    Internet Engineering Task Force (IETF)                   N. Bahadur, Ed.
    Request for Comments: 8430                                          Uber
    Category: Informational                                     S. Kini, Ed.
    ISSN: 2070-1721
                                                                   J. Medved
                                                                       Cisco
                                                              September 2018

                             RIB Information Model

    Abstract

       Routing and routing functions in enterprise and carrier networks are
       typically performed by network devices (routers and switches) using a
       Routing Information Base (RIB).  Protocols and configurations push
       data into the RIB, and the RIB manager installs state into the
       hardware for packet forwarding.  This document specifies an
       information model for the RIB to enable defining a standardized data
       model.  The IETF's I2RS WG used this document to design the I2RS RIB
       data model.  This document is being published to record the higher-
       level information model decisions for RIBs so that other developers
       of RIBs may benefit from the design concepts.

    Status of This Memo

       This document is not an Internet Standards Track specification; it is
       published for informational purposes.

       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).  Not all documents
       approved by the IESG are candidates for any level of Internet
       Standard; see Section 2 of RFC 7841.

       Information about the current status of this document, any errata,
       and how to provide feedback on it may be obtained at
       https://www.rfc-editor.org/info/rfc8430.

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    Copyright Notice

       Copyright (c) 2018 IETF Trust and the persons identified as the
       document authors.  All rights reserved.

       This document is subject to BCP 78 and the IETF Trust's Legal
       Provisions Relating to IETF Documents
       (https://trustee.ietf.org/license-info) in effect on the date of
       publication of this document.  Please review these documents
       carefully, as they describe your rights and restrictions with respect
       to this document.  Code Components extracted from this document must
       include Simplified BSD License text as described in Section 4.e of
       the Trust Legal Provisions and are provided without warranty as
       described in the Simplified BSD License.

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    Table of Contents

       1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
         1.1.  Conventions Used in This Document . . . . . . . . . . . .   6
       2.  RIB Data  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
         2.1.  RIB Definition  . . . . . . . . . . . . . . . . . . . . .   7
         2.2.  Routing Instance  . . . . . . . . . . . . . . . . . . . .   7
         2.3.  Route . . . . . . . . . . . . . . . . . . . . . . . . . .   8
         2.4.  Nexthop . . . . . . . . . . . . . . . . . . . . . . . . .  10
           2.4.1.  Base Nexthops . . . . . . . . . . . . . . . . . . . .  12
           2.4.2.  Derived Nexthops  . . . . . . . . . . . . . . . . . .  14
           2.4.3.  Nexthop Indirection . . . . . . . . . . . . . . . . .  15
       3.  Reading from the RIB  . . . . . . . . . . . . . . . . . . . .  16
       4.  Writing to the RIB  . . . . . . . . . . . . . . . . . . . . .  16
       5.  Notifications . . . . . . . . . . . . . . . . . . . . . . . .  17
       6.  RIB Grammar . . . . . . . . . . . . . . . . . . . . . . . . .  17
         6.1.  Nexthop Grammar Explained . . . . . . . . . . . . . . . .  20
       7.  Using the RIB Grammar . . . . . . . . . . . . . . . . . . . .  20
         7.1.  Using Route Preference  . . . . . . . . . . . . . . . . .  20
         7.2.  Using Different Nexthop Types . . . . . . . . . . . . . .  20
           7.2.1.  Tunnel Nexthops . . . . . . . . . . . . . . . . . . .  21
           7.2.2.  Replication Lists . . . . . . . . . . . . . . . . . .  21
           7.2.3.  Weighted Lists  . . . . . . . . . . . . . . . . . . .  21
           7.2.4.  Protection  . . . . . . . . . . . . . . . . . . . . .  22
           7.2.5.  Nexthop Chains  . . . . . . . . . . . . . . . . . . .  22
           7.2.6.  Lists of Lists  . . . . . . . . . . . . . . . . . . .  23
         7.3.  Performing Multicast  . . . . . . . . . . . . . . . . . .  24
       8.  RIB Operations at Scale . . . . . . . . . . . . . . . . . . .  25
         8.1.  RIB Reads . . . . . . . . . . . . . . . . . . . . . . . .  25
         8.2.  RIB Writes  . . . . . . . . . . . . . . . . . . . . . . .  25
         8.3.  RIB Events and Notifications  . . . . . . . . . . . . . .  25
       9.  Security Considerations . . . . . . . . . . . . . . . . . . .  25
       10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  26
       11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  26
         11.1.  Normative References . . . . . . . . . . . . . . . . . .  26
         11.2.  Informative References . . . . . . . . . . . . . . . . .  27
       Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  28
       Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  28

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    1.  Introduction

       Routing and routing functions in enterprise and carrier networks are
       traditionally performed in network devices.  Customarily, routers run
       routing protocols, and the routing protocols (along with static
       configuration information) populate the Routing Information Base
       (RIB) of the router.  The RIB is managed by the RIB manager, and the
       RIB manager provides a northbound interface to its clients (i.e., the
       routing protocols) to insert routes into the RIB.  The RIB manager
       consults the RIB and decides how to program the Forwarding
       Information Base (FIB) of the hardware by interfacing with the FIB
       manager.  The relationship between these entities is shown in
       Figure 1.

             +-------------+        +-------------+
             |RIB Client 1 | ...... |RIB Client N |
             +-------------+        +-------------+
                    ^                      ^
                    |                      |
                    +----------------------+
                               |
                               V
                    +---------------------+
                    |    RIB Manager      |
                    |                     |
                    |     +--------+      |
                    |     | RIB(s) |      |
                    |     +--------+      |
                    +---------------------+
                               ^
                               |
              +---------------------------------+
              |                                 |
              V                                 V
       +----------------+               +----------------+
       | FIB Manager 1  |               | FIB Manager M  |
       |   +--------+   |  ..........   |   +--------+   |
       |   | FIB(s) |   |               |   | FIB(s) |   |
       |   +--------+   |               |   +--------+   |
       +----------------+               +----------------+

               Figure 1: RIB Manager, RIB Clients, and FIB Managers

       Routing protocols are inherently distributed in nature, and each
       router makes an independent decision based on the routing data
       received from its peers.  With the advent of newer deployment
       paradigms and the need for specialized applications, there is an
       emerging need to guide the router's routing function [RFC7920].  The

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       traditional network-device RIB population that is protocol based
       suffices for most use cases where distributed network control is
       used.  However, there are use cases that the network operators
       currently address by configuring static routes, policies, and RIB
       import/export rules on the routers.  There is also a growing list of
       use cases in which a network operator might want to program the RIB
       based on data unrelated to just routing (within that network's
       domain).  Programming the RIB could be based on other information
       (such as routing data in the adjacent domain or the load on storage
       and compute) in the given domain.  Or, it could simply be a
       programmatic way of creating on-demand dynamic overlays (e.g., GRE
       tunnels) between compute hosts (without requiring the hosts to run
       traditional routing protocols).  If there was a standardized,
       publicly documented programmatic interface to a RIB, it would enable
       further networking applications that address a variety of use cases
       [RFC7920].

       A programmatic interface to the RIB involves two types of operations:
       reading from the RIB and writing (adding/modifying/deleting) to the
       RIB.

       In order to understand what is in a router's RIB, methods like per-
       protocol SNMP MIBs and screen scraping are used.  These methods are
       not scalable since they are client pull mechanisms and not proactive
       push (from the router) mechanisms.  Screen scraping is error prone
       (since the output format can change) and is vendor dependent.
       Building a RIB from per-protocol MIBs is error prone since the MIB
       data represents protocol data and not the exact information that went
       into the RIB.  Thus, just getting read-only RIB information from a
       router is a hard task.

       Adding content to the RIB from a RIB client can be done today using
       static configuration mechanisms provided by router vendors.  However,
       the mix of what can be modified in the RIB varies from vendor to
       vendor, and the method of configuring it is also vendor dependent.
       This makes it hard for a RIB client to program a multi-vendor network
       in a consistent and vendor-independent way.

       The purpose of this document is to specify an information model for
       the RIB.  Using the information model, one can build a detailed data
       model for the RIB.  That data model could then be used by a RIB
       client to program a network device.  One data model that has been
       based on this document is the I2RS RIB data model [RFC8431].

       The rest of this document is organized as follows.  Section 2 goes
       into the details of what constitutes and can be programmed in a RIB.
       Guidelines for reading and writing the RIB are provided in Sections 3
       and 4, respectively.  Section 5 provides a high-level view of the

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       events and notifications going from a network device to a RIB client
       to update the RIB client on asynchronous events.  The RIB grammar is
       specified in Section 6.  Examples of using the RIB grammar are shown
       in Section 7.  Section 8 covers considerations for performing RIB
       operations at scale.

    1.1.  Conventions Used in This Document

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

    2.  RIB Data

       This section describes the details of a RIB.  It makes forward
       references to objects in the RIB grammar (see Section 6).  A high-
       level description of the RIB contents is as shown in Figure 2.
       Please note that for ease of representation in ASCII art, this
       drawing shows a single routing instance, a single RIB, and a single
       route.  Subsections of this section describe the logical data nodes
       that should be contained within a RIB.  Sections 3 and 4 describe the
       high-level read and write operations.

                              network-device
                                    |
                                    | 0..N
                                    |
                             routing instance(s)
                              |             |
                              |             |
                        0..N  |             | 0..N
                              |             |
                         interface(s)     RIB(s)
                                            |
                                            |
                                            | 0..N
                                            |
                                          route(s)

                          Figure 2: RIB Information Model

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    2.1.  RIB Definition

       A RIB, in the context of the RIB information model, is an entity that
       contains routes.  It is identified by its name and is contained
       within a routing instance (see Section 2.2).  A network device MAY
       contain routing instances, and each routing instance MAY contain
       RIBs.  The name MUST be unique within a routing instance.  All routes
       in a given RIB MUST be of the same address family (e.g., IPv4).  Each
       RIB MUST belong to a routing instance.

       A routing instance may contain two or more RIBs of the same address
       family (e.g., IPv6).  A typical case where this can be used is for
       multi-topology routing [RFC4915] [RFC5120].

       Each RIB MAY be associated with an ENABLE_IP_RPF_CHECK attribute that
       enables Reverse Path Forwarding (RPF) checks on all IP routes in that
       RIB.  The RPF check is used to prevent spoofing and limit malicious
       traffic.  For IP packets, the IP source address is looked up and the
       RPF interface(s) associated with the route for that IP source address
       is found.  If the incoming IP packet's interface matches one of the
       RPF interfaces, then the IP packet is forwarded based on its IP
       destination address; otherwise, the IP packet is discarded.

    2.2.  Routing Instance

       A routing instance, in the context of the RIB information model, is a
       collection of RIBs, interfaces, and routing parameters.  A routing
       instance creates a logical slice of the router.  It allows different
       logical slices across a set of routers to communicate with each
       other.  Layer 3 VPNs, Layer 2 VPNs (L2VPNs), and Virtual Private LAN
       Service (VPLS) can be modeled as routing instances.  Note that
       modeling an L2VPN using a routing instance only models the Layer 3
       (RIB) aspect and does not model any Layer 2 information (like ARP)
       that might be associated with the L2VPN.

       The set of interfaces indicates which interfaces are associated with
       this routing instance.  The RIBs specify how incoming traffic is to
       be forwarded, and the routing parameters control the information in
       the RIBs.  The intersection set of interfaces of two routing
       instances MUST be the null set.  In other words, an interface MUST
       NOT be present in two routing instances.  Thus, a routing instance
       describes the routing information and parameters across a set of
       interfaces.

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       A routing instance MUST contain the following mandatory fields:

       o  INSTANCE_NAME: A routing instance is identified by its name,
          INSTANCE_NAME.  This MUST be unique across all routing instances
          in a given network device.

       o  rib-list: This is the list of RIBs associated with this routing
          instance.  Each routing instance can have multiple RIBs to
          represent routes of different types.  For example, one would put
          IPv4 routes in one RIB and MPLS routes in another RIB.  The list
          of RIBs can be an empty list.

       A routing instance MAY contain the following fields:

       o  interface-list: This represents the list of interfaces associated
          with this routing instance.  The interface list helps constrain
          the boundaries of packet forwarding.  Packets coming in on these
          interfaces are directly associated with the given routing
          instance.  The interface list contains a list of identifiers, with
          each identifier uniquely identifying an interface.

       o  ROUTER_ID: This field identifies the network device in control
          plane interactions with other network devices.  This field is to
          be used if one wants to virtualize a physical router into multiple
          virtual routers.  Each virtual router MUST have a unique
          ROUTER_ID.  A ROUTER_ID MUST be unique across all network devices
          in a given domain.

       A routing instance may be created purely for the purposes of packet
       processing and may not have any interfaces associated with it.  For
       example, an incoming packet in routing instance A might have a
       nexthop of routing instance B, and after packet processing in B, the
       nexthop might be routing instance C.  Thus, routing instance B is not
       associated with any interface.  And, given that this routing instance
       does not do any control-plane interaction with other network devices,
       a ROUTER_ID is also not needed.

    2.3.  Route

       A route is essentially a match condition and an action following the
       match.  The match condition specifies the kind of route (IPv4, MPLS,
       etc.) and the set of fields to match on.  Figure 3 represents the
       overall contents of a route.  Please note that for ease of depiction
       in ASCII art, only a single instance of the route-attribute, match
       flags, and nexthop is depicted.

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                                     route
                                     | | |
                           +---------+ | +----------+
                           |           |            |
                      0..N |           |            |

             route-attribute         match         nexthop
                                       |
                                       |
                       +-------+-------+-------+--------+
                       |       |       |       |        |
                       |       |       |       |        |

                      IPv4    IPv6    MPLS    MAC    Interface

                               Figure 3: Route Model

       This document specifies the following match types:

       o  IPv4: Match on destination and/or source IP address in the IPv4
          header

       o  IPv6: Match on destination and/or source IP address in the IPv6
          header

       o  MPLS: Match on an MPLS label at the top of the MPLS label stack

       o  MAC: Match on Media Access Control (MAC) destination addresses in
          the Ethernet header

       o  Interface: Match on the incoming interface of the packet

       A route MAY be matched on one or more of these match types by policy
       as either an "AND" (to restrict the number of routes) or an "OR" (to
       combine two filters).

       Each route MUST have the following mandatory route-attributes
       associated with it:

       o  ROUTE_PREFERENCE: This is a numerical value that allows for
          comparing routes from different protocols.  Static configuration
          is also considered a protocol for the purpose of this field.  It
          is also known as "administrative distance".  The lower the value,
          the higher the preference.  For example, there can be an OSPF
          route for 192.0.2.1/32 (or IPv6 2001:DB8::1/128) with a preference
          of 5.  If a controller programs a route for 192.0.2.1/32 (or IPv6
          2001:DB8::1/128) with a preference of 2, then the controller's
          route will be preferred by the RIB manager.  Preference should be

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          used to dictate behavior.  For more examples of preference, see
          Section 7.1.

       Each route can have one or more optional route-attributes associated
       with it.

       o  route-vendor-attributes: Vendors can specify vendor-specific
          attributes using this.  The details of this attribute are outside
          the scope of this document.

       Each route has a nexthop associated with it.  Nexthops are described
       in Section 2.4.

       Additional features to match multicast packets were considered (e.g.,
       TTL of the packet to limit the range of a multicast group), but these
       were not added to this information model.  Future RIB information
       models should investigate these multicast features.

    2.4.  Nexthop

       A nexthop represents an object resulting from a route lookup.  For
       example, if a route lookup results in sending the packet out of a
       given interface, then the nexthop represents that interface.

       Nexthops can be either fully resolved or unresolved.  A resolved
       nexthop has adequate information to send the outgoing packet to the
       destination by forwarding it on an interface to a directly connected
       neighbor.  For example, a nexthop to a point-to-point interface or a
       nexthop to an IP address on an Ethernet interface has the nexthop
       resolved.  An unresolved nexthop is something that requires the RIB
       manager to determine the final resolved nexthop.  For example, a
       nexthop could be an IP address.  The RIB manager would resolve how to
       reach that IP address; for example, is the IP address reachable by
       regular IP forwarding, by an MPLS tunnel, or by both?  If the RIB
       manager cannot resolve the nexthop, then the nexthop remains in an
       unresolved state and is NOT a candidate for installation in the FIB.
       Future RIB events can cause an unresolved nexthop to get resolved
       (e.g., an IP address being advertised by an IGP neighbor).
       Conversely, resolved nexthops can also become unresolved (e.g., in
       the case of a tunnel going down); hence, they would no longer be
       candidates to be installed in the FIB.

       When at least one of a route's nexthops is resolved, then the route
       can be used to forward packets.  Such a route is considered eligible
       to be installed in the FIB and is henceforth referred to as a FIB-
       eligible route.  Conversely, when all the nexthops of a route are
       unresolved, that route can no longer be used to forward packets.
       Such a route is considered ineligible to be installed in the FIB and

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       is henceforth referred to as a FIB-ineligible route.  The RIB
       information model allows a RIB client to program routes whose
       nexthops may be unresolved initially.  Whenever an unresolved nexthop
       gets resolved, the RIB manager will send a notification of the same
       (see Section 5).

       The overall structure and usage of a nexthop is as shown in the
       figure below.  For ease of description using ASCII art, only a single
       instance of any component of the nexthop is shown in Figure 4.

                                   route
                                     |
                                     | 0..N
                                     |
                                   nexthop <-------------------------------+
                                     |                                     |
              +-------+----------------------------+-------------+         |
              |       |              |             |             |         |
              |       |              |             |             |         |
           base   load-balance   protection      replicate     chain       |
              |       |              |             |             |         |
              |       |2..N          |2..N         |2..N         |1..N     |
              |       |              |             |             |         |
              |       |              V             |             |         |
              |       +------------->+<------------+-------------+         |
              |                      |                                     |
              |                      +-------------------------------------+
              |
              +-------------------+
                                  |
                                  |
                                  |
                                  |
         +---------------+--------+--------+--------------+----------+
         |               |                 |              |          |
         |               |                 |              |          |
      nexthop-id  egress-interface  ip-address     logical-tunnel    |
                                                                     |
                                                                     |
                              +--------------------------------------+
                              |
           +----------------------+------------------+-------------+
           |                      |                  |             |
           |                      |                  |             |
     tunnel-encapsulation   tunnel-decapsulation  rib-name   special-nexthop

                              Figure 4: Nexthop Model

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       This document specifies a very generic, extensible, and recursive
       grammar for nexthops.  A nexthop can be a base nexthop or a derived
       nexthop.  Section 2.4.1 details base nexthops, and Section 2.4.2
       explains various kinds of derived nexthops.  There are certain
       special nexthops, and those are described in Section 2.4.1.1.
       Lastly, Section 2.4.3 delves into nexthop indirection and its use.
       Examples of when and how to use tunnel nexthops and derived nexthops
       are shown in Section 7.2.

    2.4.1.  Base Nexthops

       At the lowest level, a nexthop can be one of the following:

       o  Identifier: This is an identifier returned by the network device
          representing a nexthop.  This can be used as a way of reusing a
          nexthop when programming derived nexthops.

       o  Interface nexthops: These are nexthops that are pointing to an
          interface.  Various attributes associated with these nexthops are:

          *  Egress-interface: This represents a physical, logical, or
             virtual interface on the network device.  Address resolution
             must not be required on this interface.  This interface may
             belong to any routing instance.

          *  IP address: A route lookup on this IP address is done to
             determine the egress-interface.  Address resolution may be
             required depending on the interface.

             +  An optional rib-name can also be specified to indicate the
                RIB in which the IP address is to be looked up.  One can use
                the rib-name field to direct the packet from one domain into
                another domain.  By default the RIB will be the same as the
                one that route belongs to.

          These attributes can be used in combination as follows:

          *  Egress-interface and IP address: This can be used in cases
             where, e.g., the IP address is a link-local address.

          *  Egress-interface and MAC address: The egress-interface must be
             an Ethernet interface.  Address resolution is not required for
             this nexthop.

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       o  Tunnel nexthops: These are nexthops that are pointing to a tunnel.
          The types of tunnel nexthops are:

          *  tunnel-encapsulation: This can be an encapsulation representing
             an IP tunnel, MPLS tunnel, or others as defined in this
             document.  An optional egress-interface can be chained to the
             tunnel-encapsulation to indicate which interface to send the
             packet out on.  The egress-interface is useful when the network
             device contains Ethernet interfaces and one needs to perform
             address resolution for the IP packet.

          *  tunnel-decapsulation: This is to specify decapsulating a tunnel
             header.  After decapsulation, further lookup on the packet can
             be done via chaining it with another nexthop.  The packet can
             also be sent out via an egress-interface directly.

          *  logical-tunnel: This can be an MPLS Label Switched Path (LSP)
             or a GRE tunnel (or others as defined in this document) that is
             represented by a unique identifier (e.g., name).

       o  rib-name: A nexthop pointing to a RIB.  This indicates that the
          route lookup needs to continue in the specified RIB.  This is a
          way to perform chained lookups.

       Tunnel nexthops allow a RIB client to program static tunnel headers.
       There can be cases where the remote tunnel endpoint does not support
       dynamic signaling (e.g., no LDP support on a host); in those cases,
       the RIB client might want to program the tunnel header on both ends
       of the tunnel.  The tunnel nexthop is kept generic with
       specifications provided for some commonly used tunnels.  It is
       expected that the data model will model these tunnel types with
       complete accuracy.

    2.4.1.1.  Special Nexthops

       Special nexthops are for performing specific well-defined functions
       (e.g., DISCARD).  The purpose of each of them is explained below:

       o  DISCARD: This indicates that the network device should drop the
          packet and increment a drop counter.

       o  DISCARD_WITH_ERROR: This indicates that the network device should
          drop the packet, increment a drop counter, and send back an
          appropriate error message (like ICMP error).

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       o  RECEIVE: This indicates that the traffic is destined for the
          network device, for example, protocol packets or Operations,
          Administration, and Maintenance (OAM) packets.  All locally
          destined traffic SHOULD be throttled to avoid a denial-of-service
          attack on the router's control plane.  An optional rate limiter
          can be specified to indicate how to throttle traffic destined for
          the control plane.  The description of the rate limiter is outside
          the scope of this document.

    2.4.2.  Derived Nexthops

       Derived nexthops can be:

       o  weighted lists, which are used for load-balancing;

       o  preference lists, which are used for protection using primary and
          backup;

       o  replication lists, which are lists of nexthops to which to
          replicate a packet;

       o  nexthop chains, which are for chaining multiple operations or
          attaching multiple headers; or

       o  lists of lists, which are a recursive application of the above.

       Nexthop chains (see Section 7.2.5 for usage) are a way to perform
       multiple operations on a packet by logically combining them.  For
       example, one can chain together "decapsulate MPLS header" and "send
       it out a specific egress-interface".  Chains can be used to specify
       multiple headers over a packet before a packet is forwarded.  One
       simple example is that of MPLS over GRE, wherein the packet has an
       inner MPLS header followed by a GRE header followed by an IP header.
       The outermost IP header is decided by the network device, whereas the
       MPLS header or GRE header is specified by the controller.  Not every
       network device will be able to support all kinds of nexthop chains
       and an arbitrary number of headers chained together.  The RIB data
       model SHOULD provide a way to expose a nexthop chaining capability
       supported by a given network device.

       It is expected that all network devices will have a limit on how many
       levels of lookup can be performed, and not all hardware will be able
       to support all kinds of nexthops.  RIB capability negotiation becomes
       very important for this reason, and a RIB data model MUST specify a
       way for a RIB client to learn about the network device's
       capabilities.

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    2.4.2.1.  Nexthop List Attributes

       For nexthops that are of the form of a list(s), attributes can be
       associated with each member of the list to indicate the role of an
       individual member of the list.  Two attributes are specified:

       o  NEXTHOP_PREFERENCE: This is used for protection schemes.  It is an
          integer value between 1 and 99.  A lower value indicates higher
          preference.  To download a primary/standby pair to the FIB, the
          nexthops that are resolved and have the two highest preferences
          are selected.  Each <NEXTHOP_PREFERENCE> should have a unique
          value within a <nexthop-protection> (see Section 6).

       o  NEXTHOP_LB_WEIGHT: This is used for load-balancing.  Each list
          member MUST be assigned a weight between 1 and 99.  The weight
          determines the proportion of traffic to be sent over a nexthop
          used for forwarding as a ratio of the weight of this nexthop
          divided by the weights of all the nexthops of this route that are
          used for forwarding.  To perform equal load-balancing, one MAY
          specify a weight of "0" for all the member nexthops.  The value
          "0" is reserved for equal load-balancing and, if applied, MUST be
          applied to all member nexthops.  Note that a weight of 0 is
          special because of historical reasons.

    2.4.3.  Nexthop Indirection

       Nexthops can be identified by an identifier to create a level of
       indirection.  The identifier is set by the RIB manager and returned
       to the RIB client on request.

       One example of usage of indirection is a nexthop that points to
       another network device (e.g., a BGP peer).  The returned nexthop
       identifier can then be used for programming routes to point to the
       this nexthop.  Given that the RIB manager has created an indirection
       using the nexthop identifier, if the transport path to the network
       device (BGP peer) changes, that change in path will be seamless to
       the RIB client and all routes that point to that network device will
       automatically start going over the new transport path.  Nexthop
       indirection using identifiers could be applied to not only unicast
       nexthops but also nexthops that contain chains and nested nexthops.
       See Section 2.4.2 for examples.

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    3.  Reading from the RIB

       A RIB data model MUST allow a RIB client to read entries for RIBs
       created by that entity.  The network device administrator MAY allow
       reading of other RIBs by a RIB client through access lists on the
       network device.  The details of access lists are outside the scope of
       this document.

       The data model MUST support a full read of the RIB and subsequent
       incremental reads of changes to the RIB.  When sending data to a RIB
       client, the RIB manager SHOULD try to send all dependencies of an
       object prior to sending that object.

    4.  Writing to the RIB

       A RIB data model MUST allow a RIB client to write entries for RIBs
       created by that entity.  The network device administrator MAY allow
       writes to other RIBs by a RIB client through access lists on the
       network device.  The details of access lists are outside the scope of
       this document.

       When writing an object to a RIB, the RIB client SHOULD try to write
       all dependencies of the object prior to sending that object.  The
       data model SHOULD support requesting identifiers for nexthops and
       collecting the identifiers back in the response.

       Route programming in the RIB MUST result in a return code that
       contains the following attributes:

       o  Installed: Yes/No (indicates whether the route got installed in
          the FIB)

       o  Active: Yes/No (indicates whether a route is fully resolved and is
          a candidate for selection)

       o  Reason: E.g., "Not authorized"

       The data model MUST specify which objects can be modified.  An object
       that can be modified is one whose contents can be changed without
       having to change objects that depend on it and without affecting any
       data forwarding.  To change a non-modifiable object, one will need to
       create a new object and delete the old one.  For example, routes that
       use a nexthop that is identified by a nexthop identifier should be
       unaffected when the contents of that nexthop changes.

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    5.  Notifications

       Asynchronous notifications are sent by the network device's RIB
       manager to a RIB client when some event occurs on the network device.
       A RIB data model MUST support sending asynchronous notifications.  A
       brief list of suggested notifications is as below:

       o  Route change notification (with a return code as specified in
          Section 4)

       o  Nexthop resolution status (resolved/unresolved) notification

    6.  RIB Grammar

       This section specifies the RIB information model in Routing Backus-
       Naur Form (rBNF) [RFC5511].  This grammar is intended to help the
       reader better understand Section 2 in order to derive a data model.

     <routing-instance> ::= <INSTANCE_NAME>
                            [<interface-list>] <rib-list>
                            [<ROUTER_ID>]

     <interface-list> ::= (<INTERFACE_IDENTIFIER> ...)

     <rib-list> ::= (<rib> ...)
     <rib> ::= <rib-name> <address-family>
                         [<route> ... ]
                         [ENABLE_IP_RPF_CHECK]
     <address-family> ::= <IPV4_ADDRESS_FAMILY> | <IPV6_ADDRESS_FAMILY> |
                          <MPLS_ADDRESS_FAMILY> | <IEEE_MAC_ADDRESS_FAMILY>

     <route> ::= <match> <nexthop>
                 [<route-attributes>]
                 [<route-vendor-attributes>]

     <match> ::= <IPV4> <ipv4-route> | <IPV6> <ipv6-route> |
                 <MPLS> <MPLS_LABEL> | <IEEE_MAC> <MAC_ADDRESS> |
                 <INTERFACE> <INTERFACE_IDENTIFIER>
     <route-type> ::= <IPV4> | <IPV6> | <MPLS> | <IEEE_MAC> | <INTERFACE>

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     <ipv4-route> ::= <ip-route-type>
                      (<destination-ipv4-address> | <source-ipv4-address> |
                       (<destination-ipv4-address> <source-ipv4-address>))
     <destination-ipv4-address> ::= <ipv4-prefix>
     <source-ipv4-address> ::= <ipv4-prefix>
     <ipv4-prefix> ::= <IPV4_ADDRESS> <IPV4_PREFIX_LENGTH>

     <ipv6-route> ::= <ip-route-type>
                      (<destination-ipv6-address> | <source-ipv6-address> |
                       (<destination-ipv6-address> <source-ipv6-address>))
     <destination-ipv6-address> ::= <ipv6-prefix>
     <source-ipv6-address> ::= <ipv6-prefix>
     <ipv6-prefix> ::= <IPV6_ADDRESS> <IPV6_PREFIX_LENGTH>
     <ip-route-type> ::= <SRC> | <DEST> | <DEST_SRC>

     <route-attributes> ::= <ROUTE_PREFERENCE> [<LOCAL_ONLY>]
                            [<address-family-route-attributes>]

     <address-family-route-attributes> ::= <ip-route-attributes> |
                                           <mpls-route-attributes> |
                                           <ethernet-route-attributes>
     <ip-route-attributes> ::= <>
     <mpls-route-attributes> ::= <>
     <ethernet-route-attributes> ::= <>
     <route-vendor-attributes> ::= <>

     <nexthop> ::= <nexthop-base> |
                   (<NEXTHOP_LOAD_BALANCE> <nexthop-lb>) |
                   (<NEXTHOP_PROTECTION> <nexthop-protection>) |
                   (<NEXTHOP_REPLICATE> <nexthop-replicate>) |
                   <nexthop-chain>

     <nexthop-base> ::= <NEXTHOP_ID> |
                        <nexthop-special> |
                        <egress-interface> |
                        <ipv4-address> | <ipv6-address> |
                        (<egress-interface>
                            (<ipv4-address> | <ipv6-address>)) |
                        (<egress-interface> <IEEE_MAC_ADDRESS>) |
                        <tunnel-encapsulation> | <tunnel-decapsulation> |
                        <logical-tunnel> |
                        <rib-name>

     <egress-interface> ::= <INTERFACE_IDENTIFIER>

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     <nexthop-special> ::= <DISCARD> | <DISCARD_WITH_ERROR> |
                           (<RECEIVE> [<COS_VALUE>])

     <nexthop-lb> ::= <NEXTHOP_LB_WEIGHT> <nexthop>
                      (<NEXTHOP_LB_WEIGHT> <nexthop) ...

     <nexthop-protection> = <NEXTHOP_PREFERENCE> <nexthop>
                           (<NEXTHOP_PREFERENCE> <nexthop>)...

     <nexthop-replicate> ::= <nexthop> <nexthop> ...

     <nexthop-chain> ::= <nexthop> ...

     <logical-tunnel> ::= <tunnel-type> <TUNNEL_NAME>
     <tunnel-type> ::= <IPV4> | <IPV6> | <MPLS> | <GRE> | <VxLAN> | <NVGRE>

     <tunnel-encapsulation> ::= (<IPV4> <ipv4-header>) |
                                (<IPV6> <ipv6-header>) |
                                (<MPLS> <mpls-header>) |
                                (<GRE> <gre-header>) |
                                (<VXLAN> <vxlan-header>) |
                                (<NVGRE> <nvgre-header>)

     <ipv4-header> ::= <SOURCE_IPv4_ADDRESS> <DESTINATION_IPv4_ADDRESS>
                       <PROTOCOL> [<TTL>] [<DSCP>]

     <ipv6-header> ::= <SOURCE_IPV6_ADDRESS> <DESTINATION_IPV6_ADDRESS>
                       <NEXT_HEADER> [<TRAFFIC_CLASS>]
                       [<FLOW_LABEL>] [<HOP_LIMIT>]

     <mpls-header> ::= (<mpls-label-operation> ...)
     <mpls-label-operation> ::= (<MPLS_PUSH> <MPLS_LABEL> [<S_BIT>]
                                             [<TOS_VALUE>] [<TTL_VALUE>]) |
                                (<MPLS_SWAP> <IN_LABEL> <OUT_LABEL>
                                            [<TTL_ACTION>])

     <gre-header> ::= <GRE_IP_DESTINATION> <GRE_PROTOCOL_TYPE> [<GRE_KEY>]
     <vxlan-header> ::= (<ipv4-header> | <ipv6-header>)
                        [<VXLAN_IDENTIFIER>]
     <nvgre-header> ::= (<ipv4-header> | <ipv6-header>)
                        <VIRTUAL_SUBNET_ID>
                        [<FLOW_ID>]

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     <tunnel-decapsulation> ::= ((<IPV4> <IPV4_DECAP> [<TTL_ACTION>]) |
                                (<IPV6> <IPV6_DECAP> [<HOP_LIMIT_ACTION>]) |
                                (<MPLS> <MPLS_POP> [<TTL_ACTION>]))

                            Figure 5: RIB rBNF Grammar

    6.1.  Nexthop Grammar Explained

       A nexthop is used to specify the next network element to forward the
       traffic to.  It is also used to specify how the traffic should be
       load-balanced, protected using preference, or multicast using
       replication.  This is explicitly specified in the grammar.  The
       nexthop has recursion built in to address complex use cases like the
       one defined in Section 7.2.6.

    7.  Using the RIB Grammar

       The RIB grammar is very generic and covers a variety of features.
       This section provides examples on using objects in the RIB grammar
       and examples to program certain use cases.

    7.1.  Using Route Preference

       Using route preference, a client can preinstall alternate paths in
       the network.  For example, if OSPF has a route preference of 10, then
       another client can install a route with a route preference of 20 to
       the same destination.  The OSPF route will get precedence and will
       get installed in the FIB.  When the OSPF route is withdrawn, the
       alternate path will get installed in the FIB.

       Route preference can also be used to prevent denial-of-service
       attacks by installing routes with the best preference, which either
       drops the offending traffic or routes it to some monitoring/analysis
       station.  Since the routes are installed with the best preference,
       they will supersede any route installed by any other protocol.

    7.2.  Using Different Nexthop Types

       The RIB grammar allows one to create a variety of nexthops.  This
       section describes uses for certain types of nexthops.

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    7.2.1.  Tunnel Nexthops

       A tunnel nexthop points to a tunnel of some kind.  Traffic that goes
       over the tunnel gets encapsulated with the tunnel-encapsulation.
       Tunnel nexthops are useful for abstracting out details of the network
       by having the traffic seamlessly route between network edges.  At the
       end of a tunnel, the tunnel will get decapsulated.  Thus, the grammar
       supports two kinds of operations: one for encapsulation and another
       for decapsulation.

    7.2.2.  Replication Lists

       One can create a replication list for replicating traffic to multiple
       destinations.  The destinations, in turn, could be derived nexthops
       in themselves (at a level supported by the network device); point to
       multipoint and broadcast are examples that involve replication.

       A replication list (at the simplest level) can be represented as:

       <nexthop> ::= <NEXTHOP_REPLICATE> <nexthop> [ <nexthop> ... ]

       The above can be derived from the grammar as follows:

       <nexthop> ::= <nexthop-replicate>
       <nexthop> ::= <NEXTHOP_REPLICATE> <nexthop> <nexthop> ...

    7.2.3.  Weighted Lists

       A weighted list is used to load-balance traffic among a set of
       nexthops.  From a modeling perspective, a weighted list is very
       similar to a replication list, with the difference that each member
       nexthop MUST have a NEXTHOP_LB_WEIGHT associated with it.

       A weighted list (at the simplest level) can be represented as:

       <nexthop> ::= <NEXTHOP_LOAD_BALANCE> (<nexthop> <NEXTHOP_LB_WEIGHT>)
                          [(<nexthop> <NEXTHOP_LB_WEIGHT>)... ]

       The above can be derived from the grammar as follows:

       <nexthop> ::= <nexthop-lb>
       <nexthop> ::= <NEXTHOP_LOAD_BALANCE>
                       <NEXTHOP_LB_WEIGHT> <nexthop>
                       (<NEXTHOP_LB_WEIGHT> <nexthop>) ...
       <nexthop> ::= <NEXTHOP_LOAD_BALANCE> (<NEXTHOP_LB_WEIGHT> <nexthop>)
                       (<NEXTHOP_LB_WEIGHT> <nexthop>) ...

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    7.2.4.  Protection

       A primary/backup protection can be represented as:

       <nexthop> ::= <NEXTHOP_PROTECTION> <1> <interface-primary>
                                          <2> <interface-backup>)

       The above can be derived from the grammar as follows:

    <nexthop> ::= <nexthop-protection>
    <nexthop> ::= <NEXTHOP_PROTECTION> (<NEXTHOP_PREFERENCE> <nexthop>
                          (<NEXTHOP_PREFERENCE> <nexthop>)...)
    <nexthop> ::= <NEXTHOP_PROTECTION> (<NEXTHOP_PREFERENCE> <nexthop>
                          (<NEXTHOP_PREFERENCE> <nexthop>))
    <nexthop> ::= <NEXTHOP_PROTECTION> ((<NEXTHOP_PREFERENCE> <nexthop-base>
                          (<NEXTHOP_PREFERENCE> <nexthop-base>))
    <nexthop> ::= <NEXTHOP_PROTECTION> (<1> <interface-primary>
                          (<2> <interface-backup>))

       Traffic can be load-balanced among multiple primary nexthops and a
       single backup.  In such a case, the nexthop will look like:

       <nexthop> ::= <NEXTHOP_PROTECTION> (<1>
                     (<NEXTHOP_LOAD_BALANCE>
                      (<NEXTHOP_LB_WEIGHT> <nexthop-base>
                      (<NEXTHOP_LB_WEIGHT> <nexthop-base>) ...))
                       <2> <nexthop-base>)

       A backup can also have another backup.  In such a case, the list will
       look like:

       <nexthop> ::= <NEXTHOP_PROTECTION> (<1> <nexthop>
                     <2> <NEXTHOP_PROTECTION>(<1> <nexthop> <2> <nexthop>))

    7.2.5.  Nexthop Chains

       A nexthop chain is a way to perform multiple operations on a packet
       by logically combining them.  For example, when a VPN packet comes on
       the WAN interface and has to be forwarded to the correct VPN
       interface, one needs to pop the VPN label before sending the packet
       out.  Using a nexthop chain, one can chain together "pop MPLS header"
       and "send it out a specific egress-interface".

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       The above example can be derived from the grammar as follows:

       <nexthop-chain> ::= <nexthop> <nexthop>
       <nexthop-chain> ::= <nexthop-base> <nexthop-base>
       <nexthop-chain> ::= <tunnel-decapsulation> <egress-interface>
       <nexthop-chain> ::= (<MPLS> <MPLS_POP>) <interface-outgoing>

       Elements in a nexthop chain are evaluated left to right.

       A nexthop chain can also be used to put one or more headers on an
       outgoing packet.  One example is a pseudowire, which is MPLS over
       some transport (MPLS or GRE, for instance).  Another example is
       Virtual eXtensible Local Area Network (VXLAN) over IP.  A nexthop
       chain thus allows a RIB client to break up the programming of the
       nexthop into independent pieces (one per encapsulation).

       A simple example of MPLS over GRE can be represented as follows:

       <nexthop-chain> ::= (<MPLS> <mpls-header>) (<GRE> <gre-header>)
                           <interface-outgoing>

       The above can be derived from the grammar as follows:

       <nexthop-chain> ::= <nexthop> <nexthop> <nexthop>
       <nexthop-chain> ::= <nexthop-base> <nexthop-base> <nexthop-base>
       <nexthop-chain> ::= <tunnel-encapsulation> <tunnel-encapsulation>
                           <egress-interface>
       <nexthop-chain> ::= (<MPLS> <mpls-header>) (<GRE> <gre-header>)
                           <interface-outgoing>

    7.2.6.  Lists of Lists

       Lists of lists is a derived construct.  One example of usage of such
       a construct is to replicate traffic to multiple destinations with
       load-balancing.  In other words, for each branch of the replication
       tree, there are multiple interfaces on which traffic needs to be
       load-balanced.  So, the outer list is a replication list for
       multicast and the inner lists are weighted lists for load-balancing.
       Let's take an example of a network element that has to replicate
       traffic to two other network elements.  Traffic to the first network
       element should be load-balanced equally over two interfaces:
       outgoing-1-1 and outgoing-1-2.  Traffic to the second network element
       should be load-balanced over three interfaces: outgoing-2-1,
       outgoing-2-2, and outgoing-2-3 (in the ratio 20:20:60).

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       This can be derived from the grammar as follows:

    <nexthop> ::= <nexthop-replicate>
    <nexthop> ::= <NEXTHOP_REPLICATE> (<nexthop> <nexthop>...)
    <nexthop> ::= <NEXTHOP_REPLICATE> (<nexthop> <nexthop>)
    <nexthop> ::= <NEXTHOP_REPLICATE> ((<NEXTHOP_LOAD_BALANCE> <nexthop-lb>)
                  (<NEXTHOP_LOAD_BALANCE> <nexthop-lb>))
    <nexthop> ::= <NEXTHOP_REPLICATE> ((<NEXTHOP_LOAD_BALANCE>
                  (<NEXTHOP_LB_WEIGHT> <nexthop>
                  (<NEXTHOP_LB_WEIGHT> <nexthop>) ...))
                   ((<NEXTHOP_LOAD_BALANCE>
                    (<NEXTHOP_LB_WEIGHT> <nexthop>
                    (<NEXTHOP_LB_WEIGHT> <nexthop>) ...))
    <nexthop> ::= <NEXTHOP_REPLICATE> ((<NEXTHOP_LOAD_BALANCE>
                  (<NEXTHOP_LB_WEIGHT> <nexthop>
                   (<NEXTHOP_LB_WEIGHT> <nexthop>)))
                    ((<NEXTHOP_LOAD_BALANCE>
                    (<NEXTHOP_LB_WEIGHT> <nexthop>
                    (<NEXTHOP_LB_WEIGHT> <nexthop>)
                    (<NEXTHOP_LB_WEIGHT> <nexthop>)))
    <nexthop> ::= <NEXTHOP_REPLICATE> ((<NEXTHOP_LOAD_BALANCE>
                   (<NEXTHOP_LB_WEIGHT> <nexthop>)
                   (<NEXTHOP_LB_WEIGHT> <nexthop>)))
                   ((<NEXTHOP_LOAD_BALANCE>
                   (<NEXTHOP_LB_WEIGHT> <nexthop>)
                   (<NEXTHOP_LB_WEIGHT> <nexthop>)
                   (<NEXTHOP_LB_WEIGHT> <nexthop>)))
    <nexthop> ::= <NEXTHOP_REPLICATE>
                   ((<NEXTHOP_LOAD_BALANCE>
                     (50 <outgoing-1-1>)
                     (50 <outgoing-1-2>)))
                    ((<NEXTHOP_LOAD_BALANCE>
                      (20 <outgoing-2-1>)
                      (20 <outgoing-2-2>)
                      (60 <outgoing-2-3>)))

    7.3.  Performing Multicast

       IP multicast involves matching a packet on (S,G) or (*,G), where both
       S (Source) and G (Group) are IP prefixes.  Following the match, the
       packet is replicated to one or more recipients.  How the recipients
       subscribe to the multicast group is outside the scope of this
       document.

       In PIM-based multicast, the packets are IP forwarded on an IP
       multicast tree.  The downstream nodes on each point in the multicast
       tree are one or more IP addresses.  These can be represented as a
       replication list (see Section 7.2.2).

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       In MPLS-based multicast, the packets are forwarded on a Point-to-
       Multipoint (P2MP) LSP.  The nexthop for a P2MP LSP can be represented
       in the nexthop grammar as a <logical-tunnel> (P2MP LSP identifier) or
       a replication list (see Section 7.2.2) of <tunnel-encapsulation>,
       with each tunnel-encapsulation representing a single MPLS downstream
       nexthop.

    8.  RIB Operations at Scale

       This section discusses the scale requirements for a RIB data model.
       The RIB data model should be able to handle a large scale of
       operations to enable deployment of RIB applications in large
       networks.

    8.1.  RIB Reads

       Bulking (grouping of multiple objects in a single message) MUST be
       supported when a network device sends RIB data to a RIB client.
       Similarly, the data model MUST enable a RIB client to request data in
       bulk from a network device.

    8.2.  RIB Writes

       Bulking (grouping of multiple write operations in a single message)
       MUST be supported when a RIB client wants to write to the RIB.  The
       response from the network device MUST include a return-code for each
       write operation in the bulk message.

    8.3.  RIB Events and Notifications

       There can be cases where a single network event results in multiple
       events and/or notifications from the network device to a RIB client.
       On the other hand, due to timing of multiple things happening at the
       same time, a network device might have to send multiple events and/or
       notifications to a RIB client.  The network-device-originated event/
       notification message MUST support the bulking of multiple events and
       notifications in a single message.

    9.  Security Considerations

       The information model specified in this document defines a schema for
       data models that are designed to be accessed via network management
       protocols such as NETCONF [RFC6241] or RESTCONF [RFC8040].  The
       lowest NETCONF layer is the secure transport layer, and the
       mandatory-to-implement secure transport is Secure Shell (SSH)
       [RFC6242].  The lowest RESTCONF layer is HTTPS, and the mandatory-to-
       implement secure transport is TLS [RFC8446].

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       The NETCONF access control model [RFC8341] provides the means to
       restrict access for particular NETCONF or RESTCONF users to a
       preconfigured subset of all available NETCONF or RESTCONF protocol
       operations and content.

       The RIB information model specifies read and write operations to
       network devices.  These network devices might be considered sensitive
       or vulnerable in some network environments.  Write operations to
       these network devices without proper protection can have a negative
       effect on network operations.  Due to this factor, it is recommended
       that data models also consider the following in their design:

       o  Require utilization of the authentication and authorization
          features of the NETCONF or RESTCONF suite of protocols.

       o  Augment the limits on how much data can be written or updated by a
          remote entity built to include enough protection for a RIB data
          model.

       o  Expose the specific RIB data model implemented via NETCONF/
          RESTCONF data models.

    10.  IANA Considerations

       This document has no IANA actions.

    11.  References

    11.1.  Normative References

       [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
                  Requirement Levels", BCP 14, RFC 2119,
                  DOI 10.17487/RFC2119, March 1997,
                  <https://www.rfc-editor.org/info/rfc2119>.

       [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
                  and A. Bierman, Ed., "Network Configuration Protocol
                  (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
                  <https://www.rfc-editor.org/info/rfc6241>.

       [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
                  Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
                  <https://www.rfc-editor.org/info/rfc6242>.

       [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
                  Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
                  <https://www.rfc-editor.org/info/rfc8040>.

    Bahadur, et al.               Informational                    [Page 26]

    RFC 8430                  RIB Information Model           September 2018

       [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
                  2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
                  May 2017, <https://www.rfc-editor.org/info/rfc8174>.

       [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
                  Access Control Model", STD 91, RFC 8341,
                  DOI 10.17487/RFC8341, March 2018,
                  <https://www.rfc-editor.org/info/rfc8341>.

       [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
                  Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
                  <https://www.rfc-editor.org/info/rfc8446>.

    11.2.  Informative References

       [RFC4915]  Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
                  Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
                  RFC 4915, DOI 10.17487/RFC4915, June 2007,
                  <https://www.rfc-editor.org/info/rfc4915>.

       [RFC5120]  Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
                  Topology (MT) Routing in Intermediate System to
                  Intermediate Systems (IS-ISs)", RFC 5120,
                  DOI 10.17487/RFC5120, February 2008,
                  <https://www.rfc-editor.org/info/rfc5120>.

       [RFC5511]  Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax
                  Used to Form Encoding Rules in Various Routing Protocol
                  Specifications", RFC 5511, DOI 10.17487/RFC5511, April
                  2009, <https://www.rfc-editor.org/info/rfc5511>.

       [RFC7920]  Atlas, A., Ed., Nadeau, T., Ed., and D. Ward, "Problem
                  Statement for the Interface to the Routing System",
                  RFC 7920, DOI 10.17487/RFC7920, June 2016,
                  <https://www.rfc-editor.org/info/rfc7920>.

       [RFC8431]  Wang, L., Chen, M., Dass, A., Ananthakrishnan, H., Kini,
                  S., and N. Bahadur, "A YANG Data Model for the Routing
                  Information Base (RIB)", RFC 8431, DOI 10.17487/RFC8431,
                  September 2018, <http://www.rfc-editor.org/info/rfc8431>.

    Bahadur, et al.               Informational                    [Page 27]

    RFC 8430                  RIB Information Model           September 2018

    Acknowledgements

       The authors would like to thank Ron Folkes, Jeffrey Zhang, the WG
       co-Chairs, and reviewers for their comments and suggestions on this
       document.  The following people contributed to the design of the RIB
       information model as part of the I2RS Interim meeting in April 2013:

       Wes George, Chris Liljenstolpe, Jeff Tantsura, Susan Hares, and
       Fabian Schneider.

    Authors' Addresses

       Nitin Bahadur (editor)
       Uber
       900 Arastradero Rd
       Palo Alto, CA  94304
       United States of America

       Email: nitin_bahadur@yahoo.com

       Sriganesh Kini (editor)

       Email: sriganeshkini@gmail.com

       Jan Medved
       Cisco

       Email: jmedved@cisco.com

    Bahadur, et al.               Informational                    [Page 28]