PCE Working Group                                               X. Zhang
Internet-Draft                                                  H. Zheng
Intended status: Standards Track                     Huawei Technologies
Expires: April 27, 2022                              O. Gonzales de Dios
                                                              Telefonica
                                                                V. Lopez
                                                                   Nokia
                                                                   Y. Xu
                                                                   CAICT
                                                        October 24, 2021


 Extensions to the Path Computation Element Protocol (PCEP) to Support
                Resource Sharing-based Path Computation
                  draft-zhang-pce-resource-sharing-15

Abstract

   Resource sharing in a network means two or more Label Switched Paths
   (LSPs) use common pieces of resource along their paths.  This can
   help save network resources and is useful in scenarios such as LSP
   recovery or when two LSPs do not need to be active at the same time.
   A Path Computation Element (PCE) is responsible for path computation
   with such requirement.

   Existing extensions to the Path Computation Element Protocol (PCEP)
   allow one path computation request for an LSP to be associated with
   other (existing) LSPs through the use of the PCEP Association Object.

   This document extends PCEP in order to support resource-sharing-based
   path computation as another use of the Association Object to enable
   better efficiency in the computation and in the resultant paths and
   network resource usage.

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 https://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."



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   This Internet-Draft will expire on April 27, 2022.

Copyright Notice

   Copyright (c) 2021 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
   (https://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.  Requirements Language . . . . . . . . . . . . . . . . . . .   4
   2.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.1.  Single Domain Use Case  . . . . . . . . . . . . . . . . . .   4
   2.2.  Multiple Layers/Domains Use Case  . . . . . . . . . . . . .   6
   2.3.  Bulk Path Computation Use Case  . . . . . . . . . . . . . .   8
   3.  Extensions to PCEP  . . . . . . . . . . . . . . . . . . . . .  10
   3.1.  Association Group and Type  . . . . . . . . . . . . . . . .  10
   3.2.  Resource Sharing TLV  . . . . . . . . . . . . . . . . . . .  10
   3.3.  Processing Rules  . . . . . . . . . . . . . . . . . . . . .  11
   4.  Implementation Status . . . . . . . . . . . . . . . . . . . .  12
   5.  Manageability Considerations  . . . . . . . . . . . . . . . .  12
   5.1.  Control of Function and Policy  . . . . . . . . . . . . . .  12
   5.2.  Information and Data Models . . . . . . . . . . . . . . . .  12
   5.3.  Liveness Detection and Monitoring . . . . . . . . . . . . .  13
   5.4.  Verify Correct Operations . . . . . . . . . . . . . . . . .  13
   5.5.  Requirements on Other Protocols . . . . . . . . . . . . . .  13
   5.6.  Impact on Network Operations  . . . . . . . . . . . . . . .  13
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   7.1.  Association Object Type Indicators  . . . . . . . . . . . .  14
   7.2.  PCEP TLV Definitions  . . . . . . . . . . . . . . . . . . .  14
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
   8.1.  Normative References  . . . . . . . . . . . . . . . . . . .  15
   8.2.  Informational References  . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16






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1.  Introduction

   A Path Computation Element (PCE) is a way to provide path computation
   function, and it is especially useful in the scenarios where complex
   constraints and/or a demanding amount of computation resource are
   required [RFC4655].  The development of PCE standardization has
   evolved from stateless to stateful.  A stateful PCE has access to the
   LSP database information of the networks it serves as a computation
   engine [RFC8231].  Unless specified, this document assumes a PCE
   mentioned is a stateful PCE..

   Resource sharing denotes that two or more Label Switched Paths (LSPs)
   share common pieces of resource, (such as a common time slot of a
   link in an Optical Transport Network (OTN)).  This is usually useful
   in the scenario where only one of the LSPs is active and the benefit
   is to save network resources.  A simple example of this is
   dynamically calculating a recovery LSP for an existing LSP undergoing
   a link failure.  Note that resource sharing can be worked out using a
   stateless PCE, but the mechanism may be complex and is out the scope
   of this document.

   This document considers the requirement that a new LSP may request
   for resource sharing with one or multiple existing LSPs.
   Furthermore, if there is resource sharing between a new LSP and
   existing an LSP, the two LSPs cannot be used to carry traffic
   simultaneously, the new LSP will take over the traffic from the
   existing LSP.

   In a single domain, this is a common requirement in the recovery
   cases especially in order to increase traffic resilience against
   failure while reducing the amount of network resource used for
   recovery purposes [RFC4428]

   The current protocol supporting the communication between a PCE and a
   Path Computation Client (PCC), i.e. PCE Protocol (PCEP), allows for
   re-optimization of an existing LSP [RFC5440].  This is achieved by
   setting the R bit in the Request Parameter (RP) object, together with
   some additional information if applicable, in the Path Computation
   Request (PCReq) message sent from a PCC to the PCE.  To support this
   type of resource sharing, a PCC needs to ask a PCE to compute a new
   path with the constraints of sharing resource with one or multiple
   existing LSPs.  It is worth noting the "resource sharing" in this
   draft not only means one LSP re-using the same links of another LSP,
   but also the same slice of bandwidth in the network.  This may occur
   when an LSP is required for re-routing, or online re-optimization.
   Current PCEP specifications do not provide such function.  More
   specifically, this document describes the resource sharing issue
   during the procedure when a new LSP is required to replace an



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   existing LSP for use together with Make-before-break (MBB) described
   in [RFC3209].

   As mentioned in [RFC8231], the PLSP-ID provides a unique identifier
   for an LSP during a PCEP session between PCC and PCE.  Such
   identification is helpful in supporting the resource sharing
   requirement for stateful PCEs because it greatly simplifies the
   operation of a PCC.  Instead of the PCC determining all the resources
   to be shared, the PCC can request that the PCE share the resources of
   a specific LSP: the stateful PCE is able to determine those resource
   itself.

   Resource sharing can also be required in an inter-layer PCEP session.
   This is similar to the previous requirement.  However, it is more
   complex and therefore deserves a more detailed explanation here.

   In a multi-layer network, LSPs in a lower layer are used to carry
   higher-layer LSPs across the lower-layer network [RFC5623].
   Therefore, the resource sharing constraints in the higher layer might
   actually relate to resource sharing in the lower layer.  Thus, it is
   useful to consider how this can be achieved and whether additional
   extensions are needed using the models defined in [RFC5623].

   In the next sections, use cases are provided to show what information
   needs to be exchanged to fulfill these requirements.  This memo then
   provides extensions to PCEP to enable this function.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Motivation

2.1.  Single Domain Use Case

   There are two potential cases that request resource to be shared:
   restoration and re-optimization.  Figure 1 shows a single domain
   network with a stateful PCE, and is used as an example for the
   resource sharing application.








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                 +--------------+
                 |              |
                 | Stateful PCE |
                 |              |
                 +--------------+


            +------+          +------+          +------+
            |  N1  +----------+  N2  +-----X----+  N3  |
            +--+---+          +---+--+          +---+--+
               |                  |                 |
               |                  +---------+       |
               |                            |       |
               |     +------+          +------+     |
               +-----+  N5  +----------+  N4  +-----+
                     +------+          +------+




                     Figure 1: A Single Domain Example

   LSP0 (existing): N1-N2-N3.

   LSP1 (restoration): N1-N2-N4-N3.

   LSP2 (re-optimization): N1-N5-N4-N3.

   For the failure restoration, we can assume a working LSP (LSP0)
   exists in the network.  When there is failure on the link N2-N3, it
   is desired to set up a restoration path for this working LSP.
   Suppose N1 serves as the PCC and sends a request to the stateful PCE
   for such an LSP.  Besides the head-end and tail-end node of the
   working LSP, N1 may also need to check what policy should be applied
   for the restoration.  For example, it may evaluate resource sharing
   and prefer to share as much resource with the working LSP as possible
   and specify this policy as a special object in the PCReq message.
   Given such policy, a probable outcome from the path computation would
   be LSP1, which shares the link 'N1-N2' with the existing LSP.  The
   LSP1 will be set up by PCC via either PCInitiate of RSVP.

   Re-optimization does not usually result from a specific failure in
   the network, but takes place on a stable network when more optimal
   paths may have become available.  Thus switching from the existing
   LSP to the new LSP happens with live traffic.  An example can be
   found in Figure 1 without failure on the link N2-N3.  Instead, an
   online re-optimization is needed for the working LSP (LSP0) from the
   stateful PCE.  In such cases, the best choice is to set up a backup



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   LSP for the working LSP with totally separate routing (for example,
   LSP2), and move the traffic to that backup LSP.  After that, the
   working LSP can be torn down, which will not result in any
   interruption during the optimization procedure.  This can actually be
   implemented with existing PCEP mechanisms.  However, if there is no
   such separate path, existing PCEP mechanisms will return an error.  A
   secondary option for this case is to set up an LSP and complete re-
   optimization with resource sharing, even if some interruption is
   introduced.

   In the example from Figure 1 it is assumed that the restored LSP or
   re-optimized LSP have the same source and destination nodes.  But in
   some applications there is no restriction for this assumption, i.e.,
   after an LSP is failed, it can be restored as a new LSP with
   different source/destination.

   In the use cases above it is also assumed that the characteristics of
   the restored LSP or re-optimized LSP are unchanged.  However, it is
   possible to have parameter changes during the resource sharing
   computation.  For example, the bandwidth of the request LSP may be
   different from the existing LSP, while resource sharing is still
   preferred by the PCC.  The PCE should consider the sharing request
   together with the policy and available resources in the network.
   Details can be found in Section 3.3.

   Conversely to resource sharing, it may also be required to apply a
   disjoint constraint for the path computation.  [RFC8800] discusses
   the solution under such a scenario, which is a companion work to this
   document.

2.2.  Multiple Layers/Domains Use Case

   As Discussed in Section 3 of [RFC5623], there are three models for
   inter-layer path computation.  They are single PCE computation,
   multiple PCE with inter-PCE communication, and multiple PCE without
   inter-PCE communication.  For the single PCE computation, the process
   would be similar to that of the use case in Section 2.1.

   An inter-layer path computation example is shown in Figure 2.  Assume
   an LSP (LSP1: H2-H3) has been established already, visible as H2-H3
   from the view of the higher-layer PCE, and as H2-L1-L2-H3 from the
   global view (or from the view of the lower-layer PCE).  A new request
   is received by H2 to establish a new LSP (LSP2: from H2 to H5), given
   the constraint that it can share resources with LSP1.  This
   requirement is possible if only one of the LSPs needs to be active
   and resource sharing is the target.





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                                                                  -----
                                .................................| LSR |
                              .:                                 | H5  |
                            .:                                   /-----
                          .:                                    /   |
          -----    -----.:                       -----    -----/    |
         | LSR |--| LSR |.......................| LSR |--| LSR |   /
         | H1  |  | H2  |                       | H3  |  | H4  |  /
          -----    -----\                       /-----    -----  /
                         \                     /                /
                          \                   /                /
                           \                 /                /
                            \               /                /
                             \-----   -----/                /
                             | LSR |-| LSR |               /
                             | L1  | | L2  |              /
                              -----   -----\             /
                                |           \           /
                                |            \         /
                                |             \       /
                              -----            \-----/
                             | LSR |-----------| LSR |
                             | L3  |           | L4  |
                              -----             -----



                   Figure 2: A Two-layer Network Example

   If the model of multiple PCEs with inter-PCE communication is
   employed, the path computation request sent by H2 to higher-layer PCE
   will be forwarded to lower-layer PCE since there is no resource
   readily available in the higher layer.  So it leaves the lower-layer
   PCE to compute a path in the lower layer in order to support the
   higher layer request.  In this case, the lower-layer PCE is required
   to compute a path between H2 and H5 under the constraint that it can
   share the resource with that of LSP1.  At this moment the lower-layer
   PCE has knowledge of the mapping relationship between the higher-
   layer link H2-H3 and the lower layer link L1-L2, and therefore can
   convert the resource to be shared from higher layer to lower layer.
   So when the lower-layer PCE computes the path for LSP2, it can
   consider the resource used by L1-L2 as available with higher
   priority.  For example, the lower-layer PCE may choose H2-L1-L2-L4-H5
   as the computation result.  On the other hand, if the path
   computation policy is to have a separate path with LSP1, the lower-
   layer PCE may choose H2-L1-L3-L4-H5.





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   During this procedure the higher-layer PCE can only use information
   about LSP1 (such as its five-tuple LSP information).  An issue to
   solve is how the lower-layer PCE can resolve this information to the
   actual resource usage in its own layer, i.e. the lower layer.  This
   could be solved by the edge LSR (L1) reporting this higher-lower LSP
   correlation to the lower-layer PCE as part of the LSP information
   during the LSP state synchronization process.  If needed, it can be
   updated later when there is a change in this information.
   Alternatively, the lower-layer PCE can get this information from
   other sources, such as a network management system, where this
   information should be stored.

   If the model of multiple PCEs without inter-PCE communication is
   employed, the path computation request in the lower layer will be
   initiated by the border LSR node, i.e., L1.  The process would be
   similar to that of the previous scenario.  A point worth noting is
   that the border LSR node may be able to resolve the higher layer LSP
   information itself, such as by mapping it to the corresponding LSP in
   the lower layer, in this way the lower-layer PCE does not need to
   perform this function.  Otherwise, the mapping method mentioned above
   can still be used.

2.3.  Bulk Path Computation Use Case

   There is a potential need for resource sharing during bulk path
   computation, especially the processing of the "sticky resources" in
   [RFC7399].  It would be useful to specify the resources that can be
   shared among different paths, i.e., the bandwidth information.

   Considering the H-PCE architecture in [RFC8751], when the parent PCE
   asks for a single path across a few domains, such a request may
   become a bulk path computation to a certain child PCE.  Figure 3
   shows an example of 3 domains.  The parent PCE will select one of
   these path for establishment.

















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                              +-------+
                             /| P-PCE |\
                            / +---+---+ \
                           /       |     \
                          /        |      \
                         /         |       \
                        /          |        \
                       /           |         \
                      /            |          \
               +-----/+        +---+---+      +\------+
               |C-PCE1|        |C-PCE2 |      |C-PCE3 |
               +------+        +-------+      +-------+
                /                  |                  \
    ---------------      -----------------------       -------------
   /                \   /                       \    /              \
   | +---+     +---+ |  |  +---+   +---+   +---+ |  | +---+    +---+ |
   | | A +-----+ B +-+--+--+ D +---+ E +---+ H +-+--+-+ J +----+ L | |
   | +-\-+     +---+ |  |  +---+   +---+   +--\+ |  | +---+    +-/-+ |
   |     \           |  |          /           \ |  |           /    |
   |      \          |  |         /             \|  |          /     |
   |        \  +---+ |  |  +---+ /               |\\|    +---+/      |
   |          \+ C +-+--+--+ G +/                |  |----| K |       |
   \           +---+/   \  +---+                /    \   +---+      /
    ----------------     -----------------------      --------------



           Figure 3: Bulk Request example with Hierarchical PCEs

   A 3-domain example is shown in Figure 3, with the hierarchical PCE
   architecture.  In this example nodes A/B/C belong to domain 1, nodes
   D/E/G/H belong to domain 2, and nodes J/K/L belong to domain 3.
   Inter-domain links are B-D/C-G between domains 1 and 2, and H-J/H-K
   between domains 2 and 3.  Given a path computation request from A to
   L, a bulk request from P-PCE would be helpful to understand whether
   it is possible to have different combinations on the inter-domain
   links.  However, the resources on some specific links become 'sticky'
   and have to be indicated as 'sharing allowed' to avoid unnecessary
   resource competition.  For example, both the route A-B-D-E-H-J-L and
   A-C-G-E-H-K-L are qualified, but these routes are competing for the
   resource on the link E-H and cannot be established simultaneously, so
   there must be one route failed to be reported to P-PCE.  Given the
   indication of allowing resource sharing on the link E-H, both of
   these routes can be reported for P-PCE's decision, and there will not
   be any competition as the P-PCE understands that only one path needs
   to be set up.





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3.  Extensions to PCEP

3.1.  Association Group and Type

   According to the definition in [RFC8697], the association group is
   used to associate multiple LSPs into one group for further path
   computation considerations, such as disjointness and resource
   sharing, in the messages when requesting path computation.  An
   association ID will be used to identify the resource sharing group.
   An association type that described disjointness has been defined in
   [RFC8800].  In this document, a new association type is defined as
   follows:

   o  Association type = TBD1 ("Sharing Association Type").

   A sharing group should have multiple LSPs.  The number of LSPs and
   the criteria for how LSPs share among each other are dependent on
   local policy.

3.2.  Resource Sharing TLV

   The PCEP Resource Sharing group MAY carry the following TLV.  It MAY
   be carried within a PCReq message from the network element (or other
   PCCs) so as to indicate the desired resource sharing requirements to
   be applied by the stateful PCE during path computation.


        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         Type = [TBD2]         |            Length             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                 Flags                                 |B|S|N|L|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                          Optional TLVs                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



   The following flags are defined:

   o  L (Link share) bit: when set, this flag indicates that the PCE
      should prioritize the links shared by existing LSPs within the
      sharing group for path computation.  The existing LSP identifier
      and its available link identifiers can be contained in the
      optional TLVs.





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   o  N (Node share) bit: when set, this flag indicates that the PCE
      should prioritize the nodes shared by existing LSPs within the
      sharing group for path computation.  The existing LSP identifier
      and its available node identifiers can be contained in the
      optional TLVs.

   o  S (SRLG share) bit: when set, this flag indicates that the PCE
      should set the SRLG (Shared Risk Link Group) of the computed LSP
      to the same as existing LSPs within the sharing group for path
      computation.  The existing LSP identifier and SRLG information can
      be contained in the optional TLVs.

   o  B (Bandwidth share) bit: when set, this flag indicates that the
      PCE should prioritize the bandwidth to be shared by LSPs within
      the sharing group for bulk path computation.  The LSP identifiers
      can be contained in the optional TLVs.

   It is worth noting that there can be multiple flags set which may
   conflict with each other.  In this scenario, the result for path
   computation may not be unique, and is dependent on the
   implementation.  The selection among multiple computation results is
   out of the scope of this document.

3.3.  Processing Rules

   To request a path allowing resource sharing with one or multiple
   existing LSPs, a PCC includes a Resource Sharing TLV in the
   Association Group Object in any kind of path computation request
   message, such as the PCReq, PCUpd, or PCInitiate messages specified
   in [RFC8231] and [RFC8281].

   On receipt of a PCEP message with a Resource Sharing TLV, a stateful
   PCE MUST proceed as follows:

   o  If the Resource Sharing TLV is unknown/unsupported, the PCE will
      follow procedures defined in [RFC5440].  That is, the PCE sends a
      PCErr message with error type 26 (Association Error) and error
      value 6 (Association Information Mismatch), and the related path
      computation request is discarded.

   o  If the Resource Sharing TLV is extracted correctly, the PCE MUST
      apply the requested resource sharing requirement, i.e., try to
      share as much resource as possible with the LSP specified in
      Resource Sharing TLV.

   The procedure of setting flags follows the rules defined in
   Section 3.1.  The flags in the Resource Sharing TLV may be locally
   configured on the requesting nodes via external entities, such as a



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   network management system or the entity that imposes the resource
   sharing requirement.

   It is worth noting that the Resource Sharing TLV can be used together
   with other path indication objects like the IRO/XRO, with different
   objectives.  The first difference is, the use of the Resource Sharing
   TLV is to set up an alternative path, instead a new path.  It is also
   dependent on the knowledge held be the PCC, e.g., if the PCC has full
   knowledge of the path information and has a strong preference on the
   route, it may send the request message with an IRO to specify the
   route.  On the other hand, if the PCC does not know how the path
   should go but just wants to set up a new LSP to replace the old one,
   it may use the Resource Sharing TLV instead of an IRO.  The second
   difference is that the Resource Sharing TLV is a loose requirement.
   For example, if the constraint specified in an IRO/XRO in an A-Z path
   computation request cannot be satisfied, the reply message from PCE
   to PCC would be unsuccessful.  However it is still possible to have a
   path from the A-Z.  If the target node/link/SRLG/Bandwidth is set in
   the Resource Sharing TLV rather than an IRO, the PCE may feedback a
   path from A-Z that does not share the target specified in the
   Resource Sharing TLV.

4.  Implementation Status

   [Note to the RFC Editor - remove this section before publication, as
   well as remove the reference to [RFC7942].

   Currently the authors are not aware of any implementations.

5.  Manageability Considerations

   All manageability requirements and considerations listed in [RFC5440]
   and [RFC8231] apply to the PCEP protocol extensions defined in this
   document.  In addition, requirements and considerations listed in
   this section apply.

5.1.  Control of Function and Policy

   A PCE or PCC implementation MUST allow operator-configured
   associations and SHOULD allow setting of the resource sharing TLV
   (Section 3.2) as described in this document.

5.2.  Information and Data Models

   An implementation SHOULD allow the operator to view the resource
   sharing configured or created dynamically.  Further implementation
   SHOULD allow to view resource sharing associations reported by each
   peer, and the current set of LSPs in the association.  The PCEP YANG



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   module [I-D.ietf-pce-pcep-yang] includes association groups
   information.

5.3.  Liveness Detection and Monitoring

   Mechanisms defined in this document do not imply any new liveness
   detection and monitoring requirements in addition to those already
   listed in [RFC5440].

5.4.  Verify Correct Operations

   Mechanisms defined in this document do not imply any new operation
   verification requirements in addition to those already listed in
   [RFC5440] and [RFC8231].

5.5.  Requirements on Other Protocols

   Mechanisms defined in this document do not imply any new requirements
   on other protocols.  The configuration on local policy may be
   accomplished by other protocols, such as Netconf.

5.6.  Impact on Network Operations

   Mechanisms defined in [RFC5440] and [RFC8231] also apply to PCEP
   extensions defined in this document.

6.  Security Considerations

   Security of PCEP is discussed in [RFC5440] and [RFC6952].  The
   extensions in this document do not change the fundamentals of
   security for PCEP.

   However, the introduction of the Resource Sharing TLV in the
   Association Group Object provides a vector that may be used to probe
   for information from a network.  For example, a PCC that wants to
   discover the path of an LSP with which it is not involved can issue a
   request message with a Resource Sharing TLV and may be able to get
   back quite a lot of information about the path of the LSP through
   issuing multiple such requests for different endpoints and analyzing
   the received results.  To protect against this, a PCE SHOULD be
   configured with access and authorization controls such that only
   authorized PCCs (for example, those within the network) can make
   computation requests, only specifically authorized PCCs can make
   requests for resource sharing, and such requests relating to specific
   LSPs are further limited to a select few PCCs.  How such access
   controls and authorization is managed is outside the scope of this
   document, but it will at the least include Access Control Lists.




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   Furthermore, a PCC must be aware that setting up an LSP that shares
   resources with another LSP may be a way of attacking the other LSP,
   for example by depriving it of the resources it needs to operate
   correctly.  Thus it is important that, both in PCEP and the
   associated signaling protocols, only authorized resource sharing is
   allowed.

7.  IANA Considerations

7.1.  Association Object Type Indicators

   IANA maintains a registry called the "Path Computation Element
   Protocol (PCEP) Numbers" registry with a subregistry called the
   "Association Type Field" subregistry.  IANA is requested to make an
   assignment from that subregistry as follows:


   Object    Name              Object          Reference
   Class                       Type
   ------------------------------------------------------------
    TBD1    Sharing-group     Association Type   [this document]


7.2.  PCEP TLV Definitions

   This document defines the following TLVs to support the resource
   sharing scenario:


   Value    Name                      Reference
   ------------------------------------------------------------
    TBD2    Resource-sharing TLV     [this document]



   IANA is requested to allocate the following bit numbers in the flag
   spaces of Resource-sharing TLV:


    Bit      Flag name                         Reference
    31      Link Share                      [this document]
    30      Node Share                      [this document]
    29      SRLG Share                      [this document]
    28      Bandwidth Share                 [this document]







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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,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <https://www.rfc-editor.org/info/rfc5440>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8231]  Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
              Computation Element Communication Protocol (PCEP)
              Extensions for Stateful PCE", RFC 8231,
              DOI 10.17487/RFC8231, September 2017,
              <https://www.rfc-editor.org/info/rfc8231>.

   [RFC8281]  Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
              Computation Element Communication Protocol (PCEP)
              Extensions for PCE-Initiated LSP Setup in a Stateful PCE
              Model", RFC 8281, DOI 10.17487/RFC8281, December 2017,
              <https://www.rfc-editor.org/info/rfc8281>.

   [RFC8697]  Minei, I., Crabbe, E., Sivabalan, S., Ananthakrishnan, H.,
              Dhody, D., and Y. Tanaka, "Path Computation Element
              Communication Protocol (PCEP) Extensions for Establishing
              Relationships between Sets of Label Switched Paths
              (LSPs)", RFC 8697, DOI 10.17487/RFC8697, January 2020,
              <https://www.rfc-editor.org/info/rfc8697>.

   [RFC8800]  Litkowski, S., Sivabalan, S., Barth, C., and M. Negi,
              "Path Computation Element Communication Protocol (PCEP)
              Extension for Label Switched Path (LSP) Diversity
              Constraint Signaling", RFC 8800, DOI 10.17487/RFC8800,
              July 2020, <https://www.rfc-editor.org/info/rfc8800>.

8.2.  Informational References







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   [I-D.ietf-pce-pcep-yang]
              Dhody, D., Hardwick, J., Beeram, V. P., and J. Tantsura,
              "A YANG Data Model for Path Computation Element
              Communications Protocol (PCEP)", draft-ietf-pce-pcep-
              yang-16 (work in progress), February 2021.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
              <https://www.rfc-editor.org/info/rfc3209>.

   [RFC4428]  Papadimitriou, D., Ed. and E. Mannie, Ed., "Analysis of
              Generalized Multi-Protocol Label Switching (GMPLS)-based
              Recovery Mechanisms (including Protection and
              Restoration)", RFC 4428, DOI 10.17487/RFC4428, March 2006,
              <https://www.rfc-editor.org/info/rfc4428>.

   [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
              Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,
              <https://www.rfc-editor.org/info/rfc4655>.

   [RFC5623]  Oki, E., Takeda, T., Le Roux, JL., and A. Farrel,
              "Framework for PCE-Based Inter-Layer MPLS and GMPLS
              Traffic Engineering", RFC 5623, DOI 10.17487/RFC5623,
              September 2009, <https://www.rfc-editor.org/info/rfc5623>.

   [RFC6952]  Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
              BGP, LDP, PCEP, and MSDP Issues According to the Keying
              and Authentication for Routing Protocols (KARP) Design
              Guide", RFC 6952, DOI 10.17487/RFC6952, May 2013,
              <https://www.rfc-editor.org/info/rfc6952>.

   [RFC7942]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", BCP 205,
              RFC 7942, DOI 10.17487/RFC7942, July 2016,
              <https://www.rfc-editor.org/info/rfc7942>.

Authors' Addresses

   Xian Zhang
   Huawei Technologies
   China

   Email: zhang.xian@huawei.com






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   Haomian Zheng
   Huawei Technologies
   H1, Xiliu Beipo Village, Songshan Lake,
   Dongguan, Guangdong  523808
   China

   Email: zhenghaomian@huawei.com


   Oscar Gonzales de Dios
   Telefonica
   Spain

   Email: oscar.gonzalezdedios@telefonica.com


   Victor Lopez
   Nokia
   Spain

   Email: victor.lopez@nokia.com


   Yunbin Xu
   CAICT
   China

   Email: xuyunbin@caict.ac.cn























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