Network Working Group M. Bjorklund
Internet-Draft Tail-f Systems
Intended status: Standards Track December 18, 2015
Expires: June 20, 2016
YANG Structural Mount
draft-bjorklund-netmod-structural-mount-00
Abstract
This document defines a mechanism to combine YANG modules into the
schema defined in other YANG modules.
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 June 20, 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
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2
1.1.1. Tree Diagrams . . . . . . . . . . . . . . . . . . . . 2
2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Structural Mount . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Validation of Mounted Data . . . . . . . . . . . . . . . 4
3.2. Top-level RPCs . . . . . . . . . . . . . . . . . . . . . 4
3.3. Top-level Notifications . . . . . . . . . . . . . . . . . 4
4. Data Model . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Structural Mount YANG Module . . . . . . . . . . . . . . . . 5
6. Usage Example . . . . . . . . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
8. Security Considerations . . . . . . . . . . . . . . . . . . . 11
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
10.1. Normative References . . . . . . . . . . . . . . . . . . 12
10.2. Informative References . . . . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
1.1. Terminology
The keywords "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].
1.1.1. Tree Diagrams
A simplified graphical representation of the data model is used in
this document. The meaning of the symbols in these diagrams is as
follows:
o Brackets "[" and "]" enclose list keys.
o Abbreviations before data node names: "rw" means configuration
data (read-write) and "ro" state data (read-only).
o Symbols after data node names: "?" means an optional node, "!"
means a presence container, and "*" denotes a list and leaf-list.
o Parentheses enclose choice and case nodes, and case nodes are also
marked with a colon (":").
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o Ellipsis ("...") stands for contents of subtrees that are not
shown.
2. Background
YANG has two mechanisms for extending a data model with additional
nodes; "uses" and "augment". The "uses" statement explicitly
incorporates the contents of a "grouping" defined in some other
module. The "augment" statement explicitly adds contents to a target
node defined in some other module. In both these cases, the source
and/or target model explicitly defines the relationship between the
models.
In some cases these mechanisms are not sufficient. For example,
suppose we have a model like ietf-interfaces [RFC7223] that is
defined to be implemented in a device. Now suppose we want to model
a device that supports multiple logical devices
[I-D.rtgyangdt-rtgwg-device-model], where each such logical device
has its own instantiation of ietf-interfaces (and other models), but
at the same time, we'd like to be able to manage all these logical
devices from the main device. We would like something like this:
+--rw interfaces
| +--rw interface* [name]
| ...
+--rw logical-device* [name]
+--rw name string
| ...
+--rw interfaces
+--rw interface* [name]
...
With the "uses" approach, ietf-interfaces would have to define a
grouping with all its nodes, and the new model for logical devices
would have to use this grouping. This is a not a scalable solution,
since every time there is a new model defined, we would have to
update our model for logical devices to use a grouping from the new
model. Another problem is that this approach cannot handle vendor-
specific modules.
With the "augment" approach, ietf-interfaces would have to augment
the logical-device list with all its nodes, and at the same time
define all its nodes on the top-level. This approach is also not
scalable, since there may be other models to which we would like to
add the interface list.
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3. Structural Mount
The structural mount mechanism defined in this document takes a
different approach. It decouples the definition of the relation
between the source and target models from the definitions of the
models themselves.
This is accomplished with a YANG extension statement that is used to
specify a mount point in a data model. The purpose of a mount point
is to define a place in the node hierarchy where other YANG data
models may be attached, without any special notation in the other
YANG data models.
For each mount point supported by a server, the server populates an
operational state node hierarchy with information about which models
it has mounted. This node hierarchy can be read by a client in order
to learn what is implemented on a server.
Structural mount applies to the schema, and specifically does not
assume anything about how the mounted data is implemented. It may be
implemented using the same instrumentation as the rest of the system,
or it may be implemented by querying some other system.
This document allows mounting of complete data models only. Other
specifications may extend this model by defining additional
mechanisms, for example mounting of sub-hierarchies of a module.
3.1. Validation of Mounted Data
All paths (in leafrefs, instance-identifiers, XPath expressions, and
target nodes of augments) in the data models mounted at a mount point
are interpreted with the mount point as the root node, and the
mounted data nodes as its children. This means that data within a
mounted subtree can never refer to data outside of this subtree.
3.2. Top-level RPCs
If any mounted data model defines RPCs, these RPCs can be invoked by
treating them as actions defined where the mount point is specified.
3.3. Top-level Notifications
If the server emits a notification defined at the top-level in any
mounted data model, it is treated as if the notification was attached
to the data node where the mount point is specified.
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4. Data Model
This document defines the YANG module "ietf-yang-structural-mount",
which has the following structure:
module: ietf-yang-structural-mount
+--ro mount-points
+--ro mount-point* [module name]
+--ro module yang:yang-identifier
+--ro name yang:yang-identifier
+--ro (data-model)?
+--:(inline-yang-library)
| +--ro inline-yang-library? empty
+--:(modules)
+--ro modules
+--ro module* [name revision]
+--ro name yang:yang-identifier
+--ro revision union
+--ro schema? inet:uri
+--ro namespace inet:uri
+--ro feature* yang:yang-identifier
+--ro deviation* [name revision]
| +--ro name yang:yang-identifier
| +--ro revision union
+--ro conformance enumeration
+--ro submodules
+--ro submodule* [name revision]
+--ro name yang:yang-identifier
+--ro revision union
+--ro schema? inet:uri
5. Structural Mount YANG Module
<CODE BEGINS> file "ietf-yang-structural-mount@2015-12-17.yang"
module ietf-yang-structural-mount {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-yang-structural-mount";
prefix yangmnt;
import ietf-yang-types {
prefix yang;
}
import ietf-yang-library {
prefix yanglib;
}
organization
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"IETF NETMOD (NETCONF Data Modeling Language) Working Group";
contact
"WG Web: <http://tools.ietf.org/wg/netmod/>
WG List: <mailto:netmod@ietf.org>
WG Chair: Thomas Nadeau
<mailto:tnadeau@lucidvision.com>
WG Chair: Juergen Schoenwaelder
<mailto:j.schoenwaelder@jacobs-university.de>
WG Chair: Kent Watsen
<mailto:kwatsen@juniper.net>
Editor: Martin Bjorklund
<mailto:mbj@tail-f.com>";
// RFC Ed.: replace XXXX with actual RFC number and remove this
// note.
description
"This module defines a YANG extension statement that can be used
to incorporate data models defined in other YANG modules in a
module. It also defines a operational state data so that
clients can learn which data models a server implements for the
mount points.
Copyright (c) 2015 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject to
the license terms contained in, the Simplified BSD License set
forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(http://trustee.ietf.org/license-info).
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY', and
'OPTIONAL' in the module text are to be interpreted as described
in RFC 2119 (http://tools.ietf.org/html/rfc2119).
This version of this YANG module is part of RFC XXXX
(http://tools.ietf.org/html/rfcXXXX); see the RFC itself for
full legal notices.";
// RFC Ed.: update the date below with the date of RFC publication
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// and remove this note.
revision 2015-12-17 {
description
"Initial revision.";
reference
"RFC XXXX: YANG Structural Mount";
}
/*
* Extension statements
*/
extension mount-point {
argument name;
description
"The argument 'name' is a yang-identifier. The name of
the mount point MUST be unique within the module where it
is defined.
The 'mount-point' statement can be present in 'container' and
'list'.
A mount point defines a place in the node hierarchy where other
data models may be attached. A server that implements a module
with a mount point, populates the /mount-points/mount-point
list with detailed information on which data models are mounted
at each mount point.";
}
/*
* Operational state data nodes
*/
container mount-points {
config false;
description
"Contains information about which mount points are implemented
in the server, and their data models.";
list mount-point {
key "module name";
description
"Contains information about which data models are implemented
for the mountpoint 'name' defined in 'module'.";
leaf module {
type yang:yang-identifier;
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description
"The name of the module where the mount point is defined.";
}
leaf name {
type yang:yang-identifier;
description
"The name of the mount point.";
}
choice data-model {
mandatory true;
description
"Indicates which data models the server implements
for this mount point.
It is expected that this choice may be augmented with new
data model discovery mechansisms.";
leaf inline-yang-library {
type empty;
description
"This leaf indicates that the server has mounted
'ietf-yang-library' at the mount point, and that this
instantiation of 'ietf-yang-library' contains the
information about which modules are mounted.
This is useful if the mount point is defined in a
list, and different list entries may mount a different
set of modules.";
}
container modules {
description
"The 'module' list contains the set of modules that are
mounted at the mount point.";
uses yanglib:module-list;
}
}
}
}
}
<CODE ENDS>
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6. Usage Example
A data model for logical devices may be defined as:
module example-logical-devices {
namespace "http://example.com/logical-device";
prefix exld;
import ietf-yang-structural-mount {
prefix yangmnt;
}
container logical-devices {
list logical-device {
key name;
leaf name {
type string;
}
yangmnt:mount-point logical-device;
}
}
}
A server that implements two logical devices might populate the
"mount-points" container with:
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<mount-points
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-structural-mount">
<mount-point>
<module>example-logical-devices</module>
<name>device-root</name>
<modules>
<module>
<name>ietf-interface</name>
<revision>2014-05-08</revision>
<namespace>
urn:ietf:params:xml:ns:yang:ietf-interfaces
</namespace>
<conformance>implement</conformance>
</module>
<module>
<name>ietf-yang-types</name>
<revision>2013-07-15</revision>
<namespace>
urn:ietf:params:xml:ns:yang:ietf-yang-types
</namespace>
<conformance>import</conformance>
</module>
</modules>
</mount-point>
</mount-points>
and the "logical-devices" container might have:
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<logical-devices xmlns="http://example.com/logical-device">
<logical-device>
<name>vrtrA</name>
<interfaces
xmlns="urn:ietf:params:xml:ns:yang:ietf-interfaces">
<interface>
<name>eth0</name>
...
</interface>
</interfaces>
</logical-device>
<logical-device>
<name>vrtrB</name>
<interfaces
xmlns="urn:ietf:params:xml:ns:yang:ietf-interfaces">
<interface>
<name>eth0</name>
...
</interface>
</interfaces>
</logical-device>
</logical-devices>
7. IANA Considerations
This document registers a URI in the IETF XML registry [RFC3688].
Following the format in RFC 3688, the following registration is
requested to be made.
URI: urn:ietf:params:xml:ns:yang:ietf-yang-structural-mount
Registrant Contact: The IESG.
XML: N/A, the requested URI is an XML namespace.
This document registers a YANG module in the YANG Module Names
registry [RFC6020].
name: ietf-yang-structural-mount
namespace: urn:ietf:params:xml:ns:yang:ietf-yang-structural-mount
prefix: yangmnt
reference: RFC XXXX
8. Security Considerations
TBD
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9. Acknowledgements
The author would like to thank Lou Berger, Alexander Clemm, Ladislav
Lhotka, and Jan Medved for useful comments and discussions on this
topic.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
January 2004.
[RFC6020] Bjorklund, M., "YANG - A Data Modeling Language for the
Network Configuration Protocol (NETCONF)", RFC 6020,
October 2010.
10.2. Informative References
[I-D.rtgyangdt-rtgwg-device-model]
Lindem, A., Berger, L., Bogdanovic, D., and C. Hopps,
"Network Device YANG Organizational Model", draft-
rtgyangdt-rtgwg-device-model-01 (work in progress),
September 2015.
[RFC7223] Bjorklund, M., "A YANG Data Model for Interface
Management", RFC 7223, DOI 10.17487/RFC7223, May 2014,
<http://www.rfc-editor.org/info/rfc7223>.
Author's Address
Martin Bjorklund
Tail-f Systems
Email: mbj@tail-f.com
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