YANG Metadata Annotation for Immutable Flag
draft-ietf-netmod-immutable-flag-00
| Document | Type | Active Internet-Draft (netmod WG) | |
|---|---|---|---|
| Authors | Qiufang Ma , Qin Wu , Balázs Lengyel , Hongwei Li | ||
| Last updated | 2024-03-18 | ||
| 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-00
NETMOD Q. Ma
Internet-Draft Q. Wu
Intended status: Standards Track Huawei
Expires: 17 September 2024 B. Lengyel
Ericsson
H. Li
HPE
16 March 2024
YANG Metadata Annotation for Immutable Flag
draft-ietf-netmod-immutable-flag-00
Abstract
This document defines a way to formally document existing behavior,
implemented by servers in production, on the immutability of some
system configuration 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 existing behavior, not
proscriptive, dictating server behavior.
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 17 September 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
Ma, et al. Expires 17 September 2024 [Page 1]
Internet-Draft Immutable Flag March 2024
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. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Applicability . . . . . . . . . . . . . . . . . . . . . . 5
2. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 5
3. "Immutable" Metadata Annotation . . . . . . . . . . . . . . . 5
3.1. Definition . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. "with-immutable" Parameter . . . . . . . . . . . . . . . 6
4. Use of "immutable" Flag for Different Statements . . . . . . 6
4.1. The "leaf" Statement . . . . . . . . . . . . . . . . . . 7
4.2. The "leaf-list" Statement . . . . . . . . . . . . . . . . 7
4.3. The "container" Statement . . . . . . . . . . . . . . . . 7
4.4. The "list" Statement . . . . . . . . . . . . . . . . . . 7
4.5. The "anydata" Statement . . . . . . . . . . . . . . . . . 7
4.6. The "anyxml" Statement . . . . . . . . . . . . . . . . . 7
5. Immutability of Interior Nodes . . . . . . . . . . . . . . . 8
6. Interaction between Immutable Flag and <system> . . . . . . . 8
7. Interaction between Immutable Flag and NACM . . . . . . . . . 9
8. YANG Module . . . . . . . . . . . . . . . . . . . . . . . . . 9
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
9.1. The "IETF XML" Registry . . . . . . . . . . . . . . . . . 12
9.2. The "YANG Module Names" Registry . . . . . . . . . . . . 12
10. Security Considerations . . . . . . . . . . . . . . . . . . . 12
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 12
References . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Normative References . . . . . . . . . . . . . . . . . . . . . 12
Informative References . . . . . . . . . . . . . . . . . . . . 13
Appendix A. Detailed Use Cases . . . . . . . . . . . . . . . . . 14
A.1. UC1 - Modeling of server capabilities . . . . . . . . . . 14
A.2. UC2 - HW based auto-configuration - Interface Example . . 15
A.3. UC3 - Predefined Administrator Roles . . . . . . . . . . 15
A.4. UC4 - Declaring immutable system configuration from an
LNE's perspective . . . . . . . . . . . . . . . . . . . . 16
Appendix B. Existing implementations . . . . . . . . . . . . . . 16
Appendix C. Changes between revisions . . . . . . . . . . . . . 16
Appendix D. Open Issues tracking . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
Ma, et al. Expires 17 September 2024 [Page 2]
Internet-Draft Immutable Flag March 2024
1. Introduction
This document defines a way to formally document as a YANG metadata
annotation 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. See Appendix B for
existing implementations.
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 data 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;
If the server always rejects the client attempts to override
immutable system configuration [I-D.ietf-netmod-system-config]
because it internally thinks it immutable, it should document this
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 existing behavior,
implemented by servers in production, on the immutability of some
system configuration 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 HW based auto-configuration
Ma, et al. Expires 17 September 2024 [Page 3]
Internet-Draft Immutable Flag March 2024
UC3 Predefined administrator roles
UC4 Declaring immutable system configuration from an LNE's
perspective
Appendix A describes the use cases in detail.
1.1. Terminology
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 following terms are defined in [RFC6241]:
* configuration data
The following terms are defined in [RFC7950]:
* data node
* leaf
* leaf-list
* container
* list
* anydata
* anyxml
* interior node
* data tree
The following terms are defined in [RFC8341]:
* access operation
* write access
The following terms are defined in this document:
immutable flag: A read-only state value the server provides to
Ma, et al. Expires 17 September 2024 [Page 4]
Internet-Draft Immutable Flag March 2024
describe system data it considers immutable. The immutability of
data nodes is conveyed via a YANG metadata annotation called
"immutable".
1.2. Applicability
This document focuses on the configuration which can only be created,
updated and deleted by the server.
The immutable annotation information is also visible in read-only
datastores like <system> (if exists), <intended> and <operational>
when a "with-immutable" parameter is carried (see Section 3.2),
however this only serves as descriptive information about the
instance node itself, but has no effect on the handling of the read-
only datastore.
Configuration data must have the same immutability in different
writable datastores. The immutability of data nodes is protocol and
user independent. The immutability and configured value of an
existing node must only change by software upgrade or hardware
resource/license change.
2. Solution Overview
Immutable configuration can only be created by the system regardless
of the implementation of <system> [I-D.ietf-netmod-system-config].
Immutable configuration is present in <system> (if implements). It
may be updated or deleted depending on factors like software upgrade
or hardware resources/license change. Immutable configuration does
not appear in <running> unless it is copied explicitly or
automatically (e.g., by "resolve-system" parameter)
[I-D.ietf-netmod-system-config].
A client may create/delete immutable nodes with same values as found
in <system> (if exists) in read-write configuration datastore (e.g.,
<running>), which merely mean making immutable nodes visible/
invisible in read-write configuration datastore (e.g., <running>).
The "immutable" flag is intended to be descriptive.
3. "Immutable" Metadata Annotation
Ma, et al. Expires 17 September 2024 [Page 5]
Internet-Draft Immutable Flag March 2024
3.1. Definition
The "immutable" metadata annotation takes as an value which is a
boolean type, it is not returned unless a client explicitly requests
through a "with-immutable" parameter (see Section 3.2). If the
"immutable" metadata annotation for data node instances is not
specified, the default "immutable" value is the same as the
immutability of its parent node in the data tree. The immutable
metadata annotation value for a top-level instance node is false if
not specified.
Note that "immutable" metadata annotation is used to annotate data
node instances. A list may have multiple entries/instances in the
data tree, "immutable" can annotate some of the instances as read-
only, while others are read-write.
3.2. "with-immutable" Parameter
The YANG model defined in this document (see Section 8) augments the
<get-config>, <get> operation defined in RFC 6241, and the <get-data>
operation defined in RFC 8526 with a new parameter named "with-
immutable". When this parameter is present, it requests that the
server includes "immutable" metadata annotations in its response.
This parameter may be used for read-only configuration datastores,
e.g., <system> (if exists), <intended> and <operational>, but the
"immutable" metadata annotation returned indicates the immutability
towards read-write configuration datastores, e.g., <startup>,
<candidate> and <running>. If the "immutable" metadata annotation
for returned child nodes are omitted, it has the same immutability as
its parent node. The immutability of top hierarchy of returned nodes
is false by default.
Note that "immutable" metadata annotation is not included in a
response unless a client explicitly requests them with a "with-
immutable" parameter.
4. 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.
Ma, et al. Expires 17 September 2024 [Page 6]
Internet-Draft Immutable Flag March 2024
4.1. The "leaf" Statement
When a leaf node instance is immutable, its value cannot change.
4.2. The "leaf-list" Statement
When a leaf-list node instance is immutable, its value cannot change.
When the "immutable" YANG metadata annotation is used on all existing
leaf-list instances, or if a leaf-list inherits immutability from an
ancestor, it means that the leaf-list as a whole cannot change:
entries cannot be added, removed, or reordered, in case the leaf-list
is "ordered-by user".
4.3. 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 (see Section 5).
4.4. The "list" Statement
When a list node instance is immutable, it cannot change, unless the
immutability of its descendant node is toggled, per the description
elsewhere in this section.
By default, as with all interior nodes, immutability is recursively
applied to descendants (see Section 5). This statement is applicable
only to the "immutable" YANG extension, as the "list" node does not
itself appear in data trees.
4.5. 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 (see Section 5).
4.6. 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 (see Section 5).
Ma, et al. Expires 17 September 2024 [Page 7]
Internet-Draft Immutable Flag March 2024
5. 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.
For example, given the following application configuration XML
snippets:
<application im:immutable="true">
<name>predefined-ftp</name>
<protocol>ftp</protocol>
<port-number im:immutable="false">69</port-number>
</application>
The list entry named "predefined-ftp" is immutable="true", but its
child node "port-number" has the immutable="false" (thus the client
can override this value). The other child node (e.g., "protocol")
not specifying its immutability explicitly inherits immutability from
its parent node thus is also immutable="true".
6. Interaction between Immutable Flag and <system>
The system datastore is defined to hold system configuration provided
by the device itself and make system configuration visible to clients
in order for being referenced or configurable prior to present in
<operational>. However, the device may allow some system-initialized
node to be overridden, while others may not. System configuration
exists regardless of whether <system> is implemented.
This document defines a way to allow a server annotate instances of
non-modifiable system configuration with metadata when system
configuration is retrieved. A client aware of the "immutable"
annotation can explicitly ask the server to return it via the "with-
immutable" parameter in the request, thus is able to avoid making
unnecessary modification attempts to immutable configuration. Legacy
clients unaware of the "immutable" annotation don't see any changes
and encounter an error as always.
Ma, et al. Expires 17 September 2024 [Page 8]
Internet-Draft Immutable Flag March 2024
7. Interaction between Immutable Flag and NACM
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.
8. YANG Module
<CODE BEGINS>
file="ietf-immutable@2023-10-16.yang"
//RFC Ed.: replace XXXX with RFC number and remove this note
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";
}
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>
Ma, et al. Expires 17 September 2024 [Page 9]
Internet-Draft Immutable Flag March 2024
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) 2023 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 2023-10-16 {
description
"Initial revision.";
// 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.
Ma, et al. Expires 17 September 2024 [Page 10]
Internet-Draft Immutable Flag March 2024
The 'immutable' metadata annotation takes as a value 'true'
or 'false'. If the 'immutable' metadata annotation for data
node instances 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.";
}
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 will return the
'immutable' annotation for configuration that it
internally thinks it immutable. When present, this
parameter allows the server to formally document existing
behavior on the mutability of some configuration nodes.";
}
}
augment "/ncds:get-data/ncds:input" {
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" {
description
"Allows the server to include 'immutable' metadata
annotations in its response to get-config operation.";
uses with-immutable-grouping;
}
augment "/nc:get/nc:input" {
description
"Allows the server to include 'immutable' metadata
annotations in its response to get operation.";
uses with-immutable-grouping;
}
}
<CODE ENDS>
9. IANA Considerations
Ma, et al. Expires 17 September 2024 [Page 11]
Internet-Draft Immutable Flag March 2024
9.1. The "IETF XML" Registry
This document registers one XML namespace URN in the 'IETF XML
registry', following the format defined in [RFC3688].
URI: urn:ietf:params:xml:ns:yang:ietf-immutable
Registrant Contact: The IESG.
XML: N/A, the requested URIs are XML namespaces.
9.2. 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
// RFC Ed.: replace XXXX and remove this comment
10. Security Considerations
The YANG module specified in this document defines a YANG extension
and a metadata Annotation. These can be used to further restrict
write access but cannot be used to extend access rights.
This document does not define any protocol-accessible data nodes.
Since immutable information is tied to applied configuration values,
it is only accessible to clients that have the permissions to read
the applied configuration values.
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.
Acknowledgements
Thanks to Kent Watsen, Andy Bierman, Robert Wilton, Jan Lindblad,
Reshad Rahman, Anthony Somerset, Lou Berger, Joe Clarke, Scott
Mansfield, and Juergen Schoenwaelder for reviewing, and providing
important inputs to, this document.
References
Normative References
Ma, et al. Expires 17 September 2024 [Page 12]
Internet-Draft Immutable Flag March 2024
[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/info/rfc2119>.
[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/info/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/info/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/info/rfc7950>.
[RFC7952] Lhotka, L., "Defining and Using Metadata with YANG",
RFC 7952, DOI 10.17487/RFC7952, August 2016,
<https://www.rfc-editor.org/info/rfc7952>.
[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/info/rfc8341>.
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-05, 21 February 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-netmod-
system-config-05>.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<https://www.rfc-editor.org/info/rfc3688>.
[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/info/rfc8174>.
[RFC8343] Bjorklund, M., "A YANG Data Model for Interface
Management", RFC 8343, DOI 10.17487/RFC8343, March 2018,
<https://www.rfc-editor.org/info/rfc8343>.
Ma, et al. Expires 17 September 2024 [Page 13]
Internet-Draft Immutable Flag March 2024
[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/info/rfc8530>.
[TR-531] ONF, "UML to YANG Mapping Guidelines,
<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>", February 2023.
[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 system-defined data nodes
in the model. 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. E.g.,
* 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.
Ma, et al. Expires 17 September 2024 [Page 14]
Internet-Draft Immutable Flag March 2024
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" extension making it unchangeable. After this the
'interface-timer' shall be defined as a leaf-ref pointing at the
'supported-timer-values'.
A.2. UC2 - HW 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 HW
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 modelled as "config true" and 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.
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 clients can define a new user/group and grant it
particular privileges, but the predefined administrator account and
its granted access cannot be modified.
Ma, et al. Expires 17 September 2024 [Page 15]
Internet-Draft Immutable Flag March 2024
A.4. UC4 - Declaring immutable system configuration from an LNE's
perspective
An LNE (logical network element) 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
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
Cisco using the concept at least in some YANG modules
Junos OS provides a hidden and immutable configuration group
called junos-defaults
Appendix C. Changes between revisions
Note to RFC Editor (To be removed by RFC Editor)
v08 - v09
* Remove immutable YANG extension definition to simplify the
solution
Ma, et al. Expires 17 September 2024 [Page 16]
Internet-Draft Immutable Flag March 2024
* Add a new section to discuss the interaction between immutable
flag and <system>
* Remove the error response example in Appendix A.
* rewrite UC3, rename it to "Predefined Administrator Roles"
v06 - v07
* Use a Boolean type for the immutable value in YANG extension and
metadata annotation
* Define a "with-immutable" parameter and state that immutable
metadata annotation is not included in a response unless a client
explicitly requests them with a "with-immutable" parameter
* reword the abstract and related introduction section to highlight
immutable flag is descriptive
* Add a new section to define immutability of interior nodes, and
merge with "Inheritance of Immutable configuration" section
* Add a new section to define what the immutable flag means for each
YANG data node
* Define the "immutable flag" term.
* Add an item in the open issues tracking: Should the "immutable"
metadata annotation also be returned for nodes described as
immutable in the YANG schema so that there is a single source of
truth?
v05 - v06
* Remove immutable BGP AS number case
* Fix nits
v04 - v05
* Emphasized that the proposal tries to formally document existing
allowed behavior
* Reword the abstract and introduction sections;
* Restructure the document;
* Simplified the interface example in Appendix;
Ma, et al. Expires 17 September 2024 [Page 17]
Internet-Draft Immutable Flag March 2024
* Add immutable BGP AS number and peer-type configuration example.
* Added temporary section in Appendix B about list of existing non-
standard solutions
* Clarified inheritance of immutability
* Clarified that this draft is not dependent on the existence of the
<system> datastore.
v03 - v04
* Clarify how immutable flag interacts with NACM mechanism.
v02 - v03
* rephrase and avoid using "server MUST reject" statement, and try
to clarify that this documents aims to provide visibility into
existing immutable behavior;
* Add a new section to discuss the inheritance of immutability;
* Clarify that deletion to an immutable node in <running> which is
instantiated in <system> and copied into <running> should always
be allowed;
* Clarify that write access restriction due to general YANG rules
has no need to be marked as immutable.
* Add an new section named "Acknowledgements";
* editoral changes.
v01 - v02
* clarify the relation between the creation/deletion of the
immutable data node with its parent data node;
* Add a "TODO" comment about the inheritance of the immutable
property;
* Define that the server should reject write attempt to the
immutable data node at an <edit-config> operation time, rather
than waiting until a <commit> or <validate> operation takes place;
v00 - v01
* Added immutable extension
Ma, et al. Expires 17 September 2024 [Page 18]
Internet-Draft Immutable Flag March 2024
* Added new use-cases for immutable extension and annotation
* Added requirement that an update that means no effective change
should always be allowed
* Added clarification that immutable is only applied to read-write
datastore
* Narrowed the applied scope of metadata annotation to list/leaf-
list instances
Appendix D. Open Issues tracking
* Is this needed: error-code definition for edit failure because of
immutability
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
Nanjing
Jiangsu, 210012
China
Email: bill.wu@huawei.com
Balazs Lengyel
Ericsson
Email: balazs.lengyel@ericsson.com
Hongwei Li
HPE
Email: flycoolman@gmail.com
Ma, et al. Expires 17 September 2024 [Page 19]