| Internet-Draft | Immutable Metadata Annotation | February 2022 |
| Ma, et al. | Expires 14 August 2022 | [Page] |
This document defines a metadata annotation [RFC7952] named "immutable" to indicate the immutability of a particular instantiated data node. Any instantiated data node annotated with immutable="true" by the server is read-only to the clients of YANG-driven management protocols, such as NETCONF, RESTCONF and other management operations (e.g., SNMP and CLI requests).¶
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Copyright (c) 2022 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.¶
YANG [RFC7950] is a data modeling language used to model both state and configuration data, based on the "config" statement. However, there are some configuration data which may not be writable to clients, e.g., the interface name and type values created by the system due to the hardware currently present in the device cannot be modified by clients, while configurations such as MTU created by the system are free to be modified by the client.¶
Allowing some configuration modifiable while others not is inconsistent and introduces ambiguity to clients.¶
To address this issue, this document defines a metadata annotation [RFC7952] named "immutable" to indicate the immutability characteristic of a particular instantiated data node. Any instantiated data node marked with immutable="true" by the server is read-only to the clients of YANG-driven management protocols, such as NETCONF, RESTCONF and other management operations (e.g., SNMP and CLI requests).¶
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] and [RFC8341] and are not redefined here:¶
The following terms are defined in this document:¶
A metadata annotation indicating the immutability of a data node. An immutable data node is read-only to clients. Note that "immutable" is used to annotate instances of YANG data nodes rather than schema nodes. For instance, a "list" data node may exist in multiple instances in the data tree, "immutable" can annotate some of the instances as read-only, while others are not.¶
The "immutable" flag is used to indicate the immutability of a particular instantiated data node. It applies to the container, anydata, anyxml, leaf, list and leaf-list entries. The values are boolean types indicating whether the data node instance is immutable or not.¶
When the client retrieves a particular datastore, immutable data node instances MUST be annotated with immutable="true" by the server. If the "immutable" metadata annotation is not specified, the default is the same as the "immutable" value of the parent node. The default "immutable" value for a top level data node is false.¶
Any data node instance annotated with "immutable=true" is read-only to clients, which means that the following access operations for a particular instance are not allowed:¶
However the following operations SHOULD be allowed:¶
Comment: Should we allow the client delete an "immutable" system instantiated node in <running> (see Appendix A.1.3)?¶
Comment: Annotations can only be attached to individual list/leaf-list entry, how would the client know if it's to apply to the whole list/leaf-list, the list/leaf-list entries, or both?¶
Servers MUST reject any attempt to the "create", "delete" and "update" access operations on an immutable data node. The error reporting is performed at various different time according to the selected target datastore. If the target datastore is "running" or "startup", the server should reply with an "invalid-value" at a <edit-config> operation time. If the target datastore is "candidate", the "invalid-value" error response to update an immutable data node is delayed until a <commit> or <validate> operation takes place. For an example of an "invalid-value" error response, see Appendix A.1.2.¶
<CODE BEGINS> file="ietf-immutable@2022-01-05.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;
}
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: Hongwei Li
<mailto:flycoolman@gmail.com>";
description
"This module defines a metadata annotation named 'immutable'
to indicate the immutability of a particular instantiated
data node. Any instantiated data node marked with
immutable='true' by the server is read-only to the clients
of YANG-driven management protocols, such as NETCONF,
RESTCONF as well as SNMP and CLI requests.
Copyright (c) 2021 IETF Trust and the persons identified
as authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with
or without modification, is permitted pursuant to, and
subject to the license terms contained in, the Simplified
BSD License set forth in Section 4.c of the IETF Trust's
Legal Provisions Relating to IETF Documents
(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 2022-01-05 {
description
"Initial revision.";
reference
"RFC XXX: Immutable Metadata Annotation";
}
md:annotation immutable {
type boolean;
description
"The 'immutable' annotation indicates the immutability of an
instantiated data node. Any data node instance marked as
'immutable=true' is read-only to clients and cannot be
created/deleted/changed through NETCONF, RESTCONF or CLI.
It applies to the container, anydata, anyxml and leaf
instances, list and leaf-list entries.
If not specified for a given configuration data node
instance, then the immutability is the same as its parent
node instance in the data tree. The default for any top-level
configuration data node instance is false if not specified.";
}
}
<CODE ENDS>¶
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.¶
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¶
The YANG module specified in this document defines a metadata annotation for data nodes that is designed to be accessed network management protocols such as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF layer is the secure transport layer, and the mandatory-to-implement secure transport is Secure Shell (SSH) [RFC6242]. The lowest RESTCONF layer is HTTPS, and the mandatory-to-implement secure transport is TLS [RFC8446].¶
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.¶
In this section, the following fragment of a fictional interface module is used:¶
container interfaces {
list interface {
key "name";
leaf name {
type string;
}
leaf type {
type identityref {
base ianaift:iana-interface-type;
}
}
leaf mtu {
type uint16;
}
leaf-list ip-address {
type inet:ip-address;
}
}
}¶
In this example model, when an interface is physically present, the system will create an interface entry automatically with valid name and type values. Let's say that there is a system-defined interface "eth0" in <operational>:¶
<interfaces xmlns:or="urn:ietf:params:xml:ns:yang:ietf-origin"
xmlns:ianaift="urn:ietf:params:xml:ns:yang:iana-if-type"
xmlns:im="urn:ietf:params:xml:ns:yang:ietf-immutable"
or:origin="or:system">
<interface>
<name>eth0</name>
<type im:immutable="true">ianaift:ethernetCsmacd</type>
<mtu>1500</mtu>
</interface>
</interfaces>¶
The "type" leaf instance is annotated with immutable="true" in the RPC response, which means that it is not allowed to be modified by client configuration operations. Note that although the "name" defined as a list key leaf isn't annotated with immutable="true", modification of the key value for a particular list entry is never allowed. Deletion to the whole list entry of interface "eth0" should be allowed in this case, since there is no annotation for the "type" leaf instance's parent node.¶
The server should accept the configuration to set the leaf "type" to the value same as in <operational>:¶
<rpc xmlns="urn:ietf:params:xml:ns:netconf:base:1.0"
message-id="101">
<edit-config>
<target>
<running/>
</target>
<config>
<interface xmlns:xc="urn:ietf:params:xml:ns:netconf:base:1.0"
xmlns:ianaift="urn:ietf:params:xml:ns:yang:iana-if-type"
xc:operation="create">
<name>eth0</name>
<type>ianaift:ethernetCsmacd</type>
</interface>
</config>
</edit-config>
</rpc>
<rpc-reply message-id="101"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<ok/>
</rpc-reply>¶
If a client tries to change the type of an interface to a value that doesn't match the real type of the interface used by the system, the server must reject the request:¶
<rpc message-id="101"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0"
xmlns:xc="urn:ietf:params:xml:ns:netconf:base:1.0">
<edit-config>
<target>
<running/>
</target>
<config>
<interface xc:operation="merge"
xmlns:ianaift="urn:ietf:params:xml:ns:yang:iana-if-type">
<name>eth0</name>
<type>ianaift:tunnel</type>
</interface>
</config>
</edit-config>
</rpc>
<rpc-reply message-id="101"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0"
xmlns:xc="urn:ietf:params:xml:ns:netconf:base:1.0">
<rpc-error>
<error-type>application</error-type>
<error-tag>invalid-value</error-tag>
<error-severity>error</error-severity>
<error-path xmlns:t="http://example.com/schema/1.2/config">
/interfaces/interface[name="eth0"]/type
</error-path>
<error-message xml:lang="en">
Invalid type for interface eth0
</error-message>
</rpc-error>
</rpc-reply>¶
Should the server accept the configuration of deleting the type of interface named "eth0" from the running configuration?¶
<rpc message-id="102"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0"
xmlns:xc="urn:ietf:params:xml:ns:netconf:base:1.0">
<edit-config>
<target>
<running/>
</target>
<config>
<interface>
<name>eth0</name>
<type xc:operation="delete">ianaift:ethernetCsmacd</type>
</interface>
</config>
</edit-config>
</rpc>¶
Even the type of interface named "eth0" is deleted from the running configuration, the client which performs a <get-data> towards <operational> will still get:¶
<interfaces xmlns:or="urn:ietf:params:xml:ns:yang:ietf-origin"
xmlns:ianaift="urn:ietf:params:xml:ns:yang:iana-if-type"
xmlns:im="urn:ietf:params:xml:ns:yang:ietf-immutable"
or:origin="or:intended">
<interface>
<name>eth0</name>
<type im:immutable="true" or:origin="or:intended">
ianaift:ethernetCsmacd
</type>
<mtu>1500</mtu>
</interface>
</interfaces>¶
In this example, the "ietf-netconf-acm" YANG module defined in [RFC8341] is used. Suppose when the device is powered on, the system may provide some built-in access control groups, for each access control group there exists at least one built-in user, which might be read-only and cannot be modified by the client. In addition, the system also can predefine some access control rules for a specific group. Some rules can be modified, while others are not (e.g., access control rule for a root account should be immutable). In addition, clients can also define their own groups and access control rules freely.¶
The built-in access control groups and rules are provided by the system, they are present in <operational>. The example below illustrates what the built-in groups and rules might look like for a server after it boots:¶
<nacm xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-acm"
xmlns:im="urn:ietf:params:xml:ns:yang:ietf-immutable">
<groups>
<group>
<name>admin</name>
<user-name im:immutable="true">admin</user-name>
</group>
<group>
<name>monitor</name>
<user-name im:immutable="true">user</user-name>
</group>
<group>
<name>visit</name>
<user-name im:immutable="true">guest</user-name>
</group>
</groups>
<rule-list im:immutable="true">
<name>admin-acl</name>
<group>admin</group>
<rule>
<name>permit-all</name>
<module-name>*</module-name>
<access-operations>*</access-operations>
<action>permit</action>
</rule>
</rule-list>
<rule-list>
<name>monitor-acl</name>
<group>visit</group>
<rule>
<name>permit-monitor</name>
<module-name>ietf-netconf-monitoring</module-name>
<access-operations>read</access-operations>
<action>permit</action>
</rule>
</rule-list>
<rule-list>
<name>visit-acl</name>
<group>visit</group>
<rule>
<name>deny-ncm</name>
<module-name>ietf-netconf-monitoring</module-name>
<access-operations>*</access-operations>
<action>deny</action>
</rule>
</rule-list>
</nacm>¶
As indicated in the above XML snippet, the system predefines three access control groups and for each group there is one built-in immutable user, which means that the client can define new users for a particular access control group, but deletion of a built-in user-name is not allowed. The system also provides three access control list entries, one for each predefined group. Only the access control rule for the "admin" group is read-only to clients.¶