MPLS Working Group                                              D. Frost
Internet-Draft                                                 S. Bryant                                                  Blue Sun
Intended status: Informational                             Cisco Systems                                 S. Bryant
Expires: May 22, July 21, 2014                                     Cisco Systems
                                                                M. Bocci
                                                               L. Berger
                                                         LabN Consulting
                                                       November 18, 2013
                                                        January 17, 2014

     A Framework for Point-to-Multipoint MPLS in Transport Networks


   The Multiprotocol Label Switching Transport Profile is the common set
   of MPLS protocol functions defined to enable the construction and
   operation of packet transport networks.  The MPLS-TP supports both
   point-to-point and point-to-multipoint transport paths.  This
   document defines the elements and functions of the MPLS-TP
   architecture applicable specifically to supporting point-to-
   multipoint transport paths.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on May 22, July 21, 2014.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
       1.2.1.  Additional Definitions and Terminology  . . . . . . .   3
     1.3.  Applicability . . . . . . . . . . . . . . . . . . . . . .   3
   2.  MPLS Transport Profile Point-to-Multipoint  MPLS-TP P2MP Requirements . . .   3 . . . . . . . . . . . . . . .   4
   3.  Architecture  . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  MPLS-TP Encapsulation and Forwarding  . . . . . . . . . .   6
   4.  Operations, Administration and Maintenance  . . . . . . . . .   6
   5.  Control Plane . . . . . . . . . . . . . . . . . . . . . . . .   6   7
     5.1.  Point-to-Multipoint  P2MP LSP Control Plane  . . . . . . . . . . . . . . . . .   7
     5.2.  Point-to-Multipoint  P2MP PW Control Plane . . . . . . . . . . . . . . . . . .   8
   6.  Survivability . . . . . . . . . . . . . . . . . . . . . . . .   8
   7.  Network Management  . . . . . . . . . . . . . . . . . . . . .   8
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     10.2.  Informative References . . . . . . . . . . . . . . . . .  10

1.  Introduction

   The Multiprotocol Label Switching Transport Profile (MPLS-TP) is the
   common set of MPLS protocol functions defined to meet the
   requirements specified in [RFC5654].  The MPLS-TP Framework [RFC5921]
   provides an overall introduction to the MPLS-TP and defines the
   general architecture of the Transport Profile, as well as those
   aspects specific to point-to-
   point point-to-point transport paths.  The purpose of
   this document is to define the elements and functions of the MPLS-TP
   architecture applicable specifically to supporting point-to-multipoint point-to-
   multipoint transport paths.

1.1.  Scope

   This document defines the elements and functions of the MPLS-TP
   architecture related to supporting point-to-multipoint transport
   paths.  The reader is referred to [RFC5921] for those aspects of the
   MPLS-TP architecture that are generic, or concerned specifically with
   point-to-point transport paths.

1.2.  Terminology

   Term    Definition
   ------- ---------------------------------------------------
   CE      Customer Edge
   GMPLS   Generalized MPLS
   LDP     Label Distribution Protocol
   LSP     Label Switched Path
   LSR     Label Switching Router
   MEG     Maintenance Entity Group
   MEP     Maintenance Entity Group End Point
   MIP     Maintenance Entity Group Intermediate Point
   MPLS    Multiprotocol Label Switching
   MPLS-TE MPLS Traffic Engineering
   MPLS-TP MPLS Transport Profile
   OAM     Operations, Administration Administration, and Maintenance
   OTN     Optical Transport Network
   P2MP    Point-to-multipoint
   PW      Pseudowire
   RSVP-TE Resource Reservation Protocol - Traffic Engineering
   SDH     Synchronous Digital Hierarchy
   tLDP    Targeted LDP

1.2.1.  Additional Definitions and Terminology

   Detailed definitions and additional terminology may be found in
   [RFC5921] and [RFC5654].

1.3.  Applicability

   The point-to-multipoint connectivity provided by an MPLS-TP network
   is based on the point-to-multipoint connectivity provided by MPLS
   networks.  Traffic Engineered P2MP MPLS TE-LSP LSP support is discussed in
   [RFC4875] and [RFC5332], and P2MP PW support is being developed based
   on [I-D.ietf-pwe3-p2mp-pw-requirements] and
   [I-D.ietf-l2vpn-vpms-frmwk-requirements].  MPLS-TP point-to-
   multipoint connectivity is analogous to that provided by traditional
   transport technologies such as Optical Transport Network point-to-
   multipoint [G.798] and drop-and-continue [G.780], and thus supports
   the same class of traditional applications, e.g., video distribution.

   There is no definition for MPLS TE-LSP support

   The scope of multipoint-to-
   multipoint connectivity and none this document is anticipated. limited to point-to-multipoint
   functions and it does not discuss multipoint-to-multipoint support.

2.  MPLS Transport Profile Point-to-Multipoint  MPLS-TP P2MP Requirements

   The requirements for MPLS-TP are specified in [RFC5654], [RFC5860],
   and [RFC5951].  This section provides a brief summary of point-to-
   multipoint transport requirements as set out in those documents; the
   reader is referred to the documents themselves for the definitive and
   complete list of requirements.  This summary does not include the
   [RFC2119] conformance language used in original documents as this
   document is not authoritative.

   From [RFC5654]:

   o  MPLS-TP must support traffic-engineered point-to-multipoint
      transport paths.

   o  MPLS-TP must support unidirectional point-to-multipoint transport

   o  MPLS-TP must be capable of using P2MP server (sub)layer
      capabilities as well as P2P server (sub)layer capabilities when
      supporting P2MP MPLS-TP transport paths.

   o  The MPLS-TP control plane must support establishing all the
      connectivity patterns defined for the MPLS-TP data plane (i.e.,
      unidirectional P2P, associated bidirectional P2P, co-routed
      bidirectional P2P, unidirectional P2MP) including configuration of
      protection functions and any associated maintenance functions.

   o  Recovery techniques used for P2P and P2MP should be identical to
      simplify implementation and operation.

   o  Unidirectional 1+1 and 1:n protection for P2MP connectivity must
      be supported.

   o  MPLS-TP recovery in a ring must protect unidirectional P2MP
      transport paths.

   From [RFC5860]:

   o  The protocol solution(s) developed to perform the following OAM
      functions must also apply to point-to-point associated
      bidirectional LSPs, point-to-point unidirectional LSPs, and point-
      to-multipoint LSPs:

      *  Continuity Check

      *  Connectivity Verification, proactive
      *  Lock Instruct

      *  Lock Reporting

      *  Alarm Reporting

      *  Client Failure Indication

      *  Packet Loss Measurement

      *  Packet Delay Measurement

   o  The protocol solution(s) developed to perform the following OAM
      functions may also apply to point-to-point associated
      bidirectional LSPs, point-to-point unidirectional LSPs, and point-
      to-multipoint LSPs:

      *  Connectivity Verification, on-demand

      *  Route Tracing

      *  Diagnostic Tests

      *  Remote Defect Indication

   From [RFC5951]:

   o  For unidirectional (P2P and point-to-multipoint (P2MP))
      connection, proactive measurement of packet loss and loss ratio is

   o  For a unidirectional (P2P and P2MP) connection, on-demand
      measurement of delay measurement is required.

3.  Architecture

   The overall architecture of the MPLS Transport Profile MPLS-TP is defined in [RFC5921].  The
   architecture for point-to-multipoint MPLS-TP comprises the following
   additional elements and functions:

   o  Unidirectional point-to-multipoint LSPs

   o  Unidirectional point-to-multipoint PWs

   o  Optional point-to-multipoint LSP and PW control planes

   o  Survivability, network management, and Operations, Administration
      and Maintenance functions for point-to-multipoint PWs and LSPs

   The following subsections summarise the encapsulation and forwarding
   of point-to-multipoint traffic within an MPLS-TP network, and the
   encapsulation options for delivery of traffic to and from MPLS-TP CE
   devices when the network is providing a packet transport service.

3.1.  MPLS-TP Encapsulation and Forwarding

   Packet encapsulation and forwarding for MPLS-TP point-to-multipoint
   LSPs is identical to that for MPLS-TE point-to-multipoint LSPs.
   MPLS-TE point-to-multipoint LSPs were introduced in [RFC4875] and the
   related data-plane behaviour was further clarified in [RFC5332].
   MPLS-TP allows for both upstream-assigned and downstream-assigned
   labels for use with point-to-multipoint LSPs.

   Packet encapsulation and forwarding for point-to-multipoint PWs has
   been discussed within the PWE3 Working Group
   [I-D.raggarwa-pwe3-p2mp-pw-encaps], but such definition is for
   further study.

4.  Operations, Administration and Maintenance

   The requirements for MPLS-TP OAM are specified in [RFC5860].  The
   overall OAM architecture for MPLS-TP is defined in [RFC6371], and
   P2MP OAM design considerations are described in Section 3.7 of that

   All the traffic sent over a P2MP transport path, including OAM
   packets generated by a MEP, is sent (multicast) from the root towards
   all the leaves, and thus may be processed by all the MIPs and MEPs
   associated with a P2MP MEG.  If an OAM packet is to be processed by
   only a specific leaf, it requires information to indicate to all
   other leaves that the packet must be discarded.  To address a packet
   to an intermediate node in the tree, TTL based addressing is used to
   set the radius and additional information in the OAM payload is used
   to identify the specific destination.  It is worth noting that a MIP
   and MEP may be instantiated on a single node when it is both a branch
   and leaf node.

   P2MP paths are unidirectional; therefore, any return path to an
   originating MEP for on-demand transactions will be out-of-band.  Out
   of band return paths are discussed in Section 3.8 of [RFC5921].

   A more detailed discussion of P2MP OAM considerations can be found in

5.  Control Plane

   The framework for the MPLS-TP control plane is provided in [RFC6373].
   This document reviews MPLS-TP control plane requirements as well as
   provides details on how the MPLS-TP control plane satisfies these
   requirements.  Most of the requirements identified in [RFC6373] apply
   equally to P2P and P2MP transport paths.  The key P2MP specific
   control plane requirements are:

   o  requirement 6 (P2MP transport paths),

   o  requirement 34 (use P2P sub-layers),

   o  requirement 49 (common recovery solutions for P2P and P2MP),

   o  requirement 59 (1+1 protection),

   o  requirement 62 (1:n protection),

   o  and requirement 65 (1:n shared mesh recovery).

   [RFC6373] defines the control plane approach used to support MPLS-TP
   transport paths.  It identifies GMPLS as the control plane for MPLS-
   TP LSPs tLDP as the control plane for PWs.  MPLS-TP allows that
   either, or both, LSPs and PWs to be provisioned statically or via a
   control plane.  As noted in [RFC6373]:

   The PW and LSP control planes, collectively, must satisfy the MPLS-TP
   control-plane requirements.  As with P2P services, when P2MP client
   services are provided directly via LSPs, all requirements must be
   satisfied by the LSP control plane.  When client services are
   provided via PWs, the PW and LSP control planes can operate in
   combination, and some functions may be satisfied via the PW control
   plane while others are provided to PWs by the LSP control plane.
   This is particularly noteworthy for P2MP recovery.

5.1.  Point-to-Multipoint  P2MP LSP Control Plane

   The MPLS-TP control plane for point-to-multipoint P2MP LSPs uses GMPLS and is based on
   RSVP-TE for point-to-multipoint P2MP LSPs as defined in [RFC4875].  A detailed listing of
   how GMPLS satisfies MPLS-TP control plane requirements is provided in

   Per [RFC6373], the definitions of P2MP, [RFC4875], and GMPLS
   recovery, [RFC4872] and [RFC4873], do not explicitly cover their
   interactions.  MPLS-TP requires a formal definition of

   [RFC6373]notes that recovery techniques for Traffic Engineered P2MP LSPs.  Such
   LSPs are not formally defined, and such that a definition is needed.
   A formal definition will be based on existing RFCs and may not
   require any new protocol mechanisms but, nonetheless, should be
   documented.  GMPLS recovery is defined in [RFC4872] and [RFC4873].
   Protection of P2MP LSPs is also discussed in [RFC6372] Section 4.7.3.

5.2.  Point-to-Multipoint  P2MP PW Control Plane

   The MPLS-TP control plane for point-to-multipoint P2MP PWs should be based on the LDP
   control protocol used for point-to-point PWs [RFC4447], with updates
   as required for P2MP applications.  A detailed specification of the
   control plane for P2MP PWs is for further study.

6.  Survivability

   The overall survivability architecture for MPLS-TP is defined in
   [RFC6372], and section 4.7.3 in particular describes the application
   of linear protection to unidirectional P2MP entities using 1+1 and
   1:1 protection architecture.  For 1+1, the approach is for the root
   of the P2MP tree to bridge the user traffic to both the working and
   protection entities.  Each sink/leaf MPLS-TP node selects the traffic
   from one entity according to some predetermined criteria.  For 1:1,
   the source/root MPLS-TP node needs to identify the existence of a
   fault condition impacting delivery to any of the leaves.  Fault
   notification happens from the node identifying the fault to the root
   node via an out of band path.  The root then selects the protection
   transport path for traffic transfer.  More sophisticated
   survivability approaches such as partial tree protection and 1:n
   protection are for further study.

   The IETF has no experience with P2MP PW survivability as yet, and
   therefore it is proposed that the P2MP PW survivability will
   initially rely on the LSP survivability.  Further work is needed on
   this subject, particularly if a requirement emerges to provide
   survivability for P2MP PWs in an MPLS-TP context.

7.  Network Management

   An overview of network management considerations for MPLS-TP can be
   found in Section 3.14 of "Framework for MPLS in Transport Networks"
   [RFC5921].  The provided description applies equally to P2MP
   transport paths.

   The network management architecture and requirements for MPLS-TP are
   specified in [RFC5951].  They derive from the generic specifications
   described in ITU-T G.7710/Y.1701 [G.7710] for transport technologies.
   They also incorporate the OAM requirements for MPLS Networks
   [RFC4377] and MPLS-TP Networks [RFC5860] and expand on those
   requirements to cover the modifications necessary for fault,
   configuration, performance, and security in a transport network.
   [RFC5951] covers all MPLS-TP connection types, including P2MP.

   [RFC6639] provides the MIB-based architecture for MPLS-TP.  It
   reviews the interrelationships between different non MPLS-TP specific
   MIB modules that can be leveraged for MPLS-TP network management, and
   identifies areas where additional MIB modules are required.  While
   the document does not consider P2MP transport paths, it does provide
   a foundation for an analysis of areas where MIB module modification
   and addition may be needed to fully support P2MP transport paths.
   There has also been work in the MPLS working group on a P2MP specific
   MIB, [I-D.ietf-mpls-p2mp-te-mib].

8.  Security Considerations

   General security considerations for MPLS-TP are covered in [RFC5921].
   Additional security considerations for point-to-multipoint P2MP LSPs are provided in
   [RFC4875].  This document introduces no new security considerations
   beyond those covered in those documents.

9.  IANA Considerations

   There are no requests for IANA actions in this document.

10.  References

10.1.  Normative References

   [RFC4872]  Lang, J., Rekhter, Y., and D. Papadimitriou, "RSVP-TE
              Extensions in Support of End-to-End Generalized Multi-
              Protocol Label Switching (GMPLS) Recovery", RFC 4872, May

   [RFC4873]  Berger, L., Bryskin, I., Papadimitriou, D., and A. Farrel,
              "GMPLS Segment Recovery", RFC 4873, May 2007.

   [RFC4875]  Aggarwal, R., Papadimitriou, D., and S. Yasukawa,
              "Extensions to Resource Reservation Protocol - Traffic
              Engineering (RSVP-TE) for Point-to-Multipoint TE Label
              Switched Paths (LSPs)", RFC 4875, May 2007.

   [RFC5332]  Eckert, T., Rosen, E., Aggarwal, R., and Y. Rekhter, "MPLS
              Multicast Encapsulations", RFC 5332, August 2008.

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

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

10.2.  Informative References

   [G.7710]   ITU-T Recommendation G.7710/Y.1701 (07/2007), "Common
              equipment management function requirements", 2007.

   [G.780]    ITU-T Recommendation G.780//Y.1351 (07/2010), "Terms and
              definitions for synchronous digital hierarchy (SDH)
              networks", 2010.

   [G.798]    ITU-T Recommendation G.798 (10/2010), "Characteristics of
              optical transport network hierarchy equipment functional
              blocks", 2010.

              Koike, Y., Hamano, T., and M. Namiki, "Framework for
              Point-to-Multipoint MPLS-TP OAM", draft-hmk-mpls-tp-p2mp-
              oam-framework-03 (work in progress), October 2013.

              Kamite, Y., JOUNAY, F., Niven-Jenkins, B., Brungard, D.,
              and L. Jin, "Framework and Requirements for Virtual
              Private Multicast Service (VPMS)", draft-ietf-l2vpn-vpms-
              frmwk-requirements-05 (work in progress), October 2012.

              Farrel, A., Yasukawa, S., and T. Nadeau, "Point-to-
              Multipoint Multiprotocol Label Switching (MPLS) Traffic
              Engineering (TE) Management Information Base (MIB)
              module", draft-ietf-mpls-p2mp-te-mib-09 (work in
              progress), April 2009.

              JOUNAY, F., Kamite, Y., Heron, G., and M. Bocci,
              "Requirements and Framework for Point-to-Multipoint
              Pseudowires over MPLS PSNs", draft-ietf-pwe3-p2mp-pw-
              requirements-06 (work in progress), October 2013.

              Aggarwal, R. and F. JOUNAY, "Point-to-Multipoint Pseudo-
              Wire Encapsulation", draft-raggarwa-pwe3-p2mp-pw-encaps-01
              (work in progress), March 2010.

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

   [RFC4377]  Nadeau, T., Morrow, M., Swallow, G., Allan, D., and S.
              Matsushima, "Operations and Management (OAM) Requirements
              for Multi-Protocol Label Switched (MPLS) Networks", RFC
              4377, February 2006.

   [RFC4447]  Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G.
              Heron, "Pseudowire Setup and Maintenance Using the Label
              Distribution Protocol (LDP)", RFC 4447, April 2006.

   [RFC5860]  Vigoureux, M., Ward, D., and M. Betts, "Requirements for
              Operations, Administration, and Maintenance (OAM) in MPLS
              Transport Networks", RFC 5860, May 2010.

   [RFC5951]  Lam, K., Mansfield, S., and E. Gray, "Network Management
              Requirements for MPLS-based Transport Networks", RFC 5951,
              September 2010.

   [RFC6371]  Busi, I. and D. Allan, "Operations, Administration, and
              Maintenance Framework for MPLS-Based Transport Networks",
              RFC 6371, September 2011.

   [RFC6372]  Sprecher, N. and A. Farrel, "MPLS Transport Profile (MPLS-
              TP) Survivability Framework", RFC 6372, September 2011.

   [RFC6373]  Andersson, L., Berger, L., Fang, L., Bitar, N., and E.
              Gray, "MPLS Transport Profile (MPLS-TP) Control Plane
              Framework", RFC 6373, September 2011.

   [RFC6639]  King, D. and M. Venkatesan, "Multiprotocol Label Switching
              Transport Profile (MPLS-TP) MIB-Based Management
              Overview", RFC 6639, June 2012.

Authors' Addresses

   Dan Frost
   Cisco Systems
   Blue Sun


   Stewart Bryant
   Cisco Systems

   Matthew Bocci
   Voyager Place, Shoppenhangers Road
   Maidenhead, Berks  SL6 2PJ
   United Kingdom


   Lou Berger
   LabN Consulting

   Phone: +1-301-468-9228