module bgp {

     yang-version "1";

     // namespace
     // TODO: change to an ietf or other more generic namespace
     namespace "http://google.com/yang/google-bgp-protocol-cfg";

     prefix "bgp";

     // import some basic inet types
     import ietf-inet-types { prefix inet; }
     import bgp-multiprotocol { prefix bgp-mp; }
     import bgp-policy { prefix bgp-pol; }
     import bgp-operational { prefix bgp-op; }

     // meta
     organization
       "Google, AT&T, BT, Microsoft";

     contact
       "Google, Inc.
       1600 Amphitheatre Way
       Mountain View, CA  94043

       AT&T Labs
       200 S. Laurel Avenue
       Middletown, NJ  07748

       BT
       pp. C3L, BT Centre
       81, Newgate Street
       London  EC1A 7AJ
       UK

       Microsoft
       205 108th Ave. NE, Suite 400
       Bellevue, WA 98004";

     description
       "This module describes a YANG model for BGP protocol
       configuration.It is a limited subset of all of the configuration
       parameters available in the variety of vendor implementations,
       hence it is expected that it would be augmented with vendor-
       specific configuration data as needed.Additional modules or
       submodules to handle other aspects of BGP configuration,
       including policy, VRFs, VPNs, and additional address families
       are also expected.

       This model supports the following BGP configuration level
       hierarchy:

         BGP
           |
           +-> [ global BGP configuration ]
           +-> AFI / SAFI (address family)
             +-> [AFI-specific config ]
           +-> peer group
             +-> [ peer group config ]
             +-> AFI / SAFI [ per-AFI overrides ]
             +-> neighbor
               +-> [ per-neighbor overrides ]
               +-> AFI / SAFI [ per-AFI overrides ]
           +-> neighbor
             +-> [ neighbor config ]
             +-> AFI / SAFI [ per-AFI overrides ]";

     revision "2014-09-30" {
         description
           "Initial revision";
         reference "TBD";
     }

     typedef peer-type {
       type enumeration {
         enum INTERNAL {
           description "internal (iBGP) peer";
         }
         enum EXTERNAL {
           description "external (eBGP) peer";
         }
       }
       description
         "labels a peer or peer group as explicitly internal or
         external";
     }

     typedef remove-private-as-option {
       type enumeration {
         enum ALL {
           description "remove all private ASes in the path";
         }
         enum REPLACE {
           description "replace private ASes with local AS";
         }
       }
       description
         "set of options for configuring how private AS path numbers
         are removed from advertisements";
     }

     typedef percentage {
       type uint8 {
         range "0..100";
       }
       description
         "Integer indicating a percentage value";
     }

     typedef rr-cluster-id-type {
       type union {
         type uint32;
         type inet:ipv4-address;
       }
       description
         "union type for route reflector cluster ids:
         option 1: 4-byte number
         option 2: IP address";
     }

     grouping bgp-common-configuration {
       description "Common configuration available at all hierarchy
       levels, global, AFI, groups, neighbors, etc.";

       leaf description {
         type string;
         description
           "An optional textual description (intended primarily for use
           with a peer or group";
       }

       container route-selection-options {
           // TODO: consider moving this container to AFI/SAFI level
           // config
           description
             "Set of configuration options that govern best
             path selection.";
           leaf always-compare-med {
             type boolean;
             default "false";
             description
               "Compare multi-exit discriminator (MED) value from
               different ASes when selecting the best route.  The
               default behavior is to only compare MEDs for paths
               received from the same AS.";
           }

           leaf ignore-as-path-length {
             type boolean;
             default "false";
             description
               "Ignore the AS path length when selecting the best path.
               The default is to use the AS path length and prefer paths
               with shorter length.";
           }

           leaf external-compare-router-id {
             type boolean;
             default "true";
             description
               "When comparing similar routes received from external
               BGP peers, use the router-id as a criterion to select
               the active path.";
           }

           leaf advertise-inactive-routes {
             type boolean;
             default "false";
             description
               "Advertise inactive routes to external peers.  The
               default is to only advertise active routes.";
           }

           leaf enable-aigp {
             type empty;
             description
               "Flag to enable sending / receiving accumulated IGP
               attribute in routing updates";
           }
       }

       container use-multiple-paths {

         presence
           "Presence of this container indicates that multipath
            is enabled for both eBGP and iBGP, absence indicates
            that multi-path is not used";

         description
           "Configuration of BGP multi-path for iBGP and eBGP";

         container ebgp {
           description
             "Configuration of BGP multipath to enable load sharing
             across multiple paths to eBGP peers";

           leaf allow-multiple-as {
            type boolean;
            default "false";
            description
             "Allow multipath to use paths from different neighbouring
             ASes.  The default is to only consider multiple paths from
             the same neighbouring AS.";
           }

           leaf maximum-paths {
            type uint32;
            default 1;
            description
             "Maximum number of parallel paths to consider when using
             BGP multipath. The default is use a single path.";
           }
         }

         container ibgp {
           description
             "Configuration of BGP multipath to enable load-sharing
             across multiple paths to iBGP peers";

           leaf maximum-paths {
             type uint32;
             default 1;
             description
               "Maximum number of parallel paths to consider when using
               iBGP multipath. The default is to use a single path";
           }
         }

         container eibgp {
           description
             "Configuration of BGP multipath to enable load-sharing
             across multiple paths to external confederation sub-ASes";
           leaf maximum-paths {
             type uint32;
             default 1;
             description
               "Maximum number of parallel paths to consider when using
               eiBGP multipath. The default is to use a single path";
           }

         }
       }

       container graceful-restart {
         // TODO: most impls seem to require this at the global level
         // in order to specify at neighbor or other levels
         presence "Presence of this item indicates that BGP graceful
         restart is enabled.";

         description
           "Configures BGP graceful restart, which is a negotiated
           option that indicates that a BGP speaker is able to retain
           forwarding state when a BGP session restarts";

         reference "RFC 4724: Graceful Restart Mechanism for BGP";

         leaf restart-time {
           type uint16 {
             range 0..4096;
           }
           description
             "Estimated time in seconds for the BGP session to be
             re-established after a restart.  This is a 12-bit value
             advertised by the router to peers.  Per RFC 4724, the
             suggested default value is <= the hold-time value";
         }

         leaf stale-routes-time {
           type decimal64 {
             fraction-digits 2;
           }
           description
             "Sets an upper bound on the time in seconds that stale
             routes will be retained by the router after a session is
             restarted";
         }
       }

       uses bgp-pol:apply-policy-group;
     }

     grouping  bgp-global-configuration {
         description
           "Grouping for global level configuration items";

         leaf as {
           type inet:as-number;
           mandatory "true";
           description
             "Local autonomous system number of the router.  Uses
             the 32-bit as-number type from the model in RFC 6991";
         }
         leaf router-id {
           type inet:ipv4-address;
           description
             "Router id of the router, expressed as an
             32-bit value, IPv4 address.";
         }

         container default-route-distance {
           description
             "Administrative distance (or preference) assigned to
             routes received from different sources
             (external, internal, and local).";
           leaf external-route-distance {
             type uint8 {
               range "1..255";
             }
             description
               "Administrative distance for routes learned from external
               BGP (eBGP).";
           }
           leaf internal-route-distance {
             type uint8 {
               range "1..255";
             }
             description
               "Administrative distance for routes learned from internal
               BGP (iBGP).";
           }
         }

         container confederation {

           presence "Presence of this node indicates that the local AS
             is part of a confederation";
           description
             "Configuration for a BGP confederation consisting of a
             confed id and member sub-AS list";

           leaf identifier {
             type inet:as-number;
             description
               "Confederation identifier for the autonomous system";
           }

           leaf-list member-as {
             type inet:as-number;
             description
               "Remote autonomous systems that are to be treated
               as part of the local confederation.";
           }
         }

     }

     grouping bgp-group-common-configuration {
       description "Configuration items that are applied at the peer
       group level";

       // currently a placeholder in case we identify config that is
       // really only applicable at the group level
     }

     grouping bgp-group-neighbor-common-configuration {
       description "Configuration items that are applied at the peer
       or peer group levels";

       leaf auth-password {
         type string;
         description
           "Configures an MD5 authentication password for use with
           neighboring devices.";
       }

       leaf peer-type {
           type peer-type;
           description
             "Explicitly designate the peer or peer group as internal
             (iBGP) or external (eBGP).";
       }

       container timers {
         description "Configuration of various BGP timers";
         leaf connect-retry {
           type decimal64 {
             fraction-digits 2;
           }
           default 30;
           description
             "Time interval in seconds between attempts to establish a
             session with the peer.";
         }

         leaf hold-time {
           type decimal64 {
             fraction-digits 2;
           }
           default 90;
           description
             "Time interval in seconds that a BGP session will be
             considered active in the absence of keepalive or other
             messages from the peer.  The hold-time is typically
             set to 3x the keepalive-interval.";
           reference
             "RFC 4271 - A Border Gateway Protocol 4, Sec. 10";
         }

         leaf keepalive-interval {
           type decimal64 {
             fraction-digits 2;
           }
           default 30;
           description
             "Time interval in seconds between transmission of keepalive
             messages to the neighbor.  Typically set to 1/3 the
             hold-time.";
         }

         leaf minimum-advertisement-interval {
           type decimal64 {
             fraction-digits 2;
           }
           default 30;
           description
             "Mininum time interval in seconds between transmission
             of BGP updates to neighbors";
           reference
             "RFC 4271 - A Border Gateway Protocol 4, Sec 10";
         }

         leaf send-update-delay {
           type decimal64 {
             fraction-digits 2;
           }
           description
             "Time interval between routes changing in the routing
             table and corresponding updates sent to neighbors --
             serves to batch updates";
         }

       }

       container ebgp-multihop {
         description
           "Configure multihop BGP for peers that are not directly
           connected";

         leaf multihop-ttl {
           type uint8;
           default 1;
           description
             "Time-to-live for multihop BGP sessions.  The default
             value of 1 is for directly connected peers (i.e.,
             multihop disabled";

         }

       }

       container route-reflector {
         description
           "Configure the local router as a route-reflector
           server";

         leaf route-reflector-cluster-id {
           type rr-cluster-id-type;
           description
             "route-reflector cluster id to use when local router is
             configured as a route reflector.  Commonly set at the group
             level, but allows a different cluster
             id to be set for each neighbor.";
         }

         leaf route-reflector-client {
           type boolean;
           default "false";
           description
             "Configure the neighbor as a route reflector client.";
         }
       }

       leaf remove-private-as {
         // could also make this a container with a flag to enable
         // remove-private and separate option.  here, option implies
         // remove-private is enabled.
         type remove-private-as-option;
         description
           "Remove private AS numbers from updates sent to peers.";
       }

       container bgp-logging-options {
         description
           "Configure various tracing/logging options for BGP peers
           or groups.  Expected that additional vendor-specific log
           options would augment this container.";

         leaf log-neighbor-state-changes {
           type boolean;
           default "true";
           description
             "Configure logging of peer state changes.  Default is
             to enable logging of peer state changes.";
         }
       }

       container transport-options {
         description
           "Transport protocol options for BGP sessions";

           leaf tcp-mss {
             type uint16;
             description
               "Sets the max segment size for BGP TCP sessions.";
           }

           leaf mtu-discovery {
             type boolean;
             description
               "Turns path mtu discovery for BGP TCP sessions on (true)
               or off (false)";
           }

           leaf passive-mode {
             type boolean;
             description
               "Wait for peers to issue requests to open a BGP session,
               rather than initiating sessions from the local router.";
           }
       }

       leaf local-address {
         type inet:ip-address;
         description
           "Set the local IP (either IPv4 or IPv6) address to use for
           the session when sending BGP update messages.";
       }

       leaf route-flap-damping {
         type boolean;
         description
           "Enable route flap damping.";
       }
     }

     grouping bgp-neighbor-configuration {
       description
         "Neighbor-level configuration items";

       list neighbor {
         key "neighbor-address";
         description
           "List of BGP peers, uniquely identified by neighbor
           address.";
         leaf neighbor-address {
           type inet:ip-address;
           description
             "Address of the BGP peer, either IPv4 or IPv6.";
         }

         leaf peer-as {
           type inet:as-number;
           mandatory "true";
           description
             "AS number of the peer.";

         }
         uses bgp-common-configuration;
         uses bgp-mp:address-family-configuration;
         uses bgp-group-neighbor-common-configuration;
         uses bgp-op:bgp-op-neighbor-group;
       }
     }

     container bgp {
       description "Top-level configuration data for the BGP router";

       container global {
         description
           "Top-level bgp protocol options applied at the global level
           in the hierarchy -- these apply across peer-groups,
           neighbors, and address families";

         uses bgp-global-configuration;

         // attach global level operational data
         uses bgp-op:bgp-op-global-group;
       }

       // top level AF configuration
       uses bgp-mp:address-family-configuration;

       list peer-group {
         key "group-name";
         description
           "List of peer-groups, uniquely identified by the peer group
           name.";
         leaf group-name {
           type string;
           description "Name of the peer group.";
         }
         uses bgp-op:bgp-op-peergroup-group;
         uses bgp-common-configuration;
         uses bgp-mp:address-family-configuration;
         uses bgp-group-neighbor-common-configuration;

         // list of configurations for neighbors in this peer group
         uses bgp-neighbor-configuration;
       }

       // top level neighbor configuration
       uses bgp-neighbor-configuration;

       // hook for top-level policy definitions
       uses bgp-pol:policy-definition-group;
     }
   }