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Versions: (draft-liu-i2rs-architecture) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 RFC 7921

Network Working Group                                           A. Atlas
Internet-Draft                                          Juniper Networks
Intended status: Informational                                J. Halpern
Expires: January 21, 2015                                       Ericsson
                                                                S. Hares
                                                 Hickory Hill Consulting
                                                                 D. Ward
                                                           Cisco Systems
                                                               T. Nadeau
                                                                 Brocade
                                                           July 20, 2014


        An Architecture for the Interface to the Routing System
                    draft-ietf-i2rs-architecture-05

Abstract

   This document describes an architecture for a standard, programmatic
   interface for state transfer in and out of the internet 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 January 21, 2015.

Copyright Notice

   Copyright (c) 2014 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.  Drivers for the I2RS Architecture . . . . . . . . . . . .   4
     1.2.  Architectural Overview  . . . . . . . . . . . . . . . . .   5
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   9
   3.  Key Architectural Properties  . . . . . . . . . . . . . . . .  10
     3.1.  Simplicity  . . . . . . . . . . . . . . . . . . . . . . .  10
     3.2.  Extensibility . . . . . . . . . . . . . . . . . . . . . .  11
     3.3.  Model-Driven Programmatic Interfaces  . . . . . . . . . .  11
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
     4.1.  Identity and Authentication . . . . . . . . . . . . . . .  13
     4.2.  Authorization . . . . . . . . . . . . . . . . . . . . . .  13
   5.  Network Applications and I2RS Client  . . . . . . . . . . . .  14
     5.1.  Example Network Application: Topology Manager . . . . . .  15
   6.  I2RS Agent Role and Functionality . . . . . . . . . . . . . .  15
     6.1.  Relationship to its Routing Element . . . . . . . . . . .  15
     6.2.  I2RS State Storage  . . . . . . . . . . . . . . . . . . .  16
       6.2.1.  I2RS Agent Failure  . . . . . . . . . . . . . . . . .  16
       6.2.2.  Starting and Ending . . . . . . . . . . . . . . . . .  17
       6.2.3.  Reversion . . . . . . . . . . . . . . . . . . . . . .  17
     6.3.  Interactions with Local Config  . . . . . . . . . . . . .  17
     6.4.  Routing Components and Associated I2RS Services . . . . .  18
       6.4.1.  Routing and Label Information Bases . . . . . . . . .  19
       6.4.2.  IGPs, BGP and Multicast Protocols . . . . . . . . . .  20
       6.4.3.  MPLS  . . . . . . . . . . . . . . . . . . . . . . . .  20
       6.4.4.  Policy and QoS Mechanisms . . . . . . . . . . . . . .  21
       6.4.5.  Information Modeling, Device Variation, and
               Information Relationships . . . . . . . . . . . . . .  21
         6.4.5.1.  Managing Variation: Object Classes/Types and
                   Inheritance . . . . . . . . . . . . . . . . . . .  21
         6.4.5.2.  Managing Variation: Optionality . . . . . . . . .  22
         6.4.5.3.  Managing Variation: Templating  . . . . . . . . .  22
         6.4.5.4.  Object Relationships  . . . . . . . . . . . . . .  23
           6.4.5.4.1.  Initialization  . . . . . . . . . . . . . . .  23
           6.4.5.4.2.  Correlation Identification  . . . . . . . . .  23
           6.4.5.4.3.  Object References . . . . . . . . . . . . . .  24
           6.4.5.4.4.  Active Reference  . . . . . . . . . . . . . .  24
   7.  I2RS Client Agent Interface . . . . . . . . . . . . . . . . .  24
     7.1.  One Control and Data Exchange Protocol  . . . . . . . . .  24



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     7.2.  Communication Channels  . . . . . . . . . . . . . . . . .  24
     7.3.  Capability Negotiation  . . . . . . . . . . . . . . . . .  25
     7.4.  Identity and Security Role  . . . . . . . . . . . . . . .  25
       7.4.1.  Client Redundancy . . . . . . . . . . . . . . . . . .  26
     7.5.  Connectivity  . . . . . . . . . . . . . . . . . . . . . .  26
     7.6.  Notifications . . . . . . . . . . . . . . . . . . . . . .  27
     7.7.  Information collection  . . . . . . . . . . . . . . . . .  27
     7.8.  Multi-Headed Control  . . . . . . . . . . . . . . . . . .  28
     7.9.  Transactions  . . . . . . . . . . . . . . . . . . . . . .  28
   8.  Operational and Manageability Considerations  . . . . . . . .  29
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  29
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  30
   11. Informative References  . . . . . . . . . . . . . . . . . . .  30
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  30

1.  Introduction

   Routers that form the internet 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, and BGP to exchange protocol
   state and other information about the state of the network with other
   routers.

   Routers convert all of this information into forwarding entries which
   are then used to forward packets and flows between network elements.
   The forwarding plane and the specified forwarding entries then
   contain active state information that describes the expected and
   observed operational behavior of the router and which is also needed
   by the network applications.  Network-oriented applications require
   easy access to this information to learn the network topology, to
   verify that programmed state is installed in the forwarding plane, to
   measure the behavior of various flows, routes or forwarding entries,
   as well as to understand the configured and active states 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 observation of the routing-related
   state (for example, a Routing Element RIB manager's state), as well
   as enabling network-oriented 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 routing
   system.  This I2RS architecture recognizes that the routing system
   and a router's OS provide useful mechanisms that applications could
   harness to accomplish application-level goals.





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   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 desired.

   Although the I2RS architecture is general enough to support
   information and data models for a variety of data, and aspects of the
   I2RS solution may be useful in domain other than routing, I2RS and
   this document are specifically focused on an interface for routing
   data.

1.1.  Drivers for the I2RS Architecture

   There are four key drivers that shape the I2RS architecture.  First
   is the need for an interface that is programmatic, asynchronous, and
   offers fast, interactive access for atomic operations.  Second is the
   access to structured information and state that is frequently not
   directly configurable or modeled in existing implementations or
   configuration protocols.  Third is the ability to subscribe to
   structured, filterable event notifications from the router.  Fourth,
   the operation of I2RS is to 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.ietf-i2rs-problem-statement].

   The I2RS architecture facilitates obtaining information from the
   router.  The I2RS architecture provides the ability to not only read
   specific information, but also to subscribe to targeted information
   streams and filtered and thresholded events.

   Such an interface also facilitates the injection of ephemeral state
   into the routing system.  A non-routing protocol or application could
   inject state into a routing element via the state-insertion
   functionality 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).  I2RS will only permit
   modification of state that would be safe, conceptually, to modify via
   local configuration; no direct manipulation of protocol-internal
   dynamically determined data is envisioned.







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1.2.  Architectural Overview

   Figure 1 shows the basic architecture for I2RS between applications
   using I2RS, their associated I2RS Clients, and I2RS Agents.
   Applications access I2RS services through I2RS clients.  A single
   client can provide access to one or more applications.  In the
   figure, Clients A and B provide access to a single application, while
   Client P provides access to multiple applications.

   Applications can access I2RS services through local or remote
   clients.  In the figure, Applicatons A and B access I2RS services
   through local clients, while Applications C, D and E access I2RS
   services through a remote client.  The details of how applications
   communicate with a remote client is out of scope for I2RS.

   An I2RS Client can access one or more I2RS agents.  In the figure,
   Clients B and P access I2RS Agents 1 and 2.  Likewise, an I2RS Agent
   can provide service to one or more clients.  In the figure, I2RS
   Agent 1 provides services to Clients A, B and P while Agent 2
   provides services to only Clients B and P.

   I2RS agents and clients communicate with one another using an
   asynchronous protocol.  Therefore, a single client can post multiple
   simultaneous requests, either to a single agent or to multiple
   agents.  Furthermore, an agent can process multiple requests, either
   from a single client or from multiple clients, simultaneously.

   The I2RS agent provides read and write access to selected data on the
   routing element that are organized into I2RS Services.  Section 4
   describes how access is mediated by authentication and access control
   mechanisms.  In addition to read and write access, the I2RS agent
   allows clients to subscribe to different types of notifications about
   events affecting different object instances.  An example not related
   to the creation, modification or deletion of an object instance is
   when a next-hop in the RIB is resolved enough to be used or when a
   particular route is selected by the RIB Manager for installation into
   the forwarding plane.  Please see Section 7.6 and Section 7.7 for
   details.

   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 C *   * Application D *  * Application E *
        ******************   *****************  *****************
                 ^                  ^                   ^



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


             Figure 1: Architecture of I2RS clients and agents





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   Routing Element:   A Routing Element implements some subset 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 BGP speaker acting 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 and Signaling:   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, flow data,
      and local events.  This is the subset of operational state that is
      needed by network applications based on I2RS that is not contained
      in the routing and signaling information.  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.

   Static System State:   An I2RS agent needs access to static state on
      a routing element beyond what is contained in the routing
      subsystem.  An example of such state is specifying queueing
      behavior for an interface or traffic.  How the I2RS agent modifies
      or obtains this information is out of scope, but the standardized
      information and data models for what is exposed are part of I2RS.

   I2RS Agent:   See the definition in Section 2.




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

   I2RS Client:   See the definition in Section 2.

   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.  In order to keep the protocol simple, two clients should
   not attempt to write (modify) the same piece of information on an
   I2RS Agent.  This is considered an error.  However, such collisions
   may happen and section 7.8 (multi-headed control) describes how the
   I2RS agent resolves collision by first utilizing priority to resolve
   collisions, and second by servicing the requests in a first in, first
   served basis.  The i2rs architecture includes this definition of
   behavior for this case simply for predictability not because this is
   an intended result.  This predictability will simplify the error
   handling and suppress oscillations.  If additional error cases beyond
   this simple treatment are required, these these error cases should be
   resolved by the network applications and management systems.

   In contrast, although 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 7.8.  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 6.3.

   In addition it must be noted that there may be indirect interactions
   between write operations.  A basic example of this is when two
   different but overlapping prefixes are written with different
   forwarding behavior.  Detection and avoidance of such interactions is
   outside the scope of the I2RS work and is left to agent design and
   implementation.



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2.  Terminology

   The following terminology is used in this document.

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

   client or I2RS Client:   A client implements the I2RS protocol, uses
      it to communicate with I2RS Agents, and uses the I2RS services to
      accomplish a task.  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 I2RS agents to modify the state
      of their associated routing systems to achieve operational goals.
      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.  The read scope specifies the access
      restrictions to both see the existence of data and read the value
      of that data.

   notification scope:   The set of events and associated information
      that the I2RS Client can request be pushed by the I2RS Agent.
      I2RS Clients have the ability to register for specific events and
      information streams, but must be constrained by the access
      restrictions associated with their notification scope.

   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, write scope, or
      notification scope, the term scope applies to the read scope,
      write scope, and notification scope.



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   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 may 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

   Several key architectural properties for the I2RS protocol are
   elucidated below (simplicity, extensibility, and model-driven
   programmatic interfaces).  However, some architecture principles such
   as performance and scaling are not described below because they are
   discussed in [I-D.ietf-i2rs-problem-statement] and because the
   performance and scaling requires varies based on the particular use-
   cases.

3.1.  Simplicity

   There have been many efforts over the years to improve the access to
   the information available 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 quantity and diversity 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.

   While the types of operations contemplated here are complex in their
   nature, it is critical that I2RS be easily deployable and robust.
   Adding complexity beyond what is needed to satisfy well known and
   understood requirements would hinder the ease of implementation, the



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   robustness of the protocol, and the deployability of the protocol.
   Overly complex data models tend to ossify information sets by
   attempting to describe and close off every possible option,
   complicating extensibility.

   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

   Naturally, extensibility of the protocol and data model is very
   important.  In particular, given the necessary scope limitations of
   the initial work, it is critical that the initial design include
   strong support for extensibility.

   The scope of the I2RS work is being restricted in the interests of
   achieving a deliverable and deployable result.  The I2RS Working
   Group is modeling only a subset of the data of interest.  It is
   clearly desirable for the data models defined in the I2RS to be
   useful 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.  This reinforces the criticality of
   designing the data models to be highly extensible, preferably in a
   regular and simple fashion.

   The I2RS Working Group is defining operations for the I2RS protocol.
   It would be optimistic to assume that more and different ones may not
   be needed when the scope of I2RS increases.  Thus, it is important to
   consider extensibility not only of the underlying services' data
   models, but also of the primitives and protocol operations.

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



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   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 may indicate which data-models are
   supported.

4.  Security Considerations

   This I2RS architecture describes interfaces that clearly require
   serious consideration of security.  First, here is a brief
   description of the assumed security environment for I2RS.  The I2RS
   Agent associated with a Routing Element is a trusted part of that
   Routing Element.  For example, it may be part of a vendor-distributed
   signed software image for the entire Routing Element or it may be
   trusted signed application that an operator has installed.  The I2RS
   Agent is assumed to have a separate authentication and authorization
   channel by which it can validate both the identity and permissions
   associated with an I2RS Client.  To support numerous and speedy
   interactions between the I2RS Agent and I2RS Client, it is assumed
   that the I2RS Agent can also cache that particular I2RS Clients are
   trusted and their associated authorized scope.  This implies that the
   permission information may be old either in a pull model until the
   I2RS Agent re-requests it, or in a push model until the
   authentication and authorization channel can notify the I2RS Agent of
   changes.

   Mutual authentication between the I2RS Client and I2RS Agent is
   required.  An I2RS Client must be able to trust that the I2RS Agent
   is attached to the relevant Routing Element so that write/modify
   operations are correctly applied and so that information received
   from the I2RS Agent can be trusted by the I2RS Client.

   An I2RS Client is not automatically trustworthy.  It has identity
   information and applications using that I2RS Client should be aware
   of the scope limitations of that I2RS Client.  If the I2RS Client is
   acting as a broker for multiple applications, managing the security,
   authentication and authorization for that communication is out of
   scope; nothing prevents I2RS and a separate authentication and
   authorization channel from being used.  Regardless of mechanism, an
   I2RS Client that is acting as a broker is responsible for determining
   that applications using it are trusted and permitted to make the
   particular requests.

   Different levels of integrity, confidentiality, and replay protection
   are relevant for different aspects of I2RS.  The primary
   communication channel that is used for client authentication and then



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   used by the client to write data requires integrity, privacy and
   replay protection.  Appropriate selection of a default required
   transport protocol is the preferred way of meeting these
   requirements.

   Other communications via I2RS may not require integrity,
   confidentiality, and replay protection.  For instance, if an I2RS
   Client subscribes to an information stream of prefix announcements
   from OSPF, those may require integrity but probably not
   confidentiality or replay protection.  Similarly, an information
   stream of interface statistics may not even require guaranteed
   delivery.  In Section 7.2, more reasoning for multiple communication
   channels is provided.  From the security perspective, it is critical
   to realize that an I2RS Agent may open a new communication channel
   based upon information provided by an I2RS Client (as described in
   Section 7.2).  For example, a I2RS client may request notifications
   of certain events and the agent will open a communication channel to
   report such events.  Therefore, to avoid an indirect attack, such a
   request must be done in the context of an authenticated and
   authorized client whose communications cannot have been altered.

4.1.  Identity and Authentication

   As discussed above, all control exchanges between the I2RS client and
   agent should be authenticated and integrity protected (such that the
   contents cannot be changed without detection).  Further, 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 clients may be operating on behalf of other applications.  While
   those applications' identities are not needed for authentication or
   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.

4.2.  Authorization

   All operations using I2RS, both observation and manipulation, should
   be subject to appropriate authorization controls.  Such authorization
   is based on the identity and assigned role of the I2RS client
   performing the operations and the I2RS agent in the network element.

   I2RS Agents, in performing information collection and manipulation,
   will be acting on behalf of the I2RS clients.  As such, each
   operation authorization will be based on the lower of the two



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   permissions of the agent itself and of the authenticated client.  The
   mechanism by which this authorization is applied within the device is
   outside of the scope of I2RS.

   The appropriate or necessary level of granularity for scope can
   depend upon the particular I2RS Service and the implementation's
   granularity.  An approach to a similar access control problem is
   defined in the NetConf Access Control Model[RFC6536]; it allows
   arbitrary access to be specified for a data node instance identifier
   while defining meaningful manipulable defaults.  The ability to
   specify one or more groups or roles that a particular I2RS Client
   belongs and then define access controls in terms of those groups or
   roles is expected.  When a client is authenticated, its group or role
   membership should be provided to the I2RS Agent.  The set of access
   control rules that an I2RS Agent uses would need to be either
   provided via Local Config, exposed as an I2RS Service for
   manipulation by authorized clients, or via some other method.

5.  Network Applications and I2RS Client

   I2RS is expected to be used by network-oriented applications in
   different architectures.  While the interface between a network-
   oriented application and the I2RS client is outside the scope of
   I2RS, considering the different architectures is important to
   sufficiently specify I2RS.

   In the simplest architecture, a network-oriented application has an
   I2RS client as a library or driver for communication with routing
   elements.

   In the broker architecture, multiple network-oriented applications
   communicate in an unspecified fashion to a broker application that
   contains an I2RS Client.  That broker application requires additional
   functionality for authentication and authorization of the network-
   oriented applications; such functionality is out of scope for I2RS
   but similar considerations to those described in Section 4.2 do
   apply.  As discussed in Section 4.1, the broker I2RS Client should
   determine distinct opaque identifiers for each network-oriented
   application that is using it.  The broker I2RS Client can pass along
   the appropriate value as a secondary identifier which can be used for
   tracking attribution of operations.

   In a third architecture, a routing element or network-oriented
   application that uses an I2RS Client to access services on a
   different routing element may also contain an I2RS agent to provide
   services to other network-oriented applications.  However, where the
   needed information and data models for those services differs from
   that of a conventional routing element, those models are, at least



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   initially, out of scope for I2RS.  Below is an example of such a
   network application

5.1.  Example Network Application: 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, such as interface and label-
   switched path (LSP) information.  In addition, the Topology Manager
   may collect link-state data in several ways - either via I2RS models,
   by peering with BGP-LS[I-D.ietf-idr-ls-distribution] or listening
   into the IGP.

   The set of functionality and collected information that is the
   Topology Manager may be embedded as a component of a larger
   application, such as a path computation application.  As a stand-
   alone application, the Topology Manager could be useful to other
   network applications by providing a coherent picture of the network
   state accessible via another interface.  That interface might use the
   same I2RS protocol and could provide a topology service using
   extensions to the I2RS data models.

6.  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.

6.1.  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.  There may be multiple I2RS Agents
   within the same router.  In such a case, they must have non-
   overlapping sets of information which they manipulate.





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   To facilitate operations, deployment and troubleshooting, it is
   important that traceability of the I2RS Agent's requests and actions
   be supported via a common data model.

6.2.  I2RS State Storage

   State modification requests are sent to the I2RS agent in a routing
   element by I2RS clients.  The I2RS agent is responsible for applying
   these changes to the system, subject to the authorization discussed
   above.  The I2RS agent will retain knowledge of the changes it has
   applied, and the client on whose behalf it applied the changes.  The
   I2RS agent will also store active subscriptions.  These sets of data
   form the I2RS data store.  This data is retained by the agent until
   the state is removed by the client, overridden by some other
   operation such as CLI, or the device reboots.  Meaningful logging of
   the application and removal of changes is recommended.  I2RS applied
   changes to the routing element state will not be retained across
   routing element reboot.  The I2RS data store is not preserved across
   routing element reboots; thus the I2RS agent will not attempt to
   reapply such changes after a reboot.

6.2.1.  I2RS Agent Failure

   It is expected that an I2RS Agent may fail independently of the
   associated routing element.  This could happen because I2RS is
   disabled on the routing element or because the I2RS Agent, a separate
   process or even running on a separate processor, experiences an
   unexpected failure.  Just as routing state learned from a failed
   source is removed, the ephemeral I2RS state will usually be removed
   shortly after the failure is detected or as part of a graceful
   shutdown process.  To handle I2RS Agent failure, the I2RS Agent must
   use two different notifications.

   NOTIFICATION_I2RS_AGENT_STARTING:   This notification identifies that
      the associated I2RS Agent has started.  It includes an agent-boot-
      count that indicates how many times the I2RS Agent has restarted
      since the associated routing element restarted.  The agent-boot-
      count allows an I2RS Client to determine if the I2RS Agent has
      restarted.

   NOTIFICATION_I2RS_AGENT_TERMINATING:   This notification reports that
      the associated I2RS Agent is shutting down gracefully.  Ephemeral
      state will be removed.  It can optionally include a timestamp
      indicating when the I2RS Agent will shutdown.  Use of this
      timestamp assumes that time synchronization has been done and the
      timestamp should not have granularity finer than one second
      because better accuracy of shutdown time is not guaranteed.




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   There are two different failure types that are possible and each has
   different behavior.

   Unexpected failure:   In this case, the I2RS Agent has unexpectedly
      crashed and thus cannot notify its clients of anything.  Since
      I2RS does not require a persistent connection between the I2RS
      Client and I2RS Agent, it is necessary to have a mechanism for the
      I2RS Agent to notify I2RS Clients that had subscriptions or
      written ephemeral state; such I2RS Clients should be cached by the
      I2RS Agent's system in persistent storage.  When the I2RS Agent
      starts, it should send a NOTIFICATION_I2RS_AGENT_STARTING to each
      cached I2RS Client.

   Graceful failure:   In this case, the I2RS Agent can do specific
      limited work as part of the process of being disabled.  The I2RS
      Agent Agent must send a NOTIFICATION_I2RS_AGENT_TERMINATING to all
      its cached I2RS Clients.

6.2.2.  Starting and Ending

   When an I2RS client applies changes via the I2RS protocol, those
   changes are applied and left until removed or the routing element
   reboots.  The network application may make decisions about what to
   request via I2RS based upon a variety of conditions that imply
   different start times and stop times.  That complexity is managed by
   the network application and is not handled by I2RS.

6.2.3.  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, subject to its
   notification scope, regarding state modification or removal by a
   particular I2RS Client.

6.3.  Interactions with Local Config

   Changes may originate from either Local Config or from I2RS.  The
   modifications and data stored by I2RS are separate from the local
   device configuration, but conflicts between the two must be resolved



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   in a deterministic manner that respects operator-applied policy.
   That policy can determine whether Local Config overrides a particular
   I2RS client's request or vice versa.  To achieve this end, either by
   default Local Config always wins or, optionally, a routing element
   may permit a priority to be configured on the device for the Local
   Config mechanism.  The policy mechanism in the later case is
   comparing the I2RS client's priority with that priority assigned to
   the Local Config.

   When the Local Config always wins, some communication between that
   subsystem and the I2RS Agent is still necessary.  That communication
   contains the details of each specific device configuration change
   that the I2RS Agent is permitted to modify.  In addition, when the
   system determines, that a client's I2RS state is preempted, the I2RS
   agent must notify the affected I2RS clients; how the system
   determines this is implementation-dependent.

   It is critical that policy based upon the source is used because the
   resolution cannot be time-based.  Simply allowing the most recent
   state to prevail could cause race conditions where the final state is
   not repeatably deterministic.

6.4.  Routing Components and Associated I2RS Services

   For simplicity, each logical protocol or set of functionality that
   can 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.  When a full implementation is not mandatory, an I2RS
   Service should include a capability model so that implementations can
   indicate which parts of the service are supported.  Each I2RS Service
   requires an information model that describes at least the following:
   data that can be read, data that can be written, notifications that
   can be subscribed to, and the capability model mentioned above.

   The initial services included in the I2RS architecture are as
   follows.














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    ***************************     **************    *****************
    *      I2RS Protocol      *     *            *    *    Dynamic    *
    *                         *     * Interfaces *    *    Data &     *
    *  +--------+  +-------+  *     *            *    *  Statistics   *
    *  | Client |  | Agent |  *     **************    *****************
    *  +--------+  +-------+  *
    *                         *        **************    *************
    ***************************        *            *    *           *
                                       *  Policy    *    * Base QoS  *
    ********************    ********   *  Templates *    * Templates *
    *       +--------+ *    *      *   *            *    *************
    *  BGP  | BGP-LS | *    * PIM  *   **************
    *       +--------+ *    *      *
    ********************    ********       ****************************
                                           * MPLS +---------+ +-----+ *
    **********************************     *      | RSVP-TE | | LDP | *
    *    IGPs      +------+ +------+ *     *      +---------+ +-----+ *
    *  +--------+  | OSPF | | ISIS | *     * +--------+               *
    *  | Common |  +------+ +------+ *     * | Common |               *
    *  +--------+                    *     * +--------+               *
    **********************************     ****************************

    **************************************************************
    * RIB Manager                                                *
    *  +-------------------+  +---------------+   +------------+ *
    *  | Unicast/multicast |  | Policy-Based  |   | RIB Policy | *
    *  | RIBs & LIBs       |  | Routing       |   | Controls   | *
    *  | route instances   |  | (ACLs, etc)   |   +------------+ *
    *  +-------------------+  +---------------+                  *
    **************************************************************

                    Figure 2: Anticipated I2RS Services

   There are relationships between different I2RS Services - whether
   those be the need for the RIB to refer to specific interfaces, the
   desire to refer to common complex types (e.g. links, nodes, IP
   addresses), or the ability to refer to implementation-specific
   functionality (e.g. pre-defined templates to be applied to interfaces
   or for QoS behaviors that traffic is direct into).  Section 6.4.5
   discusses information modeling constructs and the range of
   relationship types that are applicable.

6.4.1.  Routing and Label Information Bases

   Routing elements may maintain one or more Information Bases.
   Examples include Routing Information Bases such as IPv4/IPv6 Unicast
   or IPv4/IPv6 Multicast.  Another such example includes the MPLS Label
   Information Bases, per-platform- or per-interface."  This



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   functionality, exposed via an I2RS Service, must interact smoothly
   with the same mechanisms that the routing element already uses to
   handle RIB input from multiple sources, so as to safely change the
   system state.  Conceptually, this can be handled by having the I2RS
   Agent communicate with a RIB Manager as a separate routing source.

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

6.4.2.  IGPs, BGP and Multicast Protocols

   A separate I2RS Service can expose each routing protocol on the
   device.  Such I2RS services may include 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 to 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

   o  subscribing to an information stream of route changes

   o  receiving notifications about peers coming up or going down

   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 the link-state database MUST NOT be allowed in
   order to preserve network state consistency.

6.4.3.  MPLS

   I2RS Services will be needed to expose 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,



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   L2VPNs, etc).  This should include all local information about LSPs
   originating in, transiting, or terminating in this Routing Element.

6.4.4.  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 information models and supported in the expected
   interfaces between the I2RS Agent and the network element, in order
   to provide basic capabilities and the hooks for future extensibility.

   By taking advantage of extensibility and sub-classing, information
   models can specify use of a basic model that can be replaced by a
   more detailed model.

6.4.5.  Information Modeling, Device Variation, and Information
        Relationships

   I2RS depends heavily on information models of the relevant aspects of
   the Routing Elements to be manipulated.  These models drive the data
   models and protocol operations for I2RS.  It is important that these
   informational models deal well with a wide variety of actual
   implementations of Routing Elements, as seen between different
   products and different vendors.  There are three ways that I2RS
   information models can address these variations: class or type
   inheritance, optional features, and templating.

6.4.5.1.  Managing Variation: Object Classes/Types and Inheritance

   Information modelled by I2RS from a Routing Element can be described
   in terms of classes or types or object.  Different valid inheritance
   definitions can apply.  What is appropriate for I2RS to use is not
   determined in this architecture; for simplicity, class and subclass
   will be used as the example terminology.  This I2RS architecture does
   require the ability to address variation in Routing Elements by
   allowing information models to define parent or base classes and
   subclasses.

   The base or parent class defines the common aspects that all Routing
   Elements are expected to support.  Individual subclasses can
   represent variations and additional capabilities.  When applicable,
   there may be several levels of refinement.  The I2RS protocol can
   then provide mechanisms to allow an I2RS client to determine which
   classes a given I2RS Agent has available.  Clients which only want
   basic capabilities can operate purely in terms of base or parent



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   classes, while a client needing more details or features can work
   with the supported sub-class(es).

   As part of I2RS information modeling, clear rules should be specified
   for how the parent class and subclass can relate; for example, what
   changes can a subclass make to its parent?  The description of such
   rules should be done so that it can apply across data modeling tools
   until the I2RS data modeling language is selected.

6.4.5.2.  Managing Variation: Optionality

   I2RS Information Models must be clear about what aspects are
   optional.  For instance, must an instance of a class always contain a
   particular data field X?  If so, must the client provide a value for
   X when creating the object or is there a well-defined default value?
   From the Routing Element perspective, in the above example, each
   Information model should provide information that:

   o  Is X required for the data field to be accepted and applied?

   o  If X is optional, then how does "X" as an optional portion of data
      field interact with the required aspects of the data field?

   o  Does the data field have defaults for the mandatory portion of the
      field and the optional portions of the field

   o  Is X required to be within a particular set of values (E.g. range,
      length of strings)?

   The information model needs to be clear about what read or write
   values are set by client and what responses or actions are required
   by the agent.  It is important to indicate what is required or
   optional in client values and agent responses/actions.

6.4.5.3.  Managing Variation: Templating

   A template is a collection of information to address a problem; it
   cuts across the notions of class and object instances.  A template
   provides a set of defined values for a set of information fields and
   can specify a set of values that must be provided to complete the
   template.  Further, a flexible template scheme may that some of the
   defined values can be over-written.

   For instance, assigning traffic to a particular service class might
   be done by specifying a template Queueing with a parameter to
   indicate Gold, Silver, or Best Effort.  The details of how that is
   carried out are not modeled.  This does assume that the necessary
   templates are made available on the Routing Element via some



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   mechanism other than I2RS.  The idea is that by providing suitable
   templates for tasks that need to be accomplished, with templates
   implemented differently for different kinds of Routing Elements, the
   client can easily interact with the Routing Element without concern
   for the variations which are handled by values included in the
   template.

   If implementation variation can be exposed in other ways, templates
   may not be needed.  However, templates themselves could be objects
   referenced in the protocol messages, with Routing Elements being
   configured with the proper templates to complete the operation.  This
   is a topic for further discussion.

6.4.5.4.  Object Relationships

   Objects (in a Routing Element or otherwise) do not exist in
   isolation.  They are related to each other.  One of the important
   things a class definition does is represent the relationships between
   instances of different classes.  These relationships can be very
   simple, or quite complicated.  The following lists the information
   relationships that the information models need to support.
   [[Editors' note: All of these are for discussion, and it is expected
   that the list may be changed during WG discussion.]]

6.4.5.4.1.  Initialization

   The simplest relationship is that one object instance is initialized
   by copying another.  For example, one may have an object instance
   that represents the default setup for a tunnel, and all new tunnels
   have fields copied from there if they are not set as part of
   establishment.  This is closely related to the templates discussed
   above, but not identical.  Since the relationship is only momentary
   it is often not formally represented in modeling, but only captured
   in the semantic description of the default object.

6.4.5.4.2.  Correlation Identification

   Often, it suffices to indicate in one object that it is related to a
   second object, without having a strong binding between the two.  So
   an Identifier is used to represent the relationship.  This can be
   used to allow for late binding, or a weak binding that does not even
   need to exist.  A policy name in an object might indicate that if a
   policy by that name exists, it is to be applied under some
   circumstance.  In modeling this is often represented by the type of
   the value.






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6.4.5.4.3.  Object References

   Sometimes the relationship between objects is stronger.  A valid ARP
   entry has to point to the active interface over which it was derived.
   This is the classic meaning of an object reference in programming.
   It can be used for relationships like containment or dependence.
   This is usually represented by an explicit modeling link.

6.4.5.4.4.  Active Reference

   There is an even stronger form of coupling between objects if changes
   in one of the two objects are always to be reflected in the state of
   the other.  For example, if a Tunnel has an MTU, and link MTU changes
   need to immediately propagate to the Tunnel MTU, then the tunnel is
   actively coupled to the link interface.  This kind of active state
   coupling implies some sort of internal bookkeeping to ensure
   consistency, often conceptualized as a subscription model across
   objects.

7.  I2RS Client Agent Interface

7.1.  One Control and Data Exchange Protocol

   As agreed by the I2RS working group, this I2RS architecture assumes
   that there is a single I2RS protocol for control and data exchange;
   that protocol will be based on NETCONF[RFC6241] and RESTCONF
   [I-D.ietf-netconf-restconf].  This helps meet the goal of simplicity
   and thereby enhances deployability.  That protocol may need to 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.  The transports chosen should be operator and implementor
   friendly to ease adoption.

7.2.  Communication Channels

   Multiple communication channels and multiple types of communication
   channels are required.  There may be a range of requirements (e.g.
   confidentiality, reliability), and to support the scaling there may
   need to be channels originating from multiple sub-components of a
   routing element and/or to multiple parts of an I2RS client.  All such
   communication channels will use the same higher level protocol.  Use
   of additional channels for communication will be coordinated between
   the I2RS client and the I2RS agent.




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   I2RS protocol communication can be delivered in-band via the routing
   system's data plane.  I2RS protocol communication might be delivered
   out-of-band via a management interface.  Depending on what operations
   are requested, it is possible for the I2RS protocol communication to
   cause the in-band communication channels to stop working; this could
   cause the I2RS agent to become unreachable across that communication
   channel.

7.3.  Capability Negotiation

   The support for different protocol capabilities and I2RS Services
   will vary across I2RS Clients and Routing Elements supporting I2RS
   Agents.  Since each I2RS Service is required to include a capability
   model (see Section 6.4), negotiation at the protocol level can be
   restricted to protocol specifics and which I2RS Services are
   supported.

   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.

   The protocol capability negotiation can be segmented into the basic
   version negotiation (required to ensure basic communication), and the
   more complex capability exchange which can take place within the base
   protocol mechanisms.  In particular, the more complex protocol and
   mechanism negotiation can be addressed by defining information models
   for both the I2RS Agent and the I2RS Client.  These information
   models can describe the various capability options.  This can then
   represent and be used to communicate important information about the
   agent, and the capabilities thereof.

7.4.  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
   based on the primary unique identity, the I2RS Client 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.








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7.4.1.  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.

7.5.  Connectivity

   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.

   For many applications, it may be desirable to clean up state if a
   network application dies before removing the state it has created.
   Typically, this is dealt with in terms of network application
   redundancy.  If stronger mechanisms are desired, mechanisms outside
   of I2RS may allow a supervisory network application to monitor I2RS
   clients, and based on policy known to the supervisor clean up state
   if applications die.  More complex mechanism instantiated in the I2RS
   agent would add complications to the I2RS protocol and are thus left
   for future work.

   Some examples of such a mechanism include the following.  In one
   option, the client could request state clean-up if a particular
   transport session is terminated.  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.






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7.6.  Notifications

   As with any policy system interacting with the network, the I2RS
   Client 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.  A
   notification may also be due to a regular event.

   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 I2RS Agents to
   send notifications to a number of Clients.  The I2RS Client should be
   able to filter the specific notifications that will be received; the
   specific types of events and filtering operations can vary by
   information model and need to be specified as part of the information
   model.

   The I2RS information model needs to include representation of these
   events.  As discussed earlier, the capability information in the
   model will allow I2RS clients to understand which events a given I2RS
   Agent is capable of generating.

   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.

7.7.  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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7.8.  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 should be when such a
   collision happens.  Rather, the architecture mandates that there be
   decidable means by which I2RS Agents handle the collisions.  The
   mechanism for ensuring predictability 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 approach to multi-headed control to be useful for
   I2RS Clients, it is important that it be possible for an I2RS Client
   to register for changes to any changes made by I2RS to data that it
   may care about.  This is included in the I2RS event mechanisms.  This
   also needs to apply to changes made by CLI/NETCONF/SNMP within the
   write-scope of the I2RS Agent, as the same priority mechanism (even
   if it is "CLI always wins") applies there.  The I2RS client may then
   respond to the situation as it sees fit.

7.9.  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
      them 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



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      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 or write
   operations even when they fully succeed.

8.  Operational and Manageability Considerations

   In order to facilitate troubleshooting of routing elements
   implementing I2RS agents, those routing elements should provide for a
   mechanism to show actively provisioned I2RS state and other I2RS
   Agent internal information.  Note that this information may contain
   highly sensitive material subject to the Security Considerations of
   any data models implemented by that Agent and thus must be protected
   according to those considerations.  Preferably, this mechanism should
   use a different privileged means other than simply connecting as an
   I2RS client to learn the data.  Using a different mechanism should
   improve traceability and failure management.

   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 is used to provide sufficient policy
      flexibility.

9.  IANA Considerations

   This document includes no request to IANA.







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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, Ron Bonica, Joe
   Clarke, Juergen Schoenwalder, Jeff Haas, Jamal Hadi Salim, Scott
   Brim, Thomas Narten, Dean Bogdanovi, Tom Petch, Robert Raszuk,
   Sriganesh Kini, and John Mattsson for their suggestions and review.

11.  Informative References

   [I-D.ietf-i2rs-problem-statement]
              Atlas, A., Nadeau, T., and D. Ward, "Interface to the
              Routing System Problem Statement", draft-ietf-i2rs-
              problem-statement-04 (work in progress), June 2014.

   [I-D.ietf-idr-ls-distribution]
              Gredler, H., Medved, J., Previdi, S., Farrel, A., and S.
              Ray, "North-Bound Distribution of Link-State and TE
              Information using BGP", draft-ietf-idr-ls-distribution-05
              (work in progress), May 2014.

   [I-D.ietf-netconf-restconf]
              Bierman, A., Bjorklund, M., Watsen, K., and R. Fernando,
              "RESTCONF Protocol", draft-ietf-netconf-restconf-01 (work
              in progress), July 2014.

   [RFC6241]  Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
              Bierman, "Network Configuration Protocol (NETCONF)", RFC
              6241, June 2011.

   [RFC6536]  Bierman, A. and M. Bjorklund, "Network Configuration
              Protocol (NETCONF) Access Control Model", RFC 6536, March
              2012.

Authors' Addresses

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

   Email: akatlas@juniper.net





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   Joel Halpern
   Ericsson

   Email: Joel.Halpern@ericsson.com


   Susan Hares
   Hickory Hill Consulting

   Email: shares@ndzh.com


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

   Email: wardd@cisco.com


   Thomas D. Nadeau
   Brocade

   Email: tnadeau@lucidvision.com


























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