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Versions: 00 01 draft-ietf-spring-sr-yang

SPRING Working Group                                        S. Litkowski
Internet-Draft                                   Orange Business Service
Intended status: Standards Track                                   Y. Qu
Expires: December 25, 2015                                 Cisco Systems
                                                               P. Sarkar
                                                        Juniper Networks
                                                             J. Tantsura
                                                                Ericsson
                                                           June 23, 2015


                  YANG Data Model for Segment Routing
                   draft-litkowski-spring-sr-yang-01

Abstract

   This document defines a YANG data model ([RFC6020]) for segment
   routing ([I-D.ietf-spring-segment-routing]) configuration and
   operation.  This YANG model is intended to be used on network
   elements to configure or operate segment routing.  This document
   defines also generic containers that SHOULD be reused by IGP protocol
   modules to support segment routing.

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 [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 http://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 December 25, 2015.






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Copyright Notice

   Copyright (c) 2015 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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Tree diagram  . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Design of the Data Model  . . . . . . . . . . . . . . . . . .   3
   3.  Configuration . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  IGP Control plane configuration . . . . . . . . . . . . . . .   6
     4.1.  IGP interface configuration . . . . . . . . . . . . . . .   6
       4.1.1.  Adjacency SID properties  . . . . . . . . . . . . . .   6
         4.1.1.1.  Bundling  . . . . . . . . . . . . . . . . . . . .   6
         4.1.1.2.  Protection  . . . . . . . . . . . . . . . . . . .   7
   5.  States  . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   6.  Notifications . . . . . . . . . . . . . . . . . . . . . . . .   7
   7.  YANG Module . . . . . . . . . . . . . . . . . . . . . . . . .   8
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  20
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  20
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21
   11. Normative References  . . . . . . . . . . . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21

1.  Introduction

   This document defines a YANG data model for segment routing
   configuration and operation.  This document does not define the IGP
   extensions to support segment routing but defines generic groupings
   that SHOULD be reused by IGP extension modules.  The reason of this
   design choice is to not require implementations to support all IGP
   extensions.  For example, an implementation may support IS-IS
   extension but not OSPF.







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1.1.  Tree diagram

   A simplified graphical representation of the data model is presented
   in Section 2.

   The meaning of the symbols in these diagrams is as follows:

   o  Brackets "[" and "]" enclose list keys.

   o  Curly braces "{" and "}" contain names of optional features that
      make the corresponding node conditional.

   o  Abbreviations before data node names: "rw" means configuration
      (read-write), and "ro" state data (read-only).

   o  Symbols after data node names: "?" means an optional node and "*"
      denotes a "list" or "leaf-list".

   o  Parentheses enclose choice and case nodes, and case nodes are also
      marked with a colon (":").

   o  Ellipsis ("...") stands for contents of subtrees that are not
      shown.

2.  Design of the Data Model

   As the module definition is just starting, it is expected that there
   will be changes as the module matures.

module: ietf-segment-routing
augment /rt:routing/rt:routing-instance:
   +--rw segment-routing
      +--rw transport-type?   identityref
      +--rw bindings
      |  +--rw mapping-server {mapping-server}?
      |  |  +--rw policy* [name]
      |  |     +--rw name    string
      |  |     +--rw ipv4
      |  |     |  +--rw mapping-entry* [prefix]
      |  |     |     +--rw prefix        inet:ipv4-prefix
      |  |     |     +--rw value-type?   enumeration
      |  |     |     +--rw start-sid     uint32
      |  |     |     +--rw range?        uint32
      |  |     +--rw ipv6
      |  |        +--rw mapping-entry* [prefix]
      |  |           +--rw prefix        inet:ipv6-prefix
      |  |           +--rw value-type?   enumeration
      |  |           +--rw start-sid     uint32



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      |  |           +--rw range?        uint32
      |  +--rw connected-prefix-sid-map
      |     +--rw ipv4
      |     |  +--rw ipv4-prefix-sid* [prefix]
      |     |     +--rw prefix               inet:ipv4-prefix
      |     |     +--rw value-type?          enumeration
      |     |     +--rw start-sid            uint32
      |     |     +--rw range?               uint32
      |     |     +--rw last-hop-behavior?   enumeration {sid-last-hop-behavior}?
      |     +--rw ipv6
      |        +--rw ipv6-prefix-sid* [prefix]
      |           +--rw prefix               inet:ipv6-prefix
      |           +--rw value-type?          enumeration
      |           +--rw start-sid            uint32
      |           +--rw range?               uint32
      |           +--rw last-hop-behavior?   enumeration {sid-last-hop-behavior}?
      +--rw srgb* [lower-bound upper-bound]
         +--rw lower-bound    uint32
         +--rw upper-bound    uint32
augment /rt:routing-state/rt:routing-instance:
   +--ro segment-routing
      +--ro node-capabilities
      |  +--ro transport-planes* [transport-plane]
      |  |  +--ro transport-plane    identityref
      |  +--ro segment-stack-push-limit?     uint8
      |  +--ro readable-label-stack-depth?   uint8
      +--ro label-blocks*
      |  +--ro lower-bound?   uint32
      |  +--ro upper-bound?   uint32
      |  +--ro size?          uint32
      |  +--ro free?          uint32
      |  +--ro used?          uint32
      +--ro global-sid-list
         +--ro sid* [target sid source source-protocol binding-type]
            +--ro target             string
            +--ro sid                uint32
            +--ro algorithm?         uint8
            +--ro source             inet:ip-address
            +--ro used?              boolean
            +--ro source-protocol    leafref
            +--ro binding-type       enumeration
notifications:
   +---n segment-routing-global-sid-collision
   |  +--ro received-target?    string
   |  +--ro original-target?    string
   |  +--ro index?              uint32
   |  +--ro routing-protocol?   leafref
   +---n segment-routing-index-out-of-range



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      +--ro received-target?    string
      +--ro received-index?     uint32
      +--ro routing-protocol?   leafref

3.  Configuration

   This module augments the "/rt:routing/rt:routing-instance:" with a
   segment-routing container.  This container defines all the
   configuration parameters related to segment-routing for this
   particular routing-instance.

   The segment-routing configuration is split in global routing-instance
   configuration and interface configuration.

   The global configuration includes :

   o  segment-routing transport type : The underlying transport type for
      segment routing.  The version of the model limits the transport
      type to an MPLS dataplane.  The transport-type is only defined
      once for a particular routing-instance and is agnostic to the
      control plane used.  Only a single transport-type is supported in
      this version of the model.

   o  bindings : Defines prefix to SID mappings.  The operator can
      control advertisement of Prefix-SID independently for IPv4 and
      IPv6.  Two types of mappings are available :

      *  Mapping-server : maps non local prefixes to a segment ID.
         Configuration of bindings does not automatically allow
         advertisement of those bindings.  Advertisement must be
         controlled by each routing-protocol instance (see Section 4).
         Multiple mapping policies may be defined.

      *  Connected prefixes : maps connected prefixes to a segment ID.
         Advertisement of the mapping will be done by IGP when enabled
         for segment routing (see Section 4).  The SID value can be
         expressed as an index (default), or an absolute value.  The
         "last-hop-behavior" configuration dictates the PHP behavior:
         "explicit-null", "php", or "non-php".

   o  SRGB (Segment Routing Global Block): Defines a list of label
      blocks represented by a pair of lower-bound/upper-bound labels.
      The SRGB is also agnostic to the control plane used.  So all
      routing-protocol instance will have to advertise the same SRGB.







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4.  IGP Control plane configuration

   Support of segment-routing extensions for a particular IGP control
   plane is done by augmenting routing-protocol configuration with
   segment-routing extensions.  This augmentation SHOULD be part of
   separate YANG modules in order to not create any dependency for
   implementations to support all protocol extensions.

   This module defines groupings that SHOULD be used by IGP segment
   routing modules.

   The "controlplane-cfg" grouping defines the generic global
   configuration for the IGP.

   The "enabled" leaf enables segment-routing extensions for the
   routing-protocol instance.

   The "bindings" container controls the routing-protocol instance's
   advertisement of local bindings and the processing of received
   bindings.

4.1.  IGP interface configuration

   The interface configuration is part of the "igp-interface-cfg"
   grouping and includes Adjacency SID properties.

4.1.1.  Adjacency SID properties

4.1.1.1.  Bundling

   This section is a first proposal on how to use S-bit in Adj-SID to
   create bundles.  Authors would like to trigger discussion based on
   this first proposal.

   In case of parallel IP links between routers, an additional Adjacency
   SID may be advertised representing more than one adjacency (i.e., a
   bundle of adjacencies).  The "advertise-adj-group-sid" configuration
   controls whether or not an additional adjacency SID is advertised.

   The "advertise-adj-group-sid" would be a list of "group-id".  The
   "group-id" will permit to identify interfaces that must be bundled
   together.









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       +-------+                 +------+
       |       | ------- L1 ---- |      |
       |   R1  | ------- L2 ---- |  R2  |
       |       | ------- L3 ---- |      |
       |       | ------- L4 ---- |      |
       +-------+                 +------+

   In the figure above, R1 and R2 are interconnected by four links.  A
   routing protocol adjacency is established on each link.  Operator
   would like to create segment-routing Adj-SID that represent some
   bundles of links.  We can imagine two different bundles : L1/L2 and
   L2/L3.  To achieve this behavior, the service provider will configure
   a "group-id" X for both interfaces L1 and L2 and a "group-id" Y for
   both interfaces L3 and L3.  This will result in R1 advertising an
   additional Adj-SID for each adjacency, for example a Adj-SID with S
   flag set and value of 400 will be added to L1 and L2.  A Adj-SID with
   S flag set and value of 500 will be added to L3 and L4.  As L1/L2 and
   L3/L4 does not share the same "group-id", a different SID value will
   be allocated.

4.1.1.2.  Protection

   The "advertise-protection" defines how protection for an interface is
   advertised.  It does not control the activation or deactivation of
   protection.  If the "single" option is used, a single Adj-SID will be
   advertised for the interface.  If the interface is protected, the
   B-Flag for the Adj-SID advertisement will be set.  If the "dual"
   option is used and if the interface is protected, two Adj-SIDs will
   be advertised for the interface adjacencies.  One Adj-SID will always
   have the B-Flag set and the other will have the B-Flag clear.  This
   option is intended to be used in the case of traffic engineering
   where a path must use either protected segments or non-protected
   segments.

5.  States

   The operational states contains information reflecting the usage of
   allocated SRGB labels.

   It also includes a list of all global SIDs, their associated
   bindings, and other information such as the source protocol and
   algorithm.

6.  Notifications

   The model proposes two notifications for segment-routing.





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   o  segment-routing-global-sid-collision: Raised when a control plane
      advertised index is already associated with another target (in
      this version, the only defined targets are IPv4 and IPv6
      prefixes).

   o  segment-routing-index-out-of-range: Raised when a control plane
      advertised index fall outside the range of SRGBs configured for
      the network device.

7.  YANG Module

   <CODE BEGINS> file "ietf-segment-routing@2015-06-23.yang"

   module ietf-segment-routing {
     namespace "urn:ietf:params:xml:ns:"
             + "yang:ietf-segment-routing";
     prefix sr;

     import ietf-inet-types {
       prefix "inet";
     }

     import ietf-routing {
       prefix "rt";
     }

     organization
      "IETF SPRING Working Group";

     contact
       "WG List:  &lt;mailto:spring@ietf.org&gt;

       Editor:    Stephane Litkowski
             &lt;mailto:stephane.litkowski@orange.com&gt;

           Acee Lindem
             &lt;mailto:acee@cisco.com&gt;
           Yingzhen Qu
             &lt;mailto:yiqu@cisco.com&gt;
           Pushpasis Sarkar
             &lt;mailto:psarkar@juniper.net&gt;
           Ing-Wher Chen
             &lt;mailto:ing-wher.chen@ericsson.com&gt;
           Jeff Tantsura
               &lt;jeff.tantsura@ericsson.com&gt;

       ";




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     description
       "The YANG module defines a generic configuration model for
       Segment routing common across all of the vendor
       implementations.";

     revision 2015-06-22 {
       description
        "
        * Prefix SID config moved to
        connected-prefix-sid-map in global SR cfg
        rather than IGP.
        ";
        reference "draft-litkowski-spring-sr-yang-01";
     }
     revision 2015-04-23 {
       description "
        * Node flag deprecated from prefixSID
        * SR interface cfg moved to protocol
        * Adding multiple binding policies for SRMS
       ";
       reference "";
     }
     revision 2015-02-27 {
       description "Initial";
       reference "draft-litkowski-spring-sr-yang-00";
     }

     /* Identities */
     identity segment-routing-transport {
       description
       "Base identity for segment routing transport.";
     }
     identity segment-routing-transport-mpls {
       base segment-routing-transport;
       description
       "This identity represents MPLS transport for segment
       routing.";
     }

     /* Features */

     feature mapping-server {
       description
        "Support of SRMS.";
     }

     feature sid-last-hop-behavior {
       description



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         "Configurable last hop behavior.";
     }

     /* Groupings */

     grouping controlplane-cfg {
       container segment-routing {
         leaf enabled {
           type boolean;
           default false;
           description
            "Enables segment-routing
            protocol extensions.";
         }
         container bindings {
           container advertise {
             leaf-list policies {
               type string;
               description
                "List of policies to be advertised.";
             }
             description
             "Authorize the advertise
             of local mappings in binding TLV.";
           }
           leaf receive {
             type boolean;
             default true;
             description
             "Authorize the reception and usage
             of binding TLV.";
           }
           description
            "Control of binding advertisement
            and reception.";
         }

         description
         "segment routing global config.";
       }
       description
        "Defines protocol configuration.";
     }

     grouping sid-value-type {
       leaf value-type {
         type enumeration {
           enum index {



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             description
               "The value will be
                interpreted as an index.";
           }
           enum absolute {
             description
               "The value will become
                interpreted as an absolute
                value.";
           }
         }
         default index;
         description
           "This leaf defines how value
            must be interpreted.";
       }
       description
        "Defines how the SID value is expressed.";
     }

     grouping ipv4-sid-cfg {

         leaf prefix {
           type inet:ipv4-prefix;
           description
             "connected prefix sid.";
         }

       uses sid-value-type;

         leaf start-sid {
           type uint32;
           mandatory true;
           description
           "Value associated with
           prefix. The value must
           be interpreted in the
           context of value-type.";
         }

         leaf range {
           type uint32;
           description
             "Describes how many SIDs could be
              allocated.";
         }
       description
        "This grouping defines cfg of prefix SID.";



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     }

     grouping ipv6-sid-cfg {
         leaf prefix {
           type inet:ipv6-prefix;
           description
             "connected prefix sid.";
         }

       uses sid-value-type;

         leaf start-sid {
           type uint32;
           mandatory true;
           description
           "Value associated with
           prefix. The value must
           be interpreted in the
           context of value-type.";
         }

         leaf range {
           type uint32;
           description
             "Describes how many SIDs could be
              allocated.";
         }

       description
        "This grouping defines cfg of prefix SID.";
     }

     grouping last-hop-behavior {
       leaf last-hop-behavior {
         if-feature sid-last-hop-behavior;
         type enumeration {
           enum explicit-null {
             description
               "Use explicit-null for the SID.";
           }
           enum no-php {
             description
               "Do no use PHP for the SID.";
           }
           enum php {
               description
                "Use PHP for the SID.";
           }



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         }
         description
           "Configure last hop behavior.";
       }
       description
        "Defines last hop behavior";
     }

     grouping igp-interface-cfg {
       container segment-routing {

        container adjacency-sid {
           list advertise-adj-group-sid {
             key group-id;

             leaf group-id {
               type uint32;
               description

                "The value is an internal value to identify
                a group-ID. Interfaces with the same
                group-ID will be bundled together.
                ";
             }
             description
              "Control advertisement of S flag.
                Enable to advertise a common Adj-SID
                for parallel links.";
           }
           leaf advertise-protection {
             type enumeration {
               enum "single" {
                 description
                  "A single Adj-SID is associated
                  with the adjacency and reflects
                  the protection configuration.";
               }
               enum "dual" {
                 description
                  "Two Adj-SIDs will be associated
                  with the adjacency if interface
                  is protected. In this case
                  one will be enforced with
                  backup flag set, the other
                  will be enforced to backup flag unset.
                  In case, protection is not configured,
                  a single Adj-SID will be advertised
                  with backup flag unset.";



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               }
             }
             description
              "If set, the Adj-SID refers to an
             adjacency being protected.";
           }
           description
            "Defines the adjacency SID properties.";
         }
         description
          "container for SR interface cfg.";
       }
         description
          "Grouping for IGP interface cfg.";
     }

     /* Cfg */

     augment "/rt:routing/rt:routing-instance" {
       description
        "This augments routing-instance
        configuration with segment-routing.";
       container segment-routing {
         leaf transport-type {
           type identityref {
             base segment-routing-transport;
           }
           default "segment-routing-transport-mpls";
           description "Dataplane to be used.";
         }
         container bindings {
           container mapping-server {
             if-feature mapping-server;
             list policy {
               key name;
               leaf name {
                   type string;
                   description
                    "Name of the mapping policy.";
               }
                 container ipv4 {
                   list mapping-entry {
                     key prefix;
                                     uses ipv4-sid-cfg;

                     description
                      "Mapping entries.";
                   }



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                   description
                    "IPv4 mapping entries.";
                 }
                 container ipv6 {
                   list mapping-entry {
                     key prefix;
                     uses ipv6-sid-cfg;
                                     description
                      "Mapping entries.";
                   }
                   description
                    "IPv6 mapping entries.";
                 }
                 description
                  "Definition of mapping policy.";
               }
             description
              "Configuration of mapping-server
               local entries.";
           }
           container connected-prefix-sid-map {
             container ipv4 {
               list ipv4-prefix-sid {
                 key prefix;
                 uses ipv4-sid-cfg;
                 uses last-hop-behavior;
                 description
                  "List of prefix SID
                  mapped to IPv4 local prefixes.";
               }
               description
                 "Parameters associated with IPv4 prefix SID";
             }
             container ipv6 {
               list ipv6-prefix-sid {
                 key prefix;
                 uses ipv6-sid-cfg;
                 uses last-hop-behavior;
                 description
                  "List of prefix SID
                  mapped to IPv6 local prefixes.";
               }
               description
                 "Parameters associated with IPv6 prefix SID";
             }
             description
               "Prefix SID configuration.";
           }



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           description
            "List of bindings.";
         }
         list srgb {
           key "lower-bound upper-bound";
           ordered-by user;
           leaf lower-bound {
             type uint32;
             description
             "Lower value in the block.";
           }
           leaf upper-bound {
             type uint32;
             description
             "Upper value in the block.";
           }
           description
             "List of global blocks to be
                advertised.";
         }
         description
         "segment routing global config.";
       }
     }


     /* Operational states */

     augment "/rt:routing-state/rt:routing-instance" {
       description
        "This augments the operational states
         with segment-routing.";
       container segment-routing {
         container node-capabilities {
           list transport-planes {
               key transport-plane;
               leaf transport-plane {
                   type identityref {
                       base segment-routing-transport;
                   }
                   description
                    "Transport plane supported";
               }
               description
                "List of supported transport planes.";
           }
           leaf segment-stack-push-limit {
               type uint8;



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               description
                "Describes the number of segments
                that can be pushed by the node.";
           }
           leaf readable-label-stack-depth {
               type uint8;
               description
                "Number of MPLS labels that
                can be read in the stack.";
           }
           description
            "Shows the SR capability of the node.";
         }
         list label-blocks {
           leaf lower-bound {
             type uint32;
             description
              "Lower bound of the label block.";
           }
           leaf upper-bound {
             type uint32;
             description
              "Upper bound of the label block.";
           }
           leaf size {
             type uint32;
             description
              "Number of indexes in the block.";
           }
           leaf free {
             type uint32;
             description
              "Number of indexes free in the block.";
           }
           leaf used {
             type uint32;
             description
              "Number of indexes used in the block.";
           }
           description
            "List of labels blocks currently
            in use.";
         }

         container global-sid-list {
           list sid {
             key "target sid source source-protocol binding-type";
             ordered-by system;



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             leaf target {
               type string;
               description
                "Defines the target of the binding.
                It can be a prefix or something else.";
             }
             leaf sid {
               type uint32;
               description
                "Index associated with the prefix.";
             }
             leaf algorithm {
               type uint8;
               description
                "Algorithm to be used for the prefix
                SID.";
             }
             leaf source {
               type inet:ip-address;
               description
                "IP address of the router than own
                 the binding.";
             }
             leaf used {
               type boolean;
               description
                "Defines if the binding is used
                 in forwarding plane.";
             }
             leaf source-protocol {
               type leafref {
                 path "/rt:routing-state/rt:routing-instance/" +
                 "rt:routing-protocols/rt:routing-protocol/rt:name";
               }
               description
                "Rtg protocol that owns the binding";
             }
             leaf binding-type {
               type enumeration {
                 enum prefix-sid {
                   description
                    "Binding is learned from
                    a prefix SID.";
                 }
                 enum binding-tlv {
                   description
                    "Binding is learned from
                    a binding TLV.";



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                 }
               }
               description
                "Type of binding.";
             }
             description
               "Binding.";

           }
           description
            "List of prefix and SID associations.";
         }
         description
          "Segment routing operational states.";
       }
     }


     /* Notifications */

     notification segment-routing-global-sid-collision {
       leaf received-target {
         type string;
         description
         "Target received in the controlplane that
                caused SID collision.";
       }
       leaf original-target {
         type string;
         description
         "Target already available in database that have the same SID
         as the received target.";
       }
       leaf index {
         type uint32;
         description
         "Value of the index used by two different prefixes.";
       }
       leaf routing-protocol {
         type leafref {
           path "/rt:routing-state/rt:routing-instance/" +
           "rt:routing-protocols/rt:routing-protocol/rt:name";
         }
         description
          "Routing protocol reference that received the event.";
       }
       description
         "This notification is sent when a new mapping is learned



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         , containing mapping
         where the SID is already used.
         The notification generation must be throttled with at least
          a 5 second gap. ";
     }
     notification segment-routing-index-out-of-range {
       leaf received-target {
         type string;
         description
         "Target received in the controlplane
               that caused SID collision.";
       }
       leaf received-index {
         type uint32;
         description
         "Value of the index received.";
       }
       leaf routing-protocol {
         type leafref {
           path "/rt:routing-state/rt:routing-instance/" +
           "rt:routing-protocols/rt:routing-protocol/rt:name";
         }
         description
          "Routing protocol reference that received the event.";
       }
       description
         "This notification is sent when a binding
         is received, containing a segment index
         which is out of the local configured ranges.
         The notification generation must be throttled with at least
          a 5 second gap. ";
     }

   }

   <CODE ENDS>

8.  Security Considerations

   TBD.

9.  Acknowledgements

   Authors would like to thank Derek Yeung, Acee Lindem, Greg Hankins,
   Hannes Gredler, Uma Chunduri, Jeffrey Zhang, Shradda Hedge for their
   contributions.





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10.  IANA Considerations

   TBD.

11.  Normative References

   [I-D.ietf-spring-segment-routing]
              Filsfils, C., Previdi, S., Decraene, B., Litkowski, S.,
              and R. Shakir, "Segment Routing Architecture", draft-ietf-
              spring-segment-routing-03 (work in progress), May 2015.

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

   [RFC6020]  Bjorklund, M., "YANG - A Data Modeling Language for the
              Network Configuration Protocol (NETCONF)", RFC 6020,
              October 2010.

Authors' Addresses

   Stephane Litkowski
   Orange Business Service

   Email: stephane.litkowski@orange.com


   Yingzhen Qu
   Cisco Systems

   Email: yiqu@cisco.com


   Pushpasis Sarkar
   Juniper Networks

   Email: psarkar@juniper.net


   Jeff Tantsura
   Ericsson

   Email: jeff.tantsura@ericsson.com









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