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Refresh Interval Independent FRR Facility Protection
draft-chandra-mpls-ri-rsvp-frr-00

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This is an older version of an Internet-Draft whose latest revision state is "Replaced".
Authors Chandrasekar R , Ina Minei , Ebben Aries , Dante Pacella , Tarek Saad
Last updated 2015-07-05
Replaces draft-chandra-mpls-enhanced-frr-bypass
Replaced by draft-ietf-mpls-ri-rsvp-frr, draft-ietf-mpls-ri-rsvp-frr
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draft-chandra-mpls-ri-rsvp-frr-00
Network Working Group                         Chandra Ramachandran (Ed) 
 Internet Draft                                         Juniper Networks 
 Intended status: Standards Track                              Ina Minei 
                                                             Google, Inc 
                                                             Ebben Aries 
                                                                Facebook 
                                                           Dante Pacella 
                                                                 Verizon 
                                                              Tarek Saad 
                                                      Cisco Systems Inc. 
                                                                         
 Expires: January 05, 2016                                 July 05, 2015 
                                     
  
                                       
            Refresh Interval Independent FRR Facility Protection 
                      draft-chandra-mpls-ri-rsvp-frr-00 

 Status of this Memo 

    This Internet-Draft is submitted in full conformance with the 
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    Provisions Relating to IETF Documents  
  
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    (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 
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 Abstract 

    This document defines RSVP-TE extensions to facilitate refresh-
    interval independent FRR facility protection. 

 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 RFC-2119 [RFC2119]. 
     

 Table of Contents 

    1. Introduction...................................................3 
    2. Motivation.....................................................3 
    3. Problem Description............................................4 
    4. Solution Aspects...............................................6 
       4.1. Signaling Protection availability in Path RRO.............7 
          4.1.1. PLR Behavior.........................................7 
          4.1.2. Remote Signaling Adjacency...........................8 
          4.1.3. SUMMARY_FRR_BYPASS_ASSIGNMENT sub-object Propagation.9 
          4.1.4. MP Behavior..........................................9 
          4.1.5. "Remote" state on MP.................................9 
       4.2. Impact of Failures on LSP State..........................10 
          4.2.1. Non-MP Behavior on Phop Link/Node Failure...........11 
          4.2.2. LP-MP Behavior on Phop Link Failure.................11 
          4.2.3. LP-MP Behavior on Phop Node Failure.................11 
          4.2.4. NP-MP Behavior on Phop Link/Node Failure............11 
          4.2.5. NP-MP Behavior on PLR Link Failure..................11 
          4.2.6. Phop Link Failure on a Node that is LP-MP and NP-MP.12 
          4.2.7. Phop Node Failure on Node that is LP-MP and NP-MP...13 
       4.3. Conditional Path Tear....................................13 
          4.3.1. Sending Conditional Path Tear.......................13 
          4.3.2. Processing Conditional Path Tear....................14 
          4.3.3. CONDITIONS object...................................14 
       4.4. Remote State Teardown....................................15 
          4.4.1. PLR Behavior on Local Repair Failure................16 
  
  
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          4.4.2. PLR Behavior on Resv RRO Change.....................16 
          4.4.3. LSP Preemption during Local Repair..................16 
             4.4.3.1. Preemption on LP-MP after Phop Link failure....17 
             4.4.3.2. Preemption on NP-MP after Phop Link failure....17 
       4.5. Backward Compatibility Procedures........................17 
          4.5.1. Detecting Support for Refresh interval Independent FRR
          ...........................................................18 
          4.5.2. Procedures for backward compatibility...............18 
             4.5.2.1. Lack of support on Downstream Node.............19 
             4.5.2.2. Lack of support on Upstream Node...............19 
             4.5.2.3. Incremental Deployment.........................20 
    5. Security Considerations.......................................20 
    6. IANA Considerations...........................................21 
       6.1. New Object - CONDITIONS..................................21 
    7. Normative References..........................................21 
    8. Acknowledgments...............................................22 
    9. Authors' Addresses............................................22 
     
 1. Introduction 

    The facility backup protection mechanism is one of two methods 
    discussed in [RFC4090] for enabling the fast reroute of traffic onto 
    backup LSP tunnels in 10s of milliseconds, in the event of a 
    failure. This document discusses a few shortcomings with some of the 
    refresh-interval reliant procedures proposed for this method in 
    [RFC4090] and specifies mechanisms to address those shortcomings. 
    These shortcomings come to the fore under scaled conditions and get 
    highlighted even further when large RSVP-TE refresh intervals are 
    used. The RSVP-TE extensions defined in this document will enhance 
    the facility backup protection mechanism by making the corresponding 
    procedures refresh-interval independent. 

 2. Motivation 

    Standard RSVP [RFC2205] maintains state via the generation of RSVP 
    Path/Resv refresh messages. Refresh messages are used to both 
    synchronize state between RSVP neighbors and to recover from lost 
    RSVP messages. The use of Refresh messages to cover many possible 
    failures has resulted in a number of operational problems.  One 
    problem relates to RSVP control plane scaling due to periodic 
    refreshes of Path and Resv messages, another relates to the 
    reliability and latency of RSVP signaling. An additional problem is 
    the time to clean up the stale state after a tear message is lost. 
    For more on these problems see Section 1 of [RFC2961]. All these 
    problems adversely affect RSVP control plane scalability. RSVP-TE 
    inherited all these problems from standard RSVP.  
  
  
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    Procedures specified in [RFC2961] address the above mentioned 
    problems by eliminating dependency on refreshes for state 
    synchronization and for recovering from lost RSVP messages, and by 
    eliminating dependency on refresh timeout for stale state cleanup. 
    Implementing these procedures allows to improve RSVP-TE control 
    plane scalability. For more details on eliminating dependency on 
    refresh timeout for stale state cleanup, refer to "Refresh Interval 
    Independent RSVP" section in [TE-SCALE-REC]. 

    However, the procedures specified in [RFC2961] do not fully address 
    stale state cleanup for facility backup protection [RFC4090], as 
    facility backup protection still depends on refresh timeouts for 
    stale state cleanup. Thus [RFC2961] is insufficient to address the 
    problem of stale state cleanup when facility backup protection is 
    used. 

    The procedures specified in this document, in combination with 
    [RFC2961], eliminate facility backup protection dependency on 
    refresh timeouts for stale state cleanup. These procedures, in 
    combination with [RFC2961], fully address the above mentioned 
    problem of RSVP-TE stale state cleanup, including the cleanup for 
    facility backup protection. 

    The procedures specified in this document assume reliable delivery 
    of RSVP messages, as specified in [RFC2961]. Therefore this document 
    makes support for [RFC2961] a pre-requisite.  

 3. Problem Description 

                                 [E] 
                                /   \ 
                               /     \ 
                              /       \ 
                             /         \ 
                            /           \ 
                           /             \ 
                         [A]-----[B]-----[C]-----[D] 
                                   \             / 
                                    \           / 
                                     \         / 
                                      \       / 
                                       \     / 
                                        \   / 
                                         [F] 
                         Figure 1: Example Topology 
     
  
  
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    In the topology illustrated in Figure 1, consider a large number of 
    LSPs from A to D transiting B and C. Assume that refresh interval 
    has been configured to be large of the order of minutes and refresh 
    reduction extensions are enabled on all routers. 

    Also assume that node protection has been configured for the LSPs 
    and the LSPs are protected by each router in the following way 

    -  A has made node protection available using bypass LSP A -> E -> 
      C; A is the Point of Local Repair (PLR) and C is Node Protecting 
      Merge Point (NP-MP) 

    -  B has made node protection available using bypass LSP B -> F -> 
      D; B is the PLR and D is the NP-MP 

    -  C has made link protection available using bypass LSP C -> B -> F 
      -> D; C is the PLR and D is the Link Protecting Merge Point (LP-
      MP) 

    In the above condition, assume that B-C link fails. The following is 
    the sequence of events that is expected to occur for all protected 
    LSPs under normal conditions. 

   1. B performs local repair and re-directs LSP traffic over the bypass 
      LSP B -> F -> D. 
   2. B also creates backup state for the LSP and triggers sending of 
      backup LSP state to D over the bypass LSP B -> F -> D. 
   3. D receives backup LSP states and merges the backups with the 
      protected LSPs. 
   4. As the link on C, over which the LSP states are refreshed has 
      failed, C will no longer receive state refreshes. Consequently the 
      protected LSP states on C will time out and C will send tear down 
      message for all LSPs. 
    While the above sequence of events has been described in [RFC4090], 
    there are a few problems for which no mechanism has been specified 
    explicitly. 

    -  If the protected LSP on C times out before D receives signaling 
      for the backup LSP, then D would receive PathTear from C prior to 
      receiving signaling for the backup LSP, thus resulting in deleting 
      the LSP state. This would be possible at scale even with default 
      refresh time. 
  
  
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    -  If upon the link failure C is to keep state until its timeout, 
      then with long refresh interval this may result in a large amount 
      of stale state on C. Alternatively, if upon the link failure C is 
      to delete the state and send PathTear to D, this would result in 
      deleting the state on D, thus deleting the LSP. D needs a reliable 
      mechanism to determine whether it is MP or not to overcome this 
      problem. 

    -  If head-end A attempts to tear down LSP after step 1 but before 
      step 2 of the above sequence, then B may receive the tear down 
      message before step 2 and delete the LSP state from its state 
      database. If B deletes its state without informing D, with long 
      refresh interval this could cause (large) buildup of stale state 
      on D. 

    -  If B fails to perform local repair in step 1, then B will delete 
      the LSP state from its state database without informing D. As B 
      deletes its state without informing D, with long refresh interval 
      this could cause (large) buildup of stale state on D. 

    The purpose of this document is to provide solutions to the above 
    problems which will then make it practical to scale up to a large 
    number of protected LSPs in the network. 

 4. Solution Aspects 

    The solution consists of five parts. 

    -  Utilize MP determination mechanism specified in [SUMMARY-FRR] 
      that enables the PLR to signal availability of local protection to 
      MP. In addition, introduce PLR and MP procedures to establish 
      Node-ID hello session between the PLR and the MP to detect router 
      failures and to determine capability. See section 4.1 for more 
      details.  

    -  Handle upstream link or node failures by cleaning up LSP states 
      if the node has not found itself as MP through the MP 
      determination mechanism. See section 4.2 for more details. 

      The combination of "path state" maintained as Path State Block 
      (PSB) and "reservation state" maintained as Reservation State 
      Block (RSB) forms an individual LSP state on an RSVP-TE speaker. 

    -  Introduce extensions to enable a router to send tear down message 
      to downstream router that enables the receiving router to 

  
  
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      conditionally delete its local state. See section 4.3 for more 
      details. 

    -  Enhance facility protection by allowing a PLR to directly send 
      tear down message to MP without requiring the PLR to either have a 
      working bypass LSP or have already signaled backup LSP state. See 
      section 4.4 for more details. 

    -  Introduce extensions to enable the above procedures to be 
      backward compatible with routers along the LSP path running 
      implementation that do not support these procedures. See section 
      4.5 for more details. 

 4.1. Signaling Protection availability in Path RRO 

    [SUMMARY-FRR] defines a mechanism for PLR to signal the association 
    of a protected LSP to a bypass LSP by introducing a new sub-object 
    in RRO carried in Path and Resv messages. Implementations supporting 
    this document SHOULD support SUMMARY_FRR_BYPASS_ASSIGNMENT sub-
    object in RRO carried in Path message. Implementations MAY also 
    support SUMMARY_FRR_BYPASS_ASSIGNMENT sub-object in RRO carried in 
    Resv message. 

 4.1.1. PLR Behavior 

    As per the procedures specified in RFC 4090, when a protected LSP 
    comes up and if the "local protection desired" flag is set in the 
    SESSION_ATTRIBUTE object, each node along the LSP path attempts to 
    make local protection available for the LSP. 

      - If the "node protection desired" flag is set, then the node 
      tries to become a PLR by attempting to create a NP-bypass LSP to 
      the NNhop node avoiding the Nhop node on protected LSP path. In 
      case node protection could not be made available after some time 
      out, the node attempts to create a LP-bypass LSP to Nhop node 
      avoiding only the link that protected LSP takes to reach Nhop 

      - If the "node protection desired" flag is not set, then the PLR 
      attempts to create a LP-bypass LSP to Nhop node avoiding the link 
      that the protected LSP takes to reach Nhop 

    With regard to the PLR procedures described above and that are 
    specified in RFC 4090, this document specifies the following 
    recommendations involving addresses selection. 

  
  
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    -  While selecting the destination address of the bypass LSP, the 
      PLR SHOULD attempt to select the router ID of the NNhop or Nhop 
      node. If the PLR and the MP are in same area, then the PLR may 
      utilize the TED to determine the router ID from the interface 
      address in RRO (if NodeID is not included in RRO). If the PLR and 
      the MP are in different IGP areas, then the PLR SHOULD use the 
      NodeID address of NNhop MP if included in the RRO of RESV. If the 
      NP-MP in a different area has not included NodeID in RRO, then the 
      PLR SHOULD use NP-MP's interface address present in the RRO. The 
      PLR SHOULD use its router ID as the source address of the bypass 
      LSP. The PLR SHOULD also include its router ID as the NodeID in 
      PATH RRO unless configured explicitly not to include NodeID. 

    In parallel to the attempt made to create NP-bypass or LP-bypass, 
    the PLR SHOULD initiate a Node-ID based Hello session to the NNhop 
    or Nhop node respectively to establish the RSVP-TE signaling 
    adjacency. This Hello session is used to track the state of the 
    adjacency, including detection of adjacency failure. 

      - If the bypass LSP comes up, then the PLR SHOULD include 
      SUMMARY_FRR_BYPASS_ASSIGNMENT sub-object in RRO and triggers PATH 
      to be sent. If the sub-object is included in PATH RRO, then the 
      encoding rules specified in [SUMMARY-FRR] SHOULD be followed. 

      - After signaling protection availability, if the PLR finds that 
      the protection becomes unavailable then it SHOULD attempt to make 
      protection available. The PLR SHOULD wait for a time out before 
      removing SUMMARY_FRR_BYPASS_ASSIGNMENT sub-object in RRO and 
      triggering PATH downstream. On the other hand, the PLR need not 
      wait for a time out to add SUMMARY_FRR_BYPASS_ASSIGNMENT sub-
      object in RRO and may immediately trigger PATH downstream. 

 4.1.2. Remote Signaling Adjacency 

    A NodeID based RSVP-TE Hello session is one in which NodeID is used 
    in source and destination address fields in RSVP Hello. [RFC4558] 
    formalizes NodeID based Hello messages between two routers. This 
    document extends NodeID based RSVP Hello session to track the state 
    of RSVP-TE neighbor that is not directly connected by at least one 
    interface. In order to apply NodeID based RSVP-TE Hello session 
    between any two routers that are not immediate neighbors, the router 
    that supports the extensions defined in the document SHOULD set TTL 
    to 255 in the NodeID based Hello messages exchanged between PLR and 
    MP.  

  
  
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    In the rest of the document the term "signaling adjacency", or 
    "remote signaling adjacency" refers specifically to the RSVP-TE 
    signaling adjacency. 

 4.1.3. SUMMARY_FRR_BYPASS_ASSIGNMENT sub-object Propagation 

    The propagation rules for SUMMARY_FRR_BYPASS_ASSIGNMENT sub-object 
    in RRO carried in Path specified in [SUMMARY-FRR] SHOULD be 
    followed. 

 4.1.4. MP Behavior 

    When the NNhop or Nhop node receives the triggered PATH with a 
    "matching" SUMMARY_FRR_BYPASS_ASSIGNMENT sub-object, the node should 
    consider itself as the MP for the PLR IP address "corresponding" to 
    the SUMMARY_FRR_BYPASS_ASSIGNMENT sub-object in RRO. As specified in 
    [SUMMARY-FRR], a SUMMARY_FRR_BYPASS_ASSIGNMENT in PATH RRO is said 
    to "match" a node if "Bypass Destination Address" matches a local 
    address and "Bypass Tunnel ID" matches an LSP terminating on the 
    node. Also, a SUMMARY_FRR_BYPASS_ASSIGNMENT sub-object is said to 
    "correspond" to an IP address in RRO if the sub-object is present in 
    RRO after the IP address but before the next hop router's IP 
    address. The ordering rules of SUMMARY_FRR_BYPASS_ASSIGNMENT 
    specified in [SUMMARY-FRR] SHOULD be followed by implementations 
    supporting this document. 

    In addition to the above procedures, the node SHOULD check the 
    presence of remote signaling adjacency with PLR (this check is 
    needed to detect network being partitioned). If a matching 
    SUMMARY_FRR_BYPASS_ASSIGNMENT sub-object is found in RRO and the 
    RSVP-TE signaling adjacency is present, the node concludes that the 
    PLR will undertake refresh-interval independent FRR procedures 
    specified in this document. If the PLR has included NodeID in PATH 
    RRO, then that NodeID is the remote neighbor address. Otherwise, the 
    PLR's interface address in RRO will be the remote neighbor address. 
    If a matching SUMMARY_FRR_BYPASS_ASSIGNMENT sub-object is included 
    by PPhop node, then it is NP-MP. If a matching 
    SUMMARY_FRR_BYPASS_ASSIGNMENT sub-object is included by Phop node, 
    it concludes it is LP-MP. 

 4.1.5. "Remote" state on MP 

    Once a router concludes it is MP for a PLR running refresh-interval 
    independent FRR procedures, it SHOULD create a remote path state for 
    the LSP. The "remote" state is identical to the protected LSP path 
    state except for the difference in HOP object. The HOP object 
  
  
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    corresponding to the "remote" path state contains the address of 
    remote node signaling adjacency with PLR. 

    The MP SHOULD consider the "remote" path state automatically deleted 
    if: 

    -  MP later receives a PATH with no matching 
      SUMMARY_FRR_BYPASS_ASSIGNMENT sub-object corresponding to the PLR 
      RRO, or 

    -  Node signaling adjacency with PLR goes down, or 

    -  MP receives backup LSP signaling from PLR or 

    -  MP receives PathTear, or 

    -  MP deletes the LSP state on local policy or exception event 

    Unlike the normal path state that is either locally generated on 
    Ingress or created from PATH message from Phop node, the "remote" 
    path state is not signaled explicitly form PLR. The purpose of 
    "remote" path state is to enable the PLR to explicitly tear down 
    path and reservation states corresponding to the LSP by sending tear 
    message for the "remote" path state. Such message tearing down 
    "remote" path state is called "Remote PathTear. 

    The scenarios in which "Remote" PathTear is applied are described in 
    Section 4.4 - Remote State Teardown. 

 4.2. Impact of Failures on LSP State 

    This section describes the procedures for routers on the LSP path 
    for different kinds of failures. The procedures described on 
    detecting RSVP control plane adjacency failures do not impact the 
    RSVP-TE graceful restart mechanisms ([RFC3473], [RFC5063]). If the 
    router executing these procedures act as helper for neighboring 
    router, then the control plane adjacency will be declared as having 
    failed after taking into account the grace period extended for 
    neighbor by the helper. 

    It should be noted that even though this section and the subsequent 
    sections of the document mention "link failure" and "node failure" 
    separately involving upstream or downstream of a protected LSP, a 
    router implementing the procedures specified in the document need 
    not have a mechanism to distinguish between these two types of 
    failures. Optionally, a router MAY run Node-ID based RSVP-TE 
  
  
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    signaling adjacency with immediate neighbors to distinguish between 
    these two types of failures. 

 4.2.1. Non-MP Behavior on Phop Link/Node Failure 

    When a router detects Phop link or Phop node failure and the router 
    is not an MP for the LSP, then it SHOULD send Conditional PathTear 
    (refer to Section "Conditional PathTear" below) and delete PSB and 
    RSB states corresponding to the LSP. 

 4.2.2. LP-MP Behavior on Phop Link Failure 

    When the Phop link for an LSP fails on a router that is LP-MP for 
    the LSP, the LP-MP SHOULD retain PSB and RSB states corresponding to 
    the LSP till the occurrence of any of the following events. 

    - Node-ID signaling adjacency with Phop PLR goes down, or  

    - MP receives normal or "Remote" PathTear for PSB, or 

    - MP receives ResvTear RSB. 

 4.2.3. LP-MP Behavior on Phop Node Failure 

    When a router that is LP-MP for an LSP detects Phop node failure 
    from Node-ID signaling adjacency state, the LP-MP SHOULD send normal 
    PathTear and delete PSB and RSB states corresponding to the LSP. 

 4.2.4. NP-MP Behavior on Phop Link/Node Failure 

    When a router that is NP-MP for an LSP detects Phop link failure, or 
    Phop node failure from Node-ID signaling adjacency, the router 
    SHOULD retain PSB and RSB states corresponding to the LSP till the 
    occurrence of any of the following events. 

    - Remote Node-ID signaling adjacency with PPhop PLR goes down, or 

    - MP receives normal or "Remote" PathTear for PSB, or 

    - MP receives ResvTear for RSB. 

 4.2.5. NP-MP Behavior on PLR Link Failure 

    If the PLR link that is not attached to NP-MP fails and if NP-MP 
    receives Conditional PathTear from the Phop node, then the MP SHOULD 

  
  
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    retain PSB and RSB states corresponding to the LSP till the 
    occurrence of any of the following events. 

    - Remote Node-ID signaling adjacency with PPhop PLR goes down, or 

    - MP receives normal or "Remote" PathTear for PSB, or 

    - MP receives ResvTear for RSB. 

    Receiving Conditional PathTear from the Phop node will not impact 
    the "remote" state from the PLR. Note that Phop node would send 
    Conditional PathTear if it was not an MP. 

    In the example topology in Figure 1, assume C & D are NP-MP for PLRs 
    A & B respectively. Now when A-B link fails, as B is not MP and its 
    Phop link signaling adjacency has failed, B will delete LSP state 
    (this behavior is required for unprotected LSPs - Section 4.2.1). In 
    the data plane, that would require B to delete the label forwarding 
    entry corresponding to the LSP. So if B's downstream nodes C and D 
    continue to retain state, it would not be correct for D to continue 
    to assume itself as NP-MP for PLR B. 

    The mechanism that enables D to stop considering itself as NP-MP and 
    delete "remote" path state is given below. 

        1. When C receives Conditional PathTear from B, it decides to 
        retain LSP state as it is NP-MP of PLR A. C also SHOULD check 
        whether Phop B had previously signaled availability of node 
        protection. As B had previously signaled NP availability in its 
        PATH RRO, C SHOULD remove SUMMARY_FRR_BYPASS_ASSOCIATION sub-
        object corresponding to B from the RRO and trigger PATH to D.  
        2. When D receives triggered PATH, it realizes that it is no 
        longer NP-MP and so deletes the "remote" path state. D does not 
        propagate PATH further down because the only change is in PATH 
        RRO SUMMARY_FRR_BYPASS_ASSOCIATION sub-object corresponding to 
        B. 
 4.2.6. Phop Link Failure on a Node that is LP-MP and NP-MP 

    A router may be both LP-MP as well as NP-MP at the same time for 
    Phop and PPhop nodes respectively of an LSP. If Phop link fails on 
    such node, the node SHOULD retain PSB and RSB states corresponding 
    to the LSP till the occurrence of any of the following events. 

  
  
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    - Both Node-ID signaling adjacencies with Phop and PPhop nodes go 
    down, or 

    - MP receives normal or "Remote" PathTear for PSB, or 

    - MP receives ResvTear for RSB. 

 4.2.7. Phop Node Failure on Node that is LP-MP and NP-MP 

    If a router that is both LP-MP and NP-MP detects Phop node failure, 
    then the node SHOULD retain PSB and RSB states corresponding to the 
    LSP till the occurrence of any of the following events. 

    - Remote Node-ID signaling adjacency with PPhop PLR goes down, or 

    - MP receives normal or "Remote" PathTear for PSB, or 

    - MP receives ResvTear for RSB. 

 4.3. Conditional Path Tear 

    In the example provided in the Section 4.2.5 "NP-MP Behavior on PLR 
    link failure", B deletes PSB and RSB states corresponding to the LSP 
    once B detects its link to Phop went down as B is not MP. If B were 
    to send PathTear normally, then C would delete LSP state 
    immediately. In order to avoid this, there should be some mechanism 
    by which B can indicate to C that B does not require the receiving 
    node to unconditionally delete the LSP state immediately. For this, 
    B SHOULD add a new optional object called CONDITIONS object in 
    PathTear. The new optional object is defined in Section 4.3.3. If 
    node C also understands the new object, then C SHOULD delete LSP 
    state only if it is not an NP-MP - in other words C SHOULD delete 
    LSP state if there is no "remote" PLR state on C. 

 4.3.1. Sending Conditional Path Tear 

    A router that is not an MP for an LSP SHOULD delete PSB and RSB 
    states corresponding to the LSP if Phop link or Phop Node-ID 
    signaling adjacency goes down (Section 4.2.1). The router SHOULD 
    send Conditional PathTear if the following are also true. 

    - Ingress has requested node protection for the LSP, and 

    - PathTear is not received from upstream node 

  
  
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 4.3.2. Processing Conditional Path Tear 

    When a router that is not an NP-MP receives Conditional PathTear, 
    the node SHOULD delete PSB and RSB states corresponding to the LSP, 
    and process Conditional PathTear by considering it as normal 
    PathTear. Specifically, the node SHOULD NOT propagate Conditional 
    PathTear downstream but remove the optional object and send normal 
    PathTear downstream. 

    When a node that is an NP-MP receives Conditional PathTear, it 
    SHOULD NOT delete LSP state. The node SHOULD check whether the Phop 
    node had previously included SUMMARY_FRR_BYPASS_ASSOCIATION sub-
    object in PATH RRO. If the sub-object had been included previously 
    by Phop, then the node SHOULD remove the 
    SUMMARY_FRR_BYPASS_ASSOCIATION sub-object corresponding to the Phop 
    from the RRO and trigger PATH downstream. 

    If Conditional PathTear is received from a neighbor that has not 
    advertised support (refer to Section 4.5) for the new procedures 
    defined in this document, then the node SHOULD consider the message 
    as normal PathTear. The node SHOULD propagate normal PathTear 
    downstream and delete LSP state. 

 4.3.3. CONDITIONS object 

    As any implementation that does not support Conditional PathTear 
    SHOULD ignore the new object but process the message as normal 
    PathTear without generating any error, the Class-Num of the new 
    object SHOULD be 10bbbbbb where 'b' represents a bit (from Section 
    3.10 of [RFC2205]). 

    The new object is called as "CONDITIONS" object that will specify 
    the conditions under which default processing rules of the RSVP-TE 
    message SHOULD be invoked.  

    The object has the following format: 
     
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
       |          Length               |  Class        |     C-type    | 
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
       |                         Reserved                            |M| 
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
     

  
  
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    Length 

    This contains the size of the object in bytes and should be set to 
    eight. 

    Class 

    TBD 

    C-type 

    1 

    M bit 

    This bit indicates that the message SHOULD be processed based on the 
    condition whether the receiving node is Merge Point or not. 

 4.4. Remote State Teardown 

    If the Ingress wants to tear down the LSP because of a management 
    event while the LSP is being locally repaired at a transit PLR, it 
    would not be desirable to wait till backup LSP signaling to perform 
    state cleanup. To enable LSP state cleanup when the LSP is being 
    locally repaired, the PLR SHOULD send "remote" PathTear message 
    instructing the MP to delete PSB and RSB states corresponding to the 
    LSP. 

    Consider node C in example topology (Figure 1) has gone down and B 
    locally repairs the LSP. 

    1. Ingress A receives a management event to tear down the LSP. 
    2. A sends normal PathTear to B. 
    3. To enable LSP state cleanup, B SHOULD send "remote" PathTear with 
      destination IP address set to that of D used in Node-ID signaling 
      adjacency with D, and HOP object containing local address used in 
      Node-ID signaling adjacency. 
    4. B then deletes PSB and RSB states corresponding to the LSP. 
    5. On D there would be a remote signaling adjacency with B and so D 
      SHOULD accept the remote PathTear and delete PSB and RSB states 
      corresponding to the LSP. 

  
  
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 4.4.1. PLR Behavior on Local Repair Failure 

    If local repair fails on the PLR after a failure, then this should 
    be considered as a case for cleaning up LSP state from PLR to the 
    Egress. PLR would achieve this using "remote" PathTear to clean up 
    state from MP. If MP has retained state, then it would propagate 
    PathTear downstream thereby achieving state cleanup. Note that in 
    the case of link protection, the PathTear would be directed to LP-MP 
    node IP address rather than the Nhop interface address. 

 4.4.2. PLR Behavior on Resv RRO Change 

    When a router that has already made NP available detects a change in 
    the RRO carried in RESV message, and if the RRO change indicates 
    that the router's former NP-MP is no longer present in the LSP path, 
    then the router SHOULD send "Remote" PathTear directly to its former 
    NP-MP.  

    In the example topology in Figure 1, assume A has made node 
    protection available and C has concluded it is NP-MP. When the B-C 
    link fails then implementing the procedure specified in Section 
    4.2.4 of this document, C will retain state till: remote NodeID 
    control plane adjacency with A goes down, or PathTear or ResvTear is 
    received for PSB or RSB respectively. If B also has made node 
    protection available, B will eventually complete backup LSP 
    signaling with its NP-MP D and trigger RESV to A with RRO changed. 
    The new RRO of the LSP carried in RESV will not contain C. When A 
    processes the RESV with a new RRO not containing C - its former NP-
    MP, A SHOULD send "Remote" PathTear to C. When C receives a "Remote" 
    PathTear for its PSB state, C will send normal PathTear downstream 
    to D and delete both PSB and RSB states corresponding to the LSP. As 
    D has already received backup LSP signaling from B, D will retain 
    control plane and forwarding states corresponding to the LSP. 

 4.4.3. LSP Preemption during Local Repair 

    If an LSP is preempted when there is no failure along the path of 
    the LSP, the node on which preemption occurs would send PathErr and 
    ResvTear upstream and only delete the forwarding state and RSB state 
    corresponding to the LSP. But if the LSP is being locally repaired 
    upstream of the node on which the LSP is preempted, then the node 
    SHOULD delete both PSB and RSB states corresponding to the LSP and 
    send normal PathTear downstream. 

  
  
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 4.4.3.1. Preemption on LP-MP after Phop Link failure 

    If an LSP is preempted on LP-MP after its Phop or incoming link has 
    already failed but the backup LSP has not been signaled yet, then 
    the node SHOULD send normal PathTear and delete both PSB and RSB 
    states corresponding to the LSP. As the LP-MP has retained LSP state 
    because the PLR would signal the LSP through backup LSP signaling, 
    preemption would bring down the LSP and the node would not be LP-MP 
    any more requiring the node to clean up LSP state. 

 4.4.3.2. Preemption on NP-MP after Phop Link failure 

    If an LSP is preempted on NP-MP after its Phop link has already 
    failed but the backup LSP has not been signaled yet, then the node 
    SHOULD send normal PathTear and delete PSB and RSB states 
    corresponding to the LSP. As the NP-MP has retained LSP state 
    because the PLR would signal the LSP through backup LSP signaling, 
    preemption would bring down the LSP and the node would not be NP-MP 
    any more requiring the node to clean up LSP state. 

    Consider B-C link goes down on the same example topology (Figure 1). 
    As C is NP-MP for PLR A, C will retain LSP state. 

      1. The LSP is preempted on C. 
      2. C will delete RSB state corresponding to the LSP. But C cannot 
        send PathErr or ResvTear to PLR A because backup LSP has not 
        been signaled yet. 
      3. As the only reason for C having retained state after Phop node 
        failure was that it was NP-MP, C SHOULD send normal PathTear to 
        D and delete PSB state also. D would also delete PSB and RSB 
        states on receiving PathTear from C. 
      4. B starts backup LSP signaling to D. But as D does not have the 
        LSP state, it will reject backup LSP PATH and send PathErr to B. 
      5. B will delete its reservation and send ResvTear to A. 
 4.5. Backward Compatibility Procedures 

    The "Refresh interval Independent FRR" or RI-RSVP-FRR referred below 
    in this section refers to the changes that have been proposed in 
    previous sections. Any implementation that does not support them has 
    been termed as "non-RI-RSVP-FRR implementation". The extensions 
    proposed in [SUMMARY-FRR] are applicable to implementations that do 
    not support RI-RSVP-FRR. On the other hand, changes proposed 
  
  
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    relating to LSP state cleanup namely Conditional and remote PathTear 
    require support from one-hop and two-hop neighboring nodes along the 
    LSP path. So procedures that fall under LSP state cleanup category 
    SHOULD be turned on only if all nodes involved in the node 
    protection FRR i.e. PLR, MP and intermediate node in the case of NP, 
    support the extensions. Note that for LSPs requesting only link 
    protection, the PLR and the LP-MP should support the extensions. 

 4.5.1. Detecting Support for Refresh interval Independent FRR 

    An implementation supporting the extensions specified in previous 
    sections (called RI-RSVP-FRR here after) SHOULD set the flag 
    "Refresh interval Independent RSVP" or RI-RSVP in CAPABILITY object 
    in Hello messages. The RI-RSVP flag is specified in [TE-SCALE-REC]. 

    -  As nodes supporting the extensions SHOULD initiate Node Hellos 
      with adjacent nodes, a node on the path of protected LSP can 
      determine whether its Phop or Nhop neighbor supports RI-RSVP-FRR 
      enhancements from the Hello messages sent by the neighbor. 

    -  If a node attempts to make node protection available, then the 
      PLR SHOULD initiate remote Node-ID signaling adjacency with NNhop. 
      If the NNhop (a) does not reply to remote node Hello message or 
      (b) does not set "Enhanced facility protection" flag in CAPABILITY 
      object in the reply, then the PLR can conclude that NNhop does not 
      support RI-RSVP-FRR extensions. 

    -  If node protection is requested for an LSP and if (a) PPhop node 
      has not included a matching SUMMARY_FRR_BYPASS_ASSIGNMENT sub-
      object in PATH RRO or (b) PPhop node has not initiated remote node 
      Hello messages, then the node SHOULD conclude that PLR does not 
      support RI-RSVP-FRR extensions. The details are described in the 
      "Procedures for backward compatibility" section below. 

    Any node that sets the I-bit is set in its CAPABILITY object MUST 
    also set Refresh-Reduction-Capable bit in common header of all RSVP-
    TE messages. 

 4.5.2. Procedures for backward compatibility 

    The procedures defined hereafter are performed on a subset of LSPs 
    that traverse a node, rather than on all LSPs that traverse a node. 
    This behavior is required to support backward compatibility for a 
    subset of LSPs traversing nodes running non-RI-RSVP-FRR 
    implementations.  

  
  
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 4.5.2.1. Lack of support on Downstream Node 

    -  If the Nhop does not support the RI-RSVP-FRR extensions, then the 
      node SHOULD reduce the "refresh period" in TIME_VALUES object 
      carried in PATH to default small refresh default value. 

    -  If node protection is requested and the NNhop node does not 
      support the enhancements, then the node SHOULD reduce the "refresh 
      period" in TIME_VALUES object carried in PATH to a small refresh 
      default value. 

    If the node reduces the refresh time from the above procedures, it 
    SHOULD also not send remote PathTear or Conditional PathTear 
    messages. 

    Consider the example topology in Figure 1. If C does not support the 
    RI-RSVP-FRR extensions, then: 

    -  A and B SHOULD reduce the refresh time to default value of 30 
      seconds and trigger PATH 

    -  If B is not an MP and if Phop link of B fails, B cannot send 
      Conditional PathTear to C but SHOULD time out PSB state from A 
      normally. This would be accomplished if A would also reduce the 
      refresh time to default value. So if C does not support the RI-
      RSVP-FRR extensions, then Phop B and PPhop A SHOULD reduce refresh 
      time to a small default value.  

 4.5.2.2. Lack of support on Upstream Node 

    -  If Phop node does not support the RI-RSVP-FRR extensions, then 
      the node SHOULD reduce the "refresh period" in TIME_VALUES object 
      carried in RESV to default small refresh time value. 

    -  If node protection is requested and the Phop node does not 
      support the RI-RSVP-FRR extensions, then the node SHOULD reduce 
      the "refresh period" in TIME_VALUES object carried in PATH to 
      default value. 

    -  If node protection is requested and PPhop node does not support 
      the RI-RSVP-FRR extensions, then the node SHOULD reduce the 
      "refresh period" in TIME_VALUES object carried in RESV to default 
      value. 

  
  
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    -  If the node reduces the refresh time from the above procedures, 
      it SHOULD also not execute MP procedures specified in Section 4.2 
      of this document. 

 4.5.2.3. Incremental Deployment 

    The backward compatibility procedures described in the previous sub-
    sections imply that a router supporting the RI-RSVP-FRR extensions 
    specified in this document can apply the procedures specified in the 
    document either in the downstream or upstream direction of an LSP, 
    depending on the capability of the routers downstream or upstream in 
    the LSP path. 

    -  RI-RSVP-FRR extensions and procedures are enabled for downstream 
      Path,  PathTear and ResvErr messages corresponding to an LSP if 
      link protection is requested for the LSP and the Nhop node 
      supports the extensions 

    -  RI-RSVP-FRR extensions and procedures are enabled for downstream 
      Path,  PathTear and ResvErr messages corresponding to an LSP if 
      node protection is requested for the LSP and both Nhop & NNhop 
      nodes support the extensions 

    -  RI-RSVP-FRR extensions and procedures are enabled for upstream 
      PathErr, Resv and ResvTear messages corresponding to an LSP if 
      link protection is requested for the LSP and the Phop node 
      supports the extensions 

    -  RI-RSVP-FRR extensions and procedures are enabled for upstream 
      PathErr, Resv and ResvTear messages corresponding to an LSP if 
      node protection is requested for the LSP and both Phop and PPhop 
      nodes support the extensions 

    For example, if an implementation supporting the RI-RSVP-FRR 
    extensions specified in this document is deployed on all routers in 
    particular region of the network and if all the LSPs in the network 
    request node protection, then the FRR extensions will only be 
    applied for the LSP segments that traverse the particular region. 
    This will aid incremental deployment of these extensions and also 
    allow reaping the benefits of the extensions in portions of the 
    network where it is supported.  

 5. Security Considerations 

    This document extends the applicability of Node-ID based Hello 
    session between immediate neighbors. The Node-ID based Hello session 
  
  
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    between PLR and NP-MP may require the two routers to exchange Hello 
    messages with non-immediate neighbor. So, the implementations SHOULD 
    provide the option to configure Node-ID neighbor specific or global 
    authentication key to authentication messages received from Node-ID 
    neighbors. The network administrator MAY utilize this option to 
    enable RSVP-TE routers to authenticate Node-ID Hello messages 
    received with TTL greater than 1. 

 6. IANA Considerations 

 6.1. New Object - CONDITIONS 

    [RFC2205] defines the Class-Number name space for RSVP objects. The 
    name space is managed by IANA. 
     
    IANA registry: RSVP Parameters 
    Subsection: Class Names, Class Numbers, and Class Types 
     
    A new RSVP object using a Class-Number of form 10bbbbbb called the 
    "CONDITIONS" object is defined in Section 4.3 of this document. The 
    Class-Number is TBD.   
     
     
 7. Normative References 

    [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 
             Requirement Levels", BCP 14, RFC 2119, March 1997. 
     
    [RFC4090] Pan, P., "Fast Reroute Extensions to RSVP-TE for LSP         
             Tunnels", RFC 4090, May 2005. 
     
    [RFC2961] Berger, L., "RSVP Refresh Overhead Reduction Extensions",  
             RFC 2961, April 2001. 
     
    [RFC2205] Braden, R., "Resource Reservation Protocol (RSVP)", RFC  
             2205, September 1997. 
     
    [RFC4558] Ali, Z., "Node-ID Based Resource Reservation (RSVP) Hello:  
             A Clarification Statement", RFC 4558, June 2006. 
     
    [RFC3473] Berger, L., "Generalized Multi-Protocol Label Switching 
             Signaling Resource Reservation Protocol-Traffic Engineering 
             Extensions", RFC 3473, January 2003. 
     

  
  
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    [RFC5063] Satyanarayana, A., "Extensions to GMPLS Resource 
             Reservation Protocol Graceful Restart", RFC5063, October 
             2007. 
     
    [TE-SCALE-REC]  Vishnu Pavan Beeram et. al, "Implementation 
             Recommendations to improve scalability of RSVP-TE 
             Deployments", draft-beeram-teas-rsvp-te-scaling-rec (work 
             in progress) 
     
    [SUMMARY-FRR]   Mike Tallion et. al, "RSVP-TE Summary Fast Reroute 
             Extensions for LSP Tunnels", draft-mtaillon-mpls-summary-
             frr-rsvpte (work in progress) 

 8. Acknowledgments 
     
    We are very grateful to Yakov Rekhter for his contributions to the 
    development of the idea and thorough review of content of the draft. 
    Thanks to Raveendra Torvi and Yimin Shen for their comments and 
    inputs. 
     
 9. Authors' Addresses 

    Chandra Ramachandran 
    Juniper Networks 
    Email: csekar@juniper.net 
     
    Ina Minei 
    Google, Inc 
    inaminei@google.com 
     
    Ebben Aries 
    Facebook 
    Email: exa@fb.com 
     
    Dante Pacella 
    Verizon 
    Email: dante.j.pacella@verizon.com 
     
    Tarek Saad 
    Cisco Systems Inc. 
    Email: tsaad@cisco.com 
     
    Markus Jork 
    Juniper Networks 
    Email: mjork@juniper.net 
     
   
  
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    Harish Sitaraman 
    Juniper Networks 
    Email: hsitaraman@juniper.net 
     
    Vishnu Pavan Beeram 
    Juniper Networks 
    Email: vbeeram@juniper.net 
     
    Mike Tallion 
    Cisco Systems Inc. 
    Email: mtallion@cisco.com 
     

  
   
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