One document matched: draft-ietf-i2rs-ephemeral-state-03.xml
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<rfc category="std" docName="draft-ietf-i2rs-ephemeral-state-03" ipr="trust200902">
<front>
<title abbrev="I2RS Ephemeral State Requirements">I2RS Ephemeral State Requirements </title>
<author fullname="Jeff Haas" initials="J." surname="Haas">
<organization>Juniper</organization>
<address>
<postal>
<street></street>
<city> </city>
<country></country>
</postal>
<email>jhaas@juniper.net</email>
</address>
</author>
<author fullname="Susan Hares" initials="S." surname="Hares">
<organization> Huawei </organization>
<address>
<postal>
<street></street>
<city>Saline</city>
<country>US</country>
</postal>
<email>shares@ndzh.com </email>
</address>
</author>
<date year="2016" />
<area>Routing Area</area>
<workgroup>I2RS working group</workgroup>
<keyword>RFC</keyword>
<keyword>Request for Comments</keyword>
<keyword>I-D</keyword>
<keyword>Internet-Draft</keyword>
<keyword>I2RS</keyword>
<abstract>
<t>This document covers requests to the netmod and netconf Working
Groups for functionality to support the ephemeral state requirements
to implement the I2RS architecture. </t>
</abstract>
</front>
<middle>
<section anchor="intro" title="Introduction">
<t>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 <xref target="I-D.ietf-i2rs-architecture"></xref> abstractly documents a number
of requirements for implementing the I2RS requirements.</t>
<t>
The I2RS Working Group has chosen to use the YANG data modeling
language <xref target="RFC6020"></xref> as the basis to implement its mechanisms.
</t>
<t>
Additionally, the I2RS Working group has chosen to use the NETCONF
<xref target="RFC6241"></xref> and its similar but lighter-weight relative RESTCONF
<xref target="I-D.ietf-netconf-restconf"></xref> as the protocols for carrying I2RS.
</t>
<t>
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.
</t>
</section>
<section title="Review of Requirements from I2RS architecture document">
<t> The following are ten requirements that
<xref target="I-D.ietf-i2rs-architecture"></xref>
contains which are important high level requirements:
<list style="numbers">
<t>The I2RS protocol SHOULD support highly reliable notifications (but
not perfectly reliable notifications) from an I2RS agent to an I2RS client. </t>
<t>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. </t>
<t> The I2RS protocol will operate on data models which may be protocol
independent or protocol dependent. </t>
<t> 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.</t>
<t>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.</t>
<t>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. </t>
<t>An I2RS Client and I2RS Agent mutually authenticate each other based on
pre-established authenticated identities. </t>
<t>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</t>
<t>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.
</t>
<t>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.</t>
</list>
</t>
</section>
<section title="Ephemeral State Requirements">
<section title="Persistence">
<t> 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. </t>
<t>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. </t>
</section>
<section title="Constraints">
<t>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. </t>
<t>Ephemeral-REQ-03: Ephemeral state must be able to utilized
temporary operational state which (MPLS LSP-ID or a BGP IN-RIB) as a constraints.
</t>
<t>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.</t>
</section>
<section title="Hierarchy">
<t>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). </t>
</section>
<section title="changes to YANG">
<t>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.
</t>
</section>
<section title="Minimal sub-set of Changes to NETCONF">
<t>
Ephemeral-REQ-07: The minimal set of changes are: (TBD).
</t>
<t>Potential set: TBD </t>
<t>Note: I2RS protocol design team is working to
complete this set of minimal changes.</t>
</section>
<section title="Requirements regarding Identity, Secondary-Identity and Priority">
<section title="Identity Requirements">
<t>Ephemeral-REQ-08:Clients shall have identifiers, and secondary identifiers.
</t>
<t>Explanation:</t>
<t>I2RS requires clients to have an identifier. This identifier will be
used by the Agent authentication mechanism over the appropriate
protocol. </t>
<t>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.
<xref target="I-D.ietf-i2rs-traceability"></xref> provides an
example of how the secondary identity can be used for traceability.
</t>
</section>
<section title="Priority Requirements">
<t> 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.
</t>
<t>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. </t>
<t>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 state.
</t>
<t>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. </t>
<t>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.
</t>
<t> Hints for Implementation </t>
<t>
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.
</t>
</section>
<section title="Transactions">
<t> Ephemeral-REQ-13: Section 7.9 of the <xref target="I-D.ietf-i2rs-architecture"></xref>
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 in many ways.
No multi-message commands SHOULD cause errors to be
inserted into the I2RS ephemeral data-store.
</t>
<t>
Explanation:
</t>
<t>
I2RS suggests the following are some of the potential error handling techniques
for multiple message sent to the I2RS client:
<list style="numbers">
<t>Perform all or none: All operations succeed or none of them will be applied.
This useful when there are mutual dependencies.</t>
<t>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.</t>
<t>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.</t>
</list>
</t>
<t>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.
</t>
<t>
</t>
<t>Discussion of Current NETCONF/RESTCONF versus </t>
<t>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.</t>
<t> I2RS processing is dependent on the I2RS model. The I2RS model must consider
the dependencies within multiple operations work within a model.
</t>
</section>
<section title="Subscriptions to Changed State Requirements">
<t>
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.
</t>
<t>
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.
</t>
<t>The following requirements from the
<xref target="I-D.ietf-i2rs-pub-sub-requirements"></xref> apply to ephemeral
state:
<list style="symbols">
<t>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.
</t>
<t>PubSSub-REQ-2: Real time for notifications SHOULD be defined by the data models.
</t>
<t>PubSub-REQ-3: Security of the pub/sub data stream SHOULD be able to be
model dependent.</t>
<t>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.</t>
<t>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. </t>
<t>PubSub-REQ-6: I2RS Filters SHOULD be able to be dynamic. </t>
<t>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. </t>
</list></t>
</section>
</section>
</section>
<section title=" Previously Considered Ideas">
<section title="A Separate Ephemeral Datastore">
<t>
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.
</t>
<t>
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
</t>
<t>
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.
</t>
</section>
<section title=" Panes of Glass/Overlay">
<t> 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.
</t>
<t> In this overlay scenario, persistent configuration that was not
shadowed by ephemeral configuration could be "read through".
</t>
<t> There were two perceived disadvantages to this mechanism:
<list>
<t>The general complexity with managing the overlay mechanism
itself.</t>
<t>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.
</t>
</list>
</t>
</section>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>There are no IANA requirements for this document.</t>
</section>
<section title="Security Considerations">
<t>The security requirements for the I2RS protocol are
covered in <xref target="I-D.hares-i2rs-auth-trans"></xref> document.
</t>
</section>
<section anchor="Acknowledgements" title="Acknowledgements">
<t>
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:
</t>
<t>
<list style="symbols">
<t>Alia Atlas</t>
<t>Andy Bierman</t>
<t>Martin Bjorklund</t>
<t>Dean Bogdanavich</t>
<t>Rex Fernando</t>
<t>Joel Halpern</t>
<t>Thomas Nadeau</t>
<t>Juergen Schoenwaelder</t>
<t>Kent Watsen</t>
</list>
</t>
</section>
</middle>
<back>
<references title="Normative References:">
&I-D.ietf-i2rs-architecture;
&I-D.ietf-i2rs-rib-info-model;
&I-D.ietf-i2rs-traceability;
&I-D.ietf-i2rs-pub-sub-requirements;
&I-D.ietf-netmod-yang-metadata;
&I-D.hares-i2rs-auth-trans;
</references>
<references title="Informative References">
&RFC2119;
&RFC6020;
&RFC6241;
&RFC6536;
&I-D.ietf-netconf-restconf;
</references>
</back>
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