Network Working Group                                             L. Jin
Internet-Draft
Intended status: Standards Track                               F. Jounay
Expires: October 20, 2013 April 14, 2014                                   France Telecom
                                                             I. Wijnands
                                                           Cisco Systems, Inc Systems
                                                              N. Leymann
                                                        Deutsche Telekom AG
                                                          April 18,
                                                        October 11, 2013

     LDP Extensions for Hub & Spoke Multipoint Label Switched Path
                    draft-ietf-mpls-mldp-hsmp-01.txt
                    draft-ietf-mpls-mldp-hsmp-02.txt

Abstract

   This draft introduces a hub & spoke multipoint LSP (short for (or HSMP
   LSP), LSP for
   short), which allows traffic both from root to leaf through P2MP LSP
   and also leaf to root along the co-routed reverse path.  That means
   traffic entering the HSMP LSP from application/customer at the root
   node travels downstream, downstream to each leaf node, exactly as if it was traveling is
   travelling downstream along a P2MP LSP to each leaf node, and node.  Upstream
   traffic entering the HSMP LSP at any leaf node travels upstream along
   the tree to the root root, as if it is unicast to the root, except that it and strictly
   follows the downstream path of the tree rather than ordinary routing protocol
   based unicast path to the root.

Requirements 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 RFC2119 [RFC2119].

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."
   This Internet-Draft will expire on October 20, 2013. April 14, 2014.

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  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3  4
   3.  Applications . . . . . . . . . . . . . . . . . . . . . . . . .  3  4
     3.1.  Time synchronization scenario Synchronization Scenario  . . . . . . . . . . . . . .  4  5
     3.2.  VPMS scenario  . . . . . . . . . . . . . .  Virtual Private Multicast Service Scenario . . . . . . . .  4  5
     3.3.  IPTV scenario Scenario  . . . . . . . . . . . . . . . . . . . . . .  4  5
   4.  Setting up HSMP LSP with LDP . . . . . . . . . . . . . . . . .  5  6
     4.1.  Support for HSMP LSP setup Setup with LDP  . . . . . . . . . . .  5  6
     4.2.  HSMP FEC Elements  . . . . . . . . . . . . . . . . . . . .  6  7
     4.3.  Using the HSMP FEC Elements  . . . . . . . . . . . . . . .  6  7
       4.3.1.  HSMP LSP Label Map . . . . . . . . . . . . . . . . . .  6  8
       4.3.2.  HSMP LSP Label Withdraw  . . . . . . . . . . . . . . .  8 10
       4.3.3.  HSMP LSP upstream Upstream LSR change Change . . . . . . . . . . . . .  9 10
   5.  HSMP LSP on a LAN  . . . . . . . . . . . . . . . . . . . . . .  9 10
   6.  Redundancy considerations Considerations  . . . . . . . . . . . . . . . . . .  9 11
   7.  Co-routed path exceptions Path Exceptions  . . . . . . . . . . . . . . . . . .  9 11
   8.  Failure Detection of HSMP LSP  . . . . . . . . . . . . . . . . 10 11
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10 12
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10 12
   11. Acknowledgement  . . . . . . . . . . . . . . . . . . . . . . . 11 13
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 13
     12.1. Normative references . . . . . . . . . . . . . . . . . . . 11 13
     12.2. Informative References . . . . . . . . . . . . . . . . . . 12 13
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 14

1.  Introduction

   The point-to-multipoint LSP defined in [RFC6388] allows traffic to
   transmit from root to several leaf nodes, and multipoint-to-
   multipoint LSP allows traffic from every node to transmit to every
   other node.  This draft introduces a hub & spoke multipoint LSP
   (short for (or
   HSMP LSP), LSP for short), which allows traffic both from root to leaf
   through P2MP LSP and also leaf to root along the co-routed reverse
   path.  That means traffic entering the HSMP LSP at the root node
   travels downstream, exactly as if it was traveling is travelling downstream along a
   P2MP LSP, and traffic entering the HSMP LSP at any other node travels
   upstream along the tree to the root.  A packet traveling travelling upstream
   should be thought of as being unicast to the root, except that it
   follows the path of the tree rather than ordinary routing protocol based
   unicast path to the root.  The combination of upstream LSPs initiated
   from all leaf nodes forms a multipoint-to-point LSP.

2.  Terminology

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

   This document uses some terms and acronyms as follows:

      HSMP LSP: hub & spoke multipoint LSP.  An LSP allows traffic both
      from root to leaf through P2MP LSP and also leaf to root along the
      co-routed reverse path.

      mLDP: Multipoint extensions for LDP

      P2MP LSP: An LSP that has one Ingress LSR and one or more Egress
      LSRs.

      MP2MP LSP: An LSP that connects a set of nodes, such that traffic
      sent by any node in the LSP is delivered to all others.

      HSMP LSP: hub & spoke multipoint LSP.  An LSP allows traffic both
      from root to leaf through P2MP LSP and also leaf to root along the
      co-routed reverse path.

      PTP: The timing and synchronization protocol used by IEEE1588

      P2MP LSP: An LSP that has one Ingress LSR and one or more Egress
      LSRs.

3.  Applications

   In some cases, the P2MP LSP may not have a reply path for the OAM
   message
   messages (e.g, LSP Ping). Ping Echo Request).  If P2MP LSP is provided by
   HSMP LSP, LSP instead, then the upstream path could be exactly used as the OAM
   message reply path.  This is especially useful in the case of P2MP
   LSP fault detection, performance measurement, root node redundancy
   and etc.  There are several other applications that could take
   advantage of
   such kind of a LDP based HSMP LSP as described below.

3.1.  Time synchronization scenario Synchronization Scenario

   [IEEE1588] over MPLS is defined in [I-D.ietf-tictoc-1588overmpls].
   It is required that the LSP used to transport PTP event message
   between a Master Clock and a Slave Clock, and the LSP between the
   same Slave Clock and Master Clock must be co-routed.  By using point-
   to-multipoint  Using point-to-
   multipoint technology to transmit PTP event messages from Master
   Clock at root side to Slave Clock at leaf side will greatly improve
   the bandwidth usage.  Unfortunately current point-to-multipoint LSP
   only provides unidirectional path from root to leaf, which cannot
   provide
   provides a co-routed reverse path for the PTP event messages.  LDP
   based HSMP LSP described in this draft provides unidirectional point-
   to-multipoint LSP from root to leaf and co-routed reverse path LSP from
   leaf to root.

3.2.  VPMS scenario  Virtual Private Multicast Service Scenario

   Point to multipoint PW described in [I-D.ietf-pwe3-p2mp-pw] requires
   to setup set up reverse path from leaf node (referred as egress PE) to root
   node (referred as ingress PE), if HSMP LSP is used to multiplex P2MP
   PW, the reverse path can also be multiplexed to HSMP upstream path to
   avoid setup independent reverse path.  In that case, the operational
   cost will be reduced for maintaining only one HSMP LSP, instead of
   P2MP LSP and n (number of leaf nodes) P2P reverse LSPs.

   The VPMS defined in [I-D.ietf-l2vpn-vpms-frmwk-requirements] requires
   reverse path from leaf to root node.  The P2MP PW multiplexed to HSMP
   LSP can provide VPMS with reverse path, without introducing
   independent reverse path from each leaf to root.

3.3.  IPTV scenario Scenario

   The mLDP based HSMP LSP can also be applied in a typical IPTV
   scenario.  There is usually only one location with senders but there
   are many receiver locations.  If IGMP is used for signaling signalling between
   senders as IGMP querier [RFC3376] and receivers, the IGMP messages
   from the receivers are travelling only from the leaves to the root
   (and from root towards leaves) but not from leaf to leaf.  In
   addition traffic from the root is only replicated towards the leaves.
   Then leaf node receiving IGMP report message (for SSM source specific
   multicast case) will join HSMP LSP, LSP(use similar mechanism in [RFC6826]
   section 2), and then send IGMP report message upstream to root along
   HSMP upstream LSP.  Note that in above case, there is no node
   redundancy for IGMP querier.  And the node redundancy for IGMP querier
   querier[RFC3376] could be provided by two independent VPMS instances
   with HSMP applied.

4.  Setting up HSMP LSP with LDP

   HSMP LSP is similar with MP2MP LSP described in [RFC6388], with the
   difference that the leaf LSRs can only send traffic to root node
   along the same path of traffic from root node to leaf node.

   HSMP LSP consists of a downstream path and upstream path.  The
   downstream path is same as MP2MP LSP, while the upstream path is only
   from leaf to root node, without communication between leaf and leaf
   nodes.  The transmission of packets from the root node of a an HSMP LSP
   to the receivers is identical to that of a P2MP LSP.  Traffic from a
   leaf node follows the upstream path toward the root node, along the
   identical a
   path of that traverse the same nodes as the downstream path. node, but in
   reverse order.

   For setting up the upstream path of a an HSMP LSP, ordered mode MUST be
   used which is same as MP2MP.  Ordered mode can guarantee a leaf to
   start sending packets to root immediately after the upstream path is
   installed, without being dropped due to an incomplete LSP.

   Due to much of same behavior similar behaviors between HSMP LSP and MP2MP LSP, the
   following sections only describe the difference between the two
   entities.

4.1.  Support for HSMP LSP setup Setup with LDP

   HSMP LSP also needs requires the LDP capabilities [RFC5561] for nodes to
   indicate the
   supporting for the that they support setup of HSMP LSPs.  An implementation
   supporting the HSMP LSP procedures specified in this document MUST
   implement the procedures for Capability Parameters in Initialization
   Messages.  Advertisement of the HSMP LSP Capability indicates support
   of the procedures for HSMP LSP setup.

   A new Capability Parameter TLV is defined, the HSMP LSP Capability. Capability
   Parameter.  Following is the format of the HSMP LSP Capability
   Parameter.

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |1|0|   HSMP LSP Cap(TBD IANA)    |           Length (= 1)            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |1|
    |S|  Reserved   |
    +-+-+-+-+-+-+-+-+
    Figure 1. HSMP LSP Capability Parameter encoding

   The length SHOULD be 1, and the S bit and reserved bits are defined
   in [RFC5561] section 3.

   The HSMP LSP capability Capability Parameter type is to be assigned by IANA.

4.2.  HSMP FEC Elements

   Similar as MP2MP LSP, we define two new protocol entities, the HSMP
   downstream
   Downstream FEC Element and upstream Upstream FEC Element.  If a FEC TLV
   contains an one of the HSMP FEC Element, Elements, the HSMP FEC Element MUST be
   the only FEC Element in the FEC TLV.  The structure, encoding and
   error handling for the HSMP downstream Downstream FEC Element and upstream Upstream FEC Elements
   Element are the same as for the MP2MP FEC Element described in
   [RFC6388] Section 4.2. 3.2.  The difference is that two additional new FEC
   types are used: defined: HSMP downstream type Downstream FEC (TBD, IANA) and HSMP upstream type (TBD, Upstream
   FEC(TBD, IANA).

4.3.  Using the HSMP FEC Elements

   In order to describe the message processing clearly, following
   defines the entries in
   the list below define the processing of the HSMP FEC Elements, which is inherited
   from Elements.
   Additionally, the entries defined in [RFC6388] section 4.3. 3.3 are also
   reused in the following sections.

   1.  HSMP downstream LSP <X, Y> (or simply downstream <X, Y>): a an HSMP
   LSP downstream path with root node address X and opaque value Y.

   2.  HSMP upstream LSP <X, Y> (or simply upstream <X, Y>): a an HSMP LSP
   upstream path for root node address X and opaque value Y which will
   be used by any of downstream node to send traffic upstream to root
   node.

   3.  HSMP downstream FEC Element <X, Y>: a FEC Element with root node
   address X and opaque value Y used for a downstream HSMP LSP.

   4.  HSMP upstream FEC Element <X, Y>: a FEC Element with root node
   address X and opaque value Y used for an upstream HSMP LSP.

   5.  HSMP-D Label Map Mapping <X, Y, L>: A Label Map Mapping message with a
   single HSMP downstream FEC Element <X, Y> and label TLV with label L.
   Label L MUST be allocated from the per-platform label space of the
   LSR sending the Label Map Mapping Message.

   6.  HSMP-U Label Map Mapping <X, Y, Lu>: A Label Map Mapping message with a
   single HSMP upstream FEC Element <X, Y> and label TLV with label Lu.
   Label Lu MUST be allocated from the per-platform label space of the
   LSR sending the Label Map Mapping Message.

4.3.1.  HSMP LSP Label Map

   This section specifies the procedures for originating HSMP Label Map
   Mapping messages and processing received HSMP label map Label Mapping messages
   for a particular HSMP LSP.  The procedure of downstream HSMP LSP is
   same as that of downstream MP2MP LSP described in [RFC6388].  Under the
   operation of ordered mode,  When
   LDP operates in Ordered Label Distribution Control mode [RFC5036],
   the upstream LSP will be setup set up by sending HSMP LSP mapping LDP Label Mapping
   message with a label which is allocated by upstream LSR to its
   downstream LSR one hop by one hop from root to leaf node, installing the
   upstream forwarding table by every node along the LSP.
   Detail  The detail
   procedure of setting up upstream HSMP LSP is different with that of
   upstream MP2MP LSP, and is specified in below section.

   All labels discussed here are downstream-assigned [RFC5332] except
   those which are assigned using the procedures described in section 5.

   Determining the upstream LSR for a the HSMP LSP <X, Y> follows the
   procedure for a MP2MP LSP described in [RFC6388] Section 4.3.1.1. 3.3.1.1.

   Determining one's downstream HSMP downstream LSR follows the procedure is much same as defined
   in [RFC6388] section 4.3.1.2.  A 3.3.1.2.  That is, an upstream LDP peer U which
   receives a
   HSMP-D Label Map Mapping with HSMP downstream FEC Element from a an LDP
   peer D will treat D as downstream HSMP
   LSR. downstream LDP peer.

   Determining the forwarding interface to an LSR has same follows the procedure
   as defined in [RFC6388] section 2.4.1.2.

4.3.1.1.  HSMP LSP leaf node operation Leaf Node Operation

   The leaf node operation is same as the operation of MP2MP LSP defined
   in [RFC6388] section 4.3.1.4, 3.3.1.4.  The only with different difference is the FEC element
   processing and
   elements as specified below.

   A leaf node Z will send a an HSMP-D Label Map Mapping <X, Y, L> to U,
   instead of MP2MP-D Label Map Mapping <X, Y, L>. L>, and expects a an HSMP-U
   Label Map Mapping <X, Y, Lu> from node U and checks whether it already
   has forwarding state for upstream <X, Y>.  The created forwarding
   state on leaf node Z is same as the leaf node of MP2MP LSP.  Z will
   push label Lu onto the traffic that Z wants to forward over the HSMP
   LSP.

4.3.1.2.  HSMP LSP transit node operation Transit Node Operation

   Suppose node Z receives a an HSMP-D Label Map Mapping <X, Y, L> from LSR D,
   the procedure is much the same as processing MP2MP-D Label Mapping
   message defined in [RFC6388] section 4.3.1.5, 3.3.1.5, and the processing
   protocol entity is HSMP-D label mapping Label Mapping message.  The different procedure only difference
   is specified below.

   Node Z checks if upstream LSR U already has assigned a label Lu to
   upstream <X, Y>.  If not, transit node Z waits until it receives a an
   HSMP-U Label Map Mapping <X, Y, Lu> from LSR U. Once the HSMP-U Label Map
   Mapping is received from LSR U, node Z checks whether it already has
   forwarding state upstream <X, Y> with incoming label Lu' and outgoing
   label Lu.  If it does, Z sends a an HSMP-U Label Map Mapping <X, Y, Lu'> to
   downstream node.  If it does not, it allocates a label Lu' and
   creates a new label swap for Lu' with Label Lu over interface Iu.
   Interface Iu is determined via the procedures in Section section 4.3.1.  Node
   Z determines the downstream HSMP LSR as per Section section 4.3.1, and sends a
   an HSMP-U Label Map Mapping <X, Y, Lu'> to node D.

   Since a packet from any downstream node is forwarded only to the
   upstream node, the same label (representing the upstream path) can SHOULD
   be distributed to all downstream nodes.  This differs from the
   procedures for MPMP MP2MP LSPs [RFC6388], where a distinct label must be
   distributed to each downstream node.  The forwarding state upstream
   <X, Y> on node Z will be like this {<Lu'>, <Iu Lu>}.  Iu means the
   upstream interface over which Z receives HSMP-U Label Map <X, Y, Lu>
   from LSR U. Packets from any downstream interface over which Z send sends
   HSMP-U Label Map <X, Y, Lu'> with label Lu' will be forwarded to Iu
   with label Lu' swap to Lu.

4.3.1.3.  HSMP LSP root node operation Root Node Operation

   Suppose root node Z receives a an HSMP-D Label Map Mapping <X, Y, L> from
   node D, the procedure is much the same as processing MP2MP-D Label
   Mapping message defined in [RFC6388] section 4.3.1.6, 3.3.1.6, and the
   processing protocol entity is HSMP-D label mapping Label Mapping message.  The different
   procedure only
   difference is specified below.

   Node Z checks if it has forwarding state for upstream <X, Y>.  If
   not, Z creates a forwarding state for incoming label Lu' that
   indicates that Z is the LSP egress.  E.g., the forwarding state might
   specify that the label stack is popped and the packet passed to some
   specific application.  Node Z determines the downstream HSMP LSR as
   per section 4.3.1, and sends a an HSMP-U Label Map <X, Y, Lu'> to node
   D.

   Since Z is the root of the tree, Z will not send a an HSMP-D Label Map
   and will not receive a an HSMP-U Label Map. Mapping.

4.3.2.  HSMP LSP Label Withdraw

   The HSMP Label Withdraw procedure is much the same as MP2MP leaf
   operation defined in [RFC6388] section 4.3.2, 3.3.2, and the processing
   protocol entities FEC
   Elements are HSMP FECs. FEC Elements.  The only difference is the process
   of HSMP-U label release Label Release message, which is specified below.

   When a transit node Z receives a an HSMP-U label release Label Release message from
   downstream node D, Z should check if there are any incoming interface
   in forwarding state upstream <X, Y>.  If all downstream nodes are
   released and there is no incoming interface, Z should delete the
   forwarding state upstream <X, Y> and send HSMP-U label release Label Release
   message to its upstream node.  Otherwise, no HSMP-U Label Release
   message will be sent to the upstream node.

4.3.3.  HSMP LSP upstream Upstream LSR change Change

   The procedure for changing the upstream LSR is the same as defined in
   [RFC6388] section 4.3.3, except it is applied to 3.3.3, only with different processing FEC Element,
   the HSMP FECs. FEC Element.

5.  HSMP LSP on a LAN

   The procedure to process P2MP the downstream HSMP LSP on a LAN has been described in
   [RFC6388].  When is much the LSR forwards a packet
   same as downstream on one of those
   LSPs, the packet's top label must be the "upstream LSR label", and
   the packet's second label is "LSP label". MP2MP LSP described in [RFC6388] section 6.1.1.

   When establishing the downstream path of a an HSMP LSP, as defined in
   [RFC6389], a label request Label Request message for a an LSP label is send sent to the
   upstream LSR.  The upstream LSR should send label mapping Label Mapping message
   that contains the LSP label for the downstream HSMP FEC and the
   upstream LSR context
   label.  At label defined in [RFC5331].  When the same time, it LSR
   forwards a packet downstream on one of those LSPs, the packet's top
   label must also send be the "upstream LSR context label", and the packet's
   second label mapping for
   upstream is "LSP label".  The HSMP FEC to downstream node. path will be
   installed in the context-specific forwarding table corresponding to
   the upstream LSR label.  Packets sent by the upstream
   router LSR can be
   forwarded downstream using this forwarding state based on a two label two-label
   lookup.

   The upstream path of an HSMP LSP on a LAN is the same as the one on
   other kind of links.  That is, the upstream LSR must send Label
   Mapping message that contains the LSP label for upstream HSMP FEC to
   downstream node.  Packets traveling travelling upstream need to be forwarded in
   the direction of the root by using the label allocated
   by for upstream LSR.
   HSMP FEC.

6.  Redundancy considerations Considerations

   In some scenario, it is necessary to provide two root nodes for
   redundancy purpose.  One way to implement this is to use two
   independent HSMP LSPs acting as active/standby.  At one time, only
   one HSMP LSP will be active, and the other will be standby.  After
   detecting the failure of active HSMP LSP, the root and leaf nodes
   will switch the traffic to the new active standby HSMP LSP which is switched
   from former standby takes on the
   role as active HSMP LSP.  The detail of redundancy mechanism will be
   for future study. is out
   of the scope.

7.  Co-routed path exceptions Path Exceptions

   There are some exceptional cases that when mLDP based HSMP LSP could not
   achieve co-routed path.  One possible case is using static routing
   between LDP neighbors; another possible case is IGP cost asymmetric
   generated by physical link cost asymmetric, or TE-Tunnels used
   between LDP neighbors.  The LSR/LER in HSMP LSP could should detect if the
   path is co-routed or not, if not.  If not co-routed, an alarm indication could
   should be generated to the management system.

8.  Failure Detection of HSMP LSP

   The idea of LSP ping for HSMP LSPs could be expressed as an intention
   to test the LSP Ping Echo Request packets that enter at the root
   along a particular downstream path of HSMP LSP, and end their MPLS
   path on the leaf.  The leaf node then sends the LSP ping response Ping Echo Reply
   along the co-routed upstream path of HSMP LSP, and end on the root
   that are the (intended) root node.

   New sub-TLVs are required to be assigned by IANA in Target FEC Stack
   TLV to define the corresponding HSMP-upstream FEC type and HSMP-
   downstream FEC type.  In order to ensure the leaf node to send the
   LSP ping response Ping Echo Reply along the HSMP upstream path, the R bit (Validate
   Reverse Path) in Global Flags Field defined in [RFC6426] is reused
   here.

   The node processing mechanism of LSP ping Ping Echo Request and Echo Reply
   for HSMP LSP is inherited from [RFC6425] and [RFC6426] section 3.4,
   except the following:

   1.  The root node sending LSP ping Ping Echo Request message for HSMP LSP
   MUST attach Target FEC Stack with HSMP downstream FEC, and set R bit
   to '1' in Global Flags Field.

   2.  When the leaf node receiving the LSP ping, Ping Echo Request, it MUST
   send the LSP
   ping response Ping Echo Reply to the associated HSMP upstream path.
   The Reverse-path Target FEC Stack TLV attached by leaf node in reply Echo
   Reply message SHOULD contain the sub-TLV of associated HSMP upstream
   FEC.

9.  Security Considerations

   The same security considerations apply as for the MP2MP LSP described
   in [RFC6388] and [RFC6425].

   Although this document introduces new FEC Elements and corresponding
   procedures, the protocol does not bring any new security issues
   compared to [RFC6388] and [RFC6425].

10.  IANA Considerations

   This document requires allocation of two new LDP FEC Element types
   from the "Label Distribution Protocol (LDP) Parameters registry" the
   "Forwarding Equivalence Class (FEC) Type Name Space":

   1. the HSMP-upstream FEC type - requested value TBD

   2. the HSMP-downstream FEC type - requested value TBD

   This document requires allocation of one new code points for the HSMP
   LSP capability TLV from "Label Distribution Protocol (LDP) Parameters
   registry" the "TLV Type Name Space":

   HSMP LSP Capability Parameter - requested value TBD

   This document requires allocation of two new sub-TLV types for
   inclusion within the LSP ping [RFC4379] Target FEC Stack TLV (TLV
   type 1).

   1. the HSMP-upstream LDP FEC Stack - requested value TBD

   2. the HSMP-downstream LDP FEC Stack - requested value TBD

11.  Acknowledgement

   The author would like to thank Eric Rosen, Sebastien Jobert, Fei Su,
   Edward, Mach Chen, Thomas Morin Morin, Loa Andersson for their valuable
   comments.

12.  References

12.1.  Normative references

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

   [RFC5331]  Aggarwal, R., Rekhter, Y., and E. Rosen, "MPLS Upstream
              Label Assignment and Context-Specific Label Space",
              RFC 5331, August 2008.

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

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

   [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.

   [RFC6389]  Aggarwal, R. and JL. Le Roux, "MPLS Upstream Label
              Assignment for LDP", RFC 6389, November 2011.

   [RFC6425]  Saxena, S., Swallow, G., Ali, Z., Farrel, A., Yasukawa,
              S., and T. Nadeau, "Detecting Data-Plane Failures in
              Point-to-Multipoint MPLS - Extensions to LSP Ping",
              RFC 6425, November 2011.

   [RFC6426]  Gray, E., Bahadur, N., Boutros, S., and R. Aggarwal, "MPLS
              On-Demand Connectivity Verification and Route Tracing",
              RFC 6426, November 2011.

12.2.  Informative References

   [I-D.ietf-l2vpn-vpms-frmwk-requirements]
              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.

   [I-D.ietf-pwe3-p2mp-pw]
              Sivabalan, S., Boutros, S., and L. Martini, "Signaling
              Root-Initiated Point-to-Multipoint Pseudowire using LDP",
              draft-ietf-pwe3-p2mp-pw-04 (work in progress), March 2012.

   [I-D.ietf-tictoc-1588overmpls]
              Davari, S., Oren, A., Bhatia, M., Roberts, P., and L.
              Montini, "Transporting Timing messages over MPLS
              Networks", draft-ietf-tictoc-1588overmpls-04 draft-ietf-tictoc-1588overmpls-05 (work in
              progress), February June 2013.

   [IEEE1588]
              "IEEE standard for a precision clock synchronization
              protocol for networked measurement and control systems",
              IEEE1588v2 , March 2008.

   [RFC3376]  Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
              Thyagarajan, "Internet Group Management Protocol, Version
              3", RFC 3376, October 2002.

   [RFC4379]  Kompella, K. and G. Swallow, "Detecting Multi-Protocol
              Label Switched (MPLS) Data Plane Failures", RFC 4379,
              February 2006.

   [RFC4762]  Lasserre, M. and V. Kompella, "Virtual Private LAN Service
              (VPLS) Using Label Distribution Protocol (LDP) Signaling",
              RFC 4762, January 2007.

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

   [RFC6374]  Frost, D. and S. Bryant, "Packet Loss and Delay
              Measurement for MPLS Networks", RFC 6374, September 2011.

   [RFC6826]  Wijnands, IJ., Eckert, T., Leymann, N., and M. Napierala,
              "Multipoint LDP In-Band Signaling for Point-to-Multipoint
              and Multipoint-to-Multipoint Label Switched Paths",
              RFC 6826, January 2013.

Authors' Addresses

   Lizhong Jin
   Shanghai, China

   Email: lizho.jin@gmail.com

   Frederic Jounay
   France Telecom
   2, avenue Pierre-Marzin
   22307 Lannion Cedex, FRANCE

   Email: frederic.jounay@orange.ch

   IJsbrand Wijnands
   Cisco Systems, Inc
   De kleetlaan 6a
   Diegem  1831, Belgium

   Email: ice@cisco.com

   Nicolai Leymann
   Deutsche Telekom AG
   Winterfeldtstrasse 21
   Berlin  10781

   Email: N.Leymann@telekom.de