I2RS working group J. Haas
Internet-Draft Juniper
Intended status: Standards Track S. Hares
Expires: December 23, 2016 Huawei
June 21, 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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Table of Contents

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. Section 2 reviews 10 key requirements related to ephemeral state.

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

What does re-use of a protocol mean? Re-use means that while YANG, NETCONF and RESTCONF are a good starting basis for the I2RS protocol, the creation of the I2RS protocol implementations requires that the I2RS requirements

  1. select features from YANG, NETCONF, and RESTCONF per version of the I2RS protocol (See sections 4, 5, and 6)
  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),
  3. suggest protocol strawman as ideas for the NETCONF, RESTCONF, and YANG changes.

The purpose of these requirements and the suggested protocol straw man is to provide a quick turnaround on creating the I2RS protocol.

Support for ephemeral state is I2RS protocol requirement that requires 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 working groups. Sections 7 provide additional requirements that detail how write-conflicts should be resolved if two I2RS client write the same data. Section 8 provides an additional requirement that details on I2RS support of multiple message transactions. Section 9 highlights two requirements in the I2RS publication/subscription requirements [I-D.ietf-i2rs-pub-sub-requirements] 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", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].

2. Review of Requirements from I2RS architecture document

The I2RS architecture defines important high-level requirements for the I2RS protocol. The following are ten requirements that [I-D.ietf-i2rs-architecture] contains which provide context for the ephemeral data state requirements given in sections 3-8:

  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 MUST record the client identity when a node is created or modified. The I2RS Agent SHOULD 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 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 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 MUST 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 SHOULD only be recorded when the data node is written or updated or deleted
  9. 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 not put an undue strain on the I2RS agent.
  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. Ephemeral state may consists of ephemeral configured state and operational state. 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 data store 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 (e.g. 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.

Ephemeral-REQ-05: 2RS pub-sub, logging, 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.

Note: Ephemeral-REQ-05 is part of the yang-push and event notification technology drafts being worked out in NETCONF WG. It is included here to indicate that these features are necessary for ephemeral state.

3.3. Hierarchy

Ephemeral-REQ-06: The ability to augment an object with appropriate YANG structures that have the property of being ephemeral. An object defined as any one of the following: yang module, submodule or components of submodule, or schema node.

3.4. Ephemeral Configuration overlapping Local Configuration

Ephemeral-REQ-07: Ephemeral configuration state could override overlapping local configuration state, or vice-versa. Implementations MUST provide a mechanism to choose which takes precedence. This mechanism MUST include local configuration (policy) and MAY be provided via the I2RS protocol mechanisms.

4. YANG Features for Ephemeral State for I2RS Protocol version 1

Ephemeral-REQ-08: Yang MUST have a way to indicate in a data model that nodes have the following properties: ephemeral, writable/not-writable, and status/configuration.

5. NETCONF Features for Ephemeral State for I2RS Protocol version 1

Ephemeral-REQ-09: The conceptual changes to NETCONF

  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 below in requirements Ephemeral-REQ-11 through Ephemeral-REQ-14).

6. RESTCONF Features for Ephemeral State for I2RS Protocol version 1

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 below in 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 data nodes MAY store I2RS client identity and not the effective priority at the time the data node is stored. Per SEC-REQ-07 in section 3.1 of [I-D.ietf-i2rs-protocol-security-requirements], an identifier must have just one priority. Therefore, the data nodes MAY store I2RS client identity and not the effective priority of the I2RS client at the time the data node is stored. 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-12: 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-13: 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-14: 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.

8. Multiple Message Transactions

Ephemeral-REQ-15: 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 in many ways. No multi-message commands SHOULD cause errors to be inserted into the I2RS ephemeral data-store.

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.

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 publication/subscription requirements for I2RS are in [I-D.ietf-i2rs-pub-sub-requirements], and the following general requirements SHOULD be understood to be expanded to to include ephemeral state:

10. IANA Considerations

There are no IANA requirements for this document.

11. Security Considerations

The security requirements for the I2RS protocol are covered in [I-D.ietf-i2rs-protocol-security-requirements] document. The security requirements for the I2RS protocol environment are in [I-D.ietf-i2rs-security-environment-reqs].

12. 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:

13. References

13.1. 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", Internet-Draft draft-ietf-i2rs-architecture-15, April 2016.
[I-D.ietf-i2rs-protocol-security-requirements] Hares, S., Migault, D. and J. Halpern, "I2RS Security Related Requirements", Internet-Draft draft-ietf-i2rs-protocol-security-requirements-06, May 2016.
[I-D.ietf-i2rs-pub-sub-requirements] Voit, E., Clemm, A. and A. Prieto, "Requirements for Subscription to YANG Datastores", Internet-Draft draft-ietf-i2rs-pub-sub-requirements-09, May 2016.
[I-D.ietf-i2rs-security-environment-reqs] Migault, D., Halpern, J. and S. Hares, "I2RS Environment Security Requirements", Internet-Draft draft-ietf-i2rs-security-environment-reqs-01, April 2016.
[I-D.ietf-i2rs-traceability] Clarke, J., Salgueiro, G. and C. Pignataro, "Interface to the Routing System (I2RS) Traceability: Framework and Information Model", Internet-Draft draft-ietf-i2rs-traceability-11, May 2016.
[I-D.ietf-netconf-call-home] Watsen, K., "NETCONF Call Home and RESTCONF Call Home", Internet-Draft draft-ietf-netconf-call-home-17, December 2015.
[I-D.ietf-netconf-restconf] Bierman, A., Bjorklund, M. and K. Watsen, "RESTCONF Protocol", Internet-Draft draft-ietf-netconf-restconf-13, April 2016.
[I-D.ietf-netconf-server-model] Watsen, K. and J. Schönwälder, "NETCONF Server and RESTCONF Server Configuration Models", Internet-Draft draft-ietf-netconf-server-model-09, March 2016.
[I-D.ietf-netconf-yang-library] Bierman, A., Bjorklund, M. and K. Watsen, "YANG Module Library", Internet-Draft draft-ietf-netconf-yang-library-06, April 2016.
[I-D.ietf-netconf-yang-patch] Bierman, A., Bjorklund, M. and K. Watsen, "YANG Patch Media Type", Internet-Draft draft-ietf-netconf-yang-patch-08, March 2016.
[I-D.ietf-netconf-yang-push] Clemm, A., Prieto, A., Voit, E., Tripathy, A. and E. Nilsen-Nygaard, "Subscribing to YANG datastore push updates", Internet-Draft draft-ietf-netconf-yang-push-03, June 2016.
[I-D.ietf-netconf-zerotouch] Watsen, K. and M. Abrahamsson, "Zero Touch Provisioning for NETCONF or RESTCONF based Management", Internet-Draft draft-ietf-netconf-zerotouch-08, April 2016.
[I-D.ietf-netmod-yang-metadata] Lhotka, L., "Defining and Using Metadata with YANG", Internet-Draft draft-ietf-netmod-yang-metadata-07, March 2016.
[RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J. and A. Bierman, "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011.

13.2. Informative References

[I-D.hares-i2rs-protocol-strawman] Hares, S., Bierman, A. and a. amit.dass@ericsson.com, "I2RS protocol strawman", Internet-Draft draft-hares-i2rs-protocol-strawman-02, May 2016.
[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., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010.
[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 Juniper EMail: jhaas@juniper.net
Susan Hares Huawei Saline, US EMail: shares@ndzh.com