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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: February 14, 2014                                      Ericsson
                                                                S. Hares
                                                                   ADARA
                                                                 D. Ward
                                                           Cisco Systems
                                                               T. Nadeau
                                                        Juniper Networks
                                                         August 13, 2013


        An Architecture for the Interface to the Routing System
                    draft-atlas-i2rs-architecture-02

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 February 14, 2014.

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



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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Functional Overview . . . . . . . . . . . . . . . . . . .   3
     1.2.  Architectural Overview  . . . . . . . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   7
   3.  Key Architectural Properties  . . . . . . . . . . . . . . . .   8
     3.1.  Simplicity  . . . . . . . . . . . . . . . . . . . . . . .   8
     3.2.  Extensibility . . . . . . . . . . . . . . . . . . . . . .   9
     3.3.  Model-Driven Programmatic Interfaces  . . . . . . . . . .   9
     3.4.  Authorization and Authentication  . . . . . . . . . . . .  10
   4.  Network Applications and I2RS Client  . . . . . . . . . . . .  10
     4.1.  Example Network Application: Topology Manager . . . . . .  10
   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 . . . . . . . . . . . . . . . . . . . . . . . . .  15
     6.3.  Negotiation . . . . . . . . . . . . . . . . . . . . . . .  16
     6.4.  Identity and Security Role  . . . . . . . . . . . . . . .  16
       6.4.1.  Client Redundancy . . . . . . . . . . . . . . . . . .  16
     6.5.  Connectivity  . . . . . . . . . . . . . . . . . . . . . .  16
     6.6.  Notifications . . . . . . . . . . . . . . . . . . . . . .  17
     6.7.  Information collection  . . . . . . . . . . . . . . . . .  18
     6.8.  Multi-Headed Control  . . . . . . . . . . . . . . . . . .  18
     6.9.  Transactions  . . . . . . . . . . . . . . . . . . . . . .  18
   7.  Manageability Considerations  . . . . . . . . . . . . . . . .  19
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  19
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  20
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  20
   11. Informative References  . . . . . . . . . . . . . . . . . . .  20



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   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20

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 as much as desired.

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

1.1.  Functional Overview

   There are four key aspects to the I2RS.  First, the interface is a
   programmatic interface which needs to be asynchronous and offers
   fast, interactive access.  Second, the I2RS gives access to
   information and state that is not usually configurable or modeled in



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   existing implementations or configuration protocols.  Third, the I2RS
   gives applications the ability to learn additional, structured,
   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 routing element via the state-insertion
   aspects of the I2RS and that state could then be distributed in a
   routing or signaling protocol and/or be used locally (e.g. to program
   the co-located forwarding plane).

   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.

1.2.  Architectural Overview

   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     | *
          *  +----------------+ *          *  +----------------+ *
          ******* ^ *************          ***** ^ ****** ^ ******
                  |                              |        |
                  |       -----------------------|        |



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                  |       |                               |
          ******* 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:

         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.



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   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 agents 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.

   As can be seen in Figure 1, an I2RS client can communicate with
   multiple I2RS agents.  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 applications and management systems.







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   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 nuances so that writers do not
   normally collide should be handled in the information models.

   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 must 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.

   client or I2RS Client:   A client speaks the I2RS protocol to
      communicate with I2RS Agents and uses the I2RS services to
      accomplish a task.  An I2RS client can be seen as the part of an
      application that uses and 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 their 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.







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   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 data 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 based upon the
      client's security role.  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.

   secondary identity:   An I2RS Client may supply a secondary opaque
      identity that is not interpreted by the I2RS Agent.  An example
      use is when the I2RS Client is a go-between for multiple
      applications and it is necessary to track which application has
      requested a particular operation.

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.  First, the span of information
   potentially available is very large.  Second, the variation both in
   the structure of the data and in the kinds of operations required
   tends to introduce protocol complexity.








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   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 frequently makes 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?"  Protocol parsimony is clearly a goal.

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 working on 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.)  Thus, it is important to consider extensibility not only of
   the underlying services' data models, but also of the primitives and
   protocol operations.

   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.

3.3.  Model-Driven Programmatic Interfaces

   A critical component of I2RS is the standard information and data
   models with their associated semantics.  While many components of the
   routing system are standardized, associated data models for them are
   not yet available.  Instead, each router uses different information,
   different mechanisms, and different 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 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



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   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 may 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 (such that the contents cannot
   be changed without detection).  Manipulation of the system must be
   accurately attributable.  In an ideal architecture, even information
   collection and notification should be protected; this may be 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 applications.  While
   those applications' identities are not need for authorization, each
   application should have a unique opaque identifier that can be
   provided by the I2RS client to the I2RS agent for purposes of
   tracking attribution of operations to support functionality such as
   accounting and troubleshooting.

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.

   When an I2RS Client interacts with multiple network applications,
   that I2RS Client is behaving as a go-between and should indicate this
   to the I2RS Agents by, for example, specifying a secondary opaque
   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




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   One example of such an application is a Topology Manager.  A Topology
   Manager includes an I2RS client that uses the I2RS data models and
   protocol to collect information about the state of the network by
   communicating directly with one or more I2RS agents.  From these I2RS
   agents, the Topology Manager collects routing configuration and
   operational data.  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.

   The Topology Manager may be embedded as a component of a larger
   application.  It would construct internal data structures and use the
   collected data to drive functions such as path computations or
   anomalous routing detection.  Alternatively, the Topology Manager
   could combine the I2RS-collected data with other information,
   abstract a composite set, and provide a coherent picture of the
   network state accessible via another interface.  That interface might
   use the same I2RS protocol and could use extensions to 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
   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.









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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.  How much data must the I2RS Agent store
   about these state-modifying operations, 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 clients'
   overlapping operations are stored and managed, as is done in the RIB
   for routes with a preference or priority to pick between the routes.

   In answering this question, 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 protocol 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
   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.



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   As such, in this architecture it is assumed 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.

   An I2RS Client may register for notifications when state that was
   applied by a particular I2RS Client is modified or removed.

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 must
   be instrumented enough to provide suitable I2RS notifications of
   these changes.

5.4.  Routing Components and Associated I2RS Services

   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.





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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 must 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
   may need 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 out
      of scope for I2RS.

   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

   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,
   direct modification of of the link-state database is NOT allowed to
   preserve network state consistency.





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5.4.3.  MPLS

   The I2RS agent will need to interact with the protocols that create
   transport LSPs (e.g. LDP and RSVP-TE) as well as protocols (e.g. BGP,
   LDP) that provide MPLS-based services (e.g. pseudowires, L3VPNs,
   L2VPNs, etc).

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 future extensibility.
   [[Editor's note: This requires more discussion in the working
   group.]]

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 not meet the requirements elucidated
   elsewhere.  One could also view I2RS 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.
   From a deployability perspective, this would not meet the goal of
   simplicity.  As a result, this architecture views the I2RS as an
   interface supporting a single control and data exchange protocol.
   Whether such a protocol is built upon extending existing mechanisms
   or requires a new mechanism requires further investigation.  That
   protocol may use several underlying transports (TCP, SCTP, DCCP),
   with suitable authentication and integrity protection mechanisms.
   These different transports can support different types of
   communication (e.g. control, reading, notifications, and information
   collection) and different sets of data.  Whatever transport is used
   for the data exchange, it must also support suitable congestion
   control mechanisms.

6.2.  Channel





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   The uses of a single I2RS protocol does not imply that only one
   channel of communication is required.  There may be a range of
   reliability requirements, and to support the scaling there may need
   to be channels originating from multiple sub-components 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, capability
   negotiation (such as which transports are supported beyond the
   minimum required to implement) will clearly 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.

   Negotiation should be broken into several aspects, such as protocol
   capablities and I2RS services and model types supported.

6.4.  Identity and Security Role

   Each I2RS Client will have a unique identity; it can also have
   secondary identities to be used for troubleshooting.  A secondary
   identity is merely a unique, opaque identifier that may be helpful in
   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.

6.4.1.  Client Redundancy

   I2RS must support client redundancy.  At the simplest, this can be
   handled by having a primary and a backup network application that
   both use the same client identity and can successfully authenticate
   as such.  Since I2RS does not require a continuous transport
   connection and supports multiple transport sessions, this can provide
   some basic redundancy.  However, it does not address concerns for
   troubleshooting and accountability about knowing which network
   application is actually active.  At a minimum, basic transport
   information about each connection and time can be logged with the
   identity.  Further discussion is necessary to determine whether
   additional client identification information is necessary.[[Editor's
   note: This requires more discussion in the working group.]]

6.5.  Connectivity




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   A client may or may not 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 three different assumptions that can apply to handling dead
   clients.  The first is that the network applications or management
   systems will detect a dead network application and either restart
   that network application or clean up any state left behind.  The
   second is to 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.  The third is that the
   client could explicitly request state clean-up if a particular
   transport session is terminated.

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



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   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.

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:




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   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 the specified 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.

   Perform all storing errors:   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











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   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 thank Nitin Bahadur, Shane Amante, Ed
   Crabbe, Ken Gray, Carlos Pignataro, Wes George, Joe Clarke, Juergen
   Schoenwalder, and Jamal Hadi Salim 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-01 (work in progress), July 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







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   Susan Hares
   ADARA

   Email: shares@ndzh.com


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

   Email: wardd@cisco.com


   Thomas D. Nadeau
   Juniper Networks

   Email: tnadeau@juniper.net
































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