Internet Engineering Task Force                               A. Bierman
Internet-Draft                                                   Brocade
Intended status: Standards Track                            M. Bjorklund
Expires: December 16, 2011 April 6, 2012                                    Tail-f Systems
                                                           June 14,
                                                         October 4, 2011

     Network Configuration Protocol (NETCONF) Access Control Model
                  draft-ietf-netconf-access-control-04
                  draft-ietf-netconf-access-control-05

Abstract

   The standardization of network configuration interfaces for use with
   the NETCONF 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 protocol access for particular users to a pre-
   configured subset of all available NETCONF protocol operations and
   content.  This document discusses requirements for a suitable defines such an access control
   model, and provides one solution that meets these requirements. model.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 16, 2011. April 6, 2012.

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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  4
       1.1.1.  Requirements Notation  . . . .
   2.  Access Control Design Objectives . . . . . . . . . . . .  4
       1.1.2.  NETCONF Terms . . .  6
     2.1.  Access Control Points  . . . . . . . . . . . . . . . . .  4
       1.1.3.  YANG Terms .  6
     2.2.  Simplicity . . . . . . . . . . . . . . . . . . . . .  5
       1.1.4.  NACM Terms . . .  7
     2.3.  Procedural Interface . . . . . . . . . . . . . . . . . . .  5
   2.  7
     2.4.  Datastore Access Control Design Objectives . . . . . . . . . . . . . . .  6
     2.1.  Protocol Control Points . . . . . .  7
     2.5.  Users and Groups . . . . . . . . . . . .  6
     2.2.  Simplicity . . . . . . . . .  7
     2.6.  Maintenance  . . . . . . . . . . . . . . .  7
     2.3.  Procedural Interface . . . . . . . .  8
     2.7.  Configuration Capabilities . . . . . . . . . . .  7
     2.4.  Datastore Access . . . . .  8
     2.8.  Identifying Security-Sensitive Content . . . . . . . . . .  8
   3.  NETCONF Access Control Model (NACM)  . . . . . .  8
       2.4.1.  Access Rights . . . . . . . 10
     3.1.  Introduction . . . . . . . . . . . . .  8
       2.4.2.  <get> and <get-config> Operations . . . . . . . . . .  8
       2.4.3.  <edit-config> Operation 10
       3.1.1.  Features . . . . . . . . . . . . . . .  9
       2.4.4.  <copy-config> Operation . . . . . . . . 10
       3.1.2.  External Dependencies  . . . . . . . 10
     2.5.  Users and Groups . . . . . . . . . 11
       3.1.3.  Message Processing Model . . . . . . . . . . . . 10
     2.6.  Maintenance . . . 11
     3.2.  Datastore Access . . . . . . . . . . . . . . . . . . . . 11
     2.7.  Configuration Capabilities . 13
       3.2.1.  Access Rights  . . . . . . . . . . . . . . . 11
     2.8.  Identifying Security Holes . . . . . 13
       3.2.2.  <get> and <get-config> Operations  . . . . . . . . . . 14
       3.2.3.  <edit-config> Operation  . 11
     2.9.  Data Shadowing . . . . . . . . . . . . . . 14
       3.2.4.  <copy-config> Operation  . . . . . . . . 12
     2.10. NETCONF Specific Requirements . . . . . . . 15
       3.2.5.  <delete-config> Operation  . . . . . . . 12
   3.  NETCONF Access Control Model (NACM) . . . . . . . 16
       3.2.6.  <commit> Operation . . . . . . 14
     3.1.  Introduction . . . . . . . . . . . . 16
       3.2.7.  <discard-changes> Operation  . . . . . . . . . . . 14
       3.1.1.  Features . . 16
       3.2.8.  <kill-session> Operation . . . . . . . . . . . . . . . 16
     3.3.  Model Components . . . . . . 14
       3.1.2.  External Dependencies . . . . . . . . . . . . . . . 16
       3.3.1.  Users  . 15
       3.1.3.  Message Processing Model . . . . . . . . . . . . . . . 15
     3.2.  Model Components . . . . . . . . 16
       3.3.2.  Groups . . . . . . . . . . . . . 17
       3.2.1.  Users . . . . . . . . . . . 17
       3.3.3.  Global Enforcement Controls  . . . . . . . . . . . . . 17
       3.2.2.  Groups .
         3.3.3.1.  enable-nacm Switch . . . . . . . . . . . . . . . . 17
         3.3.3.2.  read-default Switch  . . . . . . . 17
       3.2.3.  Sessions . . . . . . . . 17
         3.3.3.3.  write-default Switch . . . . . . . . . . . . . . . 18
       3.2.4.  Access Permissions . . .
         3.3.3.4.  exec-default Switch  . . . . . . . . . . . . . . . 18
       3.2.5.  Global Enforcement Controls
       3.3.4.  Access Control Rules . . . . . . . . . . . . . 18
         3.2.5.1.  enable-nacm Switch . . . . 18
     3.4.  Access Control Enforcement Procedures  . . . . . . . . . . 19
       3.4.1.  Initial Operation  . . 18
         3.2.5.2.  read-default Switch . . . . . . . . . . . . . . . 19
         3.2.5.3.  write-default Switch . . 19
       3.4.2.  Session Establishment  . . . . . . . . . . . . . 19
         3.2.5.4.  exec-default Switch . . . 19
       3.4.3.  "access-denied" Error Handling . . . . . . . . . . . . 19
       3.2.6.  Access Control Rules . . . . . .
       3.4.4.  Incoming RPC Message Validation  . . . . . . . . . . . 20
     3.3.
       3.4.5.  Data Node Access Control Enforcement Procedures  . . . . . . . . . . 20
       3.3.1.  Initial Operation  . . . . . . . . . . . . . . . . . . 20
       3.3.2.  Session Establishment Validation  . . . . . . . . . . . . . 22
       3.4.6.  Outgoing <notification> Authorization  . . . 21
       3.3.3.  "access-denied" Error Handling . . . . . 24

     3.5.  Data Model Definitions . . . . . . . 21
       3.3.4.  Incoming RPC Message Validation . . . . . . . . . . . 21
       3.3.5. 26
       3.5.1.  Data Node Access Validation  . . . Organization  . . . . . . . . . . 24
       3.3.6.  Outgoing <notification> Authorization . . . . . . . . 26
     3.4.  Data Model Definitions 27
       3.5.2.  YANG Module  . . . . . . . . . . . . . . . . . . 28
       3.4.1.  Data Organization . . . 27
     3.6.  IANA Considerations  . . . . . . . . . . . . . . . 28
       3.4.2.  YANG Module . . . . 37
     3.7.  Security Considerations  . . . . . . . . . . . . . . . . . 29
     3.5.  IANA 37
       3.7.1.  NACM Configuration and Monitoring Considerations . . . 37
       3.7.2.  General Configuration Issues . . . . . . . . . . . . . . . . 38
     3.6.  Security 39
       3.7.3.  Data Model Design Considerations . . . . . . . . . . . . . . . . . 39 40
   4.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 41
     4.1.  Normative References . . . . . . . . . . . . . . . . . . . 41
     4.2.  Informative References . . . . . . . . . . . . . . . . . . 41
   Appendix A.  Usage Examples  . . . . . . . . . . . . . . . . . . . 42
     A.1.  <groups> Example . . . . . . . . . . . . . . . . . . . . . 42
     A.2.  Module Rule Example  . . . . . . . . . . . . . . . . . . . 43
     A.3.  RPC Rule Example . . . . . . . . . . . . . . . . . . . . . 44
     A.4.  Data Rule Example  . . . . . . . . . . . . . . . . . . . . 46
     A.5.  Notification Rule Example  . . . . . . . . . . . . . . . . 48
   Appendix B.  Change Log  . . . . . . . . . . . . . . . . . . . . . 50
     B.1.  03-04  04-05  . . . . . . . . . . . . . . . . . . . . . . . . . . 50
     B.2.  02-03  03-04  . . . . . . . . . . . . . . . . . . . . . . . . . . 50
     B.3.  01-02  02-03  . . . . . . . . . . . . . . . . . . . . . . . . . . 50
     B.4.  00-01  01-02  . . . . . . . . . . . . . . . . . . . . . . . . . . 50 51
     B.5.  00-01  . . . . . . . . . . . . . . . . . . . . . . . . . . 51
     B.6.  00 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 52

1.  Introduction

   The NETCONF protocol does not provide any standard mechanisms to
   restrict the protocol operations and content that each user is
   authorized to
   use. access.

   There is a need for inter-operable management of the controlled
   access to operator administrator selected portions of the available NETCONF
   content within a particular server.

   This document addresses access control mechanisms for the Operation
   and Content layers of NETCONF, as defined in
   [I-D.ietf-netconf-4741bis], and [RFC5277]. [RFC6241].  It contains
   three main sections:

   1.  Access Control Design Objectives

   2.  NETCONF Access Control Model (NACM)

   3.  YANG Data Model (ietf-netconf-acm.yang)

1.1.  Terminology

1.1.1.  Requirements Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

1.1.2.  NETCONF Terms

   The following terms are defined in [I-D.ietf-netconf-4741bis] [RFC6241] and are not redefined
   here:

   o  client

   o  datastore

   o  operation

   o  protocol operation

   o  server

   o  session

   o  user

1.1.3.  YANG Terms

   The following terms are defined in [RFC6020] and are not redefined
   here:

   o  data node

   o  data definition statement

1.1.4.  NACM Terms
   The following terms are used throughout this documentation:

   access control:  A security feature provided by the NETCONF server,
      that allows an operator administrator to restrict access to a subset of all
      NETCONF 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 operator administrator
      to enforce a particular access control policy.

   access control rule:  The conceptual criteria used to determine if a particular
      NETCONF protocol operation will be permitted or denied.

   access operation:  How a request attempts to access a conceptual
      object.  One of "none", "read", "create", "delete", "update", and
      "execute".

   recovery session:  A special administrative session that is given
      unlimited NETCONF access, and is exempt from all access control
      enforcement.  The specific mechanism(s) used by an implementation a server to control and
      identify whether a session is a recovery session or not are
      implementation-specific and outside the scope of this document.

   write access:  A shorthand for the "create", "delete", and "update"
      access operations.

2.  Access Control Design Objectives

   [Editor's note: some things described here are requirements (MUST,
   SHOULD, etc), but some things are descriptions how NACM works, e.g.
   2.4.1, 2.4.3...]

   This section documents the design objectives for the NETCONF Access
   Control Model presented in Section 3.

2.1.  Protocol  Access Control Points

   The

   NETCONF protocol allows new protocol operations to be added at any time, and
   the YANG data modeling language supports this feature.  It is not
   possible to design an ACM for NETCONF which that only focuses on a static
   set of protocol operations, 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 several three
   conceptual control points.

                 +-------------+                 +-------------+
    client       |  protocol   |                 |   prune  data node  |      client
    request -->  |  operation  | ------------->  | restricted   access    | ---> reply
                 |  allowed?   |   datastore     | <rpc-reply>  allowed?   |
                 +-------------+          |   nodes?    |
                       |   or state      +-------------+
                                   data access

                 +----------------+
                 | if any datastore or
                       | state data is accessed
                       | by the operation
                       V
                 +-------------+          +----------------+
                 |  data node  |          |   prune        |
                 |   access    |          | restricted  notification  |
    event -->    |  allowed?      |          | <notification> | ---> client
                 +-------------+          | event or data? |     session
                 +----------------+

                                 Figure 1

   The following access control points points, described in Figure 1, are defined:
   identified:

   protocol operation:  Configurable permission  Permission to invoke specific protocol operations is required.  Wildcard or multiple target
      mechanisms to reduce configuration and effort are also required.

   NETCONF
      operations.

   datastore:  Configurable permission  Permission to read and/or alter specific data nodes
      within any conceptual datastore is required.
      Wildcard or multiple target mechanisms to reduce configuration and
      effort are also required.

   RPC Reply Content:  Configurable permission to read specific data
      nodes within any conceptual RPC output section is required.
      Unauthorized data is silently omitted from the reply, instead of
      dropping the reply or sending an "access-denied" error.

   Notification Content:  Configurable permission datastore.

   notification:  Permission to receive specific notification event types is required.
      types.

2.2.  Simplicity

   Experience has shown that a complicated ACM will not be widely
   deployed, because it is too hard to use.  The key factor that is
   ignored in such solutions is the concept of "localized cost".  It
   needs to be easy to do simple things, and possible to do complex
   things, instead of hard to do everything.

   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, which may require
   additional expertise.

   A single set of access control rules SHOULD ought to be able to control all
   types of NETCONF protocol operation invocation, all conceptual datastore access,
   and all NETCONF session output. notification events.

   Access control SHOULD ought to be defined with a small and familiar set of
   permissions, while still allowing full control of NETCONF datastore
   access.

   Access control does not need to be applied to NETCONF <hello>
   messages.

2.3.  Procedural Interface

   The NETCONF protocol uses a procedural interface remote procedure call model, and an
   extensible set of protocol operations.  Access control for any
   possible protocol operation is required.

   It MUST be possible to configure the ACM to permit or deny access to
   specific NETCONF operations.

   YANG modules SHOULD be designed so that different access levels for
   input parameters to protocol operations is not required.  Use of
   generic operations should be avoided, and separate operations defined
   instead, if different access levels are needed. necessary.

2.4.  Datastore Access

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

   The same

2.5.  Users and Groups

   It is necessary that access control rules apply to all conceptual datastores.
   For example, the candidate configuration for a single user or a
   configurable group of users can be configured.

   The ACM needs to support the running
   configuration.

   Only concept of administrative groups, to
   support the standard NETCONF datastores (candidate, running, and
   startup) are controlled well-established distinction between a root account and
   other types of less-privileged conceptual user accounts.  These
   groups needs to be configurable by the ACM.  Local or remote files or
   datastores accessed via administrator.

   It is necessary that the <url> parameter are optional user-to-group mapping can be delegated to support.

   The non-volatile startup configuration a
   central server, such as a RADIUS server [RFC2865] [RFC5607].  Since
   authentication is performed by the NETCONF transport layer, and
   RADIUS performs authentication and service authorization at the same
   time, the underlying NETCONF transport needs to be loaded at boot-
   time into able to report a
   set of group names associated with the running configuration user to the server.

2.6.  Maintenance

   It ought to be possible to disable part or all of the access control
   model without applying deleting any access control rules.  Access control is applied after the server has
   booted,

2.7.  Configuration Capabilities

   Suitable configuration and user sessions monitoring mechanisms are active.

2.4.1.  Access Rights

   A small set of hard-wired datastore access rights is needed to
   control access allow
   an administrator to easily manage all possible NETCONF datastore operations,
   including vendor extensions to aspects of the ACM behavior.  A
   standard operation set.

   The familiar "CRUDX" model can support all NETCONF operations:

   o  Create: Allows data model, suitable for use with the client <edit-config> protocol
   operation needs to add a new data node instance be available for this purpose.

   Access control rules to a
      datastore.

   o  Read: Allows restrict access operations on specific
   subtrees within the client configuration datastore needs to read a data node instance from a
      datastore, or receive be supported.

2.8.  Identifying Security-Sensitive Content

   One of the notification event type.

   o  Update: Allows most important aspects of 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 model documentation,
   and biggest concerns during deployment, is the client identification of
   security-sensitive content.  This applies to execute the protocol operation.

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

   Data nodes to which the client does operations in
   NETCONF, not have read access, either
   directly or via wildcard access, are silently omitted from the <rpc-
   reply> message.  This just data and notifications.

   It is done to allow NETCONF filters mandatory for <get> and
   <get-config> security-sensitive objects to function properly, instead be documented in
   the Security Considerations section 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 RFC.  This is applied to the subset of nodes
   that the client nice, but it
   is authorized to read, not good enough, for the entire datastore.

2.4.3.  <edit-config> Operation

   The NACM access rights are not directly coupled following reasons:

   o  This documentation-only approach forces administrators to study
      the <edit-config>
   "operation" attribute, although they RFC and determine if there are similar.  Instead, any potential security risks
      introduced by a NACM
   access right applies new data model.

   o  If any security risks are identified, then the administrator can
      study some more RFC text, and determine how to all operations which would result in a
   particular access operation mitigate the
      security risk(s).

   o  The ACM on each server can be configured to mitigate the target datastore.  This section
   describes how these security
      risks, e.g., require privileged access rights apply to read or write the
      specific datastore
   operations supported by data identified in the <edit-config> operation. Security Considerations section.

   o  If the effective operation ACM is "none" (i.e., default-operation="none")
   for a particular data node, not pre-configured, then no access control is applied to that
   data node.

   A "create", "merge", or "replace" operation on there will be a datastore node which
   would result in the creation time window
      of a vulnerability, after the new data node instance, for which
   the user does not have "create" access permission, model is rejected with
   an "access-denied" error.

   A "merge" or "replace" operation on a datastore node which would
   result in loaded, and before
      the modification of an existing data node instance, new access control rules for
   which that data model are configured,
      enabled, and debugged.

   Often, the user does not have "update" administrator just wants to disable default access permission, is rejected
   with an "access-denied" error.

   A "replace", "delete", to the
   secure content, so no inadvertent or "remove" operation on a datastore node
   which would result in malicious changes can be made to
   the deletion of an existing data node instance,
   for which server.  This allows the user does not have "delete" access permission, is
   rejected with an "access-denied" error. default rules to be more lenient,
   without significantly increasing the security risk.

   A "merge" operation may include data nodes model designer needs to be able to use machine-readable
   statements to identify NETCONF content which do not alter
   portions of the existing datastore.  For example, a container or list
   node may needs to be present for naming purposes, but does not actually alter
   the corresponding datastore node.  These unaltered data nodes within
   the scope of a "merge" operation are ignored protected by the server,
   default.  This will allow client and do
   not require any access rights server tools to automatically
   identify data-model specific security risks, by denying access to
   sensitive data unless the client.

   [Editor's note: ditto for "replace" (and copy-config...)  Note that
   with this rule, user is explicitly authorized to perform
   the requested access operation.

3.  NETCONF Access Control Model (NACM)

3.1.  Introduction

   This section provides a client w/o read high-level overview of the access can guess db content by
   sending merge requests - if access-denied is not returned, it means control
   model structure.  It describes the db has that value.]

   A "merge" operation may include data nodes, but not include
   particular child data nodes that are present in NETCONF protocol message
   processing model, and the datastore.  These
   missing data nodes conceptual access control requirements
   within that model.

3.1.1.  Features

   The NACM data model provides the scope following features:

   o  Independent control of a "merge" operation are
   ignored by the server, RPC, data, and do not require any notification access.

   o  Simple access rights by the
   client. control rules configuration data model that is easy
      to use.

   o  The contents concept of an emergency recovery session is supported, but
      configuration of specific restricted datastore nodes MUST NOT be
   exposed in any <rpc-error> elements within the reply.

2.4.4.  <copy-config> Operation

   Access control server for the <copy-config> operation requires special
   consideration because the operator this purpose is replacing beyond the entire target
   datastore.  Read scope
      of this document.  An emergency recovery session will bypass all
      access control enforcement, in order to the entire source datastore, and write
   access allow it to initialize or
      repair the entire target NACM configuration.

   o  A simple and familiar set of datastore permissions is needed used.

   o  Support for this operation YANG security tagging (e.g., "nacm:default-deny-write"
      statement) allows default security modes to
   succeed.

   The server SHOULD determine the exact nodes in the target datastore
   which are actually different, and only check write automatically exclude
      sensitive data.

   o  Separate default access permissions modes for this set read, write, and execute
      permissions.

   o  Access control rules are applied to configurable groups of nodes, which could be empty.  For example, if a
   session can read the users.

   o  The entire datastore, but only change one leaf, that
   session SHOULD ACM can be able disabled during operation, in order to edit and save that one leaf.  E.g., the
   <copy-config> operation from <running> debug
      operational problems.

   o  Access control rules are simple to <startup> SHOULD succeed if configure.

   o  The number of denied protocol operation requests and denied
      datastore write requests can be monitored by the only effective changes client.

   o  Simple unconstrained YANG instance identifiers are used to
      configure access control rules for specific data nodes that session nodes.

3.1.2.  External Dependencies

   The NETCONF [RFC6241] protocol is
   authorized to change.

   A client MUST have access to every datastore node, even ones used for all management purposes
   within this document.  It is expected that are
   not present in the source configuration data.

   For example, consider a common use-case such as a simple backup and
   restore procedure.  The operator (client) MUST have full read access
   to the datastore in order to receive a complete copy of its contents.
   If the server simply omits these subtrees from mandatory transport
   mapping NETCONF Over SSH [RFC6242] is also supported by the reply, server,
   and that
   copy is later used to restore the server datastore, the server will
   interpret the missing nodes as a request has access to delete those nodes, and
   return an error.

2.5.  Users and Groups

   The server MUST obtain a the user name from associated with each
   session.

   The YANG Data Modeling Language [RFC6020] is used to define the underlying
   NETCONF
   transport, such as an SSH user name.

   It MUST be possible to specify access control rules for a single user
   or a configurable group of users. data models specified in this document.

3.1.3.  Message Processing Model

   The ACM MUST support the concept of administrative groups, to support following diagram shows the well-established distinction between a root account and other
   types of less-privileged conceptual user accounts.  These groups MUST
   be configurable by the operator.

   It MUST be possible to delegate the user-to-group mapping to a
   central server, such as a RADIUS server [RFC2865] [RFC5607].  Since
   authentication is performed by message flow model,
   including the NETCONF transport layer, and
   RADIUS performs authentication and service authorization points at the same
   time, it MUST be possible for the underlying NETCONF transport to
   report a set of group names associated with the user to the server.

2.6.  Maintenance

   It SHOULD be possible to disable part or all of the which access control
   model without deleting any configuration.

2.7.  Configuration Capabilities

   Suitable control and monitoring mechanisms are needed to allow an
   operator to easily manage all aspects of the ACM behavior.  A
   standard data model, suitable for use with the <edit-config>
   operation MUST be available for this purpose.

   Access control rules to restrict operations on specific subtrees
   within the configuration datastore MUST be supported.  Existing
   mechanisms can be used to identify the subtree(s) for this purpose.

2.8.  Identifying Security Holes

   One of the most important aspects of the data model documentation,
   and biggest concerns during deployment, is the identification of
   security-sensitive content.  This applies to operations in NETCONF,
   not just applied, during
   NETCONF message processing.

                    +-------------------------+
                    |       session           |
                    |      (username)         |
                    +-------------------------+
                       |                 ^
                       V                 |
             +--------------+     +---------------+
             |   message    |     |   message     |
             | dispatcher   |     |   generator   |
             +--------------+     +---------------+
                  |                  ^         ^
                  V                  |         |
         +===========+     +-------------+   +----------------+
         |   <rpc>   |---> | <rpc-reply> |   | <notification> |
         | acc. ctl  |     |  generator  |   |  generator     |
         +===========+     +-------------+   +----------------+
               |              ^    ^                ^
               V       +------+    |                |
         +-----------+ |   +=============+  +================+
         |   <rpc>   | |   |    read     |  | <notification> |
         | processor |-+   | 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 operators to study the RFC
      and determine if there are any potential security holes introduced
      by a new YANG module.

   o  If any security holes are identified, then the operator can study
      some more RFC text, and determine how to close the security
      hole(s).

   o  The ACM on each server can be configured to close the security
      holes, e.g., require privileged node   |  |  access to read or ctl    |
         |           |     | acc. ctl    |  |                |
         +-----------+     +=============+  +================+
               |   |                  ^        ^
               V   +----------------+ |        |
         +===========+              | |        |
         |  write the
      specific    |              | |        |
         | data identified in the Security Considerations section.

   o  If the ACM is not pre-configured, then there will be a time window node |              | |        |
         | acc. ctl  | -----------+ | |        |
         +===========+            | | |        |
               |                  | | |        |
               V                  V V |        |
         +---------------+      +-----------------+
         | configuration | ---> |     server      |
         |   datastore   |      | instrumentation |
         |               | <--- |                 |
         +---------------+      +-----------------+

                                 Figure 2

   The following high-level sequence of vulnerability, after the new module conceptual processing steps is loaded, and before the
      new access control rules
   executed for that module are configured, enabled,
      and debugged.

   Often, the operator just wants to disable default each received <rpc> message, if access control
   enforcement is enabled:

   o  Access control is applied to the
   secure content, so 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.

   A data model designer needs to be able to use machine-readable
   statements to identify NETCONF content which needs to be protected by
   default.  This will allow client and server tools to automatically
   close data-model specific security holes, all <rpc> messages (except <close-
      session>) received by denying access to
   sensitive data the server, individually, for each active
      session, unless the session is identified as a "recovery session".

   o  If the user is explicitly authorized to perform execute the requested operation.

2.9.  Data Shadowing

   One of specified protocol
      operation, then processing continues, otherwise the more complicated security administration problems request is
   identifying data nodes which shadow or mirror the content of another
   data node.  An access control rule to prevent read operations for a
   particular node may be insufficient to prevent access to the data
   node
      rejected with the copied value. an "access-denied" error.

   o  If the description statement, other documentation, configuration datastore or no
   documentation exists to identify a conceptual state data shadow problem, then it may
   not be detected.

   Since NETCONF allows any vendor operation to is
      accessed by the protocol operation, then the data node access MUST
      be added to authorized.  If the
   protocol, there user is no way authorized to reliably identify all of perform the operations
   that may expose copies of sensitive data nodes in <rpc-reply>
   messages.

   A NETCONF server MUST ensure that unauthorized requested
      access to its
   conceptual datastores and non-configuration data nodes is prevented.

   It is beyond operation on the scope requested data, then processing continues.

   The following sequence of this document to define conceptual processing steps is executed for
   each generated notification event, if access control enforcement procedures for underlying device is
   enabled:

   o  Server instrumentation that may
   exist to support the NETCONF server operation.  An operator can
   identify each operation that generates a notification, for a particular
      subscription.

   o  The notification access control enforcer checks the server provides, notification
      event type, and decide if it
   needs any access control applied is one which the user is not authorized to it.

   Proprietary protocol operations SHOULD be properly documented by
      read, then the
   vendor, so it notification is clear dropped for that subscription.

3.2.  Datastore Access

   The same access control rules apply to operators what data nodes (if any) all datastores.  For example,
   the candidate configuration datastore or the running configuration
   datastore.

   Only the standard NETCONF datastores (candidate, running, and
   startup) are
   affected controlled by the operation, and what information (if any) is returned
   in ACM.  Local or remote files or
   datastores accessed via the <rpc-reply> message.

2.10. <url> parameter are optional to support.

3.2.1.  Access Rights

   A small set of hard-wired datastore access rights is needed to
   control access to all possible NETCONF Specific Requirements

   The server MUST be able protocol operations, including
   vendor extensions to identify the specific standard protocol operation set.

   The "CRUDX" model can support all NETCONF protocol access
   request at operations:

   o  Create: Allows the 4 access control points defined above.

   The server MUST be able to identify any datastore access request,
   even for proprietary operations.

   A client MUST always be authorized to invoke add a new data node instance to a
      datastore.

   o  Read: Allows the <close-session>
   operation, defined in [I-D.ietf-netconf-4741bis].

   A client MUST always be authorized to read a data node instance from a
      datastore, or receive the <replayComplete>
   and <notificationComplete> notification events, defined event type.

   o  Update: Allows the client to update an existing data node instance
      in [RFC5277]

   The set of module name strings used within one particular server MUST
   be unique.

3.  NETCONF Access Control Model (NACM)

3.1.  Introduction

   This section provides a high-level overview of datastore.

   o  Delete: Allows the access control
   model structure.  It describes client to delete a data node instance from a
      datastore.

   o  eXec: Allows the client to execute the NETCONF protocol message
   processing model, operation.

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

   Data nodes to which the conceptual client does not have read access control requirements
   within that model.

3.1.1.  Features

   The NACM data model provides are silently
   omitted from the following features:

   o  Independent control of RPC, data, and notification access.

   o  Simple access control rules configuration data model that <rpc-reply> message.  This is easy done to use.

   o  The concept allow NETCONF
   filters for <get> and <get-config> to function properly, instead of
   causing an emergency recovery session is supported, but
      configuration of the server for this purpose is beyond "access-denied" error because the scope
      of this document.  An emergency recovery session will bypass all filter criteria would
   otherwise include unauthorized read access control enforcement, in order to allow it some data nodes.  For
   NETCONF filtering purposes, the selection criteria is applied to initialize or
      repair the NACM configuration.

   o  A simple and familiar set
   subset of datastore permissions nodes that the user is used.

   o  Support for YANG security tagging (e.g., nacm:secure extension)
      allows default security modes authorized to automatically exclude sensitive
      data.

   o  Separate default access modes for read, write, and execute
      permissions.

   o  Access control rules are applied to configurable groups of users.

   o  The not the entire ACM can be disabled during operation, in order
   datastore.

3.2.3.  <edit-config> Operation

   The NACM access rights are not directly coupled to debug
      operational problems.

   o  Access control rules the <edit-config>
   "operation" attribute, although they are simple similar.  Instead, a NACM
   access right applies to configure.

   o  The number of denied all protocol operations which would result in
   a particular access operation requests and denied
      datastore write requests can be monitored by the client.

   o  Simple unconstrained YANG instance identifiers are used to
      configure the target datastore.  This section
   describes how these access control rules for rights apply to the specific data nodes.

3.1.2.  External Dependencies

   The NETCONF [I-D.ietf-netconf-4741bis] access
   operations supported by the <edit-config> protocol operation.

   If the effective access operation is used "none" (i.e., default-
   operation="none") for all
   management purposes within this document.  It a particular data node, then no access control
   is expected applied to that data node.

   If the
   mandatory transport mapping NETCONF Over SSH
   [I-D.ietf-netconf-rfc4742bis] protocol operation would result in the creation of a data
   store node, and the user does not have "create" access permission for
   that node, the protocol operation is also supported by rejected with an "access-denied"
   error.

   If the server, protocol operation would result in the deletion of a data
   store node, and
   that the server has user does not have "delete" access to permission for
   that node, the user name associated with each
   session.

   The YANG Data Modeling Language [RFC6020] protocol operation is used to define rejected with an "access-denied"
   error.

   If the
   NETCONF data models specified protocol operation would result in this document.

3.1.3.  Message Processing Model

   The following diagram shows the NETCONF message flow model, including modification of a data
   store node, and the points at which access control is applied, during NETCONF message
   processing.

                    +-------------------------+
                    |       session           |
                    |      (username)         |
                    +-------------------------+
                       |                 ^
                       V                 |
             +--------------+     +---------------+
             |   message    |     |   message     |
             | dispatcher   |     |   generator   |
             +--------------+     +---------------+
                  |                  ^         ^
                  V                  |         |
         +===========+     +-------------+   +----------------+
         |   <rpc>   |---> | <rpc-reply> |   | <notification> |
         | acc. ctl  |     |  generator  |   |  generator     |
         +===========+     +-------------+   +----------------+
               |              ^    ^                ^
               V       +------+    |                |
         +-----------+ |   +=============+  +================+
         |   <rpc>   | |   | <rpc-reply> |  | <notification> |
         | processor |-+   |  acc. ctl   |  | user does not have "update" access ctl    |
         +-----------+     +=============+  +================+
               |   |                  ^        ^
               V   +----------------+ |        |
         +===========+              | |        |
         | data node |              | |        |
         | acc. ctl  | -----------+ | |        |
         +===========+            | | |        |
               |                  | | |        |
               V                  V V |        |
         +---------------+      +-----------------+
         | configuration | ---> |     server      |
         |   datastore   |      | instrumentation |
         |               | <--- |                 |
         +---------------+      +-----------------+

                                 Figure 2

   The following high-level sequence of conceptual processing steps permission for
   that node, the protocol operation is
   executed rejected with an "access-denied"
   error.

   A "merge" or "replace" <edit-config> operation may include data nodes
   which do not alter portions of the existing datastore.  For example,
   a container or list node may be present for each received <rpc> message, if 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.

3.2.4.  <copy-config> Operation

   Access control
   enforcement 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 enabled: 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  Access control  If the source of the <copy-config> operation is applied a datastore, then
      data nodes to all <rpc> messages (except <close-
      session>) received by 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
         data store node, and the server, individually, user does not have "create" access
         permission for each active
      session, unless that node, the session protocol operation is identified as a "recovery session".

   o rejected
         with an "access-denied" error.

         If the session is authorized to execute protocol operation would result in the specified RPC
      operation, then processing continues, otherwise deletion of a
         data store node, and the request user does not have "delete" access
         permission for that node, the protocol operation is rejected
         with an "access-denied" error.

   o

         If the configuration datastore or conceptual state data is
      accessed by the protocol operation, then operation would result in the modification of a
         data node store node, and the user does not have "update" access MUST
      be authorized.  If
         permission for that node, the session protocol operation is authorized rejected
         with an "access-denied" error.

3.2.5.  <delete-config> Operation

   Access to perform the
      requested <delete-config> protocol operation on the requested data, then processing
      continues.

   The following sequence of conceptual processing steps is executed for
   each generated notification event, if access denied by
   default.  The 'exec-default' parameter does not apply to this
   protocol operation.  Access control enforcement is
   enabled:

   o  Server instrumentation generates rules must be explicitly
   configured to allow invocation by a conceptual notification, non-recovery session.

3.2.6.  <commit> Operation

   The server MUST determine the exact nodes in the running
   configuration datastore which 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
      particular subscription.

   o session can read the entire datastore, but only
   change one leaf, that session needs to be able to edit and commit
   that one leaf.

3.2.7.  <discard-changes> Operation

   The notification access control enforcer checks client is only required to have permission to execute the notification
      event type, and if
   <discard-changes> protocol operation.  No datastore permissions are
   needed.

3.2.8.  <kill-session> Operation

   The <kill-session> operation does not directly alter a datastore.
   However, it is allows one which the session to disrupt another session which is not authorized
   editing a datastore.

   Access to read, then the notification <kill-session> protocol operation is dropped for that subscription.

3.2. denied by default.
   The 'exec-default' parameter 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 access
   control model.

3.2.1.

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 which MUST be is unique within the server.

   As described in [I-D.ietf-netconf-4741bis], [RFC6241], the user name string is derived from the
   transport layer during session establishment.  If the transport layer cannot authenticate the user, the session is
   terminated.

   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.

3.2.2.  Groups

   Access to a specific NETCONF operation is granted to a session,
   associated with a group, not a user.

   A group is identified by its name.  All group names MUST be unique
   within the server.

   A group member is identified by a user name string.

   The same user may be configured in multiple groups.

3.2.3.  Sessions

   A session is simply a NETCONF session, which is the entity that is
   granted access to specific NETCONF operations.

   A session is associated with a single user name for the lifetime of
   the session.

3.2.4.  Access Permissions

   The access permissions are the NETCONF protocol specific set of
   permissions that have been assigned to a particular session.

   The same access permissions MUST stay in effect for the processing of
   a particular message.

   The server MUST use the access control rules in effect at
   cannot authenticate the time user, the message session is processed. terminated.

   The server MAY support a "recovery session" mechanism, which will
   bypass all access control model treats protocol operation execution
   separately from configuration datastore enforcement.  This is useful for
   restricting initial access and outgoing messages:

   create:  Permission to create conceptual server data.

   read:  Read repairing a broken access control
   configuration.

3.3.2.  Groups

   Access to conceptual server data, <rpc-reply> and
      <notification> content.

   update:  Permission to modify existing conceptual server data.

   delete:  Permission to delete existing conceptual server data.

   exec:  Permission to invoke a specific NETCONF protocol operation.

3.2.5. operation is granted to a
   session, associated with a group, not a user.

   A group is identified by its name.  All group names are unique within
   the server.

   A group member is identified by a user name string.

   The same user can be a member of multiple groups.

3.3.3.  Global Enforcement Controls

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

3.2.5.1.

3.3.3.1.  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", then all access requested 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", then all access
   requested are permitted.

3.2.5.2.

3.3.3.2.  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", then this global
   switch is relevant, if no matching access control rule is found to
   explicitly permit or deny read access to the requested NETCONF
   datastore data or notification event type.

   When this global switch is set to "permit", and no matching access
   control rule is found for the NETCONF datastore read or notification
   event requested, then access is permitted.

   When this global switch is set to "deny", and no matching access
   control rule is found for the NETCONF datastore read or notification
   event requested, then access is denied.

3.2.5.3.

3.3.3.3.  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", then this global switch is relevant,
   if no matching access control rule is found to explicitly permit or
   deny write access to the requested NETCONF datastore data.

   When this global switch is set to "permit", and no matching access
   control rule is found for the NETCONF datastore write requested, then
   access is permitted.

   When this global switch is set to "deny", and no matching access
   control rule is found for the NETCONF datastore write requested, then
   access is denied.

3.2.5.4.

3.3.3.4.  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", then 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,
   then 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,
   then access is denied.

3.2.6.

3.3.4.  Access Control Rules

   There are 4 types of rules available in 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, 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.

3.3.

3.4.  Access Control Enforcement Procedures

   There are seven separate phases that need to be addressed, four of
   which are related to the NETCONF message processing model.  In
   addition, the initial start-up mode for a NETCONF server, session
   establishment, and "access-denied" error handling procedures also
   need to be considered.

3.3.1.

   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 start-up 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", if supported.

   Access control rules are not enforced before or while the non-
   volatile configuration data is processed and loaded into the running
   configuration, when the server is booting or rebooting. 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 datastore, during
   bootup.

3.3.2.

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.

   A server SHOULD NOT include any sensitive information in any
   <capability> elements within the <hello> exchange.

   Once session establishment is completed, and a user has been
   authenticated, the NETCONF transport layer reports the user name 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 user name, group names, and the
   configuration data stored on the server.

3.3.3.

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 sensitive information in any <error-
   info> elements within the <rpc-error> response.

3.3.4.

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
                  +------------+
                  | NC-base NS |
                  |   <rpc>    |
                  +------------+
                    |   |  |
                    |   |  +-------------------------+
                    |   +------------+               |
                    V                V               V
               +-----------+ +---------------+ +------------+
               | acme NS   | | NC-base NS    | | NC-base NS |
               | <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 RPC access control enforcer server verifies that the session user is authorized to invoke
   the protocol operation.

   The protocol operation is authorized 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 for ones that contain a "user-
        name" entry that equals the user name for the session making the
        request.  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 order. 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.

        *  The rule does not have a "rule-type" defined, or 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.   Otherwise, no matching rule was found in any rule-list entry.

   10.  If the requested protocol operation is defined in a YANG module
        advertised in the server capabilities, and the "rpc" statement
        contains a "nacm:secure" or a "nacm:very-secure" "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 session 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.  For
      example:

         <error-path
           xmlns:nc="urn:ietf:params:xml:ns:netconf:base:1.0">
             /nc:rpc/nc:edit-config
         </error-path>

      represents the <edit-config> protocol operation in the NETCONF
      base namespace.

   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 the session user is authorized to perform the
   requested access operation on the specified data, as defined in
   Section 3.3.5.

3.3.5. 3.4.5.

3.4.5.  Data Node Access Validation

   If a data node within a datastore is accessed, then the server MUST
   ensure that the client session user is authorized to perform the requested read,
   create, update, or delete access operation on the specified data
   node.

   The data node access request is authorized by following these steps:

   1.   If the "enable-nacm" leaf is set to "false", then the protocol access
        operation is permitted.

   2.   If the requesting session is identified as a "recovery session",
        then the protocol access operation is permitted.

   3.   Check all the "group" entries for ones that contain a "user-
        name" entry that equals the user name for the session making the
        request.  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 order. 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 protocol operation requested data node is defined.

        *  The rule does not have a "rule-type" defined, or the "rule-
           type" is "data-node" and the "path" matches the requested
           data node.

        *  For a read access operation, the rule's "access-operations"
           leaf has the "read" bit set, or has the special value "*".

        *  For a creation create access operation, the rule's "access-operations"
           leaf has the "create" bit set, or has the special value "*".

        *  For a deletion delete access operation, the rule's "access-operations"
           leaf has the "delete" bit set, or has the special value "*".

        *  For an update access operation, the rule's "access-operations" "access-
           operations" leaf has the "update" 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.   Otherwise, 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:very-secure" "nacm:default-deny-
        all" statement, then the requested data node is 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:secure" "nacm:default-deny-
        write" or a "nacm:
        very-secure" "nacm:default-deny-all" statement, then the data
        node access request is denied.

   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 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.

3.3.6.

3.4.6.  Outgoing <notification> Authorization

   Configuration of access control rules specifically for descendant
   nodes of the notification event type element are outside the scope of
   this document.  If the session user is authorized to receive the notification
   event type, then it is also authorized to receive any data it
   contains.

   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

   The generation of a notification for a specific subscription 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, type [RFC5277], then the
        notification is permitted.

   4.   Check all the "group" entries for ones that contain a "user-
        name" entry that equals the user name for the session making the
        request.  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 order. 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 notification is defined.

        *  The rule does not have a "rule-type" defined, or the "rule-
           type" is "notification" and the "notification-name" is "*",
           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.

   10.  If the requested notification is defined in a YANG module
        advertised in the server capabilities, and the "notification"
        statement contains a "nacm:very-secure" "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.

3.4.

3.5.  Data Model Definitions

   This section defines the semantics of the conceptual data structures
   found in the data model in Section 3.4.

3.4.1. 3.5.

3.5.1.  Data Organization

   The top-level element is called <nacm>, and it is defined in following diagram highlights the
   "ietf-netconf-acm" module's namespace.

   There are several data structures defined as child nodes contents and structure of the
   <nacm> element:

   leaf <enable-nacm>:  On/off
   NACM YANG module.

      +--rw nacm
         +--rw enable-nacm?            boolean switch to enable or disable
      access control enforcement.

   leaf <read-default>:  Enumeration to permit or deny default read
      access requests.

   leaf <write-default>:  Enumeration to permit or deny default write
      access requests.

   leaf <exec-default>:  Enumeration to permit or deny default protocol
      operation execution requests.

   leaf <denied-rpcs>:  Read-only counter of
         +--rw read-default?           action-type
         +--rw write-default?          action-type
         +--rw exec-default?           action-type
         +--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

3.5.2.  YANG Module

   The following YANG module specifies the number of times normative NETCONF content
   that MUST by supported by the
      server has denied an RPC operation request, since server.

   The "ietf-netconf-acm" YANG module imports typedefs from [RFC6021].

   // RFC Ed.: please update the last reboot date to the date of publication
   <CODE BEGINS> file="ietf-netconf-acm@2011-10-04.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:   <http://tools.ietf.org/wg/netconf/>
        WG List:  <mailto:netconf@ietf.org>

        WG Chair: Mehmet Ersue
                  <mailto:mehmet.ersue@nsn.com>

        WG Chair: Bert Wijnen
                  <mailto:bertietf@bwijnen.net>

        Editor:   Andy Bierman
                  <mailto:andy.bierman@brocade.com>

        Editor:   Martin Bjorklund
                  <mailto:mbj@tail-f.com>";

     description
       "NETCONF Access Control Model.

        Copyright (c) 2011 IETF Trust and the server.

   leaf <denied-data-writes>:  Read-only counter persons identified as
        authors of the number of times code. All rights reserved.

        Redistribution and use in source and binary forms, with or
        without modification, is permitted pursuant to, and subject
        to the server has denied a data node write request, since license terms contained in, the last
      reboot Simplified BSD
        License set forth in Section 4.c of the server.

   leaf <denied-notifications>:  Read-only counter IETF Trust's
        Legal Provisions Relating to IETF Documents
        (http://trustee.ietf.org/license-info).

        This version of this YANG module is part of RFC XXXX; see
        the RFC itself for full legal notices.";
     // RFC Ed.: replace XXXX with actual RFC number and
     // remove this note

     // RFC Ed.: remove this note
     // Note: extracted from draft-ietf-netconf-access-control-05.txt

     // RFC Ed.: please update the date to the date of
      times publication
     revision "2011-10-04" {
       description
         "Initial version";
       reference
         "RFC XXXX: Network Configuration Protocol
                    Access Control Model";
     }

     /*
      * Extension statements
      */

     extension default-deny-write {
       description
         "Used to indicate that the server has denied data model node
          represents a notification, since sensitive security system parameter.

          If present, and the last reboot
      of NACM module is enabled (i.e.,
          /nacm/enable-nacm object equals 'true'), the server.

   container <groups>:  Configures NETCONF server
          will only allow the groups used within designated 'recovery session' to have
          write access to the node.  An explicit access control system.

      list <group>:  A list of user names belonging rule is
          required for all other users.

          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 same
         administrative group.

   container <rules>:  Configures data model node
          controls a very sensitive security system parameter.

          If present, and the NACM module is enabled (i.e.,
          /nacm/enable-nacm object equals 'true'), the access control rules used within NETCONF server
          will only allow the server.

      list <rule-list>:  An ordered collection of related designated 'recovery session' to have
          read, write, or execute access control
         rules.

         list <rule>:  Configures to the node.  An explicit
          access control rules for protocol
            operation invocation, configuration datastore access, and rule is required for controlling delivery of <notification> events.

3.4.2.  YANG Module all other users.

          The following YANG module specifies '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 User Name 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 normative NETCONF content particular leaf using this data type.";
     }

     typedef access-operations-type {
       type bits {
         bit create {
           description
             "Any protocol operation that MUST by supported by the server.

   The ietf-netconf-acm YANG module imports typedefs from [RFC6021].

 // RFC Ed.: please update the date to creates a
              new data node.";
         }
         bit read {
           description
             "Any protocol operation or notification that
              returns the date value of publication
 <CODE BEGINS> file="ietf-netconf-acm@2011-06-14.yang"

 module ietf-netconf-acm {

   namespace "urn:ietf:params:xml:ns:yang:ietf-netconf-acm";

   prefix "nacm";

   import ietf-yang-types a data node.";
         }
         bit update {
     prefix yang;
           description
             "Any protocol operation that alters an existing
              data node.";
         }
         bit delete {
           description
             "Any protocol operation that removes a data node.";
         }
         bit exec {
           description
             "Execution access to the specified protocol operation.";
         }
       }

   organization
     "IETF NETCONF (Network Configuration) Working Group";

   contact
     "WG Web:   <http://tools.ietf.org/wg/netconf/>
      WG List:  <mailto:netconf@ietf.org>

      WG Chair: Mehmet Ersue
                <mailto:mehmet.ersue@nsn.com>

      WG Chair: Bert Wijnen
                <mailto:bertietf@bwijnen.net>

      Editor:   Andy Bierman
                <mailto:andy.bierman@brocade.com>

      Editor:   Martin Bjorklund
                <mailto:mbj@tail-f.com>";
       description
         "NETCONF Server Access Control Model.

      Copyright (c) 2011 IETF Trust and the persons identified as
      authors 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 code. server when a particular
          rule matches.";
     }

     typedef node-instance-identifier {
       type yang:xpath1.0;
       description
         "Path expression used to represent a special
          data node instance identifier string.

          A node-instance-identifier value is an
          unrestricted YANG instance-identifier expression.
          All rights reserved.

      Redistribution and use in source and binary forms, with or
      without modification, the same rules as an instance-identifier apply
          except predicates for keys are optional.  If a key
          predicate is permitted pursuant to, and subject
      to missing, then the license terms contained in, node-instance-identifier
          represents all possible server instances for that key.

          This XPath expression is evaluated in the Simplified BSD
      License following context:

            o  The set forth in Section 4.c of namespace declarations are those in scope on
               the IETF Trust's
      Legal Provisions Relating to IETF Documents
      (http://trustee.ietf.org/license-info).

      This version of leaf element where this YANG module type is part used.

            o  The set of RFC XXXX; see
      the RFC itself for full legal notices.";
   // RFC Ed.: replace XXXX with actual RFC number and
   // remove this note

   // RFC Ed.: remove this note
   // Note: extracted from draft-ietf-netconf-access-control-04.txt

   // RFC Ed.: please update variable bindings contains one variable,
               'USER', which contains the date name of user of the current
                session.

            o  The function library is the core function library, but
               note that due to the date syntax restrictions of publication
   revision "2011-06-14" an
               instance-identifier, no functions are allowed.

            o  The context node is the root node in the data tree.";
     }

     container nacm {
       nacm:default-deny-all;

       description
       "Initial version";
     reference
       "RFC XXXX: Network Configuration Protocol
         "Parameters for NETCONF Access Control Model";
   }

   /*
    * Extension statements
    */

   extension secure Model.";

       leaf enable-nacm {
         type boolean;
         default true;
         description
       "Used to indicate that the data model node
        represents a sensitive security system parameter.

        If present, and the NACM module is enabled (i.e.,
        /nacm/enable-nacm object equals 'true'), the NETCONF server
        will only allow the designated 'recovery session' to have
        write
           "Enable or execute access to the node.  An explicit disable all NETCONF access control rule
            enforcement.  If 'true', then enforcement
            is required for all other users.

        The 'secure' extension MAY appear within a data definition
        statement or rpc statement.  It enabled.  If 'false', then enforcement
            is ignored otherwise."; disabled.";
       }

   extension very-secure

       leaf read-default {
         type action-type;
         default "permit";
         description
       "Used to indicate that the data model node
        controls a very sensitive security system parameter.

        If present, and the NACM module is enabled (i.e.,
        /nacm/enable-nacm object equals 'true'), the NETCONF server
        will only allow the designated 'recovery session' to have
        read, write, or execute access to the node.  An explicit
           "Controls whether read access control is granted if
            no appropriate rule is required found for all other users.

        The 'very-secure' extension MAY appear within a data
        definition statement, rpc statement,
            particular read request.";
       }

       leaf write-default {
         type action-type;
         default "deny";
         description
           "Controls whether create, update, or notification
        statement.  It delete access
            is ignored otherwise."; granted if no appropriate rule is found for a
            particular write request.";
       }

   /*
    * Derived types
    */

   typedef user-name-type

       leaf exec-default {
         type string {
       length "1..max";
     } action-type;
         default "permit";
         description
       "General Purpose User Name string.";
           "Controls whether exec access is granted if no appropriate
            rule is found for a particular protocol operation request.";
       }

   typedef matchall-string-type
       leaf denied-operations {
         type string {
       pattern "\*";
     } yang:zero-based-counter32;
         config false;
         mandatory true;
         description
       "The string containing
           "Number of times a single asterisk '*' is used
        to conceptually represent all possible values
        for protocol operation request was denied
            since the particular leaf using this data type."; server last restarted.";
       }

   typedef access-operations-type

       leaf denied-data-writes {
         type bits {
       bit create { yang:zero-based-counter32;
         config false;
         mandatory true;
         description
           "Any
           "Number of times a protocol operation that creates request to alter
            a
            new instance of configuration datastore was denied, since the specified data is a create
            operation.";
            server last restarted.";
       }
       bit read

       leaf denied-notifications {
         type yang:zero-based-counter32;
         config false;
         mandatory true;
         description
           "Any operation or
           "Number of times a notification that
            returns data to an application is was dropped
            for a read
            operation."; subscription because access to
            the event type was denied, since the server
            last restarted.";
       }
       bit update

       container groups {
         description
           "Any operation that alters an existing
            data node is an update operation.";
       }
       bit delete
           "NETCONF Access Control Groups.";

         list group {
           key name;

           description
           "Any operation that removes a datastore
            node instance is a delete operation.";
             "One NACM Group Entry.";

           leaf name {
             type group-name-type;
             description
               "Group name associated with this entry.";
           }
       bit exec

           leaf-list user-name {
             type user-name-type;
             description
           "Execution access to
               "Each entry identifies the specified RPC operation.
            Any RPC operation invocation is an exec operation."; user name of
                a member of the group associated with
                this entry.";
           }
         }
     description
       "NETCONF Access Operation.";
       }

   typedef group-name-type

       list rule-list {
         key "name";
         ordered-by user;
         description
           "An ordered collection of access control rules.";

         leaf name {
           type string {
             length "1..max";
       pattern "[^\*].*";
           }
           description
       "Name of administrative group that can be
             "Arbitrary name assigned to the user, and specified in
        an access control rule-list.";
         }

   typedef action-type
         leaf-list group {
           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 union {
             type yang:xpath1.0;
     description
       "Path expression used to represent a special
        data node instance identifier string.

        A node-instance-identifier value is an
        unrestricted YANG instance-identifier expression.
        All the same rules as an instance-identifier apply
        except 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 XPath expression is evaluated in the following context:

          o  The set of namespace declarations are those in scope on
             the leaf element where this matchall-string-type;
             type is used.

          o  The set of variable bindings contains one variable,
             'USER', which contains the name of user group-name-type;
           }
           description
             "List of the current
              session.

          o  The function library is the core function library, but
             note administrative groups that due to will be
              assigned the syntax restrictions of an
             instance-identifier, no functions are allowed.

          o  The context node is associated access rights
              defined by the root node in 'rule' list.

              The string '*' indicates that all groups apply to the data tree.";
              entry.";
         }

   container nacm {
     nacm:very-secure;

     description
       "Parameters for NETCONF Access Control Model.";

     leaf enable-nacm

         list rule {
       type boolean;
       default true;
           key "name";
           ordered-by user;
           description
         "Enable or disable all NETCONF
             "One access control
          enforcement.  If 'true', then enforcement rule.

              Rules are processed in user-defined order until a match is enabled.
              found.  A rule matches if 'module-name', 'rule-type', and
              'access-operations' matches the request.  If 'false', then enforcement a rule
              matches, the 'action' leaf determines if access is disabled.";
     } granted
              or not.";

           leaf read-default name {
             type action-type;
       default "permit"; string {
               length "1..max";
             }
             description
         "Controls whether read access is granted if
          no appropriate rule is found for a
          particular read request.";
               "Arbitrary name assigned to the rule.";
           }

           leaf write-default module-name {
             type action-type; union {
               type matchall-string-type;
               type string;
             }
             default "deny"; "*";
             description
         "Controls whether create, update,
               "Name of the module associated with this rule.

                This leaf matches if it has the value '*', or delete access
          is granted if no appropriate rule the
                object being accessed is found for a
          particular write request."; defined in the module with the
                specified module name.";
           }
           choice rule-type {
             description
               "This choice matches if all leafs present in the rule
                matches the request.  If no leafs are present, the
                choice matches all requests.";
             case protocol-operation {
               leaf exec-default rpc-name {
                 type action-type;
       default "permit"; union {
                   type matchall-string-type;
                   type string;
                 }
                 description
         "Controls whether exec access is granted
                   "This leaf matches if no appropriate
          rule is found for a particular RPC it has the value '*', or if
                    its value equals the requested protocol operation request.";
                    name.";
               }
             }
             case notification {
               leaf denied-rpcs notification-name {
                 type union {
                   type yang:zero-based-counter32;
       config false;
       mandatory true; matchall-string-type;
                   type string;
                 }
                 description
         "Number of times an RPC operation request was denied
          since
                   "This leaf matches if it has the server last restarted."; value '*', or if its
                    value equals the requested notification name.";
               }
             }
             case data-node {
               leaf denied-data-writes path {
                 type yang:zero-based-counter32;
       config false; node-instance-identifier;
                 mandatory true;
                 description
         "Number of times
                   "Data Node Instance Identifier associated with the
                    data node controlled by this rule.

                    Configuration data or state data instance
                    identifiers start with a request top-level data node.  A
                    complete instance identifier is required for this
                    type of path value.

                    The special value '/' refers to alter a all possible data node
          was denied, since the server last restarted.";
                    store contents.";
               }
             }
           }

           leaf denied-notifications access-operations {
             type yang:zero-based-counter32;
       config false;
       mandatory true;
       description
         "Number of times a notification was denied
          since the server last restarted.";
     }

     container groups {
       description
         "NETCONF Access Control Groups.";

       list group {
         key name;

         description
           "One NACM Group Entry.";

         leaf name union {
               type group-name-type; matchall-string-type;
               type access-operations-type;
             }
             default "*";
             description
             "Group name
               "Access operations associated with this entry.";
         }

         leaf-list user-name {
           type user-name-type;
           description
             "Each entry identifies rule.

                This leaf matches if it has the user name of
              a member of value '*', or if the group associated with
              this entry.";
         }
       }
                bit corresponding to the requested operation is set.";
           }

     list rule-list {
       key "name";
       ordered-by user;
       description
         "An ordered collection of access control rules.";

           leaf name action {
             type string {
           length "1..256";
         } action-type;
             mandatory true;
             description
           "Arbitrary name assigned
               "The access control action associated with the
                rule.  If a rule is determined to match a
                particular request, then this object is used
                to determine whether to permit or deny the rule-list.";
                request.";
           }
       leaf-list group {
         type union

           leaf comment {
             type matchall-string-type;
           type group-name-type;
         } string;
             description
               "A textual description
           "List of administrative groups that will be
            assigned the associated access rights
            defined by rule.";
           }

         }
       }
     }
   }

   <CODE ENDS>

                                 Figure 5

3.6.  IANA Considerations

   There are two actions that are requested of IANA: This document
   registers one URI in "The IETF XML Registry".  Following the 'rule' list. format
   in [RFC3688], the following has been registered.

        URI: urn:ietf:params:xml:ns:yang:ietf-netconf-acm
        Registrant Contact: The string '*' indicates that all groups apply to IESG.
        XML: N/A, the
            entry.";
       }

       list rule {
         key "name";
         ordered-by user;
         description
           "One requested URI is an XML namespace.

   This document registers one module in the "YANG Module Names"
   registry.  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 XXXX
           // RFC Ed.: Replace XXX with actual RFC number
           // and remove this note

3.7.  Security Considerations

   This entire document discusses access control rule.

            Rules are processed in user-defined order until requirements and
   mechanisms for restricting NETCONF protocol behavior within a match given
   session.

   This section highlights the issues for an administrator to consider
   when configuring a NETCONF server with NACM.

3.7.1.  NACM Configuration and Monitoring Considerations

   Configuration of the access control system is
            found. highly sensitive to
   system security.  A rule matches if 'module-name', 'rule-type', and
            'access-operations' matches server may choose not to allow any user
   configuration to some portions of it, such as the request.  If a rule
            matches, global security
   level, or the groups which allowed access to system resources.

   By default, NACM enforcement is enabled.  By default, "read" access
   to all datastore contents enabled, (unless "nacm:default-deny-all" is
   specified for the 'action' leaf determines if data definition) and "exec" access is granted
            or not.";

         leaf name {
           type string {
             length "1..256";
           }
           description
             "Arbitrary name assigned enabled for
   safe protocol operations.  An administrator needs to ensure that NACM
   is enabled, and also decide if the rule.";
         }

         leaf module-name {
           type union {
             type matchall-string-type;
             type string;
           } default "*";
           description
             "Name of access parameters are set
   appropriately.  Make sure the module associated with 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 rule.

              This leaf matches if it has the value '*', or if the
              object being accessed data model.

   If write access is defined in the module with allowed for configuration of access control rules,
   then care needs to be taken not to disrupt the
              specified module name.";
         }
         choice rule-type {
           description
             "This choice matches access control
   enforcement.  For example, if all leafs present in the rule
              matches the request.  If no leafs NACM access control rules 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
   editing directly within the value '*', or if its
                  value equals 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 requested RPC operation name.";
             }
           }
           case notification {
             leaf notification-name {
               type union {
                 type matchall-string-type;
                 type string;
               }
               description
                 "This leaf matches if it has edits are being
   done.

   NACM requires some a user name in each NACM group mapping.  An
   administrator needs to make sure that the value '*', translation from a
   transport or if its
                  value equals the requested notification name.";
             }
           }
           case data-node {
             leaf path {
               type node-instance-identifier;
               mandatory true;
               description
                 "Data Node Instance Identifier associated with implementation dependant user identity to a NACM user
   name is unique.

   An administrator needs to restrict read access to the data
                  node controlled by following
   objects within this rule.

                  Configuration data or state data instance
                  identifiers start with a top-level data node.  A
                  complete instance identifier model, which reveal access control
   configuration which could be considered sensitive.

   o  /nacm/enable-nacm

   o  /nacm/read-default

   o  /nacm/write-default

   o  /nacm/exec-default

   o  /nacm/groups

   o  /nacm/rule-list

3.7.2.  General Configuration Issues

   There is required for this
                  type a risk that invocation of path value.

                  The special value '/' refers non-standard protocol operations
   will have undocumented side effects.  An administrator needs to all
   construct access control rules such that the configuration datastore
   is protected from such side effects.

   It is possible data
                  store contents.";
             }
           }
         }

         leaf access-operations {
           type union {
             type matchall-string-type;
             type access-operations-type;
           }
           default "*";
           description
             "Access operations associated for a session with this rule.

              This leaf matches if it has 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 value '*',
   presence or if the
              bit corresponding to 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 requested operation is set.";
         }

         leaf action {
           type action-type;
           mandatory true;
           description
             "The access control action associated with presence or non-presence of
   specific sensitive data even without the
              rule.  If a rule is determined to match a
              particular request, then this object "error-path" field being
   present within the "rpc-error" response.

   It is used
              to possible that the data model definition itself (e.g., YANG
   when-stmt) will help an unauthorized session determine whether to permit or deny the
              request.";
         }

         leaf comment {
           type string;
           description
             "A textual description presence
   or even value of sensitive data nodes by examining the access rule.";
         }
       }
     }
   }
 }

 <CODE ENDS>

                                 Figure 5

3.5.  IANA Considerations presence and
   values of different data nodes.

   There are two actions is a risk that are requested non-standard protocol operations, or even the
   standard <get> protocol operation, may return data which "aliases" or
   "copies" sensitive data from a different data object.  There may
   simply be multiple data model definitions which 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 IANA: sensitive data models which contain leafref
   nodes.  This document
   registers one URI in "The IETF XML Registry".  Following entails finding all the format
   in [RFC3688], leafref objects that "point" at
   the following has been registered.

        URI: urn:ietf:params:xml:ns:yang:ietf-netconf-acm
        Registrant Contact: The IESG.
        XML: N/A, sensitive data (i.e., "path-stmt" values that implicitly or
   explicitly include the requested URI sensitive data node.

   It is an XML namespace.

   This document registers one module in the "YANG Module Names"
   registry.  Following the format in [RFC6020], beyond the following has been
   registered.

        name: ietf-netconf-acm
        namespace: urn:ietf:params:xml:ns:yang:ietf-netconf-acm
        prefix: nacm
        reference: RFC XXXX
           // RFC Ed.: Replace XXX with actual RFC number
           // and remove this note

3.6.  Security Considerations

   This entire scope of this document discusses to define access control requirements and
   mechanisms
   enforcement procedures for restricting underlying device instrumentation that may
   exist to support the NETCONF server operation.  An administrator can
   identify each protocol behavior within a given
   session.

   Configuration of operation that the access control system is highly sensitive to
   system security.  A server may choose not to allow provides, and decide
   if it needs any user
   configuration to some portions of it, such as the global security
   level, or the groups which allowed access control applied to system resources. 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 which disable all
   access to the server.  The configuration and identification of such a
   recovery session mechanism are implementation-specific and outside
   the scope of this document.

   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.  Also, such protocol operations
   SHOULD never be invoked by a session during a aware of
   any "recovery session".

   There session" mechanisms available on the device, and make
   sure they are used appropriately.

   It is possible for a risk that non-standard protocol operations, or session to disrupt configuration management,
   even without any write access to the
   standard <get> operation, configuration, by locking the
   datastore.  This may return data which "aliases" be done to insure all or "copies"
   sensitive data from a different data object.  In this case, the
   namespace and/or the element name will not match the values for part of the
   sensitive data, which
   configuration remains stable while it is then fully or partially copied into being retrieved, ot it may
   be done as a
   different namespace and/or element.  An administrator needs to avoid
   using data models which use this practice.

   An administrator needs to restrict write access to all configurable
   objects within this data model.

   If write access "denial-of-service" attack.  There is allowed no way for configuration of access control rules,
   then care needs to be taken not the
   server to disrupt know the access control
   enforcement. difference.  An administrator needs may wish to restrict read
   "exec" access to the following
   objects within this data model, which reveal access control
   configuration which could be considered sensitive.

   o  enable-nacm

   o  read-default protocol operations:

   o  write-default  <lock>

   o  exec-default  <unlock>

   o  groups  <partial-lock>

   o  rules  <partial-unlock>

3.7.3.  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 SHOULD 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 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 is not required.  Use of
   generic protocol operations should be avoided, and separate protocol
   operations defined instead, if different access levels are needed.

4.  References

4.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              January 2004.

   [RFC5277]  Chisholm, S. and H. Trevino, "NETCONF Event
              Notifications", RFC 5277, July 2008.

   [RFC6020]  Bjorklund, M., "YANG - A Data Modeling Language for the
              Network Configuration Protocol (NETCONF)", RFC 6020,
              October 2010.

   [RFC6021]  Schoenwaelder, J., "Common YANG Data Types", RFC 6021,
              October 2010.

   [I-D.ietf-netconf-4741bis]

   [RFC6241]  Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
              Bierman, "Network Configuration Protocol (NETCONF)",
              draft-ietf-netconf-4741bis-10 (work in progress),
              March
              RFC 6241, June 2011.

   [I-D.ietf-netconf-rfc4742bis]

   [RFC6242]  Wasserman, M. and T. Goddard, M., "Using the NETCONF
              Configuration Protocol over Secure
              Shell (SSH)",
              draft-ietf-netconf-rfc4742bis-08 (work in progress),
              March RFC 6242, June 2011.

4.2.  Informative References

   [RFC2865]  Rigney, C., Willens, S., Rubens, A., and W. Simpson,
              "Remote Authentication Dial In User Service (RADIUS)",
              RFC 2865, June 2000.

   [RFC5607]  Nelson, D. and G. Weber, "Remote Authentication Dial-In
              User Service (RADIUS) Authorization for Network Access
              Server (NAS) Management", RFC 5607, July 2009.

Appendix A.  Usage Examples

   The following XML snippets are provided as examples only, to
   demonstrate how 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>monitor</name>
         <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 3 groups:

   1.  The "admin" group contains 2 users named "admin" and "andy".

   2.  The "monitor" "limited" group contains 2 users named "wilma" and "bam-bam".

   3.  The "guest" group contains 2 users named "guest" and
       "guest@example.com".

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 case in the "rule-type" choice.

   <nacm xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-acm">
     <rule-list>
       <name>guest</name>
       <name>guest-acl</name>
       <group>guest</group>

       <rule>
         <name>mod-1</name>
         <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>monitor example</name>
       <group>monitor</group>
       <name>limited-acl</name>
       <group>limited</group>

       <rule>
         <name>mod-2</name>
         <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>mod-3</name>
         <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>

     <rule-list>
       <name>admin example</name>
       <name>admin-acl</name>
       <group>admin</group>

       <rule>
         <name>mod-4</name>
         <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 4 module rules:

   mod-1:

   deny-ncm:  This rule prevents the guest "guest" group from reading any
      monitoring information in the ietf-netconf-monitoring "ietf-netconf-monitoring" YANG
      module.

   mod-2:

   permit-ncm:  This rule allows the monitor "limited" group to read the ietf-netconf-
      monitoring "ietf-
      netconf-monitoring" YANG module.

   mod-3:

   permit-exec:  This rule allows the monitor "limited" group to invoke any
      protocol operation supported by the server.

   mod-4:

   permit-all:  This rule allows the admin "admin" group complete access to
      all content in the server.  No subsequent rule will match for the
      admin
      "admin" group, because of this module rule.

A.3.  RPC Rule Example

   RPC 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</name>
       <group>monitor</group>
       <name>guest-limited-acl</name>
       <group>limited</group>
       <group>guest</group>

       <rule>
         <name>rpc-1</name>
         <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 monitor limited or guest group
           to kill another session.
         </comment>
       </rule>
       <rule>
         <name>rpc-2</name>
         <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 monitor limited or guest group
           to delete any configurations.
         </comment>
       </rule>
     </rule-list>

     <rule-list>
       <name>monitor</name>
       <group>monitor</group>
       <name>limited-acl</name>
       <group>limited</group>

       <rule>
         <name>rpc-3</name>
         <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 monitor limited group to edit the configuration.
         </comment>
       </rule>
     </rule-list>

   </nacm>
   This example shows 3 protocol operation rules:

   rpc-1:

   deny-kill-session:  This rule prevents the monitor "limited" or guest "guest"
      groups from invoking the NETCONF <kill-session> protocol
      operation.

   rpc-2:

   deny-delete-config:  This rule prevents the monitor "limited" or guest "guest"
      groups from invoking the NETCONF <delete-config> protocol
      operation.

   rpc-3:

   permit-edit-config:  This rule allows the monitor "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".

A.4.  Data Rule Example

   Data 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 rules</name>
       <name>guest-acl</name>
       <group>guest</group>

       <rule>
         <name>data-1</name>
         <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>monitor rules</name>
       <group>monitor</group>
       <name>limited-acl</name>
       <group>limited</group>

       <rule>
         <name>data-acme-config</name>
         <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 monitor limited group complete access to the acme
           netconf configuration parameters.  Showing long form
           of 'access-operations' instead of shorthand.
         </comment>
       </rule>
     </rule-list>

     <rule-list>
       <name>dummy-itf</name>
       <group>guest monitor</group>
       <name>guest-limited-acl</name>
       <group>guest</group>
       <group>limited</group>

       <rule>
         <name>dummy-itf</name>
         <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 monitor limited and guest groups read
           and update access to the dummy interface.
         </comment>
       </rule>
     </rule-list>

     <rule-list>
       <name>admin rules</name>
       <name>admin-acl</name>
       <rule>
         <name>admin-itf</name>
         <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 admin full access to all acme interfaces.
         </comment>
       </rule>
     </rule-list>
   </nacm>
   This example shows 4 data rules:

   data-1:

   deny-nacm:  This rule denies the guest "guest" group any access to the
      <nacm> subtree.  Note that the default namespace is only
      applicable because this subtree is defined in the same namespace
      as the <data-rule> element.

   data-acme-config:

   permit-acme-config:  This rule gives the monitor "limited" group read-write
      access to the acme <config-parameters>.

   dummy-itf:

   permit-dummy-interface:  This rule gives the monitor "limited" and guest "guest"
      groups read-update access to the acme <interface>. entry named
      "dummy".  This entry cannot be created or deleted by these groups,
      just altered.

   admin-itf:

   permit-interface:  This rule gives the admin "admin" group read-write
      access to all acme <interface>. entries.  This is an example of an
      unreachable rule because the "mod-3" rule already gives the admin
      "admin" group full access to this data.

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</name>
       <group>monitor</group>
       <name>sys-acl</name>
       <group>limited</group>
       <group>guest</group>

       <rule>
         <name>notif-1</name>
         <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 or monitor limited groups
           to receive config change events.
         </comment>
       </rule>
     </rule-list>
   </nacm>
   This example shows 1 notification rule:

   notif-1:

   deny-config-change:  This rule prevents the monitor "limited" or guest "guest"
      groups from receiving the acme <sys-config-change> event type.

Appendix B.  Change Log

   -- RFC Ed.: remove this section before publication.

B.1.  04-05

   Updated Security Considerations section.

   Changed term 'operator' to 'administrator'.

   Used the terms "access operation" and "protocol operation"
   consistently.

   Moved some normative text from section 2 to section 3.  Also made it
   more clear that section 2 is not a requirements section, but
   documentation of the objectives for NACM.

   Renamed "nacm:secure" to "nacm:default-deny-write", and "nacm:very-
   secure" to "nacm:default-deny-all".  Explained that "nacm:default-
   deny-write" is ignored on rpc statements.

   Described that <kill-session> and <delete-config> behave as if
   specified with "nacm:default-deny-all".

B.2.  03-04

   Introduced rule-lists to group related rules together.

   Moved "module-rule", "rpc-rule", "notification-rule", and "data-rule"
   into one common "rule", with a choice to select between the four
   variants.

   Changed "superuser" to "recovery session", and adjusted text
   throughout document for this change.

   Clarified behavior of global default NACM parameters, enable-nacm,
   read-default, write-default, exec-default.

   Clarified when access control is applied during system
   initialization.

B.2.

B.3.  02-03

   Fixed improper usage of RFC 2119 keywords.

   Changed term usage of "database" to "datastore".

   Clarified that "secure" and "very-secure" extensions only apply if
   the /nacm/enable-nacm object is "true".

B.3.

B.4.  01-02

   Removed authentication text and objects.

   Changed module name from ietf-nacm to ietf-netconf-acm.

   Updated NETCONF and YANG terminology.

   Removed open issues section.

   Changed some must to MUST in requirements section.

B.4.

B.5.  00-01

   Updated YANG anf YANG Types references.

   Updated module namespace URI to standard format.

   Updated module header meta-data to standard format.

   Filled in IANA section.

B.5.

B.6.  00

   Initial version cloned from
   draft-bierman-netconf-access-control-02.txt.

Authors' Addresses

   Andy Bierman
   Brocade

   Email: andy.bierman@brocade.com

   Martin Bjorklund
   Tail-f Systems

   Email: mbj@tail-f.com