I2RS Ephemeral State Requirements
draft-ietf-i2rs-ephemeral-state-00
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 | 2015-06-23 | ||
| Replaces | draft-haas-i2rs-ephemeral-state-reqs | ||
| Stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-i2rs-ephemeral-state-00
I2RS working group J. Haas
Internet-Draft Juniper
Intended status: Standards Track S. Hares
Expires: December 25, 2015 Huawei
June 23, 2015
I2RS Ephemeral State Requirements
draft-ietf-i2rs-ephemeral-state-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.
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 December 25, 2015.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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 . . . . . . . . . . . . . . . . . . . . . . . . 4
4. changes to YANG . . . . . . . . . . . . . . . . . . . . . . . 5
5. Changes to NETCONF . . . . . . . . . . . . . . . . . . . . . 5
6. Requirements regarding Identity, Secondary-Identity and
Priority . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Identity Requirements . . . . . . . . . . . . . . . . . . 6
6.2. Priority Requirements . . . . . . . . . . . . . . . . . . 6
6.3. Representing I2RS Attributes in ephemeral configuration
state . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.4. Semantics around storing and managing of priority and
client ID. . . . . . . . . . . . . . . . . . . . . . . . 7
7. Subscriptions to Changed State Requirements . . . . . . . . . 9
8. Transactions . . . . . . . . . . . . . . . . . . . . . . . . 10
9. Previously Considered Ideas . . . . . . . . . . . . . . . . . 10
9.1. A Separate Ephemeral Datastore . . . . . . . . . . . . . 10
9.2. Panes of Glass/Overlay . . . . . . . . . . . . . . . . . 11
10. Actions Required to Implement this Draft . . . . . . . . . . 11
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
12. Security Considerations . . . . . . . . . . . . . . . . . . . 12
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
14.1. Normative References: . . . . . . . . . . . . . . . . . 12
14.2. Informative References . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
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.
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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.
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
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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
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
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 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.
3.3. 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).
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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.
This state data is part of the ephemeral module and should become
inaccessible if the ephemeral module reboots.
4. 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.
5. 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.
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6. Requirements regarding Identity, Secondary-Identity and Priority
6.1. 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.:
<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.
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.
This further implies that priority is an attribute that is stored in
the NETCONF Access Control Model [RFC6536] as part of the group.
E.g.:
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+--rw nacm
+--rw enable-nacm? boolean
+--rw read-default? action-type
+--rw write-default? action-type
+--rw exec-default? action-type
+--rw enable-external-groups? boolean
+--ro denied-operations yang:zero-based-counter32
+--ro denied-data-writes yang:zero-based-counter32
+--ro denied-notifications yang:zero-based-counter32
+--rw groups
| +--rw group [name]
| +--rw name group-name-type
| +--rw user-name* user-name-type
| +--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.
6.3. 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>
6.4. Semantics around storing and managing of priority and client ID.
The semantics and desired behavior around the storing and managing of
priority and client ID have the following properties:
1. First - the priority mechanism is intended to handle "error cases
of colliding writes" in a predictable way that results in a
consistent mechanism. It is true that the same mechanism could
be used if they were not considered "errors", but it is important
to minimize the need and impact of the priority mechanism
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2. Second, if there is a priority conflict where both clients
(Client_A and Client_B) share the same priority, the client that
wrote first wins. This is to avoid network oscillation if two
clients are "fighting" over writing the same state. When there
are multiple clients and the time arrival of the messages may not
be predictable (network transit differences, which socket is
read, software differences), basing state on last arrival time
doesn't give consistent and predictable behavior. That gives
behavior ont the following time-line
1. Time_1: Client_A writes X=N with priority 10
2. Time_2: Client_B attempts to write X=K with priority 10 and
is rejected
3. Time_3: Client_A writes X=P with priority 10 and succeeds
For the I2RS Agent to properly handle these actions, it is
necessary to know that X is owned by Client_A. Priority alone is
not sufficient because the basis for rejecting Client_B's write
but accepting Client_A's write is that Client_A is the owner.
Thus it is necessary to store the Client Identity with the nodes
that it owns. This could be in an I2RS-specific overlay that is
only used by the I2RS agent and only contains the nodes that have
been written by I2RS.
3. Third, a question has come up regarding what the behavior of
priority is if a client's priority changes and whether priority
needs to be stored with each node when that node is written. In
my "keep-it-simple" perspective, priority is associated with a
Client and is only used on a conflict. This would mean that
priority is not stored with a node when that node is written.
Instead, the Client Identity is stored with the node and the
Client's priority is looked up in a client table that the I2RS
Agent can access. That client table could be populated via
configuration, via a AAA protocol, via NACM, etc. The sematic
implications are as follows:
1. Time_1: Client_A writes X=N with priority 10
2. Time_2: Client_A's priority is changed (UNUSUAL) to priority
6
3. Time_3: Client_B writes X=K with priority 8 (succeeds since 8
> 6)
4. Time_4: Client_A attempts to write X=N with priority 6 (fails
b/c 8 > > 6)
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5. Time_5: Client_B's priority is changed (UNUSUAL) to priority
7
6. Time_6 Client_B writes X=P with priority 7 and succeeds (same
> owner, no priority check)
The alternate approach would have store the priority with which a
node was written. That is more like a priority lock that could
only be changed by a client with higher priority or by the same
client, regardless of priority. This approach would require
storing a priority per node and the semantic implications would
be as follows:
1. Time_1:Client_A writes X=N with priority 10
2. Time_2:Client_A's priority is changed (UNUSUAL) to priority 6
3. Time_3: Client_B attempts to write X=K with priority 8 and
fails (10 > 8)
4. Time_4: Client_A writes X=N with priority 6 and succeeds
(same owner, no priority check)
5. Time_5: Client_B's priority is changed (UNUSUAL) to priority
7
6. Time_6 Client_B writes X=P with priority 7 and succeeds (7 >
6)
The behavior for these two models is different at Time_3 and
Time_4.
The initial preference was that the priority is not stored with the
node, but if it necessary to store it with the node additional
discussion may be needed with the I2RS WG.
7. 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.
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8. Transactions
Section 7.9 of the [I-D.ietf-i2rs-architecture] states the I2RS
architecture does not include multi-message atomicity and rollback
mechanisms, but suggests an I2RS client may inidicate 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.
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.
None of these three cases insert known errors into the I2RS ephemeral
datastore.
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.
9. Previously Considered Ideas
9.1. 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
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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.
9.2. 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:
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.
10. 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.
11. IANA Considerations
TBD.
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12. Security Considerations
TBD.
13. 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
o Kent Watsen
14. References
14.1. 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", draft-ietf-i2rs-architecture-09 (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.
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[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.
14.2. Informative 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.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
[RFC6536] Bierman, A. and M. Bjorklund, "Network Configuration
Protocol (NETCONF) Access Control Model", RFC 6536, March
2012.
Authors' Addresses
Jeff Haas
Juniper
Email: jhaas@juniper.net
Susan Hares
Huawei
Saline
US
Email: shares@ndzh.com
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