Refresh-interval Independent FRR Facility Protection
draft-ietf-mpls-ri-rsvp-frr-11

Document Type Active Internet-Draft (mpls WG)
Authors Chandrasekar R  , Tarek Saad  , Ina Minei  , Dante Pacella 
Last updated 2021-06-20
Replaces draft-chandra-mpls-ri-rsvp-frr
Stream Internet Engineering Task Force (IETF)
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MPLS Working Group                                       C. Ramachandran
Internet-Draft                                                   T. Saad
Updates: 4090 (if approved)                       Juniper Networks, Inc.
Intended status: Standards Track                                I. Minei
Expires: December 22, 2021                                  Google, Inc.
                                                              D. Pacella
                                                           Verizon, Inc.
                                                           June 20, 2021

          Refresh-interval Independent FRR Facility Protection
                     draft-ietf-mpls-ri-rsvp-frr-11

Abstract

   RSVP-TE Fast ReRoute extensions specified in RFC 4090 defines two
   local repair techniques to reroute Label Switched Path (LSP) traffic
   over pre-established backup tunnel.  Facility backup method allows
   one or more LSPs traversing a connected link or node to be protected
   using a bypass tunnel.  The many-to-one nature of local repair
   technique is attractive from scalability point of view.  This
   document enumerates facility backup procedures in RFC 4090 that rely
   on refresh timeout and hence make facility backup method refresh-
   interval dependent.  The RSVP-TE extensions defined in this document
   will enhance the facility backup protection mechanism by making the
   corresponding procedures refresh-interval independent and hence
   compatible with Refresh-interval Independent RSVP (RI-RSVP) specified
   in RFC 8370.  Hence, this document updates RFC 4090 in order to
   support RI-RSVP capability specified in RFC 8370.

Requirements Language

   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].

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

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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 22, 2021.

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.  Motivation  . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Problem Description . . . . . . . . . . . . . . . . . . . . .   5
   4.  Solution Aspects  . . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Requirement on RFC 4090 Capable Node to advertise RI-RSVP
           Capability  . . . . . . . . . . . . . . . . . . . . . . .   8
     4.2.  Signaling Handshake between PLR and MP  . . . . . . . . .   9
       4.2.1.  PLR Behavior  . . . . . . . . . . . . . . . . . . . .   9
       4.2.2.  Remote Signaling Adjacency  . . . . . . . . . . . . .  10
       4.2.3.  MP Behavior . . . . . . . . . . . . . . . . . . . . .  10
       4.2.4.  "Remote" State on MP  . . . . . . . . . . . . . . . .  11
     4.3.  Impact of Failures on LSP State . . . . . . . . . . . . .  12
       4.3.1.  Non-MP Behavior . . . . . . . . . . . . . . . . . . .  12
       4.3.2.  LP-MP Behavior  . . . . . . . . . . . . . . . . . . .  13
       4.3.3.  NP-MP Behavior  . . . . . . . . . . . . . . . . . . .  13
       4.3.4.  Behavior of a Router that is both LP-MP and NP-MP . .  14
     4.4.  Conditional PathTear  . . . . . . . . . . . . . . . . . .  15
       4.4.1.  Sending Conditional PathTear  . . . . . . . . . . . .  15
       4.4.2.  Processing Conditional PathTear . . . . . . . . . . .  15
       4.4.3.  CONDITIONS Object . . . . . . . . . . . . . . . . . .  16
     4.5.  Remote State Teardown . . . . . . . . . . . . . . . . . .  17
       4.5.1.  PLR Behavior on Local Repair Failure  . . . . . . . .  17
       4.5.2.  PLR Behavior on Resv RRO Change . . . . . . . . . . .  17
       4.5.3.  LSP Preemption during Local Repair  . . . . . . . . .  18
         4.5.3.1.  Preemption on LP-MP after Phop Link Failure . . .  18

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         4.5.3.2.  Preemption on NP-MP after Phop Link Failure . . .  18
     4.6.  Backward Compatibility Procedures . . . . . . . . . . . .  19
       4.6.1.  Detecting Support for Refresh interval Independent
               FRR . . . . . . . . . . . . . . . . . . . . . . . . .  19
       4.6.2.  Procedures for Backward Compatibility . . . . . . . .  20
         4.6.2.1.  Lack of support on Downstream Node  . . . . . . .  20
         4.6.2.2.  Lack of support on Upstream Node  . . . . . . . .  21
         4.6.2.3.  Advertising RI-RSVP without RI-RSVP-FRR . . . . .  21
         4.6.2.4.  Incremental Deployment  . . . . . . . . . . . . .  22
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  23
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  23
     6.1.  New Object - CONDITIONS . . . . . . . . . . . . . . . . .  23
     6.2.  CONDITIONS Flags  . . . . . . . . . . . . . . . . . . . .  24
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  24
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  24
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  24
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  24
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  26
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26

1.  Introduction

   RSVP-TE relies on periodic refresh of RSVP messages to synchronize
   and maintain the Label Switched Path (LSP) related states along the
   reserved path.  In the absence of refresh messages, the LSP-related
   states are automatically deleted.  Reliance on periodic refreshes and
   refresh timeouts are problematic from the scalability point of view.
   The number of RSVP-TE LSPs that a router needs to maintain has been
   growing in service provider networks and the implementations should
   be capable of handling increase in LSP scale.

   RFC 2961 specifies mechanisms to eliminate the reliance on periodic
   refresh and refresh timeout of RSVP messages, and enables a router to
   increase the message refresh interval to values much longer than the
   default 30 seconds defined in RFC 2205.  However, the protocol
   extensions defined in RFC 4090 for supporting Fast ReRoute (FRR)
   using bypass tunnels implicitly rely on short refresh timeouts to
   cleanup stale states.

   In order to eliminate the reliance on refresh timeouts, the routers
   should unambiguously determine when a particular LSP state should be
   deleted.  In scenarios involving RFC 4090 FRR using bypass tunnels,
   additional explicit tear down messages are necessary.  Refresh-
   interval Independent RSVP FRR (RI-RSVP-FRR) extensions specified in
   this document consists of procedures to enable LSP state cleanup that
   are essential in supporting RI-RSVP capability for RFC 4090 FRR using
   bypass tunnels.

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1.1.  Motivation

   Base 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 RSVP Refresh Overhead Reduction Extensions [RFC2961].

   The problems listed above adversely affect RSVP control plane
   scalability and RSVP-TE [RFC3209] inherited these problems from
   standard RSVP.  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 implementations 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 3 of RSVP-TE Scaling
   Techniques [RFC8370].

   However, the facility backup protection procedures specified in
   [RFC4090] do not fully address stale state cleanup as the procedures
   depend on refresh timeouts for stale state cleanup.  The updated
   facility backup protection procedures specified in this document, in
   combination with RSVP-TE Scaling Techniques [RFC8370], eliminate this
   dependency on refresh timeouts for stale state cleanup.

   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.

2.  Terminology

   The reader is expected to be familiar with the terminology in
   [RFC2205], [RFC3209], [RFC4090], [RFC4558], [RFC8370] and [RFC8796].

   Phop node: Previous-hop router along the label switched path

   PPhop node: Previous-Previous-hop router along the label switched
   path

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   Nhop node: Next-hop router along the label switched path

   NNhop node: Next-Next-hop router along the label switched path

   PLR: Point of Local Repair router as defined in [RFC4090]

   MP: Merge Point router as defined in [RFC4090]

   LP-MP node: Merge Point router at the tail of Link-Protecting bypass
   tunnel

   NP-MP node: Merge Point router at the tail of Node-Protecting bypass
   tunnel

   TED: Traffic Engineering Database

   LSP state: 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

   RI-RSVP: The set of procedures defined in Section 3 of RSVP-TE
   Scaling Techniques [RFC8370] to eliminate RSVP's reliance on periodic
   message refreshes

   B-SFRR-Ready: Bypass Summary FRR Ready Extended Association object
   defined in Summary FRR extensions [RFC8796] and is added by the PLR
   for each protected LSP.

   RI-RSVP-FRR: The set of procedures defined in this document to
   elimiate RSVP's reliance of periodic message refreshes when
   supporting facility backup protection [RFC4090]

   Conditional PathTear: A PathTear message containing a suggestion to a
   receiving downstream router to retain the path state if the receiving
   router is an NP-MP

   Remote PathTear: A PathTear message sent from a Point of Local Repair
   (PLR) to the MP to delete the LSP state on the MP if PLR had not
   previously sent the backup Path state reliably

3.  Problem Description

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                                 E
                               /   \
                              /     \
                             /       \
                            /         \
                           /           \
                          /             \
                         A ----- B ----- C ----- D
                                 \             /
                                  \           /
                                   \         /
                                    \       /
                                     \     /
                                      \   /
                                        F

                        Figure 1: Example Topology

   In the topology in Figure 1, let us consider a large number of LSPs
   from A to D transiting B and C.  Assume that refresh interval has
   been configured to be long of the order of minutes and refresh
   reduction extensions are enabled on all routers.

   Also let us 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 PLR and C is the 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 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.

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   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 the
      tear down messages for all LSPs.  As each router should consider
      itself as an MP, C will time out the state only after waiting for
      an additional duration equal to refresh timeout.

   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 a 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.

   -  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 a 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 an 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 RSVP-TE Summary
      FRR [RFC8796] that enables the PLR to signal the availability of
      local protection to the MP.  In addition, introduce PLR and MP

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      procedures to to establish Node-ID based hello session between the
      PLR and the MP to detect router failures and to determine
      capability.  See section 4.2 for more details.  This part of the
      solution re-uses some of the extensions defined in RSVP-TE Summary
      FRR [RFC8796] and RSVP-TE Scaling Techniques [RFC8370], and the
      subsequent sub-sections will list the extensions in these drafts
      that are utilized in this document.

   -  Handle upstream link or node failures by cleaning up LSP states if
      the node has not found itself as an MP through the MP
      determination mechanism.  See section 4.3 for more details.

   -  Introduce extensions to enable a router to send a tear down
      message to the downstream router that enables the receiving router
      to conditionally delete its local LSP state.  See section 4.4 for
      more details.

   -  Enhance facility backup protection by allowing a PLR to directly
      send a tear down message to the MP without requiring the PLR to
      either have a working bypass LSP or have already signaled backup
      LSP state.  See section 4.5 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 4.6 for more
      details.

4.1.  Requirement on RFC 4090 Capable Node to advertise RI-RSVP
      Capability

   A node supporting facility backup protection [RFC4090] MUST set the
   RI-RSVP capability (I bit) defined in Section 3.1 of RSVP-TE Scaling
   Techniques [RFC8370] only if it supports all the extensions specified
   in the rest of this document.  Hence, this document updates RFC 4090
   by defining extensions and additional procedures over facility backup
   protection [RFC4090] in order to advertise RI-RSVP capability
   [RFC8370].  However, if a node supporting facility backup protection
   [RFC4090] does set the RI-RSVP capability (I bit) but does not
   support all the extensions specified in the rest of this document,
   then it leaves room for stale state to linger around for an
   inordinate period of time given the long refresh intervals
   recommended by RFC 8370 or disruption of normal FRR operation.
   Procedures for backward compatibility Section 4.6.2.3 delves on this
   in detail.

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4.2.  Signaling Handshake between PLR and MP

4.2.1.  PLR Behavior

   As per the facility backup procedures [RFC4090], when an LSP becomes
   operational on a node and the "local protection desired" flag has
   been set in the SESSION_ATTRIBUTE object carried in the Path message
   corresponding to the LSP, then the node 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, the node attempts to
      create an LP-bypass LSP to the Nhop node avoiding only the link
      that the protected LSP takes to reach the Nhop

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

   With regard to the PLR procedures described above and that are
   specified in RFC 4090, this document specifies the following
   additional procedures to support RI-RSVP [RFC8370].

   -  While selecting the destination address of the bypass LSP, the PLR
      MUST select the router ID of the NNhop or Nhop node from the Node-
      ID sub-object included in the RRO object carried in the most
      recent Resv message corresponding to the LSP.  If the MP has not
      included a Node-ID sub-object in the Resv RRO and if the PLR and
      the MP are in the same area, then the PLR may utilize the TED to
      determine the router ID corresponding to the interface address
      included by the MP in the RRO object.  If the NP-MP in a different
      IGP area has not included a Node-ID sub-object in RRO object, then
      the PLR MUST execute backward compatibility procedures as if the
      downstream nodes along the LSP do not support the extensions
      defined in the document (see Section 4.6.2.1).

   -  The PLR MUST also include its router ID in a Node-ID sub-object in
      RRO object carried in any subsequent Path message corresponding to
      the LSP.  While including its router ID in the Node-ID sub-object
      carried in the outgoing Path message, the PLR MUST include the
      Node-ID sub-object after including its IPv4/IPv6 address or
      unnumbered interface ID sub-object.

   -  In parallel to the attempt made to create NP-bypass or LP-bypass,
      the PLR MUST initiate a Node-ID based Hello session to the NNhop
      or Nhop node respectively along the LSP to establish the RSVP-TE

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      signaling adjacency.  This Hello session is used to detect MP node
      failure as well as determine the capability of the MP node.  If
      the MP has set the I-bit in the CAPABILITY object [RFC8370]
      carried in Hello message corresponding to the Node-ID based Hello
      session, then the PLR MUST conclude that the MP supports refresh-
      interval independent FRR procedures defined in this document.  If
      the MP has not sent Node-ID based Hello messages or has not set
      the I-bit in CAPABILITY object [RFC8370], then the PLR MUST
      execute backward compatibility procedures defined in
      Section 4.6.2.1 of this document.

   -  When the PLR associates a bypass to a protected LSP, it MUST
      include a B-SFRR-Ready Extended Association object [RFC8796] and
      trigger a Path message to be sent for the LSP.  If a B-SFRR-Ready
      Extended Association object is included in the Path message
      corresponding to the LSP, the encoding and object ordering rules
      specified in RSVP-TE Summary FRR [RFC8796] MUST be followed.  In
      addition to those rules, the PLR MUST set the Association Source
      in the object to its Node-ID address.

4.2.2.  Remote Signaling Adjacency

   A Node-ID based RSVP-TE Hello session is one in which Node-ID is used
   in the source and the destination address fields of RSVP Hello
   messages [RFC4558].  This document extends Node-ID based RSVP Hello
   session to track the state of any RSVP-TE neighbor that is not
   directly connected by at least one interface.  In order to apply
   Node-ID based RSVP-TE Hello session between any two routers that are
   not immediate neighbors, the router that supports the extensions
   defined in the document MUST set TTL to 255 in all outgoing Node-ID
   based Hello messages exchanged between the PLR and the MP.  The
   default hello interval for this Node-ID hello session MUST be set to
   the default specified in RSVP-TE Scaling Techniques [RFC8370].

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

4.2.3.  MP Behavior

   With regard to the MP procedures that are defined in [RFC4090] this
   document specifies the following additional procedures to support RI-
   RSVP defined in [RFC8370].

   Each node along an LSP path supporting the extensions defined in this
   document MUST also include its router ID in the Node-ID sub-object of
   the RRO object carried in the Resv message of the corresponding LSP.
   If the PLR has not included a Node-ID sub-object in the RRO object

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   carried in the Path message and if the PLR is in a different IGP
   area, then the router MUST NOT execute the MP procedures specified in
   this document for those LSPs.  Instead, the node MUST execute
   backward compatibility procedures defined in Section 4.6.2.2 as if
   the upstream nodes along the LSP do not support the extensions
   defined in this document.

   A node receiving a Path message should determine whether the message
   contains a B-SFRR-Ready Extended Association object with its own
   address as the bypass destination address and whether it has an
   operational Node-ID signaling adjacency with the Association source.
   If the PLR has not included the B-SFRR-Ready Extended Association
   object or if there is no operational Node-ID signaling adjacency with
   the PLR identified by the Association source address or if the PLR
   has not advertised RI-RSVP capability in its Node-ID based Hello
   messages, then the node MUST execute the backward compatibility
   procedures defined in Section 4.6.2.2.

   If a matching B-SFRR-Ready Extended Association object is found in in
   the Path message and if there is an operational remote Node-ID
   signaling adjacency with the PLR (identified by the Association
   source) that has advertised RI-RSVP capability (I-bit) [RFC8370],
   then the node MUST consider itself as the MP for the PLR.  The
   matching and ordering rules for Bypass Summary FRR Extended
   Association specified in RSVP-TE Summary FRR [RFC8796] MUST be
   followed by the implementations supporting this document.

   -  If a matching Bypass Summary FRR Extended Association object is
      included by the PPhop node of an LSP and if a corresponding Node-
      ID signaling adjacency exists with the PPhop node, then the router
      MUST conclude it is the NP-MP.

   -  If a matching Bypass Summary FRR Extended Association object is
      included by the Phop node of an LSP and if a corresponding Node-ID
      signaling adjacency exists with the Phop node, then the router
      MUST conclude it is the LP-MP.

4.2.4.  "Remote" State on MP

   Once a router concludes it is the MP for a PLR running refresh-
   interval independent FRR procedures as described in the preceding
   section, it MUST create a remote path state for the LSP.  The only
   difference between the "remote" path state and the LSP state is the
   RSVP_HOP object.  The RSVP_HOP object in a "remote" path state
   contains the address that the PLR uses to send Node-ID hello messages
   to the MP.

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   The MP MUST consider the "remote" path state corresponding to the LSP
   automatically deleted if:

   -  The MP later receives a Path message for the LSP with no matching
      B-SFRR-Ready Extended Association object corresponding to the
      PLR's IP address contained in the Path RRO, or

   -  The Node-ID signaling adjacency with the PLR goes down, or

   -  The MP receives backup LSP signaling for the LSP from the PLR or

   -  The MP receives a PathTear for the LSP, or

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

   The purpose of "remote" path state is to enable the PLR to explicitly
   tear down the path and reservation states corresponding to the LSP by
   sending a tear message for the "remote" path state.  Such a message
   tearing down "remote" path state is called "Remote" PathTear.

   The scenarios in which a "Remote" PathTear is applied are described
   in Section 4.5.

4.3.  Impact of Failures on LSP State

   This section describes the procedures that must be executed upon
   different kinds of failures by nodes along the path of the LSP.  The
   procedures that must be executed upon detecting RSVP signaling
   adjacency failures do not impact the RSVP-TE graceful restart
   mechanisms ([RFC3473], [RFC5063]).  If a node executing these
   procedures acts as a helper for a neighboring router, then the
   signaling adjacency with the neighbor will be declared as having
   failed only after taking into account the grace period extended for
   the neighbor by this node acting as a helper.

   Node failures are detected from the state of Node-ID hello sessions
   established with immediate neighbors.  RSVP-TE Scaling Techniques
   [RFC8370] recommends that each node establish Node-ID hello sessions
   with all its immediate neighbors.  Non-immediate PLR or MP failure is
   detected from the state of remote signaling adjacency established
   according to Section 4.2.2 of this document.

4.3.1.  Non-MP Behavior

   When a router detects the Phop link or the Phop node failure for an
   LSP and the router is not an MP for the LSP, then it MUST send a

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   Conditional PathTear (refer to Section 4.4 "Conditional PathTear"
   below) and delete the PSB and RSB states corresponding to the LSP.

4.3.2.  LP-MP Behavior

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

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

   -  The MP receives a normal or "Remote" PathTear for its PSB, or

   -  The MP receives a ResvTear for its RSB.

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

4.3.3.  NP-MP Behavior

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

   -  The remote Node-ID signaling adjacency with the PPhop PLR goes
      down, or

   -  The MP receives a normal or "Remote" PathTear for its PSB, or

   -  The MP receives a ResvTear for its RSB.

   When a router that is an NP-MP for an LSP did not detect the Phop
   link or the Phop node failure, but receives a Conditional PathTear
   from the Phop node, then the router MUST retain the PSB and RSB
   states corresponding to the LSP till the occurrence of any of the
   following events.

   -  The remote Node-ID signaling adjacency with the PPhop PLR goes
      down, or

   -  The MP receives a normal or "Remote" PathTear for its PSB, or

   -  The MP receives a ResvTear for its RSB.

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   Receiving a Conditional PathTear from the Phop node will not impact
   the "remote" state from the PPhop PLR.  Note that the Phop node must
   have sent the Conditional PathTear as it was not an MP for the LSP
   Section 4.3.1.

   In the example topology Figure 1, we assume C & D are the NP-MPs for
   the PLRs A & B respectively.  Now when A-B link fails, as B is not an
   MP and its Phop link has failed, B will delete the LSP state (this
   behavior is required for unprotected LSPs - Section 4.3.1).  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 the NP-MP for the PLR B.

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

   1. When C receives a Conditional PathTear from B, it decides to
      retain LSP state as it is the NP-MP of the PLR A.  C also MUST
      check whether Phop B had previously signaled availability of node
      protection.  As B had previously signaled NP availability by
      including B-SFRR-Ready Extended Association object, C MUST remove
      the B-SFRR-Ready Extended Association object containing
      Association Source set to B from the Path message and trigger a
      Path to D.

   2. When D receives the Path message, it realizes that it is no longer
      the NP-MP for B and so it deletes the corresponding "remote" path
      state.  D does not propagate the Path further down because the
      only change is that the B-SFRR-Ready Extended Association object
      corresponding to Association Source B is no longer present in the
      Path message.

4.3.4.  Behavior of a Router that is both LP-MP and NP-MP

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

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

   -  The MP receives a normal or "Remote" PathTear for its PSB, or

   -  The MP receives a ResvTear for its RSB.

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

   -  The remote Node-ID signaling adjacency with the PPhop PLR goes
      down, or

   -  The MP receives a normal or "Remote" PathTear for its PSB, or

   -  The MP receives a ResvTear for its RSB.

4.4.  Conditional PathTear

   In the example provided in the Section 4.3.3, B deletes the PSB and
   RSB states corresponding to the LSP once B detects its Phop link went
   down as B is not an MP.  If B were to send a 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 MUST add a new optional CONDITIONS object
   in the PathTear.  The CONDITIONS object is defined in Section 4.4.3.
   If node C also understands the new object, then C MUST NOT delete the
   LSP state if it is an NP-MP.

4.4.1.  Sending Conditional PathTear

   A router that is not an MP for an LSP MUST delete the PSB and RSB
   states corresponding to the LSP if the Phop link or the Phop Node-ID
   signaling adjacency goes down (Section 4.3.1).  The router MUST send
   a Conditional PathTear if the following are also true.

   -  The ingress has requested node protection for the LSP, and

   -  No PathTear is received from the upstream node

4.4.2.  Processing Conditional PathTear

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

   When a node that is an NP-MP receives a Conditional PathTear, it MUST
   NOT delete LSP state.  The node MUST check whether the Phop node had
   previously included the B-SFRR-Ready Extended Association object in

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   the Path.  If the object had been included previously by the Phop,
   then the node processing the Conditional PathTear from the Phop MUST
   remove the corresponding object and trigger a Path downstream.

   If a Conditional PathTear is received from a neighbor that has not
   advertised support (refer to Section 4.6) for the new procedures
   defined in this document, then the node MUST consider the message as
   a normal PathTear.  The node MUST propagate the normal PathTear
   downstream and delete the LSP state.

4.4.3.  CONDITIONS Object

   As any implementation that does not support Conditional PathTear MUST
   ignore the new object but process the message as a normal PathTear
   without generating any error, the Class-Num of the new object MUST 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 MUST be invoked.

   The object has the following format:

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Length               |  Class        |     C-type    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Reserved                            |M|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 2: CONDITIONS Object

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

      Class: To be assigned

      C-type: 1

      Merge-point condition (M) bit: If the M bit is set to 1, then the
      PathTear message MUST be processed according to the receiver
      router role, i.e. if the receiving router is an MP or not for the
      LSP.
      If the M-bit is set to 0, then the PathTear message MUST be
      processed processed as a normal PathTear message for the LSP.

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4.5.  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 the completion of backup LSP
   signaling to perform state cleanup.  To enable LSP state cleanup when
   the LSP is being locally repaired, the PLR MUST send a "Remote"
   PathTear message instructing the MP to delete the PSB and RSB states
   corresponding to the LSP.  The TTL in the "Remote" PathTear message
   MUST be set to 255.

   Let us consider that node C in the example topology (Figure 1) has
   gone down and node B locally repairs the LSP.

   1. Ingress A receives a management event to tear down the LSP.

   2. A sends a normal PathTear for the LSP to B.

   3. Assume B has not initiated the backup signaling for the LSP during
      local repair.  To enable LSP state cleanup, B MUST send a "Remote"
      PathTear with destination IP address set to that of the node D
      used in the Node-ID signaling adjacency with D, and the RSVP_HOP
      object containing local address used in the Node-ID signaling
      adjacency.

   4. B then deletes the PSB and RSB states corresponding to the LSP.

   5. On D there would be a remote signaling adjacency with B and so D
      MUST accept the "Remote" PathTear and delete the PSB and RSB
      states corresponding to the LSP.

4.5.1.  PLR Behavior on Local Repair Failure

   If local repair fails on the PLR after a failure, then this MUST be
   considered as a case for cleaning up LSP state from the PLR to the
   Egress.  The PLR achieves state cleanup by sending "Remote" PathTear
   to the MP.  The MP MUST delete the states corresponding to the LSP
   also also propagate the PathTear downstream thereby achieving state
   cleanup from all downstream nodes up to the LSP egress.  Note that in
   the case of link protection, the PathTear MUST be directed to the LP-
   MP's Node-ID IP address rather than the Nhop interface address.

4.5.2.  PLR Behavior on Resv RRO Change

   When a PLR router that has already made NP available for an LSP
   detects a change in the RRO carried in the Resv message that
   indicates that the router's former NP-MP is no longer present on the

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   path of the LSP, then the router MUST send a "Remote" PathTear
   directly to its former NP-MP.

   In the example topology Figure 1, let us assume A has made node
   protection available for an LSP and C has concluded it is the NP-MP
   for PLR A.  When the B-C link fails then C, implementing the
   procedure specified in Section 4.3.4 of this document, will retain
   the states corresponding to the LSP until: the remote Node-ID
   signaling adjacency with A goes down, or a PathTear or a ResvTear is
   received for its 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 a Resv to A with RRO changed.  The new
   RRO of the LSP carried in the Resv will not contain C.  When A
   processes the Resv message with a new RRO not containing C - its
   former NP-MP, A MUST send a "Remote" PathTear to C.  When C receives
   the "Remote" PathTear for its PSB state, C will send a normal
   PathTear downstream to D and delete both the 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.

4.5.3.  LSP Preemption during Local Repair

4.5.3.1.  Preemption on LP-MP after Phop Link Failure

   If an LSP is preempted on an LP-MP after its Phop or the incoming
   link has already failed but the backup LSP has not been signaled yet
   as part of local repair procedure, then the node MUST send a normal
   PathTear and delete both the PSB and RSB states corresponding to the
   LSP.  As the LP-MP has retained the LSP state expecting the PLR to
   initiate 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 the LSP state.

4.5.3.2.  Preemption on NP-MP after Phop Link Failure

   If an LSP is preempted on an NP-MP after its Phop link has already
   failed but the backup LSP has not been signaled yet, then the node
   MUST send a normal PathTear and delete the PSB and RSB states
   corresponding to the LSP.  As the NP-MP has retained LSP state
   expecting the PLR to initiate 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.

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

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   1. The LSP is preempted on C.

   2. C will delete the RSB state corresponding to the LSP.  But C
      cannot send a PathErr or a ResvTear to the PLR A because the
      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 an NP-MP, C MUST send a normal PathTear to
      D and delete its PSB state also.  D would also delete the PSB and
      RSB states on receiving a PathTear from C.

   4. B starts backup LSP signaling to D.  But as D does not have the
      LSP state, it will reject the backup LSP Path and send a PathErr
      to B.

   5. B will delete its reservation and send a ResvTear to A.

4.6.  Backward Compatibility Procedures

   "Refresh interval Independent FRR" or RI-RSVP-FRR refers to the set
   of procedures defined in this document to elimiate the reliance of
   periodic refreshes.  The extensions proposed in RSVP-TE Summary FRR
   [RFC8796] may apply to implementations that do not support RI-RSVP-
   FRR.  On the other hand, RI-RSVP-FRR extensions 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 MUST NOT be
   turned on if any of the nodes involved in the node protection FRR
   i.e.  the PLR, the MP and the intermediate node in the case of NP,
   DOES NOT support RI-RSVP-FRR extensions.  Note that for LSPs
   requesting link protection, only the PLR and the LP-MP MUST support
   the extensions.

4.6.1.  Detecting Support for Refresh interval Independent FRR

   An implementation supporting RI-RSVP-FRR extensions SHOULD set the
   flag "Refresh interval Independent RSVP" or RI-RSVP flag in the
   CAPABILITY object carried in Hello messages as specified in RSVP-TE
   Scaling Techniques [RFC8370].  If an implementation does not set the
   flag even if it supports RI-RSVP-FRR extensions, then its neighbors
   will view the node as any node that does not support the extensions.

   -  As nodes supporting the RI-RSVP-FRR extensions initiate Node-ID
      based signaling adjacency with all immedate neighbors, such a node
      on the path of a protected LSP can determine whether its Phop and
      Nhop neighbors support RI-RSVP-FRR enhancements.

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   -  As nodes supporting the RI-RSVP-FRR extensions also initiate Node-
      ID based signaling adjacency with the NNhop along the path of the
      LSP requested node protection Section 4.2.1, each node along the
      LSP path can determine whether its NNhop node supports RI-RSVP-FRR
      enhancements.  If the NNhop (a) does not reply to remote Node-ID
      Hello messages or (b) does not set the RI-RSVP flag in the
      CAPABILITY object carried in its Node-ID Hello messages, then the
      node acting as the PLR can conclude that NNhop does not support
      RI-RSVP-FRR extensions.

   -  If node protection is requested for an LSP and if (a) the PPhop
      node has not included a matching B-SFRR-Ready Extended Association
      object in its Path messages or (b) the PPhop node has not
      initiated remote Node-ID Hello messages or (c) the PPhop node does
      not set the RI-RSVP flag in the CAPABILITY object carried in its
      Node-ID Hello messages, then the node MUST conclude that the PLR
      does not support RI-RSVP-FRR extensions.

4.6.2.  Procedures for Backward Compatibility

   Every node that supports RI-RSVP-FRR MUST support the procedures
   defined in this section in order to support backward compatibility
   for those subset of LSPs that also traverse nodes that do not support
   RI-RSVP-FRR.

4.6.2.1.  Lack of support on Downstream Node

   The procedures on the downstream direction are as follows.

   -  If a node finds that the Nhop node along the LSP does not support
      the RI-RSVP-FRR extensions, then the node MUST reduce the "refresh
      period" in the TIME_VALUES object carried in the Path messages to
      the default short refresh interval.

   -  If node protection is requested for the LSP and the NNhop node
      along the LSP path does not support the RI-RSVP-FRR extensions,
      then the node MUST reduce the "refresh period" in the TIME_VALUES
      object carried in the Path messages to the default short refresh
      interval.

   If a node reduces the refresh time using the above procedures, it
   MUST NOT send any "Remote" PathTear or Conditional PathTear message
   to the downstream node.

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

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   -  A and B MUST reduce the refresh time to the default short refresh
      interval of 30 seconds and trigger a Path message

   -  If B is not an MP and if Phop link of B fails, B cannot send
      Conditional PathTear to C but MUST time out the PSB state from A
      normally.  Note that B can time out the PSB state A normally only
      if A did not set long refresh in the TIME_VALUES object carried in
      the Path messages sent earlier.

4.6.2.2.  Lack of support on Upstream Node

   The procedures are as follows.

   -  If a node finds that the Phop node along the LSP path does not
      support the RI-RSVP-FRR extensions, then the node MUST reduce the
      "refresh period" in the TIME_VALUES object carried in the Resv
      messages to the default short refresh interval.

   -  If node protection is requested for the LSP and the Phop node
      along the LSP path does not support the RI-RSVP-FRR extensions,
      then the the node MUST reduce the "refresh period" in the
      TIME_VALUES object carried in the Path messages to the default
      short refresh interval (thus, the Nhop can use compatible values
      when sending a Resv).

   -  If node protection is requested for the LSP and the PPhop node
      does not support the RI-RSVP-FRR extensions, then the node MUST
      reduce the "refresh period" in the TIME_VALUES object carried in
      the Resv messages to the default short refresh interval.

   -  If the node reduces the refresh time using the above procedures,
      it MUST NOT execute MP procedures specified in Section 4.3 of this
      document.

4.6.2.3.  Advertising RI-RSVP without RI-RSVP-FRR

   If a node supporting facility backup protection [RFC4090] sets the
   RI-RSVP capability (I bit) but does not support the RI-RSVP-FRR
   extensions, then it leaves room for stale state to linger around for
   an inordinate period of time or disruption of normal FRR operation
   (Section 3).  Consider the example topology Figure 1 provided in this
   document.

   -  Assume node B does set RI-RSVP capability in its Node-ID based
      Hello messages even though it does not support RI-RSVP-FRR
      extensions.  When B detects the failure of its Phop link along an
      LSP, it will not send Conditional PathTear to C as required by the
      RI-RSVP-FRR procedures.  If B simply leaves the LSP state without

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      deleting, then B may end up holding on to the stale state until
      the (long) refresh timeout.

   -  Intead of node B, assume node C does set RI-RSVP capability in its
      Node-id based Hello messages even though it does not support RI-
      RSVP-FRR extensions.  When B details the failure of its Phop link
      along an LSP, it will send Conditional PathTear to C as required
      by the RI-RSVP-FRR procedures.  But, C would not recognize the
      condition encoded in the PathTear and end up tearing down the LSP.

   -  Assume node B does set RI-RSVP capability in its Node-ID based
      Hello messages even though it does not support RI-RSVP-FRR
      extensions.  Also assume local repair is about to commence on node
      B for an LSP that has only requested link protection.  That is, B
      has not initiated the backup LSP signaling for the LSP.  If node B
      receives a normal PathTear at this time from ingress A because of
      a management event initiated on A, then B simply deletes the LSP
      state without sending a Remote PathTear to the LP-MP C.  So, C may
      end up holding on to the stale state until the (long) refresh
      timeout.

4.6.2.4.  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

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      node protection is requested for the LSP and both Phop and the
      PPhop 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

   The security considerations pertaining to [RFC2961], [RFC4090],
   [RFC8370], [RFC8796] and [RFC5920] remain relevant.  When using RSVP
   Cryptographic Authentication [RFC2747], more robust algorithms
   [RFC2104] [FIPS-180-3] SHOULD be used when computing the keyed
   message digest where possible.

   This document extends the applicability of Node-ID based Hello
   session between immediate neighbors.  The Node-ID based Hello session
   between the PLR and the 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 SHOULD utilize this
   option to enable RSVP-TE routers to authenticate Node-ID Hello
   messages received with TTL greater than 1.  Implementations SHOULD
   also provide the option to specify a limit on the number of Node-ID
   based Hello sessions that can be established on a router supporting
   the extensions defined in this document.

6.  IANA Considerations

6.1.  New Object - CONDITIONS

   RSVP Change Guidelines [RFC3936] 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 from 128-183 range called the
   "CONDITIONS" object is defined in Section 4.4 of this document.  The
   Class-Number from 128-183 range will be allocated by IANA.

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6.2.  CONDITIONS Flags

   Apart from allocating Class-Number for the CONDITIONS object, the
   allocation of the Merge-point condition bit or M-bit Section 4.4 will
   also be done by IANA.

   Flag: 0x1 Name: Merge-point condition bit or M-bit

7.  Acknowledgements

   We are very grateful to Yakov Rekhter for his contributions to the
   development of the idea and thorough review of content of the draft.
   We are thankful to Raveendra Torvi and Yimin Shen for their comments
   and inputs on early versions of the draft.  We also thank Alexander
   Okonnikov for his review and comments on the draft.

8.  Contributors

   Markus Jork
   Juniper Networks, Inc.
   Email: mjork@juniper.net

   Harish Sitaraman
   Individual Contributor
   Email: harish.ietf@gmail.com

   Vishnu Pavan Beeram
   Juniper Networks, Inc.
   Email: vbeeram@juniper.net

   Ebben Aries
   Arrcus, Inc.
   Email: exa@arrcus.com

   Mike Taillon
   Cisco Systems, Inc.
   Email: mtaillon@cisco.com

9.  References

9.1.  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>.

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   [RFC2205]  Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, DOI 10.17487/RFC2205,
              September 1997, <https://www.rfc-editor.org/info/rfc2205>.

   [RFC2747]  Baker, F., Lindell, B., and M. Talwar, "RSVP Cryptographic
              Authentication", RFC 2747, DOI 10.17487/RFC2747, January
              2000, <https://www.rfc-editor.org/info/rfc2747>.

   [RFC2961]  Berger, L., Gan, D., Swallow, G., Pan, P., Tommasi, F.,
              and S. Molendini, "RSVP Refresh Overhead Reduction
              Extensions", RFC 2961, DOI 10.17487/RFC2961, April 2001,
              <https://www.rfc-editor.org/info/rfc2961>.

   [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>.

   [RFC3473]  Berger, L., Ed., "Generalized Multi-Protocol Label
              Switching (GMPLS) Signaling Resource ReserVation Protocol-
              Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
              DOI 10.17487/RFC3473, January 2003,
              <https://www.rfc-editor.org/info/rfc3473>.

   [RFC3936]  Kompella, K. and J. Lang, "Procedures for Modifying the
              Resource reSerVation Protocol (RSVP)", BCP 96, RFC 3936,
              DOI 10.17487/RFC3936, October 2004,
              <https://www.rfc-editor.org/info/rfc3936>.

   [RFC4090]  Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast
              Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
              DOI 10.17487/RFC4090, May 2005,
              <https://www.rfc-editor.org/info/rfc4090>.

   [RFC4558]  Ali, Z., Rahman, R., Prairie, D., and D. Papadimitriou,
              "Node-ID Based Resource Reservation Protocol (RSVP) Hello:
              A Clarification Statement", RFC 4558,
              DOI 10.17487/RFC4558, June 2006,
              <https://www.rfc-editor.org/info/rfc4558>.

   [RFC5063]  Satyanarayana, A., Ed. and R. Rahman, Ed., "Extensions to
              GMPLS Resource Reservation Protocol (RSVP) Graceful
              Restart", RFC 5063, DOI 10.17487/RFC5063, October 2007,
              <https://www.rfc-editor.org/info/rfc5063>.

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   [RFC8370]  Beeram, V., Ed., Minei, I., Shakir, R., Pacella, D., and
              T. Saad, "Techniques to Improve the Scalability of RSVP-TE
              Deployments", RFC 8370, DOI 10.17487/RFC8370, May 2018,
              <https://www.rfc-editor.org/info/rfc8370>.

   [RFC8796]  Taillon, M., Saad, T., Ed., Gandhi, R., Deshmukh, A.,
              Jork, M., and V. Beeram, "RSVP-TE Summary Fast Reroute
              Extensions for Label Switched Path (LSP) Tunnels",
              RFC 8796, DOI 10.17487/RFC8796, July 2020,
              <https://www.rfc-editor.org/info/rfc8796>.

9.2.  Informative References

   [FIPS-180-3]
              National Institute of Standards and Technology, "Secure
              Hash Standard", FIPS 180-3, October 2008.

   [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104,
              DOI 10.17487/RFC2104, February 1997,
              <https://www.rfc-editor.org/info/rfc2104>.

   [RFC5920]  Fang, L., Ed., "Security Framework for MPLS and GMPLS
              Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,
              <https://www.rfc-editor.org/info/rfc5920>.

Authors' Addresses

   Chandra Ramachandran
   Juniper Networks, Inc.

   Email: csekar@juniper.net

   Tarek Saad
   Juniper Networks, Inc.

   Email: tsaad@juniper.net

   Ina Minei
   Google, Inc.

   Email: inaminei@google.com

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   Dante Pacella
   Verizon, Inc.

   Email: dante.j.pacella@verizon.com

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