Problem Statement for the Interface to the Routing System
RFC 7920

Internet Engineering Task Force (IETF)                     A. Atlas, Ed.
Request for Comments: 7920                              Juniper Networks
Category: Informational                                   T. Nadeau, Ed.
ISSN: 2070-1721                                                  Brocade
                                                                 D. Ward
                                                           Cisco Systems
                                                               June 2016

       Problem Statement for the Interface to the Routing System

Abstract

   Traditionally, routing systems have implemented routing and signaling
   (e.g., MPLS) to control traffic forwarding in a network.  Route
   computation has been controlled by relatively static policies that
   define link cost, route cost, or import and export routing policies.
   Requirements have emerged to more dynamically manage and program
   routing systems due to the advent of highly dynamic data-center
   networking, on-demand WAN services, dynamic policy-driven traffic
   steering and service chaining, the need for real-time security threat
   responsiveness via traffic control, and a paradigm of separating
   policy-based decision-making from the router itself.  These
   requirements should allow controlling routing information and traffic
   paths and extracting network topology information, traffic
   statistics, and other network analytics from routing systems.

   This document proposes meeting this need via an Interface to the
   Routing System (I2RS).

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 a candidate 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
   http://www.rfc-editor.org/info/rfc7920.

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Copyright Notice

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   document authors.  All rights reserved.

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   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................3
   2. I2RS Model and Problem Area for the IETF ........................4
   3. Standard Data Models of Routing State for Installation ..........6
   4. Learning Router Information .....................................7
   5. Aspects to be Considered for an I2RS Protocol ...................8
   6. Security Considerations .........................................9
   7. References .....................................................10
      7.1. Normative References ......................................10
      7.2. Informative References ....................................10
   Appendix A.  Existing Management Interfaces .......................11
   Acknowledgements ..................................................12
   Authors' Addresses ................................................12

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1.  Introduction

   Traditionally, routing systems have implemented routing and signaling
   (e.g., MPLS) to control traffic forwarding in a network.  Route
   computation has been controlled by relatively static policies that
   define link cost, route cost, or import and export routing policies.
   The advent of highly dynamic data-center networking, on-demand WAN
   services, dynamic policy-driven traffic steering and service
   chaining, the need for real-time security threat responsiveness via
   traffic control, and a paradigm of separating policy-based decision-
   making from the router itself has created the need to more
   dynamically manage and program routing systems in order to control
   routing information and traffic paths and to extract network topology
   information, traffic statistics, and other network analytics from
   routing systems.

   As modern networks continue to grow in scale and complexity and
   desired policy has become more complex and dynamic, there is a need
   to support rapid control and analytics.  The scale of modern networks
   and data centers and the associated operational expense drives the
   need to automate even the simplest operations.  The ability to
   quickly interact via more complex operations to support dynamic
   policy is even more critical.

   In order to enable network applications to have access to and control
   over information in the different vendors' routing systems, a
   publicly documented interface is required.  The interface needs to
   support real-time, asynchronous interactions using efficient data
   models and encodings that are based on and extend those previously
   defined.  Furthermore, the interface must be tailored to provide a
   solid base on which a variety of use cases can be supported.

   To support the requirements of orchestration software and automated
   network applications to dynamically modify the network, there is a
   need to learn topology, network analytics, and existing state from
   the network as well as to create or modify routing information and
   network paths.  A feedback loop is needed so that changes made can be
   verifiable and so that these applications can learn and react to
   network changes.

   Proprietary solutions to partially support the requirements outlined
   above have been developed to handle specific situations and needs.
   Standardizing an interface to the routing system will make it easier
   to integrate use of it into a network.  Because there are proprietary
   partial solutions already, the standardization of a common interface
   should be feasible.

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   It should be noted that during the course of this document, the term
   "applications" is used.  This is meant to refer to an executable
   program of some sort that has access to a network, such as an IP or
   MPLS network, via a routing system.

2.  I2RS Model and Problem Area for the IETF

   Managing a network of systems running a variety of routing protocols
   and/or providing one or more additional services (e.g., forwarding,
   classification and policing, firewalling) involves interactions
   between multiple components within these systems.  Some of these
   systems or system components may be virtualized, co-located within
   the same physical system, or distributed.  In all cases, it is
   desirable to enable network applications to manage and control the
   services provided by many, if not all, of these components, subject
   to authenticated and authorized access and policies.

   A data-model-driven interface to the routing system is needed.  This
   will allow expansion of what information can be read and controlled
   and allow for future flexibility.  At least one accompanying protocol
   with clearly defined operations is needed; the suitable protocol(s)
   can be identified and expanded to support the requirements of an
   Interface to the Routing System (I2RS).  These solutions must be
   designed to facilitate rapid, isolated, secure, and dynamic changes
   to a device's routing system.  These would facilitate wide-scale
   deployment of interoperable applications and routing systems.

   The I2RS model and problem area for IETF work is illustrated in
   Figure 1.  This document uses terminology defined in [RFC7921].  The
   I2RS agent is associated with a routing element, which may or may not
   be co-located with a data plane.  The I2RS client could be integrated
   in a network application or controlled and used by one or more
   separate network applications.  For instance, an I2RS client could be
   provided by a network controller or a network orchestration system
   that provides a non-I2RS interface to network applications and an
   I2RS interface to I2RS agents on the systems being managed.  The
   scope of the data models used by I2RS extends across the entire
   routing system and the selected protocol(s) for I2RS.

   As depicted in Figure 1, the I2RS client and I2RS agent in a routing
   system are objects with in the I2RS scope.  The selected protocol(s)
   for I2RS extend between the I2RS client and I2RS agent.  All other
   objects and interfaces in Figure 1 are outside the I2RS scope for
   standardization.

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        +***************+   +***************+   +***************+
        *  Application  *   *  Application  *   *  Application  *
        +***************+   +***************+   +***************+
        |  I2RS Client  |           ^                  ^
        +---------------+           *                  *
                 ^                  *   ****************
                 |                  *   *
                 |                  v   v
                 |           +---------------+         +-------------+
                 |           |  I2RS Client  |<------->| Other I2RS  |
                 |           +---------------+         | Agents      |
                 |                   ^                 +-------------+
                 |________________   |
                                  |  |  <== I2RS Protocol
                                  |  |
       ...........................|..|..................................
       .                          v  v                                 .
       . +*************+     +---------------+      +****************+ .
       . *  Policy     *     |               |      *   Routing  &   * .
       . * Database    *<***>|  I2RS Agent   |<****>*   Signaling    * .
       . +*************+     |               |      *   Protocols    * .
       .                     +---------------+      +****************+ .
       .                        ^   ^     ^                  ^         .
       . +*************+        *   *     *                  *         .
       . *  Topology   *        *   *     *                  *         .
       . *  Database   *<*******+   *     *                  v         .
       . +*************+            *     *         +****************+ .
       .                            *     +********>*  RIB Manager   * .
       .                            *               +****************+ .
       .                            *                        ^         .
       .                            v                        *         .
       .                 +*******************+               *         .
       .                 * Subscription &    *               *         .
       .                 * Configuration     *               v         .
       .                 * Templates for     *      +****************+ .
       .                 * Measurements,     *      *  FIB Manager   * .
       .                 * Events, QoS, etc. *      *  & Data Plane  * .
       .                 +*******************+      +****************+ .
       .................................................................

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     <-->  interfaces inside the scope of I2RS Protocol

     +--+  objects inside the scope of I2RS-defined behavior

     <**>  interfaces NOT within the scope of I2RS Protocol

     +**+  objects NOT within the scope of I2RS-defined behavior

     <==   used to point to the interface where the I2RS Protocol
           would be used

     ....  boundary of a router supporting I2RS

                   Figure 1: I2RS Model and Problem Area

   The protocol(s) used to carry messages between I2RS clients and I2RS
   agents should provide the key features specified in Section 5.

   I2RS will use a set of meaningful data models for information in the
   routing system and in a topology database.  Each data model should
   describe the meaning and relationships of the modeled items.  The
   data models should be separable across different features of the
   managed components, versioned, and extendable.  As shown in Figure 1,
   I2RS needs to interact with several logical components of the routing
   element: policy database, topology database, subscription and
   configuration for dynamic measurements/events, routing and signaling
   protocols, and its Routing Information Base (RIB) manager.  This
   interaction is both for writing (e.g., to policy databases or RIB
   manager) as well as for reading (e.g., dynamic measurement or
   topology database).  An application should be able to combine data
   from individual routing elements to provide network-wide data
   model(s).

   The data models should translate into a concise transfer syntax, sent
   via the I2RS protocol, that is straightforward for applications to
   use (e.g., a web services design paradigm).  The information transfer
   should use existing transport protocols to provide the reliability,
   security, and timeliness appropriate for the particular data.

3.  Standard Data Models of Routing State for Installation

   As described in Section 1, there is a need to be able to precisely
   control routing and signaling state based upon policy or external
   measures.  One set of data models that I2RS should focus on is for
   interacting with the RIB layer (e.g., RIB, Label Information Base
   (LIB), multicast RIB, policy-based routing) to provide flexibility
   and routing abstractions.  As an example, the desired routing and
   signaling state might range from simple static routes to policy-based

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   routing to static multicast replication and routing state.  This
   means that, to usefully model next hops, the data model employed
   needs to handle next-hop indirection and recursion (e.g., a prefix X
   is routed like prefix Y) as well as different types of tunneling and
   encapsulation.

   Efforts to provide this level of control have focused on
   standardizing data models that describe the forwarding plane (e.g.,
   Forwarding and Control Element Separation (ForCES) [RFC3746]).  I2RS
   recognizes that the routing system and a router's OS provide useful
   mechanisms that applications could usefully harness to accomplish
   application-level goals.  Using routing indirection, recursion, and
   common routing abstractions (e.g., tunnels, Label Switched Paths
   (LSPs), etc.) provides significant flexibility and functionality over
   collapsing the state to individual routes in the Forwarding
   Information Base (FIB) that need to be individually modified when a
   change occurs.

   In addition to interfaces to control the RIB layer, there is a need
   to dynamically configure policies and parameter values for the
   various routing and signaling protocols based upon application-level
   policy decisions.

4.  Learning Router Information

   A router has information that applications may require so that they
   can understand the network, verify that programmed state is
   installed, measure the behavior of various flows, and understand the
   existing configuration and state of the router.  I2RS should provide
   a framework so that applications can register for asynchronous
   notifications and can make specific requests for information.

   Although there are efforts to extend the topological information
   available, even the best of these (e.g., BGP-LS [RFC7752]) still only
   provide the current active state as seen at the IGP and BGP layers.
   Detailed topological state that provides more information than the
   current functional status (e.g., active paths and links) is needed by
   applications.  Examples of missing information include paths or links
   that are potentially available (e.g., administratively down) or
   unknown (e.g., to peers or customers) to the routing topology.

   For applications to have a feedback loop that includes awareness of
   the relevant traffic, an application must be able to request the
   measurement and timely, scalable reporting of data.  While a
   mechanism such as IP Flow Information Export (IPFIX) [RFC5470] may be
   the facilitator for delivering the data, providing the ability for an
   application to dynamically request that measurements be taken and
   data delivered is important.

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   There is a wide range of events that applications could use to
   support verification of router state before other network state is
   changed (e.g., that a route has been installed) and to allow timely
   action in response to changes of relevant routes by others or to
   router events (e.g., link up/down).  While a few of these (e.g., link
   up/down) may be available via MIB notifications today, the full range
   is not (e.g., route installed, route changed, primary LSP changed,
   etc.)

5.  Aspects to be Considered for an I2RS Protocol

   This section describes required aspects of a protocol that could
   support I2RS.  Whether such a protocol is built upon extending
   existing mechanisms or requires a new mechanism requires further
   investigation.

   The key aspects needed in an interface to the routing system are:

   Multiple Simultaneous Asynchronous Operations:   A single application
      should be able to send multiple independent atomic operations via
      I2RS without being required to wait for each to complete before
      sending the next.

   Very Fine Granularity of Data Locking for Writing:   When an I2RS
      operation is processed, it is required that the data locked for
      writing be very granular (e.g., a particular prefix and route)
      rather than extremely coarse, as is done for writing
      configuration.  This should improve the number of concurrent I2RS
      operations that are feasible and reduce blocking delays.

   Multi-Headed Control:   Multiple applications may communicate to the
      same I2RS agent in a minimally coordinated fashion.  It is
      necessary that the I2RS agent can handle multiple requests in a
      well-known policy-based fashion.  Data written can be owned by
      different I2RS clients at different times; data may even be
      overwritten by a different I2RS client.  The details of how this
      should be handled are described in [RFC7921].

   Duplex:   Communications can be established by either the I2RS client
      (i.e., that resides within the application or is used by it to
      communicate with the I2RS agent) or the I2RS agent.  Similarly,
      events, acknowledgements, failures, operations, etc., can be sent
      at any time by both the router and the application.  The I2RS is
      not a pure pull model where only the application queries to pull
      responses.

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   High Throughput:   At a minimum, the I2RS agent and associated router
      should be able to handle a considerable number of operations per
      second (for example, 10,000 per second to handle many individual
      subscriber routes changing simultaneously).

   Low Latency:   Within a sub-second timescale, it should be possible
      to complete simple operations (e.g., reading or writing a single
      prefix route).

   Multiple Channels:   It should be possible for information to be
      communicated via the interface from different components in the
      router without requiring going through a single channel.  For
      example, for scaling, some exported data or events may be better
      sent directly from the forwarding plane, while other interactions
      may come from the control plane.  One channel, with authorization
      and authentication, may be considered primary; only an authorized
      client can then request that information be delivered on a
      different channel.  Writes from a client are only expected on
      channels that provide authorization and authentication.

   Scalable, Filterable Information Access:  To extract information in a
      scalable fashion that is more easily used by applications, the
      ability to specify filtering constructs in an operation requesting
      data or requesting an asynchronous notification is very valuable.

   Secure Control and Access:   Any ability to manipulate routing state
      must be subject to authentication and authorization.  Sensitive
      routing information also may need to be provided via secure access
      back to the I2RS client.  Such communications must be integrity
      protected.  Most communications will also require confidentiality.

   Extensibility and Interoperability:   Both the I2RS protocol and
      models must be extensible and interoperate between different
      versions of protocols and models.

6.  Security Considerations

   Security is a key aspect of any protocol that allows state
   installation and extracting of detailed router state.  The need for
   secure control and access is mentioned in Section 5.  More
   architectural security considerations are discussed in [RFC7921].
   Briefly, the I2RS agent is assumed to have a separate authentication
   and authorization channel by which it can validate both the identity
   and the permissions associated with an I2RS client.  Mutual
   authentication between the I2RS agent and I2RS client is required.
   Different levels of integrity, confidentiality, and replay protection
   are relevant for different aspects of I2RS.

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7.  References

7.1.  Normative References

   [RFC7921]  Atlas, A., Halpern, J., Hares, S., Ward, D., and T.
              Nadeau, "An Architecture for the Interface to the Routing
              System", RFC 7921, DOI 10.17487/RFC7921, June 2016,
              <http://www.rfc-editor.org/info/rfc7921>.

7.2.  Informative References

   [RFC3746]  Yang, L., Dantu, R., Anderson, T., and R. Gopal,
              "Forwarding and Control Element Separation (ForCES)
              Framework", RFC 3746, DOI 10.17487/RFC3746, April 2004,
              <http://www.rfc-editor.org/info/rfc3746>.

   [RFC5470]  Sadasivan, G., Brownlee, N., Claise, B., and J. Quittek,
              "Architecture for IP Flow Information Export", RFC 5470,
              DOI 10.17487/RFC5470, March 2009,
              <http://www.rfc-editor.org/info/rfc5470>.

   [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,
              <http://www.rfc-editor.org/info/rfc6241>.

   [RFC7752]  Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
              S. Ray, "North-Bound Distribution of Link-State and
              Traffic Engineering (TE) Information Using BGP", RFC 7752,
              DOI 10.17487/RFC7752, March 2016,
              <http://www.rfc-editor.org/info/rfc7752>.

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Appendix A.  Existing Management Interfaces

   This section discusses as a single entity the combination of the
   abstract data models, their representation in a data language, and
   the transfer protocol commonly used with them.  While other
   combinations of these existing standard technologies are possible,
   the ways described are ones that have significant deployment.

   There are three basic ways that routers are managed.  The most
   popular is the command-line interface (CLI), which allows both
   configuration and learning of device state.  This is a proprietary
   interface resembling a UNIX shell that allows for very customized
   control and observation of a device, and, specifically of interest in
   this case, its routing system.  Some form of this interface exists on
   almost every device (virtual or otherwise).  Processing of
   information returned to the CLI (called "screen scraping") is a
   burdensome activity because the data is normally formatted for use by
   a human operator and because the layout of the data can vary from
   device to device and between different software versions.  Despite
   its ubiquity, this interface has never been standardized and is
   unlikely to ever be standardized.  CLI standardization is not
   considered as a candidate solution for the problems motivating I2RS.

   The second most popular interface for interrogation of a device's
   state, statistics, and configuration is the Simple Network Management
   Protocol (SNMP) and a set of relevant standards-based and proprietary
   Management Information Base (MIB) modules.  SNMP has a strong history
   of being used by network managers to gather statistical and state
   information about devices, including their routing systems.  However,
   SNMP is very rarely used to configure a device or any of its systems
   for reasons that vary depending upon the network operator.  Some
   example reasons include complexity, the lack of desired configuration
   semantics (e.g., configuration rollback, sandboxing, or configuration
   versioning) and the difficulty of using the semantics (or lack
   thereof) as defined in the MIB modules to configure device features.
   Therefore, SNMP is not considered as a candidate solution for the
   problems motivating I2RS.

   Finally, the IETF's Network Configuration Protocol (NETCONF)
   [RFC6241] has made many strides at overcoming most of the limitations
   around configuration that were just described.  However, as a new
   technology and with the initial lack of standard data models, the
   adoption of NETCONF has been slow.  As needed, I2RS will identify and
   define information and data models to support I2RS applications.
   Additional extensions to handle multi-headed control may need to be
   added to NETCONF and/or appropriate data models.

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Acknowledgements

   The authors would like to thank Ken Gray, Ed Crabbe, Nic Leymann,
   Carlos Pignataro, Kwang-koog Lee, Linda Dunbar, Sue Hares, Russ
   Housley, Eric Grey, Qin Wu, Stephen Kent, Nabil Bitar, Deborah
   Brungard, and Sarah Banks for their suggestions and review.

Authors' Addresses

   Alia Atlas (editor)
   Juniper Networks

   Email: akatlas@juniper.net

   Thomas D. Nadeau (editor)
   Brocade

   Email: tnadeau@lucidvision.com

   Dave Ward
   Cisco Systems

   Email: wardd@cisco.com

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