Internet DRAFT - draft-haas-i2rs-ephemeral-state-reqs
draft-haas-i2rs-ephemeral-state-reqs
Internet Engineering Task Force J. Haas
Internet-Draft Juniper Networks
Intended status: Informational May 26, 2015
Expires: November 27, 2015
I2RS Ephemeral State Requirements
draft-haas-i2rs-ephemeral-state-reqs-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.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on November 27, 2015.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Ephemeral State Requirements . . . . . . . . . . . . . . . . 3
2.1. Persistence . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Constraints . . . . . . . . . . . . . . . . . . . . . . . 3
2.3. Hierarchy . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Changes to YANG . . . . . . . . . . . . . . . . . . . . . . . 3
4. Changes to NETCONF . . . . . . . . . . . . . . . . . . . . . 4
5. Identity, Secondary-Identity Requirements; Priority
Requirements; Implications . . . . . . . . . . . . . . . . . 4
5.1. Identity Requirements . . . . . . . . . . . . . . . . . . 4
5.2. Priority Requirements . . . . . . . . . . . . . . . . . . 5
5.3. Representing I2RS Attributes in ephemeral
configuration state . . . . . . . . . . . . . . . . . . . 6
6. Subscriptions to Changed State Requirements . . . . . . . . . 6
7. Previously Considered Ideas . . . . . . . . . . . . . . . . . 7
7.1. A Separate Ephemeral Datastore . . . . . . . . . . . . . 7
7.2. Panes of Glass/Overlay . . . . . . . . . . . . . . . . . 7
8. Actions Required to Implement this Draft . . . . . . . . . . 8
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
10. Security Considerations . . . . . . . . . . . . . . . . . . . 8
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
12. Normative References . . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9
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.
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. Ephemeral State Requirements
2.1. 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.
2.2. 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.
2.3. 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).
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.
(XXX JMH - should there be a requirement that such state data be part
of an ephemeral module and perhaps become similarly inaccessible if
the ephemeral module reboots?)
3. 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.
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4. 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.
5. Identity, Secondary-Identity Requirements; Priority Requirements;
Implications
5.1. 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.:
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<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.
5.2. 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 may vary on a per-node or sub-tree basis based for a
given identity.
This further implies that priority is an attribute that is stored in
the NETCONF Access Control Model [RFC6536] as part of a rule-list.
E.g.:
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+--rw rule-list [name]
+--rw name string
+--rw group* union
+--rw rule [name]
+--rw name string
+--rw module-name? union
+--rw (rule-type)?
| +--:(protocol-operation)
| | +--rw rpc-name? union
| +--:(notification)
| | +--rw notification-name? union
| +--:(data-node)
| +--rw path node-instance-identifier
+--rw access-operations? union
+--rw action action-type
+--rw comment? string
+--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.
5.3. 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. 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.
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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.
7. Previously Considered Ideas
7.1. 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 another.
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.
7.2. 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:
1. The general complexity with managing the overlay mechanism
itself.
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2. 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.
8. 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.
9. IANA Considerations
TBD
10. Security Considerations
TBD
11. 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 Susan Hares
o Thomas Nadeau
o Juergen Schoenwaelder
o Kent Watsen
12. Normative 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.
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[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-05 (work in
progress), July 2014.
[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-02 (work
in progress), March 2015.
[I-D.ietf-netmod-yang-metadata]
Lhotka, L., "Defining and Using Metadata with YANG",
draft-ietf-netmod-yang-metadata-00 (work in progress),
April 2015.
[I-D.rfernando-i2rs-yang-mods]
Fernando, R., pals, p., Madhayyan, M., and A. Clemm, "YANG
modifications for I2RS", draft-rfernando-i2rs-yang-mods-00
(work in progress), February 2013.
[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.
[RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure
Shell (SSH)", RFC 6242, June 2011.
[RFC6536] Bierman, A. and M. Bjorklund, "Network Configuration
Protocol (NETCONF) Access Control Model", RFC 6536, March
2012.
Author's Address
Jeffrey Haas
Juniper Networks
Email: jhaas@juniper.net
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