Network Working Group                                      A. Atlas, Ed.
Internet-Draft                                                 T. Nadeau
Intended status: Informational                          Juniper Networks
Expires: January 31, 2013                                        D. Ward
                                                           Cisco Systems
                                                           July 30, 2012

               Interface to the Routing System Framework


   This document describes a framework for a standard, programmatic
   interface for full-duplex, streaming state transfer in and out of the
   Internet's routing system.  It lists the information that might be
   exchanged over the interface, and describes the uses of an interface
   to the Internet routing system.

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
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   This Internet-Draft will expire on January 31, 2013.

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   Copyright (c) 2012 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
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   ( 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

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   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.  Example Use-Cases  . . . . . . . . . . . . . . . . . . . .  5
   2.  Programmatic Interfaces  . . . . . . . . . . . . . . . . . . .  6
   3.  Common Interface Considerations  . . . . . . . . . . . . . . .  7
     3.1.  Capabilities . . . . . . . . . . . . . . . . . . . . . . .  7
     3.2.  Identity, Authorization, Authentication, and Security  . .  8
     3.3.  Speed and Frequency of State Installation  . . . . . . . .  8
     3.4.  Lifetime of IRS-Installed Routing System State . . . . . .  9
     3.5.  Start-Time of IRS-Installed Routing System State . . . . . 10
   4.  Bidirectional Interfaces to the Routing System . . . . . . . . 10
     4.1.  Static Routing . . . . . . . . . . . . . . . . . . . . . . 11
       4.1.1.  Routing Information Base Interface . . . . . . . . . . 11
       4.1.2.  Label Forwarding Information Base Interface  . . . . . 12
       4.1.3.  Multicast Routing Information Base Interface . . . . . 13
     4.2.  Beyond Destination-based Routing . . . . . . . . . . . . . 13
       4.2.1.  Policy-Based Routing Interface . . . . . . . . . . . . 13
       4.2.2.  QoS State  . . . . . . . . . . . . . . . . . . . . . . 14
     4.3.  Protocol Interactions  . . . . . . . . . . . . . . . . . . 14
       4.3.1.  IGP Interfaces . . . . . . . . . . . . . . . . . . . . 14
       4.3.2.  BGP Interface  . . . . . . . . . . . . . . . . . . . . 15
       4.3.3.  PIM and mLDP Interfaces  . . . . . . . . . . . . . . . 15
     4.4.  Triggered Sessions and Signaling . . . . . . . . . . . . . 16
       4.4.1.  OAM-related Sessions Interface . . . . . . . . . . . . 16
       4.4.2.  Dynamic Session Creation . . . . . . . . . . . . . . . 16
       4.4.3.  Triggered Signaling  . . . . . . . . . . . . . . . . . 16
   5.  Interfaces for Learned Information from the Routing System . . 16
     5.1.  Efforts to Obtain Topological Data . . . . . . . . . . . . 17
     5.2.  Measurements . . . . . . . . . . . . . . . . . . . . . . . 18
     5.3.  Events . . . . . . . . . . . . . . . . . . . . . . . . . . 18
   6.  Manageability Considerations . . . . . . . . . . . . . . . . . 19
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 19
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 19
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
   10. Informative References . . . . . . . . . . . . . . . . . . . . 20
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21

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1.  Introduction

   Routers that form the Internet's routing infrastructure maintain
   state at various layers of detail and function.  For example, each
   router has a Routing Information Base (RIB), and the routing
   protocols (OSPF, ISIS, BGP, etc.) each maintain protocol state and
   information about the state of the network.

   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, and
   understand the existing configuration and state of the router.
   Furthermore, routers are configured or implemented with procedural or
   policy-based instructions for how to convert all of this information
   into the forwarding operations that are installed in the forwarding
   plane, and this is also state information that describes the
   behaviour of the router.

   This document sets out a framework for a common, standard interface
   to allow access to all of this information.  This Interface to the
   Routing System (IRS) would facilitate control and diagnosis of the
   routing infrastructure, as well as enabling sophisticated
   applications to be built on top of today's routed networks.  The IRS
   is a programmatic, streaming 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 IRS is a clear data model that defines the
   semantics of the information that can be written and read.  The IRS
   provides a framework for registering for and requesting the
   appropriate information for each particular application.  The IRS
   provides a way for applications to customize network behaviour while
   leveraging the existing routing system.

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

1.1.  Functional Overview

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

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   IRS is described as a streaming programmatic interface; the key
   properties that are intended are:

   Multiple Simultaneous Asynchronous Operations:   A single application
      should be able to send multiple operations to IRS without needing
      to wait for each to complete before sending the next.

   Configuration Not Re-Processed:   When an IRS operation is processed,
      it does not require that any of the configuration be processed.
      I.e. the desired behavior with regard to static configuration is
      the same as learning a new BGP route - completely orthogonal.

   Duplex:   Communications can be established by either the router or
      the application.  Similarly, events, acknowledgements, failures,
      operations, etc. can be sent at any time by both the router and
      the application.  This is not a pure pull-model where only the
      application queries to pull responses.

   High-Throughput:   At a minimum, the IRS should be able to handle
      hundreds of operations per second.

   Responsive:   It should be possible to complete simple operations
      within a sub-second time-scale.

   Multi-Channel:   It should be possible for information to be
      communicated via the interface from different components in the
      router without requiring going through a single channel.  For
      example, for scaling, some exported data or events may be better
      sent directly from the forwarding plane, while other interactions
      may come from the control-plane.  Thus a single TCP session per
      application would not be a good match.

   Such an interface facilitates the specification of non-permanent
   state into the routing system as well as the extraction of that
   information and additional dynamic information from the routing
   system.  A non-routing protocol or application could inject state
   into a networking node's OS via the state-insertion aspects of the
   interface, that could then be distributed in a routing or signaling

   Where existing mechanisms can provide part of the desired
   functionality, the coverage and gaps are briefly discussed in this

   The existing mechanisms, such as SNMP and NetConf, that allow state
   to be written and read do not meet all of the above key properties
   needed for IRS.  The overhead of infrastructure is also quite high
   and many MIBs do not, in definition or practice, allow writing of

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   state.  There is also very limited capability to add new application-
   specific state to be distributed via the routing system.  Conversely,
   NetConf is challenging for reading state from a router.

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

1.2.  Example Use-Cases

   A few brief examples of ways an application could use the IRS are
   presented here.  These are intended to give a sense of what could be
   done rather than to be primary and detailed motivational use-cases.

   Route Control via Indirection:   By enabling an application to
      install routes in the RIB, it is possible that when, for example,
      BGP resolves its IGP next-hop via the RIB, that could be to an
      application-installed route.  In general, when a route is
      redistributed from one protocol to another, this is done via the
      RIB and such a route could have been installed via the IRS

   Policy-Based Routing of Unknown Traffic:   A static route, installed
      into the RIB, could direct otherwise unrecognized traffic towards
      an application, through whatever appropriate tunnel was required,
      for further handling.  Such a static route could be programmed
      with indirection, so that its outgoing path is whatever is used by
      another particular route (e.g. to a particular server).

   Services with Fixed Hours:   If an application were to provide
      services only during fixed time-periods, the application could
      install both a specific route on the local router in the RIB and
      advertise the associated prefix as being attached to the local
      router via the IGP.  If the application knew the fixed hours, the
      state so installed could be time-based and automatically removed
      at approximately the correct time.

   Traffic Mirroring:   The interface to the multicast RIB could be used
      to mirror a particular traffic flow to both its original
      destination and a data collector.

   Static Multicast Trees:   An application could set up static (or
      partially static) multicast flows via entries in the multicast RIB
      without requiring an associated multicast protocol.  This could be
      useful in networks with a fixed topology and well-planned

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      distribution tree that provides redundancy.

2.  Programmatic Interfaces

   A number of management interfaces exist today that allow for the
   indirect programming of the routing system.  These include
   proprietary CLI, Netconf, and SNMP.  However, none of these
   mechanisms allows for the direct programming of the routing system.
   Such streaming interfaces are needed to support dynamic time-based

   These interfaces should cater to how applications typically interact
   with other applications and network services rather than forcing them
   to use older mechanisms that are more complex to understand and
   implement, as well as operate.

   The most critical component of the IRS is developing standard data
   models with their associated semantics.  While many routing protocols
   are standardized, associated data models for IRS are not yet
   available.  Instead, each router uses different information,
   mechanisms, and CLI which makes a standard interface for use by
   applications extremely cumbersome to develop and maintain.  Well-
   known data modeling languages, such as YANG [RFC6020], exist and
   might be used for defining the necessary data models; more
   investigation into alternatives is required.  It is understood that
   some portion (hopefully a small subset) will remain as proprietary
   extensions; the data models must support future extensions and
   proprietary extensions.

   Since the IRS will need to support remote access between applications
   running on a host or server and routers in the network, at least one
   standard mechanism must be identified and defined to provide the
   transfer syntax, as defined by a protocol, used to communicate
   between the application and the routing system.  Common functionality
   that IRS needs to support includes acknowledgements, dependencies,

   Appropriate candidate protocols must be identified that reduce the
   effort required by applications and, preferably, are familiar to
   application developers.  Ideally, this should not require that
   applications understand and implement existing routing protocols to
   interact with IRS.  These interfaces should instead be based on
   light-weight, rapidly deployable approaches; technology approaches
   must be evaluated but examples could include ReSTful web services,
   JSON, XMPP, and XML.  These interfaces should possess self-describing
   attributes (e.g. a web services interface) so that applications can
   quickly query and learn about the active capabilities of a device.

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   It may be desirable to also define the local syntax (e.g. programming
   language APIs) that applications running local to a router can use.

   Since evolution is anticipated in IRS over time, it is important that
   versioning and backwards compatibility are basic supported
   functionality.  Similarly, common consistent error-handling and
   acknowledgement mechanisms are required that do not severely limit
   the scalability and responsiveness of these interfaces.

3.  Common Interface Considerations

3.1.  Capabilities

   Capability negotiation is a critical requirement because different
   implementations and software versions will have different abilities.
   Similarly, applications may have different capabilities for receiving
   exported information.

   The IRS will have multiple interfaces, each with their own set of
   capabilities.  Such capabilities may include the particular data
   model and what operations can be performed at what scale.

   The capabilities negotiated may be filtered based upon different
   information, such as the application's authorization, application's
   capabilities, and the desired granularity for abstraction which the
   application understands.  Different types of authorization may
   require the router to advertise different capabilities and

   The capability negotiation may take place at different levels of
   detail based upon the application and the specific functions in the
   IRS that the application is negotiating.  The router and application
   must use the IRS to agree upon the proper level of abstraction for
   the interaction.  For example, when an application describes a route
   between two topological items, these items may vary in detail from a
   network domain's name at a high level, or down to the port forwarding
   specifics of a particular device.

   The data-model and capabilities available for an element may depend
   upon whether the element is physical or virtual; the virtual/physical
   distinction does not matter to IRS.  Similarly, the location of the
   element may influence how an application converses with the
   associated router.

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3.2.  Identity, Authorization, Authentication, and Security

   Applications that wish to manipulate or interrogate the state of the
   routing system must be appropriately authorized.  This means that at
   least one means of determining the unique identity of an application
   and its associated access privileges must be available; this implies
   that the identity and associated access privileges must be verifiable
   from the router being programmed.

   Furthermore, being able to associate a state and the modifications to
   a state with a specific application would aid in troubleshooting and
   auditing of the routing system.  By associating identity and
   authorization with installed state, other applications with
   appropriate authority can clean up state abandoned by failed
   applications, if necessary.

   Security of communication between the application and the router is
   also critical and must be considered in the design of the mechanisms
   to support these programmatic interfaces.

3.3.  Speed and Frequency of State Installation

   A programmatic interface does not by itself imply the frequency of
   state updates nor the speed at which the state installation is
   required.  These are critical aspects of an interface and govern what
   an application can use the interface for.  The difference between
   sub-second responsiveness to millions of updates and a day delay per
   update is, obviously, drastic.  The key attributes of the
   programmatic interface are described in Section 1 and include that
   the interface must be asynchronous.

   For each interface in IRS, it will be necessary to specify expected
   scaling, responsiveness, and performance so that applications can
   understand the uses to which the IRS can be used.

   IRS must support asynchronous streaming real-time interactions
   between the applications and router.  IRS must assume that there are
   many unrelated applications that may be simultaneously using IRS.
   This implies that applications must be able to subscribe to change
   events that notify them about changes done to state by other
   applications or configuration.

   Furthermore, IRS should construct interfaces that cater to different
   scaling and frequency of update parameters.  For example, slow, but
   detailed queries of the system, or fast yet higher level (less
   detailed) queries or modifications.

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3.4.  Lifetime of IRS-Installed Routing System State

   In routers today, the lifetime of different routing state depends
   upon how that state was learned and committed.  If the state is
   configuration state, then it is ephemeral when just in the running
   configuration or persistent when written to the startup
   configuration.  If the state is learned via a routing protocol or
   SNMP, it is ephemeral, lasting only until the router reboots or the
   state is withdrawn.

   Unlike previous injection mechanisms that implied the state lifetime,
   IRS requires that multiple models be supported for the lifetime of
   state it installs.  This is because the lifetime or persistence of
   state of the routing system can vary based on the application that
   programmed it, policies or security authorization of the application.

   There are four basic models to be supported.

   Ephemeral:   State installed by the application remains on the router
      in its active memory until such time as it is either removed by a
      routing or signaling protocol, removed by a configuration
      initiated by an application, or the router reboots.  In the case
      of the latter, past state is forgotten when the router reboots.

   Persistent:   State installed by the application remains on the
      router across reboots or restarts of the system.  It can be
      dynamically removed or manipulated by an application, by
      configuration, or by the routing system itself.  This state does
      not appear in the router's configuration; it is processed after
      all the configuration upon a reboot.

   Time-Based:   When state is installed by the application, it has an
      expiration time specified.  When that time has passed, the state
      is removed from the router.  It can also be dynamically removed or
      manipulated by an application, by configuration or the routing
      system itself.  State that hasn't expired will remain on a router
      through reboots.

   Time-Based Ephemeral:   When state is installed by the application,
      it has an expiration time specified.  When that time has passed,
      the state is removed from the router.  It can also be dynamically
      removed or manipulated by an application, by configuration, by the
      routing system itself, or by the router rebooting.  Past state is
      forgotten after the router reboots.

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3.5.  Start-Time of IRS-Installed Routing System State

   To provide flexibility, pre-programming, and handle dependencies, it
   is necessary to have multiple models of when a operation is to be
   handled.  There are the following basic models to be supported.

   Immediate:   When the operation is received, it should be acted upon
      as quickly as reasonable (e.g. queued with other outstanding
      requests if necessary).

   Time-Based:   An application may provide an operation that is to be
      initiated at a particular time.  When the specified time is
      reached, the operation should be acted upon as quickly as
      reasonable.  Implementations may, of course, strive to improve the
      time-accuracy at which the operation is initiated.

   Triggered:   The operation should be initiated when the specified
      triggering event has happened.  A triggering event could be the
      successful or failed completion of another operation.  A
      triggering event could be a system event, such as an interface up
      or down, or another event such as a particular route changing its

   Because it is possible to request operations in models other than
   "Immediate" and some of the start-times will be at an unknown future
   point (e.g.  "Triggered"), it is not feasible to guarantee that the
   resources required by an operation will always be available without
   reserving them from the time the operation is received.  While that
   type of resource reservation should be possible, applications must
   also be able to handle an operation failing or being preempted due to
   resources or due to a higher priority or better authorized
   application taking ownership of the associated state or resource.

4.  Bidirectional Interfaces to the Routing System

   IRS is a bidirectional programmatic interface that allows both
   routing and non-routing applications to install, remove, read, and
   otherwise manipulate the state of the routing system.

   Just as the Internet routing system is not a single protocol or
   implementation layer, neither does it make sense for the IRS to be at
   a single layer or reside within a single protocol.  For each protocol
   or layer, there are different data models, abstractions and interface
   syntaxes and semantics required.  Howeve,r with this in mind, it is
   ideal that a minimal set of mechanism(s) to define, transfer and
   manipulate this state will be specified with as few optional
   characteristics as possible.  This will foster better

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   interoperability between different vendor implementations.

   Since IRS is focused on the routing system, the layers of interest
   start with the RIB and continue up through the IGPs, BGP, RSVP-TE,
   LDP, etc.  The intent is neither to provide interfaces to the
   forwarding plane nor to provide interfaces to application layers.

   It is critical that these interfaces provide the ability to learn
   state, filtered by request, as well as install state.  IRS assumes
   that there will be multiple applications using IRS and therefore the
   ability to read state is necessary to fully know the router's state.
   In general, if an interface allows the setting of state, the ability
   to read and modify that state is also necessary.

4.1.  Static Routing

   The ability to specify static routes exists via CLI and MIBs but
   these mechanisms do not provide a streaming programmatic interface.
   IRS solves this problem by proposing interfaces to the RIB, LFIB, and
   Multicast RIBs.

   By installing static routes into the RIB layer, IRS is able to
   utilize the existing router OS and its mechanisms for distributing
   the selected routes into the FIB and LIB.  This avoids the need to
   model or standardize the forwarding plane.

4.1.1.  Routing Information Base Interface

   The RIB is populated with routes and next-hops as supplied by
   configuration, management, or routing protocols.  A route has a
   preference based upon the specific source from which the route was
   derived.  Static routes, specified via CLI, can be installed with an
   appropriate preference.  The FIB is populated by selecting from the
   RIB based on policy and tie-breaking criteria.

   The IRS interface should allow dynamic reading and writing of routes
   into the RIB.  There are several important attributes associated with
   doing so, as follows:

   Preference Value:   This allows decisions between conflicting routes,
      whether IRS-installed or otherwise.  IRS-installed routes can each
      be installed with a different preference value.

   Route Table Context:   There can be different route table contexts in
      the RIB.  Examples include multiple protocols (e.g.  IPv4, IPv6),
      multiple topologies, different uses, and multiple networks (e.g.
      VRF tables for VPNs).  Appropriate application-level abstractions
      are required to describe the desired route table context.

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   Route or Traffic Identification  The specific IP prefix or even
      interface must be specified.

   Outgoing Path and Encapsulation:   It is necessary to specify the
      outgoing path and associated encapsulation.  This may be done
      directly or indirectly.  This is one of the more complex aspects
      with the following considerations.

      Primary Next-Hops:   To support multi-path forwarding, multiple
         primary next-hops can be specified and the traffic flows split
         among them.

      Indirection:   Instead of specifying particular primary next-hops,
         it is critical to be able to provide the ability for
         indirection, such as is used between BGP routes and IGP routes.
         Thus, the outgoing path might be specified via indirection to
         be the same as another route's.

      Encapsulation:   Associated with each primary next-hop can be
         details on the type of encapsulation for the packet.  Such
         encapsulation could be MPLS, GRE, etc. as supported by the

      Protection:   For fast-reroute protection, each primary next-hop
         may have one or more alternate next-hops specified.  Those are
         to be used when the primary next-hop fails.

      DSCP:   For QoS, the desired DSCP to be used for the outgoing
         traffic can be specified.

   It is useful for an application to be able to read out the RIB state
   associated with particular traffic and be able to learn both the
   preferred route and its source as well as other candidates with lower

   Although there is no standardized model or specification of a RIB, it
   may be possible to build an interoperable bi-directional interface
   without one.

4.1.2.  Label Forwarding Information Base Interface

   The LFIB has a similar role to the RIB for MPLS labeled packets.
   Each entry has slightly different information to accommodate MPLS
   forwarding and semantics.  Although static MPLS can be used to
   configure specific state into the LFIB, there is no bidirectional
   programmatic interface to program, modify, or read the associated

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   Each entry in the LFIB requires a MPLS label context (e.g. platform,
   per-interface, or other context), incoming label, label operation,
   and next-hops with associated encapsulation, label operation, and so
   on.  Via the IRS LFIB interface, an application could supply the
   information for an entry using either a pre-allocated MPLS label or a
   newly allocated MPLS label that is returned to the application.

4.1.3.  Multicast Routing Information Base Interface

   There is no bidirectional programmatic interface to add, modify,
   remove or read state from the multicast RIB.  This IRS interface
   would add those capabilities.

   Multicast forwarding state can be set up by a variety of protocols.
   As with the unicast RIB, an application may wish to install a new
   route for multicast.  The state to add might be the full multicast
   route information - including the incoming interface, the particular
   multicast traffic (e.g. (source, group) or MPLS label), and the
   outgoing interfaces and associated encapsulations to replicate the
   traffic too.

   The multicast state added need not match to well-known protocol
   installed state.  For instance, traffic received on an specified set,
   or all, interfaces that is destined to a particular prefix from all
   sources or a particular prefix could be subject to the specified

4.2.  Beyond Destination-based Routing

   Routing decisions and traffic treatment is not merely expressable via
   destination-based routing or even (S, G) routing, such as in
   multicast.  Capturing these aspects into appropriate interfaces for
   the IRS provides the ability for applications to control them as

4.2.1.  Policy-Based Routing Interface

   A common feature of routers is the ability to specify policy-based
   routing (PBR) rules for accepting, dropping, or differently
   forwarding particular traffic.  This is a very useful functionality
   for an application to be able to rapidly add and remove state into.
   Such state would indicate the particular traffic to be affected and
   its subsequent behavior (e.g. drop, accept, forward on specified
   outgoing path and encapsulation, QoS, DSCP marking, policing, etc.).
   Such state is made more complex by the potential importance of
   ordering among the PBR rules.

   While PBR rules can be specified via CLI, this mechanism is not a

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   streaming programmatic interface nor is there generally the ability
   to specify particular time-based lifetimes for each rule.

4.2.2.  QoS State

   While per-hop behaviors are defined as well as standard DSCP
   meanings, the details of QoS configuration are not standardized and
   can be highly variable depending upon platform.  It is NOT a goal of
   this work to standardize QoS configurations.  Instead, a data object
   model can define push/pull configurations.  More investigation is
   needed to better describe the details.

4.3.  Protocol Interactions

   Providing IRS interfaces to the various routing protocols allows
   applications to specify policy, local topology changes, and
   availability to influence the routing protocols in a way that the
   detailed addition or modification of routes in the RIB does not.

   The decision to distribute the routing state via a routing or
   signaling protocol depends upon the protocol-layer at which this
   state is injected into the routing system.  It may also depend upon
   which routing domain or domains this information is injected as well.

   In addition it is necessary to have the ability to pull state
   regarding various protocols from the router, a mechanism to register
   for asynchronous events, and the means to obtain those asynchronous
   events.  An example of such state might be peer up/down.

4.3.1.  IGP Interfaces

   The lack of a streaming programmatic interface to the IGPs limits the
   ability of applications to influence and modify the desired behavior
   of the IGP.

   An application may need to indicate that a router is overloaded (via
   ISIS or the method described in [RFC3137]) because that router does
   not yet have sufficient state synchronized or installed into it.
   When critical state is provided not merely by routers but also from
   applications via the IRS, a synchronization mechanism can be needed.

   The ability for an application to modify the local topology can be
   part of this interface.  One possibility is to allow modification of
   local interface metrics to generally influence selected routes.  A
   more extensive interface might include the ability to create a OSPF
   or ISIS adjacency across a specified interface (virtual or real) with
   the appropriate associated encapsulation.

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   The ability to attach a prefix to the local router would provide a
   straightforward method for an application to program a single router
   and have the proper routes computed and installed by all other
   routers in the relevant domains.  Additional aspects to the prefix
   attachment, such as the metric with which to attach the prefix and
   fast-reroute characteristics, would be part of the interface.

   Beyond such pure routing information, the need for an application to
   be able to install state to be flooded via an IGP has already been
   recognized.  [I-D.ietf-isis-genapp] specifies a mechanism for
   flooding generalized application information via ISIS, but does not
   describe how an application can generate or consume this information.
   Similarly, [RFC5250] specifies Opaque LSAs for OSPF to provide for
   application-specific information to be flooded.  An IRS interface and
   associated data object model would provide such a mechanism.

   Additional investigation will identify other state that applications
   may wish to install.

   From the IGP, applications via IRS can extract significant
   topological information about the routers, links, and associated

4.3.2.  BGP Interface

   BGP carries significant policy and per-application specific
   information as well as internet routes.  A significant interface into
   BGP is expected, with different data object models for different
   applications.  For example, the IRS interface to BGP could provide
   the ability to specify the policy on which paths BGP chooses to
   advertise.  Additionally, the ability to specify information with an
   application-specified AFI/SAFI could provide substantial flexibility
   and control.

   An existing example of application information carried in BGP is BGP
   Flowspec [RFC5575] which can be used to provide traffic filtering and
   aid in handling denial-of-service attacks.

   The ability to extract information from BGP is also quite critical.
   A useful example of this is the information available from BGP via
   [I-D.gredler-idr-ls-distribution], which allows link-state topology
   information to be carried in BGP.

4.3.3.  PIM and mLDP Interfaces

   For PIM and mLDP, there are at least two types of state that an
   application might wish to install.  First, an application might add
   an interface to join a particular multicast group.  Second, an

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   application might provide an upstream route for traffic to be
   received from - rather than having PIM or mLDP need to consult the
   unicast RIB.

   Additional investigation will identify other state that applications
   may wish to install.

4.4.  Triggered Sessions and Signaling

4.4.1.  OAM-related Sessions Interface

   An application may need to trigger new OAM sessions (e.g.  BFD, VCCP,
   etc.) using an appropriate template.  For example, there may be
   applications that need to create a new tunnel, verify its
   functionality via new triggered OAM sessions, and then bring it into
   service if that OAM indicates successful functionality.  More
   investigation is needed to better describe the details.

4.4.2.  Dynamic Session Creation

   An application may wish to trigger a peering relationship for a
   protocol.  For instance, a targeted LDP session may be required to
   exchange state installed locally with a remote router.  More
   investigation is needed to better describe the different cases and

4.4.3.  Triggered Signaling

   To easily create dynamic state throughout the network, an application
   may need to trigger signaling via protocols such as RSVP-TE.  An
   example of such an application can be a Stateful Path Computation
   Element (PCE)[I-D.ietf-pce-stateful-pce], which has control of
   various LSPs that need to be signaled.

   More investigation is needed to better describe the different cases
   and details.

5.  Interfaces for Learned Information from the Routing System

   Just as applications need to inject state into the routing system to
   meet various application-specific and policy-based requirements, it
   is critical that applications be able to also extract necessary state
   from the routing system.

   A part of each of these interfaces is the ability to specify the
   generation of the desired information (e.g., collecting specific per-
   flow measurements) and the ability to specify appropriate filters to

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   indicate the specifics and abstraction level of the information to be

   The types of information to extract can be generally grouped into the
   following different categories.

   Topological:   The need to understand the network topology, at a
      suitable abstraction layer, is critical to applications.
      Connectivity is not sufficient - the associated costs, bandwidths,
      latencies, etc. are all important aspects of the network topology
      that strongly influence the decision-making and behavior of

   Measurements:   Applications require measurements of traffic and
      network behavior in order to have a more meaningful feedback
      control loop.  Such information may be per-interface, per-flow,
      per-firewall rule, per-queue, etc.

   Events:   There are a variety of asynchronous events that an
      application may require or use as triggering conditions for
      starting other operations.  An obvious example is interface state

   Configuration:   For some aspects, it may be necessary for
      applications to be able to learn about the routing configuration
      on a box.  This is partially available via various MIBs and
      NetConf.  What additional information needs to be exported and the
      appropriate mechanisms needs further examination.

   The need to extract information from the network is not new; there is
   on-going work in the IETF in this area.  This framework describes
   those efforts in the context of the above categories and starts the
   discussion of the aspects still required.

5.1.  Efforts to Obtain Topological Data

   Topological data can be defined and presented at different layers
   (e.g.  Layer-2, Layer-3) and with different characteristics exposed
   or hidden (e.g. physical or virtual, SRLGs, bandwidth, latency,
   etc.).  It can also have different states, such as configured but
   unavailable, configurable, active, broken, administratively disabled,

   To solve the problem of only being able to obtain topological data
   via listening to the IGP in each area, BGP-LS
   [I-D.gredler-idr-ls-distribution] defines extensions to BGP so that
   link-state topology information can be carried in BGP and a single
   BGP listener in the AS can therefore learn and distribute the entire

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   AS's current link-state topology.  BGP-LS solves the problem of
   distributing topological information throughout the network.  While
   IRS may expand the information to be distributed, IRS addresses the
   API aspect of BGP-LS and not the network-wide distribution.

   At another level, ALTO [RFC5693] provides topological information at
   a higher abstraction layer, which can be based upon network policy,
   and with application-relevant services located in it.  The mechanism
   for ALTO obtaining the topology can vary and policy can apply to what
   is provided or abstracted.

   Neither of these fully meet the need to obtain detailed, layered
   topological state that provides more information than the current
   functional status.  While there are currently no sufficiently
   complete standards, the need for such functionality can be deduced by
   the number of proprietary systems that have been developed to obtain
   and manage topology; even Element Management Systems start with the
   need for learning and manipulating the topology.  Similarly,
   orchestration layers for applications start with the need to manage
   topology and the associated database.

   Detailed topology includes aspects such as physical nodes, physical
   links, virtual links, port to interface mapping, etc.  The details
   should include the operational and administrative state as well as
   relevant parameters ranging from link bandwidth to SRLG membership.
   Layering is critical to provide the topology at the level of
   abstraction where it can be easily used by the application.

   A key aspect of this interface is the ability to easily rate-limit,
   filter and specify the desired information to be extracted.  This
   will help in allowing the interface to scale when queries are done.

5.2.  Measurements

   IPFIX [RFC5470] provides a way to measure and export per-traffic flow
   statistics.  Applications that need to collect information about
   particular flows thus have a clear need to be able to install state
   to configure IPFIX to measure and export the relevant flows to the
   appropriate collectors.

5.3.  Events

   A programmatic interface for application to subscribe to asynchronous
   events is necessary.  In addition to the interface state events
   already mentioned, an application may wish to subscribe to certain
   OAM-triggered events that aren't otherwise exported.

   A RIB-based event could be reporting when the next-hops associated

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   with a route have changed.  Other events could be used to verify that
   forwarding state has been programmed.  For example, an application
   could request an event whenever a particular route in the RIB has its
   forwarding plane installation completed.

   When an application registers for events, the application may request
   to get only the first such event, all such events, or all events
   until a certain time.

   The full set of such events, that are not specifically related to
   other interfaces, needs to be investigated and defined.

6.  Manageability Considerations

   Manageability plays a key aspect in IRS.  Some initial examples

   Data Authorization Levels:   The data-models used for IRS need the
      ability to indicate the required authorization level for
      installing or reading a particular subset of data.  This allows
      control of what interactions each application can have.

   Identity Authorization Levels:   Associated with an application's
      identity should be an identity authorization level that is in a
      heirarchy so that higher authorized applications can manage and
      remove the state and resources used by other applications.  The
      top of such a heirarchy would be the router configuration itself.

   Resource Limitations:   Using IRS, 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 critical.

   Configuration Interactions:   The interaction of state installed via
      the IRS and via a router's configuration needs to be clearly

7.  IANA Considerations

   This document includes no request to IANA.

8.  Security Considerations

   This framework describes interfaces that clearly require serious
   consideration of security.  The ability to identify, authenticate and

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   authorize applications that wish to install state is necessary and
   briefly described in Section 3.2.  Security of communications from
   the applications is also required.

   More specifics on the security requirements requires further

9.  Acknowledgements

   The authors would like to thank Ken Gray, Adrian Farrel, Bruno
   Rijsman, Rex Fernando, Jan Medved, John Scudder, and Hannes Gredler
   for their suggestions and review.

10.  Informative References

              Gredler, H., Medved, J., Previdi, S., and A. Farrel,
              "North-Bound Distribution of Link-State and TE Information
              using BGP", draft-gredler-idr-ls-distribution-02 (work in
              progress), July 2012.

              Ginsberg, L., Previdi, S., and M. Shand, "Advertising
              Generic Information in IS-IS", draft-ietf-isis-genapp-04
              (work in progress), November 2010.

              Crabbe, E., Medved, J., Varga, R., and I. Minei, "PCEP
              Extensions for Stateful PCE",
              draft-ietf-pce-stateful-pce-01 (work in progress),
              July 2012.

   [RFC3137]  Retana, A., Nguyen, L., White, R., Zinin, A., and D.
              McPherson, "OSPF Stub Router Advertisement", RFC 3137,
              June 2001.

   [RFC5250]  Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The
              OSPF Opaque LSA Option", RFC 5250, July 2008.

   [RFC5470]  Sadasivan, G., Brownlee, N., Claise, B., and J. Quittek,
              "Architecture for IP Flow Information Export", RFC 5470,
              March 2009.

   [RFC5575]  Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J.,
              and D. McPherson, "Dissemination of Flow Specification
              Rules", RFC 5575, August 2009.

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   [RFC5693]  Seedorf, J. and E. Burger, "Application-Layer Traffic
              Optimization (ALTO) Problem Statement", RFC 5693,
              October 2009.

   [RFC6020]  Bjorklund, M., "YANG - A Data Modeling Language for the
              Network Configuration Protocol (NETCONF)", RFC 6020,
              October 2010.

Authors' Addresses

   Alia Atlas (editor)
   Juniper Networks
   10 Technology Park Drive
   Westford, MA  01886


   Thomas Nadeau
   Juniper Networks
   1194 N. Mathilda Ave.
   Sunnyvale, CA  94089


   Dave Ward
   Cisco Systems
   Tasman Drive
   San Jose, CA  95134


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