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Internet Engineering Task Force (IETF) A. Bierman Request for Comments: 8341 YumaWorks STD: 91 M. Bjorklund Obsoletes: 6536 Tail-f Systems Category: Standards Track March 2018 ISSN: 2070-1721

             Network Configuration Access Control Model

Abstract

 The standardization of network configuration interfaces for use with
 the Network Configuration Protocol (NETCONF) or the RESTCONF protocol
 requires a structured and secure operating environment that promotes
 human usability and multi-vendor interoperability.  There is a need
 for standard mechanisms to restrict NETCONF or RESTCONF protocol
 access for particular users to a preconfigured subset of all
 available NETCONF or RESTCONF protocol operations and content.  This
 document defines such an access control model.
 This document obsoletes RFC 6536.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 https://www.rfc-editor.org/info/rfc8341.

Bierman & Bjorklund Standards Track [Page 1] RFC 8341 NACM March 2018

Copyright Notice

 Copyright (c) 2018 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 Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Table of Contents

 1. Introduction ....................................................4
    1.1. Terminology ................................................4
    1.2. Changes since RFC 6536 .....................................6
 2. Access Control Design Objectives ................................7
    2.1. Access Control Points ......................................7
    2.2. Simplicity .................................................8
    2.3. Procedural Interface .......................................8
    2.4. Datastore Access ...........................................8
    2.5. Users and Groups ...........................................8
    2.6. Maintenance ................................................9
    2.7. Configuration Capabilities .................................9
    2.8. Identifying Security-Sensitive Content .....................9
 3. NETCONF Access Control Model (NACM) ............................10
    3.1. Overview ..................................................10
         3.1.1. Features ...........................................10
         3.1.2. External Dependencies ..............................11
         3.1.3. Message Processing Model ...........................11
    3.2. Datastore Access ..........................................14
         3.2.1. Mapping New Datastores to NACM .....................14
         3.2.2. Access Rights ......................................14
         3.2.3. RESTCONF Methods ...................................15
         3.2.4. <get> and <get-config> Operations ..................16
         3.2.5. <edit-config> Operation ............................16
         3.2.6. <copy-config> Operation ............................18
         3.2.7. <delete-config> Operation ..........................18
         3.2.8. <commit> Operation .................................19
         3.2.9. <discard-changes> Operation ........................19
         3.2.10. <kill-session> Operation ..........................19

Bierman & Bjorklund Standards Track [Page 2] RFC 8341 NACM March 2018

    3.3. Model Components ..........................................19
         3.3.1. Users ..............................................19
         3.3.2. Groups .............................................20
         3.3.3. Emergency Recovery Session .........................20
         3.3.4. Global Enforcement Controls ........................20
                3.3.4.1. enable-nacm Switch ........................20
                3.3.4.2. read-default Switch .......................20
                3.3.4.3. write-default Switch ......................21
                3.3.4.4. exec-default Switch .......................21
                3.3.4.5. enable-external-groups Switch .............22
         3.3.5. Access Control Rules ...............................22
    3.4. Access Control Enforcement Procedures .....................22
         3.4.1. Initial Operation ..................................23
         3.4.2. Session Establishment ..............................23
         3.4.3. "access-denied" Error Handling .....................23
         3.4.4. Incoming RPC Message Validation ....................24
         3.4.5. Data Node Access Validation ........................26
         3.4.6. Outgoing <notification> Authorization ..............29
    3.5. Data Model Definitions ....................................31
         3.5.1. Data Organization ..................................31
         3.5.2. YANG Module ........................................32
 4. IANA Considerations ............................................42
 5. Security Considerations ........................................42
    5.1. NACM Configuration and Monitoring Considerations ..........43
    5.2. General Configuration Issues ..............................45
    5.3. Data Model Design Considerations ..........................47
 6. References .....................................................47
    6.1. Normative References ......................................47
    6.2. Informative References ....................................49
 Appendix A. Usage Examples ........................................50
   A.1. <groups> Example ...........................................50
   A.2. Module Rule Example ........................................51
   A.3. Protocol Operation Rule Example ............................53
   A.4. Data Node Rule Example .....................................55
   A.5. Notification Rule Example ..................................57
 Authors' Addresses ................................................58

Bierman & Bjorklund Standards Track [Page 3] RFC 8341 NACM March 2018

1. Introduction

 The Network Configuration Protocol (NETCONF) and the RESTCONF
 protocol do not provide any standard mechanisms to restrict the
 protocol operations and content that each user is authorized to
 access.
 There is a need for interoperable management of the controlled access
 to administrator-selected portions of the available NETCONF or
 RESTCONF content within a particular server.
 This document addresses access control mechanisms for the Operations
 and Content layers of NETCONF, as defined in [RFC6241]; and RESTCONF,
 as defined in [RFC8040].  It contains three main sections:
 1.  Access Control Design Objectives
 2.  NETCONF Access Control Model (NACM)
 3.  YANG Data Model (ietf-netconf-acm.yang)
 YANG version 1.1 [RFC7950] adds two new constructs that need special
 access control handling.  The "action" statement is similar to the
 "rpc" statement, except that it is located within a data node.  The
 "notification" statement can also be located within a data node.

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 [RFC8342] and are not redefined
 here:
 o  datastore
 o  configuration datastore
 o  conventional configuration datastore
 o  candidate configuration datastore
 o  running configuration datastore
 o  startup configuration datastore

Bierman & Bjorklund Standards Track [Page 4] RFC 8341 NACM March 2018

 o  operational state datastore
 o  client
 o  server
 The following terms are defined in [RFC6241] and are not redefined
 here:
 o  protocol operation
 o  session
 o  user
 The following terms are defined in [RFC7950] and are not redefined
 here:
 o  action
 o  data node
 o  data definition statement
 The following terms are defined in [RFC8040] and are not redefined
 here:
 o  data resource
 o  datastore resource
 o  operation resource
 o  target resource
 The following term is defined in [RFC7230] and is not redefined here:
 o  request URI
 The following terms are used throughout this document:
 access control:  A security feature provided by the server that
    allows an administrator to restrict access to a subset of all
    protocol operations and data, based on various criteria.
 access control model (ACM):  A conceptual model used to configure and
    monitor the access control procedures desired by the administrator
    to enforce a particular access control policy.

Bierman & Bjorklund Standards Track [Page 5] RFC 8341 NACM March 2018

 access control rule:  The criterion used to determine if a particular
    access operation will be permitted or denied.
 access operation:  How a request attempts to access a conceptual
    object.  One of "none", "read", "create", "delete", "update", or
    "execute".
 data node hierarchy:  The hierarchy of data nodes that identifies the
    specific "action" or "notification" node in the datastore.
 recovery session:  A special administrative session that is given
    unlimited NETCONF access and is exempt from all access control
    enforcement.  The mechanism or mechanisms used by a server to
    control and identify whether or not a session is a recovery
    session are implementation specific and are outside the scope of
    this document.
 write access:  A shorthand for the "create", "delete", and "update"
    access operations.

1.2. Changes since RFC 6536

 The NACM procedures and data model have been updated to support new
 data modeling capabilities in version 1.1 of the YANG data modeling
 language.  The "action" and "notification" statements can be used
 within data nodes to define data-model-specific operations and
 notifications.
 An important use case for these new YANG statements is the increased
 access control granularity that can be achieved over top-level "rpc"
 and "notification" statements.  The new "action" and "notification"
 statements are used within data nodes, and access to the action or
 notification can be restricted to specific instances of these data
 nodes.
 Support for the RESTCONF protocol has been added.  The RESTCONF
 operations are similar to the NETCONF operations, so a simple mapping
 to the existing NACM procedures and data model is possible.
 The data node access behavior for path matches has been clarified to
 also include matching descendant nodes of the specified path.
 The <edit-config> operation access rights behavior has been clarified
 to indicate that write access is not required for data nodes that are
 implicitly modified through side effects (such as the evaluation of
 YANG when-stmts, or data nodes implicitly deleted when creating a
 data node under a different branch under a YANG choice-stmt).

Bierman & Bjorklund Standards Track [Page 6] RFC 8341 NACM March 2018

 The Security Considerations section has been updated to comply with
 the "YANG module security guidelines" [YANG-SEC].  Note that the YANG
 module in this document does not define any RPC operations.

2. Access Control Design Objectives

 This section documents the design objectives for the NETCONF access
 control model presented in Section 3.

2.1. Access Control Points

 NETCONF allows server implementers to add new custom protocol
 operations, and the YANG data modeling language supports this
 feature.  These operations can be defined in standard or proprietary
 YANG modules.
 It is not possible to design an ACM for NETCONF that only focuses on
 a static set of standard protocol operations defined by NETCONF
 itself, like some other protocols.  Since few assumptions can be made
 about an arbitrary protocol operation, the NETCONF architectural
 server components need to be protected at three conceptual control
 points.
 These access control points, described in Figure 1, are as follows:
 protocol operation:  Permission to invoke specific protocol
    operations.
 datastore:  Permission to read and/or alter specific data nodes
    within any datastore.
 notification:  Permission to receive specific notification event
    types.
               +-------------+                 +-------------+
  client       |  protocol   |                 |  data node  |
  request -->  |  operation  | ------------->  |   access    |
               |  allowed?   |   datastore     |  allowed?   |
               +-------------+   or state      +-------------+
                                 data access
               +----------------+
               |  notification  |
  event -->    |  allowed?      |
               +----------------+
                               Figure 1

Bierman & Bjorklund Standards Track [Page 7] RFC 8341 NACM March 2018

2.2. Simplicity

 There is concern that a complicated ACM will not be widely deployed
 because it is too hard to use.  Configuration of the access control
 system needs to be as simple as possible.  Simple and common tasks
 need to be easy to configure and require little expertise or
 domain-specific knowledge.  Complex tasks are possible using
 additional mechanisms that may require additional expertise.
 A single set of access control rules ought to be able to control all
 types of NETCONF protocol operation invocation, all datastore access,
 and all notification events.
 Access control ought to be defined with a small and familiar set of
 permissions, while still allowing full control of datastore access.

2.3. Procedural Interface

 NETCONF uses a Remote Procedure Call (RPC) model and an extensible
 set of protocol operations.  Access control for any possible protocol
 operation is necessary.

2.4. Datastore Access

 It is necessary to control access to specific nodes and subtrees
 within the datastore, regardless of which protocol operation --
 standard or proprietary -- was used to access the datastore.

2.5. Users and Groups

 It is necessary that access control rules for a single user or a
 configurable group of users can be configured.
 The ACM needs to support the concept of administrative groups, to
 support the well-established distinction between a root account and
 other types of less-privileged conceptual user accounts.  These
 groups need to be configurable by the administrator.
 It is necessary that the user-to-group mapping can be delegated to a
 central server, such as a RADIUS server [RFC2865] [RFC5607].  Since
 authentication is performed by the transport layer and RADIUS
 performs authentication and service authorization at the same time,
 the underlying transport protocol needs to be able to report a set of
 group names associated with the user to the server.  It is necessary
 that the administrator can disable the usage of these group names
 within the ACM.

Bierman & Bjorklund Standards Track [Page 8] RFC 8341 NACM March 2018

2.6. Maintenance

 It ought to be possible to disable part or all of the access control
 model enforcement procedures without deleting any access control
 rules.

2.7. Configuration Capabilities

 Suitable configuration and monitoring mechanisms are needed to allow
 an administrator to easily manage all aspects of the ACM's behavior.
 A standard data model, suitable for use with the <edit-config>
 protocol operation, needs to be available for this purpose.
 Access control rules to restrict access operations on specific
 subtrees within the configuration datastore need to be supported.

2.8. Identifying Security-Sensitive Content

 One of the most important aspects of the data model documentation,
 and one of the biggest concerns during deployment, is the
 identification of security-sensitive content.  This applies to
 protocol operations in NETCONF, not just data and notifications.
 It is mandatory for security-sensitive objects to be documented in
 the Security Considerations section of an RFC.  This is nice, but it
 is not good enough, for the following reasons:
 o  This documentation-only approach forces administrators to study
    the RFC and determine if there are any potential security risks
    introduced by a new data model.
 o  If any security risks are identified, then the administrator must
    study some more RFC text and determine how to mitigate the
    security risk(s).
 o  The ACM on each server must be configured to mitigate the security
    risks, e.g., require privileged access to read or write the
    specific data identified in the Security Considerations section.
 o  If the ACM is not preconfigured, then there will be a time window
    of vulnerability after the new data model is loaded and before the
    new access control rules for that data model are configured,
    enabled, and debugged.
 Often, the administrator just wants to disable default access to the
 secure content so that no inadvertent or malicious changes can be
 made to the server.  This allows the default rules to be more
 lenient, without significantly increasing the security risk.

Bierman & Bjorklund Standards Track [Page 9] RFC 8341 NACM March 2018

 A data model designer needs to be able to use machine-readable
 statements to identify content that needs to be protected by default.
 This will allow client and server tools to automatically identify
 data-model-specific security risks, by denying access to sensitive
 data unless the user is explicitly authorized to perform the
 requested access operation.

3. NETCONF Access Control Model (NACM)

3.1. Overview

 This section provides a high-level overview of the access control
 model structure.  It describes the NETCONF protocol message
 processing model and the conceptual access control requirements
 within that model.

3.1.1. Features

 The NACM data model provides the following features:
 o  Independent control of RPC, action, data, and notification access
    is provided.
 o  The concept of an emergency recovery session is supported, but
    configuration of the server for this purpose is beyond the scope
    of this document.  An emergency recovery session will bypass all
    access control enforcement, in order to allow it to initialize or
    repair the NACM configuration.
 o  A simple and familiar set of datastore permissions is used.
 o  Support for YANG security tagging (e.g., a
    "nacm:default-deny-write" statement) allows default security modes
    to automatically exclude sensitive data.
 o  Separate default access modes for read, write, and execute
    permissions are provided.
 o  Access control rules are applied to configurable groups of users.
 o  The access control enforcement procedures can be disabled during
    operation, without deleting any access control rules, in order to
    debug operational problems.

Bierman & Bjorklund Standards Track [Page 10] RFC 8341 NACM March 2018

 o  The number of denied protocol operation requests and denied
    datastore write requests can be monitored by the client.
 o  Simple unconstrained YANG instance-identifiers are used to
    configure access control rules for specific data nodes.

3.1.2. External Dependencies

 NETCONF [RFC6241] and RESTCONF [RFC8040] are used for network
 management purposes within this document.
 The YANG data modeling language [RFC7950] is used to define the data
 models for use with NETCONF or RESTCONF.  YANG is also used to define
 the data model in this document.

3.1.3. Message Processing Model

 The following diagram shows the conceptual message flow model,
 including the points at which access control is applied during
 NETCONF message processing.
 RESTCONF operations are mapped to the access control model based on
 the HTTP method and resource class used in the operation.  For
 example, a POST method on a data resource is considered "write data
 node" access, but a POST method on an operation resource is
 considered "operation" access.
 The new "pre-read data node acc. ctl" boxes in the diagram below
 refer to group read access as it relates to data node ancestors of an
 action or notification.  As an example, if an action is defined as
 /interfaces/interface/reset-interface, the group must be authorized
 to (1) read /interfaces and /interfaces/interface and (2) execute on
 /interfaces/interface/reset-interface.

Bierman & Bjorklund Standards Track [Page 11] RFC 8341 NACM March 2018

                  +-------------------------+
                  |       session           |
                  |      (username)         |
                  +-------------------------+
                     |                 ^
                     V                 |
           +--------------+     +---------------+
           |   message    |     |   message     |
           | dispatcher   |     |   generator   |
           +--------------+     +---------------+
             |      |               ^         ^
             |      V               |         |
             |  +=============+     |         |
             |  | pre-read    |     |         |
             |  | data node   |     |         |
             |  | acc. ctl    |     |         |
             |  +=============+     |         |
             |    |                 |         |
             V    V                 |         |
       +===========+     +-------------+   +----------------+
       | operation |---> |    reply    |   | <notification> |
       | acc. ctl  |     |  generator  |   |  generator     |
       +===========+     +-------------+   +----------------+
             |              ^    ^                ^
             V       +------+    |                |
       +-----------+ |   +=============+  +================+
       | operation | |   |    read     |  | <notification> |
       | processor |-+   | data node   |  |  access ctl    |
       |           |     | acc. ctl    |  |                |
       +-----------+     +=============+  +================+
             |   |                  ^       ^     ^
             V   +----------------+ |       |     |
       +===========+              | |       | +============+
       |  write    |              | |       | | pre-read   |
       | data node |              | |       | | data node  |
       | acc. ctl  | -----------+ | |       | | acc. ctl   |
       +===========+            | | |       | +============+
             |                  | | |       |   ^
             V                  V V |       |   |
       +---------------+      +-------------------+
       | configuration | ---> |      server       |
       |   datastore   |      |  instrumentation  |
       |               | <--- |                   |
       +---------------+      +-------------------+
                               Figure 2

Bierman & Bjorklund Standards Track [Page 12] RFC 8341 NACM March 2018

 The following high-level sequence of conceptual processing steps is
 executed for each received <rpc> message, if access control
 enforcement is enabled:
 o  For each active session, access control is applied individually to
    all <rpc> messages (except <close-session>) received by the
    server, unless the session is identified as a recovery session.
 o  If the <action> operation defined in [RFC7950] is invoked, then
    read access is required for all instances in the hierarchy of data
    nodes that identifies the specific action in the datastore, and
    execute access is required for the action node.  If the user is
    not authorized to read all the specified data nodes and execute
    the action, then the request is rejected with an "access-denied"
    error.
 o  Otherwise, if the user is not authorized to execute the specified
    protocol operation, then the request is rejected with an
    "access-denied" error.
 o  If a datastore is accessed by the protocol operation, then the
    server checks to see if the client is authorized to access the
    nodes in the datastore.  If the user is not authorized to perform
    the requested access operation on the requested data, then the
    request is rejected with an "access-denied" error.
 The following sequence of conceptual processing steps is executed for
 each generated notification event, if access control enforcement is
 enabled:
 o  Server instrumentation generates a notification for a particular
    subscription.
 o  If the "notification" statement is specified within a data
    subtree, as specified in [RFC7950], then read access is required
    for all instances in the hierarchy of data nodes that identifies
    the specific notification in the datastore, and read access is
    required for the notification node.  If the user is not authorized
    to read all the specified data nodes and the notification node,
    then the notification is dropped for that subscription.
 o  If the "notification" statement is a top-level statement, the
    notification access control enforcer checks the notification event
    type, and if it is one that the user is not authorized to read,
    then the notification is dropped for that subscription.

Bierman & Bjorklund Standards Track [Page 13] RFC 8341 NACM March 2018

3.2. Datastore Access

 The same access control rules apply to all datastores that support
 the NACM -- for example, the candidate configuration datastore or the
 running configuration datastore.
 All conventional configuration datastores and the operational state
 datastore are controlled by the NACM.  Local files, remote files, or
 datastores accessed via the <url> parameter are not controlled by
 the NACM.

3.2.1. Mapping New Datastores to NACM

 It is possible that new datastores will be defined over time for use
 with NETCONF.  The NACM MAY be applied to other datastores that have
 similar access rights as defined in the NACM.  To apply the NACM to a
 new datastore, the new datastore specification needs to define how it
 maps to the NACM CRUDX (Create, Read, Update, Delete, eXec) access
 rights.  It is possible that only a subset of the NACM access rights
 would be applicable.  For example, only retrieval access control
 would be needed for a read-only datastore.  Operations and access
 rights not supported by the NACM CRUDX model are outside the scope of
 this document.  A datastore does not need to use the NACM, e.g., the
 datastore specification defines something else or does not use access
 control.

3.2.2. Access Rights

 A small set of hard-wired datastore access rights is needed to
 control access to all possible protocol operations, including vendor
 extensions to the standard protocol operation set.
 The CRUDX model can support all protocol operations:
 o  Create: allows the client to add a new data node instance to a
    datastore.
 o  Read: allows the client to read a data node instance from a
    datastore or receive the notification event type.
 o  Update: allows the client to update an existing data node instance
    in a datastore.
 o  Delete: allows the client to delete a data node instance from a
    datastore.
 o  eXec: allows the client to execute the operation.

Bierman & Bjorklund Standards Track [Page 14] RFC 8341 NACM March 2018

3.2.3. RESTCONF Methods

 The RESTCONF protocol utilizes HTTP methods to perform datastore
 operations, similar to NETCONF.  The NACM procedures were originally
 written for NETCONF protocol operations, so the RESTCONF methods are
 mapped to NETCONF operations for the purpose of access control
 processing.  The enforcement procedures described within this
 document apply to both protocols unless explicitly stated otherwise.
 The request URI needs to be considered when processing RESTCONF
 requests on data resources:
 o  For HEAD and GET requests, any data nodes that are ancestor nodes
    of the target resource are considered to be part of the retrieval
    request for access control purposes.
 o  For PUT, PATCH, and DELETE requests, any data nodes that are
    ancestor nodes of the target resource are not considered to be
    part of the edit request for access control purposes.  The access
    operation for these nodes is considered to be "none".  The edit
    begins at the target resource.
 o  For POST requests on data resources, any data nodes that are
    specified in the request URI, including the target resource, are
    not considered to be part of the edit request for access control
    purposes.  The access operation for these nodes is considered to
    be "none".  The edit begins at a child node of the target
    resource, specified in the message body.

Bierman & Bjorklund Standards Track [Page 15] RFC 8341 NACM March 2018

 Not all RESTCONF methods are subject to access control.  The
 following table specifies how each method is mapped to NETCONF
 protocol operations.  The value "none" indicates that the NACM is not
 applied at all to the specific RESTCONF method.
 +---------+-----------------+---------------------+-----------------+
 | Method  | Resource class  | NETCONF operation   | Access          |
 |         |                 |                     | operation       |
 +---------+-----------------+---------------------+-----------------+
 | OPTIONS | all             | none                | none            |
 | HEAD    | all             | <get>, <get-config> | read            |
 | GET     | all             | <get>, <get-config> | read            |
 | POST    | datastore, data | <edit-config>       | create          |
 | POST    | operation       | specified operation | execute         |
 | PUT     | data            | <edit-config>       | create, update  |
 | PUT     | datastore       | <copy-config>       | update          |
 | PATCH   | data, datastore | <edit-config>       | update          |
 | DELETE  | data            | <edit-config>       | delete          |
 +---------+-----------------+---------------------+-----------------+
             Table 1: Mapping RESTCONF Methods to NETCONF

3.2.4. <get> and <get-config> Operations

 The NACM access rights are not directly coupled to the <get> and
 <get-config> protocol operations but apply to all <rpc> operations
 that would result in a "read" access operation to the target
 datastore.  This section describes how these access rights apply to
 the specific access operations supported by the <get> and
 <get-config> protocol operations.
 Data nodes to which the client does not have read access are silently
 omitted, along with any descendants, from the <rpc-reply> message.
 This is done to allow NETCONF filters for <get> and <get-config> to
 function properly, instead of causing an "access-denied" error
 because the filter criteria would otherwise include unauthorized read
 access to some data nodes.  For NETCONF filtering purposes, the
 selection criteria are applied to the subset of nodes that the user
 is authorized to read, not the entire datastore.

3.2.5. <edit-config> Operation

 The NACM access rights are not directly coupled to the <edit-config>
 "operation" attribute, although they are similar.  Instead, a NACM
 access right applies to all protocol operations that would result in
 a particular access operation to the target datastore.  This section
 describes how these access rights apply to the specific access
 operations supported by the <edit-config> protocol operation.

Bierman & Bjorklund Standards Track [Page 16] RFC 8341 NACM March 2018

 If the effective access operation is "none" (i.e.,
 default-operation="none") for a particular data node, then no access
 control is applied to that data node.  This is required to allow
 access to a subtree within a larger data structure.  For example, a
 user may be authorized to create a new "/interfaces/interface" list
 entry but not be authorized to create or delete its parent container
 ("/interfaces").  If the "/interfaces" container already exists in
 the target datastore, then the effective operation will be "none" for
 the "/interfaces" node if an "/interfaces/interface" list entry is
 edited.
 If the protocol operation would result in the creation of a datastore
 node and the user does not have "create" access permission for that
 node, the protocol operation is rejected with an "access-denied"
 error.
 If the protocol operation would result in the deletion of a datastore
 node and the user does not have "delete" access permission for that
 node, the protocol operation is rejected with an "access-denied"
 error.
 If the protocol operation would result in the modification of a
 datastore node and the user does not have "update" access permission
 for that node, the protocol operation is rejected with an
 "access-denied" error.
 A "merge" or "replace" <edit-config> operation may include data nodes
 that do not alter portions of the existing datastore.  For example, a
 container or list node may be present for naming purposes but does
 not actually alter the corresponding datastore node.  These unaltered
 data nodes are ignored by the server and do not require any access
 rights by the client.
 A "merge" <edit-config> operation may include data nodes but not
 include particular child data nodes that are present in the
 datastore.  These missing data nodes within the scope of a "merge"
 <edit-config> operation are ignored by the server and do not require
 any access rights by the client.
 The contents of specific restricted datastore nodes MUST NOT be
 exposed in any <rpc-error> elements within the reply.
 An <edit-config> operation may cause data nodes to be implicitly
 created or deleted as an implicit side effect of a requested
 operation.  For example, a YANG when-stmt expression may evaluate to
 a different result, causing data nodes to be deleted, or created with
 default values; or if a data node is created under one branch of a
 YANG choice-stmt, then all data nodes under the other branches are

Bierman & Bjorklund Standards Track [Page 17] RFC 8341 NACM March 2018

 implicitly removed.  No NACM access rights are required on any data
 nodes that are implicitly changed as a side effect of another allowed
 operation.

3.2.6. <copy-config> Operation

 Access control for the <copy-config> protocol operation requires
 special consideration because the administrator may be replacing the
 entire target datastore.
 If the source of the <copy-config> protocol operation is the running
 configuration datastore and the target is the startup configuration
 datastore, the client is only required to have permission to execute
 the <copy-config> protocol operation.
 Otherwise:
 o  If the source of the <copy-config> operation is a datastore, then
    data nodes to which the client does not have read access are
    silently omitted.
 o  If the target of the <copy-config> operation is a datastore, the
    client needs access to the modified nodes.  Specifically:
  • If the protocol operation would result in the creation of a

datastore node and the user does not have "create" access

       permission for that node, the protocol operation is rejected
       with an "access-denied" error.
  • If the protocol operation would result in the deletion of a

datastore node and the user does not have "delete" access

       permission for that node, the protocol operation is rejected
       with an "access-denied" error.
  • If the protocol operation would result in the modification of a

datastore node and the user does not have "update" access

       permission for that node, the protocol operation is rejected
       with an "access-denied" error.

3.2.7. <delete-config> Operation

 Access to the <delete-config> protocol operation is denied by
 default.  The "exec-default" leaf does not apply to this protocol
 operation.  Access control rules must be explicitly configured to
 allow invocation by a non-recovery session.

Bierman & Bjorklund Standards Track [Page 18] RFC 8341 NACM March 2018

3.2.8. <commit> Operation

 The server MUST determine the exact nodes in the running
 configuration datastore that are actually different and only check
 "create", "update", and "delete" access permissions for this set of
 nodes, which could be empty.
 For example, if a session can read the entire datastore but only
 change one leaf, that session needs to be able to edit and commit
 that one leaf.

3.2.9. <discard-changes> Operation

 The client is only required to have permission to execute the
 <discard-changes> protocol operation.  No datastore permissions are
 needed.

3.2.10. <kill-session> Operation

 The <kill-session> operation does not directly alter a datastore.
 However, it allows one session to disrupt another session that is
 editing a datastore.
 Access to the <kill-session> protocol operation is denied by default.
 The "exec-default" leaf does not apply to this protocol operation.
 Access control rules must be explicitly configured to allow
 invocation by a non-recovery session.

3.3. Model Components

 This section defines the conceptual components related to the access
 control model.

3.3.1. Users

 A "user" is the conceptual entity that is associated with the access
 permissions granted to a particular session.  A user is identified by
 a string that is unique within the server.
 As described in [RFC6241], the username string is derived from the
 transport layer during session establishment.  If the transport layer
 cannot authenticate the user, the session is terminated.

Bierman & Bjorklund Standards Track [Page 19] RFC 8341 NACM March 2018

3.3.2. Groups

 Access to a specific NETCONF protocol operation is granted to a
 session.  The session is associated with a group (i.e., not with
 a user).
 A group is identified by its name.  All group names are unique within
 the server.
 Access control is applied at the level of groups.  A group contains
 zero or more group members.
 A group member is identified by a username string.
 The same user can be a member of multiple groups.

3.3.3. Emergency Recovery Session

 The server MAY support a recovery session mechanism, which will
 bypass all access control enforcement.  This is useful for
 restricting initial access and repairing a broken access control
 configuration.

3.3.4. Global Enforcement Controls

 There are five global controls that are used to help control how
 access control is enforced.

3.3.4.1. enable-nacm Switch

 A global "enable-nacm" on/off switch is provided to enable or disable
 all access control enforcement.  When this global switch is set to
 "true", all requests are checked against the access control rules and
 only permitted if configured to allow the specific access request.
 When this global switch is set to "false", all access requests are
 permitted.

3.3.4.2. read-default Switch

 An on/off "read-default" switch is provided to enable or disable
 default access to receive data in replies and notifications.  When
 the "enable-nacm" global switch is set to "true", this global switch
 is relevant if no matching access control rule is found to explicitly
 permit or deny read access to the requested datastore data or
 notification event type.

Bierman & Bjorklund Standards Track [Page 20] RFC 8341 NACM March 2018

 When this global switch is set to "permit" and no matching access
 control rule is found for the datastore read or notification event
 requested, access is permitted.
 When this global switch is set to "deny" and no matching access
 control rule is found for the datastore read or notification event
 requested, access is denied.  This means that the requested data is
 not sent to the client.  See step 11 in Section 3.4.5 for details.

3.3.4.3. write-default Switch

 An on/off "write-default" switch is provided to enable or disable
 default access to alter configuration data.  When the "enable-nacm"
 global switch is set to "true", this global switch is relevant if no
 matching access control rule is found to explicitly permit or deny
 write access to the requested datastore data.
 When this global switch is set to "permit" and no matching access
 control rule is found for the datastore write requested, access is
 permitted.
 When this global switch is set to "deny" and no matching access
 control rule is found for the datastore write requested, access is
 denied.  See step 12 in Section 3.4.5 for details.

3.3.4.4. exec-default Switch

 An on/off "exec-default" switch is provided to enable or disable
 default access to execute protocol operations.  When the
 "enable-nacm" global switch is set to "true", this global switch is
 relevant if no matching access control rule is found to explicitly
 permit or deny access to the requested NETCONF protocol operation.
 When this global switch is set to "permit" and no matching access
 control rule is found for the NETCONF protocol operation requested,
 access is permitted.
 When this global switch is set to "deny" and no matching access
 control rule is found for the NETCONF protocol operation requested,
 access is denied.  See step 12 in Section 3.4.4 and step 13 in
 Section 3.4.5 for details.

Bierman & Bjorklund Standards Track [Page 21] RFC 8341 NACM March 2018

3.3.4.5. enable-external-groups Switch

 When this global switch is set to "true", the group names reported by
 the transport layer for a session are used together with the locally
 configured group names to determine the access control rules for the
 session.
 When this switch is set to "false", the group names reported by the
 transport layer are ignored by the NACM.

3.3.5. Access Control Rules

 There are four types of rules available in the NACM:
 module rule:  controls access for definitions in a specific YANG
    module, identified by its name.
 protocol operation rule:  controls access for a specific protocol
    operation, identified by its YANG module and name.
 data node rule:  controls access for a specific data node and its
    descendants, identified by its path location within the conceptual
    XML document for the data node.
 notification rule:  controls access for a specific notification event
    type, identified by its YANG module and name.

3.4. Access Control Enforcement Procedures

 There are six separate phases that need to be addressed, four of
 which are related to the NETCONF message processing model
 (Section 3.1.3):
 1.  Initial operation
 2.  Session establishment
 3.  "access-denied" error handling
 4.  Incoming RPC message validation
 5.  Data node access validation
 6.  Outgoing <notification> authorization
 In addition, the initial startup mode for a NETCONF server, session
 establishment, and "access-denied" error-handling procedures also
 need to be considered.

Bierman & Bjorklund Standards Track [Page 22] RFC 8341 NACM March 2018

 The server MUST use the access control rules in effect at the time it
 starts processing the message.  The same access control rules MUST
 stay in effect for the processing of the entire message.

3.4.1. Initial Operation

 Upon the very first startup of the NETCONF server, the access control
 configuration will probably not be present.  If it isn't, a server
 MUST NOT allow any write access to any session role except a recovery
 session.
 Access rules are enforced any time a request is initiated from a user
 session.  Access control is not enforced for server-initiated access
 requests, such as the initial load of the running configuration
 datastore, during bootup.

3.4.2. Session Establishment

 The access control model applies specifically to the well-formed XML
 content transferred between a client and a server after session
 establishment has been completed and after the <hello> exchange has
 been successfully completed.
 Once session establishment is completed and a user has been
 authenticated, the transport layer reports the username and a
 possibly empty set of group names associated with the user to the
 NETCONF server.  The NETCONF server will enforce the access control
 rules, based on the supplied username, group names, and the
 configuration data stored on the server.

3.4.3. "access-denied" Error Handling

 The "access-denied" error-tag is generated when the access control
 system denies access to either a request to invoke a protocol
 operation or a request to perform a particular access operation on
 the configuration datastore.
 A server MUST NOT include any information the client is not allowed
 to read in any <error-info> elements within the <rpc-error> response.

Bierman & Bjorklund Standards Track [Page 23] RFC 8341 NACM March 2018

3.4.4. Incoming RPC Message Validation

 The diagram below shows the basic conceptual structure of the access
 control processing model for incoming NETCONF <rpc> messages within a
 server.
            NETCONF server
            +------------+
            |    XML     |
            |   message  |
            | dispatcher |
            +------------+
                   |
                   |
                   V
           +---------------+
           | <rpc> message |
           +---------------+
             |    |     |
             |    |     +--------------------------------+
             |    +---------------+                      |
             V                    V                      V
   +------------------+ +--------------------+ +--------------------+
   | vendor operation | | standard operation | | standard operation |
   |    <my-edit>     | |   <edit-config>    | |      <unlock>      |
   +------------------+ +--------------------+ +--------------------+
               |                 |
               |                 |
               V                 V
              +----------------------+
              |    configuration     |
              |      datastore       |
              +----------------------+
                               Figure 3
 Access control begins with the message dispatcher.
 After the server validates the <rpc> element and determines the
 namespace URI and the element name of the protocol operation being
 requested, the server verifies that the user is authorized to invoke
 the protocol operation.

Bierman & Bjorklund Standards Track [Page 24] RFC 8341 NACM March 2018

 The server MUST separately authorize every protocol operation by
 following these steps:
 1.   If the "enable-nacm" leaf is set to "false", then the protocol
      operation is permitted.
 2.   If the requesting session is identified as a recovery session,
      then the protocol operation is permitted.
 3.   If the requested operation is the NETCONF <close-session>
      protocol operation, then the protocol operation is permitted.
 4.   Check all the "group" entries to see if any of them contain a
      "user-name" entry that equals the username for the session
      making the request.  If the "enable-external-groups" leaf is
      "true", add to these groups the set of groups provided by the
      transport layer.
 5.   If no groups are found, continue with step 10.
 6.   Process all rule-list entries, in the order they appear in the
      configuration.  If a rule-list's "group" leaf-list does not
      match any of the user's groups, proceed to the next rule-list
      entry.
 7.   For each rule-list entry found, process all rules, in order,
      until a rule that matches the requested access operation is
      found.  A rule matches if all of the following criteria are met:
  • The rule's "module-name" leaf is "*" or equals the name of

the YANG module where the protocol operation is defined.

  • Either (1) the rule does not have a "rule-type" defined or

(2) the "rule-type" is "protocol-operation" and the

         "rpc-name" is "*" or equals the name of the requested
         protocol operation.
  • The rule's "access-operations" leaf has the "exec" bit set or

has the special value "*".

 8.   If a matching rule is found, then the "action" leaf is checked.
      If it is equal to "permit", then the protocol operation is
      permitted; otherwise, it is denied.
 9.   At this point, no matching rule was found in any rule-list
      entry.

Bierman & Bjorklund Standards Track [Page 25] RFC 8341 NACM March 2018

 10.  If the requested protocol operation is defined in a YANG module
      advertised in the server capabilities and the "rpc" statement
      contains a "nacm:default-deny-all" statement, then the protocol
      operation is denied.
 11.  If the requested protocol operation is the NETCONF
      <kill-session> or <delete-config>, then the protocol operation
      is denied.
 12.  If the "exec-default" leaf is set to "permit", then permit the
      protocol operation; otherwise, deny the request.
 If the user is not authorized to invoke the protocol operation, then
 an <rpc-error> is generated with the following information:
 error-tag:  access-denied
 error-path:  Identifies the requested protocol operation.  The
    following example represents the <edit-config> protocol operation
    in the NETCONF base namespace:
       <error-path
         xmlns:nc="urn:ietf:params:xml:ns:netconf:base:1.0">
           /nc:rpc/nc:edit-config
       </error-path>
 If a datastore is accessed, either directly or as a side effect of
 the protocol operation, then the server MUST intercept the access
 operation and make sure that the user is authorized to perform the
 requested access operation on the specified data, as defined in
 Section 3.4.5.

3.4.5. Data Node Access Validation

 If (1) a data node within a datastore is accessed or (2) an action or
 notification is tied to a data node, then the server MUST ensure that
 the user is authorized to perform the requested "read", "create",
 "update", "delete", or "execute" access operation on the specified
 data node.
 If an action is requested to be executed, the server MUST ensure that
 the user is authorized to perform the "execute" access operation on
 the requested action.
 If a notification tied to a data node is generated, the server MUST
 ensure that the user is authorized to perform the "read" access
 operation on the requested notification.

Bierman & Bjorklund Standards Track [Page 26] RFC 8341 NACM March 2018

 The data node access request is authorized by following these steps:
 1.   If the "enable-nacm" leaf is set to "false", then the access
      operation is permitted.
 2.   If the requesting session is identified as a recovery session,
      then the access operation is permitted.
 3.   Check all the "group" entries to see if any of them contain a
      "user-name" entry that equals the username for the session
      making the request.  If the "enable-external-groups" leaf is
      "true", add to these groups the set of groups provided by the
      transport layer.
 4.   If no groups are found, continue with step 9.
 5.   Process all rule-list entries, in the order they appear in the
      configuration.  If a rule-list's "group" leaf-list does not
      match any of the user's groups, proceed to the next rule-list
      entry.
 6.   For each rule-list entry found, process all rules, in order,
      until a rule that matches the requested access operation is
      found.  A rule matches if all of the following criteria are met:
  • The rule's "module-name" leaf is "*" or equals the name of

the YANG module where the requested data node is defined.

  • Either (1) the rule does not have a "rule-type" defined or

(2) the "rule-type" is "data-node" and the "path" matches the

         requested data node, action node, or notification node.  A
         path is considered to match if the requested node is the node
         specified by the path or is a descendant node of the path.
  • For a "read" access operation, the rule's "access-operations"

leaf has the "read" bit set or has the special value "*".

  • For a "create" access operation, the rule's

"access-operations" leaf has the "create" bit set or has the

         special value "*".
  • For a "delete" access operation, the rule's

"access-operations" leaf has the "delete" bit set or has the

         special value "*".

Bierman & Bjorklund Standards Track [Page 27] RFC 8341 NACM March 2018

  • For an "update" access operation, the rule's

"access-operations" leaf has the "update" bit set or has the

         special value "*".
  • For an "execute" access operation, the rule's

"access-operations" leaf has the "exec" bit set or has the

         special value "*".
 7.   If a matching rule is found, then the "action" leaf is checked.
      If it is equal to "permit", then the data node access is
      permitted; otherwise, it is denied.  For a "read" access
      operation, "denied" means that the requested data is not
      returned in the reply.
 8.   At this point, no matching rule was found in any rule-list
      entry.
 9.   For a "read" access operation, if the requested data node is
      defined in a YANG module advertised in the server capabilities
      and the data definition statement contains a
      "nacm:default-deny-all" statement, then the requested data node
      and all its descendants are not included in the reply.
 10.  For a "write" access operation, if the requested data node is
      defined in a YANG module advertised in the server capabilities
      and the data definition statement contains a
      "nacm:default-deny-write" or a "nacm:default-deny-all"
      statement, then the access request is denied for the data node
      and all its descendants.
 11.  For a "read" access operation, if the "read-default" leaf is set
      to "permit", then include the requested data node in the reply;
      otherwise, do not include the requested data node or any of its
      descendants in the reply.
 12.  For a "write" access operation, if the "write-default" leaf is
      set to "permit", then permit the data node access request;
      otherwise, deny the request.
 13.  For an "execute" access operation, if the "exec-default" leaf is
      set to "permit", then permit the request; otherwise, deny the
      request.

Bierman & Bjorklund Standards Track [Page 28] RFC 8341 NACM March 2018

3.4.6. Outgoing <notification> Authorization

 Configuration of access control rules specifically for descendant
 nodes of the notification event type are outside the scope of this
 document.  If the user is authorized to receive the notification
 event type, then it is also authorized to receive any data it
 contains.
 If the notification is specified within a data subtree, as specified
 in [RFC7950], then read access to the notification is required.
 Processing continues as described in Section 3.4.5.
 The following figure shows the conceptual message processing model
 for outgoing <notification> messages.
                             NETCONF server
                            +------------+
                            |    XML     |
                            |   message  |
                            | generator  |
                            +------------+
                                  ^
                                  |
                          +----------------+
                          | <notification> |
                          |  generator     |
                          +----------------+
                                  ^
                                  |
                         +=================+
                         | <notification>  |
                         |  access control |
                         |  <eventType>    |
                         +=================+
                                  ^
                                  |
                      +------------------------+
                      | server instrumentation |
                      +------------------------+
                                |     ^
                                V     |
                       +----------------------+
                       |    configuration     |
                       |      datastore       |
                       +----------------------+
                               Figure 4

Bierman & Bjorklund Standards Track [Page 29] RFC 8341 NACM March 2018

 The generation of a notification for a specific subscription
 [RFC5277] is authorized by following these steps:
 1.   If the "enable-nacm" leaf is set to "false", then the
      notification is permitted.
 2.   If the session is identified as a recovery session, then the
      notification is permitted.
 3.   If the notification is the NETCONF <replayComplete> or
      <notificationComplete> event type [RFC5277], then the
      notification is permitted.
 4.   Check all the "group" entries to see if any of them contain a
      "user-name" entry that equals the username for the session
      making the request.  If the "enable-external-groups" leaf is
      "true", add to these groups the set of groups provided by the
      transport layer.
 5.   If no groups are found, continue with step 10.
 6.   Process all rule-list entries, in the order they appear in the
      configuration.  If a rule-list's "group" leaf-list does not
      match any of the user's groups, proceed to the next rule-list
      entry.
 7.   For each rule-list entry found, process all rules, in order,
      until a rule that matches the requested access operation is
      found.  A rule matches if all of the following criteria are met:
  • The rule's "module-name" leaf is "*" or equals the name of

the YANG module where the notification is defined.

  • Either (1) the rule does not have a "rule-type" defined or

(2) the "rule-type" is "notification" and the

         "notification-name" is "*" or equals the name of the
         notification.
  • The rule's "access-operations" leaf has the "read" bit set or

has the special value "*".

 8.   If a matching rule is found, then the "action" leaf is checked.
      If it is equal to "permit", then permit the notification;
      otherwise, drop the notification for the associated
      subscription.
 9.   Otherwise, no matching rule was found in any rule-list entry.

Bierman & Bjorklund Standards Track [Page 30] RFC 8341 NACM March 2018

 10.  If the requested notification is defined in a YANG module
      advertised in the server capabilities and the "notification"
      statement contains a "nacm:default-deny-all" statement, then the
      notification is dropped for the associated subscription.
 11.  If the "read-default" leaf is set to "permit", then permit the
      notification; otherwise, drop the notification for the
      associated subscription.

3.5. Data Model Definitions

3.5.1. Data Organization

 The following diagram highlights the contents and structure of the
 NACM YANG module.
 module: ietf-netconf-acm
   +--rw nacm
      +--rw enable-nacm?              boolean
      +--rw read-default?             action-type
      +--rw write-default?            action-type
      +--rw exec-default?             action-type
      +--rw enable-external-groups?   boolean
      +--ro denied-operations         yang:zero-based-counter32
      +--ro denied-data-writes        yang:zero-based-counter32
      +--ro denied-notifications      yang:zero-based-counter32
      +--rw groups
      |  +--rw group* [name]
      |     +--rw name         group-name-type
      |     +--rw user-name*   user-name-type
      +--rw rule-list* [name]
         +--rw name     string
         +--rw group*   union
         +--rw rule* [name]
            +--rw name                 string
            +--rw module-name?         union
            +--rw (rule-type)?
            |  +--:(protocol-operation)
            |  |  +--rw rpc-name?            union
            |  +--:(notification)
            |  |  +--rw notification-name?   union
            |  +--:(data-node)
            |     +--rw path                 node-instance-identifier
            +--rw access-operations?   union
            +--rw action               action-type
            +--rw comment?             string

Bierman & Bjorklund Standards Track [Page 31] RFC 8341 NACM March 2018

3.5.2. YANG Module

 The following YANG module specifies the normative NETCONF content
 that MUST be supported by the server.
 The "ietf-netconf-acm" YANG module imports typedefs from [RFC6991].
 <CODE BEGINS> file "ietf-netconf-acm@2018-02-14.yang"
 module ietf-netconf-acm {
   namespace "urn:ietf:params:xml:ns:yang:ietf-netconf-acm";
   prefix nacm;
   import ietf-yang-types {
     prefix yang;
   }
   organization
     "IETF NETCONF (Network Configuration) Working Group";
   contact
     "WG Web:   <https://datatracker.ietf.org/wg/netconf/>
      WG List:  <mailto:netconf@ietf.org>
      Author:   Andy Bierman
                <mailto:andy@yumaworks.com>
      Author:   Martin Bjorklund
                <mailto:mbj@tail-f.com>";
   description
     "Network Configuration Access Control Model.
      Copyright (c) 2012 - 2018 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 8341; see
      the RFC itself for full legal notices.";

Bierman & Bjorklund Standards Track [Page 32] RFC 8341 NACM March 2018

   revision "2018-02-14" {
     description
       "Added support for YANG 1.1 actions and notifications tied to
        data nodes.  Clarified how NACM extensions can be used by
        other data models.";
     reference
       "RFC 8341: Network Configuration Access Control Model";
   }
   revision "2012-02-22" {
     description
       "Initial version.";
     reference
       "RFC 6536: Network Configuration Protocol (NETCONF)
                  Access Control Model";
   }
   /*
    * Extension statements
    */
   extension default-deny-write {
     description
       "Used to indicate that the data model node
        represents a sensitive security system parameter.
        If present, the NETCONF server will only allow the designated
        'recovery session' to have write access to the node.  An
        explicit access control rule is required for all other users.
        If the NACM module is used, then it must be enabled (i.e.,
        /nacm/enable-nacm object equals 'true'), or this extension
        is ignored.
        The 'default-deny-write' extension MAY appear within a data
        definition statement.  It is ignored otherwise.";
   }
   extension default-deny-all {
     description
       "Used to indicate that the data model node
        controls a very sensitive security system parameter.
        If present, the NETCONF server will only allow the designated
        'recovery session' to have read, write, or execute access to
        the node.  An explicit access control rule is required for all
        other users.

Bierman & Bjorklund Standards Track [Page 33] RFC 8341 NACM March 2018

        If the NACM module is used, then it must be enabled (i.e.,
        /nacm/enable-nacm object equals 'true'), or this extension
        is ignored.
        The 'default-deny-all' extension MAY appear within a data
        definition statement, 'rpc' statement, or 'notification'
        statement.  It is ignored otherwise.";
   }
   /*
    * Derived types
    */
   typedef user-name-type {
     type string {
       length "1..max";
     }
     description
       "General-purpose username string.";
   }
   typedef matchall-string-type {
     type string {
       pattern '\*';
     }
     description
       "The string containing a single asterisk '*' is used
        to conceptually represent all possible values
        for the particular leaf using this data type.";
   }
   typedef access-operations-type {
     type bits {
       bit create {
         description
           "Any protocol operation that creates a
            new data node.";
       }
       bit read {
         description
           "Any protocol operation or notification that
            returns the value of a data node.";
       }
       bit update {
         description
           "Any protocol operation that alters an existing
            data node.";
       }

Bierman & Bjorklund Standards Track [Page 34] RFC 8341 NACM March 2018

       bit delete {
         description
           "Any protocol operation that removes a data node.";
       }
       bit exec {
         description
           "Execution access to the specified protocol operation.";
       }
     }
     description
       "Access operation.";
   }
   typedef group-name-type {
     type string {
       length "1..max";
       pattern '[^\*].*';
     }
     description
       "Name of administrative group to which
        users can be assigned.";
   }
   typedef action-type {
     type enumeration {
       enum permit {
         description
           "Requested action is permitted.";
       }
       enum deny {
         description
           "Requested action is denied.";
       }
     }
     description
       "Action taken by the server when a particular
        rule matches.";
   }
   typedef node-instance-identifier {
     type yang:xpath1.0;
     description
       "Path expression used to represent a special
        data node, action, or notification instance-identifier
        string.
        A node-instance-identifier value is an
        unrestricted YANG instance-identifier expression.

Bierman & Bjorklund Standards Track [Page 35] RFC 8341 NACM March 2018

        All the same rules as an instance-identifier apply,
        except that predicates for keys are optional.  If a key
        predicate is missing, then the node-instance-identifier
        represents all possible server instances for that key.
        This XML Path Language (XPath) expression is evaluated in the
        following context:
           o  The set of namespace declarations are those in scope on
              the leaf element where this type is used.
           o  The set of variable bindings contains one variable,
              'USER', which contains the name of the user of the
              current session.
           o  The function library is the core function library, but
              note that due to the syntax restrictions of an
              instance-identifier, no functions are allowed.
           o  The context node is the root node in the data tree.
        The accessible tree includes actions and notifications tied
        to data nodes.";
   }
   /*
    * Data definition statements
    */
   container nacm {
     nacm:default-deny-all;
     description
       "Parameters for NETCONF access control model.";
     leaf enable-nacm {
       type boolean;
       default "true";
       description
         "Enables or disables all NETCONF access control
          enforcement.  If 'true', then enforcement
          is enabled.  If 'false', then enforcement
          is disabled.";
     }

Bierman & Bjorklund Standards Track [Page 36] RFC 8341 NACM March 2018

     leaf read-default {
       type action-type;
       default "permit";
       description
         "Controls whether read access is granted if
          no appropriate rule is found for a
          particular read request.";
     }
     leaf write-default {
       type action-type;
       default "deny";
       description
         "Controls whether create, update, or delete access
          is granted if no appropriate rule is found for a
          particular write request.";
     }
     leaf exec-default {
       type action-type;
       default "permit";
       description
         "Controls whether exec access is granted if no appropriate
          rule is found for a particular protocol operation request.";
     }
     leaf enable-external-groups {
       type boolean;
       default "true";
       description
         "Controls whether the server uses the groups reported by the
          NETCONF transport layer when it assigns the user to a set of
          NACM groups.  If this leaf has the value 'false', any group
          names reported by the transport layer are ignored by the
          server.";
     }
     leaf denied-operations {
       type yang:zero-based-counter32;
       config false;
       mandatory true;
       description
         "Number of times since the server last restarted that a
          protocol operation request was denied.";
     }

Bierman & Bjorklund Standards Track [Page 37] RFC 8341 NACM March 2018

     leaf denied-data-writes {
       type yang:zero-based-counter32;
       config false;
       mandatory true;
       description
         "Number of times since the server last restarted that a
          protocol operation request to alter
          a configuration datastore was denied.";
     }
     leaf denied-notifications {
       type yang:zero-based-counter32;
       config false;
       mandatory true;
       description
         "Number of times since the server last restarted that
          a notification was dropped for a subscription because
          access to the event type was denied.";
     }
     container groups {
       description
         "NETCONF access control groups.";
       list group {
         key name;
         description
           "One NACM group entry.  This list will only contain
            configured entries, not any entries learned from
            any transport protocols.";
         leaf name {
           type group-name-type;
           description
             "Group name associated with this entry.";
         }
         leaf-list user-name {
           type user-name-type;
           description
             "Each entry identifies the username of
              a member of the group associated with
              this entry.";
         }
       }
     }

Bierman & Bjorklund Standards Track [Page 38] RFC 8341 NACM March 2018

     list rule-list {
       key name;
       ordered-by user;
       description
         "An ordered collection of access control rules.";
       leaf name {
         type string {
           length "1..max";
         }
         description
           "Arbitrary name assigned to the rule-list.";
       }
       leaf-list group {
         type union {
           type matchall-string-type;
           type group-name-type;
         }
         description
           "List of administrative groups that will be
            assigned the associated access rights
            defined by the 'rule' list.
            The string '*' indicates that all groups apply to the
            entry.";
       }
       list rule {
         key name;
         ordered-by user;
         description
           "One access control rule.
            Rules are processed in user-defined order until a match is
            found.  A rule matches if 'module-name', 'rule-type', and
            'access-operations' match the request.  If a rule
            matches, the 'action' leaf determines whether or not
            access is granted.";
         leaf name {
           type string {
             length "1..max";
           }
           description
             "Arbitrary name assigned to the rule.";
         }

Bierman & Bjorklund Standards Track [Page 39] RFC 8341 NACM March 2018

         leaf module-name {
           type union {
             type matchall-string-type;
             type string;
           }
           default "*";
           description
             "Name of the module associated with this rule.
              This leaf matches if it has the value '*' or if the
              object being accessed is defined in the module with the
              specified module name.";
         }
         choice rule-type {
           description
             "This choice matches if all leafs present in the rule
              match the request.  If no leafs are present, the
              choice matches all requests.";
           case protocol-operation {
             leaf rpc-name {
               type union {
                 type matchall-string-type;
                 type string;
               }
               description
                 "This leaf matches if it has the value '*' or if
                  its value equals the requested protocol operation
                  name.";
             }
           }
           case notification {
             leaf notification-name {
               type union {
                 type matchall-string-type;
                 type string;
               }
               description
                 "This leaf matches if it has the value '*' or if its
                  value equals the requested notification name.";
             }
           }

Bierman & Bjorklund Standards Track [Page 40] RFC 8341 NACM March 2018

           case data-node {
             leaf path {
               type node-instance-identifier;
               mandatory true;
               description
                 "Data node instance-identifier associated with the
                  data node, action, or notification controlled by
                  this rule.
                  Configuration data or state data
                  instance-identifiers start with a top-level
                  data node.  A complete instance-identifier is
                  required for this type of path value.
                  The special value '/' refers to all possible
                  datastore contents.";
             }
           }
         }
         leaf access-operations {
           type union {
             type matchall-string-type;
             type access-operations-type;
           }
           default "*";
           description
             "Access operations associated with this rule.
              This leaf matches if it has the value '*' or if the
              bit corresponding to the requested operation is set.";
         }
         leaf action {
           type action-type;
           mandatory true;
           description
             "The access control action associated with the
              rule.  If a rule has been determined to match a
              particular request, then this object is used
              to determine whether to permit or deny the
              request.";
         }

Bierman & Bjorklund Standards Track [Page 41] RFC 8341 NACM March 2018

         leaf comment {
           type string;
           description
             "A textual description of the access rule.";
         }
       }
     }
   }
 }
 <CODE ENDS>

4. IANA Considerations

 This document reuses the URI for "ietf-netconf-acm" in the "IETF XML
 Registry".
 This document updates the module registration in the "YANG Module
 Names" registry to reference this RFC instead of RFC 6536 for
 "ietf-netconf-acm".  Following the format in [RFC6020], the following
 has been registered.
      Name: ietf-netconf-acm
      Namespace: urn:ietf:params:xml:ns:yang:ietf-netconf-acm
      Prefix: nacm
      Reference: RFC 8341

5. Security Considerations

 The YANG module specified in this document defines a schema for data
 that is designed to be accessed via 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
 [RFC5246].
 The NETCONF access control model [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.
 There is a risk related to the lack of access control enforcement for
 the RESTCONF OPTIONS and PATCH methods.  The risk here is that the
 response to OPTIONS and PATCH may vary based on the presence or
 absence of a resource corresponding to the URL's path.  If this is
 the case, then it can be used to trivially probe for the presence or
 absence of values within a tree.  Therefore, a server MUST NOT vary

Bierman & Bjorklund Standards Track [Page 42] RFC 8341 NACM March 2018

 its responses based on the existence of the underlying resource,
 which would indicate the presence or absence of resource instances.
 In particular, servers should not expose any instance information
 before ensuring that the client has the necessary access permissions
 to obtain that information.  In such cases, servers are expected to
 always return the "access-denied" error response.
 There are a number of data nodes defined in this YANG module that are
 writable/creatable/deletable (i.e., config true, which is the
 default).  These data nodes may be considered sensitive or vulnerable
 in some network environments.  Write operations (e.g., edit-config)
 to these data nodes without proper protection can have a negative
 effect on network operations.  These are the subtrees and data nodes
 and their sensitivity/vulnerability:
 o  /nacm: The entire /nacm subtree is related to security.  Refer to
    the following sections for more details.
 This section highlights the issues for an administrator to consider
 when configuring a NETCONF server with the NACM.

5.1. NACM Configuration and Monitoring Considerations

 Configuration of the access control system is highly sensitive to
 system security.  A server may choose not to allow any user
 configuration to some portions of it, such as the global security
 level or the groups that allowed access to system resources.
 By default, NACM enforcement is enabled.  By default, "read" access
 to all datastore contents is enabled (unless "nacm:default-deny-all"
 is specified for the data definition), and "exec" access is enabled
 for safe protocol operations.  An administrator needs to ensure that
 the NACM is enabled and also decide if the default access parameters
 are set appropriately.  Make sure that the following data nodes are
 properly configured:
 o  /nacm/enable-nacm (default "true")
 o  /nacm/read-default (default "permit")
 o  /nacm/write-default (default "deny")
 o  /nacm/exec-default (default "permit")
 An administrator needs to restrict write access to all configurable
 objects within this data model.

Bierman & Bjorklund Standards Track [Page 43] RFC 8341 NACM March 2018

 If write access is allowed for configuration of access control rules,
 then care needs to be taken not to disrupt the access control
 enforcement.  For example, if the NACM access control rules are
 edited directly within the running configuration datastore (i.e.,
 :writable-running capability is supported and used), then care needs
 to be taken not to allow unintended access while the edits are being
 done.
 An administrator needs to make sure that the translation from a
 transport- or implementation-dependent user identity to a NACM
 username is unique and correct.  This requirement is specified in
 detail in Section 2.2 of [RFC6241].
 An administrator needs to be aware that the YANG data structures
 representing access control rules (/nacm/rule-list and
 /nacm/rule-list/rule) are ordered by the client.  The server will
 evaluate the access control rules according to their relative
 conceptual order within the running configuration datastore.
 Note that the /nacm/groups data structure contains the administrative
 group names used by the server.  These group names may be configured
 locally and/or provided through an external protocol, such as RADIUS
 [RFC2865] [RFC5607].
 An administrator needs to be aware of the security properties of any
 external protocol used by the transport layer to determine group
 names.  For example, if this protocol does not protect against
 man-in-the-middle attacks, an attacker might be able to inject group
 names that are configured in the NACM so that a user gets more
 permissions than it should.  In such cases, the administrator may
 wish to disable the usage of such group names by setting
 /nacm/enable-external-groups to "false".
 Some of the readable data nodes in this YANG module may be considered
 sensitive or vulnerable in some network environments.  It is thus
 important to control read access (e.g., via get, get-config, or
 notification) to these data nodes.  These are the subtrees and data
 nodes and their sensitivity/vulnerability:
 o  /nacm/enable-nacm
 o  /nacm/read-default
 o  /nacm/write-default
 o  /nacm/exec-default
 o  /nacm/enable-external-groups

Bierman & Bjorklund Standards Track [Page 44] RFC 8341 NACM March 2018

 o  /nacm/groups
 o  /nacm/rule-list
 An administrator needs to restrict read access to the above-listed
 objects within this data model, as they reveal access control
 configuration that could be considered sensitive.

5.2. General Configuration Issues

 There is a risk that invocation of non-standard protocol operations
 will have undocumented side effects.  An administrator needs to
 construct access control rules such that the configuration datastore
 is protected from such side effects.
 It is possible for a session with some write access (e.g., allowed to
 invoke <edit-config>), but without any access to a particular
 datastore subtree containing sensitive data, to determine the
 presence or non-presence of that data.  This can be done by
 repeatedly issuing some sort of edit request (create, update, or
 delete) and possibly receiving "access-denied" errors in response.
 These "fishing" attacks can identify the presence or non-presence of
 specific sensitive data even without the "error-path" field being
 present within the <rpc-error> response.
 It may be possible for the set of NETCONF capabilities on the server
 to change over time.  If so, then there is a risk that new protocol
 operations, notifications, and/or datastore content have been added
 to the device.  An administrator needs to be sure that the access
 control rules are correct for the new content in this case.
 Mechanisms to detect NETCONF capability changes on a specific device
 are outside the scope of this document.
 It is possible that the data model definition itself (e.g., a YANG
 when-stmt) will help an unauthorized session determine the presence
 or even value of sensitive data nodes by examining the presence and
 values of different data nodes.
 It is possible that the data model definition itself (e.g., a YANG
 when-stmt or choice-stmt) will allow a session to implicitly create
 or delete nodes that the session does not have write access to as an
 implicit side effect from the processing of an allowed <edit-config>
 operation.

Bierman & Bjorklund Standards Track [Page 45] RFC 8341 NACM March 2018

 There is a risk that non-standard protocol operations, or even the
 standard <get> protocol operation, may return data that "aliases" or
 "copies" sensitive data from a different data object.  There may
 simply be multiple data model definitions that expose or even
 configure the same underlying system instrumentation.
 A data model may contain external keys (e.g., YANG leafref), which
 expose values from a different data structure.  An administrator
 needs to be aware of sensitive data models that contain leafref
 nodes.  This entails finding all the leafref objects that "point" at
 the sensitive data (i.e., "path-stmt" values) that implicitly or
 explicitly includes the sensitive data node.
 It is beyond the scope of this document to define access control
 enforcement procedures for underlying device instrumentation that may
 exist to support the NETCONF server operation.  An administrator can
 identify each protocol operation that the server provides and decide
 if it needs any access control applied to it.
 This document incorporates the optional use of a recovery session
 mechanism, which can be used to bypass access control enforcement in
 emergencies such as NACM configuration errors that disable all access
 to the server.  The configuration and identification of such a
 recovery session mechanism are implementation specific and are
 outside the scope of this document.  An administrator needs to be
 aware of any recovery session mechanisms available on the device and
 make sure that they are used appropriately.
 It is possible for a session to disrupt configuration management,
 even without any write access to the configuration, by locking the
 datastore.  This may be done to ensure that all or part of the
 configuration remains stable while it is being retrieved, or it may
 be done as a "denial-of-service" attack.  There is no way for the
 server to know the difference.  An administrator may wish to restrict
 "exec" access to the following protocol operations:
 o  <lock>
 o  <unlock>
 o  <partial-lock>
 o  <partial-unlock>

Bierman & Bjorklund Standards Track [Page 46] RFC 8341 NACM March 2018

5.3. Data Model Design Considerations

 Designers need to clearly identify any sensitive data, notifications,
 or protocol operations defined within a YANG module.  For such
 definitions, a "nacm:default-deny-write" or "nacm:default-deny-all"
 statement ought to be present, in addition to a clear description of
 the security risks.
 Protocol operations need to be properly documented by the data model
 designer so that it is clear to administrators what data nodes (if
 any) are affected by the protocol operation and what information (if
 any) is returned in the <rpc-reply> message.
 Data models ought to be designed so that different access levels for
 input parameters to protocol operations are not required.  The use of
 generic protocol operations should be avoided, and if different
 access levels are needed, separate protocol operations should be
 defined instead.

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>.
 [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
            (TLS) Protocol Version 1.2", RFC 5246,
            DOI 10.17487/RFC5246, August 2008,
            <https://www.rfc-editor.org/info/rfc5246>.
 [RFC5277]  Chisholm, S. and H. Trevino, "NETCONF Event
            Notifications", RFC 5277, DOI 10.17487/RFC5277, July 2008,
            <https://www.rfc-editor.org/info/rfc5277>.
 [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>.

Bierman & Bjorklund Standards Track [Page 47] RFC 8341 NACM March 2018

 [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>.
 [RFC6991]  Schoenwaelder, J., Ed., "Common YANG Data Types",
            RFC 6991, DOI 10.17487/RFC6991, July 2013,
            <https://www.rfc-editor.org/info/rfc6991>.
 [RFC7230]  Fielding, R., Ed., and J. Reschke, Ed., "Hypertext
            Transfer Protocol (HTTP/1.1): Message Syntax and Routing",
            RFC 7230, DOI 10.17487/RFC7230, June 2014,
            <https://www.rfc-editor.org/info/rfc7230>.
 [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>.
 [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>.
 [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>.
 [RFC8342]  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
            and R. Wilton, "Network Management Datastore Architecture
            (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
            <https://www.rfc-editor.org/info/rfc8342>.
 [W3C.REC-xml-20081126]
            Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and
            F. Yergeau, "Extensible Markup Language (XML) 1.0
            (Fifth Edition)", World Wide Web Consortium Recommendation
            REC-xml-20081126, November 2008,
            <https://www.w3.org/TR/2008/REC-xml-20081126>.

Bierman & Bjorklund Standards Track [Page 48] RFC 8341 NACM March 2018

6.2. Informative References

 [RFC2865]  Rigney, C., Willens, S., Rubens, A., and W. Simpson,
            "Remote Authentication Dial In User Service (RADIUS)",
            RFC 2865, DOI 10.17487/RFC2865, June 2000,
            <https://www.rfc-editor.org/info/rfc2865>.
 [RFC5607]  Nelson, D. and G. Weber, "Remote Authentication Dial-In
            User Service (RADIUS) Authorization for Network Access
            Server (NAS) Management", RFC 5607, DOI 10.17487/RFC5607,
            July 2009, <https://www.rfc-editor.org/info/rfc5607>.
 [YANG-SEC] IETF, "YANG Security Guidelines", <https://trac.ietf.org/
            trac/ops/wiki/yang-security-guidelines>.

Bierman & Bjorklund Standards Track [Page 49] RFC 8341 NACM March 2018

Appendix A. Usage Examples

 The following XML [W3C.REC-xml-20081126] snippets are provided as
 examples only, to demonstrate how the NACM can be configured to
 perform some access control tasks.

A.1. <groups> Example

 There needs to be at least one <group> entry in order for any of the
 access control rules to be useful.
 The following XML shows arbitrary groups and is not intended to
 represent any particular use case.
 <nacm xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-acm">
   <groups>
     <group>
       <name>admin</name>
       <user-name>admin</user-name>
       <user-name>andy</user-name>
     </group>
     <group>
       <name>limited</name>
       <user-name>wilma</user-name>
       <user-name>bam-bam</user-name>
     </group>
     <group>
       <name>guest</name>
       <user-name>guest</user-name>
       <user-name>guest@example.com</user-name>
     </group>
   </groups>
 </nacm>
 This example shows three groups:
 admin:  The "admin" group contains two users named "admin" and
    "andy".
 limited:  The "limited" group contains two users named "wilma" and
    "bam-bam".
 guest:  The "guest" group contains two users named "guest" and
    "guest@example.com".

Bierman & Bjorklund Standards Track [Page 50] RFC 8341 NACM March 2018

A.2. Module Rule Example

 Module rules are used to control access to all the content defined in
 a specific module.  A module rule has the "module-name" leaf set but
 no nodes from the "rule-type" choice set.
 <nacm xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-acm">
   <rule-list>
     <name>guest-acl</name>
     <group>guest</group>
     <rule>
       <name>deny-ncm</name>
       <module-name>ietf-netconf-monitoring</module-name>
       <access-operations>*</access-operations>
       <action>deny</action>
       <comment>
           Do not allow guests any access to the NETCONF
           monitoring information.
       </comment>
     </rule>
   </rule-list>
   <rule-list>
     <name>limited-acl</name>
     <group>limited</group>
     <rule>
       <name>permit-ncm</name>
       <module-name>ietf-netconf-monitoring</module-name>
       <access-operations>read</access-operations>
       <action>permit</action>
       <comment>
           Allow read access to the NETCONF
           monitoring information.
       </comment>
     </rule>
     <rule>
       <name>permit-exec</name>
       <module-name>*</module-name>
       <access-operations>exec</access-operations>
       <action>permit</action>
       <comment>
           Allow invocation of the
           supported server operations.
       </comment>
     </rule>
   </rule-list>

Bierman & Bjorklund Standards Track [Page 51] RFC 8341 NACM March 2018

   <rule-list>
     <name>admin-acl</name>
     <group>admin</group>
     <rule>
       <name>permit-all</name>
       <module-name>*</module-name>
       <access-operations>*</access-operations>
       <action>permit</action>
       <comment>
           Allow the 'admin' group complete access to all
           operations and data.
       </comment>
     </rule>
   </rule-list>
 </nacm>
 This example shows four module rules:
 deny-ncm:  This rule prevents the "guest" group from reading any
    monitoring information in the "ietf-netconf-monitoring" YANG
    module.
 permit-ncm:  This rule allows the "limited" group to read the
    "ietf-netconf-monitoring" YANG module.
 permit-exec:  This rule allows the "limited" group to invoke any
    protocol operation supported by the server.
 permit-all:  This rule allows the "admin" group complete access to
    all content in the server.  No subsequent rule will match for the
    "admin" group because of this module rule.

Bierman & Bjorklund Standards Track [Page 52] RFC 8341 NACM March 2018

A.3. Protocol Operation Rule Example

 Protocol operation rules are used to control access to a specific
 protocol operation.
 <nacm xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-acm">
   <rule-list>
     <name>guest-limited-acl</name>
     <group>limited</group>
     <group>guest</group>
     <rule>
       <name>deny-kill-session</name>
       <module-name>ietf-netconf</module-name>
       <rpc-name>kill-session</rpc-name>
       <access-operations>exec</access-operations>
       <action>deny</action>
       <comment>
         Do not allow the 'limited' group or the 'guest' group
         to kill another session.
       </comment>
     </rule>
     <rule>
       <name>deny-delete-config</name>
       <module-name>ietf-netconf</module-name>
       <rpc-name>delete-config</rpc-name>
       <access-operations>exec</access-operations>
       <action>deny</action>
       <comment>
         Do not allow the 'limited' group or the 'guest' group
         to delete any configurations.
       </comment>
     </rule>
   </rule-list>

Bierman & Bjorklund Standards Track [Page 53] RFC 8341 NACM March 2018

   <rule-list>
     <name>limited-acl</name>
     <group>limited</group>
     <rule>
       <name>permit-edit-config</name>
       <module-name>ietf-netconf</module-name>
       <rpc-name>edit-config</rpc-name>
       <access-operations>exec</access-operations>
       <action>permit</action>
       <comment>
         Allow the 'limited' group to edit the configuration.
       </comment>
     </rule>
   </rule-list>
 </nacm>
 This example shows three protocol operation rules:
 deny-kill-session:  This rule prevents the "limited" group or the
    "guest" group from invoking the NETCONF <kill-session> protocol
    operation.
 deny-delete-config:  This rule prevents the "limited" group or the
    "guest" group from invoking the NETCONF <delete-config> protocol
    operation.
 permit-edit-config:  This rule allows the "limited" group to invoke
    the NETCONF <edit-config> protocol operation.  This rule will have
    no real effect unless the "exec-default" leaf is set to "deny".

Bierman & Bjorklund Standards Track [Page 54] RFC 8341 NACM March 2018

A.4. Data Node Rule Example

 Data node rules are used to control access to specific (config and
 non-config) data nodes within the NETCONF content provided by the
 server.
 <nacm xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-acm">
   <rule-list>
     <name>guest-acl</name>
     <group>guest</group>
     <rule>
       <name>deny-nacm</name>
       <path xmlns:n="urn:ietf:params:xml:ns:yang:ietf-netconf-acm">
         /n:nacm
       </path>
       <access-operations>*</access-operations>
       <action>deny</action>
       <comment>
         Deny the 'guest' group any access to the /nacm data.
       </comment>
     </rule>
   </rule-list>
   <rule-list>
     <name>limited-acl</name>
     <group>limited</group>
     <rule>
       <name>permit-acme-config</name>
       <path xmlns:acme="http://example.com/ns/netconf">
         /acme:acme-netconf/acme:config-parameters
       </path>
       <access-operations>
         read create update delete
       </access-operations>
       <action>permit</action>
       <comment>
         Allow the 'limited' group complete access to the acme
         NETCONF configuration parameters.  Showing long form
         of 'access-operations' instead of shorthand.
       </comment>
     </rule>
   </rule-list>

Bierman & Bjorklund Standards Track [Page 55] RFC 8341 NACM March 2018

   <rule-list>
     <name>guest-limited-acl</name>
     <group>guest</group>
     <group>limited</group>
     <rule>
       <name>permit-dummy-interface</name>
       <path xmlns:acme="http://example.com/ns/itf">
         /acme:interfaces/acme:interface[acme:name='dummy']
       </path>
       <access-operations>read update</access-operations>
       <action>permit</action>
       <comment>
         Allow the 'limited' and 'guest' groups read
         and update access to the dummy interface.
       </comment>
     </rule>
   </rule-list>
   <rule-list>
     <name>admin-acl</name>
     <group>admin</group>
     <rule>
       <name>permit-interface</name>
       <path xmlns:acme="http://example.com/ns/itf">
         /acme:interfaces/acme:interface
       </path>
       <access-operations>*</access-operations>
       <action>permit</action>
       <comment>
         Allow the 'admin' group full access to all acme interfaces.
       </comment>
     </rule>
   </rule-list>
 </nacm>

Bierman & Bjorklund Standards Track [Page 56] RFC 8341 NACM March 2018

 This example shows four data node rules:
 deny-nacm:  This rule denies the "guest" group any access to the
    /nacm subtree.
 permit-acme-config:  This rule gives the "limited" group read-write
    access to the acme <config-parameters>.
 permit-dummy-interface:  This rule gives the "limited" and "guest"
    groups read-update access to the acme <interface> entry named
    "dummy".  This entry cannot be created or deleted by these groups;
    it can only be altered.
 permit-interface:  This rule gives the "admin" group read-write
    access to all acme <interface> entries.

A.5. Notification Rule Example

 Notification rules are used to control access to a specific
 notification event type.
 <nacm xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-acm">
   <rule-list>
     <name>sys-acl</name>
     <group>limited</group>
     <group>guest</group>
     <rule>
       <name>deny-config-change</name>
       <module-name>acme-system</module-name>
       <notification-name>sys-config-change</notification-name>
       <access-operations>read</access-operations>
       <action>deny</action>
       <comment>
         Do not allow the 'guest' group or the 'limited' group
         to receive config change events.
       </comment>
     </rule>
   </rule-list>
 </nacm>
 This example shows one notification rule:
 deny-config-change:  This rule prevents the "limited" group or the
    "guest" group from receiving the acme <sys-config-change>
    event type.

Bierman & Bjorklund Standards Track [Page 57] RFC 8341 NACM March 2018

Authors' Addresses

 Andy Bierman
 YumaWorks
 685 Cochran St.
 Suite #160
 Simi Valley, CA  93065
 United States of America
 Email: andy@yumaworks.com
 Martin Bjorklund
 Tail-f Systems
 Email: mbj@tail-f.com

Bierman & Bjorklund Standards Track [Page 58]

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