    Internet Engineering Task Force (IETF)                      L. Fang, Ed.
    Request for Comments: 6941                                         Cisco
    Category: Informational                            B. Niven-Jenkins, Ed.
    ISSN: 2070-1721                                                  Velocix
                                                           S. Mansfield, Ed.
                                                                    Ericsson
                                                            R. Graveman, Ed.
                                                                RFG Security
                                                                  April 2013

              MPLS Transport Profile (MPLS-TP) Security Framework

    Abstract

       This document provides a security framework for the MPLS Transport
       Profile (MPLS-TP).  MPLS-TP extends MPLS technologies and introduces
       new Operations, Administration, and Maintenance (OAM) capabilities, a
       transport-oriented path protection mechanism, and strong emphasis on
       static provisioning supported by network management systems.  This
       document addresses the security aspects relevant in the context of
       MPLS-TP specifically.  It describes potential security threats as
       well as mitigation procedures related to MPLS-TP networks and to
       MPLS-TP interconnection to other MPLS and GMPLS networks.  This
       document is built on RFC 5920 ("Security Framework for MPLS and GMPLS
       Networks") by providing additional security considerations that are
       applicable to the MPLS-TP extensions.  All the security
       considerations from RFC 5920 are assumed to apply.

       This document is a product of a joint Internet Engineering Task Force
       (IETF) / International Telecommunication Union Telecommunication
       Standardization Sector (ITU-T) effort to include an MPLS Transport
       Profile within the IETF MPLS and Pseudowire Emulation Edge-to-Edge
       (PWE3) architectures to support the capabilities and functionality of
       a packet transport network.

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    Status of This Memo

       This document is not an Internet Standards Track specification; it is
       published for informational purposes.

       This document is a product of the Internet Engineering Task Force
       (IETF).  It represents the consensus of the IETF community.  It has
       received public review and has been approved for publication by the
       Internet Engineering Steering Group (IESG).  Not all documents
       approved by the IESG are a candidate for any level of Internet
       Standard; see Section 2 of RFC 5741.

       Information about the current status of this document, any errata,
       and how to provide feedback on it may be obtained at
       http://www.rfc-editor.org/info/rfc6941.

    Copyright Notice

       Copyright (c) 2013 IETF Trust and the persons identified as the
       document authors.  All rights reserved.

       This document is subject to BCP 78 and the IETF Trust's Legal
       Provisions Relating to IETF Documents
       (http://trustee.ietf.org/license-info) in effect on the date of
       publication of this document.  Please review these documents
       carefully, as they describe your rights and restrictions with respect
       to this document.  Code Components extracted from this document must
       include Simplified BSD License text as described in Section 4.e of
       the Trust Legal Provisions and are provided without warranty as
       described in the Simplified BSD License.

    Table of Contents

       1. Introduction ....................................................3
          1.1. Terminology ................................................3
       2. Security Reference Models .......................................4
          2.1. Security Reference Model 1 .................................5
          2.2. Security Reference Model 2 .................................6
       3. Security Threats ................................................9
       4. Defensive Techniques ...........................................10
       5. Security Considerations ........................................12
       6. Acknowledgements ...............................................13
       7. References .....................................................13
          7.1. Normative References ......................................13
          7.2. Informative References ....................................13
       Contributors ......................................................14

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    1.  Introduction

       This document provides a security framework for the MPLS Transport
       Profile (MPLS-TP).

       As defined in "Requirements of an MPLS Transport Profile" [RFC5654]
       and "A Framework for MPLS in Transport Networks" [RFC5921], MPLS-TP
       uses a subset of MPLS features and introduces extensions to reflect
       the characteristics of the transport technology.  The additional
       functionality includes in-band OAM, transport-oriented path
       protection and recovery mechanisms, and new OAM capabilities that
       were developed for MPLS-TP but that also apply to MPLS and GMPLS.
       There is strong emphasis in MPLS-TP on static provisioning support
       through Network Management Systems (NMSs) or Operational Support
       Systems (OSSs).

       This document is built on [RFC5920] by providing additional security
       considerations that are applicable to the MPLS-TP extensions.  The
       security models, threats, and defense techniques previously defined
       in [RFC5920] are assumed to apply to general aspects of MPLS-TP.

       This document is a product of a joint Internet Engineering Task Force
       (IETF) / International Telecommunication Union Telecommunication
       Standardization Sector (ITU-T) effort to include an MPLS Transport
       Profile within the IETF MPLS and PWE3 architectures to support the
       capabilities and functionality of a packet transport network.

       Readers can refer to [RFC5654] and [RFC5921] for MPLS-TP
       terminologies and to [RFC5920] for security terminologies that are
       relevant to MPLS and GMPLS.

    1.1.  Terminology

       Term       Definition
       ------     -----------------------------------------------
       AC         Attachment Circuit
       BFD        Bidirectional Forwarding Detection
       CE         Customer Edge
       DoS        Denial of Service
       G-ACh      Generic Associated Channel
       GAL        G-ACh Label
       GMPLS      Generalized Multiprotocol Label Switching
       IP         Internet Protocol
       LDP        Label Distribution Protocol
       LSP        Label Switched Path
       NMS        Network Management System
       MPLS       Multiprotocol Label Switching
       MPLS-TP    MPLS Transport Profile

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       MS-PW      Multi-Segment Pseudowire
       OAM        Operations, Administration, and Maintenance
       PE         Provider Edge
       PSN        Packet-Switched Network
       PW         Pseudowire
       S-PE       PW Switching Provider Edge
       SP         Service Provider
       SS-PW      Single-Segment Pseudowire
       T-PE       PW Terminating Provider Edge

    2.  Security Reference Models

       This section defines reference models for security in MPLS-TP
       networks.

       The models are built on the architecture of MPLS-TP, as defined in
       [RFC5921].  The placement of SP boundaries plays an important role in
       determining the security models for any particular deployment.

       This document defines a trusted zone as being where a single SP has
       total operational control over that part of the network.  A primary
       concern is about security aspects that relate to breaches of security
       from the "outside" of a trusted zone to the "inside" of this zone.

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    2.1.  Security Reference Model 1

       In reference model 1, a single SP has total control of the "PE/T-PE
       to PE/T-PE" part of the MPLS-TP network.

       Security reference model 1(a) shows an MPLS-TP network with
       Single-Segment Pseudowire (SS-PW) from PE1 to PE2.  The trusted zone
       is PE1 to PE2, as illustrated in Figure 1.

               |<-------------- Emulated Service ---------------->|
               |                                                  |
               |          |<------- Pseudowire ------->|          |
               |          |                            |          |
               |          |    |<-- PSN Tunnel -->|    |          |
               |          v    v                  v    v          |
               v    AC    +----+                  +----+     AC   v
         +-----+    |     | PE1|==================| PE2|     |    +-----+
         |     |----------|............PW1.............|----------|     |
         | CE1 |    |     |    |                  |    |     |    | CE2 |
         |     |----------|............PW2.............|----------|     |
         +-----+  ^ |     |    |==================|    |     | ^  +-----+
               ^  |       +----+                  +----+     | |  ^
               |  |   Provider Edge 1         Provider Edge 2  |  |
               |  |                                            |  |
         Customer |                                            |Customer
         Edge 1   |                                            |Edge 2
                  |                                            |
            Native service                               Native service

         ---Untrusted--- >|<------- Trusted Zone ----->|<---Untrusted----

                      Figure 1.  MPLS-TP Security Model 1(a)

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       Security reference model 1(b) shows an MPLS-TP network with
       Multi-Segment Pseudowire (MS-PW) from T-PE1 to T-PE2.  The trusted
       zone is T-PE1 to T-PE2, as illustrated in Figure 2.

             Native  |<-------------Pseudowire------------>|  Native
             Service |                                     |  Service
              (AC)   |     |<- PSN ->|     |<- PSN ->|     |   (AC)
                |    v     v         v     v         v     v     |
                |    +-----+         +-----+         +-----+     |
         +----+ |    |T-PE1|=========|S-PE1|=========|T-PE2|     | +----+
         |    |------|......PW.Seg't1.......PW.Seg't3......|-------|    |
         | CE1| |    |     |         |     |         |     |     | |CE2 |
         |    |------|......PW.Seg't2.......PW.Seg't4......|-------|    |
         +----+ |    |     |=========|     |=========|     |     | +----+
              ^      +-----+    ^    +-----+     ^   +-----+        ^
              |                 |                |                  |
              |               TP LSP            TP LSP              |
              |                                                     |
              |<----------------- Emulated Service ---------------->|

         -Untrusted->|<---------- Trusted Zone ----------->|<-Untrusted--

                      Figure 2.  MPLS-TP Security Model 1(b)

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    2.2.  Security Reference Model 2

       In reference model 2, a single SP does not have the end-to-end
       control of the segment from PE/T-PE to PE/T-PE.  A given S-PE or T-PE
       may be under the control of another SP, that SP's customers, or its
       partners.  In this case, the MPLS-TP network is not contained within
       a single trusted zone.

       Security reference model 2(a) shows an MPLS-TP network with
       Multi-Segment Pseudowire (MS-PW) from T-PE1 to T-PE2.  The trusted
       zone is T-PE1 to S-PE1, as illustrated in Figure 3.

             Native  |<-------------Pseudowire------------>| Native
             Service |                                     | Service
              (AC)   |     |<--PSN-->|     |<--PSN-->|     |  (AC)
                |    V     V         V     V         V     V    |
                |    +-----+         +-----+         +-----+    |
         +----+ |    |T-PE1|=========|S-PE1|=========|T-PE2|    | +----+
         |    |------|......PW.Seg't1.......PW.Seg't3......|------|    |
         | CE1| |    |     |         |     |         |     |    | |CE2 |
         |    |------|......PW.Seg't2.......PW.Seg't4......|------|    |
         +----+ |    |     |=========|     |=========|     |    | +----+
              ^      +-----+    ^    +-----+     ^   +-----+      ^
              |                 |                |                |
              |               TP LSP            TP LSP            |
              |                                                   |
              |<---------------- Emulated Service --------------->|

         Untrusted-->|<-- Trusted Zone---->|<---------Untrusted--------

                      Figure 3.  MPLS-TP Security Model 2(a)

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       Security reference model 2(b) shows an MPLS-TP network with
       Multi-Segment Pseudowire (MS-PW) from T-PE1 to T-PE2.  The trusted
       zone is the S-PE1 only, as illustrated in Figure 4.

             Native  |<-------------Pseudowire------------>| Native
             Service |                                     | Service
              (AC)   |     |<--PSN-->|     |<--PSN-->|     |  (AC)
                |    V     V         V     V         V     V    |
                |    +-----+         +-----+         +-----+    |
         +----+ |    |T-PE1|=========|S-PE1|=========|T-PE2|    | +----+
         |    |------|......PW.Seg't1.......PW.Seg't3......|------|    |
         | CE1| |    |     |         |     |         |     |    | |CE2 |
         |    |------|......PW.Seg't2.......PW.Seg't4......|------|    |
         +----+ |    |     |=========|     |=========|     |    | +----+
              ^      +-----+    ^    +-----+     ^   +-----+      ^
              |                 |                |                |
              |               TP LSP            TP LSP            |
              |                                                   |
              |<---------------- Emulated Service --------------->|

         --------Untrusted---------->|<--->|<-------Untrusted----------
                                     Trusted
                                      Zone

                      Figure 4.  MPLS-TP Security Model 2(b)

       Security reference model 2(c) shows an MPLS-TP network with
       Multi-Segment Pseudowire (MS-PW) from different SPs with
       inter-provider PW connections.  The trusted zone is T-PE1 to S-PE3,
       as illustrated in Figure 5.

         Native  |<--------------------- PW15 ------------------>| Native
          Layer  |                                               | Layer
        Service  |     |<PSN13>|     |<PSN3X>|     |<PSNXZ>|     | Service
          (AC1)  V     V  LSP  V     V  LSP  V     V  LSP  V     V (AC2)
              |  +-----+  +-+  +-----+       +-----+  +-+  +-----+ |
        +---+ |  |T-PE1|  | |  |S-PE3|       |S-PEX|  | |  |T-PEZ| | +---+
        |   | |  |     |=======|     |=======|     |=======|     | | |   |
        |CE1|----|........PW1........|..PW3..|........PW5........|---|CE2|
        |   | |  |     |=======|     |=======|     |=======|     | | |   |
        +---+    |  1  |  |2|  |  3  |       |  X  |  |Y|  |  Z  |   +---+
                 +-----+  +-+  +-----+       +-----+  +-+  +-----+
                 |<--Subnetwork 123->|       |<--Subnetwork XYZ->|

       Untrusted>|<-- Trusted Zone-->|<-------------Untrusted-------------

                      Figure 5.  MPLS-TP Security Model 2(c)

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       In general, the boundaries of a trusted zone must be carefully
       defined when analyzing the security properties of each individual
       network.  The security boundaries determine which reference model
       should be applied to a given network topology.

    3.  Security Threats

       This section discusses various network security threats that are
       unique to MPLS-TP and may endanger MPLS-TP networks.

       Attacks against a GAL or G-ACh may include the following:

       - GAL or BFD label manipulation, which includes insertion of false
         labels and modification, deletion, or replay of messages.

       - DoS attacks through in-band OAM by generating excessive G-ACh/GAL
         and BFD messages that consume significant bandwidth and potentially
         cause congestion.

       These attacks can cause unauthorized protection switchover, inability
       to restore one or more LSPs, or loss of network connectivity.

       When an NMS is used for LSP setup, attacks on the NMS can cause the
       above effects as well.  Although this is not unique to MPLS-TP,
       MPLS-TP networks can be particularly vulnerable to NMS attacks, due
       to the fact that static provisioning through NMSs is a commonly used
       model.  In the static provisioning model, a compromised NMS can
       potentially be comparable to a compromised control plane plus a
       compromised management plane in the dynamic controlled network model.

       Attacks on NMSs may come from either external attackers or insiders.
       Outside attacks are initiated outside of the trusted zone by
       unauthorized users of the MPLS-TP NMSs.  Insider attacks are
       initiated from inside the trusted zone by an entity that has
       authorized access to the management systems but that performs
       unapproved functions that are harmful to the MPLS-TP networks.  These
       attacks may directly target the NMS; they may also take place via the
       compromised communication channels between the NMS and the network
       devices that are being provisioned, or through user access to the
       provisioning tools.  This type of security threat may include
       disclosure of information, generating false OAM messages, taking down
       MPLS-TP LSPs, connecting to the wrong MPLS-TP tunnel endpoints, and
       DoS attacks on the MPLS-TP networks.

       There are other more generic security threats, such as unauthorized
       observation of data traffic (including traffic pattern analysis),
       modification or deletion of a provider's or user's data, and replay
       or insertion of inauthentic data into a provider's or user's data

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       stream.  These types of attacks apply to MPLS-TP traffic regardless
       of how the LSP or PW is set up, in a way that is similar to how they
       apply to MPLS traffic regardless of how the LSP is set up.  More
       details on the above-mentioned threats are documented in [RFC5920].

       Such threats may result from malicious behavior or accidental errors:

       Example 1: Attacks from users: Users of the MPLS-TP network may
          attack the network infrastructure or attack other users.

       Example 2: Attacks from insiders: Employees of the operators may
          attack the MPLS-TP network, especially through NMSs.

       Example 3: Attacks from interconnecting SPs or other partners: Other
          SPs may attack the MPLS-TP network, particularly through the
          inter-provider connections.

       Example 4: Attacks as the result of operational errors: Operations
          staff may fail to follow operational procedures or may make
          operational mistakes.

    4.  Defensive Techniques

       The defensive techniques presented in this document and in [RFC5920]
       are intended to describe methods by which some security threats can
       be addressed.  They are not intended as requirements for all MPLS-TP
       deployments.  The specific operational environment determines the
       security requirements for any instance of MPLS-TP.  Therefore,
       protocol designers should provide a full set of security capabilities
       that can be selected and used where appropriate.  The MPLS-TP
       provider should determine the applicability of these techniques to
       the provider's specific service offerings, and the end user may wish
       to assess the value of these techniques to the user's service
       requirements.

       Authentication is the primary defense technique to mitigate the risk
       of the MPLS-TP security threats discussed in Section 3 (GAL or BFD
       label manipulation, and DoS attacks through in-band OAM).
       Authentication refers to methods to ensure that message sources are
       properly identified by the MPLS-TP devices with which they
       communicate.  Authentication includes the following:

       - entity authentication for identity verification

       - management system authentication

       - peer-to-peer authentication

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       - message integrity and replay detection to ensure the validity of
         message streams

       - network-based access controls such as packet filtering and
         firewalls

       - host-based access controls

       - isolation

       - aggregation

       - protection against denial of service

       - event logging

       Section 5.2 of [RFC5920] describes these techniques where they apply
       to MPLS and GMPLS in general.

       In addition to authentication, the following defense should also be
       considered in order to protect MPLS-TP networks:

       - Use of isolated infrastructure for MPLS-TP

       One way to protect the MPLS-TP infrastructure is to use dedicated
       network resources to provide MPLS-TP transport services.  For
       example, in security model 2 (Section 2.2), the potential risk of
       attacks on the S-PE1 or T-PE1 in the trusted zone may be reduced by
       using non-IP-based communication paths, so that the paths in the
       trusted zone cannot be reached from the outside via IP.

       - Verification of connectivity

       To protect against deliberate or accidental misconnection, mechanisms
       can be put in place to verify both end-to-end connectivity and
       segment-by-segment resources.  These mechanisms can trace the routes
       of LSPs in both the control plane and the data plane.  Note that the
       connectivity verification tools are now developed for general MPLS
       networks as well.

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       The defense techniques that apply generally to MPLS/GMPLS are not
       detailed here; see [RFC5920] for details regarding these techniques.
       For example:

       1) Authentication, including management system authentication,
          peer-to-peer authentication, and cryptographic techniques for
          authenticating identity

       2) Access control techniques

       3) Use of aggregated infrastructure

       4) Mitigation of denial-of-service attacks

       5) Monitoring, detection, and reporting of security attacks

       It is important to point out the following security defense
       techniques, as they are particularly critical for NMSs, due to the
       strong emphasis on static provisioning supported by NMSs in MPLS-TP
       deployments.  These techniques include the following:

       - entity authentication for identity verification

       - encryption for confidentiality

       - message integrity and replay detection to ensure the validity of
         message streams

       - user access control and event logging, which must be applied for
         NMSs and provisioning applications

    5.  Security Considerations

       Security considerations constitute the sole subject of this document
       and hence are discussed throughout.

       This document evaluates security risks specific to MPLS-TP, as well
       as mitigation mechanisms that may be used to counter potential
       threats.  All of the techniques presented here involve mature and
       widely implemented technologies that are practical to implement.  It
       is meant to assist equipment vendors and service providers who must
       ultimately decide what threats to protect against in any given
       configuration or service offering, from a customer's perspective as
       well as from a service provider's perspective.

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    6.  Acknowledgements

       The authors wish to thank the following people: Joel Halpern and
       Gregory Mirsky for their review comments and contributions to this
       document, Mach Chen for his review and suggestions, Adrian Farrel for
       his Routing Area Director review and detailed comments, Loa Andersson
       for his continued support and guidance as the MPLS WG co-chair, and
       Dan Romascanu and Barry Leiba for their helpful comments during IESG
       review.

    7.  References

    7.1.  Normative References

       [RFC5654]  Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed.,
                  Sprecher, N., and S. Ueno, "Requirements of an MPLS
                  Transport Profile", RFC 5654, September 2009.

       [RFC5920]  Fang, L., Ed., "Security Framework for MPLS and GMPLS
                  Networks", RFC 5920, July 2010.

    7.2.  Informative References

       [RFC5921]  Bocci, M., Ed., Bryant, S., Ed., Frost, D., Ed., Levrau,
                  L., and L. Berger, "A Framework for MPLS in Transport
                  Networks", RFC 5921, July 2010.

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    Contributors

       Raymond Zhang
       Alcatel-Lucent
       750D Chai Chee Road
       Singapore  469004

       EMail: raymond.zhang@alcatel-lucent.com

       Nabil Bitar
       Verizon
       40 Sylvan Road
       Waltham, MA  02145
       US

       EMail: nabil.bitar@verizon.com

       Masahiro Daikoku
       KDDI Corporation
       3-11-11 Iidabashi, Chiyodaku, Tokyo
       Japan

       EMail: ms-daikoku@kddi.com

       Lei Wang
       Lime Networks
       Strandveien 30, 1366 Lysaker
       Norway

       EMail: lei.wang@limenetworks.no

       Henry Yu
       TW Telecom
       10475 Park Meadow Drive
       Littleton, CO  80124
       US

       EMail: henry.yu@twtelecom.com

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    Authors' Addresses

       Luyuan Fang (editor)
       Cisco Systems
       111 Wood Ave. South
       Iselin, NJ  08830
       US

       EMail: lufang@cisco.com

       Ben Niven-Jenkins (editor)
       Velocix
       326 Cambridge Science Park
       Milton Road
       Cambridge  CB4 0WG
       UK

       EMail: ben@niven-jenkins.co.uk

       Scott Mansfield (editor)
       Ericsson
       300 Holger Way
       San Jose, CA  95134
       US

       EMail: scott.mansfield@ericsson.com

       Richard F. Graveman (editor)
       RFG Security, LLC
       15 Park Avenue
       Morristown, NJ  07960
       US

       EMail: rfg@acm.org

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