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Internet Engineering Task Force                                   C. Li
Internet Draft                                            China Telecom
Intended status: Informational                                 Y. Cheng
                                                           China Unicom
                                                          J. Strassner
                                                               O.Havel
                                                                  W.Xu
                                                   Huawei Technologies
                                                       October 22, 2018
Expires: April 2019



                           Intent Classification
                  draft-draft-li-intent-classification-01


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Abstract

   RFC 7575 [RFC7575] defines Intent as an abstract high-level policy
   used to operate the network.  Intent management system includes an
   interface for users to input requests and an engine to translate the
   intents into the network configuration and manage their lifecycle.
   Up to now, there is no commonly agreed definition, interface or
   model of intent.

   This document discusses what intent means to different stakeholders,
   describes different ways to classify intent, and an associated
   taxonomy of this classification.


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Table of Contents


   1. Introduction ................................................ 3
   2. Requirements Language ........................................ 4
   3. Acronyms .................................................... 4
   4. Abstract intent requirements ................................. 4
      4.1. What is Intent ......................................... 4
      4.2. Intent Solutions & Intent Users ......................... 5
      4.3. Current Problems & Requirements ......................... 5
      4.4. Intent Types that need to be supported .................. 7
   5. The Policy Continuum......................................... 7
   6. Functional Characteristics and Behavior ...................... 8
      6.1. Persistence ............................................ 8
      6.2. Granularity ............................................ 8
      6.3. Abstracting Intent Operation ............................ 9
      6.4. Policy Subjects and Policy Targets ...................... 9
      6.5. Policy Scope ........................................... 9
   7. IANA Considerations ........................................ 11
   8. Security Considerations ..................................... 11
   9. IANA Considerations ........................................ 11
   10. References ................................................ 11
      10.1. Normative References .................................. 11
      10.2. Informative References ................................ 11
   11. Acknowledgments ........................................... 12

1. Introduction

   Different SDOs (such as [ANIMA][ONF]) have proposed intent as a
   declarative interface for defining a set of network operations to
   execute.

   Although there is no common definition or model of intent which are
   agreed by all SDOs, there are several shared principles:

   o intent should be declarative, using and depending on as few
      deployment details as possible and focusing on what and not how

   o intent should provide an easy-to-use interface, and use
      terminology and concepts familiar to its target audience

   o intent should be vendor-independent and portable across platforms

   o the intent framework should be able to detect and resolve
      conflicts between multiple intents




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   SDOs have different perspectives on what intent is, what set of
   actors it is intended to serve, and how it should be used.  This
   document provides several dimensions to classify intents.



2. Requirements Language

      The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
   NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL"
   in this document are to be interpreted as described in RFC 2119
   [RFC2119].



3. Acronyms

      CLI: Command Line Interface

      SDO: Standards Development Organisation

      SUPA: Simplified Use of Policy Abstractions

      VPN: Virtual Private Network



4. Abstract intent requirements

   In order to understand the different intent requirements that would
   drive intent classification, we first need to understand what intent
   means for different intent users.

4.1. What is Intent

   The term Intent has become very widely used in the industry for
   different purposes, sometimes it is not even in agreement with SDO
   shared principles mentioned in the Introduction. Different
   stakeholders consider an intent to be an ECA policy, a GBP policy, a
   business policy, a network service, a customer service, a network
   configuration, application / application group policy, any
   operator/administrator task, network troubleshooting / diagnostics /
   test, a new app, a marketing term for existing
   management/orchestration capabilities, etc. Their intent is
   sometimes technical, non-technical, abstract or technology specific.
   For some stakeholders, intent is a subset of these and for other



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   stakeholders intent is all of these. It has in some cases become a
   term to replace a very generic 'service' or 'policy' terminology.

   While it is easier for those familiar with different standards to
   understand what service, CFS, RFS, resource, policy continuum, ECA
   policy, declarative policy, abstract policy or intent policy is, it
   may be more difficult for the wider audience. Intent is very often
   just a synonym for policy. Those familiar with policies understand
   the difference between a business, intent, declarative, imperative
   and ECA policy. But maybe the wider audience does not understand the
   difference and sometimes equates the policy to an ECA policy.

   Therefore, it is important to start a discussion in the industry
   about what intent is for different solutions and intent users. It is
   also imperative to try to propose some intent categories /
   classifications that could be understood by a wider audience. This
   would help us define intent interfaces, DSLs and models.

4.2. Intent Solutions & Intent Users

   Different Solutions and Actors have different requirements,
   expectations and priorities for intent driven networking. They
   require different intent types and have different use cases. Some
   users are more technical and require intents that expose more
   technical information. Other users do not understand networks and
   require intents that shield them from different networking concepts
   and technologies.



4.3. Current Problems & Requirements

   Network APIs and CLIs are too complex due to the fact that they
   expose technologies & topologies. App developers and end-users do
   not want to set IP Addresses, VLANs, subnets, ports, etc. Operators
   and administrators would also benefit from the simpler interfaces,
   like:

   o Allow Customer Site A to be connected to Internet via Network B

   o Allow User A to access all internal resources, except the Server
      B

   o Allow User B to access Internet via Corporate Network A

   o Move all Users from Corporate Network A to the Corporate Network
      B


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   o Request Gold VPN service between my sites A, B and C

   o Provide CE Redundancy for all Customer Sites

   o Add Access Rules to my Service

   Networks are complex, with many different protocols and
   encapsulations. Some basic questions are not easy to answer:

   o Can User A talk to User B?

   o Can Host A talk to Host B?

   o Are there any loops in my network?

   o Are Network A and Network B connected?

   o Can User A listen to communications between Users B & C?



   Operators and Administrators manually troubleshoot and fix their
   networks and services. They instead want:

   o a reliable network that is self-configured and self-assured based
      on the intent

   o to be notified about the problem before the user is aware

   o automation of network/service recovery based on intent (self-
      healing, self-optimization)

   o to get suggestions about correction/optimization steps based on
      experience (historical data & behaviour)

   Therefore, Operators and Administrators want to:

   o simplify and automate network operations

   o simplify definitions of network services

   o provide simple customer APIs for Value Added Services (operators)

   o be informed if the network or service is not behaving as
      requested




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   o enable automatic optimization and correction for selected
      scenarios

   o have systems that learn from historic information and behaviour



   End-Users cannot build their own services and policies without
   becoming technical experts and they must perform manual maintenance
   actions. Application developers and end-users/subscribers want to be
   able to:

   o build their own network services with their own policies via
      simple interfaces, without becoming networking experts

   o have their network services up and running based on intent and
      automation only, without any manual actions or maintenance



4.4. Intent Types that need to be supported

   The following intent types need to be supported, in order to address
   the requirements from different solutions and intent users:

   o Customer network service intent

   o Network resource management

   o Cloud and cloud resource management

   o Network Policy intent

   o Task based intents

   o System policies intents



5. The Policy Continuum

   The Policy Continuum defines the set of actors that will create,
   read, use, and manage policy.  Each set of actors has their own
   terminology and concepts that they are familiar with.  This captures
   the fact that business people do not want to use CLI, and network
   operations center personnel do not want to use non-technical
   languages.


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6. Functional Characteristics and Behavior

   Intent can be used to operate immediately on a target (much like
   issuing a command), or whenever it is appropriate (e.g., in response
   to an event).  In either case, intent has a number of behaviors that
   serve to further organize its purpose, as described by the following
   subsections.

6.1. Persistence

   Intents can be classified into transient/persistent intents.

   If intent is transient, it has no lifecycle management.  As soon as
   the specified operation is successfully carried out, the intent is
   finished, and can no longer affect the target object.

   If the intent is persistent, it has lifecycle management.  Once the
   intent is successfully activated and deployed, the system will keep
   all relevant intents active until they are deactivated or removed.



6.2. Granularity

   Intents can have different granularities: high granularity, low
   granularity and anything in between.



   High granularity intents are more complex to design but are the most
   valuable. Intent translation, intent conflict resolution and intent
   verification are very complex and require advanced algorithms.
   Examples: e2e network service, like customer network service over
   physical & virtual network, over access, metro, dc and wan with all
   related QoS, security and application policies.



   Low granularity intents, like some path checks (can A talk to B) or
   individual network service/network/application/user policies, are
   the least complex. Their intent translation, intent conflict
   resolution and intent verification are much simpler than for high
   granularity intents.




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6.3. Abstracting Intent Operation

   The modeling of Policies can be abstracting using the following
   three-tuple:

      {Context, Capabilities, Constraints}

   Context grounds the policy, and determines if it is relevant or not
   for the current situation.  Capabilities describe the functionality
   that the policy can perform.  Capabilities take different forms,
   depending on the expressivity of the policy as well as the
   programming paradigm(s) used.  Constraints define any restrictions
   on the capabilities to be used for that particular context. Metadata
   can be optionally attached to each of the elements of the three-
   tuple, and may be used to describe how the policy should be used and
   how it operates, as well as prescribe any operational dependencies
   that must be taken into account.

   Put another way:

   o Context selects policies based on applicability

   o Capabilities describe the functionality provided by the policy

   o Constraints restrict the capabilities offered and/or the behavior
      of the policy

   Hence, the difference between imperative, declarative, and other
   types of policies lies in how the elements of this three-tuple are
   used according to that particular programming paradigm.  This is how
   [SUPA] was designed: a Policy is a container that aggregates a set
   of statements.

6.4. Policy Subjects and Policy Targets

   Policy subject is the actor that performs the action specified in
   the policy.  It can be the intent management system which executes
   the policy.  Policy target is a set of managed objects which may be
   affected in the policy enforcement.

6.5. Policy Scope

   Policies used to manage the behavior of objects that they are
   applied to (e.g., the target of the policy).

   It is useful to differentiate between the following categories of
   targets:


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   o Policies defined for the Customer or End-User

   o Policies defined for the management system to act on objects in
      the domain that the management system controls

   o Policies defined for the management system to act on objects in
      one or more domains that the management system does not directly
      control

   The different origins and views of these three categories of actors
   lead to the following important differences:

   o Network Knowledge.  This area is explored using three exemplary
      actors that have different knowledge of the network.

   Customers and end-users do not necessarily know the functional and
   operational details of the network that they are using.
   Furthermore, most of the actors in this category lack skills to
   understand such details; in fact, such knowledge is typically not
   relevant to their job.  In addition, the network may not expose
   these details to its users.  This class of actor focuses on the
   applications that they run, and uses services offered by the
   network.  Hence, they want to specify policies that provide
   consistent behavior according to their business needs.  They do not
   have to worry about how the policies are deployed onto the
   underlying network, and especially, whether the policies need to be
   translated to different forms to enable network elements to
   understand them.

   Application developers work in a set of abstractions defined by
   their application and programming environment(s).  For example, many
   application developers think in terms of objects (for example, a
   VPN).  While this makes sense to the application developer, most
   network devices do not have a VPN object per se; rather, the VPN is
   formed through a set of configuration statements for that device in
   concert with configuration statements for the other devices that
   together make up the VPN.  Hence, the view of application developers
   matches the services provided by the network, but may not directly
   correspond to other views of other actors.

   Management personnel, such as network Administrators, have complete
   knowledge of the underlying network.  However, they may not
   understand the details of the applications and services of Customers
   and End-Users.





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   o Automation.  In theory, intents from both end-user and management
      system can be automated.  In practice, most intents from end-user
      are created manually according to business request.  End-users do
      not create or alter intents unless there is change in business.
      Intents from management systems can be created or altered to
      reflect with network policy change.  For example, end-users
      create intents to set up paths between hosts, while the
      management system creates an intent to set a global link
      utilization limit.

7. IANA Considerations

   This document includes no request to IANA.



8. Security Considerations

   This document does not have any Security Considerations.

9. IANA Considerations

   This document includes no request to IANA.

10. References

10.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC7575] Behringer, M., Pritikin, M., Bjarnason, S., Clemm, A.,
             Carpenter, B., Jiang, S., and L. Ciavaglia, "Autonomic
             Networking: Definitions and Design Goals", RFC 7575,
             DOI 10.17487/RFC7575, June 2015

   [SUPA]  Strassner, J., "Simplified Use of Policy Abstractions",
             2017, <https://datatracker.ietf.org/doc/draft-ietf-supa-
             generic-policy-info-model/?include_text=1>.

10.2. Informative References

   [ANIMA] Du, Z., "ANIMA Intent Policy and Format", 2017,
             <https://datatracker.ietf.org/doc/draft-du-anima-an-
             intent/>.




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   [ONF]   ONF, "Intent Definition Principles", 2017,
             <https://www.opennetworking.org/images/stories/downloads/
             sdn-resources/technical-reports/TR-
             523_Intent_Definition_Principles.pdf>.

   [ONOS]  ONOS, "ONOS Intent Framework", 2017,
             <https://wiki.onosproject.org/display/ONOS/
             Intent+Framework/>.

11. Acknowledgments

   The authors would like to thank Will (Shucheng) Liu and Xiaolin Song
   for their comments to this document.



































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Authors' Addresses

   Chen Li
   China Telecom
   No.118 Xizhimennei street, Xicheng District
   Beijing  100035
   P.R. China
   Email: lichen.bri@chinatelecom.cn


   Ying Cheng
   China Unicom
   No.21 Financial Street, XiCheng District
   Beijing  100033
   P.R. China
   Email: chengying10@chinaunicom.cn



   John Strassner
   Huawei Technologies
   2330 Central Expressway
   Santa Clara  95138
   Email: john.sc.strassner@huawei.com


   Olga Havel
   Huawei Technologies
   Email: olga.havel@huawei.com


   Weiping Xu
   Huawei Technologies
   Bantian, Longgang District
   shenzhen  518129
   P.R. China

   Email: xuweiping@huawei.com










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