I2RS working group                                               J. Haas
Internet-Draft                                                   Juniper
Intended status: Standards Track                                S. Hares
Expires: September 10, 2016                                       Huawei
                                                           March 9, 2016

                   I2RS Ephemeral State Requirements


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

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   This Internet-Draft will expire on September 10, 2016.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Review of Requirements from I2RS architecture document  . . .   3
   3.  Ephemeral State Requirements  . . . . . . . . . . . . . . . .   4
     3.1.  Persistence . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Constraints . . . . . . . . . . . . . . . . . . . . . . .   4
     3.3.  Hierarchy . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.4.  changes to YANG . . . . . . . . . . . . . . . . . . . . .   5
     3.5.  Minimal sub-set of Changes to NETCONF . . . . . . . . . .   5
     3.6.  Requirements regarding Identity, Secondary-Identity and
           Priority  . . . . . . . . . . . . . . . . . . . . . . . .   5
       3.6.1.  Identity Requirements . . . . . . . . . . . . . . . .   5
       3.6.2.  Priority Requirements . . . . . . . . . . . . . . . .   5
       3.6.3.  Transactions  . . . . . . . . . . . . . . . . . . . .   6
       3.6.4.  Subscriptions to Changed State Requirements . . . . .   7
   4.  Previously Considered Ideas . . . . . . . . . . . . . . . . .   8
     4.1.  A Separate Ephemeral Datastore  . . . . . . . . . . . . .   8
     4.2.  Panes of Glass/Overlay  . . . . . . . . . . . . . . . . .   9
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     8.1.  Normative References: . . . . . . . . . . . . . . . . . .  10
     8.2.  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 [I-D.ietf-i2rs-architecture] abstractly documents a number
   of requirements for implementing the I2RS requirements.

   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 use the NETCONF
   [RFC6241] and its similar but lighter-weight relative RESTCONF
   [I-D.ietf-netconf-restconf] as the protocols for carrying I2RS.

   While YANG, NETCONF and RESTCONF are a good starting basis for I2RS,
   there are some things needed from each of them in order for I2RS to
   be implemented.

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2.  Review of Requirements from I2RS architecture document

   The following are ten requirements that [I-D.ietf-i2rs-architecture]
   contains which are important high level requirements:

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

   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 needs to record the client identity when a node is
        created or modified.  The I2RS Agent needs 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 will have only one priority for the client
        identity.  A collision on writes is considered an error, but
        priority 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 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 is only recorded when the data node is
        written or updated or deleted

   9.   I2RS agent can 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

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        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.  Note: Jeff's suggests that priority is kept at the NACM
        at the client level (rather than the path level or the group
        level) will allow these lower priority clients to be filtered
        out using an extended NACM approach.  This is only a suggestion
        of a method to provide the requirement 9.

   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.

3.  Ephemeral State Requirements

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 datastore 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 utilized temporary
   operational state which (MPLS LSP-ID or a BGP IN-RIB) as a

   Ephemeral-REQ-04: Ephemeral state MAY refer to non-ephemeral state
   for purposes of implementing constraints.  The designer of ephemeral
   state modules are advised that such constraints may impact the speed
   of processing ephemeral state commits and should avoid them when
   speed is essential.

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3.3.  Hierarchy

   Ephemeral-REQ-05: The ability to add on an object (or a hierarchy of
   objects) that have the property of being ephemeral.  An object needs
   to be able to have (both) the property of being writable and the
   property of the data being ephemeral (or non-ephemeral).

3.4.  changes to YANG

   Ephemeral-REQ-06: Yang MUST have a way to indicate in a data model
   that nodes have the following properties: ephemeral, writable/not-
   writable, status/configuration, and secure/non-secure transport.

3.5.  Minimal sub-set of Changes to NETCONF

   Ephemeral-REQ-07: The minimal set of changes are: (TBD).

   Potential set: TBD

   Note: I2RS protocol design team is working to complete this set of
   minimal changes.

3.6.  Requirements regarding Identity, Secondary-Identity and Priority

3.6.1.  Identity Requirements

   Ephemeral-REQ-08:Clients shall have identifiers, and secondary


   I2RS requires clients to have an identifier.  This identifier will be
   used by the Agent authentication mechanism over the appropriate

   The Secondary identities can be carried as part of RPC or meta-data.
   The primary purpose of the secondary identity is for traceability
   information which logs (who modifies certain nodes).  This secondary
   identity is an opaque value.  [I-D.ietf-i2rs-traceability] provides
   an example of how the secondary identity can be used for

3.6.2.  Priority Requirements

   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

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   is done via a priority mechanism with the highest priority winning.
   This priority is per-client.

   Ephemeral-REQ-09: The data nodes MAY store I2RS client identity and
   not the effective priority at the time the data node is stored.  The
   I2RS Client MUST have one priority at a time.  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-10, Ephemeral-REQ-11, and Ephemeral-REQ-12.

   Ephemeral-REQ-10: 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 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

   Ephemeral-REQ-11: The requirement to support multi-headed control is
   required for collisions and the priority resolution of collisions.
   Multi-headed control is not tied to ephemeral state.  I2RS is not
   mandating how AAA supports priority.  Mechanisms which prevent
   collisions of two clients trying the same node of data are the focus.

   Ephemeral-REQ-12: If two clients have the same priority, the
   architecture says the first one wins.  The I2RS protocol has this
   requirement to prevent was the oscillation between clients.  If one
   uses the last wins scenario, you may oscillate.  That was our
   opinion, but a design which prevents oscillation is the key point.

   Hints for Implementation

   Ephemeral configuration state nodes that are created or altered by
   users that match a rule carrying i2rs-priority will have those nodes
   annotated with metadata.  Additionally, during commit processing, if
   nodes are found where i2rs-priority is already present, and the
   priority is better than the transaction's user's priority for that
   node, the commit should fail.  An appropriate error should be
   returned to the user stating the nodes where the user had
   insufficient priority to override the state.

3.6.3.  Transactions

   Ephemeral-REQ-13: Section 7.9 of the [I-D.ietf-i2rs-architecture]
   states the I2RS architecture does not include multi-message atomicity
   and roll-back mechanisms.  I2RS notes multiple operations in one or
   more messages handling can handle errors within the set of operations

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   in many ways.  No multi-message commands SHOULD cause errors to be
   inserted into the I2RS ephemeral data-store.


   I2RS suggests the following are some of the potential error handling
   techniques for multiple message sent to the I2RS client:

   1.  Perform all or none: All operations succeed or none of them will
       be applied.  This useful when there are mutual dependencies.

   2.  Perform until error: Operations are applied in order, and when
       error occurs the processing stops.  This is useful when
       dependencies exist between multiple-message operations, and order
       is important.

   3.  Perform all storing errors: Perform all actions storing error
       indications for errors.  This method can be used when there are
       no dependencies between operations, and the client wants to sort
       it out.

   Is important to reliability of the datastore that none of these error
   handling for multiple operations in one more multiple messages cause
   errors into be insert the I2RS ephemeral data-store.

   Discussion of Current NETCONF/RESTCONF versus

   RESTCONF does an atomic action within a http session, and NETCONF has
   atomic actions within a commit.  These features may be used to
   perform these features.

   I2RS processing is dependent on the I2RS model.  The I2RS model must
   consider the dependencies within multiple operations work within a

3.6.4.  Subscriptions to Changed State Requirements

   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.

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   The following requirements from the
   [I-D.ietf-i2rs-pub-sub-requirements] apply to ephemeral state:

   o  PubSub-REQ-1: The I2RS interface SHOULD support user subscriptions
      to data with the following parameters: push of data synchronously
      or asynchronously via registered subscriptions.

   o  PubSSub-REQ-2: Real time for notifications SHOULD be defined by
      the data models.

   o  PubSub-REQ-3: Security of the pub/sub data stream SHOULD be able
      to be model dependent.

   o  PubSub-REQ-4: The Pub/Sub mechanism SHOULD allow subscription to
      critical Node Events.  Examples of critical node events are BGP
      peers down or ISIS protocol overload bits.

   o  PubSub-REQ-5:I2RS telemetry data for certain protocols (E.g.  BGP)
      will require a hierarchy of filters or XPATHs.  The I2RS protocol
      design MUST balance security against the throughput of the
      telemetry data.

   o  PubSub-REQ-6: I2RS Filters SHOULD be able to be dynamic.

   o  Pub-Sub-REQ-7: I2rs protocol MUST be able to allow I2RS agent to
      set limits on the data models it will support for pub/sub and
      within data models to support knobs for maximum frequency or
      resolution of pub/sub data.

4.  Previously Considered Ideas

4.1.  A Separate Ephemeral Datastore

   The primary advantage of a fully separate datastore is that the
   semantics of its contents are always clearly ephemeral.  It also
   provides strong segregation of I2RS configuration and operational
   state from the rest of the system within the network element.

   The most obvious disadvantage of such a fully separate datastore is
   that interaction with the network element's operational or
   configuration state becomes significantly more difficult.  As an
   example, a BGP I2RS use case would be the dynamic instantiation of a
   BGP peer.  While it is readily possible to re-use any defined
   groupings from an IETF-standardized BGP module in such an I2RS
   ephemeral datastore's modules, one cannot currently reference state
   from one datastore to anothe

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   For example, XPath queries are done in the context document of the
   datastore in question and thus it is impossible for an I2RS model to
   fulfil a "must" or "when" requirement in the BGP module in the
   standard data stores.  To implement such a mechanism would require
   appropriate semantics for XPath.

4.2.  Panes of Glass/Overlay

   I2RS ephemeral configuration state is generally expected to be
   disjoint from persistent configuration.  In some cases, extending
   persistent configuration with ephemeral attributes is expected to be
   useful.  A case that is considered potentially useful but problematic
   was explored was the ability to "overlay" persistent configuration
   with ephemeral configuration.

   In this overlay scenario, persistent configuration that was not
   shadowed by ephemeral configuration could be "read through".

   There were two perceived disadvantages to this mechanism:

      The general complexity with managing the overlay mechanism itself.

      Consistency issues with validation should the ephemeral state be
      lost, perhaps on reboot.  In such a case, the previously shadowed
      persistent state may no longer validate.

5.  IANA Considerations

   There are no IANA requirements for this document.

6.  Security Considerations

   The security requirements for the I2RS protocol are covered in
   [I-D.hares-i2rs-auth-trans] document.

7.  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

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   o  Dean Bogdanavich

   o  Rex Fernando

   o  Joel Halpern

   o  Thomas Nadeau

   o  Juergen Schoenwaelder

   o  Kent Watsen

8.  References

8.1.  Normative References:

              Hares, S., Migault, D., and J. Halpern, "I2RS Security
              Related Requirements", draft-hares-i2rs-auth-trans-05
              (work in progress), August 2015.

              Atlas, A., Halpern, J., Hares, S., Ward, D., and T.
              Nadeau, "An Architecture for the Interface to the Routing
              System", draft-ietf-i2rs-architecture-13 (work in
              progress), February 2016.

              Voit, E., Clemm, A., and A. Prieto, "Requirements for
              Subscription to YANG Datastores", draft-ietf-i2rs-pub-sub-
              requirements-05 (work in progress), February 2016.

              Bahadur, N., Kini, S., and J. Medved, "Routing Information
              Base Info Model", draft-ietf-i2rs-rib-info-model-08 (work
              in progress), October 2015.

              Clarke, J., Salgueiro, G., and C. Pignataro, "Interface to
              the Routing System (I2RS) Traceability: Framework and
              Information Model", draft-ietf-i2rs-traceability-07 (work
              in progress), February 2016.

              Lhotka, L., "Defining and Using Metadata with YANG",
              draft-ietf-netmod-yang-metadata-04 (work in progress),
              February 2016.

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8.2.  Informative References

              Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", draft-ietf-netconf-restconf-09 (work in
              progress), December 2015.

   [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,

   [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,

   [RFC6536]  Bierman, A. and M. Bjorklund, "Network Configuration
              Protocol (NETCONF) Access Control Model", RFC 6536,
              DOI 10.17487/RFC6536, March 2012,

Authors' Addresses

   Jeff Haas

   Email: jhaas@juniper.net

   Susan Hares

   Email: shares@ndzh.com

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