





Internet Engineering Task Force (IETF)                       Z. Ali, Ed.
Request for Comments: 8390                                 Cisco Systems
Updates: 4874                                            G. Swallow, Ed.
Category: Standards Track                                           SETC
ISSN: 2070-1721                                            F. Zhang, Ed.
                                                                  Huawei
                                                          D. Beller, Ed.
                                                                   Nokia
                                                               July 2018


               RSVP-TE Path Diversity Using Exclude Route

Abstract

   RSVP-TE provides support for the communication of exclusion
   information during Label Switched Path (LSP) setup.  A typical LSP
   diversity use case is for protection, where two LSPs should follow
   different paths through the network in order to avoid single points
   of failure, thus greatly improving service availability.  This
   document specifies an approach that can be used for network scenarios
   where the full path(s) is not necessarily known by use of an abstract
   identifier for the path.  Three types of abstract identifiers are
   specified: client based, Path Computation Element (PCE) based, and
   network based.  This document specifies two new diversity subobjects
   for the RSVP eXclude Route Object (XRO) and the Explicit Exclusion
   Route Subobject (EXRS).

   For the protection use case, LSPs are typically created at a slow
   rate and exist for a long time so that it is reasonable to assume
   that a given (reference) path currently existing (with a well-known
   identifier) will continue to exist and can be used as a reference
   when creating the new diverse path.  Re-routing of the existing
   (reference) LSP, before the new path is established, is not
   considered.
















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Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8390.

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.























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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Conventions Used in This Document . . . . . . . . . . . .   6
     1.2.  Terms and Abbreviations . . . . . . . . . . . . . . . . .   6
     1.3.  Client-Initiated Identifier . . . . . . . . . . . . . . .   7
     1.4.  PCE-Allocated Identifier  . . . . . . . . . . . . . . . .   7
     1.5.  Network-Assigned Identifier . . . . . . . . . . . . . . .   9
   2.  RSVP-TE Signaling Extensions  . . . . . . . . . . . . . . . .  10
     2.1.  Diversity XRO Subobject . . . . . . . . . . . . . . . . .  10
     2.2.  Diversity EXRS Subobject  . . . . . . . . . . . . . . . .  16
     2.3.  Processing Rules for the Diversity XRO and EXRS
           Subobjects  . . . . . . . . . . . . . . . . . . . . . . .  16
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .  20
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21
     4.1.  New XRO Subobject Types . . . . . . . . . . . . . . . . .  21
     4.2.  New EXRS Subobject Types  . . . . . . . . . . . . . . . .  21
     4.3.  New RSVP Error Sub-codes  . . . . . . . . . . . . . . . .  22
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .  22
     5.2.  Informative References  . . . . . . . . . . . . . . . . .  23
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  24
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  24
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26

1.  Introduction

   Path diversity for multiple connections is a well-known operational
   requirement.  Diversity constraints ensure that Label Switched Paths
   (LSPs) can be established without sharing network resources, thus
   greatly reducing the probability of simultaneous connection failures.

   The source node can compute diverse paths for LSPs when it has full
   knowledge of the network topology and is permitted to signal an
   Explicit Route Object (ERO).  However, there are scenarios where
   different nodes perform path computations, and therefore there is a
   need for relevant diversity constraints to be signaled to those
   nodes.  These include (but are not limited to):

   o  LSPs with loose hops in the Explicit Route Object, e.g., inter-
      domain LSPs; and

   o  Generalized Multiprotocol Label Switching (GMPLS) User-Network
      Interface (UNI), where the core node may perform path computation
      [RFC4208].






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   [RFC4874] introduced a means of specifying nodes and resources to be
   excluded from a route using the eXclude Route Object (XRO) and
   Explicit Exclusion Route Subobject (EXRS).  It facilitates the
   calculation of diverse paths for LSPs based on known properties of
   those paths including addresses of links and nodes traversed and
   Shared Risk Link Groups (SRLGs) of traversed links.  Employing these
   mechanisms requires that the source node that initiates signaling
   knows the relevant properties of the path(s) from which diversity is
   desired.  However, there are circumstances under which this may not
   be possible or desirable, including (but not limited to):

   o  Exclusion of a path that does not originate, terminate, or
      traverse the source node of the diverse LSP, in which case the
      addresses of links and SRLGs of the path from which diversity is
      required are unknown to the source node.

   o  Exclusion of a path that is known to the source node of the
      diverse LSP for which the node has incomplete or no path
      information, e.g., due to operator policy.  In this case, the
      source node is aware of the existence of the reference path, but
      the information required to construct an XRO object to guarantee
      diversity from the reference path is not fully known.  Inter-
      domain and GMPLS overlay networks can impose such restrictions.

   This is illustrated in Figure 1, where the overlay reference model
   from [RFC4208] is shown.

























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      Overlay                                                  Overlay
      Network       +----------------------------------+       Network
    +---------+     |                                  |     +---------+
    |  +----+ |     |  +-----+    +-----+    +-----+   |     | +----+  |
    |  |    | | UNI |  |     |    |     |    |     |   | UNI | |    |  |
    | -+ EN1+-+-----+--+ CN1 +----+ CN2 +----+ CN3 +---+-----+-+ EN3+- |
    |  |    | |  +--+--+     |    |     |    |     |   | +---+-|    |  |
    |  +----+ |  |  |  +--+--+    +--+--+    +--+--+   | |   | +----+  |
    +---------+  |  |     |          |          |      | |   +---------+
                 |  |     |          |          |      | |
    +---------+  |  |  +--+--+       |       +--+--+   | |   +---------+
    |  +----+ |  |  |  |     |       +-------+     +-----+   | +----+  |
    |  |    +-+--+  |  | CN4 +---------------+ CN5 |   |     | |    |  |
    | -+ EN2+-+-----+--+     |               |     +---+-----+-+ EN4+- |
    |  |    | | UNI |  +-----+               +-----+   | UNI | |    |  |
    |  +----+ |     |                                  |     | +----+  |
    +---------+     +----------------------------------+     +---------+
      Overlay                 Core Network                     Overlay
      Network                                                  Network
                         Legend:  EN  -  Edge Node
                                  CN  -  Core Node

                Figure 1: Overlay Reference Model [RFC4208]

   Figure 1 depicts two types of UNI connectivity: single-homed and
   dual-homed ENs (which also applies to higher-order multihomed
   connectivity).  Single-homed EN devices are connected to a single CN
   device via a single UNI link.  This single UNI link may constitute a
   single point of failure.  UNI connection between EN1 and CN1 is an
   example of singled-homed UNI connectivity.

   Such a single point of failure can be avoided when the EN device is
   connected to two different CN devices, as depicted for EN2 in
   Figure 1.  For the dual-homing case, it is possible to establish two
   different UNI connections from the same source EN device to the same
   destination EN device.  For example, two connections from EN2 to EN3
   may use the two UNI links EN2-CN1 and EN2-CN4.  To avoid single
   points of failure within the provider network, it is necessary to
   also ensure path (LSP) diversity within the core network.

   In a network providing a set of UNI interfaces between ENs and CNs
   such as that shown in Figure 1, the CNs typically perform path
   computation.  Information sharing across the UNI boundary is
   restricted based on the policy rules imposed by the core network.
   Typically, the core network topology information as well as LSP path
   information is not exposed to the ENs.  In the network shown in
   Figure 1, consider a use case where an LSP from EN2 to EN4 needs to
   be SRLG diverse from an LSP from EN1 to EN3.  In this case, EN2 may



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   not know SRLG attributes of the EN1-EN3 LSP and hence cannot
   construct an XRO to exclude these SRLGs.  In this example, EN2 cannot
   use the procedures described in [RFC4874].  Similarly, an LSP from
   EN2 to EN3 traversing CN1 needs to be diverse from an LSP from EN2 to
   EN3 going via CN4.  Again, in this case, exclusions based on
   [RFC4874] cannot be used.

   This document addresses these diversity requirements by introducing
   an approach of excluding the path taken by these particular LSP(s).
   Each reference LSP or route from which diversity is required is
   identified by an abstract "identifier".  The type of identifier to
   use is highly dependent on the core network operator's networking
   deployment scenario; it could be client initiated (provided by the
   EN), provided by a PCE, or allocated by the (core) network.  This
   document defines three different types of identifiers corresponding
   to these three cases: a client-initiated identifier, a PCE-allocated
   identifier, and an identifier allocated by the CN ingress node
   (UNI-N), i.e., a network-assigned identifier.

1.1.  Conventions Used in This Document

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

1.2.  Terms and Abbreviations

   Diverse LSP:  A diverse Label Switched Path (LSP) is an LSP that has
      a path that does not have any link or SRLG in common with the path
      of a given LSP.  Diverse LSPs are meaningful in the context of
      protection or restoration.

   ERO:  Explicit Route Object as defined in [RFC3209].

   EXRS:  Explicit Exclusion Route Subobject as defined in [RFC4874].

   SRLG:  Shared Risk Link Group as defined in [RFC4202].

   Reference Path:  The reference path is the path of an existing LSP to
      which the path of a diverse LSP shall be diverse.

   XRO:  eXclude Route Object as defined in [RFC4874].







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1.3.  Client-Initiated Identifier

   The following fields MUST be used to represent the client-initiated
   identifier: IPv4/IPv6 tunnel sender address, IPv4/IPv6 tunnel
   endpoint address, Tunnel ID, and Extended Tunnel ID.  Based on local
   policy, the client MAY also include the LSP ID to identify a specific
   LSP within the tunnel.  These fields are defined in Sections 4.6.1.1
   and 4.6.2.1 of [RFC3209].

   The usage of the client-initiated identifier is illustrated by
   Figure 1.  Suppose an LSP from EN2 to EN4 needs to be diverse with
   respect to an LSP from EN1 to EN3.

   The LSP identifier of the EN1-EN3 LSP is LSP-IDENTIFIER1, where LSP-
   IDENTIFIER1 is defined by the tuple

      (tunnel-id = T1,
      LSP ID = L1,
      source address = EN1.RID (Route Identifier),
      destination address = EN3.RID,
      extended tunnel-id = EN1.RID).

   Similarly, the LSP identifier of the EN2-EN4 LSP is LSP-IDENTIFIER2,
   where LSP-IDENTIFIER2 is defined by the tuple

      (tunnel-id = T2,
      LSP ID = L2,
      source address = EN2.RID,
      destination address = EN4.RID,
      extended tunnel-id = EN2.RID).

   The EN1-EN3 LSP is signaled with an exclusion requirement from LSP-
   IDENTIFIER2, and the EN2-EN4 LSP is signaled with an exclusion
   requirement from LSP-IDENTIFIER1.  In order to maintain diversity
   between these two connections within the core network, the core
   network SHOULD implement crankback signaling extensions as defined in
   [RFC4920].  Note that crankback signaling is known to lead to slower
   setup times and suboptimal paths under some circumstances as
   described by [RFC4920].

1.4.  PCE-Allocated Identifier

   In scenarios where a PCE is deployed and used to perform path
   computation, typically the ingress node of the core network (e.g.,
   node CN1 in Figure 1) could consult a PCE to allocate identifiers,
   which are used to signal path diversity constraints.  In other
   deployment scenarios, a PCE is deployed at a network node(s) or it is




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   part of a Network Management System (NMS).  In all these cases, the
   PCE is consulted and the Path Key, as defined in [RFC5520], can be
   used in RSVP signaling as the identifier to ensure diversity.

   An example of specifying LSP diversity using a Path Key is shown in
   Figure 2, where a simple network with two domains is shown.  It is
   desired to set up a pair of path-disjoint LSPs from the source in
   Domain 1 to the destination in Domain 2, but the domains keep strict
   confidentiality about all path and topology information.

   The first LSP is signaled by the source with ERO {A, B, loose Dst}
   and is set up with the path {Src, A, B, U, V, W, Dst}.  However, when
   sending the Record Route Object (RRO) out of Domain 2, node U would
   normally strip the path and replace it with a loose hop to the
   destination.  With this limited information, the source is unable to
   include enough detail in the ERO of the second LSP to avoid it
   taking, for example, the path {Src, C, D, X, V, W, Dst} for path-
   disjointness.

          ---------------------    -----------------------------
         | Domain 1            |  |                    Domain 2 |
         |                     |  |                             |
         |        ---    ---   |  |   ---    ---     ---        |
         |       | A |--| B |--+--+--| U |--| V |---| W |       |
         |      / ---    ---   |  |   ---    ---     --- \      |
         |  ---/               |  |          /       /    \---  |
         | |Src|               |  |         /       /     |Dst| |
         |  ---\               |  |        /       /      /---  |
         |      \ ---    ---   |  |   --- /   --- /  --- /      |
         |       | C |--| D |--+--+--| X |---| Y |--| Z |       |
         |        ---    ---   |  |   ---     ---    ---        |
         |                     |  |                             |
          ---------------------    -----------------------------

                  Figure 2: A Simple Multi-domain Network

   In order to support LSP diversity, node U consults the PCE and
   replaces the path segment {U, V, W} in the RRO with a Path Key
   subobject.  The PCE function assigns an "identifier" and puts it into
   the Path Key field of the Path Key subobject.  The PCE ID in the
   message indicates that this replacement operation was performed by
   node U.

   With this additional information, the source node is able to signal
   the subsequent LSPs with the ERO set to {C, D, exclude Path Key
   (signaled in the EXRS RSVP subobject), loose Dst}.  When the
   signaling message reaches node X, it can consult the PCE function
   associated with node U to expand the Path Key in order to calculate a



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   path that is diverse with respect to the first LSP.  Alternatively,
   the source node could use an ERO of {C, D, loose Dst} and include an
   XRO containing the Path Key.

   This mechanism can work with all the Path Key resolution mechanisms,
   as detailed in Section 3.1 of [RFC5553].  A PCE, co-located or not,
   may be used to resolve the Path Key, but the node (i.e., a Label
   Switching Router (LSR)) can also use the Path Key information to
   index a path segment previously supplied to it by the entity that
   originated the Path Key (for example, the LSR that inserted the Path
   Key in the RRO or a management system).

1.5.  Network-Assigned Identifier

   There are scenarios in which the network provides diversity-related
   information for a service that allows the client device to include
   this information in the signaling message.  If the Shared Risk Link
   Group (SRLG) identifier information is both available and shareable
   (by policy) with the ENs, the procedure defined in [RFC8001] can be
   used to collect SRLG identifiers associated with an LSP (LSP1).  When
   a second LSP (LSP2) needs to be diverse with respect to LSP1, the EN
   constructing the RSVP signaling message for setting up LSP2 can
   insert the SRLG identifiers associated with LSP1 as diversity
   constraints into the XRO using the procedure described in [RFC4874].
   However, if the core network SRLG identifiers are either not
   available or not shareable with the ENs based on policies enforced by
   the core network, existing mechanisms cannot be used.

   In this document, a signaling mechanism is defined where information
   signaled to the CN via the UNI does not require shared knowledge of
   core network SRLG information.  For this purpose, the concept of a
   Path Affinity Set (PAS) is defined for abstracting SRLG information.
   The motive behind the introduction of the PAS is to minimize the
   exchange of diversity information between the core network (CNs) and
   the client devices (ENs).  The PAS contains an abstract SRLG
   identifier associated with a given path rather than a detailed SRLG
   list.  The PAS is a single identifier that can be used to request
   diversity and associate diversity.  The means by which the processing
   node determines the path corresponding to the PAS is beyond the scope
   of this document.

   A CN on the core network boundary interprets the specific PAS
   identifier (e.g., "123") as meaning to exclude the core network SRLG
   information (or equivalent) that has been allocated by LSPs
   associated with this PAS identifier value.  For example, if a path
   exists for the LSP with the PAS identifier "123", the CN would use
   local knowledge of the core network SRLGs associated with the LSPs
   tagged with PAS attribute "123" and use those SRLGs as constraints



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   for path computation.  If a PAS identifier is used as an exclusion
   identifier in the connection request, the CN (UNI-N) in the core
   network is assumed to be able to determine the existing core network
   SRLG information and calculate a path that meets the determined
   diversity constraints.

   When a CN satisfies a connection setup for an SRLG-diverse signaled
   path, the CN may optionally record the core network SRLG information
   for that connection in terms of CN-based parameters and associate
   that with the EN addresses in the Path message.  Specifically, for
   Layer 1 Virtual Private Networks (L1VPNs), Port Information Tables
   (PITs) [RFC5251] can be leveraged to translate between client (EN)
   addresses and core network addresses.

   The means to distribute the PAS information within the core network
   is beyond the scope of this document.  For example, the PAS and the
   associated SRLG information can be distributed within the core
   network by an Interior Gateway Protocol (IGP) or by other means such
   as configuration.  Regardless of means used to distribute the PAS
   information, the information is kept inside the core network and is
   not shared with the overlay network (see Figure 1).

2.  RSVP-TE Signaling Extensions

   This section describes the signaling extensions required to address
   the aforementioned requirements and use cases.

2.1.  Diversity XRO Subobject

   New Diversity XRO subobjects are defined below for the IPv4 and IPv6
   address families.  Most of the fields in the IPv4 and IPv6 Diversity
   XRO subobjects are common and are described following the definition
   of the two subobjects.

   The IPv4 Diversity XRO subobject is defined as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |L|  XRO Type   |     Length    |DI Type|A-Flags|E-Flags| Resvd |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           IPv4 Diversity Identifier Source Address            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  Diversity Identifier Value                   |
      //                            ...                              //
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




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   Similarly, the IPv6 Diversity XRO subobject is defined as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |L|  XRO Type   |     Length    |DI Type|A-Flags|E-Flags| Resvd |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           IPv6 Diversity Identifier Source Address            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         IPv6 Diversity Identifier Source Address (cont.)      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         IPv6 Diversity Identifier Source Address (cont.)      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         IPv6 Diversity Identifier Source Address (cont.)      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  Diversity Identifier Value                   |
      //                            ...                              //
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   L:
      The L flag is used in the same way as for the XRO subobjects
      defined in [RFC4874], that is:

      0 indicates that the diversity constraints MUST be satisfied, and

      1 indicates that the diversity constraints SHOULD be satisfied.

   XRO Type:
      The value is set to 38 for the IPv4 Diversity XRO subobject.  The
      value is set to 39 for the IPv6 Diversity XRO subobject.

   Length:
      Per [RFC4874], the Length contains the total length of the
      IPv4/IPv6 subobject in bytes, including the XRO Type and Length
      fields.  The Length is variable, depending on the Diversity
      Identifier Value.














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   Diversity Identifier Type (DI Type):
      Diversity Identifier Type (DI Type) indicates the way the
      reference LSP(s) or route(s) with which diversity is required is
      identified in the IPv4/IPv6 Diversity subobjects.  The following
      three DI Type values are defined in this document:

         DI Type value   Definition
         -------------   --------------------------------
               1         Client-Initiated Identifier
               2         PCE-Allocated Identifier
               3         Network-Assigned Identifier

   Attribute Flags (A-Flags):
      The Attribute Flags (A-Flags) are used to communicate desirable
      attributes of the LSP being signaled in the IPv4/IPv6 Diversity
      subobjects.  Each flag acts independently.  Any combination of
      flags is permitted.

      0x01 = Destination node exception
         Indicates that the exclusion does not apply to the destination
         node of the LSP being signaled.

      0x02 = Processing node exception
         Indicates that the exclusion does not apply to the node(s)
         performing ERO expansion for the LSP being signaled.  An
         ingress UNI-N node is an example of such a node.

      0x04 = Penultimate node exception
         Indicates that the penultimate node of the LSP being signaled
         MAY be shared with the excluded path even when this violates
         the exclusion flags.  This flag is useful, for example, when an
         EN is not dual homed (like EN4 in Figure 1, where all LSPs have
         to go through CN5).

         The "Penultimate node exception" flag is typically set when the
         destination node is single homed (e.g., EN1 or EN4 in
         Figure 2).  In such a case, LSP diversity can only be
         accomplished inside the core network up to the egress node and
         the penultimate hop must be the same for the LSPs.

      0x08 = LSP ID to be ignored
         This flag is used to indicate tunnel-level exclusion.
         Specifically, this flag is used to indicate that if the
         diversity identifier contains an LSP ID field, then the LSP ID
         is to be ignored, and the exclusion applies to any LSP matching
         the rest of the diversity identifier.





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   Exclusion Flags (E-Flags):
      The Exclusion Flags are used to communicate the desired type(s) of
      exclusion requested in the IPv4/IPv6 Diversity subobjects.  The
      following flags are defined.  Any combination of these flags is
      permitted.  Please note that the exclusion specified by these
      flags may be modified by the value of the A-Flags.  For example,
      the node exclusion flag is ignored for the penultimate node if the
      "Penultimate node exception" flag of the A-Flags is set.

      0x01 = SRLG exclusion
         Indicates that the path of the LSP being signaled is requested
         to be SRLG disjoint with respect to the excluded path specified
         by the IPv4/IPv6 Diversity XRO subobject.

      0x02 = Node exclusion
         Indicates that the path of the LSP being signaled is requested
         to be "node diverse" from the excluded path specified by the
         IPv4/IPv6 Diversity XRO subobject.

      0x04 = Link exclusion
         Indicates that the path of the LSP being signaled is requested
         to be "link diverse" from the path specified by the IPv4/IPv6
         Diversity XRO subobject.

      0x08 = Reserved
         This flag is reserved.  It MUST be set to zero on transmission
         and MUST be ignored on receipt for both IPv4/IPv6 Diversity XRO
         subobjects.

   Resvd:
      This field is reserved.  It MUST be set to zero on transmission
      and MUST be ignored on receipt for both IPv4/IPv6 Diversity XRO
      subobjects.

   IPv4/IPv6 Diversity Identifier Source Address:
      This field MUST be set to the IPv4/IPv6 address of the node that
      assigns the diversity identifier.  Depending on the Diversity
      Identifier Type, the diversity identifier source may be a client
      node, PCE entity, or network node.  Specifically:

      *  When the Diversity Identifier Type is set to the "Client-
         Initiated Identifier", the value MUST be set to IPv4/IPv6
         tunnel sender address of the reference LSP against which
         diversity is desired.  The IPv4/IPv6 tunnel sender address is
         as defined in [RFC3209].






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      *  When the Diversity Identifier Type is set to "PCE-Allocated
         Identifier", the value MUST be set to the IPv4/IPv6 address of
         the node that assigned the Path Key identifier and that can
         return an expansion of the Path Key or use the Path Key as
         exclusion in a path computation.  The Path Key is defined in
         [RFC5553].  The PCE ID is carried in the Diversity Identifier
         Source Address field of the subobject.

      *  When the Diversity Identifier Type is set to "Network-Assigned
         Identifier", the value MUST be set to the IPv4/IPv6 address of
         the node allocating the Path Affinity Set (PAS).

   Diversity Identifier Value:  Encoding for this field depends on the
      Diversity Identifier Type, as defined in the following.

      When the Diversity Identifier Type is set to "Client-Initiated
      Identifier" in the IPv4 Diversity XRO subobject, the Diversity
      Identifier Value MUST be encoded as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 IPv4 Tunnel Endpoint Address                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Must Be Zero         |     Tunnel ID                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Extended Tunnel ID                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Must Be Zero         |            LSP ID             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      The IPv4 Tunnel Endpoint Address, Tunnel ID, Extended Tunnel ID,
      and LSP ID are as defined in [RFC3209].


















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      When the Diversity Identifier Type is set to "Client-Initiated
      Identifier" in the IPv6 Diversity XRO subobject, the Diversity
      Identifier Value MUST be encoded as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 IPv6 Tunnel Endpoint Address                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |             IPv6 Tunnel Endpoint Address (cont.)              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |             IPv6 Tunnel Endpoint Address (cont.)              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |             IPv6 Tunnel Endpoint Address (cont.)              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Must Be Zero         |     Tunnel ID                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Extended Tunnel ID                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   Extended Tunnel ID (cont.)                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   Extended Tunnel ID (cont.)                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   Extended Tunnel ID (cont.)                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Must Be Zero         |            LSP ID             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      The IPv6 Tunnel Endpoint Address, Tunnel ID, IPv6 Extended Tunnel
      ID, and LSP ID are as defined in [RFC3209].

      When the Diversity Identifier Type is set to "PCE-Allocated
      Identifier" in the IPv4 or IPv6 Diversity XRO subobject, the
      Diversity Identifier Value MUST be encoded as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Must Be Zero          |           Path Key            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      The Path Key is defined in [RFC5553].









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      When the Diversity Identifier Type is set to "Network-Assigned
      Identifier" in the IPv4 or IPv6 Diversity XRO subobject, the
      Diversity Identifier Value MUST be encoded as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |             Path Affinity Set (PAS) Identifier                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      The Path Affinity Set (PAS) Identifier field is a 32-bit value
      that is scoped by (i.e., is only meaningful when used in
      combination with) the Diversity Identifier Source Address field.
      There are no restrictions on how a node selects a PAS identifier
      value.  Section 1.3 defines the PAS term and provides context on
      how values may be selected.

2.2.  Diversity EXRS Subobject

   [RFC4874] defines the EXRS ERO subobject.  An EXRS is used to
   identify abstract nodes or resources that must not or should not be
   used on the path between two inclusive abstract nodes or resources in
   the explicit route.  An EXRS contains one or more subobjects of its
   own, called EXRS subobjects [RFC4874].

   An EXRS MAY include a Diversity subobject as specified in this
   document.  The same type values 38 and 39 MUST be used.

2.3.  Processing Rules for the Diversity XRO and EXRS Subobjects

   The procedure defined in [RFC4874] for processing the XRO and EXRS is
   not changed by this document.  The processing rules for the Diversity
   XRO and EXRS subobjects are similar unless the differences are
   explicitly described.  Similarly, IPv4 and IPv6 Diversity XRO
   subobjects and IPv4 and IPv6 Diversity EXRS subobjects follow the
   same processing rules.

   If the processing node cannot recognize the Diversity XRO/EXRS
   subobject, the node is expected to follow the procedure defined in
   [RFC4874].

   An XRO/EXRS object MAY contain multiple Diversity subobjects of the
   same DI Type.  For example, in order to exclude multiple Path Keys, a
   node MAY include multiple Diversity XRO subobjects, each with a
   different Path Key.  Similarly, in order to exclude the routes taken
   by multiple LSPs, a node MAY include multiple Diversity XRO/EXRS
   subobjects, each with a different LSP identifier.  Likewise, to
   exclude multiple PAS identifiers, a node MAY include multiple



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   Diversity XRO/EXRS subobjects, each with a different PAS identifier.
   However, all Diversity subobjects in an XRO/EXRS MUST contain the
   same Diversity Identifier Type.  If a Path message contains an XRO/
   EXRS with multiple Diversity subobjects of different DI Types, the
   processing node MUST return a PathErr with the error code "Routing
   Problem" (24) and error sub-code "XRO/EXRS Too Complex" (68/69).

   If the processing node recognizes the Diversity XRO/EXRS subobject
   but does not support the DI Type, it MUST return a PathErr with the
   error code "Routing Problem" (24) and error sub-code "Unsupported
   Diversity Identifier Type" (36).

   In the case of DI Type "Client-Initiated Identifier", all nodes along
   the path SHOULD process the diversity information signaled in the
   XRO/EXRS Diversity subobjects to verify that the signaled diversity
   constraint is satisfied.  If a diversity violation is detected,
   crankback signaling MAY be initiated.

   In the case of DI Type "PCE-Allocated Identifier" and "Network-
   Assigned Identifier", the nodes in the domain that perform path
   computation SHOULD process the diversity information signaled in the
   XRO/EXRS Diversity subobjects as follows.  In the PCE case, the
   ingress node of a domain sends a path computation request for a path
   from ingress node to egress node, including diversity constraints to
   a PCE.  Or, in the PAS case, the ingress node is capable of
   calculating the path for the new LSP from ingress node to the egress
   node, taking the diversity constraints into account.  The calculated
   path is then carried in the Explicit Route Object (ERO).  Hence, the
   transit nodes in a domain and the domain egress node SHOULD NOT
   process the signaled diversity information unless path computation is
   performed.

   While processing the EXRS object, if a loose hop expansion results in
   the creation of another loose hop in the outgoing ERO, the processing
   node MAY include the EXRS in the newly created loose hop for further
   processing by downstream nodes.

   The A-Flags affect the processing of the Diversity XRO/EXRS subobject
   as follows:

   o  When the "Processing node exception" flag is set, the exclusion
      MUST be ignored for the node processing the XRO or EXRS subobject.

   o  When the "Destination node exception" flag is set, the exclusion
      MUST be ignored for the destination node in processing the XRO
      subobject.  The destination node exception for the EXRS subobject
      applies to the explicit node identified by the ERO subobject that




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      identifies the next abstract node.  When the "Destination node
      exception" flag is set in the EXRS subobject, exclusion MUST be
      ignored for said node (i.e., the next abstract node).

   o  When the "Penultimate node exception" flag is set in the XRO
      subobject, the exclusion MUST be ignored for the penultimate node
      on the path of the LSP being established.

      The penultimate node exception for the EXRS subobject applies to
      the node before the explicit node identified by the ERO subobject
      that identifies the next abstract node.  When the "Penultimate
      node exception" flag is set in the EXRS subobject, the exclusion
      MUST be ignored for said node (i.e., the node before the next
      abstract node).

   If the L-flag of the Diversity XRO subobject or Diversity EXRS
   subobject is not set, the processing node proceeds as follows.

   o  If the Diversity Identifier Type is set to "Client-Initiated
      Identifier", the processing node MUST ensure that the path
      calculated/expanded for the signaled LSP is diverse from the route
      taken by the LSP identified in the Diversity Identifier Value
      field.

   o  If the Diversity Identifier Type is set to "PCE-Allocated
      Identifier", the processing node MUST ensure that any path
      calculated for the signaled LSP is diverse from the route
      identified by the Path Key.  The processing node MAY use the PCE
      identified by the Diversity Identifier Source Address in the
      subobject for route computation.  The processing node MAY use the
      Path Key resolution mechanisms described in [RFC5553].

   o  If the Diversity Identifier Type is set to "Network-Assigned
      Identifier", the processing node MUST ensure that the path
      calculated for the signaled LSP is diverse with respect to the
      values associated with the PAS Identifier and Diversity Identifier
      Source Address fields.

   o  Regardless of whether the path computation is performed locally or
      at a remote node (e.g., PCE), the processing node MUST ensure that
      any path calculated for the signaled LSP is diverse from the
      requested Exclusion Flags.

   o  If the excluded path referenced in the XRO subobject is unknown to
      the processing node, the processing node SHOULD ignore the
      Diversity XRO subobject and SHOULD proceed with the signaling
      request.  After sending the Resv for the signaled LSP, the




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      processing node MUST return a PathErr with the error code "Notify
      Error" (25) and error sub-code "Route of XRO LSP identifier
      unknown" (14) for the signaled LSP.

   o  If the processing node fails to find a path that meets the
      requested constraint, the processing node MUST return a PathErr
      with the error code "Routing Problem" (24) and error sub-code
      "Route blocked by Exclude Route" (67).

   If the L-flag of the Diversity XRO subobject or Diversity EXRS
   subobject is set, the processing node proceeds as follows:

   o  If the Diversity Identifier Type is set to "Client-Initiated
      Identifier", the processing node SHOULD ensure that the path
      calculated/expended for the signaled LSP is diverse from the route
      taken by the LSP identified in the Diversity Identifier Value
      field.

   o  If the Diversity Identifier Type is set to "PCE-Allocated
      Identifier", the processing node SHOULD ensure that the path
      calculated for the signaled LSP is diverse from the route
      identified by the Path Key.

   o  If the Diversity Identifier Type is set to "Network-Assigned
      Identifier", the processing node SHOULD ensure that the path
      calculated for the signaled LSP is diverse with respect to the
      values associated with the PAS Identifier and Diversity Identifier
      Source Address fields.

   o  If the processing node fails to find a path that meets the
      requested constraint, it SHOULD proceed with signaling using a
      suitable path that meets the constraint as far as possible.  After
      sending the Resv for the signaled LSP, it MUST return a PathErr
      message with error code "Notify Error" (25) and error sub-code
      "Failed to satisfy Exclude Route" (15) to the source node.

   If, subsequent to the initial signaling of a diverse LSP, an excluded
   path referenced in the XRO subobject becomes known to the processing
   node or a change in the excluded path becomes known to the processing
   node, the processing node MUST re-evaluate the exclusion and
   diversity constraints requested by the diverse LSP to determine
   whether they are still satisfied.

   o  In the case where the L-flag was not set in the initial setup
      message, the exclusion and diversity constraints were satisfied at
      the time of the initial setup.  If the processing node re-
      evaluating the exclusion and diversity constraints for a diverse
      LSP detects that the exclusion and diversity constraints are no



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      longer met, it MUST send a PathErr message for the diverse LSP
      with the error code "Routing Problem" (24) and error sub-code
      "Route blocked by Exclude Route" (67).  The Path_State_Removed
      (PSR) flag [RFC3473] MUST NOT be set.  A source node receiving a
      PathErr message with this error code and sub-code combination
      SHOULD take appropriate actions and move the diverse LSP to a new
      path that meets the original constraints.

   o  In the case where the L-flag was set in the initial setup message,
      the exclusion and diversity constraints may or may not be
      satisfied at any given time.  If the exclusion constraints for a
      diverse LSP were satisfied before, and if the processing node re-
      evaluating the exclusion and diversity constraints for a diverse
      LSP detects that exclusion and diversity constraints are no longer
      met, it MUST send a PathErr message for the diverse LSP with the
      error code "Notify Error" (25) and error sub-code "Failed to
      satisfy Exclude Route" (15).  The PSR flag MUST NOT be set.  The
      source node MAY take no consequent action and keep the LSP along
      the path that does not meet the original constraints.  Similarly,
      if the exclusion constraints for a diverse LSP were not satisfied
      before, and if the processing node re-evaluating the exclusion and
      diversity constraints for a diverse LSP detects that the exclusion
      constraints are met, it MUST send a PathErr message for the
      diverse LSP with the error code "Notify Error" (25) and a new
      error sub-code "Compliant path exists" (16).  The PSR flag MUST
      NOT be set.  A source node receiving a PathErr message with this
      error code and sub-code combination MAY move the diverse LSP to a
      new path that meets the original constraints.

3.  Security Considerations

   This document does not introduce any additional security issues in
   addition to those identified in [RFC5920], [RFC2205], [RFC3209],
   [RFC3473], [RFC2747], [RFC4874], [RFC5520], and [RFC5553].

   The diversity mechanisms defined in this document rely on the new
   diversity subobject that is carried in the XRO or EXRS, respectively.
   In Section 7 of [RFC4874], it is noted that some administrative
   boundaries may remove the XRO due to security concerns on explicit
   route information exchange.  However, when the diversity subobjects
   specified in this document are used, removing at the administrative
   boundary an XRO containing these diversity subobjects would result in
   the request for diversity being dropped at the boundary, and path
   computation would be unlikely to produce the requested diverse path.
   As such, diversity subobjects MUST be retained in an XRO crossing an
   administrative boundary, even if other subobjects are removed.  This





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   retention would be based on operator policy.  The use of diversity
   subobjects is based on mutual agreement.  This avoids the need to
   share the identity of network resources when supporting diversity.

4.  IANA Considerations

   IANA has assigned new values defined in this document and summarized
   in this section.

4.1.  New XRO Subobject Types

   In the IANA registry for RSVP parameters, under "Class Names, Class
   Numbers, and Class Types", this document defines two new subobjects
   for the EXCLUDE_ROUTE object [RFC4874], C-Type 1 (see "Class Types or
   C-Types - 232 EXCLUDE_ROUTE" on <https://www.iana.org/assignments/
   rsvp-parameters>).

                        +----------------+-------+
                        | Description    | Value |
                        +----------------+-------+
                        | IPv4 Diversity | 38    |
                        | IPv6 Diversity | 39    |
                        +----------------+-------+

4.2.  New EXRS Subobject Types

   The Diversity XRO subobjects are also defined as new EXRS subobjects
   (see "Class Types or C-Types - 20 EXPLICIT_ROUTE" on
   <https://www.iana.org/assignments/rsvp-parameters>).  The same
   numeric values have been assigned:

                        +----------------+-------+
                        | Description    | Value |
                        +----------------+-------+
                        | IPv4 Diversity | 38    |
                        | IPv6 Diversity | 39    |
                        +----------------+-------+














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4.3.  New RSVP Error Sub-codes

   In the IANA registry for RSVP parameters, under "Error Codes and
   Globally Defined Error Value Sub-Codes", for Error Code "Routing
   Problem" (24) (see [RFC3209]), the following sub-codes are defined
   (see "Sub-Codes - 24 Routing Problem" on
   <https://www.iana.org/assignments/rsvp-parameters>).

       +-------+---------------------------------------+-----------+
       | Value | Description                           | Reference |
       +-------+---------------------------------------+-----------+
       | 36    | Unsupported Diversity Identifier Type | RFC 8390  |
       +-------+---------------------------------------+-----------+

   For Error Code "Notify Error" (25) (see [RFC3209]), the following
   sub-codes are defined (see "Sub-Codes - 25 Notify Error" on
   <https://www.iana.org/assignments/rsvp-parameters>).

        +-------+-------------------------------------+-----------+
        | Value | Description                         | Reference |
        +-------+-------------------------------------+-----------+
        | 14    | Route of XRO LSP identifier unknown | RFC 8390  |
        | 15    | Failed to satisfy Exclude Route     | RFC 8390  |
        | 16    | Compliant path exists               | RFC 8390  |
        +-------+-------------------------------------+-----------+

5.  References

5.1.  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>.

   [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>.

   [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>.








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   [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>.

   [RFC4202]  Kompella, K., Ed. and Y. Rekhter, Ed., "Routing Extensions
              in Support of Generalized Multi-Protocol Label Switching
              (GMPLS)", RFC 4202, DOI 10.17487/RFC4202, October 2005,
              <https://www.rfc-editor.org/info/rfc4202>.

   [RFC4874]  Lee, CY., Farrel, A., and S. De Cnodder, "Exclude Routes -
              Extension to Resource ReserVation Protocol-Traffic
              Engineering (RSVP-TE)", RFC 4874, DOI 10.17487/RFC4874,
              April 2007, <https://www.rfc-editor.org/info/rfc4874>.

   [RFC4920]  Farrel, A., Ed., Satyanarayana, A., Iwata, A., Fujita, N.,
              and G. Ash, "Crankback Signaling Extensions for MPLS and
              GMPLS RSVP-TE", RFC 4920, DOI 10.17487/RFC4920, July 2007,
              <https://www.rfc-editor.org/info/rfc4920>.

   [RFC5553]  Farrel, A., Ed., Bradford, R., and JP. Vasseur, "Resource
              Reservation Protocol (RSVP) Extensions for Path Key
              Support", RFC 5553, DOI 10.17487/RFC5553, May 2009,
              <https://www.rfc-editor.org/info/rfc5553>.

   [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>.

5.2.  Informative References

   [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>.

   [RFC4208]  Swallow, G., Drake, J., Ishimatsu, H., and Y. Rekhter,
              "Generalized Multiprotocol Label Switching (GMPLS) User-
              Network Interface (UNI): Resource ReserVation Protocol-
              Traffic Engineering (RSVP-TE) Support for the Overlay
              Model", RFC 4208, DOI 10.17487/RFC4208, October 2005,
              <https://www.rfc-editor.org/info/rfc4208>.

   [RFC5251]  Fedyk, D., Ed., Rekhter, Y., Ed., Papadimitriou, D.,
              Rabbat, R., and L. Berger, "Layer 1 VPN Basic Mode",
              RFC 5251, DOI 10.17487/RFC5251, July 2008,
              <https://www.rfc-editor.org/info/rfc5251>.



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   [RFC5520]  Bradford, R., Ed., Vasseur, JP., and A. Farrel,
              "Preserving Topology Confidentiality in Inter-Domain Path
              Computation Using a Path-Key-Based Mechanism", RFC 5520,
              DOI 10.17487/RFC5520, April 2009,
              <https://www.rfc-editor.org/info/rfc5520>.

   [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>.

   [RFC8001]  Zhang, F., Ed., Gonzalez de Dios, O., Ed., Margaria, C.,
              Hartley, M., and Z. Ali, "RSVP-TE Extensions for
              Collecting Shared Risk Link Group (SRLG) Information",
              RFC 8001, DOI 10.17487/RFC8001, January 2017,
              <https://www.rfc-editor.org/info/rfc8001>.

Acknowledgements

   The authors would like to thank Xihua Fu for his contributions.  The
   authors also would like to thank Luyuan Fang and Walid Wakim for
   their review and comments.

Contributors

   Igor Bryskin
   Huawei Technologies
   Email: Igor.Bryskin@huawei.com

   Daniele Ceccarelli
   Ericsson
   Email: Daniele.Ceccarelli@ericsson.com

   Dhruv Dhody
   Huawei Technologies
   Email: dhruv.ietf@gmail.com

   Don Fedyk
   Hewlett-Packard Enterprise
   Email: don.fedyk@hpe.com

   Clarence Filsfils
   Cisco Systems, Inc.
   Email: cfilsfil@cisco.com

   Gabriele Maria Galimberti
   Cisco Systems
   Email: ggalimbe@cisco.com




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   Ori Gerstel
   SDN Solutions Ltd.
   Email: origerstel@gmail.com

   Oscar Gonzalez de Dios
   Telefonica I+D
   Email: ogondio@tid.es

   Matt Hartley
   Cisco Systems
   Email: mhartley@cisco.com

   Kenji Kumaki
   KDDI Corporation
   Email: ke-kumaki@kddi.com

   Ruediger Kunze
   Deutsche Telekom AG
   Email: Ruediger.Kunze@telekom.de

   Lieven Levrau
   Nokia
   Email: Lieven.Levrau@nokia.com

   Cyril Margaria
   Email: cyril.margaria@gmail.com

   Julien Meuric
   France Telecom Orange
   Email: julien.meuric@orange.com

   Yuji Tochio
   Fujitsu
   Email: tochio@jp.fujitsu.com

   Xian Zhang
   Huawei Technologies
   Email: zhang.xian@huawei.com













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Authors' Addresses

   Zafar Ali (editor)
   Cisco Systems.

   Email: zali@cisco.com


   George Swallow (editor)
   Southend Technical Center

   Email: swallow.ietf@gmail.com


   Fatai Zhang (editor)
   Huawei Technologies

   Email: zhangfatai@huawei.com


   Dieter Beller (editor)
   Nokia

   Email: Dieter.Beller@nokia.com



























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