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Versions: (draft-ietf-mpls-interas-lspping) 00 01 02 03 04 05 06 07 08 09 draft-ietf-mpls-inter-domain-p2mp-rsvp-te-lsp

MPLS Working Group                                             Zafar Ali
Internet-Draft                                             Rakesh Gandhi
Intended status: Standards Track                              Tarek Saad
Expires: April 18, 2013                              Cisco Systems, Inc.
                                                       Robert H. Venator
                                      Defense Information Systems Agency
                                                             Yuji Kamite
                                          NTT Communications Corporation
                                                        October 15, 2012


       Signaling RSVP-TE P2MP LSPs in an Inter-domain Environment
            draft-ali-mpls-inter-domain-p2mp-rsvp-te-lsp-09


Abstract

   Point-to-MultiPoint (P2MP) Multiprotocol Label Switching (MPLS) and
   Generalized MPLS (GMPLS) Traffic Engineering Label Switched Paths (TE
   LSPs) are established using signaling procedures defined in
   [RFC4875]. However, [RFC4875] does not address several issues that
   arise when a P2MP-TE LSP is signaled in inter-domain networks. One
   such issue is the computation of a loosely routed inter-domain P2MP-
   TE LSP paths that are re-merge free. Another issue is the
   reoptimization of the inter-domain P2MP-TE LSP tree vs. an individual
   destination(s), since the loosely routing domain ingress border node
   is not aware of the reoptimization scope. This document defines the
   required protocol extensions needed for establishing and reoptimizing
   P2MP MPLS and GMPLS TE LSPs in inter-domain networks.


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 April 18, 2013.




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Copyright Notice

   Copyright (c) 2012 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
     1.1.  Summary of Solutions . . . . . . . . . . . . . . . . . . .  4
     1.2.  Path Computation Techniques  . . . . . . . . . . . . . . .  5
     1.3.  Use cases  . . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  Conventions used in this document  . . . . . . . . . . . . . .  6
   3.  Control Plane Solution For Re-merge Handling . . . . . . . . .  6
     3.1.  Single Border Node For All S2Ls  . . . . . . . . . . . . .  6
     3.2.  Crankback and PathErr Signaling Procedure  . . . . . . . .  6
   4.  Data Plane Solution For Re-merge Handling  . . . . . . . . . .  8
     4.1.  P2MP-TE Re-merge Recording Request Flag  . . . . . . . . .  8
     4.2.  P2MP-TE Re-merge Present Flag  . . . . . . . . . . . . . .  8
     4.3.  Signaling Procedure  . . . . . . . . . . . . . . . . . . .  9
   5.  Intra-domain P2MP-TE LSP Re-merge Handling . . . . . . . . . . 10
   6.  Reoptimization Handling  . . . . . . . . . . . . . . . . . . . 11
     6.1.  P2MP-TE Tree Re-evaluation Request Flag  . . . . . . . . . 11
     6.2.  Preferable P2MP-TE Tree Exists Flag  . . . . . . . . . . . 11
     6.3.  Signaling Procedure  . . . . . . . . . . . . . . . . . . . 11
   7.  Compatibility  . . . . . . . . . . . . . . . . . . . . . . . . 13
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   10.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
   11.  References  . . . . . . . . . . . . . . . . . . . . . . . . . 15
     11.1.  Normative References  . . . . . . . . . . . . . . . . . . 15
     11.2.  Informative References  . . . . . . . . . . . . . . . . . 15
   Author's Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16




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1.  Introduction

   [RFC4875] describes procedures to set up Point-to-Multipoint (P2MP)
   Traffic Engineering Label Switched Paths (TE LSPs) for use in
   MultiProtocol Label Switching (MPLS) and Generalized MPLS (GMPLS)
   networks.

   As with Point-to-Point (P2P) TE LSPs, P2MP TE LSP state is managed
   using RSVP messages. While the use of RSVP messages is mostly similar
   to their P2P counterpart, P2MP LSP state differs from P2P LSP in a
   number of ways. In particular, the P2MP LSP must also handle the
   "re-merge" problem described in [RFC4875] section 18.

   The term "re-merge" refers to the situation when two source-to-leaf
   (S2L) sub-LSPs branch at some point in the P2MP tree, and then
   intersect again at a another node further downstream the tree. This
   may occur due to discrepancies in the routing algorithms used by
   different nodes, errors in path calculation or manual configuration,
   or network topology changes during the establishment of the P2MP LSP.
   Such re-merges are inefficient due to the unnecessary duplication of
   data and also consume additional network resources. Consequently one
   of the requirements for signaling P2MP LSPs is to choose a P2MP path
   that is re-merge free. In some deployments, it may also be required
   to signal P2MP-TE LSPs that are both re-merge and crossover free
   [RFC4875].

   For the purposes of this document, a domain is considered to be any
   collection of network elements within a common sphere of address
   management or path computational responsibility. Examples of such
   domains include Interior Gateway Protocol (IGP) areas and Autonomous
   Systems (ASes). A border node is a node between different routing
   domains.

   The re-merge free requirement becomes more acute to address when P2MP
   LSP spans multiple domains. This is because in an inter-domain
   environment, the ingress node may not have topological visibility
   into other domains to be able to compute and signal a re-merge free
   P2MP LSP. In that case, the border node for a new domain will be
   given loose next hops for one or more destinations in a P2MP LSP. A
   border node computes paths in its domain by individually expanding
   the loose next hops for the destinations when signaled to it. A
   border node can ensure that it computes the re-merge free paths while
   performing loose hop ERO expansions by individually grafting
   destinations. Note that the computed P2MP tree by a border node in
   this case may not be optimal. When processing a Path message, the
   border node may not have knowledge of all the destinations of the
   P2MP LSP; for example, in the case when not all S2L sub-LSPs pass
   through this border node. In that case, existing protocol mechanisms



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   do not provide sufficient information for it to be able to expand the
   loose hop(s) such that the overall P2MP LSP tree is guaranteed to be
   re-merge free.

   [RFC4875] specifies two approaches to handle re-merge conditions. The
   first method is based on control plane handling the re-merge. In this
   case the node detecting the re-merge condition, i.e. the re-merge
   node initiates the removal of the re-merge sub-LSP(s) by sending a
   PathErr message(s) towards the ingress node. However, this can lead
   to a deadlock in setting up the P2MP LSP in certain cases; for
   example, when the first S2L setup causes the re-merge with all
   subsequent S2Ls in the tree. The second method is based on the data
   plane handling the re-merge condition. In this case, the re-merge
   node allows the re-merge condition to persist, but data from all but
   one incoming interface is dropped at the re-merge node. This ensures
   that duplicate data is not sent on any outgoing interface. However,
   network resources (such as bandwidth capacity) are wasted as long as
   re-merge condition persists which is inefficient.

   [RFC4736] defines procedures and signaling extensions for
   reoptimizing an inter-domain P2P LSP. Specifically, an ingress node
   sends a "path re-evaluation request" to a border node by setting a
   flag (0x20) in SESSION_ATTRIBUTES object in a Path message. A border
   node sends a PathErr code 25 (notify error defined in [RFC3209]) with
   sub-code 6 to indicate "preferable path exists" to the ingress node.
   The ingress node upon receiving this PathErr may initiate
   reoptimization of the LSP. [RFC4736] however does not define a
   procedure to reoptimize the entire P2MP LSP as a whole tree.

   As per [RFC4875] Section 14, for a P2MP LSP, an ingress node may
   reoptimize the entire P2MP LSP by resignaling all destinations
   (Section 14.1, "Make-before-Break") or may reoptimize individual the
   destinations (Section 14.2 "Sub-Group-Based Re-Optimization").
   Generally speaking make-before-break is considered available for
   "whole" P2MP LSP reoptimization, but it can also be used for
   reoptimizing physical routes for specific sub-LSP(s). The
   Sub-Group-Based reoptimization is not always applicable because it
   can lead to data duplication inside the backbone.

1.1.  Summary of Solutions

   This document defines RSVP-TE signaling procedures for P2MP LSP to
   handle the re-merge condition when using either the control plane or
   data plane approach. The procedures are applicable to both MPLS TE
   and GMPLS networks.

   The control plane solution for the re-merge problem makes use of the
   crankback signaling mechanism of the RSVP protocol. [RFC5151]



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   describes such mechanisms for applying crankback to inter-domain P2P
   LSPs, but does not cover P2MP LSPs. Also, crankback mechanisms for
   P2MP LSPs are not addressed by [RFC4875]. This document describes how
   crankback signaling extensions for MPLS and GMPLS RSVP-TE defined in
   [RFC4920] can be used for setting up P2MP TE LSPs to resolve
   re-merges.

   The data plane solution for the re-merge problem described in
   [RFC4875] is extended by using a new flag in the LSP_ATTRIBUTES TLV
   (in a Path message) and a new flag in RRO Attributes Sub-object (in a
   Resv message) in RSVP. The LSP_ATTRIBUTES TLV (in a Path message) and
   RRO Attributes Sub-object (in a Resv message) have been defined in
   [RFC5420]. This document describes how these new flags can be used to
   handle P2MP re-merge conditions efficiently.

   For P2MP LSP, a border node may have loosely routed entire or part of
   the P2MP LSP by expanding EROs in Path messages of the destinations.
   Border node does not know with the signaling procedure defined in
   [RFC4736] if an ingress node is requesting a reoptimization for an
   individual destination(s) or reoptimization of the entire P2MP tree.
   Signaling extension and procedure are defined in this document to
   handle reoptimization of an individual destination(s) and the
   reoptimization of the entire P2MP tree. Basically, a new query
   message is defined in LSP_ATTRIBUTES TLV to request for a "P2MP-TE
   Tree Re-evaluation" and a new sub-code is defined for PathErr message
   to indicate "Preferable P2MP-TE Tree Exists".

1.2.  Path Computation Techniques

   This document focuses on the case where the ingress node does not
   have full visibility of the topology of all domains and is therefore
   not able to compute the complete P2MP tree. Rather, it includes loose
   hops to traverse the domains for which it does not have full
   visibility and ingress border nodes(s) of each transit domain is
   responsible for expanding those loose hops.

   The solution presented in this document do not guarantee optimization
   of the overall P2MP tree across all domains. Path Computation Element
   (PCE) can be used, instead, to address global optimization of the
   overall P2MP tree.

1.3.  Use cases

   Service providers having a network with multiple routing domains are
   interested to use the network for P2MP-TE LSPs. This allows the
   service providers to use the network to carry multicast and broadcast
   traffic (such as video). Service providers can deploy the VPLS and
   MVPN services in the network using inter-domain P2MP TE LSPs. The use



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   case is for P2MP TE LSPs across multiple routing domains that belong
   to a single administrative area. Use case for the Multiple
   administrative domains (e.g. autonomous systems) is outside the scope
   of this document.

2.  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 [RFC2119].


3.  Control Plane Solution For Re-merge Handling

   It is RECOMMENDED that boundary re-routing is requested for P2MP LSPs
   traversing multiple domains. This is because border nodes that are
   expanding loose hops are typically best placed to correct any re-
   merge errors that occur within their domain, not the ingress node.

3.1.  Single Border Node For All S2Ls

   It is RECOMMENDED that the ingress node of a P2MP LSP selects the
   same ingress border node in the loose hop ERO for all sibling S2L
   sub-LSPs that transit through a given domain. The reason is that it
   will increase the possibility of re-merge downstream if two or more
   border nodes have roles simultaneously to expand loose EROs. An
   ingress border node that performs the loose ERO expansion for
   individual sub-LSP(s) has the necessary state information for the
   destinations transiting through its domain to ensure computed P2MP
   tree is re-merge free.

3.2.  Crankback and PathErr Signaling Procedure

   As mentioned in [RFC4875], in order to avoid duplicate traffic, the
   re-merge node MAY initiate the removal of the re-merge S2L sub-LSPs
   by sending a PathErr message to the ingress node of the S2L sub-LSP.

   Crankback procedures for rerouting around failures for P2P RSVP-TE
   LSPs are defined in [RFC4920]. These techniques can also be applied
   to P2MP LSPs to handle re-merge conditions, as described in this
   section.

   If an ingress border node on the path of the P2MP LSP is unable to
   find a route that can supply the required resources or that is re-
   merge free, it MUST generate a PathErr message for the subset of the
   S2L sub-LSPs which it is not able to route. For this purpose the
   ingress border node SHOULD try to find a minimum subset of S2L sub-
   LSPs for which the PathErr needs to be generated towards the ingress



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   node. These are the S2L sub-LSPs on an incoming interface that has
   less number of S2L sub-LSPs compared to the second incoming interface
   that is causing the re-merge condition.

   The RSVP-TE Notify messages do not include S2L_SUB_LSP objects and
   cannot be used to send errors for a subset of the S2L sub-LSPs in a
   Path message. For that reason, the error generating node SHOULD use a
   PathErr message rather than a Notify message to communicate the
   error. In the case of a re-merge error, the node SHOULD use the error
   code "Routing Problem" and the error value "ERO resulted in re-merge"
   as specified in [RFC4875].

   A border node receiving a PathErr message for a set of S2L sub-LSPs
   MAY hold the message and attempt to signal an alternate path that can
   avoid re-merge through its domain for those S2L sub-LSPs that pass
   through it. However, in the case of a re-merge error for which some
   of the re-merging S2L sub-LSPs do not pass through the border node,
   it SHOULD propagate the PathErr upstream towards the ingress node. If
   the subsequent attempt by the border node is successful, the border
   node discards the held PathErr and follows the crankback roles of
   [RFC4920] and [RFC5151]. If repeated subsequent attempts by the
   border node are unsuccessful, the border node MUST send the held
   PathErr upstream towards the ingress node.

   If the ingress node receives a PathErr message with error code
   "Routing Problem" and error value "ERO resulted in re-merge", then it
   SHOULD attempt to signal an alternate path through a different domain
   or through a different border node for the affected S2L sub-LSPs. The
   ingress node MAY use the error node information from the PathErr for
   this purpose.

   However, it may be that the ingress node or an ingress border node
   does not have sufficient topology information to compute an Explicit
   Route that is guaranteed to avoid the re-merge link or node. In this
   case, Route Exclusions [RFC4874] may be particularly helpful. To
   achieve this, [RFC4874] allows the re-merge information to be
   presented as route exclusions to force avoidance of the re-merge link
   or node.

   As discussed in [RFC4920] section 3.3, border node MAY keep the
   history of PathErrs. In case of P2MP LSPs, ingress node and border
   nodes may keep re-merge PathErrs in history table until S2L sub-LSPs
   have been successfully established or until local timer expires.








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4.  Data Plane Solution For Re-merge Handling

   As mentioned in [RFC4875], a node may accept the re-merging S2Ls but
   only send the data from one of these interfaces to its outgoing
   interfaces. That is, the node MUST drop data from all but one
   incoming interface causing the re-merge. This ensures that duplicate
   data is not sent on any outgoing interface. Note that data plane may
   be either programmed to drop the incoming traffic for the S2L sub-LSP
   or not programmed at all.

   It is desirable to avoid the persistent re-merge condition associated
   with data plane based solution in the network in order to optimize
   bandwidth resources in the network.

   The following sections define the RSVP-TE signaling extensions for
   "P2MP- TE Re-merge Recording Request" and "P2MP-TE Re-merge Present"
   messages.

4.1.  P2MP-TE Re-merge Recording Request Flag

   In order to indicate to traversed nodes that P2MP-TE re-merge
   recording is desired, a new flag in the Attribute Flags TLV of the
   LSP_ATTRIBUTES object defined in [RFC5420] is defined as follows:


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


   The "P2MP-TE Re-merge Recording Request" flag is meaningful in a Path
   message and is inserted by the ingress node or a border node in the
   LSP_ATTRIBUTES object.

   If the "P2MP-TE Re-merge Recording Request" Flag is set, it implies
   that the "P2MP-TE Re-merge Present" flag defined in the next section
   MUST be used to indicate to the ingress and ingress border nodes of
   the transit domains that a re-merge condition is present for this S2L
   sub-LSP but accepted, and that incoming traffic is being dropped for
   this S2L sub-LSP.

   The rules of the processing of the Attribute Flags TLV of the
   LSP_ATTRIBUTES object follow [RFC5420].

4.2.  P2MP-TE Re-merge Present Flag

   The "P2MP-TE Re-merge Present" Flag is the counter part of the
   "P2MP-TE Re-merge Recording Request" flag defined above.
   Specifically, RSVP signaling extension is defined to indicate to the



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   upstream node of the re-merge condition and that incoming traffic is
   being dropped for the given S2L.

   When a node accepts a re-merge condition by dropping traffic from an
   incoming interface for an S2L due to the re-merge condition, and if
   it understands the "P2MP-TE Re-merge Recording Request" in the
   Attribute Flags TLV of the LSP_ATTRIBUTES object of the Path message,
   the node MUST set the newly defined "P2MP-TE Re-merge Present" flag
   in the RRO Attributes sub-object defined in [RFC5420] in RRO.

   The following new flag for RRO Attributes Sub-object is defined as
   follows:


      Bit Number (same as bit number assigned for "P2MP-TE Re-merge
            Recording Request" flag): P2MP-TE Re-merge Present flag


   The "P2MP-TE Re-merge Present" flag indicates that the S2L is causing
   a re-merge. The re-merge has been accepted but the incoming traffic
   on this S2L is dropped by the reporting node.

   The rules of the processing of the RRO Attribute Sub-object in the
   Resv message follow [RFC5420].

4.3.  Signaling Procedure

   When a node that does not support data plane based re-merge handling
   receives an S2L sub-LSP Path message with LSP Attributes sub-object
   that has "P2MP-TE Re-merge Recording Request" Flag set, and if the
   S2L is causing a re-merge condition, the node MUST reject the S2L
   sub-LSP Path message and send the PathErr with the error code
   "Routing Problem" and the error value "ERO resulted in re-merge" as
   specified in [RFC4875]. If a node is capable of data plane based re-
   merge handling but operator may have disabled it via a configuration,
   the  the node MUST also reject the re-merge and send this PathErr.

   When a Path message is received at a transit node for an S2L sub-LSP
   and "P2MP-TE Re-merge Recording Request" Flag is set in the LSP
   Attributes sub-object, the node MAY decide to accept the re-merge S2L
   sub-LSP based on the local policy and node capability. In this case,
   before the Resv message is sent to the upstream node for this S2L
   sub-LSP, the node MUST add the RRO Attributes sub-object in the Resv
   RRO if not already present and set the "P2MP-TE Re-merge Present"
   Flag if traffic from the incoming interface of this S2L sub-LSP will
   be dropped. This same incoming interface can still be used for a
   different S2L sub-LSP in the P2MP LSP to forward traffic and "P2MP-TE
   Re-merge Present" flag will not be set for that S2L sub-LSP. Note



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   that rules for adding or modifying the other RRO sub-objects do not
   change due to this flag.

   When a transit node receives a Resv message for an S2L that is
   causing a re-merge condition, the node MUST set the "P2MP-TE Re-merge
   Present" flag in the RRO Attributes sub-object in the Resv message if
   it decides to drop the incoming traffic of this S2L. The "P2MP-TE Re-
   merge Present" flag in RRO Attribute sub-object is not set for the
   S2L(s) whose incoming interface is selected to receive and forward
   the traffic.

   An ingress node MAY immediately start sending traffic on all S2Ls in
   up state even when re-merge conditions are present on some S2Ls of
   the P2MP LSP.

   The proposed signaling extensions allow an ingress node and an
   ingress border node to have a complete view of the re-merge
   conditions on the entire S2L path and on all S2Ls of the P2MP tree.
   The ingress or ingress border node in this case can take appropriate
   actions to resolve the re-merge conditions and optimize network
   bandwidth resources usage. This can be achieved by computing and
   selecting alternate path(s) for the S2L(s) bypassing the re-merge
   node(s).

   The proposed signaling extensions are equally applicable to single
   domain scenarios.

   A node where re-merge is present, may decide to select a different
   incoming interface to forward traffic from in the future. In that
   case, a Resv change message with updated "P2MP-TE Re-merge Present"
   flag in the RRO is sent upstream for all effected S2Ls. For the new
   set of S2L sub-LSPs whose traffic from the incoming interface is
   dropped, "P2MP-TE Re-merge Present" flag will bet set.

   A border node due to local policy MAY remove the record route object
   from the Resv message of the S2L sub-LSP and propagate Resv message
   towards the ingress node. When such a policy is provisioned, the
   border node may attempt to correct the re-merge condition in its
   domain. If the border node is not able to resolve the re-merge
   condition, the border node SHOULD send the PathErr with the error
   code "Routing Problem" and the error value "ERO resulted in re-merge"
   as specified in [RFC4875].


5.  Intra-domain P2MP-TE LSP Re-merge Handling

   Re-merges between S2Ls in a single domain can occur due to
   provisioning errors or path computation errors in the environment



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   where IGP-TE or PCE is used. Re-merges can also happen in the
   environment where static routing or static path selection policy is
   applied at ingress (e.g., CSPF calculation is disabled due to some
   operational reasons), regardless of using loose or static hops. In
   either case, procedures described in this document are equally
   applicable to the intra-domain (i.e. single domain) P2MP-TE LSPs.


6.  Reoptimization Handling

6.1.  P2MP-TE Tree Re-evaluation Request Flag

   In order to query border nodes to check if a preferable P2MP tree
   exists, 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 an S2L sub-LSP and is inserted by the ingress node.

6.2.  Preferable P2MP-TE Tree Exists Flag

   In order to indicate to an ingress node that a preferable P2MP-TE
   tree is available, following new sub-code for PathErr code 25 (notify
   error) is defined:

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


   When a preferable P2MP-TE tree is found, the border node MUST send
   "Preferable P2MP-TE Tree Exists" to the ingress node in order to
   reoptimize the entire P2MP LSP.

6.3.  Signaling Procedure

   Using signaling procedure defined in [RFC4736], an ingress node MUST
   initiate "path re-evaluation request" query to reoptimize a
   destination in a P2MP LSP. Note that this message MUST be used to
   reoptimize a single or a sub-set of the destinations in a P2MP LSP.
   Ingress node MUST send this query in a Path message for each
   destination it is reoptimizing.

   When a Path message for a destination in a P2MP LSP with "path
   re-evaluation request" flag [RFC4736] is received at the border node,



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   it MUST re-compute the loose-hop ERO to see if a preferable path
   exists for that destination. A border node MUST send PathErr code 25
   (notify error defined in [RFC3209]) with "preferable path exists"
   sub-code to indicate that a preferable path exists for the requested
   destination AND border node is capable of per destination
   reoptimization. A border node MUST terminate the path query.
   Alternatively, a border node not capable of per destination
   reoptimization MAY respond with "Preferable P2MP-TE Tree Exists"
   PathErr by checking for a preferable P2MP tree instead of a
   preferable single destination.

   It is often desired to reoptimize the entire P2MP LSP. In order to
   query border nodes to check if a preferable P2MP tree exists, an
   ingress node MUST send a Path message with "P2MP-TE Tree
   Re-evaluation Request" defined in this document. An ingress node MAY
   send this message for all destinations in a P2MP LSP or a sub-set of
   the destinations.

   A border node receiving the "P2MP-TE Tree Re-evaluation Request" MUST
   check for a preferable P2MP LSP for the destinations it is loosely
   routing by loose-hop ERO expansions. The border node if a preferable
   P2MP-TE tree is found, MUST reply with "Preferable P2MP-TE Tree
   Exists" sub-code defined in this document with PathErr 25 (notify
   error defined in [RFC3209] and terminate the path query.

   Note that a border node MAY send "Preferable P2MP-TE Tree Exists"
   with PathErr code 25 to indicate the ingress node in order to
   reoptimize the entire P2MP LSP message unsolicited or in a response
   to "path re-evaluation query" for a destination or in a response to
   "P2MP-TE Tree Re-evaluation Request" message.

   If an ingress node initiated a "path re-evaluation request" query for
   a single destination for per S2L sub-LSP reoptimization and receives
   "Preferable P2MP-TE Tree Exists" PathErr, the ingress node MAY cancel
   the per S2L reoptimization and initiate P2MP-TE tree reoptimization.
   This may happen in case when a border node is not capable of per
   destination reoptimization.

   Note that even if per destination reoptimization, not whole P2MP LSP
   Tree reoptimization, is sufficient, ingress node often needs to re-
   signal whole P2MP LSP tree to complete route optimization for that
   destination. In this case, make-before-break reoptimization scheme is
   used (see [RFC4875] Section 14.1), and all S2L sub-LSPs are re-
   signaled with a different LSP-ID. That is, the procedure of signaling
   a re-optimization by an ingress node is separate from the matter if
   PathErr reply was "Preferable Path Exists" or "Preferable P2MP-TE
   Tree Exists".




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7.  Compatibility

   The LSP_ATTRIBUTES TLV and RRO Attributes sub-object have been
   defined [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 TLV, sub-object
   and the new flags defined in this document but forward it, unexamined
   and unmodified, in all messages resulting from this message.


8.  Security Considerations

   This document does not introduce any additional security issues above
   those identified in [RFC3209], [RFC4875], [RFC5151], [RFC4920] and
   [RFC5920].


9.  IANA Considerations

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

   o  P2MP-TE Re-merge Recording Request Flag:

        - Bit Number: To be assigned by IANA.

        - Attribute flag carried in Path message: Yes

        - Attribute flag carried in Resv message: No



   The following new flag is defined for the RRO Attributes sub-object
   in the RECORD_ROUTE object [RFC5420]. The numeric values are to be
   assigned by IANA.

   o  P2MP-TE Re-merge Present Flag:

        - Bit Number: To be assigned by IANA.


        - Attribute flag carried in Path message: No

        - Attribute flag carried in RRO Attributes sub-object in RRO of
            the Resv message: Yes





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

   o  P2MP-TE Tree Re-evaluation Request Flag:

        - Bit Number: To be assigned by IANA.

        - Attribute flag carried in Path message: Yes

        - Attribute flag carried in Resv message: No

   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 as follows for this PathErr:

   o  Preferable P2MP-TE Tree Exists sub-code:

        - Sub-code for Notify PathErr code 25. To be assigned by
              IANA.


10.  Acknowledgments

   The authors would like to thank N. Neate for his contributions on the
   draft.

























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11.  References

11.1.  Normative References

   [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.

   [RFC5151]  Farrel, A., Ayyangar, A., and JP. Vasseur, "Inter-Domain
              MPLS and GMPLS Traffic Engineering -- Resource Reservation
              Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC
              5151, February 2008.

   [RFC4920]  Farrel, A., Satyanarayana, A., Iwata, A., Fujita, N., and
              G. Ash, "Crankback Signaling Extensions for MPLS and GMPLS
              RSVP-TE", RFC 4920, July 2007.

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

   [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.

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

11.2.  Informative References

   [RFC4726]  Farrel, A., Vasseur, J., and A. Ayyangar, "A Framework for
              Inter-Domain Multiprotocol Label Switching Traffic
              Engineering", RFC 4726, November 2006.











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Author's Addresses


   Zafar Ali
   Cisco Systems

   Email: zali@cisco.com


   Rakesh Gandhi
   Cisco Systems

   Email: rgandhi@cisco.com


   Tarek Saad
   Cisco Systems

   Email: tsaad@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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