I2RS Ephemeral State Requirements
draft-ietf-i2rs-ephemeral-state-01
The information below is for an old version of the document.
| Document | Type | Active Internet-Draft (i2rs WG) | |
|---|---|---|---|
| Authors | Jeffrey Haas , Susan Hares | ||
| Last updated | 2015-08-28 | ||
| Replaces | draft-haas-i2rs-ephemeral-state-reqs | ||
| Stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-i2rs-ephemeral-state-01
I2RS working group J. Haas
Internet-Draft Juniper
Intended status: Standards Track S. Hares
Expires: February 29, 2016 Huawei
August 28, 2015
I2RS Ephemeral State Requirements
draft-ietf-i2rs-ephemeral-state-01
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.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 29, 2016.
Copyright Notice
Copyright (c) 2015 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
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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 . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Normative References: . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . 10
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
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-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
constraints.
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.
3.5. Minimal sub-set of Changes
Ephemeral-REQ-07: The minimal set is ...
Potential set:
3.6. Requirements regarding Identity, Secondary-Identity and Priority
3.6.1. Identity Requirements
Ephemeral-REQ-08:Clients shall have identities, and secondary
identities.
Explanation
I2RS requires clients to have an identity. This identity will be
used by the Agent authentication mechanism over the appropriate
protocol.
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
traceability.
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
is done via a priority mechanism with the highest priority winning.
This priority is per-client.
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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
state.
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, but suggests an I2RS client may indicates
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.
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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.
I2RS-REQ-XX: None of these three error handling for multi-message
cases SHOULD 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
model.
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.
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 BEdefined
defined by the data models.
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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
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
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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
o Dean Bogdanavich
o Rex Fernando
o Joel Halpern
o Thomas Nadeau
o Juergen Schoenwaelder
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o Kent Watsen
8. References
8.1. Normative References:
[I-D.hares-i2rs-auth-trans]
Hares, S., Migault, D., and J. Halpern, "I2RS Security
Related Requirements", draft-hares-i2rs-auth-trans-05
(work in progress), August 2015.
[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-pub-sub-requirements]
Voit, E., Clemm, A., and A. Prieto, "Requirements for
Subscription to YANG Datastores", draft-ietf-i2rs-pub-sub-
requirements-02 (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.
[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.
8.2. Informative References
[I-D.ietf-netconf-restconf]
Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", draft-ietf-netconf-restconf-07 (work in
progress), July 2015.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<http://www.rfc-editor.org/info/rfc6020>.
[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,
<http://www.rfc-editor.org/info/rfc6241>.
[RFC6536] Bierman, A. and M. Bjorklund, "Network Configuration
Protocol (NETCONF) Access Control Model", RFC 6536,
DOI 10.17487/RFC6536, March 2012,
<http://www.rfc-editor.org/info/rfc6536>.
Authors' Addresses
Jeff Haas
Juniper
Email: jhaas@juniper.net
Susan Hares
Huawei
Saline
US
Email: shares@ndzh.com
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