Network Modeling Q. Ma
Internet-Draft Q. Wu
Intended status: Standards Track Huawei
Expires: 24 April 2025 21 October 2024
YANG Templates
draft-ma-netmod-yang-config-template-00
Abstract
NETCONF and RESTCONF protocols provide programmatic operation
interfaces for accessing configuration data modeled by YANG. This
document defines the use of YANG-based configuration template
mechanism so that the configuration data could be defined as template
and applied repeatedly to avoid the redundant definition of identical
Configuration and ensure consistency of it.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the Network Modeling
Working Group mailing list (netmod@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/netmod/.
Source for this draft and an issue tracker can be found at
https://github.com/QiufangMa/template-mechanism.
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 24 April 2025.
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Copyright Notice
Copyright (c) 2024 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 (https://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 Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Editorial Note (To be removed by RFC Editor) . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 4
3. Hierarchical Template Overview . . . . . . . . . . . . . . . 4
3.1. Validity of Templates . . . . . . . . . . . . . . . . . . 5
4. Inheriting Templates . . . . . . . . . . . . . . . . . . . . 5
4.1. The "stmt-extend" Metadata . . . . . . . . . . . . . . . 6
4.2. Template Extension . . . . . . . . . . . . . . . . . . . 7
5. Overriding Templates . . . . . . . . . . . . . . . . . . . . 8
5.1. Modification . . . . . . . . . . . . . . . . . . . . . . 8
5.2. Deletion . . . . . . . . . . . . . . . . . . . . . . . . 8
5.3. List/leaf-list Reordering . . . . . . . . . . . . . . . . 9
6. Interaction with NMDA datastores . . . . . . . . . . . . . . 12
7. Different Levels of Templates . . . . . . . . . . . . . . . . 13
8. The "ietf-template" YANG Module . . . . . . . . . . . . . . . 13
8.1. Data Model Overview . . . . . . . . . . . . . . . . . . . 13
8.2. YANG Module . . . . . . . . . . . . . . . . . . . . . . . 13
9. Security Considerations . . . . . . . . . . . . . . . . . . . 15
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
10.1. The "IETF XML" Registry . . . . . . . . . . . . . . . . 16
10.2. The "YANG Module Names" Registry . . . . . . . . . . . . 16
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
11.1. Normative References . . . . . . . . . . . . . . . . . . 16
11.2. Informative References . . . . . . . . . . . . . . . . . 17
Appendix A. template Syntax . . . . . . . . . . . . . . . . . . 18
A.1. Variable Declaration . . . . . . . . . . . . . . . . . . 18
A.2. Loop Statement . . . . . . . . . . . . . . . . . . . . . 18
A.3. If-Else Statement . . . . . . . . . . . . . . . . . . . . 18
Appendix B. Usage Examples . . . . . . . . . . . . . . . . . . . 18
B.1. Creating Templates . . . . . . . . . . . . . . . . . . . 19
B.2. Inheriting Templates . . . . . . . . . . . . . . . . . . 20
B.3. Overriding Templates . . . . . . . . . . . . . . . . . . 25
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Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27
1. Introduction
It is not unusual for the YANG data model [RFC7950] to define some
shared profiles that could be referenced in order to simplify the
configuration of network services or functionalities. For example,
[I-D.ietf-opsawg-ntw-attachment-circuit] defines a set of profiles at
the network level which could be referred to under the node level to
factorize some common configuration shared by a group of attachment
circuits (ACs).
However, it is not trivial to always take care of the definition of
shared profiles/policies/templates during the design of every data
model. There is a desire to make use of common YANG-based templates
without relying on specific definition in YANG data models.
NMDA [RFC8342] allows the configuration templates to be defined in
<running> and expanded in <intended>, but it does not specify details
about how configuration templates could be created and applied.
This document defines the use of configuration templates in the
context of YANG-driven network management protocols such as NETCONF
[RFC6241] and RESTCONF [RFC8040]. By defining a common set of nodes
as a configuration template and applying the configuration template
repeatedly, it avoids the redundant definition of identical
configuration and also ensures consistency of it. Configuration
template could be used based on any existing YANG data models, this
document doesn't make any assumption on the YANG data model design,
i.e., it does not rely on the shared profile/group defined in the
YANG data model.
1.1. Editorial Note (To be removed by RFC Editor)
Note to the RFC Editor: This section is to be removed prior to
publication.
This document contains placeholder values that need to be replaced
with finalized values at the time of publication. This note
summarizes all of the substitutions that are needed. No other RFC
Editor instructions are specified elsewhere in this document.
Please apply the following replacements:
* XXXX --> the assigned RFC number for this draft
* 2024-08-27 --> the actual date of the publication of this document
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2. Conventions and Definitions
The key words "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] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
The meanings of the symbols in tree diagrams are defined in
[RFC8340].
This document uses the YANG terminology defined in Section 3 of
[RFC7950].
Besides, this document defines the following terminology:
configuration template: A chunk of reusable configuration data that
could be applied to the configuration repeatedly, in order to
simplify the delivery of network configuration and ensure the
consistency of it. A configuration template can also be called
"hierarchical template", or "template" for short.
inherited template: A configuration template that is applied in the
configuration data tree or reused by other templates.
parent template: A configuration template that is an inherited
template.
3. Hierarchical Template Overview
A configuration template must first be defined before it can be
inherited Section 4. The creation, modification, and deletion of
configuration templates are achieved by network management operations
via NETCONF or RESTCONF protocols. The content of the configuration
template must be an instantiated chunk of data starting from any
level node in the module hierarchies.
For example, Figure 1 provides an interface configuration template
that sets "mtu" as 1500 for ethernet interfaces:
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<templates>
<template>
<id>interface-type-mtu</id>
<interface>
<type>ianaift:ethernetCsmacd</type>
<mtu>1500</mtu>
<description>MTU value is set by template</description>
</interface>
</template>
</templates>
Figure 1: Example of An Interface template
The YANG data model of configuration templates is defined in
Section 8.
3.1. Validity of Templates
The contents of the template alone is not always sufficient to
enforce the constraints of the data model. Some constraints may
depend on configuration outside of the templates to satisfy, e.g., a
list may contain a mandatory leaf node which is not defined in the
template but explicitly provided by the client. However, servers
should parse the template and enforce the constraints if it is
possible during the processing of template creation, e.g., servers
may validate type constraints for the leaf, including those defined
in the type's "range", "length", and "pattern" properties.
That said, if a template is applied in the configuration data tree,
the results of the template configuration merging with configuration
explicitly provided by the client MUST always be valid, as defined in
Section 8.1 of [RFC7950].
4. Inheriting Templates
This document allows configuration templates to be inherited by
configuration nodes in the data tree or new templates at
corresponding level. A node inherits at most one configuration
template.
If a configuration template is inherited by a node in the data tree,
it acts as if the configuration defined in the template is contained
and is merged with the configuration provided explicitly at the
corresponding level in the data tree with the explicitly provided
configuration takes precedence.
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If a configuration template is inherited by another new template, the
configuration of the new template is the merging result of
configuration defined in both templates with the new template takes
precedence over its parent template. This is useful when some
additional configuration is intended to be defined on the basis of
the parent template.
Any modification to the parent template also applies where the
template is inherited.
4.1. The "stmt-extend" Metadata
Template inheritance is indicated by declaring the metadata object
called "stmt-extend".
If the template is inherited by a node in the data tree, the metadata
object is added to that specific node.
If the template is inherited by other templates, the metadata object
is added to the node at corresponding level of the template contents.
The "stmt-extend" metadata MUST have only one value to specify the
parent template identifier that is inherited. The encoding of "stmt-
extend" metadata object follows the way defined in Section 5 of
[RFC7952].
For example, a client may configure physically present interfaces
"eth0" and "eth1" with the list node "interface" inheriting the
template defined in Figure 1:
<interfaces xmlns:template="urn:ietf:params:xml:ns:yang:ietf-template">
<interface template:stmt-extend="interface-type-mtu">
<name>eth0</name>
</interface>
<interface template:stmt-extend="interface-type-mtu">
<name>eth1</name>
</interface>
</interfaces>
And the above interface configuration renders the following expanded
configuration:
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<interfaces>
<interface>
<name>eth0</name>
<type>ianaift:ethernetCsmacd</type>
<mtu>1500</mtu>
<description>MTU value is set by template</description>
</interface>
<interface>
<name>eth1</name>
<type>ianaift:ethernetCsmacd</type>
<mtu>1500</mtu>
<description>MTU value is set by template</description>
</interface>
</interfaces>
4.2. Template Extension
If there is some further configuration data that needs to be created
but not included in the parent template, it can be provided at the
corresponding level when inheriting the configuration template. For
example, the client may want to define another template and provide
an additional "enabled" leaf value on the basis of template defined
in Figure 1:
<templates>
<template>
<id>interface-type-mtu-enabled</id>
<interface xmlns:template="urn:ietf:params:xml:ns:yang:ietf-template"
template:stmt-extend="interface-type-mtu">
<enabled>true</enabled>
</interface>
</template>
</templates>
And the above interface configuration defined in the template
"interface-type-mtu-enabled" renders the following expanded
configuration:
<interface>
<type>ianaift:ethernetCsmacd</type>
<mtu>1500</mtu>
<description>MTU value is set by template</description>
<enabled>true</enabled>
</interface>
Appendix B.2 provides more examples of inheriting an existing
template by indicating the "stmt-extend" metadata object.
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5. Overriding Templates
It may be desired to override some configuration in an existing
template when it is interited. This may be achieved by directly
editing the configuration template that is inherited, however, the
parent template may have also been inherited by other instance nodes
or templates, and direct modification of the parent template may
yield unexpected results.
This document allows a configuration template to be overridden by
other templates or configuration explicitly provided by the client.
5.1. Modification
If there is some configuration values that need to be modified, the
desired value can be provided at the corresponding level when
inheriting the configuation template.
For example, a client may configure physically present interfaces
"eth0" and "eth1" inheriting the template defined in Figure 1, but
the "mtu" value of "eth1" needs to be 9122, and the "description"
value also needs to be modified accordingly:
<interfaces xmlns:template="urn:ietf:params:xml:ns:yang:ietf-template">
<interface template:stmt-extend="interface-type-mtu">
<name>eth0</name>
</interface>
<interface template:stmt-extend="interface-type-mtu">
<name>eth1</name>
<mtu>9122</mtu>
<description>MTU value is set explicitly</description>
</interface>
</interfaces>
5.2. Deletion
The deletion of configuration data is flagged by declaring the
metadata object called "operation-tag" with a value "delete". If
some node instance defined in the configuration template is intended
to be deleted in the configuration explicitly by the client or by new
templates, the "operation-tag" metadata annotation is added to that
specific node. Servers MUST ignore this metadata if the
configuration identified currently does not exist in the
configuration template.
The "operation-tag" metadata MUST have only one value to specify the
intended operation. The encoding of "operation-tag" metadata object
follows the way defined in Section 5 of [RFC7952].
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For example, a client may want to delete the "description" node
instance defined in Figure 1 for interface "eth1", and the following
shows the example configuration:
<interfaces xmlns:template="urn:ietf:params:xml:ns:yang:ietf-template">
<interface template:stmt-extend="interface-type-mtu">
<name>eth0</name>
</interface>
<interface template:stmt-extend="interface-type-mtu">
<name>eth1</name>
<mtu>9122</mtu>
<description template:operation-tag="delete">MTU value is set by template</description>
</interface>
</interfaces>
And it renders the following expanded configuration:
<interfaces>
<interface>
<name>eth0</name>
<type>ianaift:ethernetCsmacd</type>
<mtu>1500</mtu>
<description>MTU value is set by template</description>
</interface>
<interface>
<name>eth1</name>
<type>ianaift:ethernetCsmacd</type>
<mtu>9122</mtu>
</interface>
</interfaces>
5.3. List/leaf-list Reordering
There may be a desire to reorder some existing list/leaf-list entries
defined in an existing template, or specify the ordering of new
instances when they are created. It only applies to lists and leaf-
lists indicated with the "ordered-by user" statement.
The reordering of list/leaf-list entry data is flagged by declaring
the metadata object called "operation-tag" with different values.
The "operation-tag" used for reordering has one of the following
values:
* position-first: The attached entry is positioned as the first
entry in the list/leaf-list. There must be no more than one
entry that is annotated as "position-first" within the same
operation request.
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* position-last: The attached entry is positioned as the last entry
in the list/leaf-list. There must be no more than one entry
that is annotated as "position-last" within the same operation
request.
* position-before: The attached entry is positioned before some
other specified entries in the list/leaf-list. This value MUST
be followed by one or more space-seperated key values to
indicate the entries that the attached entry is just positioned
before. The "position-before" metadata and key values are
seperated by colon ":". There must not be any other entries
that use "position-before" to target the entry attached as
"position-first" within the same operation rquest.
* position-after: The attached entry is positioned after some other
specified entries in the list/leaf-list. This value MUST be
followed by one or more space-seperated key values to indicate
the entries that the attached entry is just positioned after.
The "position-after" metadata and key values are seperated by
colon ":". There must not be any other entries that use
"position-after" to target the entry attached as "position-
last" within the same operation request.
For example, the following template provides the user-ordered ACL
configuration:
<templates>
<template>
<id>ACL-rules-template</id>
<acls>
<acl>
<name>allow-access-from-tcp</name>
<matches>
<protocol>tcp</protocol>
</matches>
<action>permit</action>
</acl>
<acl>
<name>allow-access-from-udp</name>
<matches>
<protocol>udp</protocol>
</matches>
<action>permit</action>
</acl>
</acls>
</template>
</templates>
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If the client wants to create another template with an additional ACL
entry named "deny-traffic-from-ftp" ordered as the first entry and
ACL entry named "allow-access-from-tcp" as the last one:
<templates>
<template>
<id>ACL-rules-template2</id>
<acls xmlns:template="urn:ietf:params:xml:ns:yang:ietf-template"
template:stmt-extend="acl-rule-template">
<acl template:operation-tag="position-first">
<name>deny-traffic-from-ftp</name>
<matches>
<protocol>ftp</protocol>
</matches>
</acl>
<acl template:operation-tag="position-last">
<name>allow-access-from-tcp</name>
</acl>
</acls>
</template>
</templates>
The client may also deliver the configuration defined in template
"acl-rule-template" with some other additional ACL entries that is
properly ordered:
<acls xmlns:template="urn:ietf:params:xml:ns:yang:ietf-template"
template:stmt-extend="acl-rule-template">
<acl template:operation-tag="position-before:\
'allow-access-from-tcp allow-access-from-udp'">
<name>deny-access-to-ipv4</name>
<matches>
<destination-ipv4-network>192.0.2.0/24</destination-ipv4-network>
</matches>
</acl>
<acl template:operation-tag="position-after:'deny-access-to-ipv4'">
<name>deny-access-to-ipv6</name>
<matches>
<destination-ipv6-network>2001:db8::/32</destination-ipv6-network>
</matches>
</acl>
</acls>
The applied ACL configuration renders the following expanded
configuration:
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<acls>
<acl>
<name>deny-access-to-ipv4</name>
<matches>
<destination-ipv4-network>192.0.2.0/24</destination-ipv4-network>
</matches>
</acl>
<acl>
<name>deny-access-to-ipv6</name>
<matches>
<destination-ipv6-network>2001:db8::/32</destination-ipv6-network>
</matches>
</acl>
<acl>
<name>allow-access-from-tcp</name>
<matches>
<protocol>tcp</protocol>
</matches>
<action>permit</action>
</acl>
<acl>
<name>allow-access-from-udp</name>
<matches>
<protocol>udp</protocol>
</matches>
<action>permit</action>
</acl>
</acls>
6. Interaction with NMDA datastores
Some implementation may have predefined configuration templates for
the convenience of clients, which are present in <system> (if
implemented, see [I-D.ietf-netmod-system-config]). In addition,
clients can always define their own templates in <running>. However,
configuration template data defined by "ietf-template" YANG data
model should not be visible in <operational> until being inherited by
a node in the data tree.
If a node in the data tree inherits a configuration template, the
configuration template does not expand in <running>, a read back of
<running> returns what is sent by the client with the "stmt-extend"
metadata attached to the specific node. Configuration template which
is inherited or overridden by the node instance MUST be expanded in
<intended>.
Editor's Note: The read-back of <running> might break legacy
clients that don't understand template?
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7. Different Levels of Templates
The configuration templates may be defined at different levels,
depending on where it is used and maintained. For exmaple, A
network-level template maintained by the software-defined networking
(SDN) [RFC7149] [RFC7426] controller defines configuration that may
be shared by multiple network elements. While device-level template
maintained by the network element defines configuration that can only
be applied to specific network element. Refer to Appendix B for
examples of network-level templates.
8. The "ietf-template" YANG Module
8.1. Data Model Overview
The following tree diagram [RFC8340] illustrates the "ietf-template"
module:
module: ietf-template
+--rw templates
+--rw template* [id]
+--rw id string
+--rw description? string
+--rw content? <anydata>
+--ro last-modified? yang:timestamp
+--ro parent-template* -> ../../template/id
+--ro inherited-by* union
Editor's Note: Should the 'stmt-extend' and 'operation-tag'
metadata annotations be defined here?
8.2. YANG Module
<CODE BEGINS> file "ietf-template@2024-08-27.yang"
module ietf-template {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-template";
prefix template;
import ietf-yang-types {
prefix yang;
reference
"RFC 6991: Common YANG Data Types";
}
organization
"IETF NETMOD (Network Modeling) Working Group";
contact
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"WG Web: <https://datatracker.ietf.org/wg/netmod/>
WG List: <mailto:netmod@ietf.org>
Author: Qiufang Ma
<mailto:maqiufang1@huawei.com>";
description
"This module defines a template list with a RPC to expand
the template.
Copyright (c) 2024 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 Revised
BSD License set forth in Section 4.c of the IETF Trust's
Legal Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX
(https://www.rfc-editor.org/info/rfcXXXX); see the RFC
itself for full legal notices.
The key words '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 (RFC 2119)
(RFC 8174) when, and only when, they appear in all
capitals, as shown here.";
revision 2024-08-27 {
description
"Initial revision.";
reference
"RFC XXXX: YANG Templates";
}
container templates {
description
"Specifies the template parameters.";
list template {
key id;
description
"The list of templates managed on this device.";
leaf id {
type string;
description
"The identifier of the template that uniquely identifies a
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template.";
}
leaf description {
type string;
description
"A textual description of the template.";
}
anydata content {
description
"inline template content.";
}
leaf last-modified {
type yang:timestamp;
config false;
description
"Timestamp when the template is modified last time.";
}
leaf-list parent-template {
type leafref {
path "../../template/id";
}
config false;
description
"The identifier of the template that this template is
inherited from.";
}
leaf-list inherited-by {
type union {
type instance-identifier;
type leafref {
path "../../template/id";
}
}
config false;
description
"The data tree node or an identifier of the template that
inherits this template.";
}
}
}
}
<CODE ENDS>
9. Security Considerations
TODO Security
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10. IANA Considerations
10.1. The "IETF XML" Registry
This document registers the following URI in the "IETF XML Registry"
[RFC3688].
URI: urn:ietf:params:xml:ns:yang:ietf-template
Registrant Contact: The IESG.
XML: N/A, the requested URI is an XML namespace.
10.2. The "YANG Module Names" Registry
This document registers the following YANG module in the "YANG Module
Names" registry [RFC6020].
name: ietf-template
namespace: urn:ietf:params:xml:ns:yang:ietf-template
prefix: template
maintained by IANA? N
reference: RFC XXXX
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<https://www.rfc-editor.org/rfc/rfc3688>.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<https://www.rfc-editor.org/rfc/rfc6020>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/rfc/rfc6241>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/rfc/rfc7950>.
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[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/rfc/rfc8040>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
11.2. Informative References
[I-D.ietf-netmod-system-config]
Ma, Q., Wu, Q., and C. Feng, "System-defined
Configuration", Work in Progress, Internet-Draft, draft-
ietf-netmod-system-config-09, 29 September 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-netmod-
system-config-09>.
[I-D.ietf-opsawg-ntw-attachment-circuit]
Boucadair, M., Roberts, R., de Dios, O. G., Barguil, S.,
and B. Wu, "A Network YANG Data Model for Attachment
Circuits", Work in Progress, Internet-Draft, draft-ietf-
opsawg-ntw-attachment-circuit-13, 5 September 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-opsawg-
ntw-attachment-circuit-13>.
[RFC7149] Boucadair, M. and C. Jacquenet, "Software-Defined
Networking: A Perspective from within a Service Provider
Environment", RFC 7149, DOI 10.17487/RFC7149, March 2014,
<https://www.rfc-editor.org/rfc/rfc7149>.
[RFC7426] Haleplidis, E., Ed., Pentikousis, K., Ed., Denazis, S.,
Hadi Salim, J., Meyer, D., and O. Koufopavlou, "Software-
Defined Networking (SDN): Layers and Architecture
Terminology", RFC 7426, DOI 10.17487/RFC7426, January
2015, <https://www.rfc-editor.org/rfc/rfc7426>.
[RFC7952] Lhotka, L., "Defining and Using Metadata with YANG",
RFC 7952, DOI 10.17487/RFC7952, August 2016,
<https://www.rfc-editor.org/rfc/rfc7952>.
[RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
<https://www.rfc-editor.org/rfc/rfc8340>.
[RFC8342] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
and R. Wilton, "Network Management Datastore Architecture
(NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
<https://www.rfc-editor.org/rfc/rfc8342>.
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Appendix A. template Syntax
Some implementations support richer syntax in the template definition
so that the use of configuration template could be more flexible.
A.1. Variable Declaration
TBD
A.2. Loop Statement
TBD
A.3. If-Else Statement
TBD
Appendix B. Usage Examples
This section provides some examples to show the use of templates.
JSON encodings are used to not imply a preference in this document.
The fictional data model used throughout this section is shown as
follows:
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module example-network-systime {
yang-version 1.1;
namespace "urn:example:network-system-time";
prefix "ex-nesyst";
import ietf-inet-types {
prefix "inet";
}
list network-device {
key device-id;
leaf device-id {
type string;
}
container ntp {
leaf enabled {
type boolean;
mandatory true;
}
list server {
ordered-by user;
key name;
leaf name {
type string;
}
leaf-list alias {
type string;
}
leaf address {
type inet:host;
mandatory true;
}
leaf port {
type inet:port-number;
default 123;
}
}
}
}
}
B.1. Creating Templates
The NTP configuration on multiple network devices may be consistent.
To create a template for NTP configuration, the following template
configuration might be sent to a SDN controller:
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{
"ietf-templates:templates": {
"template": [
{
"id": "template-ntp",
"content": {
"network-device": [
{
"ntp": {
"enabled": "true",
"server": [
{
"name": "ntp-server-1",
"alias": [
"primary"
],
"address": "ntp.example-1.com"
},
{
"name": "ntp-server-2",
"alias": [
"secondary"
],
"address": "ntp.example-2.com"
}
]
}
}
]
}
}
]
}
}
B.2. Inheriting Templates
The operator may create another template with an additional NTP
server instance when inheriting the template created in Appendix B.1.
The configuration is shown as follows:
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{
"ietf-templates:templates": {
"template": [
{
"id": "template-ntp2",
"content": {
"network-device": [
{
"@": {
"ietf-template:stmt-extend": "template-ntp"
},
"ntp": {
"server": [
{
"name": "ntp-server-3",
"alias": [
"secondary"
],
"address": "ntp.example-3.com"
}
]
}
}
]
}
}
]
}
}
The configuration of template "template-ntp2" renders the following
expanded configuration:
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{
"ietf-templates:templates": {
"template": [
{
"id": "template-ntp2",
"content": {
"network-device": [
{
"ntp": {
"enabled": "true",
"server": [
{
"name": "ntp-server-1",
"alias": [
"primary"
],
"address": "ntp.example-1.com",
"prefer": true
},
{
"name": "ntp-server-2",
"alias": [
"secondary"
],
"address": "ntp.example-2.com"
},
{
"name": "ntp-server-3",
"alias": [
"secondary"
],
"address": "ntp.example-3.com"
}
]
}
}
]
}
}
]
}
}
the following shows the network-level ntp configuration using
"template-ntp" and "template-ntp2" that may be sent to a SDN
controller:
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{
"example-network-systime:network-device": [
{
"@": {
"ietf-template:stmt-extend": "template-ntp"
},
"device-id": "ne-0"
},
{
"@": {
"ietf-template:stmt-extend": "template-ntp"
},
"device-id": "ne-1"
},
{
"@": {
"ietf-template:stmt-extend": "template-ntp2"
},
"device-id": "ne-2"
},
{
"@": {
"ietf-template:stmt-extend": "template-ntp2"
},
"device-id": "ne-3"
}
]
}
And it renders the following expanded configuration:
{
"example-network-systime:network-device": [
{
"device-id": "ne-0",
"ntp": {
"enabled": "true",
"server": [
{
"name": "ntp-server-1",
"alias": [
"primary"
],
"address": "ntp.example-1.com"
},
{
"name": "ntp-server-2",
"alias": [
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"secondary"
],
"address": "ntp.example-2.com"
}
]
}
},
{
"device-id": "ne-1",
"ntp": {
"enabled": "true",
"server": [
{
"name": "ntp-server-1",
"alias": [
"primary"
],
"address": "ntp.example-1.com"
},
{
"name": "ntp-server-2",
"alias": [
"secondary"
],
"address": "ntp.example-2.com"
}
]
}
},
{
"device-id": "ne-2",
"ntp": {
"enabled": "true",
"server": [
{
"name": "ntp-server-1",
"alias": [
"primary"
],
"address": "ntp.example-1.com"
},
{
"name": "ntp-server-2",
"alias": [
"secondary"
],
"address": "ntp.example-2.com"
},
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{
"name": "ntp-server-3",
"alias": [
"secondary"
],
"address": "ntp.example-3.com"
}
]
}
},
{
"device-id": "ne-3",
"ntp": {
"enabled": "true",
"server": [
{
"name": "ntp-server-1",
"alias": [
"primary"
],
"address": "ntp.example-1.com"
},
{
"name": "ntp-server-2",
"alias": [
"secondary"
],
"address": "ntp.example-2.com"
},
{
"name": "ntp-server-3",
"alias": [
"secondary"
],
"address": "ntp.example-3.com"
}
]
}
}
]
}
B.3. Overriding Templates
The client may override the template created in Appendix B.1 to
specify the NTP server named "ntp-server-2" as the perferred one for
device "ne-4":
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{
"example-network-systime:network-device": [
{
"@": {
"ietf-template:stmt-extend": "template-ntp"
},
"device-id": "ne-4",
"server": [
{
"name": "ntp-server-1",
"alias": [
"primary",
"secondary"
],
"@alias": [
{
"ietf-template:operation-tag": "delete"
}
],
"address": "ntp.example-1.com"
},
{
"@": {
"ietf-template:operation-tag": "position-first"
},
"name": "ntp-server-2",
"alias": [
"primary",
"secondary"
],
"@alias": [
null,
{
"ietf-template:operation-tag": "delete"
}
],
"address": "ntp.example-2.com"
}
]
}
]
}
It is equivalent to the configuration as follows:
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{
"example-network-systime:network-device": [
{
"device-id": "ne-4",
"ntp": {
"enabled": "true",
"server": [
{
"name": "ntp-server-2",
"alias": [
"primary"
],
"address": "ntp.example-2.com"
},
{
"name": "ntp-server-1",
"alias": [
"secondary"
],
"address": "ntp.example-1.com"
}
]
}
}
]
}
Acknowledgments
TODO acknowledge.
Authors' Addresses
Qiufang Ma
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu
210012
China
Email: maqiufang1@huawei.com
Qin Wu
Huawei
101 Software Avenue, Yuhua District
Jiangsu
210012
China
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Email: bill.wu@huawei.com
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