Immutable Metadata Annotation
draft-ma-netmod-immutable-flag-00

NETMOD                                                        Q. Ma, Ed.
Internet-Draft                                                     Q. Wu
Intended status: Standards Track                                  Huawei
Expires: 14 August 2022                                            H. Li
                                                                     HPE
                                                        10 February 2022

                     Immutable Metadata Annotation
                   draft-ma-netmod-immutable-flag-00

Abstract

   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).

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
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 14 August 2022.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  "Immutable" Metadata Annotation Definition  . . . . . . . . .   3
   3.  YANG Module . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  The "IETF XML" Registry . . . . . . . . . . . . . . . . .   6
     4.2.  The "YANG Module Names" Registry  . . . . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Appendix A.  Usage Examples . . . . . . . . . . . . . . . . . . .   8
     A.1.  Interface Example . . . . . . . . . . . . . . . . . . . .   8
       A.1.1.  Creating an "immutable" Interface Type  . . . . . . .  10
       A.1.2.  Changing an "immutable" Interface Type  . . . . . . .  10
       A.1.3.  Deleting an "immutable" Interface Type  . . . . . . .  11
     A.2.  Built-in Access Control Example . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   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.

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   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).

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] and [RFC8341] and are
   not redefined here:

   *  configuration data

   *  access operation

   The following terms are defined in this document:

   immutable:  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.

2.  "Immutable" Metadata Annotation Definition

   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.

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   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:

   *  Create: add descendant node instances for a container instance
      annotated with "immutable";

   *  Delete: delete a data node instance annotated with "immutable" or
      its child node instances from a datastore, e.g., delete an
      immutable list or leaf-list entry;

   *  Update: update an existing data node instance annotated with
      "immutable" or its child node instances in a datastore, e.g.,
      modify the value of an immutable leaf data node;

   However the following operations SHOULD be allowed:

   *  Create an immutable data node with a same value initially set by
      the system if it doesn't exist in the datastore, e.g., explicitly
      configure a system generated interface name in <running>;

   *  Delete the parent node of an immutable data node unless the parent
      node is also annotated with "immutable=true", e.g.,
      /interfaces/interface/type leaf instance is immutable, but the
      deletion to the /interfaces/interface list entry is 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.

3.  YANG Module

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   <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

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          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>

4.  IANA Considerations

4.1.  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.

4.2.  The "YANG Module Names" Registry

   This document registers one module name in the 'YANG Module Names'
   registry, defined in [RFC6020].

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         name: ietf-immutable
         prefix: im
         namespace: urn:ietf:params:xml:ns:yang:ietf-immutable
         RFC: XXXX // RFC Ed.: replace XXXX and remove this comment

5.  Security Considerations

   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.

6.  References

6.1.  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/info/rfc2119>.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/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/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>.

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   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
              <https://www.rfc-editor.org/info/rfc6242>.

   [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>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

   [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>.

   [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/info/rfc8446>.

6.2.  Informative References

   [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>.

Appendix A.  Usage Examples

A.1.  Interface Example

   In this section, the following fragment of a fictional interface
   module is used:

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        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.

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A.1.1.  Creating an "immutable" Interface Type

   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>

A.1.2.  Changing an "immutable" Interface Type

   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:

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   <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>

A.1.3.  Deleting an "immutable" Interface Type

   Should the server accept the configuration of deleting the type of
   interface named "eth0" from the running configuration?

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   <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>

A.2.  Built-in Access Control Example

   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.

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   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:

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       <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>

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   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.

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

   Hongwei Li
   HPE

   Email: flycoolman@gmail.com

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