Network Working Group                                           A. Karan
Internet-Draft                                               C. Filsfils
Intended status: Informational                              D. Farinacci                       Cisco Systems, Inc.
Expires: July 21, November 15, 2014                                  D. Farinacci
                                                             lispers.net
                                                       IJ. Wijnands, Ed.
                                                     Cisco Systems, Inc.
                                                             B. Decraene
                                                          France Telecom
                                                                  Orange
                                                               U. Joorde
                                                        Deutsche Telekom
                                                           W. Henderickx
                                                          Alcatel-Lucent
                                                        January 17,
                                                            May 14, 2014

                      Multicast only Fast Re-Route
                       draft-ietf-rtgwg-mofrr-03
                       draft-ietf-rtgwg-mofrr-04

Abstract

   As IPTV deployments grow in number and size, service providers are
   looking for solutions that minimize the service disruption due to
   faults in the IP network carrying the packets for these services.
   This draft describes a mechanism for minimizing packet loss in a
   network when node or link failures occur.  Multicast only Fast Re-
   Route (MoFRR) works by making simple enhancements to multicast
   routing protocols such as PIM and mLDP.

Status of this This Memo

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   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on July 21, November 15, 2014.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3   2
     1.1.  Conventions used in this document . . . . . . . . . . . .   3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Basic Overview  . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Upstream Multicast Hop Selection . .  Determination of the secondary UMH  . . . . . . . . . . . . .  4   5
     3.1.  PIM  ECMP-mode MoFRR . . . . . . . . . . . . . . . . . . . . .   5
     3.2.  Non-ECMP-mode MoFRR . . . . . .  4
     3.2.  mLDP . . . . . . . . . . . . .   5
   4.  Upstream Multicast Hop Selection  . . . . . . . . . . . . . .   5
   4.  Topologies for MoFRR
     4.1.  PIM . . . . . . . . . . . . . . . . . . . . . .  5
     4.1.  Dual-Plane Topology . . . . .   6
     4.2.  mLDP  . . . . . . . . . . . . . .  5 . . . . . . . . . . . .   6
   5.  Detecting Failures  . . . . . . . . . . . . . . . . . . . . . .  8   6
   6.  ECMP-mode  MoFRR applicability . . . . . . . . . . . . . . . . . . . . .   7
     6.1.  Dual-Plane Topology . .  9
   7.  Non-ECMP-mode MoFRR  . . . . . . . . . . . . . . . . . .   7
     6.2.  Capacity Planning for MoFRR . . .  9
   8.  Keep It Simple Principle . . . . . . . . . . . .  10
     6.3.  PE nodes  . . . . . . . 10
   9.  Capacity Planning for MoFRR . . . . . . . . . . . . . . . . .  11
   10.
     6.4.  Other Applications  . . . . . . . . . . . . . . . . . . .  11
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   11.
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   12.
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  12
   13.
   10. Contributor Addresses . . . . . . . . . . . . . . . . . . . .  12
   14.
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . . .  12
     14.1.
     11.1.  Normative References . . . . . . . . . . . . . . . . . . .  12
     14.2.
     11.2.  Informative References . . . . . . . . . . . . . . . . . . 13  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   Multiple techniques

   Different solutions have been developed and deployed to improve
   service guarantees, both for multicast video traffic and Video on
   Demand traffic.  Most existing of these solutions are geared towards finding
   an alternate path around one or more failed network elements (link,
   node, path failures).

   This draft describes a mechanism for minimizing packet loss in a
   network when node or link failures occur.  Multicast only Fast Re-
   Route (MoFRR) works by making simple changes to the way selected
   routers use multicast protocols such as PIM and mLDP.  No changes to
   the protocols themselves are required.  With MoFRR, in many cases,
   multicast routing protocols don't necessarily have to depend on or
   have to wait on unicast routing protocols to detect network failures. failures,
   see Section 5

   On a merge point Merge Point MoFRR logic determines a primary Upstream Multicast
   Hop (UMH) and a secondary UMH and joins the tree via both
   simultaneously.  Data packets are received over the primary and
   secondary paths.  Only the packets from the primary UMH are accepted
   and forwarded down the tree, the packets from the secondary UMH are
   discarded.  The UMH determination is different for PIM and mLDP and
   explained later in this document. Section 4.  When a failure is detected on the path to
   the primary UMH, the repair occurs by changing the secondary UMH into
   the primary and the primary into the secondary.  Since the repair is
   local, it is fast - greatly improving convergence times in the event
   of node or link failures on the path to the primary UMH.

1.1.  Conventions used in this document

   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].

1.2.  Terminology

   MoFRR :

   MoFRR:  Multicast only Fast Re-Route.

   ECMP :

   ECMP:  Equal Cost Multi-Path.

   mLDP :

   mLDP:  Multi-point Label Distribution Protocol.

   PIM :

   PIM:  Protocol Independent Multicast.

   UMH :

   UMH:  Upstream Multicast Hop, a candidate next-hop that can be used
      to reach the root of the tree.

   tree :

   tree:  Either a PIM (S,G)/(*,G) tree or a mLDP P2MP or MP2MP LSP.

   OIF :

   OIF:  Outgoing InterFace, an interface used to forward multicast
      packets down the tree towards the receivers.  Either a PIM
      (S,G)/(*,G) (S,G)/
      (*,G) tree or a mLDP P2MP or MP2MP LSP.

   LFA :

   LFA:  Loop Free Alternate, a candidate UMH that Alternate as defined in [RFC5286].  In unicast Fast
      ReRoute, this is an alternate next-hop which can be used for to reach
      a unicast destination without using the
      secondary MoFRR path. protected link or node.

   Merge Point:  A router that joins a multicast stream via two
      divergent upstream paths.

   RPF:  Reverse Path Forwarding.

   RP:  Rendezvous Point.

   LSR:  Label Switched Router.

   BFD:  Bidirectional Forwarding Detection.

   IGP:  Interior Gateway Protocol.

   MVPN:  Multicast Virtual Private Networks.

2.  Basic Overview

   The basic idea of MoFRR is for a merge point Merge Point router to join a
   multicast tree via two divergent upstream paths in order to get
   maximum redundancy.  The determination of this alternate upstream is
   defined in Section 3.

   In order to maximize robustness against any failure, the two divergent paths SHOULD never
   should be as diverse as possible.  Ideally, they should not merge
   upstream, otherwise the maximal redundancy is compromised.
   upstream.  Sometimes the topology guarantees maximal redundancy,
   other times additional configuration or techniques are needed to
   enforce it.  See later in
   this document. Section 6 for more discussion on the applicability
   of MoFRR depending on the network topology.

   A merge point Merge Point router should only accept and forward on one of the
   upstream paths at the a time in order to avoid duplicate packet
   forwarding.  The selection of the primary and secondary UMH is done
   by the MoFRR logic and normally based on unicast routing to find loop
   free candidates.  This is described in Section 4.

   Note, the impact of additional amount of data on the network is
   mitigated when tree membership is densely populated.  When a part of
   the network has redundant data flowing, join latency for new joining
   members is reduced because its likely a tree merge point Merge Point is not far
   away.

3.  Upstream Multicast Hop Selection

   An Upstream Multicast Hop (UMH) is a candidate next-hop that can be
   used to reach the root  Determination of the tree.  This is normally based on
   unicast routing to find loop free candidate(s).  With MoFRR
   procedures we select a primary and a backup UMH.  The procedures for
   determining the secondary UMH are different for PIM and mLDP.  See below;

3.1.  PIM

   The secondary UMH selection in PIM is also known a Loop Free Alternate (LFA) as per [RFC5286].

3.1.  ECMP-mode MoFRR

   If the Reverse Path Forwarding
   (RPF) procedure.  Based on IGP installs two ECMP paths to the source, then as per
   [RFC5286] the LFA is a unicast route lookup on either primary Next-hop.  If the
   Source address or Rendezvous Point (RP) [RFC4601], an upstream
   interface Multicast tree is selected
   enabled for sending the PIM Joins/Prunes AND accepting ECMP-Mode MoFRR, the multicast packets.  The interface router installs them as primary and
   secondary UMH.  Before the failure, only packets are received on is
   used to pass or fail from the RPF check.  If packets
   primary UMH path are processed while packets received on an
   interface that was not selected by the RPF procedure, or not the
   primary, from the packets
   secondary UMH are discarded.

3.2.  mLDP dropped.

   The selected primary UMH selection in mLDP also depends on unicast routing, but SHOULD be the
   difference with PIM is that same as if the acceptance of multicast packets MoFRR extension
   was not enabled.

   If more than two ECMP paths exist, one is
   based on MPLS labels selected as primary and independent on the interface
   another one as secondary UMH.  The selection of the packet primary and
   secondary is
   received on.  Using a local decision.  Information from the procedures as defined in [RFC6388] an
   upstream Label Switched Router (LSR) is elected.  The upstream LSR IGP link-state
   topology could be leveraged to optimize this selection such that was elected for a Label Switched Path (LSP) gets a unique local
   MPLS Label allocated.  Multicast packets are only forwarded if the
   MPLS label matches
   primary and secondary path are maximal divergent and don't lead to
   the MPLS label that was allocated for that LSPs
   (primary) same upstream LSR.

4.  Topologies for MoFRR node.  Note that MoFRR works best in topologies illustrated in does not restrict the figure below.
   MoFRR number
   of UMH paths that are joined.  Implementations may be enabled on any use as many paths
   as are configured.

3.2.  Non-ECMP-mode MoFRR

   A router in the network.  In the figures
   below, configured for non-ECMP-mode MoFRR is shown enabled on the Provider Edge (PE) routers to
   illustrate one way in which the technology may be deployed.

4.1.  Dual-Plane Topology
                         S
                   P    / \ P
                       /   \
                ^    G1     R1  ^
                P    /       \  P
                    /         \
                   G2----------R2   ^
                   | \         | \  P
               ^   |  \        |  \
               P   |   G3----------R3
                   |    |      |    |
                   |    |      |    | ^
                   G4---|------R4   | P
                 ^   \  |        \  |
                 P    \ |         \ |
                       G5----------R5
                   ^   |           | ^
                   P   |           | P
                       |           |
                      Gi           Ri
                       \ \__    ^  /|
                        \   \   S1/ | ^
                       ^ \  ^\   /  |P2
                       P1 \ S2\_/__ |
                           \   /   \|
                            PE1     PE2
   P = Primary path
   S = Secondary path

         FIG1. Two-Plane Network Design

   The topology has two planes, for a Multicast tree
   joins a primary plane path to its primary UMH and a secondary plane
   that are fully disjoint from each other all the way into the POPs.
   This two plane design is common in service provider networks as it
   eliminates single point of failures in their core network.  The links
   marked PJ indicate the normal path of how to LFA
   UMH.  In order to prevent control-plane loops a router MUST stop
   joining the PIM joins flow from secondary UMH if this UMH is the
   POPs towards only member in the source of OIF
   list.

   To illustrate the network.  Multicast streams,
   especially reason for this rule, let's consider the densely watched channels, typically flow along
   both the planes example in
   FIG3.  If PE1 and PE2 have received an IGMP request for a Multicast
   tree, they will both join the network anyways.

   The only change MoFRR adds to this is primary path on the links marked S where the
   PE routers join their plane and a
   secondary path to the neighbor PE.  If their secondary ECMP UMH.  As a
   result of this, each PE router receives two copies of receivers would leave at
   the same
   stream, one from time, it could be possible for the primary plane Multicast tree on PE1 and the
   PE2 to never get deleted as each PE refresh each other from via the
   secondary
   plane.  As path joins (remember that a result secondary path join is not
   distinguishable from a primary join).

4.  Upstream Multicast Hop Selection

   An Upstream Multicast Hop (UMH) is a candidate next-hop that can be
   used to reach the root of normal the tree.  This is normally based on
   unicast routing to find loop free candidate(s).  With MoFRR
   procedures we select a primary and a backup UMH.  The procedures for
   determining the UMH behavior, are different for PIM and mLDP.  See below;

4.1.  PIM

   The UMH selection in PIM is also known as the multicast stream
   received over Reverse Path Forwarding
   (RPF) procedure.  Based on a unicast route lookup on either the
   Source address or Rendezvous Point (RP) [RFC4601], an upstream
   interface is selected for sending the primary path is accepted and forwarded to PIM Joins/Prunes AND accepting
   the
   downstream receivers. multicast packets.  The copy of interface the stream packets are received from the
   secondary UNH is discarded.

   When a router detects a routing failure on the path to its its
   primary UMH, it will switch is
   used to pass or fail the secondary UMH and accept RPF check.  If packets
   for are received on an
   interface that stream.  If was not selected by the failure is repaired RPF procedure, or not the router may switch
   back.
   primary, the packets are discarded.

4.2.  mLDP

   The primary and secondary UMHs have only local context and not
   end-to-end context.

   As one can see, MoFRR achieves UMH selection in mLDP also depends on unicast routing, but the faster convergence by pre-building
   difference with PIM is that the secondary acceptance of multicast tree packets is
   based on MPLS labels and receiving independent of the traffic on that
   secondary path.  The example discussed above interface the packet is
   received on.  Using the procedures as defined in [RFC6388] an
   upstream Label Switched Router (LSR) is elected.  The upstream LSR
   that was elected for a simple case where
   there Label Switched Path (LSP) gets a unique local
   MPLS Label allocated.  Multicast packets are two ECMP paths from each PE device towards only forwarded if the source, one
   along
   MPLS label matches the primary plane and one along MPLS label that was allocated for that LSPs
   (primary) upstream LSR.

5.  Detecting Failures

   Once the secondary.  In cases where two paths are established, the topology is asymmetric or next step is detecting a ring, this ECMP nature does not
   hold, and additional rules have to be taken into account
   failure on the primary path to choose know when and where to join switch to the secondary backup
   path.

   MoFRR  This is appealing in such topologies for a local issue but this section explore some
   possibilities.

   The first (and simplest) option is to detect the following reasons:

   1.  Ease failure of deployment and simplicity: the functionality is only
       required on the PE devices although local
   interface as it may be configured on all
       routers in the topology.  Furthermore, each PE device it's done for unicast Fast ReRoute.  Detection can be
       enabled separately.  PEs not enabled for MoFRR do not see any
       change or degradation.  Inter-operability testing is not required
       as there are no PIM or mLDP protocol change.

   2.  End-to-end failure detection and recovery: any failure along the
       path from
   performed using the source to loss of signal or the PE loss of probing packets
   (e.g.  BFD).  This option can be detected and repaired used in combination with the secondary disjoint stream.

   3.  Capacity Efficiency: other
   options as illustrated in the previous example, documented below.  Just like for unicast fast reroute,
   50msec switch-over is possible.

   A second option consists of comparing the
       Multicast trees corresponding to IPTV channels cover packets received on the backbone
   primary and distribution topology in a very dense manner.  As a
       consequence, the secondary path graft into the normal Multicast
       trees (ie. trees signaled by PIM or mLDP without MoFRR extension)
       at the aggregation level and hence do not demand any extra
       capacity either on the distribution links or in the backbone.
       They simply use the capacity that is normally used, without any
       duplication.  This is different from conventional FRR mechanisms
       which often duplicate streams but only forwarding one of them -- the capacity requirements (the backup path
       crosses links/nodes
   first one received, no matter which already carry the primary/normal tree
       and hence twice as much capacity interface it is required).

   4.  Loop free: the secondary path join received on.
   Zero packet loss is sent possible for RTP-based streams.

   A third option assumes a minimum known packet rate for a given data
   stream.  If a packet is not received on an ECMP disjoint
       path.  By definition, the neighbor receiving primary RPF within this request is
       closer to
   time frame, the source and hence will not cause a loop.

   The topology we just analyzed is very frequent router assumes primary path failure and can be modeled as
   per Fig2.  The PE has two ECMP disjoint paths switches to
   the source.  Each
   ECMP path uses secondary RPF interface. 50msec switch-over may be possible for
   high rate stream (e.g. IP TV where SD video has a disjoint plane continuous inter-
   packet gap of ~ 3msec) but in general the network.

                            Source
                            /    \
                        Plane1  Plane2
                           |      |
                           A1    A2
                             \  /
                              PE

           FIG2. PE delay is dual-homed dependant on the
   rate of the multicast stream.

   A fourth option leverages the significant improvements of the IGP
   convergence speed.  When the primary path to Dual-Plane Backbone

   Another frequent topology the source is described in Fig 3.  PEs are grouped withdrawn
   by
   pairs.  In each pair, each PE is connected the IGP, the MoFRR-enabled router switches over to a different plane.
   Each PE has one single shortest-path the backup
   path, the UMH is changed to a source (via its connected
   plane).  There the secondary UMH.  Since the secondary
   path is no ECMP like already in Fig 2.  However, there place, and assuming it is clearly a
   way disjoint from the
   primary path, convergence times would not include the time required
   to provide MoFRR benefits as each PE can offer build a disjoint
   secondary path new tree and hence are smaller.  Sub-second to sub-200msec
   switch-over should be possible.

6.  MoFRR applicability

   MoFRR applicability is topology dependent.  The applicability is the other plane PE (via the disjoint path).
   same as LFA FRR which is discussed in [RFC6571].

   The following section will discuss MoFRR secondary neighbor selection process needs applicability to be extended dual-plane
   network topologies.

6.1.  Dual-Plane Topology

   MoFRR works best in
   this case dual-planes topologies as one cannot simply rely illustrated in the
   figures below.  MoFRR may be enabled on using an ECMP path as
   secondary neighbor.  This extension any router in the network.
   In the figures below, MoFRR is referred shown enabled on the Provider Edge
   (PE) routers to as non-ecmp
   extension and is described later illustrate one way in which the document.

                                Source technology may be
   deployed.

                         S
                   P    / \
                            Plane1  Plane2 P
                       /   \
                ^    G1     R1  ^
                P    /       \  P
                    /         \
                   G2----------R2   ^
                   | \         |
                               A1    A2 \  P
               ^   |  \        |
                              PE1----PE2

           FIG3. PEs are connected in pairs to Dual-Plane Backbone

5.  Detecting Failures

   Once the two paths are established, the next step is detecting a
   failure on the primary  \
               P   |   G3----------R3
                   |    |      |    |
                   |    |      |    | ^
                   G4---|------R4   | P
                 ^   \  |        \  |
                 P    \ |         \ |
                       G5----------R5
                   ^   |           | ^
                   P   |           | P
                       |           |
                      Gi           Ri
                       \ \__    ^  /|
                        \   \   S1/ | ^
                       ^ \  ^\   /  |P2
                       P1 \ S2\_/__ |
                           \   /   \|
                            PE1     PE2
   P = Primary path to know when to switch to the backup
   path.
   S = Secondary path

         FIG1. Two-Plane Network Design

   The first (and simplest) option to detect topology has two planes, a path failure is if primary plane and a
   directly connected link secondary plane
   that are fully disjoint from each other all the way into the POPs.
   This two plane design is used common in service provider networks as MoFRR UMH goes down.  This
   option can be used it
   eliminates single point of failures in combination with their core network.  The links
   marked P indicate the other options as
   documented below. 50msec switchover is possible.

   A second option consists normal path of comparing how the packets received on PIM joins flow from the
   primary and secondary streams but only forwarding one
   POPs towards the source of them -- the
   first one received, no matter which interface it is received on.
   Zero packet loss is possible for RTP-based streams.

   A third option assumes a minimum known packet rate network.  Multicast streams,
   especially for a given data
   stream.  If a packet the densely watched channels, typically flow along
   both the planes in the network anyway.

   The only change MoFRR adds to this is not received on the primary RPF within this
   time frame, links marked S where the router assumes primary
   PE routers join a secondary path failure and switches to
   the their secondary RPF interface. 50msec switchover is possible.

   A fourth option leverages the significant improvements ECMP UMH.  As a
   result of this, each PE router receives two copies of the IGP
   convergence speed.  When same
   stream, one from the primary path to the source is withdrawn
   by the IGP, the MoFRR-enabled router switches over to plane and the backup
   path, other from the secondary
   plane.  As a result of normal UMH is changed to behavior, the secondary UMH.  Since multicast stream
   received over the secondary primary path is already in place, accepted and assuming it is disjoint from forwarded to the
   primary path, convergence times would not include
   downstream receivers.  The copy of the time required
   to build stream received from the
   secondary UNH is discarded.

   When a new tree and hence are smaller.  Realistic availability
   requirements (sub-second to sub-200msec) should be possible.

6.  ECMP-mode MoFRR

   If router detects a routing failure on the IGP installs two ECMP paths path to its primary
   UMH, it will switch to the source secondary UMH and if accept packets for that
   stream.  If the Multicast
   tree failure is enabled for ECMP-Mode MoFRR, repaired the router installs them as may switch back.  The
   primary and secondary UMH.  Only packets received from UMHs have only local context and not end-to-end
   context.

   As one can see, MoFRR achieves the primary
   UMH path are processed.  Packets received from faster convergence by pre-building
   the secondary UMH are
   dropped.

   The selected primary UMH should be multicast tree and receiving the same as if MoFRR extension was
   not enabled.

   If more than traffic on that
   secondary path.  The example discussed above is a simple case where
   there are two ECMP paths exist, two are selected as from each PE device towards the source, one
   along the primary plane and
   secondary UMH.  Information from one along the secondary.  In cases where
   the IGP link-state topology could be
   leveraged to optimize is asymmetric or is a ring, this selection.

   Note, MoFRR ECMP nature does not restrict the number of UMH paths that are
   joined.  Implementations may use as many paths as are configured.

7.  Non-ECMP-mode MoFRR
                    SourceS
                    /    \
                   /      \
                   Backbone
                  |        |
                  |        |
                  |        |
                  X--------N

           Fig5. Non-ECMP-Mode
   hold, and additional rules have to be taken into account to choose
   when and where to join the secondary path.

   MoFRR

   X is configured for MoFRR appealing in such topologies for a Multicast tree
   R(X) is the primary UMH to S for X
   N is a neighbor following reasons:

   1.  Ease of X
   R(N) deployment and simplicity: the functionality is only
       required on the LFA UMH to S for X

   Router X PE devices although it may be configured on all
       routers in FIG5 has one primary path R(X) and one secondary LFA path
   R(N) to reach the source.  How it is determined that N topology.  Furthermore, each PE device can be
       enabled separately, there is no need for a LFA network wide
       coordination in order to deploy MoFRR.  Inter-operability testing
       is not required as there are no PIM or mLDP protocol change.

   2.  End-to-end failure detection and recovery: any failure along the
       path from X the source to S follows the procedures PE can be detected and repaired with
       the secondary disjoint stream.(see Section 5 options 2, 3, 4)

   3.  Capacity Efficiency: as documented illustrated in [RFC5286].  A
   router X configured for non-ECMP-mode MoFRR for a the previous example, the
       Multicast tree
   joins a primary path trees corresponding to its primary UMH R(X) IPTV channels cover the backbone
       and distribution topology in a very dense manner.  As a
       consequence, the secondary path to
   LFA UMH N. Router X MUST stop joining graft into the seconday path if normal Multicast
       trees (ie. trees signaled by PIM or mLDP without MoFRR extension)
       at the
   following as described below occurs;

   Consider aggregation level and hence do not demand any extra
       capacity either on the example distribution links or in FIG3, if PE1 and PE2 have received an igmp
   request for a Multicast tree, they will both join the primary backbone.
       They simply use the capacity that is normally used, without any
       duplication.  This is different from conventional multicast FRR
       mechanisms which often duplicate the capacity requirements when
       the backup path on
   their plane crosses links/nodes which already carry the
       primary/normal tree and a hence twice as much capacity is required.

   4.  Loop free: the secondary path to join is sent on an ECMP disjoint
       path.  By definition, the neighbor PE.  If their
   receivers would leave at the same time, it could be possible for receiving this request is
       closer to the
   Multicast tree on PE1 source and PE2 to never get deleted hence will not cause a loop.

   The topology we just analyzed is very frequent and can be modelled as each
   per Fig2.  The PE refresh
   each other via has two ECMP disjoint paths to the secondary source.  Each
   ECMP path joins (remember that uses a secondary
   path join disjoint plane of the network.

                            Source
                            /    \
                        Plane1  Plane2
                           |      |
                           A1    A2
                             \  /
                              PE

           FIG2. PE is not distinguishable from a primary join). dual-homed to Dual-Plane Backbone

   Another frequent topology is described in Fig 3.  PEs are grouped by
   pairs.  In order each pair, each PE is connected to
   prevent control-plane loops a router MUST never setup a secondary
   path different plane.
   Each PE has one single shortest-path to a LFA UMH if this UMH source (via its connected
   plane).  There is the only member no ECMP like in the OIF list.

8.  Keep It Simple Principle

   Many Service Providers devise their topology such that PEs have
   disjoint paths to the multicast sources.  MoFRR leverages the
   existence of these disjoint paths without any PIM or mLDP protocol
   modification.  Interoperability testing Fig 2.  However, there is thus not required.  In
   such topologies, clearly a
   way to provide MoFRR only needs benefits as each PE can offer a disjoint
   secondary path to be deployed on the other plane PE devices.
   Each PE device can (via the disjoint path).

   MoFRR secondary neighbor selection process needs to be enabled extended in
   this case as one by one.  PEs not enabled for MoFRR
   do not see any change or degradation.

   Multicast streams with Tight SLA requirements are often characterized
   by a continuous high packet rate (SD video has a continuous
   interpacket gap of ~ 3msec).  MoFRR cannot simply leverages the stream
   characteristic to detect any failures along the primary branch and
   switch-over rely on the using an ECMP path as
   secondary branch neighbor.  This extension is referred to as non-ecmp
   extension and is described in a few 10s of msec.

9. Section 3.2.

                                Source
                                /    \
                            Plane1  Plane2
                               |      |
                               A1    A2
                               |      |
                              PE1----PE2

           FIG3. PEs are connected in pairs to Dual-Plane Backbone

6.2.  Capacity Planning for MoFRR

   As for LFA FRR (draft-ietf-rtgwg-lfa-applicability-00), MoFRR
   applicability is topology dependent.

   In this document, we have

   The previous section has described two very frequent designs (Fig 2
   and Fig 3) which provide maximum MoFRR benefits.

   Designers with topologies different than Fig2 and 3 can still benefit
   from MoFRR benefits thanks to the use of capacity planning tools.

   Such tools are able to simulate the ability of each PE to build two
   disjoint branches of the same tree.  This for hundreds of PEs and
   hundreds of sources.

   This allows to assess the MoFRR protection coverage of a given
   network, for a set of sources.

   If the protection coverage is deemed insufficient, the designer can
   use such tool to optimize the topology (add links, change igp IGP
   metrics).

10.

6.3.  PE nodes

   Many Service Providers devise their topology such that PEs have
   disjoint paths to the multicast sources.  MoFRR leverages the
   existence of these disjoint paths without any PIM or mLDP protocol
   modification.  Interoperability testing is thus not required.  In
   such topologies, MoFRR only needs to be deployed on the PE devices.
   Each PE device can be enabled one by one.

6.4.  Other Applications

   While all the examples in this document show the MoFRR applicability
   on PE devices, it is clear that MoFRR could be enabled on aggregation
   or core routers.

   MoFRR can be popular in Data Center network configurations.  With the
   advent of lower cost ethernet and increasing port density in routers,
   there is more meshed connectivity than ever before.  When using a
   3-level access, distribution, and core layers in a Data Center, there
   is a lot of inexpensive bandwidth connecting the layers.  This will
   lend itself to more opportunities for ECMP paths at multiple layers.
   This allows for multiple layers of redundancy protecting link and
   node failure at each layer with minimal redundancy cost.

   Redundancy costs are reduced because only one packet is forwarded at
   every link along the primary and secondary data paths so there is no
   duplication of data on any link thereby providing make-before-break
   protection at a very small cost.

   Alternate methods to detect failures such as MPLS-OAM or BFD may be
   considered.

   The MoFRR principle may be applied to MVPNs.

11.

7.  IANA Considerations

   This document makes no request of IANA.

8.  Security Considerations

   There are no security considerations for this design other than what
   is already in the main PIM specification [RFC4601] and mLDP
   specification [RFC6388] .

12. [RFC6388].

9.  Acknowledgments

   The authors would like to thank John Zwiebel, Greg Shepherd and Shepherd, Dave
   Oran and Alvaro Retana for their review of the draft.

13.

10.  Contributor Addresses

   Below is a list of other contributing authors in alphabetical order:

   Nicolai Leymann
   Deutsche Telekom
   Winterfeldtstrasse 21
   Berlin  10781
   DE
   Email: N.Leymann@telekom.de

   Jeff Tantsura
   Ericsson
   300 Holger Way
   San Jose CA 95134
   USA

14.

11.  References

14.1.

11.1.  Normative References

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

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

   [RFC5286]  Atlas, A. and A. Zinin, "Basic Specification for IP Fast
              Reroute: Loop-Free Alternates", RFC 5286, September 2008.

14.2.

11.2.  Informative References

   [RFC4601]  Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
              "Protocol Independent Multicast - Sparse Mode (PIM-SM):
              Protocol Specification (Revised)", RFC 4601, August 2006.

   [RFC6388]  Wijnands, IJ., Minei, I., Kompella, K., and B. Thomas,
              "Label Distribution Protocol Extensions for Point-to-
              Multipoint and Multipoint-to-Multipoint Label Switched
              Paths", RFC 6388, November 2011.

   [RFC6571]  Filsfils, C., Francois, P., Shand, M., Decraene, B.,
              Uttaro, J., Leymann, N., and M. Horneffer, "Loop-Free
              Alternate (LFA) Applicability in Service Provider (SP)
              Networks", RFC 6571, June 2012.

Authors' Addresses

   Apoorva Karan
   Cisco Systems, Inc.
   3750 Cisco Way
   San Jose  CA, 95134
   USA

   Email: apoorva@cisco.com

   Clarence Filsfils
   Cisco Systems, Inc.
   De kleetlaan 6a
   Diegem  BRABANT 1831
   Belgium

   Email: cfilsfil@cisco.com

   Dino Farinacci
   Cisco Systems, Inc.
   425 East Tasman Drive
   San Jose  CA, 95134
   lispers.net
   USA

   Email: dino@cisco.com farinacci@gmail.com

   IJsbrand Wijnands (editor)
   Cisco Systems, Inc.
   De Kleetlaan 6a
   Diegem  1831
   BE

   Email: ice@cisco.com

   Bruno Decraene
   France Telecom
   Orange
   38-40 rue du General Leclerc
   Issy Moulineaux  cedex  Cedex 9, 92794
   FR

   Email: bruno.decraene@orange.com
   Uwe Joorde
   Deutsche Telekom
   Hammer Str. 216-226
   Muenster  D-48153
   DE

   Email: Uwe.Joorde@telekom.de

   Wim Henderickx
   Alcatel-Lucent
   Copernicuslaan 50
   Antwerp  2018
   Belgium

   Email: wim.henderickx@alcatel-lucent.com