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Versions: (draft-chandra-mpls-ri-rsvp-frr) 00 01 02 03 04

MPLS Working Group                                       C. Ramachandran
Internet-Draft                                          Juniper Networks
Updates: 4090 (if approved)                                     I. Minei
Intended status: Standards Track                             Google, Inc
Expires: February 10, 2019                                    D. Pacella
                                                                 Verizon
                                                                 T. Saad
                                                      Cisco Systems Inc.
                                                          August 9, 2018


          Refresh Interval Independent FRR Facility Protection
                     draft-ietf-mpls-ri-rsvp-frr-04

Abstract

   RSVP-TE relies on periodic refresh of RSVP messages to synchronize
   and maintain the 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.  Coupling LSP state with the corresponding RSVP-TE signaling
   adjacencies as recommended in RFC 8370 will apply in scenarios other
   than RFC 4090 FRR using bypass tunnels.  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 scenarios not covered
   by procedures defined in RSVP-TE Scaling Recommendations.  Hence,
   this document updates the procedures defined in RFC 4090 to support
   Refresh-Interval Independent RSVP (RI-RSVP) capability specified in
   RFC 8370.





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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
   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 February 10, 2019.

Copyright Notice

   Copyright (c) 2018 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 . . . . . . . . . . . . . . . . . . . . . . . . .   5
   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  . . . . . . . . .   8



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       4.2.1.  PLR Behavior  . . . . . . . . . . . . . . . . . . . .   8
       4.2.2.  Remote Signaling Adjacency  . . . . . . . . . . . . .   9
       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  . . . . . . . . . . . . . . . . . . .  12
       4.3.3.  NP-MP Behavior  . . . . . . . . . . . . . . . . . . .  12
       4.3.4.  Behavior of a Router that is both LP-MP and NP-MP . .  14
     4.4.  Conditional Path Tear . . . . . . . . . . . . . . . . . .  14
       4.4.1.  Sending Conditional Path Tear . . . . . . . . . . . .  14
       4.4.2.  Processing Conditional Path Tear  . . . . . . . . . .  15
       4.4.3.  CONDITIONS object . . . . . . . . . . . . . . . . . .  15
     4.5.  Remote State Teardown . . . . . . . . . . . . . . . . . .  16
       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  . . . . . . . . .  17
         4.5.3.1.  Preemption on LP-MP after Phop Link failure . . .  17
         4.5.3.2.  Preemption on NP-MP after Phop Link failure . . .  18
     4.6.  Backward Compatibility Procedures . . . . . . . . . . . .  18
       4.6.1.  Detecting Support for Refresh interval Independent
               FRR . . . . . . . . . . . . . . . . . . . . . . . . .  19
       4.6.2.  Procedures for backward compatibility . . . . . . . .  19
         4.6.2.1.  Lack of support on Downstream Node  . . . . . . .  19
         4.6.2.2.  Lack of support on Upstream Node  . . . . . . . .  20
         4.6.2.3.  Incremental Deployment  . . . . . . . . . . . . .  20
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  21
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  22
     6.1.  New Object - CONDITIONS . . . . . . . . . . . . . . . . .  22
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  22
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  22
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  23
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  23
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  24
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  24

1.  Introduction

   RSVP-TE Fast Reroute [RFC4090] 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




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   protection mechanism by making the corresponding procedures refresh-
   interval independent.

1.1.  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 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 procedures specified in RSVP-TE Scaling Techniques
   [RFC8370] 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.

   The procedures specified in this document, in combination with RSVP-
   TE Scaling Techniques [RFC8370], eliminate facility backup protection
   dependency on refresh timeouts for stale state cleanup including the
   cleanup for facility backup protection.  The document hence updates
   the semantics of Refresh-Interval Independent RSVP (RI-RSVP)
   capability specified in Section 3 of RSVP-TE Scaling Techniques
   [RFC8370].

   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.




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2.  Terminology

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

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

   PPhop node: Previous-Previous-hop router along the LSP

   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

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

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

3.  Problem Description

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

                        Figure 1: Example Topology



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   In the topology 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 long 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.  As each router should consider itself
      as a Merge Point, 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 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 RSVP-TE Summary
      FRR [I-D.ietf-mpls-summary-frr-rsvpte] that enables the PLR to
      signal the availability of local protection to the MP.  In
      addition, introduce PLR and MP procedures 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 [I-D.ietf-mpls-summary-frr-rsvpte]
      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 MP through the MP determination
      mechanism.  See section 4.3 for more details.

   -  Introduce extensions to enable a router to send 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.



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   -  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 4.5 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 RFC 4090 facility protection FRR MAY set the RI-
   RSVP capability (I bit) defined in Section 3 of RSVP-TE Scaling
   Techniques [RFC8370] only if it supports all the extensions specified
   in the rest of this document.  A node supporting RFC 4090 facility
   bypass FRR but not supporting the extensions specified in this
   document MUST reset RI-RSVP capability (I bit) in the outgoing Node-
   ID based Hello messages.  Hence, this document updates RFC 4090 by
   defining extensions and additional procedures over facility
   protection FRR defined in RFC 4090 in order to advertise RI-RSVP
   capability [RFC8370].

4.2.  Signaling Handshake between PLR and MP

4.2.1.  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, 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
   additional procedures to support RI-RSVP defined in RFC 8370.




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   -  While selecting the destination address of the bypass LSP, the PLR
      SHOULD select the router ID of the NNhop or Nhop node from the
      Node-ID sub-object included RRO object carried in RESV message.
      If the MP has not included Node-ID sub-object in 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 Node-ID sub-object in RRO
      object, then the PLR SHOULD 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 SHOULD also include its router ID in a Node-ID sub-object
      in RRO object carried in PATH message.  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 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 detect MP node failure
      as well as determine the capability of the MP node.  If the MP has
      set the I-bit in CAPABILITY object [RFC8370] carried in Hello
      message corresponding to Node-ID based Hello session, then the PLR
      SHOULD 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 SHOULD execute backward
      compatibility procedures defined in Section 4.6.2.1 of this
      document.

   -  If the bypass LSP comes up and the PLR has made local protection
      available for one or more LSPs, then the PLR SHOULD include B-
      SFRR-Ready Extended Association object and triggers PATH message
      to be sent for those LSPs.  If a B-SFRR-Ready Extended Association
      object is included in the PATH message, then the encoding and
      ordering rules object specified in RSVP-TE Summary FRR
      [I-D.ietf-mpls-summary-frr-rsvpte] MUST be followed.

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



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   not immediate neighbors, the router that supports the extensions
   defined in the document SHOULD set TTL to 255 in all outgoing Node-ID
   based Hello messages exchanged between PLR and MP.  The default hello
   interval for this Node-ID hello session SHOULD 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 RFC 4090, this
   document specifies the following additional procedures to support RI-
   RSVP defined in RFC 8370.

   Each node along an LSP path supporting the extensions defined in this
   document SHOULD also include its router ID in the Node-ID sub-object
   in the RRO object carried in the RESV message of the LSPs.  If the
   PLR has not included Node-ID sub-object in the RRO object carried in
   PATH message and if the PLR is in a different IGP area, then the
   router SHOULD NOT execute the MP procedures specified in this
   document for those LSPs.  Instead, the node SHOULD 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.

   The node should determine whether the incoming PATH messages contains
   B-SFRR-Ready Extended Association object with the Node-ID address of
   the PLR as the source and its own Node-ID as the destination.  In
   addition the node should determine whether it has an operational
   remote Node-ID signaling adjacency with the PLR.  If either the PLR
   has not included B-SFRR-Ready Extended Association object or if there
   is no operational Node-ID signaling adjacency with the PLR or if the
   PLR has not advertised RI-RSVP capability in its Node-ID based Hello
   messages, then the node SHOULD execute backward compatibility
   procedures defined in Section 4.6.2.2.

   If a matching B-SFRR-Ready Extended Association object is found in
   the PATH message and if there is an operational remote signaling
   adjacency with the PLR that has advertised RI-RSVP capability (I-bit)
   [RFC8370] in its Node-ID based Hello messages, then the node SHOULD
   consider itself as the MP for the corresponding PLR.  The matching
   and ordering rules for Bypass Summary FRR Extended Association
   specified in RSVP-TE Summary FRR [I-D.ietf-mpls-summary-frr-rsvpte]
   MUST be followed by implementations supporting this document.





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   -  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
      SHOULD conclude it is 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
      SHOULD conclude it is 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, 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 RSVP_HOP object.  The
   RSVP_HOP object in "remote" Path state contains the address that the
   PLR uses to send Node-ID hello messages to MP.

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

   -  MP later receives a PATH with no matching B-SFRR-Ready Extended
      Association object corresponding to the PLR's IP address contained
      in PATH 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 the
   Ingress or created from a PATH message from the Phop node, the
   "remote" path state is not signaled explicitly from 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 4.5.







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4.3.  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.

   Immediate node failures are detected from the state of Node-ID hello
   sessions established with immediate neighbors.  RSVP-TE Scaling
   Techniques [RFC8370] recommends each router to establish Node-ID
   hello sessions with all its immediate neighbors.  PLR or MP node
   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 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 4.4 "Conditional PathTear" below) and delete 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 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.

   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.

4.3.3.  NP-MP Behavior

   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.




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   -  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.

   When a router that is NP-MP does not detect Phop link or node
   failure, but receives Conditional PathTear from the Phop node, then
   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.

   Receiving Conditional PathTear from the Phop node will not impact the
   "remote" state from the PPhop 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 has failed, B will delete 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 NP-MP for 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 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 by including B-SFRR-
      Ready Extended Association object, C SHOULD remove the B-SFRR-
      Ready Extended Association object containing Association Source
      set to B from the PATH message and trigger PATH to D.

   2. When D receives triggered PATH, 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 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.



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4.3.4.  Behavior of a Router that is both 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.

   -  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.

   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.

4.4.  Conditional Path Tear

   In the example provided in the Section 4.3.3, 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 4.4.3.  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 path state on C.

4.4.1.  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 4.3.1).  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 the upstream node



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4.4.2.  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 B-SFRR-Ready Extended Association object in
   PATH.  If the object had been included previously by the Phop, then
   the node processing Conditional PathTear from the Phop SHOULD remove
   the corresponding object and trigger PATH downstream.

   If 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 SHOULD consider the message
   as normal PathTear.  The node SHOULD propagate normal PathTear
   downstream and delete the LSP state.

4.4.3.  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|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                        Figure 2: CONDITIONS Object

      Length




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

      Class
      To be assigned

      C-type
      1

      M bit
      If M-bit is set to 1, then the PathTear message SHOULD be
      processed based on the condition if the receiver router is a Merge
      Point or not.
      If M-bit is set to 0, then the PathTear message SHOULD be
      processed as normal PathTear message.

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 SHOULD send "remote"
   PathTear message instructing the MP to delete PSB and RSB states
   corresponding to the LSP.  The TTL in "remote" PathTear message
   SHOULD be set to 255.

   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. Assume B has not initiated backup signaling for the LSR.  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 RSVP_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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4.5.1.  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.

4.5.2.  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 the NP-MP for A.  When
   the B-C link fails then C, implementing the procedure specified in
   Section 4.3.4 of this document, will retain state till: remote Node-
   ID signaling 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.

4.5.3.  LSP Preemption during Local Repair

4.5.3.1.  Preemption on LP-MP after Phop Link failure

   If an LSP is preempted on 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
   expecting the PLR to perform 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.






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4.5.3.2.  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
   expecting the PLR to perform 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.

4.6.  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 RSVP-TE Summary FRR [I-D.ietf-mpls-summary-frr-rsvpte]
   are applicable to implementations that do not support RI-RSVP-FRR.
   On the other hand, changes proposed 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.






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4.6.1.  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 carried in
   Hello messages.  The RI-RSVP flag is specified in RSVP-TE Scaling
   Techniques [RFC8370].

   -  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 RI-RSVP flag in CAPABILITY object carried in its
      Node-ID Hello messages, 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 B-SFRR-Ready Extended Association
      object in PATH or (b) PPhop node has not initiated remote node
      Hello messages or (c) PPhop node does not set RI-RSVP flag in
      CAPABILITY object carried in its Node-ID Hello messages, then the
      node SHOULD conclude that the PLR does not support RI-RSVP-FRR
      extensions.  The details are described in the "Procedures for
      backward compatibility" section below.

4.6.2.  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.

4.6.2.1.  Lack of support on Downstream Node

   The procedures on the downstream direction are as follows.

   -  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 short refresh default value.

   -  If node protection is requested and the NNhop node does not
      support the enhancements, then the node SHOULD reduce the "refresh




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      period" in TIME_VALUES object carried in PATH to a short 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.

4.6.2.2.  Lack of support on Upstream Node

   The procedures on the upstream direction are as follows.

   -  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 short 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.

   -  If the node reduces the refresh time from the above procedures, it
      SHOULD also not execute MP procedures specified in Section 4.3 of
      this document.

4.6.2.3.  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,



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   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

   The security considerations pertaining to the original RSVP protocol
   [RFC2205], [RFC3209] and [RFC5920] remain relevant.

   This document extends the applicability of Node-ID based Hello
   session between immediate neighbors.  The Node-ID based Hello session
   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.  Implementations SHOULD also
   provide the option to specify a limit on the number of Node-ID based




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   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.

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.
   Thanks to Raveendra Torvi and Yimin Shen for their comments and
   inputs.

8.  Contributors

   Markus Jork
   Juniper Networks
   Email: mjork@juniper.net

   Harish Sitaraman
   Juniper Networks
   Email: hsitaraman@juniper.net

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

   Ebben Aries
   Juniper Networks
   Email: exa@juniper.net

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






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9.  References

9.1.  Normative References

   [I-D.ietf-mpls-summary-frr-rsvpte]
              Taillon, M., Saad, T., Gandhi, R., Deshmukh, A., Jork, M.,
              and V. Beeram, "RSVP-TE Summary Fast Reroute Extensions
              for LSP Tunnels", draft-ietf-mpls-summary-frr-rsvpte-01
              (work in progress), April 2018.

   [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>.

   [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>.

   [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>.






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   [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>.

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

   [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>.

9.2.  Informative References

   [RFC5439]  Yasukawa, S., Farrel, A., and O. Komolafe, "An Analysis of
              Scaling Issues in MPLS-TE Core Networks", RFC 5439,
              DOI 10.17487/RFC5439, February 2009,
              <https://www.rfc-editor.org/info/rfc5439>.

   [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

   Email: csekar@juniper.net


   Ina Minei
   Google, Inc

   Email: inaminei@google.com








Ramachandran, et al.    Expires February 10, 2019              [Page 24]


Internet-Draft             RI-RSVP FRR Bypass                August 2018


   Dante Pacella
   Verizon

   Email: dante.j.pacella@verizon.com


   Tarek Saad
   Cisco Systems Inc.

   Email: tsaad@cisco.com









































Ramachandran, et al.    Expires February 10, 2019              [Page 25]


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