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
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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
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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.
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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.
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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>.
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[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>.
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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
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