I2RS Ephemeral State Requirements
draft-ietf-i2rs-ephemeral-state-00

I2RS working group                                               J. Haas
Internet-Draft                                                   Juniper
Intended status: Standards Track                                S. Hares
Expires: December 25, 2015                                        Huawei
                                                           June 23, 2015

                   I2RS Ephemeral State Requirements
                   draft-ietf-i2rs-ephemeral-state-00

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.

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   This Internet-Draft will expire on December 25, 2015.

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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 . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  changes to YANG . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Changes to NETCONF  . . . . . . . . . . . . . . . . . . . . .   5
   6.  Requirements regarding Identity, Secondary-Identity and
       Priority  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Identity Requirements . . . . . . . . . . . . . . . . . .   6
     6.2.  Priority Requirements . . . . . . . . . . . . . . . . . .   6
     6.3.  Representing I2RS Attributes in ephemeral configuration
           state . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     6.4.  Semantics around storing and managing of priority and
           client ID.  . . . . . . . . . . . . . . . . . . . . . . .   7
   7.  Subscriptions to Changed State Requirements . . . . . . . . .   9
   8.  Transactions  . . . . . . . . . . . . . . . . . . . . . . . .  10
   9.  Previously Considered Ideas . . . . . . . . . . . . . . . . .  10
     9.1.  A Separate Ephemeral Datastore  . . . . . . . . . . . . .  10
     9.2.  Panes of Glass/Overlay  . . . . . . . . . . . . . . . . .  11
   10. Actions Required to Implement this Draft  . . . . . . . . . .  11
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   12. Security Considerations . . . . . . . . . . . . . . . . . . .  12
   13. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     14.1.  Normative References:  . . . . . . . . . . . . . . . . .  12
     14.2.  Informative References . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

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.bierman-netconf-restconf] as the protocols for carrying I2RS.

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   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.

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

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   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
        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

   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 datastore in NETCONF, running-config can be copied to a
   persistant data store, like startup config.  I2RS ephemeral state
   MUST NOT be persisted.

3.2.  Constraints

   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.

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

3.3.  Hierarchy

   Similar to configuration state (config true, see [RFC6020], section
   7.19.1), ephemeral state is not permitted to be configured underneath
   nodes that are "config false" (state data).

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   Configuration of ephemeral state underneath "config true" is
   permitted.  This permits augmentation of configuration state with
   ephemeral nodes.

   Configuration of "config true" state underneath ephemeral state MUST
   NOT be done.

   State data, "config false", is permitted underneath ephemeral state.
   This state data is part of the ephemeral module and should become
   inaccessible if the ephemeral module reboots.

4.  changes to YANG

   The YANG "config" keyword ([RFC6020], section 7.19.1) is extended to
   support the keyword "ephemeral" in addition to "true" and "false".
   "config ephemeral" declares the nodes underneath to be ephemeral
   configuration.

5.  Changes to NETCONF

   A capability is registered declaring that the server supports
   ephemeral configuration.  E.g.:

     :ephemeral-config
          urn:ietf:params:netconf:capability:ephemeral-config:1.0

   <get-config> will normally return "config ephemeral" nodes as it is a
   form of configuration.  It is further extended to add a new
   parameter, "filter-ephemeral".  This parameter accepts the following
   arguments:

   o  none (default): No filtering of persistent or ephemeral state is
      done.

   o  ephemeral-only: Only nodes representing ephemeral state are
      returned.

   o  exclude-ephemeral: Only persistent configuration is returned.

   <get> is similarly extended to support "filter-ephemeral".

   When a <copy-config> is done, regardless of datastore, nodes that are
   "config ephemeral" are excluded from the target output.

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6.  Requirements regarding Identity, Secondary-Identity and Priority

6.1.  Identity Requirements

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

   I2RS also permits clients to have a secondary identity which may be
   used for troubleshooting.  This secondary identity is an opaque
   value.  [I-D.ietf-i2rs-traceability] provides an example of how the
   secondary identity can be used for traceability.

   The secondary identity is carried in the configuration operation
   using a new parameter to <edit-config>.  E.g.:

  <rpc message-id="101" xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <edit-config>
      <i2rs:irs-secondary-identity>user1</i2rs>
      <target>
          <running/>
      </target>
      <config>
          <top xmlns="http://example.com/schema/1.2/config">
          <interface>
              <name>Ethernet0/0</name>
              <mtu>1500</mtu>
          </interface>
          </top>
      </config>
      </edit-config>
  </rpc>

   "config ephemeral" nodes that are created or altered as part of the
   config operation will carry the secondary-identity as read-only
   metadata.

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

   This further implies that priority is an attribute that is stored in
   the NETCONF Access Control Model [RFC6536] as part of the group.
   E.g.:

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   +--rw nacm
      +--rw enable-nacm?            boolean
      +--rw read-default?           action-type
      +--rw write-default?          action-type
      +--rw exec-default?           action-type
      +--rw enable-external-groups? boolean
      +--ro denied-operations       yang:zero-based-counter32
      +--ro denied-data-writes      yang:zero-based-counter32
      +--ro denied-notifications    yang:zero-based-counter32
      +--rw groups
      |  +--rw group [name]
      |     +--rw name         group-name-type
      |     +--rw user-name*   user-name-type
      |     +--rw i2rs:i2rs-priority i2rs-priority-type

   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 SHALL fail.  An appropriate error should be returned
   to the user stating the nodes where the user had insufficient
   priority to override the state.

6.3.  Representing I2RS Attributes in ephemeral configuration state

   I2RS attributes may be modeled as meta-data,
   [I-D.ietf-netmod-yang-metadata].  This meta-data MUST be read-only;
   operations attempting to alter it MUST be silently ignored.  An I2RS
   module will be defined to document this meta data.  An example of its
   use:

       <foo xmlns:i2rs="https://ietf.example.com/i2rs"
           i2rs:i2rs-secondary-identity="user1" i2rs:i2rs-priority="47">
          ...
      </foo>

6.4.  Semantics around storing and managing of priority and client ID.

   The semantics and desired behavior around the storing and managing of
   priority and client ID have the following properties:

   1.  First - the priority mechanism is intended to handle "error cases
       of colliding writes" in a predictable way that results in a
       consistent mechanism.  It is true that the same mechanism could
       be used if they were not considered "errors", but it is important
       to minimize the need and impact of the priority mechanism

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   2.  Second, if there is a priority conflict where both clients
       (Client_A and Client_B) share the same priority, the client that
       wrote first wins.  This is to avoid network oscillation if two
       clients are "fighting" over writing the same state.  When there
       are multiple clients and the time arrival of the messages may not
       be predictable (network transit differences, which socket is
       read, software differences), basing state on last arrival time
       doesn't give consistent and predictable behavior.  That gives
       behavior ont the following time-line

       1.  Time_1: Client_A writes X=N with priority 10

       2.  Time_2: Client_B attempts to write X=K with priority 10 and
           is rejected

       3.  Time_3: Client_A writes X=P with priority 10 and succeeds

       For the I2RS Agent to properly handle these actions, it is
       necessary to know that X is owned by Client_A.  Priority alone is
       not sufficient because the basis for rejecting Client_B's write
       but accepting Client_A's write is that Client_A is the owner.
       Thus it is necessary to store the Client Identity with the nodes
       that it owns.  This could be in an I2RS-specific overlay that is
       only used by the I2RS agent and only contains the nodes that have
       been written by I2RS.

   3.  Third, a question has come up regarding what the behavior of
       priority is if a client's priority changes and whether priority
       needs to be stored with each node when that node is written.  In
       my "keep-it-simple" perspective, priority is associated with a
       Client and is only used on a conflict.  This would mean that
       priority is not stored with a node when that node is written.
       Instead, the Client Identity is stored with the node and the
       Client's priority is looked up in a client table that the I2RS
       Agent can access.  That client table could be populated via
       configuration, via a AAA protocol, via NACM, etc.  The sematic
       implications are as follows:

       1.  Time_1: Client_A writes X=N with priority 10

       2.  Time_2: Client_A's priority is changed (UNUSUAL) to priority
           6

       3.  Time_3: Client_B writes X=K with priority 8 (succeeds since 8
           > 6)

       4.  Time_4: Client_A attempts to write X=N with priority 6 (fails
           b/c 8 > > 6)

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       5.  Time_5: Client_B's priority is changed (UNUSUAL) to priority
           7

       6.  Time_6 Client_B writes X=P with priority 7 and succeeds (same
           > owner, no priority check)

       The alternate approach would have store the priority with which a
       node was written.  That is more like a priority lock that could
       only be changed by a client with higher priority or by the same
       client, regardless of priority.  This approach would require
       storing a priority per node and the semantic implications would
       be as follows:

       1.  Time_1:Client_A writes X=N with priority 10

       2.  Time_2:Client_A's priority is changed (UNUSUAL) to priority 6

       3.  Time_3: Client_B attempts to write X=K with priority 8 and
           fails (10 > 8)

       4.  Time_4: Client_A writes X=N with priority 6 and succeeds
           (same owner, no priority check)

       5.  Time_5: Client_B's priority is changed (UNUSUAL) to priority
           7

       6.  Time_6 Client_B writes X=P with priority 7 and succeeds (7 >
           6)

       The behavior for these two models is different at Time_3 and
       Time_4.

   The initial preference was that the priority is not stored with the
   node, but if it necessary to store it with the node additional
   discussion may be needed with the I2RS WG.

7.  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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8.  Transactions

   Section 7.9 of the [I-D.ietf-i2rs-architecture] states the I2RS
   architecture does not include multi-message atomicity and rollback
   mechanisms, but suggests an I2RS client may inidicate one of the
   following error handling techniques for a given 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.

   None of these three cases insert known errors into the I2RS ephemeral
   datastore.

   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
   model.

9.  Previously Considered Ideas

9.1.  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

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   ephemeral datastore's modules, one cannot currently reference state
   from one datastore to anothe

   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.

9.2.  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.

10.  Actions Required to Implement this Draft

   o  Draft for adding "config ephemeral" to YANG.

   o  Draft defining NETCONF changes including capability, RPC operation
      changes and support of secondary identity, RPC changes to support
      priority.

   o  I2RS draft to define meta-data for priority and secondary-
      identity.

11.  IANA Considerations

   TBD.

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12.  Security Considerations

   TBD.

13.  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

14.  References

14.1.  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-09 (work in
              progress), March 2015.

   [I-D.ietf-i2rs-rib-info-model]
              Bahadur, N., Folkes, R., Kini, S., and J. Medved, "Routing
              Information Base Info Model", draft-ietf-i2rs-rib-info-
              model-06 (work in progress), March 2015.

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   [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-03 (work
              in progress), May 2015.

   [I-D.ietf-netmod-yang-metadata]
              Lhotka, L., "Defining and Using Metadata with YANG",
              draft-ietf-netmod-yang-metadata-01 (work in progress),
              June 2015.

14.2.  Informative References

   [I-D.bierman-netconf-restconf]
              Bierman, A., Bjorklund, M., Watsen, K., and R. Fernando,
              "RESTCONF Protocol", draft-bierman-netconf-restconf-04
              (work in progress), February 2014.

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

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

   [RFC6241]  Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
              Bierman, "Network Configuration Protocol (NETCONF)", RFC
              6241, June 2011.

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

Authors' Addresses

   Jeff Haas
   Juniper

   Email: jhaas@juniper.net

   Susan Hares
   Huawei
   Saline
   US

   Email: shares@ndzh.com

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