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Network Working Group                                            Q. Zhao
Internet-Draft                                                   E. Chen
Intended status: Standards Track                       Huawei Technology
Expires: April 26, 2012                                 October 24, 2011


 Protection Mechanisms for Label Distribution Protocol P2MP/MP2MP Label
                             Switched Paths
                draft-zhao-mpls-mldp-protections-00.txt

Abstract

   Service providers continue to deploy real-time multicast applications
   using Multicast LDP (mLDP) across MPLS networks.  There is a clear
   need to protect these real-time applications and to provide the
   shortest switching times in the event of failure.  This document
   outlines the requirements, describes the protection mechanisms
   available, and where neccessary proposes extensions to facilitate
   mLDP P2MP and MP2MP LSP protection within an MPLS network.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on April 26, 2012.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
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   This document is subject to BCP 78 and the IETF Trust's Legal
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   to this document.  Code Components extracted from this document must



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   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.

   This document may contain material from IETF Documents or IETF
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   than English.


Table of Contents

   1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Requirement Language . . . . . . . . . . . . . . . . . . . . .  4
   3.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Requirements . . . . . . . . . . . . . . . . . . . . . . .  6
     3.2.  Scope  . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   4.  Local protection using P2P LSP . . . . . . . . . . . . . . . .  6
     4.1.  Signaling procedures for local protection  . . . . . . . .  8
     4.2.  Protocol extensions for local protection . . . . . . . . .  8
   5.  Territorial protection using mLDP LSP  . . . . . . . . . . . .  9
     5.1.  Signaling Procedures for Territorial Protection  . . . . . 10
     5.2.  Protocol extensions for Territorial Protection . . . . . . 11
   6.  End-to-end protection using LDP Multiple Topology  . . . . . . 12
     6.1.  Signaling Procedures for End-to-end Protection . . . . . . 12
     6.2.  Protocol extensions for End-to-end Protection  . . . . . . 13
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   9.  Manageability Considerations . . . . . . . . . . . . . . . . . 13
     9.1.  Control of Function and Policy . . . . . . . . . . . . . . 13
     9.2.  Information and Data Models  . . . . . . . . . . . . . . . 13
     9.3.  Liveness Detection and Monitoring  . . . . . . . . . . . . 13
     9.4.  Verifying Correct Operation  . . . . . . . . . . . . . . . 13
     9.5.  Requirements on Other Protocols and Functional
           Component  . . . . . . . . . . . . . . . . . . . . . . . . 13
     9.6.  Impact on Network Operation  . . . . . . . . . . . . . . . 13
     9.7.  Policy Control . . . . . . . . . . . . . . . . . . . . . . 13
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 14
     11.2. Informative References . . . . . . . . . . . . . . . . . . 15



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   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15


















































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1.  Terminology

   For a clear narrative, this section gives a general conceptional
   overview of the terms.

   o  PLR: The node where the traffic is logically redirected onto the
      preset backup path is called Point of Local Repair.

   o  MP: The node where the backup path merges with the primary path is
      called Merge Point.

   o  FD: The node that detects the failure on primary path, and then
      triggers the action(s) for traffic protection is called Failure
      Detector.  Either traffic sender or receiver can be the FD,
      depending on which protection mode are deployed.  More details are
      described in later sections of this document.

   o  SP: The node where the traffic is physically switched/duplicated
      onto the backup path is called Switchover Point.  In multicast
      cases, PLR and SP can be two different nodes.  More details are
      described in later sections of this document.


2.  Requirement Language

   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 RFC 2119 [RFC2119].


3.  Introduction

   In order to meet user demands, operators and service providers
   continue to deploy multicast applications using mLDP across MPLS
   networks.  In certain scenarios, traditional IGP-mLDP convergence
   mechanisms fail to meet protection switching times required to
   minimise, or negate entirely, application interruptions for real-time
   applications, including stock trading, on-line games, and multimedia
   teleconferencing.

   Current best practice for protecting services, and higher
   applications includes the pre-computation and establishment of a
   backup path, this can decrease the convergence time efficiently.
   Once a failure has been detected on the primary path, the traffic
   should be transmitted across the back-up path.

   However, two major challenges exist with the aforementioned solution.
   The first is how to build an absolutely disjointed backup path for



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   each node in a multicast tree; the second is how to balance between
   convergence time and resource consumption.

   This document provides several ways to setup the backup path for mLDP
   LSP, including local protection, territorial protection, and end-to-
   end protection.  The goal is to build a reliable umbrella to against
   traffic black hole.  How to detect failure is outside the scope of
   this document.

   More and more users are apt to deploy multicast applications on MPLS
   mLDP network.  In some scenarios, traditional IGP-mLDP convergence is
   hard to meet the requirements of those real-time applications, such
   as stock business, on-line game, and multimedia teleconference.

   The industry has reached a consensus that setting up a backup path
   previously can decrease the convergence time efficiently.  No matter
   how the above-mentioned backup path was established, once the failure
   is detected, the traffic should be transmitted at that path as soon
   as possible.  Even so, there are still two major challenges left for
   us, one is how to build an absolutely disjointed backup path for each
   node in a multicast tree; the other is how to balance between
   convergence time and resource consumption.

   It is getting urgent to find the ideal protection mechanism(s) to
   improve the convergence time, and at the meantime minimize the side-
   effects, such as bandwidth wastage.

   For a primary LDP P2MP/MP2MP LSP, there are several ways to set up
   its backup path.  It can use RSVP-TE P2P tunnel as a logical out-
   going interface, consequently utilize the mature high availability
   technologies of RSVP-TE.  Or, it can make use of LDP P2P backup LSP
   as a packet encapsulation, so that the complex configuration of P2P
   RSVP-TE can be skipped.  Or, it can build its own P2MP/MP2MP backup
   LSP according to IGP's loop-free alternative route, thus avoid double
   label stack.  Other than these, it can also build a totally
   disjointed LSP in another topology, accordingly take advantage of the
   real end-to-end protection.

   When the backup path is present, there are two options for packet
   forwarding and switchover.  If the traffic sender feeds the stream on
   both paths, and the traffic receiver drops packet on backup path, the
   switchover will be very quick once the failure is detected, because
   the whole switchover action is a local behavior on traffic receiver.
   The disadvantage of this manner is that traffic will be duplicated on
   both paths, and consume double bandwidth.  Contrastively, if the
   traffic sender feeds stream only on the primary path, the resource
   wastage can be waived.  Cooperation is needed in this manner, so
   there will be some protocol extensions.  But if the performance can



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   be equal or better than the previous option, it is reasonable to
   choose the second one.

   This document describes several methods to setup and switch paths for
   options to setup the backup LDP P2MP/MP2MP LSP. mLDP LSPs, including
   local protection, territorial protection, and end-to-end protection.
   The goal is to identify strengths, weaknesses and gaps, in order to
   build a reliable set of tools to shield against traffic black holes
   that would severely impact real-time applications, in the event of
   primary path failure.

3.1.  Requirements

   A number of requirements have been identified that allow the optimal
   set of mechanisms to developed.  These currently include:

   o  Computation of a disjointed (link and node) backup path within the
      multicast tree;

   o  Minimisation of protection convergence time;

   o  Optimisation of bandwitdth usage.

3.2.  Scope

   The method to detect failure is outside the scope of this document.
   Also this document does not provide any authorization mechanism for
   controlling the set of LSRs that may attempt to join a mLDP
   protection session.


4.  Local protection using P2P LSP

   By encapsulating mLDP packets within an P2P TE tunnel or P2P LDP
   backup LSP, the LDP P2MP/MP2MP LSP can be protected by the P2P
   protection mechanisms.  However, this protection mechanism is not
   capable of detecting, and recovering, if the failure occurs on the
   destination node of the P2P backup LSP.  Thus, this section provides
   a unified method to protect both node and link with P2P backup LSP.












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                             +------------+ Point of Local Repair/
                             |     R1     | Switchover Point
                             +------------+ (Upstream LSR)
                                /       \
                               /         \
                            10/           \20
                             /             \
                            /               \
                           /                 \
                     +----------+        +-----------+
                     |    R2    |        |     R3    |
                     +----------+        +-----------+
                       |       \                  |
                       |        \                 |
                       |         \                |
                     10|        10\             20|
                       |           \              |
                       |            \             |
                       |             \            |
                       |              \           |
                       |               \          |
                       |                \         |
                     +-----------+  10  +-----------+ Merge Point
                     |    R4     |------|    R5     | (Downstream LSR)
                     +-----------+      +-----------+


                       mLDP Local Protection Example

                                 Figure 1

   In Figure 1 (mLDP Local Protection Example) above, the preferential
   path from R1 to R4/R5 is through R2, and the secondary path is
   through R3.  In this case, the mLDP LSP will be established according
   to the IGP preferential path as R1--R2--R4/R5.

   It is the responsibility of R2 to inform R1 of its downstream LSRs
   (in this example R4 and R5) and the respective labels (L4 and L5).
   Once the link between R1 and R2 fails, or R2 node fails, R1 will
   duplicate the traffic to R4 and R5, with inner label as L4/L5, and
   outer label as the P2P backup LSP R1--R3--R5--R4 and R1--R3--R5.

   Finally, the previous forwarding states will be removed after R4 and
   R5 finish their Make-Before-Break (MBB) procedure.







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4.1.  Signaling procedures for local protection

   Continuing to use Figure 1 (mLDP Local Protection Example), R2 sends
   a notification message to R1 to inform the node that R2 has two
   downstream nodes, R4 and R5 with forwarding labels L4 and L5
   respectively.

   When R1 sees R2 node going down, it takes mLDP packets as it would
   send them to R4 and R5 through R2 and sends them into the two P2P
   backup tunnels:

   o  P2P tunnel R1--R3--R5--R4, using inner label L4.

   o  P2P tunnel R1--R3--R5, using inner label L5.

   So that R4/R5 will receive same packets as from the interface between
   R2 and R4/R5, just from different interface.

   At the same time, R1 sends notifications with MBB request status code
   to R4 and R5.  So that after R4 and R5 are done with MBB, they will
   send the notifications to R3 with MBB done status code.  And then R3
   will remove the old forwarding state which is being protected by the
   P2P backup tunnels.

4.2.  Protocol extensions for local protection

   A new type of LDP MP Status Value Element is introduced, for
   notifying downstream LSRs and respective labels.  It is encoded as
   follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |mLDP P2P Type=2|      Length                   |   Reserved    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                   Downstream Element 1                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       ~                                                               ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                   Downstream Element N                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                    mLDP P2P Encapsulation Status Code

                                 Figure 2




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   The Downstream Element is encoded as follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                   Downstream Label    |                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                   Downstream LSR-ID                           |
       +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


         Downstream Element in mLDP P2P Encapsulation Status Code

                                 Figure 3


5.  Territorial protection using mLDP LSP

   Making use of IGP-FRR results, LDP can build the backup mLDP LSP for
   territorial protection.  Note that in some scenarios, such as the
   following example, Failure Detector and Point of Local Repair,
   Switchover Point and Merge Point can be different nodes.



























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                               +------------+ Point of Local Repair
                               |     R1     | (Upstream LSR)
                               +------------+
                                  /       \
                                 /         \
                                /           &
                               /             &
                              /               \
           Switchover Point \/_                \  Failure Detector
                   +----------+            +-----------+
                   |    R2    |            |     R3    |
                   +----------+            +-----------+
                       /     \                  /
                      /       \                /
                     /         \              /
                    /           \            /
                   /             \          /
                 \/_              \        /
           +----------+          +-----------+  Merge Point
           |    R4    |          |     R5    | (Downstream LSR)
           +----------+          +-----------+



                    mLDP Territorial Protection Example

                                 Figure 4

   In Figure 4 (mLDP Territorial Protection Example), normally R1 feeds
   traffic to R4 through R2, and feeds traffic to R5 through R3.  Once
   the link between R1 and R3 fails, R1 will be the logical Point of
   Local Repair node, which feeds the traffic to R5 through backup path
   on R2.  Because R2 is already receiving traffic, so that R1 does not
   need to take any action.  It is responsibility of R2 to duplicate the
   traffic to R5, as a Switchover Point.  In this case, as the Failure
   Detector, R3 will need to send out the notification to R2, in order
   to trigger the switchover procedure.

5.1.  Signaling Procedures for Territorial Protection

   Merge Point (R5) determines the primary and secondary paths according
   to the IGP-FRR results.  Then it sends out label mapping message
   including an LDP MP Status TLV that carries a FRR Status Code to
   indicate the primary path and secondary path.  At the same time, it
   triggers a reverse path for failure notification by sending out label
   request message with an LDP MP Status TLV.  The reverse path is
   uniquely identified by root address, opaque value, and MP address.




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   When failure is detected by Failure Detector (R3), it will send out
   the failure notification, then traffic will switch to the secondary
   path.

   When Merge Point (R5) sees the next hop to Root changed, it will
   advertise the new mapping, and the traffic will re-converge to the
   new primary path.

5.2.  Protocol extensions for Territorial Protection

   A new type of LDP MP Status Value Element is introduced, for setting
   up secondary mLDP LSP.  It is encoded as follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |mLDP FRR Type=3|      Length                   | Status code   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ~                    MP Node Address                            ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                           mLDP FRR Status Code

                                 Figure 5



   mLDP FRR Type:  Type 3 (to be assigned by IANA)

   Length:  If the Address Family is IPv4, the Address Length MUST be 5; if the Address
   Family is IPv6, the Address Length MUST be 17.

   Status code:  1 = Primary path for traffic forwarding (used in Label Mapping message)
                 2 = Secondary path for traffic forwarding (used in Label Mapping message)
                 3 = Reverse path for failure notification (used in Label Request message)
                 4 = Failure notification (used in Notification message)

   MP Node Address:  A host address encoded according to the Address Family of this LSP.


             mLDP Bandwidth Reservation Status Code Parameters

                                 Figure 6








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6.  End-to-end protection using LDP Multiple Topology

   [I-D.ietf-mpls-ldp-multi-topology] provides a mechanism to setup
   disjointed LSPs within different topologies.  So that applications
   can use these redundant LSPs for end-to-end protection.


                             +------------+ Point of Local Repair/
                             |    Root    | Switchover Point
                             +------------+
                                /       *
                               /         *
                              /           *
                             /             *
                            /               *
                           /                 *
                   +----------+            +-----------+
                   |    R1    |            |     R2    |
                   +----------+            +-----------+
                       |   \                   *  *
                       |    \                 *   *
                       |     \               *    *
                       |      \             *     *
                       |       - - - * * * *      *
                       |           *  \           *
                       |          *    \          *
                       |         *      \         *
                       |        *        \        *
                       |       *          \       *
                     +-----------+      +-----------+
                     |  Leaf 1   |      |  Leaf 2   |
                     +-----------+      +-----------+


                    mLDP End-to-end Protection Example

                                 Figure 7

   In Figure 7 (mLDP End-to-end Protection Example), there are two
   separated topologies from Root node to Leaf 1 and Leaf 2.  For the
   same FEC element, the Leaf node can trigger mLDP LSPs in each
   topology.  Root node can setup 1:1 or 1+1 end-to-end protection,
   using these two mLDP LSPs.

6.1.  Signaling Procedures for End-to-end Protection

   Using Figure 7 (mLDP Local Protection Example), Leaf 1 and Leaf 2 may
   trigger mLDP LSPs in different topologies, sending label mapping



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   messages with same FEC element, different MT-ID and different label.
   When the Root node receives the label mapping messages from different
   topologies, it will set up two mLDP LSPs for application as end-to-
   end protection.  Failure detection for the primary mLDP LSP is
   outside the scope of this document.  But either Root node or Leaf
   node can be the Failure Detector.

6.2.  Protocol extensions for End-to-end Protection

   The protocol extensions required to build mLDP LSPs in different
   topologies is defined in [I-D.ietf-mpls-ldp-multi-topology].


7.  Acknowledgements

   We would like to thank authors of draft-ietf-mpls-mp-ldp-reqs and the
   authors of draft-ietf-mpls-ldp-multi-topology from which some text of
   this document has been inspired.


8.  IANA Considerations

   This memo includes the following requests to IANA:

   o  mLDP P2P Encapsulation type for LDP MP Status Value Element.

   o  mLDP FRR type for LDP MP Status Value Element.


9.  Manageability Considerations

   [Editors Note - This section requires further discussion]

9.1.  Control of Function and Policy

9.2.  Information and Data Models

9.3.  Liveness Detection and Monitoring

9.4.  Verifying Correct Operation

9.5.  Requirements on Other Protocols and Functional Component

9.6.  Impact on Network Operation

9.7.  Policy Control





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10.  Security Considerations

   The same security considerations apply as for the base LDP
   specification, as described in [RFC5036].  The protocol extensions
   specified in this document do not provide any authorization mechanism
   for controlling the set of LSRs that may attempt to join a mLDP
   protection session.  If such authorization is desirable, additional
   mechanisms, outside the scope of this document, are needed.

   Note that authorization policies should be implemented and/or
   configure at all the nodes involved .


11.  References

11.1.  Normative References

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

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031, January 2001.

   [RFC5036]  Andersson, L., Minei, I., and B. Thomas, "LDP
              Specification", RFC 5036, October 2007.

   [RFC5561]  Thomas, B., Raza, K., Aggarwal, S., Aggarwal, R., and JL.
              Le Roux, "LDP Capabilities", RFC 5561, July 2009.

   [RFC6348]  Le Roux, JL. and T. Morin, "Requirements for Point-to-
              Multipoint Extensions to the Label Distribution Protocol",
              RFC 6348, September 2011.

   [I-D.ietf-mpls-ldp-p2mp]
              Minei, I., Wijnands, I., Kompella, K., and B. Thomas,
              "Label Distribution Protocol Extensions for Point-to-
              Multipoint and Multipoint-to-Multipoint Label Switched
              Paths", draft-ietf-mpls-ldp-p2mp-15 (work in progress),
              August 2011.

   [I-D.ietf-mpls-ldp-multi-topology]
              Zhao, Q., Fang, L., Zhou, C., Li, L., So, N., and R.
              Torvi, "LDP Extension for Multi Topology Support",
              draft-ietf-mpls-ldp-multi-topology-00 (work in progress),
              October 2011.






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11.2.  Informative References

   [RFC3468]  Andersson, L. and G. Swallow, "The Multiprotocol Label
              Switching (MPLS) Working Group decision on MPLS signaling
              protocols", RFC 3468, February 2003.


Authors' Addresses

   Quintin Zhao
   Huawei Technology
   125 Nagog Technology Park
   Acton, MA  01719
   US

   Email: quintin.zhao@huawei.com


   Emily Chen
   Huawei Technology
   2330 Central Expressway
   Santa Clara, CA  95050
   US

   Email: emily.chenying@huawei.com


























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