I2RS working group                                               J. Haas
Internet-Draft                                                   Juniper
Intended status: Informational                                  S. Hares
Expires: April 8, 30, 2017                                           Huawei
                                                        October 5, 27, 2016

                   I2RS Ephemeral State Requirements


   The I2RS (interface to the routing system) Architecture document
   (RFC7921) abstractly describes a number of requirements for ephemeral
   state (in terms of capabilities and behaviors) which any protocol
   suite attempting to meet the needs of I2RS has to provide.  This
   document describes, in detail, requirements for ephemeral state for
   those implementing the I2RS protocol.

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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  . . . . . . . . . . . . . . . .   4
     3.1.  Persistence . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Constraints . . . . . . . . . . . . . . . . . . . . . . .   4   5
     3.3.  Hierarchy . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.4.  Ephemeral Configuration overlapping Local Configuration .   5
   4.  YANG Features for Ephemeral State . . . . . . . . . . . . . .   5   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 . . . . . . . . . . . . . . . . . . . . . . .   6
   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  10
     13.1.  Normative References:  . . . . . . . . . . . . . . . . .   9  10
     13.2.  Informative References . . . . . . . . . . . . . . . . .  11
   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 [RFC7921] abstractly documents a number of requirements for
   implementing the I2RS requirements.  Section 2 reviews 10 key
   requirements related to ephemeral state.  [RFC7921] defines ephemeral
   state as "state which does not survive the reboot of a routing device
   or the reboot of the software handling the I2RS software on a routing
   device" (see section 1.1 of [RFC7921]).

   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

   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),

   The purpose of these requirements is to ensure clarity during I2RS
   protocol creation.

   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.  Section 7 provided additional requirements that detail how
   write-conflicts should be resolved if two I2RS client write the same
   data.  Section 8 describes I2RS requirements for support of multiple
   message transactions.  Section 9 highlights two requirements in the
   I2RS publication/subscription requirements [RFC7923] that must be
   expanded for ephemeral state.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   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 requirements distilled from
   [RFC7921] that provide context for the ephemeral data state
   requirements given in sections 3-8:

   1.  The I2RS protocol SHOULD support a high bandwidth, an interface asynchronous
       programmatic interface interface with real-time guarantees on getting data from properties of described in
       section 5 of [RFC7920] (e.g. high throughput) with support for
       target information streams, filtered evens, and thresholded
       events (real-time events) sent by an I2RS agent by to an I2RS client. Client
       (Key points from section 1.1 of [RFC7921]).

   2.  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.  (Key points from
       section 4 of [RFC7921].)

   3.  An I2RS 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.  (Key
       points from section 7.8 of [RFC7921].)

   4.  I2RS Client's secondary identity data is read-only meta-data that
       is recorded by the I2RS agent associated with a data model's node
       is written.  Just like the primary client identity, the secondary
       identity SHOULD only be recorded when the data node is written.
       (Key points from sections 7.4 of [RFC7921].)

   5.  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.  (See section 7.8 of [RFC7921] augmented by the resource
       limitation language in section 8 [RFC7921].)

3.  Ephemeral State Requirements

   In requirements Ephemeral-REQ-01 to Ephemeral-REQ-15, Ephemeral state
   is defined as potentially including in a data model ephemeral
   configuration and operational state which is flagged as ephemeral.

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

   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
   (label switched path ID) or a BGP Adj-RIB-IN (Adjacent RIB Inboud).
   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 [RFC7923], tracing [RFC7922], 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-

3.3.  Hierarchy

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

   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 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 this 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 a 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 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 (see
       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 (see
       requirements Ephemeral-REQ-11 through Ephemeral-REQ-14).

7.  Requirements regarding Supporting Multi-Head Control via client

   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 following requirements must be supported by the
   I2RS protocol I2RS Protocol (e.g.  NETCONF/RESTCONF + yang) in order
   to support I2RS client identity and priority:

   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 4.3 of
      [I-D.ietf-i2rs-protocol-security-requirements], an I2RS Identifier
      MUST have just one priority.  The I2RS protocol MUST support the
      ability to have data nodes store I2RS client identity and not the
      effective priority of the I2RS client at the time the data node is

   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 error.
   The I2RS priorities were created are used to give provide a deterministic result. resolution to
   the conflict.  When there is a collision, and the data node is
   changed, 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.

   Explanation: RESTCONF and NETCONF updates can come in concurrently
   from alternative sources.  Therefore the collision detection and
   comparison of priority needs to occur for any type of update.

   For example, RESTCONF tracks the source of configuration change via
   the entity-Tag (section 3.5.2 of [I-D.ietf-netconf-restconf]) which
   the server returns to the client along with the value in GET or HEAD
   methods.  RESTCONF requires that this resource entity-tag be updated
   whenever a resource or configuration resource within the resource is
   altered.  In the RESTCONF processing, when the resource or a
   configuration resource within the resource is altered, then the
   processing of the configuration change for two I2RS clients must
   detect an I2RS collision and resolve the collision using the priority

   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 the internal
   mechanism for how AAA protocols (E.g.  Radius or Diameter) or
   mechanisms distribute priority per identity except that any AAA
   protocols MUST operate over a secure transport layer (See Radius
   [RFC6614] and Diameter [RFC6733].  Mechanisms that prevent collisions
   of two clients trying to modify the same node of data are the focus.

   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 [RFC7921] 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 I2RS
   protocol should support:

      multiple operations in one messge; an error in one operation MUST
      NOT stop additional operations from being carried out nor can it
      cause previous operations to be rolled back.

      multiple operations in multiple messages, but multiple message
      commands error handling MUST NOT insert errors 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 [RFC7923],
   and the following general requirements SHOULD be understood to be
   expanded 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.

   o  Pub-Sub-REQ-03: The subscription service must 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

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, and

   o  Joe Clarke,

13.  References

13.1.  Normative References:

              Hares, S., Migault, D., and J. Halpern, "I2RS Security
              Related Requirements", draft-ietf-i2rs-protocol-security-
              requirements-17 (work in progress), September 2016.

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

              Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", draft-ietf-netconf-restconf-17 (work in
              progress), September 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,

   [RFC6614]  Winter, S., McCauley, M., Venaas, S., and K. Wierenga,
              "Transport Layer Security (TLS) Encryption for RADIUS",
              RFC 6614, DOI 10.17487/RFC6614, May 2012,

   [RFC6733]  Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn,
              Ed., "Diameter Base Protocol", RFC 6733,
              DOI 10.17487/RFC6733, October 2012,

   [RFC7920]  Atlas, A., Ed., Nadeau, T., Ed., and D. Ward, "Problem
              Statement for the Interface to the Routing System",
              RFC 7920, DOI 10.17487/RFC7920, June 2016,

   [RFC7921]  Atlas, A., Halpern, J., Hares, S., Ward, D., and T.
              Nadeau, "An Architecture for the Interface to the Routing
              System", RFC 7921, DOI 10.17487/RFC7921, June 2016,

   [RFC7922]  Clarke, J., Salgueiro, G., and C. Pignataro, "Interface to
              the Routing System (I2RS) Traceability: Framework and
              Information Model", RFC 7922, DOI 10.17487/RFC7922, June
              2016, <http://www.rfc-editor.org/info/rfc7922>.

   [RFC7923]  Voit, E., Clemm, A., and A. Gonzalez Prieto, "Requirements
              for Subscription to YANG Datastores", RFC 7923,
              DOI 10.17487/RFC7923, June 2016,

13.2.  Informative References

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

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,

Authors' Addresses

   Jeff Haas

   Email: jhaas@juniper.net

   Susan Hares

   Email: shares@ndzh.com