YANG Metadata Annotation for Immutable Flag
draft-ietf-netmod-immutable-flag-02
| Document | Type | Active Internet-Draft (netmod WG) | |
|---|---|---|---|
| Authors | Qiufang Ma , Qin Wu , Balázs Lengyel , Hongwei Li | ||
| Last updated | 2024-09-27 | ||
| Replaces | draft-ma-netmod-immutable-flag | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Yang Validation | 0 errors, 0 warnings | ||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-netmod-immutable-flag-02
netmod Q. Ma, Ed.
Internet-Draft Q. Wu
Updates: 6241, 8040, 8526 (if approved) Huawei
Intended status: Standards Track B. Lengyel, Ed.
Expires: 31 March 2025 Ericsson
H. Li
HPE
27 September 2024
YANG Metadata Annotation for Immutable Flag
draft-ietf-netmod-immutable-flag-02
Abstract
This document defines a way to formally document an existing
behavior, implemented by servers in production, on the immutability
of some system-provided nodes, using a YANG metadata annotation
called "immutable" to flag which nodes are immutable.
Clients may use "immutable" annotations provided by the server, to
know beforehand why certain otherwise valid configuration requests
will cause the server to return an error.
The immutable flag is descriptive, documenting an existing behavior,
not proscriptive, dictating server behaviors.
This document updates [RFC6241], [RFC8040], and [RFC8526].
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/netmod-wg/immutable-flag.
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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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 31 March 2025.
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. Updates to RFC 6241 and RFC 8526 . . . . . . . . . . . . 4
1.2. Updates to RFC 8040 . . . . . . . . . . . . . . . . . . . 4
1.3. Editorial Note (To be removed by RFC Editor) . . . . . . 4
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 5
3. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 6
4. "Immutable" Metadata Annotation . . . . . . . . . . . . . . . 6
4.1. Definition . . . . . . . . . . . . . . . . . . . . . . . 6
4.2. "with-immutable" Parameter . . . . . . . . . . . . . . . 6
4.2.1. NETCONF Extensions to Support "with-immutable" . . . 7
4.2.2. RESTCONF Extensions to Support "with-immutable" . . . 7
5. Use of Immutable Flag for Different Statements . . . . . . . 7
5.1. The "leaf" Statement . . . . . . . . . . . . . . . . . . 8
5.2. The "leaf-list" Statement . . . . . . . . . . . . . . . . 8
5.3. The "container" Statement . . . . . . . . . . . . . . . . 8
5.4. The "list" Statement . . . . . . . . . . . . . . . . . . 8
5.5. The "anydata" Statement . . . . . . . . . . . . . . . . . 8
5.6. The "anyxml" Statement . . . . . . . . . . . . . . . . . 8
6. Immutability of Interior Nodes . . . . . . . . . . . . . . . 9
7. System Configuration Datastore Interactions . . . . . . . . . 10
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8. NACM Interactions . . . . . . . . . . . . . . . . . . . . . . 10
9. YANG Module . . . . . . . . . . . . . . . . . . . . . . . . . 10
10. Security Considerations . . . . . . . . . . . . . . . . . . . 13
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
11.1. The "IETF XML" Registry . . . . . . . . . . . . . . . . 13
11.2. The "YANG Module Names" Registry . . . . . . . . . . . . 14
11.3. RESTCONF Capability URN Registry . . . . . . . . . . . . 14
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
12.1. Normative References . . . . . . . . . . . . . . . . . . 14
12.2. Informative References . . . . . . . . . . . . . . . . . 15
Appendix A. Detailed Use Cases . . . . . . . . . . . . . . . . . 16
A.1. UC1 - Modeling of server capabilities . . . . . . . . . . 16
A.2. UC2 - Hardware based auto-configuration - Interface
Example . . . . . . . . . . . . . . . . . . . . . . . . . 17
A.3. UC3 - Predefined Administrator Roles . . . . . . . . . . 18
A.4. UC4 - Declaring immutable system configuration from an
LNE's perspective . . . . . . . . . . . . . . . . . . . . 18
Appendix B. Existing Implementations . . . . . . . . . . . . . . 18
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
This document defines a YANG metadata annotation [RFC7952] to
formally document an existing model handling behavior that has been
used by multiple standard organizations and vendors. It is the aim
to create one single standard solution for documenting non-modifiable
system data declared as configuration, instead of the multiple
existing vendor and organization specific solutions.
YANG [RFC7950] is a data modeling language used to model both state
and configuration data, based on the "config" statement. However,
there exists some system configuration data that cannot be modified
by the client (it is immutable), but still needs to be declared as
"config true" to:
* allow configuration of data nodes under immutable lists or
containers;
* place "when", "must" and "leafref" constraints between
configuration and immutable nodes;
* ensure the existence of specific list entries that are provided
and needed by the system, while additional list entries can be
created, modified or deleted.
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If the server always rejects a client's attempt to override some
system-provided data because it internally thinks immutable, it
should document it towards the clients in a machine-readable way
rather than writing as plain text in the "description" statement.
This document defines a way to formally document the existing
behavior, implemented by servers in production, on the immutability
of some system-provided nodes, using a YANG metadata annotation
[RFC7952] called "immutable" to flag which nodes are immutable.
This document does not apply to the server not having any immutable
system configuration. While in some cases immutability may be
needed, it also has disadvantages, therefore it SHOULD be avoided
wherever possible.
The following is a list of already implemented and potential use
cases:
* UC1 Modeling of server capabilities
* UC2 Hardware based auto-configuration
* UC3 Predefined administrator roles
* UC4 Declaring immutable system configuration from an LNE's
perspective
Appendix A describes the use cases in detail.
1.1. Updates to RFC 6241 and RFC 8526
This document updates [RFC6241] and [RFC8526]. The NETCONF <get> and
<get-config> operations defined in [RFC6241], and <get-data>
operation defined in [RFC8526] are augmented with an additional input
parameter named "with-immutable", as specified in Section 4.2.1.
1.2. Updates to RFC 8040
This document updates Sections 4.8 and 9.1.1 of [RFC8040] to add an
additional input parameter named "with-immutable", as specified in
Section 4.2.2.
1.3. Editorial Note (To be removed by RFC Editor)
Note to the RFC Editor: This section is to be removed prior to
publication.
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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
* 2024-06-04 --> the actual date of the publication of this document
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 document uses the following definition in [RFC6241]:
* configuration data
The document uses the following definition in [RFC7950]:
* data node
* leaf
* leaf-list
* container
* list
* anydata
* anyxml
* interior node
* data tree
The document uses the following definition in [RFC8341]:
* access operation
This document defines the following term:
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immutable flag: A read-only state value the server provides to
describe immutability of the configuration, which is conveyed via
a YANG metadata annotation called "immutable" with a boolean
value.
3. Applicability
While immutable flag applies to all configuration nodes, its value
"true" can only be used for system configuration.
The immutable flag is also visible in read-only datastores like
<system> (if implemented, see [I-D.ietf-netmod-system-config]),
<intended> and <operational> when a "with-immutable" parameter is
carried (Section 4.2), however this only serves as descriptive
information about the instance node itself, but has no effect on the
handling of the read-only datastore.
An instance has the same immutability if it appears in different
writable datastores, the immutability of data object is also protocol
and user independent. The immutability and configured value of an
existing node MUST only change via software upgrade, hardware
resources change, or license change.
4. "Immutable" Metadata Annotation
4.1. Definition
The immutable flag which is defined as the metadata annotation takes
a boolean value, and it is returned as requested by the client using
a "with-immutable" parameter (Section 4.2). If the "immutable"
metadata annotation for a configuration node is not specified, the
default "immutable" value is the same as the value of its parent node
in the data tree (Section 6). The immutable metadata annotation
value for a top-level instance node is "false" if not specified.
Note that "immutable" metadata annotations are used to annotate data
node instances. A list may have multiple instances in the data tree,
servers may annotate some of the instances as immutable, while others
as mutable.
Servers MUST ignore any immutable annotations sent from the client.
4.2. "with-immutable" Parameter
This section specifies the NETCONF [RFC6241] and RESTCONF [RFC8040]
protocol extensions to support the "with-immutable" parameter. The
"immutable" metadata annotations are not returned in a response
unless explicitly requested by the client using this parameter.
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4.2.1. NETCONF Extensions to Support "with-immutable"
This doument updates [RFC6241] to augment the <get-config> and <get>
operations with an additional parameter named "with-immutable". The
<get-data> operation defined in [RFC8526] is also updated to support
this parameter. If present, this parameter requests that the server
includes the "immutable" metadata annotations in its response.
Figure 1 provides the tree structure [RFC8340] of augmentations to
NETCONF operations, as defined in the "ietf-immutable" module
(Section 9).
module: ietf-immutable
augment /ncds:get-data/ncds:input:
+---w with-immutable? empty {immutable}?
augment /nc:get-config/nc:input:
+---w with-immutable? empty {immutable}?
augment /nc:get/nc:input:
+---w with-immutable? empty {immutable}?
Figure 1: Augmentations to NETCONF Operations
Servers' support for accepting "with-immutable" parameter and
returning "immutable" annotations is identified with the feature
"immutable".
4.2.2. RESTCONF Extensions to Support "with-immutable"
This document extends Sections 4.8 and 9.1.1 of [RFC8040] to add a
query parameter named "with-immutable" to the GET operation. If
present, this parameter requests that the server includes the
"immutable" metadata annotations in its response. This parameter is
only allowed with no values carried. If it has any unexpected value,
then a "404 Bad Request" status-line is returned.
To enable a RESTCONF client to discover if the "with-immutable" query
parameter is supported by the server, the following capability URI is
defined:
urn:ietf:params:restconf:capability:with-immutable:1.0
5. Use of Immutable Flag for Different Statements
This section defines what the immutable flag means to the client for
each instance of YANG data node statement.
Throughout this section, the word "change" refers to create, update,
and delete.
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5.1. The "leaf" Statement
When a leaf node instance is immutable, its value cannot change.
5.2. The "leaf-list" Statement
When a leaf-list node instance is immutable, its value cannot change.
The immutable annotation attached to the individual leaf-list
instance provides immutability with respect to the instance itself.
If a leaf-list inherits immutability from an ancestor (e.g.,
container), it is identical to each individual leaf-list entry being
annotated without any bearing on the entry ordering and addition of
new entries.
5.3. The "container" Statement
When a container node instance is immutable, it cannot change, unless
the immutability of its descendant node is toggled.
By default, as with all interior nodes, immutability is recursively
applied to descendants (Section 6).
5.4. The "list" Statement
When a list node instance is immutable, it cannot change, unless the
immutability of its descendant node is toggled.
By default, as with all interior nodes, immutability is recursively
applied to descendants (Section 6).
The immutable annotation attached to the individual list instance
provides immutability with respect to the instance itself. If a list
inherits immutability from an ancestor (e.g., container), it is
identical to each individual list entry being annotated without any
bearing on the entry ordering and addition of new entries.
5.5. The "anydata" Statement
When an anydata node instance is immutable, it cannot change.
Additionally, as with all interior nodes, immutability is recursively
applied to descendants (Section 6).
5.6. The "anyxml" Statement
When an "anyxml" node instance is immutable, it cannot change.
Additionally, as with all interior nodes, immutability is recursively
applied to descendants (Section 6).
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6. Immutability of Interior Nodes
Immutability is a conceptual operational state value that is
recursively applied to descendants, which may reset the immutability
state as needed, thereby affecting their descendants. There is no
limit to the number of times the immutability state may change in a
data tree.
If the "immutable" metadata annotation for returned child node is
omitted, it has the same immutability as its parent node. The
immutability of top hierarchy of returned nodes is false by default.
Servers may suppress the annotation if it is inherited from its
parent node or uses the default value as the top-level node, but are
not precluded from returning the annotation on every single element.
For example, the following XML snippets shows application
configuration a server might return:
<applications im:immutable="false">
<application im:immutable="true">
<name>ssh</name>
<protocol>tcp</protocol>
<port-number im:immutable="false">22</port-number>
</application>
<application im:immutable="false">
<name>my-ssh</name>
<protocol>tcp</protocol>
<port-number>10022</port-number>
</application>
</applications>
In the example, there are two "application" list entries inside
"applications" container node. The "immutable" metadata attribute
for applications container instance is "false", which is also its
default value as the top-level element, and thus can be omitted. The
"application" list entry named "ssh" is immutable with the
immutability of its child node "port-number" being explicitly
toggled. The other child nodes inside "ssh" application instance
inherit immutability from their parent node thus are also immutable.
The "immutable" metadata attribute for application list entry named
"my-ssh" is "false", which is also the same value as its parent node,
and thus can be omitted.
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7. System Configuration Datastore Interactions
Immutable configuration can only be created, updated and deleted by
the server, and it is present in <system>, if implemented. That
said, the existence of immutable configuration is independent of
whether <system> is implemented or not. Not all system configuration
data is immutable. Immutable configuration does not appear in
<running> unless it is explicitly configured.
A client may create/delete immutable nodes with same values as found
in <system> (if implemented) in read-write configuration datastore
(e.g., <candidate>, <running>), which merely mean making immutable
nodes visible/invisible in the datastore.
8. NACM Interactions
The server rejects an operation request due to immutability when it
tries to perform the operation on the request data. It happens after
any access control processing, if the Network Configuration Access
Control Model (NACM) [RFC8341] is implemented on a server. For
example, if an operation requests to override an immutable
configuration data, but the server checks the user is not authorized
to perform the requested access operation on the request data, the
request is rejected with an "access-denied" error.
9. YANG Module
This module imports definitions from [RFC6241] and [RFC8526].
<CODE BEGINS> file "ietf-immutable@2024-06-04.yang"
module ietf-immutable {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-immutable";
prefix im;
import ietf-yang-metadata {
prefix md;
}
import ietf-netconf {
prefix nc;
reference
"RFC 6241: Network Configuration Protocol (NETCONF)";
}
import ietf-netconf-nmda {
prefix ncds;
reference
"RFC 8526: NETCONF Extensions to Support the Network
Management Datastore Architecture";
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}
organization
"IETF Network Modeling (NETMOD) Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/netmod/>
WG List: <mailto:netmod@ietf.org>
Author: Qiufang Ma
<mailto:maqiufang1@huawei.com>
Author: Qin Wu
<mailto:bill.wu@huawei.com>
Author: Balazs Lengyel
<mailto:balazs.lengyel@ericsson.com>
Author: Hongwei Li
<mailto:flycoolman@gmail.com>";
description
"This module defines a metadata annotation called 'immutable'
to allow the server to formally document existing behavior on
the mutability of some system configuration. Clients may use
'immutable' metadata annotation provided by the server to know
beforehand why certain otherwise valid configuration requests
will cause the server to return an error.
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 HHHH
(https://www.rfc-editor.org/info/rfcHHHH); 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 2024-06-04 {
description
"Initial revision.";
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// RFC Ed.: replace XXXX and remove this comment
reference
"RFC XXXX: YANG Metadata Annotation for Immutable Flag";
}
md:annotation immutable {
type boolean;
description
"The 'immutable' metadata annotation indicates the
immutability of an instantiated data node. It takes as a
value 'true' or 'false'. If the 'immutable' metadata
annotation is not specified, the default value is the
same as the value of its parent node in the data tree. The
default value for a top-level instance node is false if not
specified.";
}
feature immutable {
description
"Indicates that the server supports the 'immutable' metadata
annotation.";
}
grouping with-immutable-grouping {
description
"Grouping for the with-immutable parameter that augments the
RPC operations.";
leaf with-immutable {
type empty;
description
"If this parameter is present, the server returns the
'immutable' annotation for configuration that it
internally thinks immutable.";
}
}
augment "/ncds:get-data/ncds:input" {
if-feature "immutable";
description
"Allows the server to include 'immutable' metadata
annotations in its response to get-data operation.";
uses with-immutable-grouping;
}
augment "/nc:get-config/nc:input" {
if-feature "immutable";
description
"Allows the server to include 'immutable' metadata
annotations in its response to get-config operation.";
uses with-immutable-grouping;
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}
augment "/nc:get/nc:input" {
if-feature "immutable";
description
"Allows the server to include 'immutable' metadata
annotations in its response to get operation.";
uses with-immutable-grouping;
}
}
<CODE ENDS>
10. Security Considerations
This section is modeled after the template described in Section 3.7
of [I-D.ietf-netmod-rfc8407bis].
The "ietf-immutable" YANG module defines a data model that is
designed to be accessed via YANG-based management protocols, such as
NETCONF [RFC6241] or RESTCONF [RFC8040]. These protocols have to use
a secure transport layer (e.g., SSH [RFC4252], TLS [RFC8446], and
QUIC [RFC9000]) and have to use mutual authentication.
The Network Configuration Access Control Model (NACM) [RFC8341]
provides the means to restrict access for particular NETCONF or
RESTCONF users to a preconfigured subset of all available NETCONF or
RESTCONF protocol operations and content.
The YANG module specified in this document defines a metadata
annotation, it also extends the RPC operations of the NETCONF
protocol in [RFC6241] and [RFC8526].
The security considerations for the Defining and Using Metadata with
YANG (see Section 9 of [RFC7952]) apply to the metadata annotation
defined in this document.
The security considerations for the NETCONF protocol operations (see
Section 9 of [RFC6241] and Section 6 of [RFC8526]) still apply to the
operations extended in this document.
11. IANA Considerations
11.1. The "IETF XML" Registry
This document registers one XML namespace URN in the 'IETF XML
registry', following the format defined in [RFC3688].
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URI: urn:ietf:params:xml:ns:yang:ietf-immutable
Registrant Contact: The IESG.
XML: N/A, the requested URIs are XML namespaces.
11.2. The "YANG Module Names" Registry
This document registers one module name in the 'YANG Module Names'
registry, defined in [RFC6020].
name: ietf-immutable
prefix: im
namespace: urn:ietf:params:xml:ns:yang:ietf-immutable
RFC: XXXX
11.3. RESTCONF Capability URN Registry
This document defines the following capability identifier URNs in the
"RESTCONF Capability URNs" registry defined in [RFC8040]:
Index Capability Identifier
----------------------------------------------------------------------
:with-immutable urn:ietf:params:restconf:capability:with-immutable:1.0
12. References
12.1. 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>.
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[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>.
[RFC7952] Lhotka, L., "Defining and Using Metadata with YANG",
RFC 7952, DOI 10.17487/RFC7952, August 2016,
<https://www.rfc-editor.org/rfc/rfc7952>.
[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>.
[RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration
Access Control Model", STD 91, RFC 8341,
DOI 10.17487/RFC8341, March 2018,
<https://www.rfc-editor.org/rfc/rfc8341>.
[RFC8526] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
and R. Wilton, "NETCONF Extensions to Support the Network
Management Datastore Architecture", RFC 8526,
DOI 10.17487/RFC8526, March 2019,
<https://www.rfc-editor.org/rfc/rfc8526>.
12.2. Informative References
[I-D.ietf-netmod-rfc8407bis]
Bierman, A., Boucadair, M., and Q. Wu, "Guidelines for
Authors and Reviewers of Documents Containing YANG Data
Models", Work in Progress, Internet-Draft, draft-ietf-
netmod-rfc8407bis-16, 20 September 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-netmod-
rfc8407bis-16>.
[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-08, 18 June 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-netmod-
system-config-08>.
[RFC4252] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252,
January 2006, <https://www.rfc-editor.org/rfc/rfc4252>.
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[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>.
[RFC8343] Bjorklund, M., "A YANG Data Model for Interface
Management", RFC 8343, DOI 10.17487/RFC8343, March 2018,
<https://www.rfc-editor.org/rfc/rfc8343>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/rfc/rfc8446>.
[RFC8530] Berger, L., Hopps, C., Lindem, A., Bogdanovic, D., and X.
Liu, "YANG Model for Logical Network Elements", RFC 8530,
DOI 10.17487/RFC8530, March 2019,
<https://www.rfc-editor.org/rfc/rfc8530>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/rfc/rfc9000>.
[TR-531] ONF, "UML to YANG Mapping Guidelines", February 2023,
<https://wiki.opennetworking.org/download/
attachments/376340494/Draft_TR-531_UML-YANG_Mapping_Gdls_v
1.1.03.docx?version=5&modificationDate=1675432243513&api=v
2>.
[TS28.623] 3GPP, "Telecommunication management; Generic Network
Resource Model (NRM) Integration Reference Point (IRP);
Solution Set (SS) definitions",
<https://www.3gpp.org/ftp/Specs/
archive/28_series/28.623/28623-i02.zip>.
[TS32.156] 3GPP, "Telecommunication management; Fixed Mobile
Convergence (FMC) Model repertoire",
<https://www.3gpp.org/ftp/Specs/
archive/32_series/32.156/32156-h10.zip>.
Appendix A. Detailed Use Cases
A.1. UC1 - Modeling of server capabilities
System capabilities might be represented as immutable configuration.
Configurable data nodes might need constraints specified as "when",
"must" or "path" statements to ensure that configuration is set
according to the system's capabilities. For example,
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* A timer can support the values 1,5,8 seconds. This is defined in
the leaf-list 'supported-timer-values'.
* When the configurable 'interface-timer' leaf is set, it should be
ensured that one of the supported values is used. The natural
solution would be to make the 'interface-timer' a leaf-ref
pointing at the 'supported-timer-values'.
However, this is not possible as 'supported-timer-values' must be
read-only thus config=false while 'interface-timer' must be writable
thus config=true. According to the rules of YANG it is not allowed
to put a constraint between config true and false data nodes.
The solution is that the supported-timer-values data node in the YANG
Model shall be defined as "config true" and shall also be marked with
the "immutable" annotation making it unchangeable. After this the
'interface-timer' shall be defined as a leaf-ref pointing at the
'supported-timer-values'.
A.2. UC2 - Hardware based auto-configuration - Interface Example
[RFC8343] defines a YANG data model for the management of network
interfaces. When a system-controlled interface is physically
present, the system creates an interface entry with valid name and
type values in <system> (if exists, see
[I-D.ietf-netmod-system-config]).
The system-generated type value is dependent on and represents the
hardware present, and as a consequence cannot be changed by the
client. If a client tries to set the type of an interface to a value
that can never be used by the system, the request will be rejected by
the server. The data is modeled as "config true" and thus should be
annotated as immutable.
Seemingly an alternative would be to model the list and these leaves
as "config false", but that does not work because:
* The list cannot be marked as "config false", because it needs to
contain configurable child nodes, e.g., ip-address or enabled;
* The key leaf (name) cannot be marked as "config false" as the list
itself is config true;
* The type cannot be marked "config false", because we MAY need to
reference the type to make different configuration nodes
conditionally available.
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A.3. UC3 - Predefined Administrator Roles
User and group management is fundamental for setting up access
control rules (see Section 2.5 of [RFC8341]).
A device may provide a predefined user account (e.g., a system
administrator that is always available and has full privileges) for
initial system set up and management of other users/groups. It is
possible that a new user/group can be defined granted particular
privileges, but the predefined administrator account and its granted
access are immutable.
A.4. UC4 - Declaring immutable system configuration from an LNE's
perspective
An logical network element (LNE) is an independently managed virtual
network device made up of resources allocated to it from its host or
parent network device [RFC8530]. The host device may allocate some
resources to an LNE, which from an LNE's perspective is provided by
the system and may not be modifiable.
For example, a host may allocate an interface to an LNE with a valid
MTU value as its management interface, so that the allocated
interface should then be accessible as the LNE-specific instance of
the interface model. The assigned MTU value is system-created and
immutable from the context of the LNE.
Appendix B. Existing Implementations
Note to the RFC Editor: Please remove this section prior to
publication.
There are already a number of full or partial implementations of
immutability:
* 3GPP TS 32.156 [TS32.156] and 28.623 [TS28.623]: Requirements and
a partial solution
* ITU-T using ONF TR-531 [TR-531] concept on information model level
but no YANG representation.
* Ericsson: requirements and solution
* YumaPro: requirements and solution
* Nokia: partial requirements and solution
* Huawei: partial requirements and solution
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* Cisco using the concept at least in some YANG modules
* Junos OS provides a hidden and immutable configuration group
called junos-defaults
Acknowledgments
Thanks to Kent Watsen, Jan Lindblad, Jason Sterne, Robert Wilton,
Andy Bierman, Juergen Schoenwaelder, Reshad Rahman, Anthony Somerset,
Lou Berger, Joe Clarke, and Scott Mansfield for reviewing, and
providing important inputs to this document.
Authors' Addresses
Qiufang Ma (editor)
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu
210012
China
Email: maqiufang1@huawei.com
Qin Wu
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu
210012
China
Email: bill.wu@huawei.com
Balazs Lengyel (editor)
Ericsson
Email: balazs.lengyel@ericsson.com
Hongwei Li
HPE
Email: flycoolman@gmail.com
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