside nodes, then the following pattern
   will allow the HoTI messages to reach these nodes:

      Destination Address: CN Address

      Mobility Header Type: 1 (HoTI)

   where CN Address describes the address(es) of the priviledged
   node(s).  This pinhole allows the HoTI message from the HA to the CN
   to traverse the firewall.  The HoT message from the CN to the MN
   through the HA can traverse the firewall without any assistance.
   Hence no pinhole is required.

5.2.  Route optimization signaling between MN and CN

   Route Optimization allows direct communication of data packets
   between the MN and a CN without tunnelling it back through the HA.
   To get route optimization work, the MN has to send a CoTI message
   directly to the CN, which response with a CoT message.  However, a
   stateful firewall would prevent the CoTI message to pass through as
   there is no established state on the firewall.  When only a few
   priviledged nodes (like servers) are allowed to be contacted by
   outside nodes, then the following pattern will allow the CoTI
   messages to reach these nodes:







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      Destination Address: CN Address

      Mobility Header Type: 2 (CoTI)

   where CN Address describes the address(es) of the priviledged
   node(s).The CoT message from the CN to the MN can traverse the
   firewall without any assistance.  Hence no pinhole is required.

5.3.  Binding Update from MN to CN

   After successfully performing the return routability procedure, the
   MN sends the BU to the CN and expects the BA.  Since this BU does not
   match any previous installed pinhole rules, an additional pinhole
   with the following format is required.When only a few priviledged
   nodes (like servers) are allowed to be contacted by outside nodes,
   then the following pattern will allow the BU messages to reach these
   nodes:

      Destination Address: CN Address

      Mobility Header Type: 5

   where CN Address describes the address(es) of the priviledged
   node(s).This allows the BU to traverse the firewall and the BA can
   pass the firewall without any assistance.  Therefore, the Binding
   Update sequence can be performed successfully.

5.4.  Route Optimization data traffic from MN

   Also the Route Optimization data traffic from MN directly to the CN
   can not traverse the firewall without assistance.  A dynamically
   created pinhole such as the one specified in [MIP6FWVENDOR] will
   allow this traffic to pass.


6.  Mobile Node behind a firewall

   This section presents the recommendations for configuring a firewall
   that protects the network a mobile node visiting.












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        +----------------+       +----+
        |                |       | HA |
        |                |       +----+
        |                |      Home Agent
        |  +---+      +----+      of A               +---+
        |  | A |      | FW |                         | B |
        |  +---+      +----+                         +---+
        |Internal        |                         External
        |   MN           |                           Node
        |                |
        +----------------+
        Network protected
          by a firewall

                      Figure 3: MN behind a firewall

   For each type of traffic that needs to pass through this firewall,
   recommendations are presented on how to identify that traffic.  The
   following types of traffic are considered

   o  Signaling between MN and HA

   o  Route Optimization Signaling between MN and CN

   o  IKEv2 signaling between MN and HA for establishing SAs

6.1.  Signaling between MN and HA

   As described in Section 4.1, the signaling between the MN and HA is
   protected using IPSec ESP.  Currently, a lot of firewalls are
   configured to block the incoming ESP packets.  Moreover, from the
   view of the firewall, both source and destination addresses of these
   messages from/to mobile node are variable.  Fortunately, for a
   stateful firewall, if the initial traffic is allowed through the
   firewall, then the return traffic is also allowed.  A mobile node is
   always the initiator for the BU.  Since MN's CoA is not able to be
   known in advance, the firewall can use following patterns to permit
   these messages through.

     Source Address: Visited subnet prefix

     Destination Address: Address of HA
     Next Header: 50 (ESP)
     Mobility Header Type: 5 (BU)

   This pattern will allow the Binding Update packets to pass through
   the firewall.  Then the return packets (BA from HA to MN) will also
   able to pass through accordingly.



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6.2.  Signaling between MN and CN

   Route Optimization allows direct communication of data packets
   between the MN and a CN without tunneling it back through the HA.  It
   includes 3 pairs of messages: HoTI/HoT, CoTI/CoT and BU/BA.  The
   first pair can pass through the firewall using the pattern described
   in section 5.1.  Here we discuss CoTI/CoT and BU/BA messages.
   Following pattern permits these messages through the firewall.

   Source Address: Visited subnet prefix
     Mobility Header Type: 2 (CoTI)

   Source Address: Visited subnet prefix
     Mobility Header Type: 5 (BU)

   This pattern allows the initial messages (CoTI and BU) from the MN to
   the CN pass through the firewall.  The return messages (CoT and BA)
   from the CN to the MN can also passes through the firewall
   accordingly.

6.3.  IKEv2 signaling between MN and HA for establishing SAs

   The MN and HA exchange IKEv2 signaling in order to establish the
   security associations.  The security associations so established will
   later be used for securing the mobility signaling messages.  Due to
   variable source/destination IP addresses and MN always as initiator,
   the following pattern will let the negotiation pass.

   Source Address: Visited subnet prefix
   Transport Protocol: UDP
   Destination UDP Port: 500



7.  Related documents

   There are other IETF published documents that provide recommendations
   for firewall configuration that can affect Mobile IPv6 messages.
   [RFC4890] that provides recommendations for filtering ICMPv6 messages
   (especially Section 4.3.2).  [RFC4942] describes security issues
   present in IPv6 and related protocols (especially Sections 2.1.2 and
   2.1.15).


8.  Acknowledgements

   The authors would like to thank the following members of the MIPv6
   firewall design team for contributing to this document: Hannes



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   Tschofenig, Hesham Soliman, Yaron Sheffer, and Vijay Devarapalli.
   The authors would also like to thank William Ivancic, Ryuji Wakikawa,
   Jari Arkko, Henrik Levkowetz, Pasi Eronen and Noriaki Takamiya for
   their thorough reviews of the document and for providing comments to
   improve the quality of the document.


9.  IANA Considerations

   This document does not require any IANA action.


10.  Security Considerations

   This document specifies recommendations for firewall administrators
   to allow Mobile IPv6 traffic to pass through unhindered.  Since some
   of this traffic is encrypted it is not possible for firewalls to
   discern whether it is safe or not.  This document recommends a
   liberal setting so that all legitimate traffic can pass.  This means
   that some malicious traffic may be permitted by these rules.  These
   rules may allow the initiation of Denial of Service attacks against
   Mobile IPv6 capable nodes (the MNs, CNs and the HAs).


11.  References

11.1.  Normative References

   [MIP6FWVENDOR]
              Krishnan, S., Sheffer, Y., Steinleitner, N., and G. Bajko,
              "Guidelines for firewall vendors regarding MIPv6 traffic",
              draft-ietf-mext-firewall-vendor-0 (work in progress),
              October 2008.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3775]  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
              in IPv6", RFC 3775, June 2004.

   [RFC4487]  Le, F., Faccin, S., Patil, B., and H. Tschofenig, "Mobile
              IPv6 and Firewalls: Problem Statement", RFC 4487,
              May 2006.

11.2.  Informative References

   [RFC4890]  Davies, E. and J. Mohacsi, "Recommendations for Filtering
              ICMPv6 Messages in Firewalls", RFC 4890, May 2007.



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   [RFC4942]  Davies, E., Krishnan, S., and P. Savola, "IPv6 Transition/
              Co-existence Security Considerations", RFC 4942,
              September 2007.


Authors' Addresses

   Suresh Krishnan
   Ericsson
   8400 Decarie Blvd.
   Town of Mount Royal, QC
   Canada

   Phone: +1 514 345 7900 x42871
   Email: suresh.krishnan@ericsson.com


   Niklas Steinleitner
   University of Goettingen
   Lotzestr. 16-18
   Goettingen
   Germany

   Email: steinleitner@cs.uni-goettingen.de


   Ying Qiu
   Institute for Infocomm Research
   21 Heng Mui Keng Terrace
   Singapore

   Phone: +65-6874-6742
   Email: qiuying@i2r.a-star.edu.sg


   Gabor Bajko
   Nokia

   Email: gabor.bajko@nokia.com












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