YANG Data Model for Segment Routing

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.

A simplified graphical representation of the data model is presented in . The meaning of the symbols in these diagrams is as follows: Brackets "[" and "]" enclose list keys. Curly braces "{" and "}" contain names of optional features that make the corresponding node conditional. Abbreviations before data node names: "rw" means configuration (read-write), and "ro" state data (read-only). Symbols after data node names: "?" means an optional node and "*" denotes a "list" or "leaf-list". Parentheses enclose choice and case nodes, and case nodes are also marked with a colon (":"). Ellipsis ("...") stands for contents of subtrees that are not shown.

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: +--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 algorithm] | | | +--rw prefix inet:ipv4-prefix | | | +--rw value-type? enumeration | | | +--rw start-sid uint32 | | | +--rw range? uint32 | | | +--rw algorithm identityref | | +--rw ipv6 | | +--rw mapping-entry* [prefix algorithm] | | +--rw prefix inet:ipv6-prefix | | +--rw value-type? enumeration | | +--rw start-sid uint32 | | +--rw range? uint32 | | +--rw algorithm identityref | +--rw connected-prefix-sid-map | +--rw ipv4 | | +--rw ipv4-prefix-sid* [prefix algorithm] | | +--rw prefix inet:ipv4-prefix | | +--rw value-type? enumeration | | +--rw start-sid uint32 | | +--rw range? uint32 | | +--rw algorithm identityref | | +--rw last-hop-behavior? enumeration {sid-last-hop-behavior}? | +--rw ipv6 | +--rw ipv6-prefix-sid* [prefix algorithm] | +--rw prefix inet:ipv6-prefix | +--rw value-type? enumeration | +--rw start-sid uint32 | +--rw range? uint32 | +--rw algorithm identityref | +--rw last-hop-behavior? enumeration {sid-last-hop-behavior}? +--rw global-srgb +--rw srgb* [lower-bound upper-bound] +--rw lower-bound uint32 +--rw upper-bound uint32 augment /rt:routing-state: +--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 -> /rt:routing-state/control-plane-protocols /control-plane-protocol/name +--ro binding-type enumeration notifications: +---n segment-routing-global-srgb-collision | +--ro srgb-collisions* | +--ro lower-bound? uint32 | +--ro upper-bound? uint32 | +--ro routing-protocol? -> /rt:routing-state/control-plane-protocols | /control-plane-protocol/name | +--ro originating-rtr-id? router-id +---n segment-routing-global-sid-collision | +--ro received-target? string | +--ro new-sid-rtr-id? router-id | +--ro original-target? string | +--ro original-sid-rtr-id? router-id | +--ro index? uint32 | +--ro routing-protocol? -> /rt:routing-state/control-plane-protocols | /control-plane-protocol/name +---n segment-routing-index-out-of-range +--ro received-target? string +--ro received-index? uint32 +--ro routing-protocol? -> /rt:routing-state/control-plane-protocols /control-plane-protocol/name

This module augments the "/rt:routing:" with a segment-routing container. This container defines all the configuration parameters related to segment-routing. The segment-routing configuration is split in global configuration and interface configuration. The global configuration includes : 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. 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 ). 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 ). 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". 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.

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.

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

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.

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

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.

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.

The model defines the following notifications for segment-routing. segment-routing-global-srgb-collision: Rasied when a control plan advertised SRGB blocks have conflicts. 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). segment-routing-index-out-of-range: Raised when a control plane advertised index fall outside the range of SRGBs configured for the network device.

file "ietf-segment-routing-common@2016-10-24.yang" module ietf-segment-routing-common { namespace "urn:ietf:params:xml:ns:" + "yang:ietf-segment-routing-common"; prefix sr-cmn; import ietf-inet-types { prefix "inet"; } organization "IETF SPRING Working Group"; contact "WG List: Editor: Stephane Litkowski Author: Acee Lindem Author: Yingzhen Qu Author: Pushpasis Sarkar Author: Ing-Wher Chen Author: Jeff Tantsura "; description "The YANG module defines a collection of types and groupings for Segment routing."; revision 2016-10-24 { description "Initial"; reference "RFC XXXX: YANG Data Model for Segment Routing."; } /* 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."; } identity prefix-sid-algorithm { description "Base identity for prefix-sid algorithm."; } identity prefix-sid-algorithm-shortest-path { base prefix-sid-algorithm; description "The default behavior of prefix-sid algorithm."; } identity prefix-sid-algorithm-strict-spf { base prefix-sid-algorithm; description "This algorithm mandates that the packet is forwared according to ECMP-aware SPF algorithm."; } /* Features */ feature sid-last-hop-behavior { description "Configurable last hop behavior."; } /* Groupings */ grouping srgb-cfg { 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 "Grouping for SRGB configuration."; } grouping sid-value-type { leaf value-type { type enumeration { enum index { 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 prefix-sid-attributes; description "This grouping defines cfg of prefix SID."; } grouping ipv6-sid-cfg { leaf prefix { type inet:ipv6-prefix; description "connected prefix sid."; } uses prefix-sid-attributes; 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."; } } description "Configure last hop behavior."; } description "Defines last hop behavior"; } grouping node-capabilities { description "Containing SR node capabilities."; 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; 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."; } // node-capabilities } // sr-node-capabilities grouping prefix-sid-attributes { description "Containing SR attributes for a prefix."; 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."; } leaf algorithm { type identityref { base prefix-sid-algorithm; } description "Prefix-sid algorithm."; } } //prefix-sid-attributes }


 file "ietf-segment-routing@2016-10-24.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-yang-types {
    prefix "yang";
  }

  import ietf-routing {
    prefix "rt";
  }

  import ietf-segment-routing-common {
    prefix "sr-cmn";
  }

  organization
   "IETF SPRING Working Group";

  contact
    "WG List:  

    Editor:    Stephane Litkowski
               

    Author:    Acee Lindem
               
    Author:    Yingzhen Qu
               
    Author:    Pushpasis Sarkar
               
    Author:    Ing-Wher Chen
               
    Author:    Jeff Tantsura
               

    ";

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

  revision 2016-10-24 {
    description "
      * Moved common SR types and groupings to a seperate module
    ";
    reference
      "RFC XXXX: YANG Data Model for Segment Routing.";
  }
  revision 2016-07-07 {
    description "
      * Add support of prefix-sid algorithm configuration
      * change routing-protocols to control-plane-protocols
    ";
    reference
      "RFC XXXX: YANG Data Model for Segment Routing.";
  }
  revision 2016-03-17 {
    description "
      * Add notification segment-routing-global-srgb-collision
      * Add router-id to segment-routing-global-sid-collision
      * Remove routing-instance
      * Add typedef router-id
    ";
    reference
      "RFC XXXX: YANG Data Model for Segment Routing.";
  }
  revision 2015-10-17 {
    description "
      * Add per-protocol SRGB config feature
      * Move SRBG config to a grouping
    ";
    reference
      "RFC XXXX: YANG Data Model for Segment Routing.";
  }
  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";
  }

  /* Features */

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

  feature protocol-srgb {
    description
      "Support per-protocol srgb configuration.";
  }

  /* Type Definitions */

  typedef system-id {
    type string {
      pattern
       '[0-9A-Fa-f]{4}\.[0-9A-Fa-f]{4}\.[0-9A-Fa-f]{4}\.00';
    }
    description
      "This type defines ISIS system id using pattern,
       system id looks like : 0143.0438.AeF0.00";
  }

  typedef router-id {
    type union {
      type system-id;
      type yang:dotted-quad;
    }
    description
      "OSPF/BGP router id or ISIS system ID.";
  }

  /* 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 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.";
            }
          }
          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" {
    description
      "This augments routing-instance
       configuration with segment-routing.";
    container segment-routing {
      leaf transport-type {
        type identityref {
          base sr-cmn:segment-routing-transport;
        }
        default "sr-cmn: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 algorithm";
                uses sr-cmn:ipv4-sid-cfg;

                description
                  "Mapping entries.";
              }
              description
                "IPv4 mapping entries.";
            }
            container ipv6 {
              list mapping-entry {
                key "prefix algorithm";
                uses sr-cmn: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 algorithm";
              uses sr-cmn:ipv4-sid-cfg;
              uses sr-cmn: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 algorithm";
              uses sr-cmn:ipv6-sid-cfg;
              uses sr-cmn:last-hop-behavior;
              description
                "List of prefix SID
                 mapped to IPv6 local prefixes.";
            }
            description
              "Parameters associated with IPv6 prefix SID";
          }
          description
            "Prefix SID configuration.";
        }
        description
          "List of bindings.";
      }
      container global-srgb {
        uses sr-cmn:srgb-cfg;
        description
          "Global SRGB configuration.";
      }
      description
        "segment routing global config.";
    }
  }


  /* Operational states */

  augment "/rt:routing-state" {
    description
     "This augments the operational states
      with segment-routing.";
    container segment-routing {
      uses sr-cmn:node-capabilities;
      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;
          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:control-plane-protocols/"
                 + "rt:control-plane-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.";
              }
            }
            description
             "Type of binding.";
          }
          description
            "Binding.";

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


  /* Notifications */

  notification segment-routing-global-srgb-collision {
    list srgb-collisions {
      leaf lower-bound {
        type uint32;
          description
            "Lower value in the block.";
      }
      leaf upper-bound {
        type uint32;
          description
            "Upper value in the block.";
      }
      leaf routing-protocol {
        type leafref {
          path "/rt:routing-state/rt:control-plane-protocols/"
             + "rt:control-plane-protocol/rt:name";
        }
        description
          "Routing protocol reference that received the event.";
      }
      leaf originating-rtr-id {
        type router-id;
        description
          "Originating router id of this SRGB block.";
      }
      description
        "List of SRGB blocks that conflict.";
    }
    description
      "This notification is sent when received SRGB blocks from
       a router conflict.";
  }
  notification segment-routing-global-sid-collision {
    leaf received-target {
      type string;
      description
      "Target received in the controlplane that
                         caused SID collision.";
    }
    leaf new-sid-rtr-id {
      type router-id;
      description
        "Router Id that advertising the conflicting SID.";
    }
    leaf original-target {
      type string;
      description
      "Target already available in database that have the same SID
      as the received target.";
    }
    leaf original-sid-rtr-id {
      type router-id;
      description
        "Original router ID that advertised the conflicting SID.";
    }
    leaf index {
      type uint32;
      description
      "Value of the index used by two different prefixes.";
    }
    leaf routing-protocol {
      type leafref {
        path "/rt:routing-state/rt:control-plane-protocols/"
           + "rt:control-plane-protocol/rt:name";
      }
      description
       "Routing protocol reference that received the event.";
    }
    description
      "This notification is sent when a new mapping is learned
      , 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:control-plane-protocols/" +
        "rt:control-plane-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. ";
  }

}

]]>


	
    
    TBD. 
    

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

    
      TBD.