I2RS Ephemeral State Requirements
draft-ietf-i2rs-ephemeral-state-15

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I2RS working group                                               J. Haas
Internet-Draft                                                   Juniper
Intended status: Standards Track                                S. Hares
Expires: January 22, 2017                                         Huawei
                                                           July 21, 2016

                   I2RS Ephemeral State Requirements
                   draft-ietf-i2rs-ephemeral-state-15

Abstract

   This document covers requests to the NETMOD and NETCONF Working
   Groups for functionality to support the ephemeral state requirements
   to implement the I2RS architecture.

Status of This Memo

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

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   This Internet-Draft will expire on January 22, 2017.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Review of Requirements from I2RS architecture document  . . .   3
   3.  Ephemeral State Requirements  . . . . . . . . . . . . . . . .   5
     3.1.  Persistence . . . . . . . . . . . . . . . . . . . . . . .   5
     3.2.  Constraints . . . . . . . . . . . . . . . . . . . . . . .   5
     3.3.  Hierarchy . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.4.  Ephemeral Configuration overlapping Local Configuration .   6
   4.  YANG Features for Ephemeral State . . . . . . . . . . . . . .   6
   5.  NETCONF Features for Ephemeral State  . . . . . . . . . . . .   6
   6.  RESTCONF Features for Ephemeral State . . . . . . . . . . . .   6
   7.  Requirements regarding Supporting Multi-Head Control via
       Client Priority . . . . . . . . . . . . . . . . . . . . . . .   7
   8.  Multiple Message Transactions . . . . . . . . . . . . . . . .   8
   9.  Pub/Sub Requirements Expanded for Ephemeral State . . . . . .   8
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   11. Security Considerations . . . . . . . . . . . . . . . . . . .   9
   12. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     13.1.  Normative References:  . . . . . . . . . . . . . . . . .  10
     13.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   The Interface to the Routing System (I2RS) Working Group is chartered
   with providing architecture and mechanisms to inject into and
   retrieve information from the routing system.  The I2RS Architecture
   document [I-D.ietf-i2rs-architecture] abstractly documents a number
   of requirements for implementing the I2RS requirements.  Section 2
   reviews 10 key requirements related to ephemeral state.

   The I2RS Working Group has chosen to use the YANG data modeling
   language [RFC6020] as the basis to implement its mechanisms.

   Additionally, the I2RS Working group has chosen to re-use two
   existing protocols, NETCONF [RFC6241] and its similar but lighter-
   weight relative RESTCONF [I-D.ietf-netconf-restconf], as the
   protocols for carrying I2RS.

   What does re-use of a protocol mean?  Re-use means that while YANG,
   NETCONF and RESTCONF are a good starting basis for the I2RS protocol,
   the creation of the I2RS protocol implementations requires that the
   I2RS requirements

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   1.  select features from YANG, NETCONF, and RESTCONF per version of
       the I2RS protocol (See sections 4, 5, and 6)

   2.  propose additions to YANG, NETCONF, and RESTCONF per version of
       the I2RS protocol for key functions (ephemeral state, protocol
       security, publication/subscription service, traceability),

   3.  suggest protocol strawman (e.g.
       [I-D.hares-i2rs-protocol-strawman]) as ideas for the NETCONF,
       RESTCONF, and YANG changes.

   The purpose of these requirements and the suggested protocol straw
   man is to provide a quick turnaround on creating the I2RS protocol.

   Support for ephemeral state is an I2RS protocol requirement that
   requires datastore changes (see section 3), YANG additions (see
   section 4), NETCONF additions (see section 5), and RESTCONF additions
   (see section 6).

   Sections 7-9 provide details that expand upon the changes in sections
   3-6 to clarify requirements discussed by the I2RS and NETCONF working
   groups.  Sections 7 provide additional requirements that detail how
   write-conflicts should be resolved if two I2RS client write the same
   data.  Section 8 provides an additional requirement that details on
   I2RS support of multiple message transactions.  Section 9 highlights
   two requirements in the I2RS publication/subscription requirements
   [I-D.ietf-i2rs-pub-sub-requirements] that must be expanded for
   ephemeral state.

1.1.  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].

2.  Review of Requirements from I2RS architecture document

   The I2RS architecture defines important high-level requirements for
   the I2RS protocol.  The following are ten requirements that
   [I-D.ietf-i2rs-architecture] contains which provide context for the
   ephemeral data state requirements given in sections 3-8:

   1.   The I2RS protocol SHOULD support highly reliable notifications
        (but not perfectly reliable notifications) from an I2RS agent to
        an I2RS client.

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   2.   The I2RS protocol SHOULD support a high bandwidth, asynchronous
        interface, with real-time guarantees on getting data from an
        I2RS agent by an I2RS client.

   3.   The I2RS protocol will operate on data models which MAY be
        protocol independent or protocol dependent.

   4.   I2RS Agent MUST record the client identity when a node is
        created or modified.  The I2RS Agent SHOULD to be able to read
        the client identity of a node and use the client identity's
        associated priority to resolve conflicts.  The secondary
        identity is useful for traceability and may also be recorded.

   5.   Client identity MUST have only one priority for the client's
        identifier.  A collision on writes is considered an error, but
        the priority associated with each client identifier is utilized
        to compare requests from two different clients in order to
        modify an existing node entry.  Only an entry from a client
        which is higher priority can modify an existing entry (First
        entry wins).  Priority only has meaning at the time of use.

   6.   The Agent identity and the Client identity SHOULD be passed
        outside of the I2RS protocol in a authentication and
        authorization protocol (AAA).  Client priority may be passed in
        the AAA protocol.  The values of identities are originally set
        by operators, and not standardized.

   7.   An I2RS Client and I2RS Agent MUST mutually authenticate each
        other based on pre-established authenticated identities.

   8.   Secondary identity data is read-only meta-data that is recorded
        by the I2RS agent associated with a data model's node is
        written, updated or deleted.  Just like the primary identity,
        the secondary identity SHOULD only be recorded when the data
        node is written or updated or deleted

   9.   I2RS agent MAY have a lower priority I2RS client attempting to
        modify a higher priority client's entry in a data model.  The
        filtering out of lower priority clients attempting to write or
        modify a higher priority client's entry in a data model SHOULD
        be effectively handled and not put an undue strain on the I2RS
        agent.

   10.  The I2RS protocol MUST support the use of a secure transport.
        However, certain functions such as notifications MAY use a non-
        secure transport.  Each model or service (notification, logging)
        must define within the model or service the valid uses of a non-
        secure transport.

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3.  Ephemeral State Requirements

   In requirements Ephemeral-REQ-01 to Ephemeral-15, Ephemeral state is
   defined as potentially including both ephemeral configured state and
   operational state.

3.1.  Persistence

   Ephemeral-REQ-01: I2RS requires ephemeral state; i.e. state that does
   not persist across reboots.  If state must be restored, it should be
   done solely by replay actions from the I2RS client via the I2RS
   agent.

   While at first glance this may seem equivalent to the writable-
   running data store in NETCONF, running-config can be copied to a
   persistent data store, like startup config.  I2RS ephemeral state
   MUST NOT be persisted.

3.2.  Constraints

   Ephemeral-REQ-02: Non-ephemeral state MUST NOT refer to ephemeral
   state for constraint purposes; it SHALL be considered a validation
   error if it does.

   Ephemeral-REQ-03: Ephemeral state MUST be able to have constraints
   that refer to operational state, this includes potentially fast
   changing or short lived operational state nodes, such as MPLS LSP-ID
   or a BGP IN-RIB.  Ephemeral state constraints should be assessed when
   the ephemeral state is written, and if any of the constraints change
   to make the constraints invalid after that time the I2RS agent should
   notify the I2RS Client.

   Ephemeral-REQ-04: Ephemeral state MUST be able to refer to non-
   ephemeral state as a constraint.  Non-ephemeral state can be
   configuration state or operational state.

   Ephemeral-REQ-05: I2RS pub-sub, logging, RPC or other mechanisms may
   lead to undesirable or unsustainable resource consumption on a system
   implementing an I2RS Agent.  It is RECOMMENDED that mechanisms be
   made available to permit prioritization of I2RS operations, when
   appropriate, to permit implementations to shed work load when
   operating under constrained resources.  An example of such a work
   shedding mechanism is rate-limiting.

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3.3.  Hierarchy

   Ephemeral-REQ-06: YANG MUST have the ability to:

   1.  to define a YANG module or submodule schema that only contains
       data nodes with the property of being ephemeral, and

   2.  to augment a YANG data model with additional YANG schema nodes
       that have the property of being ephemeral.

3.4.  Ephemeral Configuration overlapping Local Configuration

   Ephemeral-REQ-07: Local configuration MUST have a priority that is
   comparable with individual I2RS client priorities for making changes.
   This priority will determine whether local configuration changes or
   individual ephemeral configuration changes take precedence as
   described in RFC7921.  The I2RS protocol MUST support his mechanism.

4.  YANG Features for Ephemeral State

   Ephemeral-REQ-08:In addition to config true/false, there MUST be a
   way to indicate that YANG schema nodes represent ephemeral state.  It
   is desirable to allow for, and have to way to indicate, config false
   YANG schema nodes that are writable operational state.

5.  NETCONF Features for Ephemeral State

   Ephemeral-REQ-09: The changes to NETCONF/RESTCONF must include:

   1.  Support for communication mechanisms to enable an I2RS client to
       determine that an I2RS agent supports the mechanisms needed for
       I2RS operation.

   2.  The ephemeral state MUST support notification of write conflicts
       using the priority requirements defined in section 7 below in
       requirements Ephemeral-REQ-11 through Ephemeral-REQ-14).

6.  RESTCONF Features for Ephemeral State

   Ephemeral-REQ-10: The conceptual changes to RESTCONF are:

   1.  Support for communication mechanisms to enable an I2RS client to
       determine that an I2RS agent supports the mechanisms needed for
       I2RS operation.

   2.  The ephemeral state must support notification of write conflicts
       using the priority requirements defined in section 7 below in
       requirements Ephemeral-REQ-11 through Ephemeral-REQ-14).

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7.  Requirements regarding Supporting Multi-Head Control via Client
    Priority

   To support Multi-Headed Control, I2RS requires that there be a
   decidable means of arbitrating the correct state of data when
   multiple clients attempt to manipulate the same piece of data.  This
   is done via a priority mechanism with the highest priority winning.
   This priority is per-client.

   Ephemeral-REQ-11: The I2RS Protocol (e.g.  NETCONF/RESTCONF + yang)
   MUST be able to support

   o  the data nodes MAY store I2RS client identity and not the
      effective priority at the time the data node is stored.

   o  Per SEC-REQ-07 in section 3.1 of
      [I-D.ietf-i2rs-protocol-security-requirements], an identifier MUST
      have just one priority.  The I2RS protocol MUST support the
      ability to have data nodes MAY store I2RS client identity and not
      the effective priority of the I2RS client at the time the data
      node is stored.

   o  The priority MAY be dynamically changed by AAA, but the exact
      actions are part of the protocol definition as long as collisions
      are handled as described in Ephemeral-REQ-12, Ephemeral-REQ-13,
      and Ephemeral-REQ-14.

   Ephemeral-REQ-12: When a collision occurs as two clients are trying
   to write the same data node, this collision is considered an error
   and priorities were created to give a deterministic result.  When
   there is a collision, a notification (which includes indicating data
   node the collision occurred on) MUST BE sent to the original client
   to give the original client a chance to deal with the issues
   surrounding the collision.  The original client may need to fix their
   state.

   Note:RESTCONF and NETCONF posts can come in concurrently from
   alternative sources (see ETag in [I-D.ietf-netconf-restconf] section
   3.4.1.2 usage).  Therefore the collision detection and comparison of
   priority needs to occur both for both type of updates (POST or edit-
   config) at the point of comparison.

   Ephemeral-REQ-13: Multi-headed control is required for collisions and
   the priority resolution of collisions.  Multi-headed control is not
   tied to ephemeral state.  I2RS protocol MUST NOT mandate how AAA
   supports priority.  Mechanisms which prevent collisions of two
   clients trying to modify the same node of data are the focus.

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   Ephemeral-REQ-14: A deterministic conflict resolution mechanism MUST
   be provided to handle the error scenario that two clients, with the
   same priority, update the same configuration data node.  The I2RS
   architecture gives one way that this could be achieved, by specifying
   that the first update wins.  Other solutions, that prevent
   oscillation of the config data node, are also acceptable.

8.  Multiple Message Transactions

   Ephemeral-REQ-15: Section 7.9 of the [I-D.ietf-i2rs-architecture]
   states the I2RS architecture does not include multi-message atomicity
   and roll-back mechanisms.  The I2RS protocol implementation MUST not
   require the support of these features.  As part of this requirement,
   the I2SR protocol should support:

      multiple operations in one or more messages handling can handle
      errors within the set of operations in many ways.

      No multi-message commands SHOULD cause errors to be inserted into
      the I2RS ephemeral state.

9.  Pub/Sub Requirements Expanded for Ephemeral State

   I2RS clients require the ability to monitor changes to ephemeral
   state.  While subscriptions are well defined for receiving
   notifications, the need to create a notification set for all
   ephemeral configuration state may be overly burdensome to the user.

   There is thus a need for a general subscription mechanism that can
   provide notification of changed state, with sufficient information to
   permit the client to retrieve the impacted nodes.  This should be
   doable without requiring the notifications to be created as part of
   every single I2RS module.

   The publication/subscription requirements for I2RS are in
   [I-D.ietf-i2rs-pub-sub-requirements], and the following general
   requirements SHOULD be understood to be expanded to to include
   ephemeral state:

   o  Pub-Sub-REQ-01: The Subscription Service MUST support
      subscriptions against ephemeral state in operational data stores,
      configuration data stores or both.

   o  Pub-Sub-REQ-02: The Subscription Service MUST support filtering so
      that subscribed updates under a target node might publish only
      ephemeral state in operational data or configuration data, or
      publish both ephemeral and operational data.

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   o  Pub-Sub-REQ-03: The subscription service must support
      subscriptions which are ephemeral.  (E.g.  An ephemeral data model
      which has ephemeral subscriptions.)

10.  IANA Considerations

   There are no IANA requirements for this document.

11.  Security Considerations

   The security requirements for the I2RS protocol are covered in
   [I-D.ietf-i2rs-protocol-security-requirements] document.  The
   security requirements for the I2RS protocol environment are in
   [I-D.ietf-i2rs-security-environment-reqs].

12.  Acknowledgements

   This document is an attempt to distill lengthy conversations on the
   I2RS mailing list for an architecture that was for a long period of
   time a moving target.  Some individuals in particular warrant
   specific mention for their extensive help in providing the basis for
   this document:

   o  Alia Atlas

   o  Andy Bierman

   o  Martin Bjorklund

   o  Dean Bogdanavich

   o  Rex Fernando

   o  Joel Halpern

   o  Thomas Nadeau

   o  Juergen Schoenwaelder

   o  Kent Watsen

   o  Robert Wilton

13.  References

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13.1.  Normative References:

   [I-D.ietf-i2rs-architecture]
              Atlas, A., Halpern, J., Hares, S., Ward, D., and T.
              Nadeau, "An Architecture for the Interface to the Routing
              System", draft-ietf-i2rs-architecture-15 (work in
              progress), April 2016.

   [I-D.ietf-i2rs-protocol-security-requirements]
              Hares, S., Migault, D., and J. Halpern, "I2RS Security
              Related Requirements", draft-ietf-i2rs-protocol-security-
              requirements-06 (work in progress), May 2016.

   [I-D.ietf-i2rs-pub-sub-requirements]
              Voit, E., Clemm, A., and A. Prieto, "Requirements for
              Subscription to YANG Datastores", draft-ietf-i2rs-pub-sub-
              requirements-09 (work in progress), May 2016.

   [I-D.ietf-i2rs-security-environment-reqs]
              Migault, D., Halpern, J., and S. Hares, "I2RS Environment
              Security Requirements", draft-ietf-i2rs-security-
              environment-reqs-01 (work in progress), April 2016.

   [I-D.ietf-i2rs-traceability]
              Clarke, J., Salgueiro, G., and C. Pignataro, "Interface to
              the Routing System (I2RS) Traceability: Framework and
              Information Model", draft-ietf-i2rs-traceability-11 (work
              in progress), May 2016.

   [I-D.ietf-netconf-restconf]
              Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", draft-ietf-netconf-restconf-15 (work in
              progress), July 2016.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <http://www.rfc-editor.org/info/rfc6241>.

13.2.  Informative References

   [I-D.hares-i2rs-protocol-strawman]
              Hares, S. and a. amit.dass@ericsson.com, "I2RS protocol
              strawman", draft-hares-i2rs-protocol-strawman-03 (work in
              progress), July 2016.

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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <http://www.rfc-editor.org/info/rfc6020>.

Authors' Addresses

   Jeff Haas
   Juniper

   Email: jhaas@juniper.net

   Susan Hares
   Huawei
   Saline
   US

   Email: shares@ndzh.com

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