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Internet Engineering Task Force (IETF)                     F. Zhang, Ed.
Request for Comments: 8001                                        Huawei
Category: Standards Track                       O. Gonzalez de Dios, Ed.
ISSN: 2070-1721                                    Telefonica Global CTO
                                                             C. Margaria
                                                              M. Hartley
                                                                  Z. Ali
                                                            January 2017

                   RSVP-TE Extensions for Collecting
               Shared Risk Link Group (SRLG) Information


   This document provides extensions for Resource Reservation Protocol -
   Traffic Engineering (RSVP-TE), including GMPLS, to support automatic
   collection of Shared Risk Link Group (SRLG) information for the TE
   link formed by a Label Switched Path (LSP).

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

Copyright Notice

   Copyright (c) 2017 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Applicability Example: Dual-Homing . . . . . . . . . . . .  3
   2.  Requirements Language  . . . . . . . . . . . . . . . . . . . .  5
   3.  RSVP-TE Requirements . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  SRLG Collection Indication . . . . . . . . . . . . . . . .  5
     3.2.  SRLG Collection  . . . . . . . . . . . . . . . . . . . . .  6
     3.3.  SRLG Update  . . . . . . . . . . . . . . . . . . . . . . .  6
     3.4.  SRLG ID Definition . . . . . . . . . . . . . . . . . . . .  6
   4.  Encodings  . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     4.1.  SRLG Collection Flag . . . . . . . . . . . . . . . . . . .  6
     4.2.  RRO SRLG Subobject   . . . . . . . . . . . . . . . . . . .  7
   5.  Signaling Procedures . . . . . . . . . . . . . . . . . . . . .  8
     5.1.  SRLG Collection  . . . . . . . . . . . . . . . . . . . . .  8
     5.2.  SRLG Update  . . . . . . . . . . . . . . . . . . . . . . . 10
     5.3  Domain Boundaries . . . . . . . . . . . . . . . . . . . . . 10
     5.4.  Compatibility  . . . . . . . . . . . . . . . . . . . . . . 11
   6.  Manageability Considerations . . . . . . . . . . . . . . . . . 11
     6.1.  Policy Configuration . . . . . . . . . . . . . . . . . . . 11
     6.2.  Coherent SRLG IDs  . . . . . . . . . . . . . . . . . . . . 11
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
     8.1.  RSVP Attribute Bit Flags . . . . . . . . . . . . . . . . . 12
     8.2.  ROUTE_RECORD Object  . . . . . . . . . . . . . . . . . . . 12
     8.3.  Policy Control Failure Error Subcodes  . . . . . . . . . . 13
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 13
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 14
   Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . 15
   Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16

1.  Introduction

   It is important to understand which Traffic Engineering (TE) links in
   a given network might be at risk from the same failures.  In this
   sense, a set of links can constitute a Shared Risk Link Group (SRLG)
   if they share a resource whose failure can affect all links in the
   set [RFC4202].

   On the other hand, as described in [RFC4206] and [RFC6107], a
   Hierarchical LSP (H-LSP) or stitched LSP (S-LSP) can be used for
   carrying one or more other LSPs.  Both the H-LSP and S-LSP can be
   formed as a TE link.  In such cases, it is important to know the SRLG
   information of the LSPs that will be used to carry further LSPs.

   This document provides a signaling mechanism that collects the SRLGs
   that are used by an LSP and can then be advertised as properties of
   the TE link formed by that LSP.

1.1.  Applicability Example: Dual-Homing

   An interesting use case for the SRLG collection procedures defined in
   this document is achieving LSP diversity in a dual-homing scenario.
   The use case is illustrated in Figure 1, when the overlay model is
   applied as defined in [RFC4208].  In this example, the exchange of
   routing information over the User-Network Interface (UNI) is
   prohibited by operator policy.

                            +---+    +---+
                            | P |....| P |
                            +---+    +---+
                           /              \
                      +-----+               +-----+
             +---+    | PE1 |               | PE3 |    +---+
             |CE1|----|     |               |     |----|CE2|
             +---+\   +-----+               +-----+   /+---+
                   \     |                     |     /
                    \ +-----+               +-----+ /
                     \| PE2 |               | PE4 |/
                      |     |               |     |
                      +-----+               +-----+
                            \              /
                            +---+    +---+
                            | P |....| P |
                            +---+    +---+

                         Figure 1: Dual-Homing Configuration

   Single-homed customer edge (CE) devices are connected to a single
   provider edge (PE) device via a single UNI link (which could be a
   bundle of parallel links, typically using the same fiber cable).
   This single UNI link can constitute a single point of failure.  Such
   a single point of failure can be avoided if the CE device is
   connected to two PE devices via two UNI interfaces for CE1 and CE2,
   respectively, as depicted in Figure 1.

   For the dual-homing case, it is possible to establish two connections
   (LSPs) from the source CE device to the same destination CE device
   where one connection is using one UNI link to PE1, for example, and
   the other connection is using the UNI link to PE2.  In order to avoid
   single points of failure within the provider network, it is necessary
   to also ensure path (LSP) diversity within the provider network to
   achieve end-to-end diversity for the two LSPs between the two CE
   devices CE1 and CE2.  This use case describes how it is possible to
   achieve path diversity within the provider network based on collected
   SRLG information.  As the two connections (LSPs) enter the provider
   network at different PE devices, the PE device that receives the
   connection request for the second connection needs to know the
   additional path computation constraints such that the path of the
   second LSP is disjoint with respect to the already established first

   As SRLG information is normally not shared between the provider
   network and the client network, i.e., between PE and CE devices, the
   challenge is how to solve the diversity problem when a CE is dual-
   homed.  The RSVP extensions for collecting SRLG information defined
   in this document make it possible to retrieve SRLG information for an
   LSP and hence solve the dual-homing LSP diversity problem.  For
   example, CE1 in Figure 1 may have requested an LSP1 to CE2 via PE1
   that is routed via PE3 to CE2.  CE1 can then subsequently request an
   LSP2 to CE2 via PE2 with the constraint that it needs to be maximally
   SRLG disjoint with respect to LSP1.  PE2, however, does not have any
   SRLG information associated with LSP1, and this is needed as input
   for its constraint-based path computation function.  If CE1 is
   capable of retrieving the SRLG information associated with LSP1 from
   PE1, it can pass this discovered information to PE2 as part of the
   LSP2 setup request (RSVP PATH message) in an EXCLUDE_ROUTE Object
   (XRO) or Explicit Exclusion Route Subobject (EXRS) as described in
   [RFC4874], and PE2 can now calculate a path for LSP2 that is SRLG
   disjoint with respect to LSP1.  The SRLG information associated with
   LSP1 can be retrieved when LSP1 is established or at any time before
   LSP2 is set up.

   When CE1 sends the setup request for LSP2 to PE2, it can also request
   the collection of SRLG information for LSP2 and send that information
   to PE1 by re-signaling LSP1 with SRLG-exclusion based on LSP2's

   discovered SRLGs.  This will ensure that the two paths for the two
   LSPs remain mutually diverse; this is important when the provider
   network is capable of restoring connections that failed due to a
   network failure (fiber cut) in the provider network.

   Note that the knowledge of SRLG information even for multiple LSPs
   does not allow a CE device to derive the provider network topology
   based on the collected SRLG information.  It would, however, be
   possible for an entity controlling multiple CE devices to derive some
   information related to the topology.  This document therefore allows
   PE devices to control the communication of SRLGs outside the provider
   network if desired.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

3.  RSVP-TE Requirements

   The SRLG collection process takes place in three stages:

   o  The LSP's ingress node requests that SRLG collection take place;

   o  SRLG data is added to the Path and Resv ROUTE_RECORD Objects
      (RROs) by all nodes during signaling;

   o  Changes to previously signaled SRLG data are made by sending
      updated Path and Resv messages as required.

3.1.  SRLG Collection Indication

   The ingress node of the LSP needs be capable of indicating whether
   the SRLG information of the LSP is to be collected during the
   signaling procedure of setting up an LSP.  There is no need for SRLG
   information to be collected without an explicit request by the
   ingress node.

   It may be preferable for the SRLG collection request to be understood
   by all nodes along the LSP's path, or it may be more important for
   the LSP to be established successfully even if it traverses nodes
   that cannot supply SRLG information or have not implemented the
   procedures specified in this document.  It is desirable for the
   ingress node to make the SRLG collection request in a manner that
   best suits its own policy.

3.2.  SRLG Collection

   If requested, the SRLG information is collected during the setup of
   an LSP.  SRLG information is added by each hop to the Path RRO during
   Path message processing.  The same information is also added to the
   Resv RRO during Resv processing at each hop.

3.3.  SRLG Update

   When the SRLG information of an existing LSP for which SRLG
   information was collected during signaling changes, the relevant
   nodes of the LSP need to be capable of updating the SRLG information
   of the LSP.  This means that the signaling procedure needs to be
   capable of updating the new SRLG information.

3.4.  SRLG ID Definition

   The identifier of an SRLG (SRLG ID) is defined as a 32-bit quantity
   in [RFC4202].  This definition is used in this document.

4.  Encodings

4.1.  SRLG Collection Flag

   In order to indicate to nodes that SRLG collection is desired, this
   document defines a new flag in the Attribute Flags TLV (see
   [RFC5420]).  This document defines a new SRLG Collection Flag in the
   Attribute Flags TLV.  A node that wishes to indicate that SRLG
   collection is desired MUST set this flag in an Attribute Flags TLV in
   an LSP_REQUIRED_ATTRIBUTES object (if collection is to be mandatory)
   or an LSP_ATTRIBUTES object (if collection is desired but not

   o  Bit Number (specified in Section 8.1): SRLG Collection Flag

   The SRLG Collection Flag is meaningful on a Path message.  If the
   SRLG Collection Flag is set to 1, it means that the SRLG information
   SHOULD be reported to the ingress and egress node along the setup of
   the LSP.

   The rules for the processing of the Attribute Flags TLV are not

4.2.  RRO SRLG Subobject

   This document defines a new RRO subobject (ROUTE_RECORD subobject) to
   record the SRLG information of the LSP.  Its format is modeled on the
   RRO subobjects defined in [RFC3209].

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      |      Type     |     Length    |D|          Reserved           |
      |                 SRLG ID 1 (4 octets)                          |

      ~                           ......                              ~
      |                 SRLG ID n (4 octets)                          |

   Type (8 bits)

   The type of the subobject.  The value is specified in Section 8.2.

   Length (8 bits)

   The Length field contains the total length of the subobject in
   octets, including the Type and Length fields.  The Length depends on
   the number of SRLG IDs.

   Direction bit (D-bit) (1 bit)

   If not set, the SRLGs contained in this subobject apply to the
   downstream direction.  If set, they apply to the upstream direction.

   Reserved (15 bits)

   This 15-bit field is reserved.  It SHOULD be set to zero on
   transmission and MUST be ignored on receipt.

   SRLG ID (4 octets)

   This field contains one SRLG ID.  There is one SRLG ID field per SRLG
   collected.  There MAY be multiple SRLG ID fields in an SRLG

   A node MUST NOT push an SRLG subobject in the ROUTE_RECORD without
   also pushing either an IPv4 subobject, an IPv6 subobject, an
   Unnumbered Interface ID subobject, or a Path Key Subobject (PKS).

   As described in [RFC3209], the ROUTE_RECORD object is managed as a
   stack.  The SRLG subobject MUST be pushed by the node before the node
   IP address or link identifier.  The SRLG subobject SHOULD be pushed
   after the Attribute subobject, if present, and after the LABEL
   subobject, if requested.  It MUST be pushed within the hop to which
   it applies.

   [RFC5553] describes mechanisms to carry a PKS in the RRO so as to
   facilitate confidentiality in the signaling of inter-domain TE LSPs.
   RFC 5553 allows the path segment that needs to be hidden (that is, a
   Confidential Path Segment (CPS)) to be replaced in the RRO with a
   PKS.  If the CPS contains SRLG subobjects, these MAY be retained in
   the RRO by adding them again after the PKS in the RRO.  The CPS is
   defined in [RFC5520].

   The rules for the processing of the LSP_REQUIRED_ATTRIBUTES,
   LSP_ATTRIBUTES, and ROUTE_RECORD objects are not changed.

5.  Signaling Procedures

   The ingress node of the LSP MUST be capable of indicating whether the
   SRLG information of the LSP is to be collected during the signaling
   procedure of setting up an LSP.

5.1.  SRLG Collection

   Per [RFC3209], an ingress node initiates the recording of the route
   information of an LSP by adding an RRO to a Path message.  If an
   ingress node also desires SRLG recording, it MUST set the SRLG
   Collection Flag in the Attribute Flags TLV, which MAY be carried in
   either an LSP_REQUIRED_ATTRIBUTES object (when the collection is
   mandatory) or an LSP_ATTRIBUTES object (when the collection is
   desired, but not mandatory).

   A node MUST NOT add SRLG information without an explicit request by
   the ingress node in the Path message.

   When a node receives a Path message that carries an
   LSP_REQUIRED_ATTRIBUTES object with the SRLG Collection Flag set, if
   local policy determines that the SRLG information is not to be
   provided to the endpoints, it MUST return a PathErr message with

   o  Error Code 2 (policy) and

   o  Error subcode "SRLG Recording Rejected" (see Section 8.3 for

   to reject the Path message.

   When a node receives a Path message that carries an LSP_ATTRIBUTES
   object with the SRLG Collection Flag set, if local policy determines
   that the SRLG information is not to be provided to the endpoints, the
   Path message MUST NOT be rejected due to the SRLG recording
   restriction, and the Path message MUST be forwarded without any SRLG
   subobject(s) added to the RRO of the corresponding outgoing Path

   If local policy permits the recording of the SRLG information, the
   processing node SHOULD add local SRLG information, as defined below,
   to the RRO of the corresponding outgoing Path message.  The
   processing node MAY add multiple SRLG subobjects to the RRO if
   necessary.  It then forwards the Path message to the next node in the
   downstream direction.  The processing node MUST retain a record of
   the SRLG recording request for reference during Resv processing
   described below.

   If the addition of SRLG information to the RRO would result in the
   RRO exceeding its maximum possible size or becoming too large for the
   Path message to contain it, the requested SRLGs MUST NOT be added.
   If the SRLG collection request was contained in an
   LSP_REQUIRED_ATTRIBUTES object, the processing node MUST behave as
   specified by [RFC3209] and drop the RRO from the Path message
   entirely.  If the SRLG collection request was contained in an
   LSP_ATTRIBUTES object, the processing node MAY omit some or all of
   the requested SRLGs from the RRO; otherwise, it MUST behave as
   specified by [RFC3209] and drop the RRO from the Path message
   entirely.  Subsequent processing of the LSP proceeds as further
   specified in [RFC3209].

   Following the steps described above, the intermediate nodes of the
   LSP can collect the SRLG information in the RRO during the processing
   of the Path message hop by hop.  When the Path message arrives at the
   egress node, the egress node receives SRLG information in the RRO.

   Per [RFC3209], when issuing a Resv message for a Path message that
   contains an RRO, an egress node initiates the RRO process by adding
   an RRO to the outgoing Resv message.  The processing for RROs
   contained in Resv messages then mirrors that of the Path messages.

   When a node receives a Resv message for an LSP for which SRLG
   Collection was specified in the corresponding Path message, then when
   local policy allows recording SRLG information, the node MUST add
   SRLG information to the RRO of the corresponding outgoing Resv
   message as specified below.  When the Resv message arrives at the
   ingress node, the ingress node can extract the SRLG information from
   the RRO in the same way as the egress node.

   Note that a link's SRLG information for the upstream direction cannot
   be assumed to be the same as that for the downstream direction.

   o  For Path and Resv messages for a unidirectional LSP, a node SHOULD
      include SRLG subobjects in the RRO for the downstream data link

   o  For Path and Resv messages for a bidirectional LSP, a node SHOULD
      include SRLG subobjects in the RRO for both the upstream data link
      and the downstream data link from the local node.  In this case,
      the node MUST include the information in the same order for both
      Path messages and Resv messages.  That is, the SRLG subobject for
      the upstream link is added to the RRO before the SRLG subobject
      for the downstream link.

      If SRLG data is added for both the upstream and downstream links,
      the two sets of SRLG data MUST be added in separate SRLG
      subobjects.  A single SRLG subobject MUST NOT contain a mixture of
      upstream and downstream SRLGs.  When adding a SRLG subobject to an
      RRO, the D-bit MUST be set appropriately to indicate the direction
      of the SRLGs.  If an SRLG ID applies in both directions, it SHOULD
      be added to both the upstream and downstream SRLG subobjects.

   Based on the above procedure, the endpoints can get the SRLG
   information automatically.  Then, for instance, the endpoints can
   advertise it as a TE link to the routing instance based on the
   procedure described in [RFC6107] and configure the SRLG information
   of the Forwarding Adjacency (FA) automatically.

5.2.  SRLG Update

   When the SRLG information of a link is changed, the endpoints of LSPs
   using that link need to be made aware of the changes.  When a change
   to the set of SRLGs associated with a link occurs, the procedures
   defined in Section 4.4.3 of [RFC3209] MUST be used to refresh the
   SRLG information for each affected LSP if the local node's policy
   dictates that the SRLG change be communicated to other nodes.

5.3  Domain Boundaries

   If mandated by local policy as specified by the network operator, a
   node MAY remove SRLG information from any RRO in a Path or Resv
   message being processed.  It MAY add a summary of the removed SRLGs
   or map them to other SRLG values.  However, this SHOULD NOT be done
   unless explicitly mandated by local policy.

5.4.  Compatibility

   A node that does not recognize the SRLG Collection Flag in the
   Attribute Flags TLV is expected to proceed as specified in [RFC5420].
   It is expected to pass the TLV on unaltered if it appears in an
   LSP_ATTRIBUTES object or to reject the Path message with the
   appropriate Error Code and Value if it appears in a

   A node that does not recognize the SRLG RRO subobject is expected to
   behave as specified in [RFC3209]: unrecognized subobjects are to be
   ignored and passed on unchanged.

6.  Manageability Considerations

6.1.  Policy Configuration

   In a border node of an inter-domain or inter-layer network, the
   following SRLG processing policy MUST be capable of being configured:

   o  Whether the node is allowed to participate in SRLG collection and
      notify changes to collected SRLG information to endpoint nodes as
      described in Section 5.2.

   o  Whether the SRLG IDs of the domain or specific layer network can
      be exposed to the nodes outside the domain or layer network, or
      whether they SHOULD be summarized, mapped to values that are
      comprehensible to nodes outside the domain or layer network, or
      removed entirely as described in Section 5.3.

   A node using [RFC5553] and PKS MAY apply the same policy.

6.2.  Coherent SRLG IDs

   In a multi-layer, multi-domain scenario, SRLG IDs can be configured
   by different management entities in each layer or domain.  In such
   scenarios, maintaining a coherent set of SRLG IDs is a key
   requirement in order to be able to use the SRLG information properly.
   Thus, SRLG IDs SHOULD be unique.  Note that current procedures are
   targeted towards a scenario where the different layers and domains
   belong to the same operator or to several coordinated administrative
   groups.  Ensuring the aforementioned coherence of SRLG IDs is beyond
   the scope of this document.

   Further scenarios, where coherence in the SRLG IDs cannot be
   guaranteed, are out of the scope of the present document and are left
   for further study.

7.  Security Considerations

   This document builds on the mechanisms defined in [RFC3473], which
   also discusses related security measures.  In addition, [RFC5920]
   provides an overview of security vulnerabilities and protection
   mechanisms for the GMPLS control plane.  The procedures defined in
   this document permit the transfer of SRLG data between layers or
   domains during the signaling of LSPs, subject to policy at the layer
   or domain boundary.  As described in Sections 5.3 and 6.1, local
   policy as specified by the network operator will explicitly mandate
   the processing of information at domain or layer boundaries.

8.  IANA Considerations

8.1.  RSVP Attribute Bit Flags

   IANA has created a registry and manages the space of the Attribute
   bit flags of the Attribute Flags TLV, as described in Section 11.3 of
   [RFC5420], in the "Attribute Flags" subregistry of the "Resource
   Reservation Protocol-Traffic Engineering (RSVP-TE) Parameters"
   registry located at

   This document introduces a new Attribute bit flag:

      Bit No     Name        Attribute   Attribute   RRO  ERO  Reference
                             Flags Path  Flags Resv
      ---------  ----------  ----------  ----------- ---  ---  ---------
      12         SRLG        Yes         No          Yes  No   RFC 8001,
                 Collection                                    [RFC7570]

8.2.  ROUTE_RECORD Object

   IANA manages the "Resource Reservation Protocol (RSVP) Parameters"
   registry located at
   <http://www.iana.org/assignments/rsvp-parameters>.  This document
   introduces a new RRO subobject under the "Sub-object type - 21
   ROUTE_RECORD - Type 1 Route Record" subregistry:

      Value    Description           Reference
      -----    -------------------   ---------
      34       SRLG subobject        RFC 8001

8.3.  Policy Control Failure Error Subcodes

   IANA manages the assignments in the "Error Codes and Globally-Defined
   Error Value Sub-Codes" section of the "Resource Reservation Protocol
   (RSVP) Parameters" registry located at

   This document introduces a new value under "Sub-Codes - 2 Policy
   Control Failure":

      Value   Description               Reference
      -----   -----------------------   ---------
      21      SRLG Recording Rejected   RFC 8001

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [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,

   [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,

   [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, <http://www.rfc-editor.org/info/rfc4202>.

   [RFC5420]  Farrel, A., Ed., Papadimitriou, D., Vasseur, JP., and A.
              Ayyangarps, "Encoding of Attributes for MPLS LSP
              Establishment Using Resource Reservation Protocol Traffic
              Engineering (RSVP-TE)", RFC 5420, DOI 10.17487/RFC5420,
              February 2009, <http://www.rfc-editor.org/info/rfc5420>.

   [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,

   [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,

9.2.  Informative References

   [RFC4206]  Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
              Hierarchy with Generalized Multi-Protocol Label Switching
              (GMPLS) Traffic Engineering (TE)", RFC 4206,
              DOI 10.17487/RFC4206, October 2005,

   [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,

   [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, <http://www.rfc-editor.org/info/rfc4874>.

   [RFC5920]  Fang, L., Ed., "Security Framework for MPLS and GMPLS
              Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,

   [RFC6107]  Shiomoto, K., Ed., and A. Farrel, Ed., "Procedures for
              Dynamically Signaled Hierarchical Label Switched Paths",
              RFC 6107, DOI 10.17487/RFC6107, February 2011,

   [RFC7570]  Margaria, C., Ed., Martinelli, G., Balls, S., and B.
              Wright, "Label Switched Path (LSP) Attribute in the
              Explicit Route Object (ERO)", RFC 7570,
              DOI 10.17487/RFC7570, July 2015,


   The authors would like to thank Dieter Beller, Vishnu Pavan Beeram,
   Lou Berger, Deborah Brungard, Igor Bryskin, Ramon Casellas, Niclas
   Comstedt, Alan Davey, Elwyn Davies, Dhruv Dhody, Himanshu Shah, and
   Xian Zhang for their useful comments and improvements to this


   Dan Li
   F3-5-B RD Center
   Bantian, Longgang District, Shenzhen  518129

   Email: danli@huawei.com

Authors' Addresses

   Fatai Zhang (editor)
   F3-5-B RD Center
   Bantian, Longgang District, Shenzhen  518129

   Email: zhangfatai@huawei.com

   Oscar Gonzalez de Dios (editor)
   Telefonica Global CTO
   Distrito Telefonica, edificio sur, Ronda de la Comunicacion 28045
   Madrid  28050
   Phone: +34 913129647

   Email: oscar.gonzalezdedios@telefonica.com

   Cyril Margaria
   200 Somerset Corporate Blvd., Suite 4001
   Bridgewater, NJ  08807
   United States of America

   Email: cmargaria@juniper.net

   Matt Hartley

   Email: mhartley@cisco.com

   Zafar Ali

   Email: zali@cisco.com