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Versions: (draft-ietf-mpls-p2mp-loose-path-reopt) 00 01 02 03 04 05 06 07 08 09 RFC 8149

TEAS Working Group                                          T. Saad, Ed.
Internet-Draft                                            R. Gandhi, Ed.
Intended status: Standards Track                                  Z. Ali
Expires: March 8, 2017                               Cisco Systems, Inc.
                                                              R. Venator
                                      Defense Information Systems Agency
                                                               Y. Kamite
                                          NTT Communications Corporation
                                                       September 4, 2016


         RSVP Extensions For Re-optimization of Loosely Routed
  Point-to-Multipoint Traffic Engineering Label Switched Paths (LSPs)
                draft-ietf-teas-p2mp-loose-path-reopt-06


Abstract

   Re-optimization of a Point-to-Multipoint (P2MP) Traffic Engineered
   (TE) Label Switched Path (LSP) may be triggered based on the need to
   re-optimize an individual source-to-leaf (S2L) sub-LSP or a set of
   S2L sub-LSPs, both using Sub-Group-Based Re-optimization method, or
   the entire P2MP-TE LSP tree using the Make-Before-Break (MBB) method.
    Mechanisms that facilitate path re-optimization of loosely routed
   Point-to-Point (P2P) TE LSPs include a method for the ingress node to
   trigger a new path re-evaluation request and a method for the mid-
   point node to notify availability of a preferred path.  This document
   discusses the application of these mechanisms to the re-optimization
   of loosely routed P2MP-TE LSPs, identifies issues in doing so and
   proposes procedures to address them.

   This document defines Resource Reservation Protocol (RSVP) signaling
   extensions to allow the ingress node of a loosely routed P2MP-TE LSP
   to request the re-evaluation of the entire LSP tree, and a mid-point
   node to notify to the ingress node that a preferable tree exists for
   the entire P2MP-TE LSP.  For re-optimizing a group of S2L sub-LSPs in
   a tree using the Sub-Group-Based Re-optimization method, an S2L sub-
   LSP descriptor list can be used to signal one or more S2L sub-LSPs in
   an RSVP message.  This RSVP message may need to be fragmented when
   large number of S2L sub-LSPs are added to the descriptor list.  This
   document introduces the notion of a fragment identifier to help
   recipient nodes unambiguously reconstruct the fragmented S2L sub-LSP
   descriptor list.








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Status of this Memo

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   described in the Simplified BSD License.




















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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Loosely Routed Inter-domain P2MP-TE LSP Tree . . . . . . .  5
     1.2.  Existing Mechanism For Tree-Based P2MP-TE LSP
           Re-optimization  . . . . . . . . . . . . . . . . . . . . .  5
     1.3.  Existing Mechanism For Sub-Group-Based P2MP-TE LSP
           Re-optimization  . . . . . . . . . . . . . . . . . . . . .  6
   2.  Conventions Used in This Document  . . . . . . . . . . . . . .  7
     2.1.  Key Word Definitions . . . . . . . . . . . . . . . . . . .  7
     2.2.  Abbreviations  . . . . . . . . . . . . . . . . . . . . . .  7
     2.3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  8
   3.  Signaling Procedure For Loosely Routed P2MP-TE LSP
       Re-optimization  . . . . . . . . . . . . . . . . . . . . . . .  8
     3.1.  Tree-Based Re-optimization . . . . . . . . . . . . . . . .  8
     3.2.  Sub-Group-Based Re-optimization Using Fragment
           Identifier . . . . . . . . . . . . . . . . . . . . . . . .  9
   4.  Message and Object Definitions . . . . . . . . . . . . . . . . 10
     4.1.  P2MP-TE Tree Re-evaluation Request Flag  . . . . . . . . . 10
     4.2.  Preferable P2MP-TE Tree Exists Path Error Sub-code . . . . 10
     4.3.  Fragment Identifier For S2L sub-LSP Descriptor . . . . . . 11
   5.  Compatibility  . . . . . . . . . . . . . . . . . . . . . . . . 12
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
     6.1.  P2MP-TE Tree Re-evaluation Request Flag  . . . . . . . . . 12
     6.2.  Preferable P2MP-TE Tree Exists Path Error Sub-code . . . . 13
     6.3.  Fragment Identifier For S2L sub-LSP Descriptor . . . . . . 13
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 15
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 15
   Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . . . 16
   Author's Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16



















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1.  Introduction

   This document defines Resource Reservation Protocol - Traffic
   Engineering (RSVP-TE) [RFC2205] [RFC3209] signaling extensions for
   re-optimizing loosely routed Point-to-Multipoint (P2MP) Traffic
   Engineered (TE) Label Switched Paths (LSPs) [RFC4875] in a
   Multi-Protocol Label Switching (MPLS) or Generalized MPLS (GMPLS)
   network.

   A P2MP-TE LSP is comprised of one or more source-to-leaf (S2L)
   sub-LSPs.  A loosely routed P2MP-TE S2L sub-LSP is defined as one
   whose path does not contain the full explicit route identifying each
   node along the path to the egress node at the time of its signaling
   by the ingress node.  Such an S2L sub-LSP is signaled with no
   Explicit Route Object (ERO) [RFC3209], or with an ERO that contains
   at least one loose hop, or with an ERO that contains an abstract node
   which identifies more than one node.  This is often the case with
   inter-domain P2MP-TE LSPs where Path Computation Element (PCE) is not
   used [RFC5440].

   As per [RFC4875], an ingress node may re-optimize the entire P2MP-TE
   LSP by re-signaling all its S2L sub-LSP(s) or may re-optimize
   individual or group of S2L sub-LSP(s) i.e. individual or group of
   destination(s).

   [RFC4736] defines RSVP signaling extensions for re-optimizing loosely
   routed Point-to-Point (P2P) TE LSP(s) as follows:

   o  A mid-point LSR that expands loose next-hop(s) sends a solicited
   or unsolicited PathErr with the Notify error code (25 as defined in
   [RFC3209]) with sub-code 6 to indicate "Preferable Path Exists" to
   the ingress node.

   o  An ingress node triggers a path re-evaluation request at all
   mid-point LSR(s) that expands loose next-hop(s) by setting the "Path
   Re-evaluation Request" flag (0x20) in SESSION_ATTRIBUTES Object in
   the Path message.

   o  The ingress node upon receiving this PathErr either solicited or
   unsolicited initiates re-optimization of the LSP with a different
   LSP-ID.


   The following sections discuss the issues that may arise when
   applying the mechanisms defined in [RFC4736] for re-optimizing
   loosely routed P2MP-TE LSPs.





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1.1.  Loosely Routed Inter-domain P2MP-TE LSP Tree

   An example of a loosely routed inter-domain P2MP-TE LSP tree is shown
   in Figure 1.  In this example, the P2MP-TE LSP tree consists of 3 S2L
   sub-LSPs, to destinations (i.e. leafs) R10, R11 and R12 from the
   ingress node (i.e. source) R1.  Nodes R2 and R5 are branch nodes and
   nodes ABR3, ABR4, ABR7, ABR8 and ABR9 are area border routers.  For
   the S2L sub-LSP to destination R10, nodes ABR3, ABR7 and R10 are
   defined as loose hops.  For the S2L sub-LSP to destination R11, nodes
   ABR3, ABR8 and R11 are defined as loose hops.  For the S2L sub-LSP to
   destination R12, nodes ABR4, ABR9 and R12 are defined as loose hops.


         <--area1--><--area0--><-area2->

                              ABR7---R10
                             /
                            /
                   ABR3---R5
                  /         \
                 /           \
          R1---R2             ABR8---R11
                 \
                  \
                   ABR4---R6
                            \
                             \
                              ABR9---R12


   Figure 1: An Example of Loosely Routed Inter-domain P2MP-TE LSP Tree


1.2.  Existing Mechanism For Tree-Based P2MP-TE LSP Re-optimization

   Mechanisms defined in [RFC4736] can be easily applied to trigger the
   re-optimization of individual or group of S2L sub-LSP(s).  However,
   to apply these [RFC4736] mechanisms for triggering the
   re-optimization of an entire P2MP-TE LSP tree, an ingress node needs
   to send path re-evaluation requests on all (typically 100s of) S2L
   sub-LSPs and the mid-point LSR needs to send notify PathErrs for all
   S2L sub-LSPs.  Such mechanisms may lead to the following issues:

   o  A mid-point LSR that expands loose next-hop(s) may have to
   accumulate the received path re-evaluation request(s) for all S2L
   sub-LSPs (e.g. by using a wait timer) and interpret them as a
   re-optimization request for the whole P2MP-TE LSP tree.  Otherwise, a
   mid-point LSR may prematurely notify "Preferable Path Exists" for one



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   or a sub-set of S2L sub-LSPs.

   o  Similarly, the ingress node may have to heuristically determine
   when to perform entire P2MP-TE LSP tree re-optimization and when to
   perform S2L sub-LSP re-optimization.  For example, an implementation
   may choose to delay re-optimization long enough to allow all
   PathErr(s) to be received.  Such timer-based procedures may produce
   undesired results.


   o  The ingress node that receives (un)solicited PathErr
   notification(s) for individual S2L sub-LSP(s), may prematurely start
   re-optimizing the sub-set of S2L sub-LSPs.  However, as mentioned in
   [RFC4875] Section 14.2, such sub-group based re-optimization
   procedure may result in data duplication that can be avoided if the
   entire P2MP-TE LSP tree is re-optimized using a different LSP-ID,
   especially if the ingress node eventually receives PathErr
   notifications for all S2L sub-LSPs of the P2MP-TE LSP tree.


   In order to address above mentioned issues and to align
   re-optimization of P2MP-TE LSP with P2P LSP [RFC4736], there is a
   need for a mechanism to trigger re-optimization of the LSP tree by
   re-signaling all S2L sub-LSPs with a different LSP-ID.  To meet this
   requirement, this document defines RSVP-TE signaling extensions for
   the ingress node to trigger the re-evaluation of the P2MP LSP tree on
   every hop that has a next-hop defined as a loose or abstract hop for
   one or more S2L sub-LSP path, and a mid-point LSR to signal to the
   ingress node that a preferable LSP tree exists (compared to the
   current path) or that the whole P2MP-TE LSP must be re-optimized
   (because of maintenance required on the TE LSP path).


1.3.  Existing Mechanism For Sub-Group-Based P2MP-TE LSP Re-optimization

   Applying the procedures discussed in RFC4736 in conjunction with the
   Sub-Group-Based Re-Optimization procedures ([RFC4875], Section 14.2),
   an ingress node MAY trigger path re-evaluation requests for a set of
   S2L sub-LSPs in a single Path message using S2L sub-LSP descriptor
   list.  Similarly, a mid-point LSR may send a PathErr message (with
   Error code 25, sub-code 6) containing a list of S2L sub-LSPs
   transiting through the LSR using an S2L sub-LSP descriptor list to
   notify the ingress node.  This method can be used for re-optimizing a
   sub-group of S2L sub-LSPs within an LSP tree using the same LSP-ID.
   This method can alleviate the scale issue associated with sending
   RSVP messages for individual S2L sub-LSPs.  However, this procedure
   can lead to the following issues when used to re-optimize the LSP
   tree:



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   o  Path message that is intended to carry the path re-evaluation
   request as defined in [RFC4736] with a full list of S2L sub-LSPs in
   S2L sub-LSPs descriptor list will be decomposed at branching LSRs,
   and only a subset of the S2L sub-LSPs that are routed over the same
   next-hop will be added in the descriptor list of the Path message
   propagated to downstream mid-point LSRs.  Consequently, when a
   preferable path exists at such mid-point LSRs, the PathErr can only
   include the sub-set of S2L sub-LSPs traversing the LSR.  In this
   case, at the ingress node there is no way to distinguish which mode
   of re-optimization to invoke, i.e. sub-group based re-optimization
   using the same LSP-ID or tree based re-optimization using a different
   LSP-ID.

   o  An LSR may fragment a large RSVP message (when a combined message
   may not be large enough to fit all S2L sub-LSPs).  In this case, the
   ingress node may receive multiple PathErrs with sub-sets of S2L sub-
   LSPs in each (due to either the combined Path message getting
   fragmented or the combined PathErr message getting fragmented) and
   would require additional logic to determine how to re-optimize the
   LSP tree (for example, waiting for some time to aggregate all
   possible PathErr messages before taking an action).  When fragmented,
   RSVP messages may arrive out of order, and the receiver has no way of
   knowing the beginning and end of the S2L sub-LSP list.


   In order to address the above mentioned issues caused by RSVP message
   fragmentation, this document proposes the use of fragment identifier
   for the S2L sub-LSP descriptor list when combining large number of
   S2L sub-LSPs in an RSVP message.


2.  Conventions Used in This Document

2.1.  Key Word Definitions

   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].

2.2.  Abbreviations

   ABR: Area Border Router.

   AS: Autonomous System.

   ERO: Explicit Route Object.

   LSR: Label Switching Router.



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   TE LSP: Traffic Engineering Label Switched Path.

   TE LSP ingress: Head-end/source of the TE LSP.

   TE LSP egress: Tail-end/destination of the TE LSP.

2.3.  Terminology

   Domain: Routing or administrative domain such as an IGP area and an
   autonomous system.

   Interior Gateway Protocol Area (IGP Area): OSPF area or IS-IS level.

   Inter-area TE LSP: A TE LSP whose path transits across at least two
   different IGP areas.

   Inter-AS MPLS TE LSP: A TE LSP whose path transits across at least
   two different Autonomous Systems (ASes) or sub-ASes (BGP
   confederations).

   S2L sub-LSP: Source-to-leaf sub Label Switched Path.


   The reader is assumed to be familiar with the terminology in
   [RFC4875] and [RFC4736].

3.  Signaling Procedure For Loosely Routed P2MP-TE LSP Re-optimization

3.1.  Tree-Based Re-optimization

   To evaluate an entire P2MP-TE LSP tree on mid-point LSRs that expand
   loose next-hop(s), an ingress node MAY send a Path message with
   "P2MP-TE Tree Re-evaluation Request" defined in this document.  The
   ingress node SHOULD select one of the S2L sub-LSPs of the P2MP-TE LSP
   tree transiting a mid-point LSR to trigger the re-evaluation request.
    The ingress node MAY send a re-evaluation request to each border LSR
   on the path of the LSP tree.

   A mid-point LSR that expands loose next-hop(s) for one or more S2L
   sub-LSP path(s) SHOULD do the following upon receiving a Path message
   with the "P2MP-TE Tree Re-evaluation Request" bit set:

   o  The mid-point LSR SHOULD check for a preferable P2MP-TE LSP tree
   by re-evaluating all S2L sub-LSP(s) that are expanded paths of the
   loose next-hops of the P2MP-TE LSP.

   o  If a preferable P2MP-TE LSP tree is found, the mid-point LSR MAY
   send an RSVP PathErr to the ingress node with Error code 25 (Notify



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   Error) defined in [RFC3209] and sub-code "Preferable P2MP-TE Tree
   Exists" defined in this document.  The mid-point LSR, in turn, SHOULD
   NOT propagate the "P2MP-TE Tree Re-evaluation Request" bit in
   subsequent RSVP Path messages sent downstream for the re-evaluated
   P2MP-TE LSP.

   o  If no preferable tree for P2MP-TE LSP can be found, the
   recommended mode is that the mid-point LSR that expands loose next-
   hop(s) for one or more S2L sub-LSP path(s) SHOULD propagate the
   request downstream by setting the "P2MP-TE Tree Re-evaluation
   Request" bit in the LSP_ATTRIBUTES Object of RSVP Path message.


   A mid-point LSR MAY send an unsolicited PathErr message with
   "Preferable P2MP-TE Tree Exists" PathErr to the ingress node to
   notify of a preferred P2MP-TE LSP tree when it determines it exists.
   In this case, the mid-point LSR that expands loose next-hop(s) for
   one or more S2L sub-LSP path(s) SHOULD select one of the S2L sub-
   LSP(s) of the P2MP-TE LSP tree to send this PathErr message to the
   ingress node.

   The sending of an RSVP PathErr Notify message "Preferable P2MP-TE
   Tree Exists" to the ingress node SHALL notify the ingress node of the
   existence of a preferable P2MP-TE LSP tree and upon receiving this
   PathErr, the ingress node MAY trigger re-optimization of the LSP
   using a different LSP-ID.

3.2.  Sub-Group-Based Re-optimization Using Fragment Identifier

   It might be preferable, as per [RFC4875], to re-optimize the entire
   P2MP-TE LSP by re-signaling all of its S2L sub-LSP(s) (Section 14.1,
   "Make-before-Break") or to re-optimize individual or group of S2L
   sub-LSP(s) i.e. individual or group of destination(s) (Section 14.2
   "Sub-Group-Based Re-Optimization" in [RFC4875]), both using the same
   LSP-ID.  For loosely routed S2L sub-LSPs, this can be achieved by
   using the procedures defined in [RFC4736] to re-optimize one or more
   S2L sub-LSP(s) of the P2MP-TE LSP.

   An ingress node may trigger path re-evaluation requests using the
   procedures defined in [RFC4736] for a set of S2L sub-LSPs by
   combining multiple Path messages using an S2L sub-LSP descriptor list
   [RFC4875].  An S2L sub-LSP descriptor list is created using a series
   of S2L_SUB_LSP Objects as defined in [RFC4875].  Similarly, a mid-
   point LSR may send a PathErr message (with Error code 25, sub-code 6,
   Preferable Path Exists) containing a list of S2L sub-LSPs transiting
   through the LSR using an S2L sub-LSP descriptor list to notify the
   ingress node of preferable paths available.




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   As per [RFC4875] (Section 5.2.3, "Transit Fragmentation of Path State
   Information"), when a Path message is not large enough to fit all S2L
   sub-LSPs in the descriptor list, an LSR may fragment the message.  In
   this case, the LSR MAY add S2L_SUB_LSP_FRAG Object defined in this
   document in the S2L sub-LSP descriptor list to be able to rebuild the
   list from the received fragments that may arrive out of order.

   The S2L_SUB_LSP_FRAG Object defined in this document is optional.
   However, a node MUST add the S2L_SUB_LSP_FRAG Object for each
   fragment in S2L sub-LSP descriptor list when the RSVP message needs
   to be fragmented.

   A mid-point LSR SHOULD wait to accumulate all S2L sub-LSPs before
   attempting to re-evaluate preferable path when a Path message for
   "Path Re-evaluation Request" is received with S2L_SUB_LSP_FRAG
   Object.  If a mid-point LSR does not receive all fragments of the
   Path message (for example, when fragments are lost), it SHOULD
   trigger re-evaluation of all S2L sub-LSPs of the P2MP-TE LSP
   transiting on the node.  An ingress node SHOULD wait to accumulate
   all S2L sub-LSPs before attempting to trigger re-optimization when a
   PathErr message with "Preferable Path Exists" is received with a
   S2L_SUB_LSP_FRAG Object.  If an ingress node does not receive all
   fragments of the PathErr message (for example, when fragments are
   lost), it SHOULD trigger re-optimization of all S2L sub-LSPs of the
   P2MP-TE LSP transiting on the mid-point node that had sent the
   PathErr message.

   The new object S2L_SUB_LSP_FRAG defined in this document has a wider
   applicability other than the P2MP-TE LSP re-optimization but it is
   outside the scope of this document.


4.  Message and Object Definitions

4.1.  P2MP-TE Tree Re-evaluation Request Flag

   In order to trigger a tree re-evaluation request, a new flag is
   defined in Attributes Flags TLV of the LSP_ATTRIBUTES Object
   [RFC5420] as follows:

      Bit Number (to be assigned by IANA): P2MP-TE Tree Re-evaluation
            Request flag


   The "P2MP-TE Tree Re-evaluation Request" flag is meaningful in a Path
   message of a P2MP-TE S2L sub-LSP and is inserted by the ingress node.

4.2.  Preferable P2MP-TE Tree Exists Path Error Sub-code



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   In order to indicate to an ingress node that a preferable P2MP-TE LSP
   tree exists, the following new sub-code for PathErr code 25 (Notify
   Error) [RFC3209] is defined:

      Sub-code (to be assigned by IANA): Preferable P2MP-TE Tree Exists
            sub-code


   When a preferable path for P2MP-TE LSP tree exists, the mid-point LSR
   sends a solicited or unsolicited "Preferable P2MP-TE Tree Exists"
   PathErr notification to the ingress node of the P2MP-TE LSP.

4.3.  Fragment Identifier For S2L sub-LSP Descriptor

   An S2L_SUB_LSP Object [RFC4875] identifies a particular S2L sub-LSP
   belonging to the P2MP-TE LSP.  An S2L sub-LSP descriptor list is
   created using a series of S2L_SUB_LSP Objects as defined in
   [RFC4875].  The RSVP message may need to be fragmented due to large
   number of S2L sub-LSPs added in the descriptor list, and such
   fragments may be received our of order.  To be able to rebuild the
   fragmented S2L sub-LSP descriptor list correctly, the following new
   type is defined for the S2L_SUB_LSP Object [RFC4875] to identify the
   fragments.


   S2L_SUB_LSP_FRAG: Class-Num 50, C-Type TBA3 by IANA


   +---------------+---------------+---------------+---------------+
   |          Length (12 bytes)    | Class-Num 50  |  C-Type TBA3  |
   +---------------+---------------+---------------+---------------+
   |      Reserved                 |        Fragment ID            |
   +---------------+---------------+---------------+---------------+
   |      Fragments Total          |        Fragment Number        |
   +---------------+---------------+---------------+---------------+


     Fragment ID: 16-bit integer in the range of 1 to 65535.  This value
     is incremented for each new RSVP message that needs to be
     fragmented.  The scope of the fragment ID is limited to the RSVP
     message type (e.g. Path) carrying the fragment.  In other words,
     fragment IDs do not have any correlation between different RSVP
     message types (e.g. Path and PathErr).

     Fragments Total: 16-bit integer in the range of 1 to 65535.  This
     value indicates the number of fragments sent for the given RSVP
     message.




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     Fragment Number: 16-bit integer in the range of 1 to 65535.  This
     value indicates the position of this fragment in the given RSVP
     message.


   The S2L_SUB_LSP_FRAG Object is added before adding the
   S2L_SUB_LSP_IPv4 or S2L_SUB_LSP_IPv6 Object in the fragmented RSVP
   message.

5.  Compatibility

   The LSP_ATTRIBUTES Object has been defined in [RFC5420] with class
   numbers in the form 11bbbbbb, which ensures compatibility with
   non-supporting nodes.  Per [RFC2205], nodes not supporting this
   extension will ignore the new flag defined in this document but
   forward it without modification.

   The S2L_SUB_LSP_FRAG Object has been defined with class numbers in
   the form 11bbbbbb, which ensures compatibility with non-supporting
   nodes.  Per [RFC2205], nodes not supporting new S2L_SUB_LSP_FRAG
   Object will ignore them but forward it without modification.

6.  IANA Considerations

   IANA is requested to administer assignment of new values for
   namespace defined in this document and summarized in this section.

6.1.  P2MP-TE Tree Re-evaluation Request Flag

   IANA maintains a name space for RSVP-TE TE parameters "Resource
   Reservation Protocol-Traffic Engineering (RSVP-TE) Parameters" (see
   http://www.iana.org/assignments/rsvp-te-parameters).  From the
   registries in this name space "Attribute Flags", allocation of new
   flag is requested (Section 4.1).

   The following new flag is defined for the Attributes Flags TLV in the
   LSP_ATTRIBUTES Object [RFC5420].  The numeric value is to be assigned
   by IANA.

   o  P2MP-TE Tree Re-evaluation Request Flag:

   +--------+---------------+---------+---------+---------+------------+
   | Bit No | Attribute     | Carried | Carried | Carried | Reference  |
   |        | Flag Name     | in Path | in Resv | in RRO  |            |
   +--------+---------------+---------+---------+---------+------------+
   | TBA1 by| P2MP-TE Tree  | Yes     | No      | No      | This       |
   | IANA   | Re-evaluation |         |         |         | document   |
   +--------+---------------+---------+---------+---------+------------+



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6.2.  Preferable P2MP-TE Tree Exists Path Error Sub-code

   IANA maintains a name space for RSVP protocol parameters "Resource
   Reservation Protocol (RSVP) Parameters" (see
   http://www.iana.org/assignments/rsvp-parameters).  From the
   sub-registry "Sub-Codes - 25 Notify Error" in registry "Error Codes
   and Globally-Defined Error Value Sub-Codes", allocation of a new
   error code is requested (Section 4.2).

   As defined in [RFC3209], the Error Code 25 in the ERROR SPEC Object
   corresponds to a Notify Error PathErr.  This document adds a new
   sub-code for this PathErr as follows:

   o  Preferable P2MP-TE Tree Exists sub-code:

   +----------+--------------------+---------+---------+-----------+
   | Sub-code | Sub-code           | PathErr | PathErr | Reference |
   | value    | Description        | Code    | Name    |           |
   +----------+--------------------+---------+---------+-----------+
   | TBA2 by  | Preferable P2MP-TE | 25      | Notify  | This      |
   | IANA     | Tree Exists        |         | Error   | document  |
   +----------+--------------------+---------+---------+-----------+


6.3.  Fragment Identifier For S2L sub-LSP Descriptor

   IANA maintains a name space for RSVP protocol parameters "Resource
   Reservation Protocol (RSVP) Parameters" (see
   http://www.iana.org/assignments/rsvp-parameters).  From the
   sub-registry "Class Types or C-Types 50 S2L_SUB_LSP" in registry
   "Class Names, Class Numbers, and Class Types", allocation of new
   C-Types is requested (Section 4.3).

   As defined in [RFC4875], S2L_SUB_LSP Object is defined with
   Class-Number 50 to identify a particular S2L sub-LSP belonging to the
   P2MP-TE LSP.  This document adds one new object type for this object
   as follows:

   o  S2L_SUB_LSP_FRAG Object type:

   +-----------------+---------------------------+-----------------+
   | C-Type value    | Description               | Reference       |
   +-----------------+---------------------------+-----------------+
   | TBA3 by IANA    | S2L_SUB_LSP_FRAG          | This document   |
   +-----------------+---------------------------+-----------------+






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7.  Security Considerations

   This document defines RSVP-TE signaling extensions to allow an
   ingress node of a P2MP-TE LSP to request the re-evaluation of the
   entire LSP tree, and for a mid-point LSR to notify the ingress node
   of the existence of a preferable tree by sending a PathErr.  As per
   [RFC4736], in the case of a P2MP-TE LSP S2L sub-LSP spanning multiple
   domains, it may be desirable for a mid-point LSR to modify the RSVP
   PathErr message defined in this document to preserve confidentiality
   across domains.  Furthermore, an ingress node may decide to ignore
   this PathErr message coming from a mid-point LSR residing in another
   domain.  Similarly, a mid-point LSR may decide to ignore the P2MP-TE
   tree re-evaluation request originating from another ingress domain.

   This document also defines fragment identifier for the S2L sub-LSP
   descriptor list when combining large number of S2L sub-LSPs in an
   RSVP message and the message needs to be fragmented.  The
   introduction of the fragment identifier, by itself, introduce no
   additional information to signaling.  For a general discussions on
   MPLS and GMPLS related security issues, see the MPLS/GMPLS security
   framework [RFC5920].






























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8.  References

8.1.  Normative References

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

   [RFC2205]  Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, September 1997.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, December 2001.

   [RFC4736]  Vasseur, JP., Ikejiri, Y. and Zhang, R, "Reoptimization of
              Multiprotocol Label Switching (MPLS) Traffic Engineering
              (TE) Loosely Routed Label Switched Path (LSP)", RFC 4736,
              November 2006.

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

   [RFC5420]  Farrel, A., Papadimitriou, D., Vasseur, JP., and Ayyangar,
              A., "Encoding of Attributes for MPLS LSP Establishment
              Using Resource Reservation Protocol Traffic Engineering
              (RSVP-TE)", RFC 5420, February 2009.


8.2.  Informative References

   [RFC5440]  Vasseur, JP., Ed., and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              March 2009.

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












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Acknowledgments

   The authors would like to thank Loa Andersson, Sriganesh Kini, Curtis
   Villamizar, Dimitri Papadimitriou, Nobo Akiya and Vishnu Pavan Beeram
   for reviewing this document and providing many useful comments and
   suggestions.  The authors would also like to thank Ling Zeng with
   Cisco Systems for implementing mechanisms defined in this document.


Author's Addresses


   Tarek Saad (editor)
   Cisco Systems

   EMail: tsaad@cisco.com


   Rakesh Gandhi (editor)
   Cisco Systems

   EMail: rgandhi@cisco.com


   Zafar Ali
   Cisco Systems

   EMail: zali@cisco.com


   Robert H. Venator
   Defense Information Systems Agency

   EMail: robert.h.venator.civ@mail.mil


   Yuji Kamite
   NTT Communications Corporation

   EMail: y.kamite@ntt.com











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