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rfc:rfc8242

Internet Engineering Task Force (IETF) J. Haas Request for Comments: 8242 Juniper Category: Informational S. Hares ISSN: 2070-1721 Huawei

                                                        September 2017
Interface to the Routing System (I2RS) Ephemeral State Requirements

Abstract

 "An Architecture for the Interface to the Routing System" (RFC 7921)
 abstractly describes a number of requirements for ephemeral state (in
 terms of capabilities and behaviors) that any protocol suite
 attempting to meet the needs of the Interface to the Routing System
 (I2RS) protocol has to provide.  This document describes, in detail,
 requirements for ephemeral state for those implementing the I2RS
 protocol.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Not all documents
 approved by the IESG are a candidate for any level of Internet
 Standard; see Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 https://www.rfc-editor.org/info/rfc8242.

Haas & Hares Informational [Page 1] RFC 8242 I2RS Ephemeral State Requirements September 2017

Copyright Notice

 Copyright (c) 2017 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (https://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Table of Contents

 1. Introduction ....................................................3
    1.1. Requirements Language ......................................4
 2. Architectural Requirements for Ephemeral State ..................4
 3. Ephemeral State Requirements ....................................5
    3.1. Persistence ................................................5
    3.2. Constraints ................................................6
    3.3. Hierarchy ..................................................6
    3.4. Ephemeral Configuration Overlapping Local Configuration ....6
 4. YANG Features for Ephemeral State ...............................7
 5. NETCONF Features for Ephemeral State ............................7
 6. RESTCONF Features for Ephemeral State ...........................7
 7. Requirements regarding Supporting Multi-Head Control via
    Client ..........................................................7
 8. Multiple Message Transactions ...................................9
 9. Pub/Sub Requirements Expanded for Ephemeral State ...............9
 10. IANA Considerations ...........................................10
 11. Security Considerations .......................................10
 12. Normative References ..........................................10
 Acknowledgements ..................................................12
 Authors' Addresses ................................................12

Haas & Hares Informational [Page 2] RFC 8242 I2RS Ephemeral State Requirements September 2017

1. Introduction

 The Interface to the Routing System (I2RS) Working Group (WG) 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 and defines ephemeral state as
 "state that 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]).  Section 2 of this document
 describes the specific requirements that the I2RS WG has identified
 based on the I2RS architecture's abstract requirements.  The
 Interface to the Routing System (I2RS) Working Group (WG) 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 and defines ephemeral state as
 "state that 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]).  Section 2 of this document
 provides a summary of these abstract requirements, and section 3
 recasts these abstract requirements into specific requirements for
 the Ephemeral state for any IETF network management system.
 The I2RS WG has chosen to use the YANG data modeling language
 [RFC7950] as the basis to implement its mechanisms.
 Additionally, the I2RS WG has chosen to reuse two existing protocols,
 NETCONF [RFC6241] and its similar but lighter-weight relative
 RESTCONF [RFC8040], as the protocols for carrying I2RS.
 What does reuse of a protocol mean?  Reuse means that while the
 combination of the YANG modeling language and the NETCONF and
 RESTCONF protocols is a good starting basis for the I2RS data
 modeling language and protocol, the requirements for I2RS protocol
 implementations should:
 1.  select features from the YANG modeling language and the NETCONF
     and RESTCONF protocols per version of the I2RS protocol (see
     Sections 4, 5, and 6), and
 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.

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 Support for ephemeral state is an I2RS protocol requirement that
 necessitates 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 WGs.
 Section 7 provides 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 for I2RS
 publication/subscription [RFC7923] 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", "NOT RECOMMENDED", "MAY", and
 "OPTIONAL" in this document are to be interpreted as described in
 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
 capitals, as shown here.

2. Architectural Requirements for Ephemeral State

 The I2RS architecture [RFC7921] and the I2RS problem statement
 [RFC7920] define the important high-level requirements for the I2RS
 protocol in abstract terms.  This section distills this high-level
 abstract guidance into specific requirements for the I2RS protocol.
 To aid the reader, there are references back to the abstract
 descriptions in the I2RS architecture document and the I2RS problem
 statement, but the reader should note the requirements below are not
 explicitly stated in the I2RS architecture document or in the I2RS
 problem statement.
 Requirements:
 1.  The I2RS protocol SHOULD support an asynchronous programmatic
     interface with properties described in Section 5 of [RFC7920]
     (e.g., high throughput) with support for target information
     streams, filtered events, and thresholded events (real-time
     events) sent by an I2RS agent to an I2RS client (from Section 1.1
     of [RFC7921]).

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 2.  An I2RS agent MUST record the client identity when a node is
     created or modified.  The I2RS agent SHOULD 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 (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
     that is higher priority can modify an existing entry (first entry
     wins).  Priority only has meaning at the time of use (from
     Section 7.8 of [RFC7921]).
 4.  An I2RS client's secondary identity data is read-only metadata
     that is recorded by the I2RS agent associated with a data model's
     node when the data node is written.  Just like the primary client
     identity, the secondary identity SHOULD only be recorded when the
     data node is written (from Sections 7.4 of [RFC7921].)
 5.  An 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 SHOULD 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 agent.
 At first glance, the I2RS ephemeral state may seem equivalent to the
 writable-running datastore in NETCONF (e.g., running-config), which
 can be copied to a datastore that persists across a reboot (software
 or hardware).  However, I2RS ephemeral state MUST NOT persist across
 a reboot (software or hardware).

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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 Inbound).
 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-
 limiting.

3.3. Hierarchy

 Ephemeral-REQ-06: YANG MUST have the ability to do the following:
 1.  define a YANG module or submodule schema that only contains data
     nodes with the property of being ephemeral, and
 2.  augment a YANG module 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.

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

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 following requirements must be supported by the
 I2RS protocol in order to support I2RS client identity and priority:
 o  the data nodes MUST store I2RS client identity and MAY store the
    effective priority at the time the data node is stored.

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 o  Per SEC-REQ-07 in Section 4.3 of [RFC8241], 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
    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 I2RS clients are
 trying to write the same data node, this collision is considered an
 error.  The I2RS priorities are used to provide a deterministic
 resolution to the conflict.  When there is a collision, and the data
 node is changed, a notification (which includes indicating the 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 (see Section 3.5.2 of [RFC8040]), 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, the processing of the
 configuration change for two I2RS clients must detect an I2RS
 collision and resolve the collision using the priority mechanism.
 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.  The 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.

Haas & Hares Informational [Page 8] RFC 8242 I2RS Ephemeral State Requirements September 2017

 Ephemeral-REQ-14: A deterministic conflict resolution mechanism MUST
 be provided to handle the error scenario in which 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 message.  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-
    command 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.
 Thus, there is 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 datastores,
    configuration datastores, or both.

Haas & Hares Informational [Page 9] RFC 8242 I2RS Ephemeral State Requirements September 2017

 o  Pub-Sub-REQ-02: The subscription service MUST support filtering so
    that subscribed updates under a target node might publish either:
    1.  only ephemeral state in operational data or configuration
        data, or
    2.  both ephemeral and operational data.
 o  Pub-Sub-REQ-03: The subscription service MUST support
    subscriptions that are ephemeral.  (For example, an ephemeral data
    model that has ephemeral subscriptions.)

10. IANA Considerations

 This document does not require any IANA actions.

11. Security Considerations

 The security requirements for the I2RS protocol are covered in
 [RFC8241].

12. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <https://www.rfc-editor.org/info/rfc2119>.
 [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,
            <https://www.rfc-editor.org/info/rfc6241>.
 [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,
            <https://www.rfc-editor.org/info/rfc6614>.
 [RFC6733]  Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn,
            Ed., "Diameter Base Protocol", RFC 6733,
            DOI 10.17487/RFC6733, October 2012,
            <https://www.rfc-editor.org/info/rfc6733>.
 [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,
            <https://www.rfc-editor.org/info/rfc7920>.

Haas & Hares Informational [Page 10] RFC 8242 I2RS Ephemeral State Requirements September 2017

 [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,
            <https://www.rfc-editor.org/info/rfc7921>.
 [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, <https://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,
            <https://www.rfc-editor.org/info/rfc7923>.
 [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
            RFC 7950, DOI 10.17487/RFC7950, August 2016,
            <https://www.rfc-editor.org/info/rfc7950>.
 [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
            Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
            <https://www.rfc-editor.org/info/rfc8040>.
 [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
            2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
            May 2017, <https://www.rfc-editor.org/info/rfc8174>.
 [RFC8241]  Hares, S., Migault, D., and J. Halpern, "Interface to the
            Routing System (I2RS) Security-Related Requirements",
            RFC 8241, DOI 10.17487/RFC8241, September 2017,
            <https://www.rfc-editor.org/info/rfc8241>.

Haas & Hares Informational [Page 11] RFC 8242 I2RS Ephemeral State Requirements September 2017

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:
    Alia Atlas,
    Andy Bierman,
    Martin Bjorklund,
    Dean Bogdanavic,
    Rex Fernando,
    Joel Halpern,
    Thomas Nadeau,
    Juergen Schoenwaelder,
    Kent Watsen,
    Robert Wilton, and
    Joe Clarke.

Authors' Addresses

 Jeff Haas
 Juniper
 Email: jhaas@juniper.net
 Susan Hares
 Huawei
 Saline
 United States of America
 Email: shares@ndzh.com

Haas & Hares Informational [Page 12]

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