Extensions to the Path Computation Element Protocol (PCEP) to Support Resource Sharing-based Path Computation
draft-zhang-pce-resource-sharing-12

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PCE Working Group                                            Xian Zhang 
Internet Draft                                            Haomian Zheng 
Category: Standards track                           Huawei Technologies 
                                               Oscar Gonzales de Dios  
                                                            Victor Lopez 
                                                          Telefonica I+D
                                                             Yunbin Xu 
                                                                 CAICT 
 
Expires: October 21, 2020                                April 21, 2020 
 
                                    
                                    
  Extensions to the Path Computation Element Protocol (PCEP) to Support 
                Resource Sharing-based Path Computation 
                                    
                                    
                    draft-zhang-pce-resource-sharing-12 

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 to IETF in full conformance with   
   the provisions of BCP 78 and BCP 79. 

   Internet-Drafts are working documents of the Internet Engineering   
   Task Force (IETF), its areas, and its working groups.  Note that   
   other groups may also distribute working documents as Internet-   
   Drafts. 

 
 
 
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   Internet-Drafts are draft documents valid for a maximum of six 
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   document authors.  All rights reserved. 

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Table of Contents 

   1. Introduction and Motivation .................................. 3 
      1.1. Requirements Language ................................... 4 
   2. Motivation ................................................... 5 
      2.1. Single Domain Use Case .................................. 5 
      2.2. Multiple Layers/Domains Use Case ........................ 6 
      2.3. Bulk Path Computation Use Case .......................... 8 
   3. Extensions to PCEP ........................................... 9 
      3.1. Association Group and Type .............................. 9 
      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 
 
 
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      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. Informative References ................................. 15 
   9. Acknowledgements ............................................ 16 
   10. Contributor's Address ...................................... 16 
   11. Authors' Addresses ......................................... 17 
 
1. Introduction and Motivation 

   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 

 
 
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   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 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 
 
 
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   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.  
     
    
                 +--------------+ 
               |              | 
                 | 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. Before sending the request, N1 may need to check 
   what policy should be applied for the restoration. For example, it 
   might value resource sharing and prefer to share as much resource 
   with the working LSP as possible and specify this policy in the 
   PCReq message.  Given such policy, a probable outcome from the path 

 
 
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   computation would be LSP1, which shares the link 'N1-N2' with the 
   existing LSP.  
    
   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 
   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. [ietf-pce-association-
   diversity] 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.  
 
 
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   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. 
 
                                                                                       
                                                   ----- 
                             .................................| 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 explicit route of LSP1 (H2-L1-L2-H3), and 
   therefore can map the lower layer LSP with the higher-layer one. So 
   when the lower-layer PCE computes the path for LSP2, it can consider 
 
 
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   the resource used by LSP1 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.  
    
   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.   
    
    
                              +-------+ 
                             /| P-PCE |\ 
                            / +---+---+ \ 
                           /       |     \ 
                          /        |      \ 
 
 
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                         /         |       \ 
                        /          |        \ 
                       /           |         \ 
                      /            |          \ 
               +-----/+        +---+---+      +\------+ 
               |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. 
    
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. An association ID will be used to identify the resource 
 
 
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   sharing group. An association type that described disjointness has 
   been defined in [ietf-pce-association-diversity]. In this document, 
   a new association type is defined as follows:  

      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:  

   *  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. 

   *  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. 

 
 
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   *  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.  

   *  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.  

   It is worth noting that there can be multiple flags set which may 
   conflict with each. In this scenario, the result for path 
   computation will be dependent on the policy of PCE.  

   Optional TLVs may be needed to indicate the LSPs with which the 
   resource is shared. If multiple LSPs are required, the PCE may need 
   to consider different sharing policies, which is implementation 
   dependent and may result in a different computing result. The 
   selection policy among multiple computation result 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: 

     - 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.   

     - If the Resource Sharing TLV is extracted correctly, the PCE MUST 
     apply the requested resource sharing requirement.   

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

 
 
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   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 3.4) 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 
   module [ietf-pce-pcep-yang] includes association groups information. 

 
 
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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 
             requirements levels", RFC 2119, March 1997. 
             <https://www.rfc-editor.org/info/rfc2119>. 

   [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. <https://www.rfc-
             editor.org/info/rfc3209>. 

   [RFC5440] Vasseur, J.-P., and Le Roux, JL., "Path Computation 
             Element (PCE) Communication Protocol (PCEP)", RFC 5440, 
             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., Medved, J., Minei, I., and R. Varga, "PCEP 
             Extensions for Stateful PCE", RFC8231, June 2017. 
             <https://www.rfc-editor.org/info/rfc8231>. 

   [RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "PCEP 
             Extensions for PCE-initiated LSP Setup in a Stateful PCE 
             Model", RFC 8281, October 2017. <https://www.rfc-
             editor.org/info/rfc8281>. 

   [RFC8697] Minei, I., Crabbe E., Sivabalan S., Ananthakrishnan H., 
             Dhody D., Tanaka Y., "PCEP Extensions for Establishing 
             Relationships Between Sets of LSPs", RFC8697, January 
             2020. <https://www.rfc-editor.org/info/rfc8697>.  

   [ietf-pce-association-diversity] Litkowski, S., Sivabalan, S., 
             Barth, C., Dhody, D., "Path Computation Element 
             communication Protocol extension for signaling LSP 
             diversity constraint", work in progress. 

8.2. Informative References 

   [RFC4428] Papadimitriou, D., Mannie., E., "Analysis of Generalized 
             Multi-Protocol Label Switching (GMPLS)-based Recovery 
             Mechanisms (including Protection and Restoration)", 
             RFC4428, March 2006. <https://www.rfc-
             editor.org/info/rfc4428>. 
 
 
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   [RFC4655] Farrel, A., Vasseur, J.-P., and Ash, J., "A Path 
             Computation Element (PCE)-Based Architecture", RFC 4655, 
             August 2006. <https://www.rfc-editor.org/info/rfc4655>. 

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

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

   [RFC7399] Farrel, A., King, D., "Unanswered Questions in the Path 
             Computation Element Architecture", RFC7399, October 2014. 
             <https://www.rfc-editor.org/info/rfc7399>. 

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

   [RFC8751] Dhody, D., Lee, Y., Ceccarelli, D., Shin, J., King, D., 
             Gonzalez de Dios, O., "Hierarchical Stateful Path 
             Computation Element (PCE)", RFC8751, March 2020. 
             <https://www.rfc-editor.org/info/rfc8751>. 

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

9. Acknowledgements 

   The authors would like to thank Adrian Farrel for his review and 
   valuable comments. 
    
10. Contributor's Address 

   Dhruv Dhody  
   Huawei Technologies 
   Email: dhruv.dhody@huawei.com 
    
   Igor Bryskin 
   Huawei Technologies 
 
 
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   Email: Igor.Bryskin@huawei.com 
    
11. Authors' Addresses 

   Xian Zhang 
   Huawei Technologies 
   Email: zhang.xian@huawei.com  
    
   Haomian Zheng 
   Huawei Technologies 
   Email: zhenghaomian@huawei.com  
    
   Oscar Gonzalez de Dios  
   Telefonica I+D/gCTIO  
   Distrito Telefonica 
   E-28050 Madrid, Spain 
   EMail: oscar.gonzalezdedios@telefonica.com  
    
   Victor Lopez  
   Telefonica I+D/gCTIO  
   Distrito Telefonica 
   E-28050 Madrid, Spain 
   EMail: victor.lopezalvarez@telefonica.com 
    
   Yunbin Xu 
   CAICT 
   xuyunbin@caict.ac.cn  
    

 
 
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