Internet Engineering Task Force M. Veillette, Ed.
Internet-Draft Trilliant Networks Inc.
Intended status: Standards Track July 24, 2017
Expires: January 25, 2018
Constrained YANG Module Library
draft-veillette-core-yang-library-01
Abstract
This document describes a YANG library that provides information
about all the YANG modules used by a constrained network management
server (e.g., a CoAP Management Interface (CoMI) server). Simple
caching mechanisms are provided to allow clients to minimize
retrieval of this information.
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 January 25, 2018.
Copyright Notice
Copyright (c) 2017 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. Major differences between ietf-constrained-yang-library
and ietf-yang-library . . . . . . . . . . . . . . . . . . 3
2. Terminology and Notation . . . . . . . . . . . . . . . . . . 3
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Tree diagram . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Description . . . . . . . . . . . . . . . . . . . . . . . 4
3.2.1. modules-state . . . . . . . . . . . . . . . . . . . . 5
3.2.2. modules-state/module-set-id . . . . . . . . . . . . . 5
3.2.3. modules-state/module . . . . . . . . . . . . . . . . 5
4. YANG Module "ietf-constrained-yang-library" . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
5.1. YANG Module Registry . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
The YANG library specified in this document is available to clients
of a given server to discover the YANG modules supported by this
constrained network management server. A CoMI server provides a link
to this library in the /mod.uri resource. The following YANG module
information is provided to client applications to fully utilize the
YANG data modeling language:
o module list: The list of YANG modules implemented by a server,
each module is identified by its assigned YANG Schema Item
iDentifier (SID) and revision.
o submodule list: The list of YANG submodules included by each
module, each submodule is identified by its assigned SID and
revision.
o feature list: The list of features supported by the server, each
feature is identified by its assigned SID.
o deviation list: The list of YANG modules used for deviation
statements associated with each YANG module, each module is
identified by its assigned SID and revision.
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1.1. Major differences between ietf-constrained-yang-library and ietf-
yang-library
YANG module ietf-constrained-yang-library targets the same
functionality and shares the same approach as YANG module ietf-yang-
library. The following changes with respect to ietf-yang-library are
specified to make ietf-constrained-yang-library compatible with SID
[I-D.ietf-core-yang-cbor] used by CoMI [I-D.ietf-core-comi] and to
improve its applicability to constrained devices and networks.
o YANG module ietf-constrained-yang-library extends the caching
mechanism supported by ietf-yang-library to multiple servers.
This is accomplished by supporting the identityref datatype for
"module-set-id". This enables the use of a managed identifier
(i.e. a SID) to identify a specific assembly of YANG modules,
deviations and features implemented by a group of constrained
servers.
o Modules, sub-modules, deviations and features are identified using
a numerical value (SID) instead of a string (yang-identifier).
o The "namespace" leaf, not required for SIDs, but mandatory in
ietf-yang-library is not included in ietf-constrained-yang-
library.
o Schemas can be located using the already available module or sub-
module identifier (SID) and revision. For this reason, support of
module and sub-module schema URIs have been removed.
o To minimize their size, each revision date is encoded in binary.
2. Terminology and Notation
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 [RFC2119].
The following terms are defined in [RFC7950]:
o module
o submodule
o feature
o deviation
The following terms are defined in [I-D.ietf-core-yang-cbor]:
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o YANG Schema Item iDentifier (SID)
The following terms are defined in [I-D.ietf-core-comi]:
o client
o server
The following terms are used within this document:
o library: a collection of YANG modules used by a server.
3. Overview
The "ietf-constrained-yang-library" module provides information about
the YANG library used by a given server. This module is defined
using YANG version 1 as defined by [RFC7950], but it supports the
description of YANG modules written in any revision of YANG.
3.1. Tree diagram
The tree diagram of YANG module ietf-constrained-yang-library is
provided below. This graphical representation of a YANG module is
defined in [I-D.ietf-netmod-yang-tree-diagrams].
module: ietf-constrained-yang-library
+--ro modules-state
+--ro module-set-id union
+--ro module* [sid revision]
+--ro sid sid
+--ro revision revision
+--ro feature* sid
+--ro deviation* [sid revision]
| +--ro sid sid
| +--ro revision revision
+--ro conformance-type enumeration
+--ro submodule* [sid revision]
+--ro sid sid
+--ro revision revision
notifications:
+---n yang-library-change
+--ro module-set-id -> /modules-state/module-set-id
3.2. Description
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3.2.1. modules-state
This mandatory container specifies the module set identifier and the
list of modules supported by the server.
3.2.2. modules-state/module-set-id
This mandatory leaf contains an identifier representing the current
set of modules and submodules used by a server. This identifier is
server-specific when implemented as unit32 or can be used by multiple
servers when implemented as identityref. The value of this leaf MUST
change whenever the set of modules and submodules in the library
changes. There is no requirement that the same set always results in
the same 'module-set-id' value.
This leaf allows a client to fetch the module list once, cache it,
and only re-fetch it if the value of this leaf has been changed.
If the value of this leaf changes, the server also generates a 'yang-
library-change' notification, with the new value of 'module-set-id'.
3.2.3. modules-state/module
This mandatory list contains one entry for each YANG module supported
by the server. There MUST be an entry in this list for each revision
of each YANG module that is used by the server. It is possible for
multiple revisions of the same module to be imported, in addition to
an entry for the revision that is implemented by the server.
4. YANG Module "ietf-constrained-yang-library"
RFC Ed.: update the date below with the date of RFC publication and
remove this note.
<CODE BEGINS> file "ietf-constrained-yang-library@2017-01-20.yang"
module ietf-constrained-yang-library {
namespace
"urn:ietf:params:xml:ns:yang:ietf-constrained-yang-library";
prefix "lib";
organization
"IETF CORE (Constrained RESTful Environments) Working Group";
contact
"WG Web: <http://datatracker.ietf.org/wg/core/>
WG List: <mailto:core@ietf.org>
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WG Chair: Carsten Bormann
<mailto:cabo@tzi.org>
WG Chair: Jaime Jimenez
<mailto:jaime.jimenez@ericsson.com>
Editor: Michel Veillette
<mailto:michel.veillette@trilliantinc.com>";
description
"This module contains the list of YANG modules and submodules
implemented by a server.
Copyright (c) 2016 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).
This version of this YANG module is part of RFC XXXX; see
the RFC itself for full legal notices.";
// RFC Ed.: replace XXXX with actual RFC number and remove
// this note.
// RFC Ed.: update the date below with the date of the RFC
// publication and remove this note.
revision 2017-01-20 {
description
"Initial revision.";
reference
"RFC XXXX: Constrained YANG Module Library.";
}
/*
* Typedefs
*/
typedef revision {
type binary {
length "4";
}
description
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"Revision date encoded as a binary string as follow:
- First byte = Year divided by 100
- Second byte = Year modulo 100 (0 to 99)
- Third byte = Month (1 = January to 12 = december)
- Forth byte = Day (1 to 31)";
}
typedef sid {
type uint64;
description
"Identifier assigned to different YANG items such as
data nodes, RPCs and actions, notifications, modules,
sub-modules, features and deviations.";
}
/*
* Groupings
*/
grouping identification-info {
description
"YANG modules and submodules identification information.";
leaf sid {
type sid;
mandatory true;
description
"SID assigned to this module or submodule.";
}
leaf revision {
type revision;
description
"Revision date assigned to this module or submodule.
A zero-length binary string is used if no revision statement
is present in the YANG module or submodule.";
}
}
identity module-set {
description
"Base identity from which shared module-set identifiers
are derived.";
}
/*
* Operational state data nodes
*/
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container modules-state {
config false;
description
"Contains information about the different data models
implemented by the server.";
leaf module-set-id {
type union {
type uint32;
type identityref {
base "lib:module-set";
}
}
mandatory true;
description
"Identifier representing the current set of modules
and submodules listed in the 'module' list. This
identifier is server-specific when implemented as
unit32 or shared between multiple servers when
implemented as identityref. The server MUST change
the value of this leaf each time the content of the
'module' list instance change.";
}
list module {
key "sid revision";
description
"Each entry represents one revision of one module
currently supported by the server.";
uses identification-info;
leaf-list feature {
type sid;
description
"List of YANG features from this module that are
supported by the server, regardless whether
they are defined in the module or in any included
submodules.";
}
list deviation {
key "sid revision";
description
"List of YANG deviation modules used by this server
to modify the conformance of the module associated
with this entry. Note that the same module can be
used for deviations for multiple modules, so the
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same entry MAY appear within multiple 'module' entries.
The deviation module MUST be present in the 'module'
list, with the same sid and revision values.
The 'conformance-type' value will be 'implement' for
the deviation module.";
uses identification-info;
}
leaf conformance-type {
type enumeration {
enum implement {
value 0;
description
"Indicates that the server implements one or more
protocol-accessible objects defined in the YANG
module identified in this entry. This includes
deviation statements defined in the module.
For YANG version 1.1 modules, there is at most one
module entry with conformance type 'implement' for a
particular module, since YANG 1.1 requires that
at most one revision of a module is implemented.
For YANG version 1 modules, there SHOULD NOT be more
than one module entry for a particular module.";
}
enum import {
value 1;
description
"Indicates that the server imports reusable definitions
from the specified revision of the module, but does
not implement any protocol accessible objects from
this revision.
Multiple module entries for the same module MAY
exist. This can occur if multiple modules import the
same module, but specify different revision-dates in
the import statements.";
}
}
mandatory true;
description
"Indicates the type of conformance the server is claiming
for the YANG module identified by this entry.";
}
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list submodule {
key "sid revision";
description
"Each entry represents one submodule within the
parent module.";
uses identification-info;
}
}
}
/*
* Notifications
*/
notification yang-library-change {
description
"Generated when the set of modules and submodules supported
by the server has changed.";
leaf module-set-id {
type leafref {
path "/lib:modules-state/lib:module-set-id";
}
mandatory true;
description
"Contains the module-set-id value representing the
set of modules and submodules supported by the server
at the time the notification is generated.";
}
}
}
<CODE ENDS>
5. IANA Considerations
5.1. YANG Module Registry
This document registers one YANG module in the YANG Module Names
registry [RFC7950].
name: ietf-constrained-yang-library
namespace: urn:ietf:params:xml:ns:yang:ietf-constrained-yang-library
prefix: lib
reference: RFC XXXX
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// RFC Ed.: replace XXXX with RFC number and remove this note
6. Security Considerations
This YANG module is designed to be accessed via the CoMI protocol
[I-D.ietf-core-comi]. Some of the readable data nodes in this YANG
module may be considered sensitive or vulnerable in some network
environments. It is thus important to control read access to these
data nodes.
Specifically, the 'module' list may help an attacker to identify the
server capabilities and server implementations with known bugs.
Server vulnerabilities may be specific to particular modules, module
revisions, module features, or even module deviations. This
information is included in each module entry. For example, if a
particular operation on a particular data node is known to cause a
server to crash or significantly degrade device performance, then the
module list information will help an attacker identify server
implementations with such a defect, in order to launch a denial of
service attack on the device.
7. Acknowledgments
The YANG module defined by this memo have been derived from an
already existing YANG module, ietf-yang-library [RFC7895], we will
like to thanks to the authors of this YANG module. A special thank
also to Andy Bierman for his initial recommendations for the creation
of this YANG module.
8. References
8.1. Normative References
[I-D.ietf-core-comi]
Veillette, M., Stok, P., Pelov, A., and A. Bierman, "CoAP
Management Interface", draft-ietf-core-comi-01 (work in
progress), July 2017.
[I-D.ietf-core-yang-cbor]
Veillette, M., Pelov, A., Somaraju, A., Turner, R., and A.
Minaburo, "CBOR Encoding of Data Modeled with YANG",
draft-ietf-core-yang-cbor-04 (work in progress), February
2017.
[I-D.ietf-netmod-yang-tree-diagrams]
Bjorklund, M. and L. Berger, "YANG Tree Diagrams", draft-
ietf-netmod-yang-tree-diagrams-01 (work in progress), June
2017.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<http://www.rfc-editor.org/info/rfc7950>.
8.2. Informative References
[RFC7895] Bierman, A., Bjorklund, M., and K. Watsen, "YANG Module
Library", RFC 7895, DOI 10.17487/RFC7895, June 2016,
<http://www.rfc-editor.org/info/rfc7895>.
Author's Address
Michel Veillette (editor)
Trilliant Networks Inc.
610 Rue du Luxembourg
Granby, Quebec J2J 2V2
Canada
Phone: +14503750556
Email: michel.veillette@trilliantinc.com
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