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Versions: (draft-ward-i2rs-framework) 00 01 02 draft-ietf-i2rs-architecture

Network Working Group                                           A. Atlas
Internet-Draft                                          Juniper Networks
Intended status: Informational                                J. Halpern
Expires: December 30, 2013                                      Ericsson
                                                                S. Hares
                                                                   ADARA
                                                                 D. Ward
                                                           Cisco Systems
                                                           June 28, 2013


        An Architecture for the Interface to the Routing System
                    draft-atlas-i2rs-architecture-00

Abstract

   This document describes an architecture for a standard, programmatic
   interface for state transfer in and out of the Internet's routing
   system.  It describes the basic architecture, the components, and
   their interfaces with particular focus on those to be standardized as
   part of I2RS.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 30, 2013.

Copyright Notice

   Copyright (c) 2013 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Functional Overview . . . . . . . . . . . . . . . . . . .   3
     1.2.  Architectural Overview  . . . . . . . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   7
   3.  Key Architectural Properties  . . . . . . . . . . . . . . . .   9
     3.1.  Simplicity  . . . . . . . . . . . . . . . . . . . . . . .   9
     3.2.  Extensibility . . . . . . . . . . . . . . . . . . . . . .   9
     3.3.  Model-Driven Programmatic Interfaces  . . . . . . . . . .  10
     3.4.  Authorization and Authentication  . . . . . . . . . . . .  10
   4.  Network Applications and I2RS Client  . . . . . . . . . . . .  10
     4.1.  Example Network Application: Topology Manager . . . . . .  11
   5.  I2RS Agent Role and Functionality . . . . . . . . . . . . . .  11
     5.1.  Relationship to its Routing Element . . . . . . . . . . .  11
     5.2.  State Storage . . . . . . . . . . . . . . . . . . . . . .  12
       5.2.1.  Starting and Ending . . . . . . . . . . . . . . . . .  12
       5.2.2.  Reversion . . . . . . . . . . . . . . . . . . . . . .  13
     5.3.  Interactions with Local Config  . . . . . . . . . . . . .  13
     5.4.  Routing Components and Associated I2RS Services . . . . .  13
       5.4.1.  Unicast and Multicast RIB and LFIB  . . . . . . . . .  14
       5.4.2.  IGPs, BGP and Multicast Protocols . . . . . . . . . .  14
       5.4.3.  MPLS  . . . . . . . . . . . . . . . . . . . . . . . .  15
       5.4.4.  Policy and QoS Mechanisms . . . . . . . . . . . . . .  15
   6.  I2RS Client Agent Interface . . . . . . . . . . . . . . . . .  15
     6.1.  Protocol Structure  . . . . . . . . . . . . . . . . . . .  15
     6.2.  Channel . . . . . . . . . . . . . . . . . . . . . . . . .  16
     6.3.  Negotiation . . . . . . . . . . . . . . . . . . . . . . .  16
     6.4.  Identity and Security Role  . . . . . . . . . . . . . . .  16
     6.5.  Connectivity  . . . . . . . . . . . . . . . . . . . . . .  16
     6.6.  Notifications . . . . . . . . . . . . . . . . . . . . . .  17
     6.7.  Information collection  . . . . . . . . . . . . . . . . .  17
     6.8.  Multi-Headed Control  . . . . . . . . . . . . . . . . . .  18
     6.9.  Transactions  . . . . . . . . . . . . . . . . . . . . . .  18
   7.  Manageability Considerations  . . . . . . . . . . . . . . . .  19
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  19
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  19
   11. Informative References  . . . . . . . . . . . . . . . . . . .  20
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20





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1.  Introduction

   Routers that form the Internet's routing infrastructure maintain
   state at various layers of detail and function.  For example, a
   typical router maintains a Routing Information Base (RIB), and
   implements routing protocols such as OSPF, ISIS, BGP to exchange
   protocol state and other information about the state of the network
   with other routers.

   A router also has information that may be required for applications
   to understand the network, verify that programmed state is installed
   in the forwarding plane, measure the behavior of various flows,
   routes or forwarding entries, as well as understand the configured
   and active states of the router.  Furthermore, routers are typically
   configured with procedural or policy-based instructions that tell
   them how to convert all of this information into the forwarding
   operations that are installed in the forwarding plane.  It is also
   the active state information that describes the expected and observed
   operational behavior of the router.

   This document sets out an architecture for a common, standards-based
   interface to this information.  This Interface to the Routing System
   (I2RS) facilitates control and diagnosis of the RIB manager's state,
   as well as enabling network applications to be built on top of
   today's routed networks.  The I2RS is a programmatic asynchronous
   interface for transferring state into and out of the Internet's
   routing system, and recognizes that the routing system and a router's
   OS provide useful mechanisms that applications could harness to
   accomplish application-level goals.

   Fundamental to the I2RS are clear data models that define the
   semantics of the information that can be written and read.  The I2RS
   provides a framework for registering for and requesting the
   appropriate information for each particular application.  The I2RS
   provides a way for applications to customize network behavior while
   leveraging the existing routing system.

   The I2RS, and therefore this document, is specifically focused on an
   interface for routing and forwarding data.

1.1.  Functional Overview

   There are four key aspects to the I2RS.  First, the interface is a
   programmatic interface meaning that it is asynchronous and offers
   fast, interactive access.  Second, the I2RS gives access to
   information and state that is not usually configurable or modeled in
   existing implementations or configuration protocols.  Third, the I2RS
   gives applications the ability to learn additional, structured,



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   filterable information and events from the router.  Fourth, the I2RS
   will be data-model driven to facilitate extensibility and provide
   standard data-models to be used by network applications.

   I2RS is described as an asynchronous programmatic interface; the key
   properties of which are described in Section 5 of
   [I-D.atlas-i2rs-problem-statement].

   Such an interface facilitates the specification of implicitly non-
   permanent state into the routing system, that can optionally be made
   permanent.  In addition, the extraction of that information and
   additional dynamic information from the routing system is a critical
   component of the interface.  A non-routing protocol or application
   could inject state into a network element's OS via the state-
   insertion aspects of the interface and that state could then be
   distributed in a routing or signaling protocol.

   There are several types of information that the I2RS will facilitate
   an I2RS Client obtaining.  These range from dynamic event
   notifications (e.g. changes to a particular next-hop, interface up/
   down, etc.)to information collection streams (statistics, topology,
   route changes, etc) to simply read operations.  The I2RS provides the
   ability for an I2RS client to request filtered and thresholded
   information as well as events.

   The existing mechanisms, such as SNMP and NetConf, that allow state
   to be written and read do not meet all of the key properties given in
   [I-D.atlas-i2rs-problem-statement] for I2RS.  The overhead of
   infrastructure is also quite high and many MIBs do not, in definition
   or practice, allow writing of state.  There is also very limited
   capability to add new application-specific state to be distributed
   via the routing system.

   ForCES is another data-model-driven method for writing state into a
   router, but its focus is on the forwarding plane.  By focusing on the
   forwarding plane, it requires that the forwarding plane be modeled
   and programmable and ignores the existence and intelligence of the
   router OS and routing system.  ForCES provides a lower-level
   interface than I2RS is intended to address.

1.2.  Architectural Overview










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   The figure in Figure 1 shows the basic architecture for I2RS.  Inside
   a Routing Element, the I2RS agent interacts with both the routing
   subsystem and with local configuration.  A network application uses
   an I2RS client to communicate with one or more I2RS agents on their
   routing elements.  The scope of I2RS is to define the interactions
   between the I2RS agent and the I2RS client and the associated proper
   behavior of the I2RS agent and I2RS client.


          ***********************          ***********************
          *    Application A    *          *    Application B    *
          *                     *          *                     *
          *  +----------------+ *          *  +----------------+ *
          *  |   Client A     | *          *  |   Client B     | *
          *  +----------------+ *          *  +----------------+ *
          ******* ^ *************          ***** ^ ****** ^ ******
                  |                              |        |
                  |       -----------------------|        |
                  |       |                               |
          ******* v ***** v ************   ************** v **********
          *  +----------------+        *   *  +----------------+     *
          *  |     Agent 1    |        *   *  |    Agent 2     |     *
          *  +----------------+        *   *  +----------------+     *
          *     ^        ^   ^         *   *    ^        ^   ^       *
          *     |        |   |         *   *    |        |   |       *
          *     v        |   v         *   *    v        |   v       *
          * ***********  |  ********** *   * *********** | ********* *
          * * Routing *  |  * Local  * *   * * Routing * | * Local * *
          * ***********  |  * Config * *   * *********** | * Config* *
          *              |  ********** *   *             | ********* *
          *              v             *   *             v           *
          *       ************         *   *      ***********        *
          *       *  Dynamic *         *   *      * Dynamic *        *
          *       *  System  *         *   *      * System  *        *
          *       *  State   *         *   *      * State   *        *
          *       ************         *   *      ***********        *
          *                            *   *                         *
          *  Routing Element 1         *   *  Routing Element 2      *
          ******************************   ***************************


             Figure 1: Architecture of I2RS clients and agents

   Routing Element:   A Routing Element implements at least some portion
      of the routing system.  It does not need to have a forwarding
      plane associated with it.  Examples of Routing Elements can
      include:




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         A router with a forwarding plane and RIB Manager that runs
         ISIS, OSPF, BGP, PIM, etc.

         A server that runs BGP as a Route Reflector

         An LSR that implements RSVP-TE, OSPF-TE, and PCEP and has a
         forwarding plane and associated RIB Manager.

         A server that runs ISIS, OSPF, BGP and uses ForCES to control a
         remote forwarding plane.

      A Routing Element may be locally managed, whether via CLI, SNMP,
      or NetConf.

   Routing:   This block represents that portion of the Routing Element
      that implements part of the Internet routing system.  It includes
      not merely standardized protocols (i.e. IS-IS, OSPF, BGP, PIM,
      RSVP-TE, LDP, etc.), but also the RIB Manager layer.

   Local Config:   A Routing Element will provide the ability to
      configure and manage it.  The Local Config may be provided via a
      combination of CLI, NetConf, SNMP, etc.  The black box behavior
      for interactions between the state that I2RS installs into the
      routing element and the Local Config must be defined.

   Dynamic System State:   An I2RS agent needs access to state on a
      routing element beyond what is contained in the routing subsystem.
      Such state may include various counters, statistics, and local
      events.  How this information is provided to the I2RS agent is out
      of scope, but the standardized information and data models for
      what is exposed are part of I2RS.

   I2RS Agent:   The I2RS agent implements the I2RS protocol(s) and
      interacts with the routing element to provide specified behavior.

   Application:   A network application that needs to manipulate the
      network to achieve its service requirements.

   I2RS Client:   The I2RS client implements the I2RS protocol(s).  It
      interacts with other elements of the policy, provisioning, and
      configuration system by means outside of the scope of the I2RS
      effort.  It interacts with the I2RS clients to collect information
      from the routing and forwarding system.  Based on the information
      and the policy oriented interactions, the I2RS client may also
      interact with the I2RS agent to modify the state of the routing
      system the client interacts with to achieve operational goals.





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   As can be seen in Figure 1, an I2RS client can communicate with
   multiple I2RS agents.  The application associated with an I2RS client
   may connect to one or more I2RS agents based upon its needs.
   Similarly, an I2RS agent may communicate with multiple I2RS clients -
   whether to respond to their requests, to send notifications, etc.
   Timely notifications are critical so that several simultaneously
   operating applications have up-to-date information on the state of
   the network.

   As can also be seen in Figure 1, an I2RS Agent may communicate with
   multiple clients.  Each client may send the agent a variety of write
   operations.  The handling of this situation has been a source of
   discussion in the working group.  In order to keep the protocol
   simple, the current view is that two clients should not be attempting
   to write (modify) the same piece of information.  Such collisions may
   happen, but are considered error cases that should be resolved by the
   network application layer.

   Multiple I2RS clients may need to supply data into the same list
   (e.g. a prefix or filter list); this is not considered an error and
   must be correctly handled.

   The architectural goal for the I2RS is that such errors should
   produce predictable behaviors, and be reportable to interested
   clients.  The details of the associated policy is discussed in
   Section 6.8.  The same policy mechanism (simple priority per I2RS
   client) applies to interactions between the I2RS agent and the CLI/
   SNMP/NetConf as described in Section 5.3.

   In addition it can be noted that there may be indirect interactions
   between write operations.  Detection and avoidance of such
   interactions is outside the scope of the I2RS work and is left to
   agent design and implementation for now.  [[Editor's note: This topic
   needs more discussion in the working group.]]

2.  Terminology

   The following terminology is used in this document.

   agent or I2RS Agent:   An I2RS agent provides the supported I2RS
      services to the local system's routing sub-systems.  The I2RS
      agent understands the I2RS protocol and can be contacted by I2RS
      clients.








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   client or I2RS Client:   A client speaks the I2RS protocol to
      communicate with I2RS Agents and uses the I2RS services to
      accomplish a task as instructed by the client's local application.
      An I2RS client can be seen as the part of an application that
      supports I2RS and could be a software library.

   service or I2RS Service:   For the purposes of I2RS, a service refers
      to a set of related state access functions together with the
      policies that control its usage.  The expectation is that a
      service will be represented by a data-model.  For instance, 'RIB
      service' could be an example of a service that gives access to
      state held in a device's RIB.

   read scope:   The set of information which the I2RS client is
      authorized to read.  This access includes the permission to see
      the existence of data and the ability to retrieve the value of
      that data.

   write scope:   The set of field values which the I2RS client is
      authorized to write (i.e. add, modify or delete).  This access can
      restrict what fields can be modified or created, and what specific
      value sets and ranges can be installed.

   scope:   When unspecified as either read scope or write scope, the
      term scope applies to both the read scope and write scope.

   resources:   A resource is an I2RS-specific use of memory, storage,
      or execution that a client may consume due to its I2RS operations.
      The amount of each such resource that a client may consume in the
      context of a particular agent can be constrained.  An example of
      such a resource could include the number of notifications
      registered for.  These are not protocol-specific resources or
      network-specific resources.

   role or security role:   A security role specifies the scope,
      resources, priorities, etc. that a client or agent has.

   identity:   A client is associated with exactly one specific
      identity.  State can be attributed to a particular identity.  It
      is possible for multiple communication channels to use the same
      identity; in that case, the assumption is that the associated
      client is coordinating such communication.









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3.  Key Architectural Properties

3.1.  Simplicity

   There have been many efforts over the years to improve the access to
   the information known to the routing and forwarding system.  Making
   such information visible and usable to network management and
   applications has many well-understood benefits.  There are two
   related challenges in doing so.  The span of information potentially
   available is very large.  And the variation in the structure and
   kinds of operations tends to introduce protocol complexity.

   Having noted that, it is also critical to the utility of I2RS that it
   be easily deployed and robust.  Complexity in the protocol hinders
   implementation, robustness, and deployability.  Also, complexity in
   the data models tends to actually make it harder to extend rather
   than easier.

   Thus, one of the key aims for I2RS is the keep the protocol and
   modeling architecture simple.  So for each architectural component or
   aspect, we ask ourselves "do we need this complexity, or is the
   behavior merely nice to have?"

3.2.  Extensibility

   There are several ways that the scope of the I2RS work is being
   restricted in the interests of achieving a deliverable and deployable
   result.  We are only looking at the models to be used over the single
   identified interface.  We are only looking at modeling a subset of
   the data of interest.  And we are probably only representing a subset
   of the operations that may eventually be needed (although there is
   some hope that we are closer on that aspect than others to what is
   needed.)

   At the same time, it is clearly desirable for the data models and
   protocol operations we define in the I2RS to be useful the in more
   general settings.  It should be easy to integrate data models from
   the I2RS with other data.  Other work should be able to easily extend
   it to represent additional aspects of the network elements or network
   systems.  Hence, the data model and protocol definitions need to be
   designed to be highly extensible, preferably in a regular and simple
   fashion.









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3.3.  Model-Driven Programmatic Interfaces

   A critical component of I2RS is the standard information and data
   models with their associated semantics.  While many routing protocols
   are standardized, associated data models for them are not yet
   available.  Instead, each router uses different information,
   mechanisms, and CLI which makes a standard interface for use by
   applications extremely cumbersome to develop and maintain.  Well-
   known data modeling languages exist and may be used for defining the
   necessary data models for I2RS.

   There are several key benefits for I2RS in using model-driven
   architecture and protocol(s).  First, it allows for transferring
   data-models whose content is not explicitly implemented or
   understood.  Second, tools can automate checking and manipulating
   data; this is particularly valuable for both extensibility and for
   the ability to easily manipulate and check proprietary data-models.

   The different services provided by I2RS can correspond to separate
   data-models.  An I2RS agent can indicate which data-models are
   supported.

3.4.  Authorization and Authentication

   All control exchanges between the I2RS client and agent MUST be
   authenticated and integrity protected (so that the contents cannot be
   changed without detection).  Manipulation of the system has to be
   accurately attributable.  Architecturally, even information
   collection and notification should be protected, although this is
   subject to engineering tradeoffs during the design.

   I2RS Agents, in performing information collection and manipulation,
   will be acting on behalf of the I2RS clients.  As such, they will
   operate based on the lower of the two permissions of the agent itself
   and of the client.

   I2RS clients may be operating on behalf of other entities, in any one
   of a range of broker models.  While those identities are not need for
   authorization, they should still be provided by the I2RS client to
   the I2RS agent for purposes of tracking attribution of operations.

4.  Network Applications and I2RS Client

   An I2RS Client has a standardized interface that uses the I2RS
   protocol(s) to communicate with I2RS Agents.  The interface between
   an I2RS client and the network applications is outside the scope of
   I2RS.




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   When an I2RS Client interacts with multiple network applications,
   that I2RS Client is behaving as a broker and may indicate this to the
   I2RS Agents by, for example, specifying a secondary identity to allow
   improved troubleshooting.

   A network application that uses an I2RS client may also be considered
   a routing element and include an I2RS agent for interactions.
   However, where the needed information and data models for that upper
   interface differs from that of a conventional routing element, those
   models are, at least initially, out of scope for I2RS.

4.1.  Example Network Application: Topology Manager

   One example of such an application is a Topology Manager.  Such an
   application includes an I2RS client which uses the I2RS protocol to
   collect information about the state of the network.  The Topology
   Manager would collect device and interface state from devices it
   interacts with directly.  It also collects routing configuration and
   operation data from those devices.  Most importantly, it collects
   information about the routing system, including the contents of the
   IGP (e.g. IS-IS or OSPF) and BGP data sets.  This information is
   provided to the I2RS client using the I2RS data models and protocols.

   The Topology Manager may be an integral part of an application.  It
   would build internal data structures, and use the collected data to
   drive applications like path computations or anomalous routing
   detection.  Alternatively, the Topology manager could combine the
   I2RS collected data with other information, abstract the result, and
   provide a coherent picture of the network state over another
   interface.  That interface might use the same I2RS protocols, and
   could use extensions of the I2RS data models.  Developing such
   mechanisms is outside the initial scope of the I2RS work.

5.  I2RS Agent Role and Functionality

   The I2RS Agent is part of a routing element.  As such, it has
   relationships with that routing element as a whole, and with various
   components of that routing element.

5.1.  Relationship to its Routing Element

   A Routing Element may be implemented with a wide variety of different
   architectures: an integrated router, a split architecture,
   distributed architecture, etc.  The architecture does not need to
   affect the general I2RS agent behavior.

   For scalability and generality, the I2RS agent may be responsible for
   collecting and delivering large amounts of data from various parts of



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   the routing element.  Those parts may or may not actually be part of
   a single physical device.  Thus, for scalability and robustness, it
   is important that the architecture allow for a distributed set of
   reporting components providing collected data from the I2RS agent
   back to the relevant I2RS clients.  As currently envisioned, a given
   I2RS agent would have only one locus per I2RS service for
   manipulation of routing element state; distributing the manipulations
   would inducing complications and fragility instead of scalability and
   robustness.

5.2.  State Storage

   State modification requests are sent to the I2RS agent in a network
   element by I2RS clients.  The I2RS agent is responsible for applying
   these changes to the system.  One dimension of the storage for I2RS
   Clients requests is how much data must the I2RS Agent store about
   this configuration, and with what persistence.  There are range of
   possible answers.  One extreme is where it stores nothing, cannot
   indicate why or by whom state was placed into the routing element,
   and relies on clients reapplying things in all possible cases.  The
   other extreme is where multiple possibilities are stored and managed,
   as is done in the RIB for routes with a preference or priority to
   pick between the routes.  This architecture tries to provide
   sufficient power to keep client operations effective, while still
   being simple to implement in the I2RS Agent, and to observe
   meaningfully during operation.

   The I2RS agent stores the set of operations it has applied.  Simply,
   the I2RS agent stores who did what operation to which entity.  New
   changes replace any data about old ones.  If an I2RS client does an
   operation to remove some state, that state is removed and the I2RS
   agent stores no more information about it.  This allows any
   interested party to determine what the current effect of I2RS on the
   system is, and why.  Meaningful logging is also recommended.

   The I2RS Agent will not attempt to retain or reapply state across
   routing element reboot.  Determination of whether state still applies
   depends heavily on the causes of reboots, and reapplication is at
   least as likely to cause problems as it is to provide for correct
   operation.  [[Editor's note: This topics needs more discussion in the
   working group.]]

5.2.1.  Starting and Ending

   An I2RS client applies changes via the I2RS interface based on policy
   and other application inputs.  While these changes may be of the form
   "do this now, and leave it there forever", they are frequently driven
   by other conditions which may have start times, stop times, or are



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   only to be used under certain conditions.  The I2RS interface
   protocol could be designed to allow an I2RS Client to provide a wide
   range of such conditional information to the I2RS Agent for
   application.  At the other extreme, the I2RS client could provide all
   such functionality based on its own clocking and network event
   reporting from the relevant I2RS Agents.

   Given that the complexity of possible conditions is very large, and
   that some conditions may even cross network element boundaries,
   clearly some degree of handling must be provided on the I2RS client.
   As such, this architecture takes the view that all the complexity
   associated with this should be left to the I2RS client.  This
   architectural view does mean that reliability of the communication
   path between the I2RS client and I2RS agent is critical.  [[Editor's
   note: This requires more discussion in the working group.]]

5.2.2.  Reversion

   An I2RS Agent may decide that some state should no longer be applied.
   An I2RS Client may instruct an Agent to remove state it has applied.
   In all such cases, the state will revert to what it would have been
   without the I2RS; that state is generally whatever was specified via
   the CLI, NetConf, SNMP, etc.  I2RS Agents will not store multiple
   alternative states, nor try to determine which one among such a
   plurality it should fall back to.  Thus, the model followed is not
   like the RIB, where multiple routes are stored at different
   preferences.

5.3.  Interactions with Local Config

   As described above, local device configuration is considered to be
   separate from the I2RS data store.  Thus, changes may originate from
   either source.  Policy (i.e. comparisons between a CLI/SNMP/NetConf
   priority and a I2RS agent priority) can determine whether the local
   configuration should overwrite any state written by I2RS and
   attributed to a particular I2RS Client or whether I2RS as attributed
   to a particular I2RS Client can overwrite local configuration state.

   Simply allowing the most recent state to prevail could cause race
   conditions where the final state is not repeatably deterministic.
   One important aspect is that if CLI/SNMP/NetConf changes data that is
   subject to monitoring or manipulating by I2RS, then the system has to
   be instrumented enough to provide suitable I2RS notifications of
   these changes.

5.4.  Routing Components and Associated I2RS Services





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   For simplicity, each logical protocol or set of functionality that be
   compactly described in a separable information and data model is
   considered as a separate I2RS Service.  A routing element need not
   implement all routing components described nor provide the associated
   I2RS services.  The initial services included in the I2RS
   architecture are as follows.

5.4.1.  Unicast and Multicast RIB and LFIB

   Network elements concerned with routing IP maintain IP unicast RIBs.
   Similarly, there are RIBs for IP Multicast, and a Label Information
   Base (LIB) for MPLS.  The I2RS Agent needs to be able to read and
   write these sets of data.  The I2RS data model has to include models
   for this information.

   In particular, with regard to writing this information, the I2RS
   Agent should use the same mechanisms that the routing element already
   uses to handle RIB input from multiple sources, so as to compatibly
   change the system state.

   The multicast state added to the multicast RIB does not need to match
   to well-known protocol installed state.  The I2RS Agent can create
   arbitrary replication state in the RIB, subject to the advertised
   capabilities of the routing element.

5.4.2.  IGPs, BGP and Multicast Protocols

   In addition to interacting with the consolidated RIB, the I2RS agent
   needs to interact with the individual routing protocols on the
   device.  This interaction includes a number of different kinds of
   operations:

   o  reading the various internal rib(s) of the routing protocol is
      often helpful for understanding the state of the network.
      Directly writing these protocol-specific RIBs or databases is NOT
      part of the system.

   o  reading the various pieces of policy information the particular
      protocol instance is using to drive its operations.

   o  writing policy information such as interface attributes that are
      specific to the routing protocol or BGP policy that may indirectly
      manipulate attributes of routes carried in BGP.

   o  writing routes or prefixes to be advertised via the protocol.

   o  joining/removing interfaces from the multicast trees




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   For example, the interaction with OSPF might include modifying the
   local routing element's link metrics, announcing a locally-attached
   prefix, or reading some of the OSPF link-state database.  However,
   modifying the link-state database itself would clearly not be
   permitted; that could lead to inconsistency.

5.4.3.  MPLS

   The I2RS Agent will need to interact with the knobs that policy
   attributes that control LDP operation as well as RSVP-TE based LSPs.
   To avoid duplication, the I2RS interface will not duplicate the path
   computation and active path setup components of the PCE protocols.

5.4.4.  Policy and QoS Mechanisms

   Many network elements have separate policy and QoS mechanisms,
   including knobs which affect local path computation and queue control
   capabilities.  These capabilities vary widely across implementations,
   and I2RS cannot model the full range of information collection or
   manipulation of these attributes.  A core set does need to be
   included in the I2RS data models and in the expected interfaces
   between the I2RS Agent and the network element, in order to provide
   basic capabilities and the hooks for extensibility.

6.  I2RS Client Agent Interface

6.1.  Protocol Structure

   One could view I2RS merely as a way to talk about the existing
   network management interfaces to a network element.  That would be
   quite limiting, and would have trouble meeting the requirements
   elucidated elsewhere.  One could also view it as a collection of
   protocols, some existing and some new, that meet the needs.  While
   that could be made to work, the complexity of such a mechanism would
   be quite high.  One would need to develop means to coordinate
   information across a set of protocols that were not designed to work
   together.  As a result, this architecture views the I2RS interface as
   an interface supporting a single control and data exchange protocol.
   That protocol may use several underlying transports (TCP, SCTP,
   DCCP), with suitable authentication and integrity protection
   mechanisms.  Whatever transport is used for the data exchange, it
   must also support suitable congestion control mechanisms.









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6.2.  Channel

   The uses of a single I2RS protocol does not imply that only one
   channel of communication is needed.  There may be a range of
   reliability needs, and to support the scaling there may need to be
   channels from multiple parts of a routing element.  These will all
   use the date exchange protocol, and establishment of additional
   channels for communication will be coordinated between the I2RS
   client and the I2RS agent.

6.3.  Negotiation

   Protocol support capabilities will vary across I2RS Clients and
   Routing Elements supporting I2RS Agents.  As such, it is likely that
   capability negotiation (such as which transports are supported beyond
   the minimum required to implement) will be necessary.  It is
   important that such negotiations be kept simple and robust, as such
   mechanisms are often a source of difficulty in implementation and
   deployment.

6.4.  Identity and Security Role

   Each I2RS Client will have an identity; it can also have secondary
   identities to be used for troubleshooting.  Via authentication and
   authorization mechanisms, the I2RS agent will have a specific scope
   for reading data, for writing data, and limitations on the resources
   that can be consumed.  The scopes need to specify both the data and
   the value ranges.

6.5.  Connectivity

   A client does not need to maintain an active communication channel
   with an agent.  Therefore, an agent may need to open a communication
   channel to the client to communicate previously requested
   information.  The lack of an active communication channel does not
   imply that the associated client is non-functional.  When
   communication is required, the agent or client can open a new
   communication channel.

   State held by an agent that is owned by a client should not be
   removed or cleaned up when a client is no longer communicating - even
   if the agent cannot successfully open a new communication channel to
   the client.

   There are two different assumptions that can apply to handling dead
   clients.  The first is that the network application layer will detect
   a dead network application and either restart that network
   application or clean up any state left behind.  The second is to



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   allow state expiration, expressed as a policy associated with the
   I2RS client's role.  The state expiration could occur after there has
   been no successful communication channel to or from the I2RS client
   for the policy-specified duration.

6.6.  Notifications

   As with any policy system interacting with the network, the I2RS
   Agent needs to be able to receive notifications of changes in network
   state.  Notifications here refers to changes which are unanticipated,
   represent events outside the control of the systems (such as
   interface failures on controlled devices), or are sufficiently sparse
   as to be anomalous in some fashion.

   Such events may be of interest to multiple I2RS Clients controlling
   data handled by an I2RS Agent, and to multiple other I2RS clients
   which are collecting information without exerting control.  The
   architecture therefore requires that it be practical for I2RS Clients
   to register for a range of notifications, and for the I2R Agents to
   send notifications to a number of Clients.

   As the I2RS is developed, it is likely that a management information-
   model and data-model will be required to describe event notifications
   for general or I2RS errors.

   For performance and scaling by the I2RS client and general
   information privacy, an I2RS Client needs to be able to register for
   just the events it is interested in.  It is also possible that I2RS
   might might provide a stream of notifications via a publish/subscribe
   mechanism that is not amenable to having the I2RS agent do the
   filtering.

6.7.  Information collection

   One of the other important aspects of the I2RS is that it is intended
   to simplify collecting information about the state of network
   elements.  This includes both getting a snapshot of a large amount of
   data about the current state of the network element, and subscribing
   to a feed of the ongoing changes to the set of data or a subset
   thereof.  This is considered architecturally separate from
   notifications due to the differences in information rate and total
   volume.









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6.8.  Multi-Headed Control

   As was described earlier, an I2RS Agent interacts with multiple I2RS
   Clients who are actively controlling the network element.  From an
   architecture and design perspective, the assumption is that by means
   outside of this system the data to be manipulated within the network
   element is appropriately partitioned so that any given piece of
   information is only being manipulated by a single I2RS Client.

   Nonetheless, unexpected interactions happen and two (or more) I2RS
   clients may attempt to manipulate the same piece of data.  This is
   considered an error case.  This architecture does not attempt to
   determine what the right state of data is in such a collision Rather,
   the architecture mandates that there be decidable means by which I2RS
   Agents will handle the collisions.  The current recommendation is to
   have a simple priority associated with each I2RS clients, and the
   highest priority change remains in effect.  In the case of priority
   ties, the first client whose attribution is associated with the data
   will keep control

   In order for this to be useful for I2RS Clients, it is important that
   it be possible for an I2RS Client to register for changes to any I2RS
   manipulatable data that it may care about.  The I2RS client may then
   respond to the situation as it sees fit.

6.9.  Transactions

   In the interest of simplicity, the I2RS architecture does not include
   multi-message atomicity and rollback mechanisms.  Rather, it includes
   a small range of error handling for a set of operations included in a
   single message.  An I2RS Client may indicate one of the following
   three error handling for a given message with multiple operations
   which it sends to an I2RS Agent:

   Perform all or none:   This traditional SNMP semantic indicates that
      other I2RS agent will keep enough state when handling a single
      message to roll back the operations within that message.  Either
      all the operations will succeed, or none of them will be applied
      and an error message will report the single failure which caused
      the not to be applied.  This is useful when there are, for
      example, mutual dependencies across operations in the message.

   Perform until error:   In this case, the operations in the message
      are applied in order.  When an error occurs, no further operations
      are applied, and an error is returned indicating the failure.
      This is useful if there are dependencies among the operations and
      they can be topologically sorted.




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   Perform all:   In this case, the I2RS Agent will attempt to perform
      all the operations in the message, and will return error
      indications for each one that fails.  This is useful when there is
      no dependency across the operation, or where the client would
      prefer to sort out the effect of errors on its own.

   In the interest of robustness and clarity of protocol state, the
   protocol will include an explicit reply to modification operations
   even when they fully succeed.

7.  Manageability Considerations

   Manageability plays a key aspect in I2RS.  Some initial examples
   include:

   Resource Limitations:   Using I2RS, applications can consume
      resources, whether those be operations in a time-frame, entries in
      the RIB, stored operations to be triggered, etc.  The ability to
      set resource limits based upon authorization is important.

   Configuration Interactions:   The interaction of state installed via
      the I2RS and via a router's configuration needs to be clearly
      defined.  As described in this architecture, a simple priority
      that is configured can be used to express the desired policy.

8.  Security Considerations

   This framework describes interfaces that clearly require serious
   consideration of security.  The ability to identify, authenticate and
   authorize applications that wish to install state is necessary and
   briefly described in Section 3.4.  Security of communications from
   the applications is also required as discussed in Section 6.1.
   Scopes for reading and writing data specified in the context of the
   data models and the value ranges are discussed briefly in
   Section 6.4.

9.  IANA Considerations

   This document includes no request to IANA.

10.  Acknowledgements

   Significant portions of this draft came from draft-ward-i2rs-
   framework-00 and draft-atlas-i2rs-policy-framework-00.  The authors
   would like to acknowledge Tom Nadeau, who was a co-author on draft-
   ward-i2rs-framework-00.





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   The authors would like to thank Nitin Bahadur, Shane Amante, and Ken
   Gray for their suggestions and review.

11.  Informative References

   [I-D.atlas-i2rs-problem-statement]
              Atlas, A., Nadeau, T., and D. Ward, "Interface to the
              Routing System Problem Statement", draft-atlas-i2rs-
              problem-statement-00 (work in progress), February 2013.

Authors' Addresses

   Alia Atlas
   Juniper Networks
   10 Technology Park Drive
   Westford, MA  01886
   USA

   Email: akatlas@juniper.net


   Joel Halpern
   Ericsson

   Email: Joel.Halpern@ericsson.com


   Susan Hares
   ADARA

   Email: shares@ndzh.com


   Dave Ward
   Cisco Systems
   Tasman Drive
   San Jose, CA  95134
   USA

   Email: wardd@cisco.com











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