Network Working Group                                    N. Bahadur, Ed.
Internet-Draft                                         Bracket Computing
Intended status: Informational                              S. Kini, Ed.
Expires: December 18, 2017 May 26, 2018
                                                               J. Medved
                                                           June 16,
                                                       November 22, 2017

                  Routing Information Base Info Model


   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 configuration push
   data into the RIB and the RIB manager installs state into the
   hardware; for packet forwarding.  This draft specifies a information
   model for the RIB to enable defining a standardized data model.  Such
   a data model can be used to define an interface to the RIB from an
   entity that may even be external to the network device.  This
   interface can be used to support new use-cases being defined by the

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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 . . . . . . . . . . . . . . . . . . . . . .  6
     2.2.  Routing instance . . . . . . . . . . . . . . . . . . . . .  7
     2.3.  Route  . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     2.4.  Nexthop  . . . . . . . . . . . . . . . . . . . . . . . . .  9
       2.4.1.  Nexthop types  . . . . . . . . . . . . . . . . . . . . 11 12
       2.4.2.  Nexthop list attributes  . . . . . . . . . . . . . . . 12 13
       2.4.3.  Nexthop content  . . . . . . . . . . . . . . . . . . . 12 13
       2.4.4.  Special nexthops . . . . . . . . . . . . . . . . . . . 13 14
   3.  Reading from the RIB . . . . . . . . . . . . . . . . . . . . . 14
   4.  Writing to the RIB . . . . . . . . . . . . . . . . . . . . . . 14 15
   5.  Notifications  . . . . . . . . . . . . . . . . . . . . . . . . 14 15
   6.  RIB grammar  . . . . . . . . . . . . . . . . . . . . . . . . . 15 16
     6.1.  Nexthop grammar explained  . . . . . . . . . . . . . . . . 18
   7.  Using the RIB grammar  . . . . . . . . . . . . . . . . . . . . 18 19
     7.1.  Using route preference . . . . . . . . . . . . . . . . . . 18 19
     7.2.  Using different nexthops types . . . . . . . . . . . . . . 18 19
       7.2.1.  Tunnel nexthops  . . . . . . . . . . . . . . . . . . . 18 19
       7.2.2.  Replication lists  . . . . . . . . . . . . . . . . . . 19
       7.2.3.  Weighted lists . . . . . . . . . . . . . . . . . . . . 19 20
       7.2.4.  Protection . . . . . . . . . . . . . . . . . . . . . . 20
       7.2.5.  Nexthop chains . . . . . . . . . . . . . . . . . . . . 20 21
       7.2.6.  Lists of lists . . . . . . . . . . . . . . . . . . . . 21 22
     7.3.  Performing multicast . . . . . . . . . . . . . . . . . . . 22 23
   8.  RIB operations at scale  . . . . . . . . . . . . . . . . . . . 23 24
     8.1.  RIB reads  . . . . . . . . . . . . . . . . . . . . . . . . 23 24
     8.2.  RIB writes . . . . . . . . . . . . . . . . . . . . . . . . 23 24
     8.3.  RIB events and notifications . . . . . . . . . . . . . . . 23 24
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 23 24
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 24 25
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 24 25
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24 25
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 24 25
     12.2. Informative References . . . . . . . . . . . . . . . . . . 24 25

   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25 26

1.  Introduction

   Routing and routing functions in enterprise and carrier networks are
   traditionally performed in network devices.  Traditionally routers
   run routing protocols and the routing protocols (along with static
   config) populate the Routing information base (RIB) of the router.
   The RIB is managed by the RIB manager and the RIB manager provides a
   north-bound 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 |
         +-------------+        +-------------+
                ^                      ^
                |                      |
                |RIB manager          |
                |                     |
                |       +-----+       |
                |       | RIB |       |
                |       +-----+       |
          |                                 |
          V                                 V
   +-------------+                   +-------------+
   |FIB manager 1|                   |FIB manager M|
   |   +-----+   |    ..........     |   +-----+   |
   |   | FIB |   |                   |   | FIB |   |
   |   +-----+   |                   |   +-----+   |
   +-------------+                   +-------------+

            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].
   Traditional network-device protocol-based RIB population suffices for
   most use cases where distributed network control is used.  However
   there are use cases which 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
   [I-D.white-i2rs-use-case], [I-D.hares-i2rs-use-case-vn-vc] 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 2 types of operations -
   reading from the RIB and writing (adding/modifying/deleting) to the
   RIB.  [I-D.white-i2rs-use-case] lists various use-cases which require
   read and/or write manipulation of the RIB.

   In order to understand what is in a router's RIB, methods like per-
   protocol SNMP MIBs and show output 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 represent 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 an external entity 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 an external entity to program a multi-vendor
   network in a consistent and vendor-independent way.

   The purpose of this draft 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 an external
   entity to program a network device.

   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 Section 3
   and Section 4 respectively.  Section 5 provides a high-level view of
   the events and notifications going from a network device to an
   external entity, to update the external entity 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",
   document are to be interpreted as described in [RFC2119].

2.  RIB data

   This section describes the details of a RIB.  It makes forward
   references to objects in the RIB grammar (Section 6).  A high-level
   description of the RIB contents is as shown below.

                          |             |
                          |             |
                    0..N  |             | 1..N
                          |             |
                     interface(s)     RIB(s)
                                        | 0..N

                            Figure 2: RIB model

2.1.  RIB definition

   A RIB is an entity that contains routes.  A RIB is identified by its
   name and a RIB is contained within a routing instance (Section 2.2).
   The name MUST be unique within a routing instance.  All routes in a
   given RIB MUST be of the same rib family (e.g.  IPv4).  Each RIB MUST
   belong to a routing instance.

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

   Each RIB can be optionally associated with a ENABLE_IP_RPF_CHECK
   attribute that enables Reverse path forwarding (RPF) checks on all IP
   routes in that RIB.  Reverse path forwarding (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 interface(s), 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 Virtual Private Networks (VPN), Layer 2 VPNs (L2VPN)
   and Virtual Private Lan Service (VPLS) can be modeled as routing
   instances.  Note that modeling a Layer 2 VPN 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 2 routing instances
   MUST be the null set.  In other words, an interface MUST NOT be
   present in 2 routing instances.  Thus a routing instance describes
   the routing information and parameters across a set of interfaces.

   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.

   A routing instance MAY contain the following optional 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 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: The router-id 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.  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.

                                 | | |
                       +---------+ | +----------+
                       |           |            |
                  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
   o  IPv6: Match on destination and/or source IP address in the IPv6
   o  MPLS: Match on a MPLS label at the top of the MPLS label stack
   o  MAC: Match on MAC destination addresses in the ethernet header
   o  Interface: Match on incoming interface of the packet
   o  IP multicast: Match on (S, G) or (*, G), where S and G are IP

   Each route MUST have associated with it the following mandatory route
   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 (or IPv6 2001:DB8::1/32) with a preference of 5.
      If a controller programs a route for (or IPv6 2001:
      DB8::1/32) with a preference of 2, then the controller's route
      will be preferred by the RIB manager.  Preference should be used
      to dictate behavior.  For more examples of preference, see
      Section 7.1.

   Each route can have associated with it one or more optional route
   o  route-vendor-attributes: Vendors can specify vendor-specific
      attributes using this.  The details of this attribute is outside
      the scope of this document.

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 a given
   interface, then the nexthop represents that interface.

   Nexthops can be fully resolved nexthops or unresolved nexthop.  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, e.g. is the IP address
   reachable by regular IP forwarding or by a 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 (like that IP address being advertised by an
   IGP neighbor).  Conversely resolved nexthops can also become
   unresolved (e.g. in case of a tunnel going down) and hence 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 is
   henceforth referred to as a FIB-ineligible route.  The RIB
   information model allows an external entity 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.

                                 | 0..N
                               nexthop <-------------------------------+
                                 |                                     |
          +-------+----------------------------+-------------+         |
          |       |              |             |             |         |
          |       |              |             |             |         |
       base   load-balance   protection      replicate     chain       |
          |       |              |             |             |         |
          |       |2..N          |2..N         |2..N         |1..N     |
          |       |              |             |             |         |
          |       |              V             |             |         |
          |       +------------->+<------------+-------------+         |
          |                      |                                     |
          |                      +-------------------------------------+
     |               |                 |              |
     |               |                 |              |
  nexthop-id  egress-interface  logical-tunnel        |
       |              |           |
       |              |           |
 tunnel-encap  tunnel-decap  special-nexthop

                          Figure 4: Nexthop model

   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 external entity on request.  The RIB data-model SHOULD support
   a way to optionally receive a nexthop identifier for a given nexthop.
   For example, one can create a nexthop that points to a BGP peer.  The
   returned nexthop identifier can then be used for programming routes
   to point to the same nexthop.  Given that the RIB manager has created
   an indirection for that BGP peer using the nexthop identifier, if the
   transport path to the BGP peer changes, that change in path will be
   seamless to the external entity and all routes that point to that BGP
   peer will automatically start going over the new transport path.
   Nexthop indirection using identifiers could be applied to not just
   unicast nexthops, but even to nexthops that contain chains and nested
   nexthops (Section 2.4.1).

2.4.1.  Nexthop types

   This document specifies a very generic, extensible and recursive
   grammar for nexthops.  Nexthops can be
   o  Interface nexthops - pointing to an interface
   o  Tunnel nexthops - pointing to a tunnel
   o  Replication lists - list of nexthops to which to replicate a
   o  Weighted lists - for load-balancing
   o  Preference lists - for protection using primary and backup
   o  Nexthop chains - for chaining multiple operations or attaching
      multiple headers
   o  Lists of lists - recursive application of the above
   o  Indirect nexthops - pointing to a nexthop identifier
   o  Special nexthops - for performing specific well-defined functions
      (e.g. drop)
   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 an external entity to learn about the network device's
   capabilities.  Examples of when and how to use various kinds of
   nexthops are shown in Section 7.2.

   Tunnel nexthops allow an external entity to program static tunnel
   headers.  There can be cases where the remote tunnel end-point does
   not support dynamic signaling (e.g. no LDP support on a host) and in
   those cases the external entity 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.

   Nexthop chains Section 7.2.5, is 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 and
   GRE header are specified by the controller.  Not every network device
   will be able to support all kinds of nexthop chains and an arbitrary
   number of header chained together.  The RIB data-model SHOULD provide
   a way to expose nexthop chaining capability supported by a given
   network device.

2.4.2.  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 two highest preferences are
      selected.  Each <NEXTHOP_PREFERENCE> should have a unique value
      within a <nexthop-protection>
      (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.

2.4.3.  Nexthop content

   At the lowest level, a nexthop can be one of:
   o  identifier: This is an identifier returned by the network device
      representing a nexthop.  This can be used as a way of re-using a
      nexthop when programming complex nexthops.
   o  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.
   o  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.
   o  EGRESS_INTERFACE and IP address: This can be used in cases e.g.
      where the IP address is a link-local address.

   o  EGRESS_INTERFACE and MAC address: The egress interface must be an
      ethernet interface.  Address resolution is not required for this
   o  tunnel encap: This can be an encap representing an IP tunnel or
      MPLS tunnel or others as defined in this document.  An optional
      egress interface can be chained to the tunnel encap 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.
   o  tunnel decap: This is to specify decapsulating a tunnel header.
      After decap, further lookup on the packet can be done via chaining
      it with another nexthop.  The packet can also be sent out via a
      EGRESS_INTERFACE directly.
   o  logical tunnel: This can be a MPLS 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 indicates that the route
      lookup needs to continue in the specified RIB.  This is a way to
      perform chained lookups.

2.4.4.  Special nexthops

   This document specifies certain special nexthops.  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).
   o  RECEIVE: This indicates that that the traffic is destined for the
      network device.  For example, protocol packets or 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.

3.  Reading from the RIB

   A RIB data-model MUST allow an external entity to read entries, for
   RIBs created by that entity.  The network device administrator MAY
   allow reading of other RIBs by an external entity 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.  An external agent SHOULD be
   able to request a full read at any time in the lifecycle of the
   connection.  When sending data to an external entity, 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 an external entity to write entries, for
   RIBs created by that entity.  The network device administrator MAY
   allow writes to other RIBs by an external entity 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 external entity 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 are modify-able objects.  A
   modify-able object 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.

5.  Notifications

   Asynchronous notifications are sent by the network device's RIB
   manager to an external entity 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 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 [RFC5511].  This grammar is intended to help the reader
   better understand the english text description in order to derive a
   data model.  However it may not provide all the detail provided by
   the english text.  When there is a lack of clarity in the grammar the
   english text will take precedence.

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

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

  <rib-list> ::= (<rib> ...)
  <rib> ::= <RIB_NAME> <rib-family>
                      [<route> ... ]
  <rib-family> ::= <IPV4_RIB_FAMILY> | <IPV6_RIB_FAMILY> |
                   <MPLS_RIB_FAMILY> | <IEEE_MAC_RIB_FAMILY>

  <route> ::= <match> <nexthop>

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

  <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> ::= <ip-route-attributes> |
                                        <mpls-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-base> ::= <NEXTHOP_ID> |
                     <nexthop-special> |
                     <EGRESS_INTERFACE> |
                     <ipv4-address> | <ipv6-address> |
                         (<ipv4-address> | <ipv6-address>)) |
                     (<EGRESS_INTERFACE> <IEEE_MAC_ADDRESS>) |
                     <tunnel-encap> | <tunnel-decap> |
                     <logical-tunnel> |


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

                    <PROTOCOL> [<TTL>] [<DSCP>]

                    <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>

  <vxlan-header> ::= (<ipv4-header> | <ipv6-header>)
  <nvgre-header> ::= (<ipv4-header> | <ipv6-header>)

  <tunnel-decap> ::= ((<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 multicasted 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 pre-install alternate paths in
   the network.  For example, if OSPF has a route preference of 10, then
   another client can install a route with 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 nexthops types

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

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 encap.  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 encap and another for

7.2.2.  Replication lists

   One can create a replication list for replicating traffic to multiple
   destinations.  The destinations, in turn, could be complex 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>) ...

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_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_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".

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

   <nexthop-chain> ::= <nexthop> <nexthop>
   <nexthop-chain> ::= <nexthop-base> <nexthop-base>
   <nexthop-chain> ::= <tunnel-decap> <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 VxLAN
   over IP.  A nexthop chain thus allows an external entity to break up
   the programming of the nexthop into independent pieces - one per

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

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

   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-encap> <tunnel-encap> <EGRESS_INTERFACE>
   <nexthop-chain> ::= (<MPLS> <mpls-header>) (<GRE> <gre-header>)

7.2.6.  Lists of lists

   Lists of lists is a complex 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 on.  So the outer list is a replication list for
   multicast and the inner lists are weighted lists for load balancing.
   Lets take an example of a network element 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.

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_LB_WEIGHT> <nexthop>
              (<NEXTHOP_LB_WEIGHT> <nexthop>) ...))
                (<NEXTHOP_LB_WEIGHT> <nexthop>
                (<NEXTHOP_LB_WEIGHT> <nexthop>) ...))
              (<NEXTHOP_LB_WEIGHT> <nexthop>
               (<NEXTHOP_LB_WEIGHT> <nexthop>)))
                (<NEXTHOP_LB_WEIGHT> <nexthop>
                (<NEXTHOP_LB_WEIGHT> <nexthop>)
                (<NEXTHOP_LB_WEIGHT> <nexthop>)))
               (<NEXTHOP_LB_WEIGHT> <nexthop>)
               (<NEXTHOP_LB_WEIGHT> <nexthop>)))
               (<NEXTHOP_LB_WEIGHT> <nexthop>)
               (<NEXTHOP_LB_WEIGHT> <nexthop>)
               (<NEXTHOP_LB_WEIGHT> <nexthop>)))
<nexthop> ::= <NEXTHOP_REPLICATE>
                 (50 <outgoing-1-1>)
                 (50 <outgoing-1-2>)))
                  (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 is one or more IP addresses.  These can be represented as a
   replication list ( Section 7.2.2 ).

   In MPLS-based multicast, the packets are forwarded on a point to
   multipoint (P2MP) label-switched path (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 ( Section 7.2.2) of
   <tunnel-encap>, with each tunnel encap 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 large scale of
   operations, to enable deployment of RIB applications in large

8.1.  RIB reads

   Bulking (grouping of multiple objects in a single message) MUST be
   supported when a network device sends RIB data to an external entity.
   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 an external entity 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 an external
   entity.  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 an external entity.  The
   network device originated event/notification message MUST support
   bulking of multiple events and notifications in a single message.

9.  Security Considerations

   All interactions between a RIB manager and an external entity MUST be
   authenticated and authorized.  The RIB manager MUST protect itself
   against a denial of service attack by a rogue external entity, by
   throttling request processing.  A RIB manager MUST enforce limits on
   how much data can be programmed by an external entity and return
   error when such a limit is reached.

   The RIB manager MUST expose a data-model that it implements.  An
   external agent MUST send requests to the RIB manager that comply with
   the supported data-model.  The data-model MUST specify the behavior
   of the RIB manager on handling of unsupported data requests.

10.  IANA Considerations

   This document does not generate any considerations for IANA.

11.  Acknowledgements

   The authors would like to thank Ron Folkes, Jeffrey Zhang, the
   working group co-chairs and reviewers on their comments and
   suggestions on this draft.  The following people contributed to the
   design of the RIB model as part of the I2RS Interim meeting in April
   2013 - Wes George, Chris Liljenstolpe, Jeff Tantsura, Susan Hares and
   Fabian Schneider.

12.  References

12.1.  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,

12.2.  Informative References

              Hares, S. and M. Chen, "Use Cases for Virtual Connections
              on Demand (VCoD) and Virtual Network on Demand (VNoD)
              using Interface to Routing System",
              draft-hares-i2rs-use-case-vn-vc-03 (work in progress),
              July 2014.

              White, R., Hares, S., and A. Retana, "Protocol Independent
              Use Cases for an Interface to the Routing System",
              draft-white-i2rs-use-case-06 (work in progress),
              July 2014.

   [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,

   [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,

   [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, <>. <>.

   [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,

Authors' Addresses

   Nitin Bahadur (editor)
   Bracket Computing
   150 West Evelyn Ave, Suite 200
   Mountain View, CA  94041


   Sriganesh Kini (editor)


   Jan Medved