[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-bierman-netconf-access-control) 00 01 02 03 04 05 06 07 RFC 6536

Internet Engineering Task Force                               A. Bierman
Internet-Draft                                                   Brocade
Intended status: Standards Track                            M. Bjorklund
Expires: September 12, 2011                               Tail-f Systems
                                                          March 11, 2011


          Network Configuration Protocol Access Control Model
                  draft-ietf-netconf-access-control-03

Abstract

   The standardization of network configuration interfaces for use with
   the NETCONF protocol requires a structured and secure operating
   environment, which 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 operations and content.
   This document discusses requirements for a suitable access control
   model, and provides one solution which meets these requirements.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at 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
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 12, 2011.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect



Bierman & Bjorklund    Expires September 12, 2011               [Page 1]


Internet-Draft                    NACM                        March 2011


   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  4
       1.1.1.  Requirements Notation  . . . . . . . . . . . . . . . .  4
       1.1.2.  NETCONF Terms  . . . . . . . . . . . . . . . . . . . .  4
       1.1.3.  YANG Terms . . . . . . . . . . . . . . . . . . . . . .  5
       1.1.4.  NACM Terms . . . . . . . . . . . . . . . . . . . . . .  5
   2.  Access Control Requirements  . . . . . . . . . . . . . . . . .  6
     2.1.  Protocol Control Points  . . . . . . . . . . . . . . . . .  6
     2.2.  Simplicity . . . . . . . . . . . . . . . . . . . . . . . .  7
     2.3.  Procedural Interface . . . . . . . . . . . . . . . . . . .  7
     2.4.  Datastore Access . . . . . . . . . . . . . . . . . . . . .  7
       2.4.1.  Access Rights  . . . . . . . . . . . . . . . . . . . .  8
       2.4.2.  <get> and <get-config> Operations  . . . . . . . . . .  8
       2.4.3.  <edit-config> Operation  . . . . . . . . . . . . . . .  8
       2.4.4.  <copy-config> Operation  . . . . . . . . . . . . . . .  9
     2.5.  Users and Groups . . . . . . . . . . . . . . . . . . . . . 10
     2.6.  Maintenance  . . . . . . . . . . . . . . . . . . . . . . . 10
     2.7.  Configuration Capabilities . . . . . . . . . . . . . . . . 10
     2.8.  Identifying Security Holes . . . . . . . . . . . . . . . . 11
     2.9.  Data Shadowing . . . . . . . . . . . . . . . . . . . . . . 12
     2.10. NETCONF Specific Requirements  . . . . . . . . . . . . . . 12
   3.  NETCONF Access Control Model (NACM)  . . . . . . . . . . . . . 14
     3.1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . 14
       3.1.1.  Features . . . . . . . . . . . . . . . . . . . . . . . 14
       3.1.2.  External Dependencies  . . . . . . . . . . . . . . . . 15
       3.1.3.  Message Processing Model . . . . . . . . . . . . . . . 15
     3.2.  Model Components . . . . . . . . . . . . . . . . . . . . . 17
       3.2.1.  Users  . . . . . . . . . . . . . . . . . . . . . . . . 17
       3.2.2.  Groups . . . . . . . . . . . . . . . . . . . . . . . . 18
       3.2.3.  Sessions . . . . . . . . . . . . . . . . . . . . . . . 18
       3.2.4.  Access Permissions . . . . . . . . . . . . . . . . . . 18
       3.2.5.  Global Enforcement Controls  . . . . . . . . . . . . . 19
       3.2.6.  Access Control Rules . . . . . . . . . . . . . . . . . 19
     3.3.  Access Control Enforcement Procedures  . . . . . . . . . . 19
       3.3.1.  Initial Operation  . . . . . . . . . . . . . . . . . . 19
       3.3.2.  Session Establishment  . . . . . . . . . . . . . . . . 20
       3.3.3.  'access-denied' Error Handling . . . . . . . . . . . . 20
       3.3.4.  Incoming RPC Message Validation  . . . . . . . . . . . 20
       3.3.5.  Data Node Access Validation  . . . . . . . . . . . . . 23
       3.3.6.  Outgoing <rpc-reply> Authorization . . . . . . . . . . 26



Bierman & Bjorklund    Expires September 12, 2011               [Page 2]


Internet-Draft                    NACM                        March 2011


       3.3.7.  Outgoing <notification> Authorization  . . . . . . . . 26
     3.4.  Data Model Definitions . . . . . . . . . . . . . . . . . . 29
       3.4.1.  High Level Procedures  . . . . . . . . . . . . . . . . 29
       3.4.2.  Data Organization  . . . . . . . . . . . . . . . . . . 29
       3.4.3.  YANG Module  . . . . . . . . . . . . . . . . . . . . . 30
     3.5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . 41
     3.6.  Security Considerations  . . . . . . . . . . . . . . . . . 41
   4.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 44
     4.1.  Normative References . . . . . . . . . . . . . . . . . . . 44
     4.2.  Informative References . . . . . . . . . . . . . . . . . . 44
   Appendix A.  Usage Examples  . . . . . . . . . . . . . . . . . . . 45
     A.1.  <groups> Example . . . . . . . . . . . . . . . . . . . . . 45
     A.2.  <module-rule> Example  . . . . . . . . . . . . . . . . . . 46
     A.3.  <rpc-rule> Example . . . . . . . . . . . . . . . . . . . . 47
     A.4.  <data-rule> Example  . . . . . . . . . . . . . . . . . . . 49
     A.5.  <notification-rule> Example  . . . . . . . . . . . . . . . 51
   Appendix B.  Change Log  . . . . . . . . . . . . . . . . . . . . . 52
     B.1.  02-03  . . . . . . . . . . . . . . . . . . . . . . . . . . 52
     B.2.  01-02  . . . . . . . . . . . . . . . . . . . . . . . . . . 52
     B.3.  00-01  . . . . . . . . . . . . . . . . . . . . . . . . . . 52
     B.4.  00 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 53





























Bierman & Bjorklund    Expires September 12, 2011               [Page 3]


Internet-Draft                    NACM                        March 2011


1.  Introduction

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

   There is a need for inter-operable management of the controlled
   access to operator 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].  It contains three main
   sections:

   1.  Access Control Requirements

   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] and are
   not redefined here:

   o  client

   o  datastore

   o  operation

   o  protocol operation

   o  server

   o  session

   o  user




Bierman & Bjorklund    Expires September 12, 2011               [Page 4]


Internet-Draft                    NACM                        March 2011


1.1.3.  YANG Terms

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

   o  data node

1.1.4.  NACM Terms

   The following terms are used throughout this documentation:

   access control:  A security feature provided by the NETCONF server,
      which allows an operator 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 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.

   authentication:  The process of verifying a user's identity.

   superuser:  The special administrative user account which is given
      unlimited NETCONF access, and is exempt from all access control
      enforcement.
























Bierman & Bjorklund    Expires September 12, 2011               [Page 5]


Internet-Draft                    NACM                        March 2011


2.  Access Control Requirements

2.1.  Protocol Control Points

   The NETCONF protocol allows new 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 only focuses on a static
   set of 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
   conceptual control points.


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


                                 Figure 1

   The following access control points are defined:

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

   NETCONF datastore:  Configurable 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.



Bierman & Bjorklund    Expires September 12, 2011               [Page 6]


Internet-Draft                    NACM                        March 2011


   Notification Content:  Configurable permission to receive specific
      notification event types is required.

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 hard to do complex things,
   instead of hard to do everything.

   Configuration of the access control system needs to be simple to use.
   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 be able to control all
   types of NETCONF protocol operation invocation, all conceptual
   datastore access, and all NETCONF session output.

   Default access control policy needs to be as secure as possible.

   Protocol access SHOULD 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 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.

2.4.  Datastore Access

   It MUST be possible to control access to specific nodes and sub-trees
   within the conceptual NETCONF datastore.

   In order for a user to obtain access to a particular datastore node,



Bierman & Bjorklund    Expires September 12, 2011               [Page 7]


Internet-Draft                    NACM                        March 2011


   the user MUST be authorized to have the same requested access to the
   specified node, and all of its ancestors.

   The same access control rules apply to all conceptual datastores.
   For example, the candidate configuration or the running
   configuration.

   Only the standard NETCONF datastores (candidate, running, and
   startup) are controlled by the ACM.  Local or remote files or
   datastores accessed via the <url> parameter are optional to support.

   The non-volatile startup configuration needs to be loaded into the
   running configuration without applying any access control rules.

2.4.1.  Access Rights

   A small set of hard-wired datastore access rights is needed to
   control access to all possible NETCONF datastore operations,
   including vendor extensions to the standard operation set.

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

   o  Create: Allows the client to add a new data node instance to a
      datastore.

   o  Read: Allows the client to read a data node instance from a
      datastore, or receive the notification event type.

   o  Update: Allows the client to update an existing data node instance
      in a datastore.

   o  Delete: Allows the client to delete a data node instance from a
      datastore.

   o  eXec: Allows the client to execute the protocol operation.

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

   Data nodes to which the client does not have 'read' access, either
   directly or via wildcard access, are silently omitted from the <rpc-
   reply> message.

2.4.3.  <edit-config> Operation

   The NACM access rights are not directly coupled to the <edit-config>
   "operation" attribute, although they are similar.  Instead, a NACM
   access right applies to all operations which would result in a
   particular access operation to the target datastore.  This section



Bierman & Bjorklund    Expires September 12, 2011               [Page 8]


Internet-Draft                    NACM                        March 2011


   describes how these access rights apply to the specific datastore
   operations supported by the <edit-config> operation.

   If the effective operation is 'none' (i.e., default-operation='none')
   for a particular data node, then no access control is applied to that
   data node.

   A 'create', 'merge', or 'replace' operation on a datastore node which
   would result in the creation of a new data node instance, for which
   the user does not have 'create' access permission, is rejected with
   an 'access-denied' error.

   A 'merge' or 'replace' operation on a datastore node which would
   result in the modification of an existing data node instance, for
   which the user does not have 'update' access permission, is rejected
   with an 'access-denied' error.

   A 'replace', 'delete', or 'remove' operation on a datastore node
   which would result in the deletion of an existing data node instance,
   for which the user does not have 'delete' access permission, is
   rejected with an 'access-denied' error.

   A 'merge' operation may include data nodes which do not alter
   portions of the existing datastore.  For example, a container or list
   nodes may be present for naming purposes, which do not actually alter
   the corresponding datastore node.  These unaltered data nodes within
   the scope of a 'merge' operation are ignored by the server, and do
   not require any access rights by the client.

   A 'merge' 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' 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.

2.4.4.  <copy-config> Operation

   Access control for the <copy-config> operation requires special
   consideration because the operator is replacing the entire target
   datastore.  Read access to the entire source datastore, and write
   access to the entire target datastore is needed for this operation to
   succeed.

   A client MUST have access to every datastore node, even ones that are
   not present in the source configuration data.



Bierman & Bjorklund    Expires September 12, 2011               [Page 9]


Internet-Draft                    NACM                        March 2011


   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 not, the server will simply omit these sub-trees from the reply.
   If that copy is later used to restore the server datastore, the
   server will interpret the missing nodes as a request to delete those
   nodes, and return an error.

2.5.  Users and Groups

   The server MUST obtain a user name from 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.

   A configurable superuser account may be needed which bypasses all
   access control rules.  This could be needed in case the access
   control rules are mis-configured, and all access is denied by
   mistake.

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

   It MUST be possible to delegate the user-to-group mapping to a
   central server, such as RADIUS [RFC2865] [RFC5607].  Since
   authentication is performed by the NETCONF transport layer, and
   RADIUS performs authentication and service authorization 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 access control
   model without deleting any configuration.  By default, only the
   'superuser' SHOULD be able to perform this task.

   It SHOULD be possible to configure a 'superuser' account so that all
   access control is disabled for just this user.  This allows the
   access control rules to always be modified without completely
   disabling access control for all users.

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



Bierman & Bjorklund    Expires September 12, 2011              [Page 10]


Internet-Draft                    NACM                        March 2011


   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 sub-trees
   within the configuration datastore MUST be supported.  Existing
   mechanisms can be used to identify the sub-tree(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 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 access to read or 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
      of vulnerability, after the new module is loaded, and before the
      new access control rules for that module are configured, enabled,
      and debugged.

   Often, the operator just wants to disable default access 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, by denying access to
   sensitive data unless the user is explicitly authorized to perform
   the requested operation.





Bierman & Bjorklund    Expires September 12, 2011              [Page 11]


Internet-Draft                    NACM                        March 2011


2.9.  Data Shadowing

   One of the more complicated security administration problems 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 with the copied value.

   If the YANG leafref data type is used, then this data shadowing can
   be detected by applications (and the server stack), and prevented.

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

   Since NETCONF allows any vendor operation to be added to the
   protocol, there is no way to reliably identify all of the operations
   that may expose copies of sensitive data nodes in <rpc-reply>
   messages.

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

   It is beyond the scope of this document to define access control
   enforcement procedures for underlying device instrumentation that may
   exist to support the NETCONF server operation.  An operator can
   identify each operation that the server provides, and decide if it
   needs any access control applied to it.

   Proprietary protocol operations SHOULD be properly documented by the
   vendor, so it is clear to operators what data nodes (if any) are
   affected by the operation, and what information (if any) is returned
   in the <rpc-reply> message.

2.10.  NETCONF Specific Requirements

   The server MUST be able to identify the specific protocol access
   request at 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 the <close-session>
   operation, defined in [I-D.ietf-netconf-4741bis].

   A client MUST always be authorized to receive the <replayComplete>
   and <notificationComplete> notification events, defined in [RFC5277]




Bierman & Bjorklund    Expires September 12, 2011              [Page 12]


Internet-Draft                    NACM                        March 2011


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

















































Bierman & Bjorklund    Expires September 12, 2011              [Page 13]


Internet-Draft                    NACM                        March 2011


3.  NETCONF Access Control Model (NACM)

3.1.  Introduction

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

3.1.1.  Features

   The NACM data model provides the following features:

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

   o  Very simple access control rules configuration data model which is
      easy to use.

   o  The concept of a 'superuser' type of account is supported, but
      configuration such an account is beyond the scope of this
      document.  If the server supports a 'superuser' account, then it
      MUST be able to determine the actual user name for this account.
      A session associated with the superuser account will bypass all
      access control enforcement.

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

   o  Support for YANG security tagging (e.g., nacm:secure extension)
      allows default security modes 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 entire ACM can be disabled during operation, in order to debug
      operational problems.

   o  Access control rules are simple to configure.

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

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





Bierman & Bjorklund    Expires September 12, 2011              [Page 14]


Internet-Draft                    NACM                        March 2011


3.1.2.  External Dependencies

   The NETCONF [I-D.ietf-netconf-4741bis] protocol is used for all
   management purposes within this document.  It is expected that the
   mandatory transport mapping NETCONF Over SSH
   [I-D.ietf-netconf-rfc4742bis] is also supported by the server, and
   that the server has access to the user name associated with each
   session.

   The YANG Data Modeling Language [RFC6020] is used to define the
   NETCONF data models specified in this document.  The YANG instance-
   identifier data type is used to configure data-node-specific access
   control rules.

3.1.3.  Message Processing Model

   The following diagram shows the NETCONF message flow model, including
   the points at which access control is applied, during NETCONF message
   processing.
































Bierman & Bjorklund    Expires September 12, 2011              [Page 15]


Internet-Draft                    NACM                        March 2011


                    +-------------------------+
                    |       session           |
                    |      (username)         |
                    +-------------------------+
                       |                 ^
                       V                 |
             +--------------+     +---------------+
             |   message    |     |   message     |
             | dispatcher   |     |   generator   |
             +--------------+     +---------------+
                  |                  ^         ^
                  V                  |         |
         +===========+     +-------------+   +----------------+
         |   <rpc>   |---> | <rpc-reply> |   | <notification> |
         | acc. ctl  |     |  generator  |   |  generator     |
         +===========+     +-------------+   +----------------+
               |              ^    ^                ^
               V       +------+    |                |
         +-----------+ |   +=============+  +================+
         |   <rpc>   | |   | <rpc-reply> |  | <notification> |
         | processor |-+   |  acc. ctl   |  |  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 is
   executed for each received <rpc> message, if access control
   enforcement is enabled:

   o  Access control is applied to all <rpc> messages (except <close-
      session>) received by the server, individually, for each active
      session, unless the session is associated with the 'superuser'
      account.



Bierman & Bjorklund    Expires September 12, 2011              [Page 16]


Internet-Draft                    NACM                        March 2011


   o  If the session is authorized to execute the specified RPC
      operation, then processing continues, otherwise the request is
      rejected with an 'access-denied' error.

   o  If the configuration datastore or conceptual state data is
      accessed by the protocol operation, then the data node access MUST
      be authorized.  If the session is authorized to perform the
      requested operation on the requested data, then processing
      continues.

   The following sequence of conceptual processing steps is executed for
   each generated notification event, if access control enforcement is
   enabled:

   o  Server instrumentation generates a conceptual notification, for a
      particular subscription.

   o  The notification access control enforcer checks the notification
      event type, and if it is one which the session is not authorized
      to read, then the notification is dropped for that subscription.

3.2.  Model Components

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

3.2.1.  Users

   A 'user' is the conceptual entity, which is associated with the
   access permissions granted to a particular session.  A user is
   identified by a string which MUST be unique within the server.

   As described in [I-D.ietf-netconf-4741bis], 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 'superuser' administrative user account,
   which will bypass all access control enforcement.  This is useful for
   restricting initial access and repairing a broken access control
   configuration.  This account may be configurable to use a specific
   user, or disabled completely.  Some systems have factory-selected
   superuser account names.  There is no need to standardize the exact
   user name for the superuser account.  If no such account exists, then
   all NETCONF access will be controlled by NACM.






Bierman & Bjorklund    Expires September 12, 2011              [Page 17]


Internet-Draft                    NACM                        March 2011


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 which 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 the time
   the message is processed.

   The access control model treats protocol operation execution
   separately from configuration datastore access and outgoing messages:

   create:  Permission to create conceptual server data.

   read:  Read 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 an protocol operation.







Bierman & Bjorklund    Expires September 12, 2011              [Page 18]


Internet-Draft                    NACM                        March 2011


3.2.5.  Global Enforcement Controls

   A global on/off switch is provided to enable or disable all access
   control enforcement.

   An on/off switch is provided to enable or disable default access to
   invoke protocol operations.

   An on/off switch is provided to enable or disable default permission
   to receive data in replies and notifications.

   An on/off switch is provided to enable or disable default access to
   alter configuration data.

3.2.6.  Access Control Rules

   There are 4 types of rules available in NACM:

   module rule:  Controls access for definitions in a specific module,
      identified by its name.

   protocol operation rule:  Controls access for a specific protocol
      operation, identified by its 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 module and name.

3.3.  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.  Initial Operation

   Upon the very first start-up of the NETCONF server, the access
   control configuration will probably not be present.  If not, a server
   MUST NOT allow any write access to any session role except
   'superuser' type of account in this state.

   There is no requirement to enforce access control rules before or
   while the non-volatile configuration data is processed and loaded



Bierman & Bjorklund    Expires September 12, 2011              [Page 19]


Internet-Draft                    NACM                        March 2011


   into the running configuration.

3.3.2.  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 identity has been
   authenticated, the NETCONF transport layer reports the username and a
   possibly empty set of group names associated with the user to the
   NETCONF server.  The NETCONF server will enforce the access control
   rules, based on the supplied user identity, group names, and the
   configuration data stored on the server.

3.3.3.  '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 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.  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.

















Bierman & Bjorklund    Expires September 12, 2011              [Page 20]


Internet-Draft                    NACM                        March 2011


                   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.  Only well-formed
   XML messages will be processed by the server.

   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 verifies that the session
   is authorized to invoke the protocol operation.

   The protocol operation is authorized by following these steps:

   1.   If the <enable-nacm> parameter is set to 'false', then the
        protocol operation is permitted.





Bierman & Bjorklund    Expires September 12, 2011              [Page 21]


Internet-Draft                    NACM                        March 2011


   2.   If the session is associated with the 'superuser' account, then
        the protocol operation is permitted.

   3.   If the requested operation is the NETCONF <close-session>
        operation, then the protocol operation is permitted.

   4.   Check all the <group> entries for ones that contain a <user-
        name> entry that matches 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:

        *  If the requested protocol operation is associated with a YANG
           module advertised in the server capabilities, and the rpc
           statement contains a nacm:secure or nacm:very-secure
           extension, then the protocol operation is denied.

        *  If the <exec-default> parameter is set to 'permit', then
           permit the protocol operation, otherwise deny the request.

   6.   Check if there are any matching <rpc-rule> entries for the
        requested protocol operation.  Any matching rules are processed
        in user-defined order, in case there are multiple <rpc-rule>
        entries for the requested protocol operation.

   7.   If an <rpc-rule> entry is found, then check the <allowed-rights>
        bits field for the entry, otherwise continue.  The 'exec' bit
        MUST be present in the <allowed-rights> bits field for an <rpc-
        rule>, so it is not used in this procedure.

   8.   If the <rpc-rule> entry is considered a match, then the 'nacm-
        action' leaf is checked.  If is equal to 'permit', then the
        protocol operation is permitted, otherwise it is denied.

   9.   Check if there are any matching <module-rule> entries for the
        same module as the requested protocol operation.  Any matching
        rules are processed in user-defined order, in case there are
        multiple <module-rule> entries for the module containing the
        requested protocol operation.

   10.  If a <module-rule> entry is found, then check the <allowed-
        rights> bits field for the entry, otherwise continue.  If the
        'exec' bit is present in the <allowed-rights> bits field then
        the RPC rule is considered a match. otherwise it is not
        considered to match the request.





Bierman & Bjorklund    Expires September 12, 2011              [Page 22]


Internet-Draft                    NACM                        March 2011


   11.  If the <module-rule> entry is considered a match, then the
        'nacm-action' leaf is checked.  If is equal to 'permit', then
        the protocol operation is permitted, otherwise it is denied.

   12.  If the requested operation is identified an a nacm:secure or
        nacm:very-secure protocol operation, then the protocol operation
        is denied.

   13.  If the <exec-default> parameter is set to 'permit', then permit
        the protocol operation, otherwise the protocol operation is
        denied.

   If the session is not authorized to invoke the protocol operation
   then an <rpc-error> is generated with the following information:

   error-tag:  access-denied

   error-path:  /rpc/method-QName, where 'method-QName' is a qualified
      name identifying the actual protocol operation name.  For example,
      '/rpc/edit-config' represents the <edit-config> operation in the
      NETCONF base namespace.

   If the configuration datastore is accessed, either directly or as a
   side effect of the protocol operation, then the server MUST intercept
   the operation and make sure the session is authorized to perform the
   requested operation on the specified data.

3.3.5.  Data Node Access Validation

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

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

   1.   If the <enable-nacm> parameter is set to 'false', then the data
        node access request is permitted.

   2.   If the session is associated with the 'superuser' account, then
        the data node access request is permitted.

   3.   Check all the <group> entries for ones that contain a <user-
        name> entry that matches the user name for the session making
        the request.  Add to these groups the set of groups provided by
        the transport layer.




Bierman & Bjorklund    Expires September 12, 2011              [Page 23]


Internet-Draft                    NACM                        March 2011


   4.   If no groups are found:

        *  If the requested data node is associated with a YANG module
           advertised in the server capabilities, and the data
           definition statement or any of its ancestors contains a nacm:
           secure or nacm:very-secure extension, then the data node
           access request is denied.

        *  For a read request, if the <read-default> parameter is set to
           'permit', then permit the data node access request, otherwise
           deny the request.  For a read operation, this means that the
           requested node is not included in the rpc-reply.

        *  For a write request, if the <write-default> parameter is set
           to 'permit', then permit the data node access request,
           otherwise deny the request.

   5.   Check if there are any matching <data-rule> entries for the
        requested data node access request.  Any matching rules are
        processed in user-defined order, in case there are multiple
        <data-rule> entries for the requested data node.

   6.   If an <data-rule> entry is found, then check the <allowed-
        rights> bits field for the entry, otherwise continue.

        1.  For a creation operation, if the 'create' bit is present in
            the <allowed-rights> bits field then the entry is considered
            to be a match.

        2.  For a read operation, if the 'read' bit is present in the
            <allowed-rights> bits field, then the entry is considered to
            be a match.

        3.  For an update (e.g., 'merge' or 'replace') operation, if the
            'update' bit is present in the <allowed-rights> bits field
            then the entry is considered to be a match.

        4.  For a deletion (e.g., 'delete') operation, if the 'delete'
            bit is present in the <allowed-rights> bits field then the
            entry is considered to be a match.

   7.   If the <data-rule> entry is considered a match, then the 'nacm-
        action' leaf is checked.  If it is equal to 'permit', then the
        data operation is permitted, otherwise it is denied.  For 'read'
        operations, 'denied' means the requested data is not returned in
        the reply.





Bierman & Bjorklund    Expires September 12, 2011              [Page 24]


Internet-Draft                    NACM                        March 2011


   8.   Check if there are any matching <module-rule> entries for the
        same module as the requested data node.  Any matching rules are
        processed in user-defined order, in case there are multiple
        <module-rule> entries for the module containing the requested
        data node.

   9.   If a <module-rule> entry is found, then check the <allowed-
        rights> bits field for the entry, otherwise continue.

        1.  For a creation operation, if the 'create' bit is present in
            the <allowed-rights> bits field then the entry is considered
            to be a match.

        2.  For a read operation, if the 'read' bit is present in the
            <allowed-rights> bits field, then the entry is considered to
            be a match.

        3.  For an update (e.g., 'merge' or 'replace') operation, if the
            'update' bit is present in the <allowed-rights> bits field
            then the entry is considered to be a match.

        4.  For a deletion (e.g., 'delete') operation, if the 'delete'
            bit is present in the <allowed-rights> bits field then the
            entry is considered to be a match.

   10.  If the <module-rule> entry is considered a match, then the
        'nacm-action' leaf is checked.  If it is equal to 'permit', then
        the data operation is permitted, otherwise it is denied.  For
        'read' operations, 'denied' means the requested data is not
        returned in the reply.

   11.  For a read request, if the requested data node is identified an
        a nacm:very-secure definition, then the requested data node is
        not included in the reply.

   12.  For a write request, if the requested data node is identified an
        a nacm:secure or nacm:very-secure definition, then the data node
        access request is denied.

   13.  For a read request, if the <read-default> parameter is set to
        'permit', then include the requested data in the reply,
        otherwise do not include the requested data in the reply.

   14.  For a write request, if the <write-default> parameter is set to
        'permit', then permit the data node access request, otherwise
        deny the request.





Bierman & Bjorklund    Expires September 12, 2011              [Page 25]


Internet-Draft                    NACM                        March 2011


3.3.6.  Outgoing <rpc-reply> Authorization

   The <rpc-reply> message MUST be checked by the server to make sure no
   unauthorized data is contained within it.  If so, the restricted data
   MUST be removed from the message before it is sent to the client.

   For protocol operations which do not access any data nodes, then any
   client authorized to invoke the protocol operation is also authorized
   to receive the <rpc-reply> for that protocol operation.

3.3.7.  Outgoing <notification> Authorization

   The <notification> message MUST be checked by the server to make sure
   no unauthorized data is contained within it.  If so, the restricted
   data MUST be removed from the message before it is sent to the
   client.

   Configuration of access control rules specifically for descendent
   nodes of the notification event type element are outside the scope of
   this document.  If the session 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.


























Bierman & Bjorklund    Expires September 12, 2011              [Page 26]


Internet-Draft                    NACM                        March 2011


                   NETCONF server
                  +------------+
                  |    XML     |
                  |   message  |
                  | generator  |
                  +------------+
                        ^
                        |
                +----------------+
                | <notification> |
                |  generator     |
                +----------------+
                        ^
                        |
               +=================+
               | <notification>  |
               |  access control |
               |  <eventType>    |
               +=================+
                        ^
                        |
            +------------------------+
            | server instrumentation |
            +------------------------+
                      |     ^
                      V     |
             +----------------------+
             |    configuration     |
             |      datastore       |
             +----------------------+



                                 Figure 4

   The generation of a notification event for a specific subscription is
   authorized by following these steps:

   1.   If the <enable-nacm> parameter is set to 'false', then the
        notification event is permitted.

   2.   If the session is associated with the 'superuser' account, then
        the notification event is permitted.

   3.   If the requested operation is the NETCONF <replayComplete> or
        <notificationComplete> event type, then the notification event
        is permitted.




Bierman & Bjorklund    Expires September 12, 2011              [Page 27]


Internet-Draft                    NACM                        March 2011


   4.   Check all the <group> entries for ones that contain a <user-
        name> entry that matches the user name for the session that
        started the notification subscription.  Add to these groups the
        set of groups provided by the transport layer.

   5.   If no groups are found:

        *  If the requested notification is associated with a YANG
           module advertised in the server capabilities, and the
           notification statement contains a nacm:secure or nacm:very-
           secure extension, then the notification event is dropped for
           the associated subscription.

        *  If the <read-default> parameter is set to 'permit', then
           permit the notification event, otherwise drop this event type
           for the associated subscription.

   6.   Check if there are any matching <notification-rule> entries for
        the specific notification event type being delivered to the
        subscription.  Any matching rules are processed in user-defined
        order, in case there are multiple <notification-rule> entries
        for the requested notification event type.

   7.   If a <notification-rule> entry is found, then check the
        <allowed-rights> bits field for the entry, otherwise continue.
        If the 'read' bit is present in the <allowed-rights> bits field
        then the notification event type is permitted, otherwise it is
        dropped for the associated subscription.

   8.   Check if there are any matching <module-rule> entries for the
        same module as the notification event type.  Any matching rules
        are processed in user-defined order, in case there are multiple
        <module-rule> entries for the module containing the notification
        event type.

   9.   If a <module-rule> entry is found, then check the <allowed-
        rights> bits field for the entry, otherwise continue.  If the
        'read' bit is present in the <allowed-rights> bits field then
        the notification event type is permitted, otherwise it is
        dropped for the associated subscription.

   10.  If the requested event type is identified an a nacm:very-secure
        notification definition, then the notification event type is
        denied.

   11.  If the <read-default> parameter is set to 'permit', then permit
        the notification event type, otherwise it is dropped for the
        associated subscription.



Bierman & Bjorklund    Expires September 12, 2011              [Page 28]


Internet-Draft                    NACM                        March 2011


3.4.  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.  High Level Procedures

   There are some high level management procedures that an administrator
   needs to consider before using this access control model:

   1.  Configure the global settings.

   2.  Configure one or more user groups.

   3.  Configure zero or more access control rules for specific modules.

   4.  Configure zero or more access control rules for specific protocol
       operations.

   5.  Configure zero or more access control rules for data node access.

   6.  Configure zero or more access control rules for notification
       event type access.

3.4.2.  Data Organization

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

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

   leaf <enable-nacm>:  On/off 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 the number of times the
      server has denied an RPC operation request, since the last reboot
      of the server.




Bierman & Bjorklund    Expires September 12, 2011              [Page 29]


Internet-Draft                    NACM                        March 2011


   leaf <denied-data-writes>:  Read-only counter of the number of times
      the server has denied a data node write request, since the last
      reboot of the server.

   container <groups>:  Configures the groups used within the access
      control system.

      list <group>:  A list of user names belonging to the same
         administrative group.

   container <rules>:  Configures the access control rules used within
      the server.

      list <module-rule>:  Configures the access control rules for a
         specific module.

      list <rpc-rule>:  Configures the access control rules for protocol
         operation invocation.

      list <data-rule>:  Configures the access control rules for
         configuration datastore access.

      list <notification-rule>:  Configures the access control rules for
         controlling delivery of <notification> events.

3.4.3.  YANG Module

   The following YANG module is provided to specify the normative
   NETCONF content that MUST by supported by the server.

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


  // RFC Ed.: please update the date to the date of publication
  <CODE BEGINS> file="ietf-netconf-acm@2011-03-11.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";



Bierman & Bjorklund    Expires September 12, 2011              [Page 30]


Internet-Draft                    NACM                        March 2011


    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 of the code. All rights reserved.

       Redistribution and use in source and binary forms, with or
       without modification, is permitted pursuant to, and subject
       to the license terms contained in, the Simplified BSD
       License set forth in Section 4.c of the IETF Trust's
       Legal Provisions Relating to IETF Documents
       (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-03.txt

    // RFC Ed.: please update the date to the date of publication
    revision "2011-03-11" {
      description
        "Initial version";
      reference
        "RFC XXXX: Network Configuration Protocol
                   Access Control Model";
    }

    /*
     * Extension statements



Bierman & Bjorklund    Expires September 12, 2011              [Page 31]


Internet-Draft                    NACM                        March 2011


     */

    extension secure {
      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 'superuser' to have write or execute
         default nacm-rights-type for the node.  An explicit access
         control rule is required for all other users.

         The 'secure' extension MAY appear within a data, rpc,
         or notification node definition.  It is ignored
         otherwise.";
    }

    extension very-secure {
      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 'superuser' to have read, write, or execute
         default nacm-rights-type for the node.  An explicit access
         control rule is required for all other users.

         The 'very-secure' extension MAY appear within a data, rpc,
         or notification node definition.  It is ignored
         otherwise.";
    }

    /*
     * Derived types
     */

    typedef nacm-user-name-type {
      type string {
        length "1..max";
      }
      description
        "General Purpose User Name string.";
    }




Bierman & Bjorklund    Expires September 12, 2011              [Page 32]


Internet-Draft                    NACM                        March 2011


    typedef nacm-matchall-string-type {
      type string {
        pattern "\*";
      }
      description
        "The string containing a single asterisk '*' is used
         to conceptually represent all possible values
         for the particular leaf using this data type.";
    }

    typedef nacm-rights-type {
      type union {
        type nacm-matchall-string-type;

        type bits {
          bit create {
            description
              "Create access allowed to all specified data.
               Any protocol operation that creates a
               new instance of the specified data is a create
               operation.";
          }
          bit read {
            description
              "Read access allowed to all specified data.
               Any protocol operation or notification that
               returns data to an application is a read
               operation.";
          }
          bit update {
            description
              "Update access allowed to all specified data.
               Any protocol operation that alters an existing
               data node is an update operation.";
          }
          bit delete {
            description
              "Delete access allowed to all specified data.
               Any protocol operation that removes a datastore
               node instance is a delete operation.";
          }
          bit exec {
            description
              "Execution access to the specified RPC operation.
               Any RPC operation invocation is an exec operation.";
          }
        }
      }



Bierman & Bjorklund    Expires September 12, 2011              [Page 33]


Internet-Draft                    NACM                        March 2011


      description
        "NETCONF Access Rights.
         The string '*' indicates that all possible access
         rights apply to the access rule.  Otherwise, only
         the specific access rights represented by the bit names
         that are present apply to the access rule.";
    }

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

    typedef nacm-action-type {
      type enumeration {
        enum permit {
          description
            "Requested action is permitted.";
        }
        enum deny {
          description
            "Requested action is denied.";
        }
      }
      description
        "Action taken by the server when a particular
         rule matches.";
    }

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

         A schema-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 schema-instance-identifier
         represents all possible server instances for that key.




Bierman & Bjorklund    Expires September 12, 2011              [Page 34]


Internet-Draft                    NACM                        March 2011


         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 type is used.

           o  The set of variable bindings contains one variable,
              'USER', which contains the name of user of the current
               session.

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

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

    container nacm {
      nacm:very-secure;

      description
        "Parameters for NETCONF Access Control Model.";

      leaf enable-nacm {
        type boolean;
        default true;
        description
          "Enable or disable all NETCONF access control
           enforcement.  If 'true', then enforcement
           is enabled.  If 'false', then enforcement
           is disabled.";
      }

      leaf read-default {
        type nacm-action-type;
        default "permit";
        description
          "Controls whether read access is granted if
           no appropriate rule is found for a
           particular read request.";
      }

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



Bierman & Bjorklund    Expires September 12, 2011              [Page 35]


Internet-Draft                    NACM                        March 2011


      }

      leaf exec-default {
        type nacm-action-type;
        default "permit";
        description
          "Controls whether exec access is granted if no appropriate
           rule is found for a particular RPC operation request.";
      }

      leaf denied-rpcs {
        type yang:zero-based-counter32;
        config false;
        mandatory true;
        description
          "Number of times an RPC operation request was denied
           since the server last restarted.";
      }

      leaf denied-data-writes {
        type yang:zero-based-counter32;
        config false;
        mandatory true;
        description
          "Number of times a request to alter a data node
           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 {
            type nacm-group-name-type;
            description
              "Group name associated with this entry.";
          }

          leaf-list user-name {
            type nacm-user-name-type;
            description
              "Each entry identifies the user name of



Bierman & Bjorklund    Expires September 12, 2011              [Page 36]


Internet-Draft                    NACM                        March 2011


               a member of the group associated with
               this entry.";
          }
        }
      }

      container rules {
        description
          "NETCONF Access Control Rules.";

        grouping common-rule-parms {
          description
            "Common rule parameters.";

          leaf rule-name {
            type string {
              length "1..256";
            }
            description
              "Arbitrary name assigned to the
               access control rule.";
          }

          leaf allowed-rights {
            type nacm-rights-type;
            description
              "List of access rights granted to
               specified administrative groups for the
               content specified by the associated path.";
          }

          leaf-list allowed-group {
            type union {
              type nacm-matchall-string-type;
              type nacm-group-name-type;
            }
            min-elements 1;
            description
              "List of administrative groups which will be
               assigned the associated access rights
               for the content specified by the associated path.

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

          leaf nacm-action {
            type nacm-action-type;



Bierman & Bjorklund    Expires September 12, 2011              [Page 37]


Internet-Draft                    NACM                        March 2011


            mandatory true;
            description
              "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
               request.";
          }

          leaf comment {
            type string {
              length "1..4095";
            }
            description
              "A textual description of the access rule.";
          }
        }

        list module-rule {
          key "module-name rule-name";
          ordered-by user;

          description
            "One Module Access Rule.

             Rules are processed in user-defined order.  A module rule
             is considered a match if the XML namespace for the
             specified module name matches the XML namespace used
             within a NETCONF PDU, and the administrative group
             associated with the requesting session is specified in the
             'allowed-group' leaf-list, and the requested operation
             is included in the 'allowed-rights' leaf.";

          leaf module-name {
            type string;
            description
              "Name of the module associated with this rule.";
          }

          uses common-rule-parms {
            refine allowed-rights {
              mandatory true;
            }
          }
        }

        list rpc-rule {
          key "module-name rpc-name rule-name";



Bierman & Bjorklund    Expires September 12, 2011              [Page 38]


Internet-Draft                    NACM                        March 2011


          ordered-by user;

          description
            "One RPC Operation Access Rule.

             Rules are processed in user-defined order.  An RPC rule is
             considered a match if the module name of the requested RPC
             operation matches 'module-name', the requested RPC
             operation matches 'rpc-name', and an administrative group
             associated with the session user is listed in the
             'allowed-group' leaf-list.  The 'allowed-rights' leaf
             is ignored by the server if it is present.
             Only the 'exec' bit can possibly cause
             a match for an RPC rule.";

          leaf module-name {
            type string;
            description
              "Name of the module defining this RPC operation.";
          }

          leaf rpc-name {
            type string;
            description
              "Name of the RPC operation.";
          }

          uses common-rule-parms;
        }

        list data-rule {
          key "rule-name";
          ordered-by user;

          description
            "One Data Access Control Rule.

             Rules are processed in user-defined order.  A data rule is
             considered to match when the path expression identifies
             the same node that is being accessed in the NETCONF
             datastore, and the administrative group associated with the
             session is identified in the 'allowed-group' leaf-list,
             and the requested operation is included in the
             'allowed-rights' leaf.";

          leaf path {
            type schema-instance-identifier;
            mandatory true;



Bierman & Bjorklund    Expires September 12, 2011              [Page 39]


Internet-Draft                    NACM                        March 2011


            description
              "Schema Instance Identifier associated with the data node
               controlled by this rule.

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

               The special value '/' refers to all possible datastore
               contents.";
          }

          uses common-rule-parms {
            refine allowed-rights {
              mandatory true;
            }
          }
        }

        list notification-rule {
          key "module-name
               notification-name
               rule-name";
          ordered-by user;

          description
            "One Notification Access Rule.

             A notification is considered a match if the module name of
             the requested event type matches
             'module-name', the requested event type
             matches the 'notification-name', and the administrative
             group associated with the requesting session is listed in
             the 'allowed-group' leaf-list.  If the 'allowed-rights'
             leaf is present, it is ignored by the server.
             Only the 'read' bit can possibly cause
             a match for a notification rule.";

          leaf module-name {
            type string;
            description
              "Name of the module defining this
               notification event type.";
          }

          leaf notification-name {
            type string;
            description



Bierman & Bjorklund    Expires September 12, 2011              [Page 40]


Internet-Draft                    NACM                        March 2011


              "Name of the notification event.";
          }

          uses common-rule-parms;
        }
      }
    }
  }


  <CODE ENDS>

                                 Figure 5

3.5.  IANA Considerations

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


        URI: urn:ietf:params:xml:ns:yang:ietf-netconf-acm
        Registrant Contact: The IESG.
        XML: N/A, the 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

3.6.  Security Considerations

   This entire document discusses access control requirements and
   mechanisms for restricting NETCONF protocol behavior within a given
   session.

   Configuration of the access control system is highly sensitive to
   system security.  A server may choose not to allow any user
   configuration to some portions of it, such as the global security
   level, or the groups which allowed access to system resources.

   This document incorporates the optional use of a 'superuser' account,



Bierman & Bjorklund    Expires September 12, 2011              [Page 41]


Internet-Draft                    NACM                        March 2011


   which can be used to bypass access control enforcement.  It is
   suggested that the 'root' account not be used for NETCONF over SSH
   servers, because 'root' SSH logins SHOULD be disabled in the SSH
   server.

   If the server chooses to allow user configuration of the access
   control system, then only sessions using the 'superuser'
   administrative user SHOULD be allowed to have write access to the
   data model.

   If the server chooses to allow user retrieval of the access control
   system configuration, then only sessions using the 'superuser'
   administrative user SHOULD be allowed to have read access to the data
   model.

   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 using the 'superuser'
   administrative user.

   There is a risk that non-standard protocol operations, or even the
   standard <get> operation, may return data which 'aliases' 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 the
   sensitive data, which is then fully or partially copied into 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.  It is suggested that only sessions
   using the 'superuser' administrative role be permitted to configure
   the data model defined in this document.

   If write access is allowed for configuration of access control rules,
   then care needs to be taken not to disrupt the access control
   enforcement.

   An administrator needs to restrict read 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





Bierman & Bjorklund    Expires September 12, 2011              [Page 42]


Internet-Draft                    NACM                        March 2011


   o  write-default

   o  exec-default

   o  groups

   o  rules












































Bierman & Bjorklund    Expires September 12, 2011              [Page 43]


Internet-Draft                    NACM                        March 2011


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]
              Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
              Bierman, "Network Configuration Protocol (NETCONF)",
              draft-ietf-netconf-4741bis-09 (work in progress),
              February 2011.

   [I-D.ietf-netconf-rfc4742bis]
              Wasserman, M. and T. Goddard, "Using the NETCONF
              Configuration Protocol over Secure Shell (SSH)",
              draft-ietf-netconf-rfc4742bis-07 (work in progress),
              February 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.










Bierman & Bjorklund    Expires September 12, 2011              [Page 44]


Internet-Draft                    NACM                        March 2011


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>
         <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 nacm:admin group contains 2 users named 'admin' and 'andy'.

   2.  The nacm:monitor group contains 2 users named 'wilma' and 'bam-
       bam'.





Bierman & Bjorklund    Expires September 12, 2011              [Page 45]


Internet-Draft                    NACM                        March 2011


   3.  The nacm: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.  These rules are checked after none of the
   specific rules (i.e., rpc-rule, data-rule, or notification-rule)
   matched the current access request.


   <nacm xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-acm">
     <rules>
       <module-rule>
         <module-name>ietf-netconf-monitoring</module-name>
         <rule-name>mod-1</rule-name>
         <allowed-rights>*</allowed-rights>
         <allowed-group>guest</allowed-group>
         <nacm-action>deny</nacm-action>
         <comment>
             Do not allow guests any access to the netconf
             monitoring information.
         </comment>
       </module-rule>

       <module-rule>
         <module-name>ietf-netconf-monitoring</module-name>
         <rule-name>mod-2</rule-name>
         <allowed-rights>read</allowed-rights>
         <allowed-group>monitor</allowed-group>
         <nacm-action>permit</nacm-action>
         <comment>
             Allow the monitor group read access to the netconf
             monitoring information.
         </comment>
       </module-rule>

       <module-rule>
         <module-name>*</module-name>
         <rule-name>mod-3</rule-name>
         <allowed-rights>exec</allowed-rights>
         <allowed-group>monitor</allowed-group>
         <nacm-action>permit</nacm-action>
         <comment>
             Allow the monitor group to invoke any of the
             supported server operations.
         </comment>
       </module-rule>



Bierman & Bjorklund    Expires September 12, 2011              [Page 46]


Internet-Draft                    NACM                        March 2011


       <module-rule>
         <module-name>*</module-name>
         <rule-name>mod-4</rule-name>
         <allowed-rights>*</allowed-rights>
         <allowed-group>admin</allowed-group>
         <nacm-action>permit</nacm-action>
         <comment>
             Allow the admin group complete access to all
             operations and data.
         </comment>
       </module-rule>

     </rules>
   </nacm>




   This example shows 4 module rules:

   mod-1:  This rule prevents the guest group from reading any
      monitoring information in the ietf-netconf-monitoring YANG module.

   mod-2:  This rule allows the monitor group to read the ietf-netconf-
      monitoring YANG module.

   mod-3:  This rule allows the monitor group to invoke any protocol
      operation supported by the server.

   mod-4:  This rule allows the admin group complete access to all
      content in the server.  No subsequent rule will match for the
      admin group, because of this module rule.

A.3.  <rpc-rule> Example

   RPC rules are used to control access to a specific protocol
   operation.














Bierman & Bjorklund    Expires September 12, 2011              [Page 47]


Internet-Draft                    NACM                        March 2011


   <nacm xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-acm">
     <rules>
       <rpc-rule>
         <module-name>ietf-netconf</module-name>
         <rpc-name>kill-session</rpc-name>
         <rule-name>rpc-1</rule-name>
         <allowed-group>monitor</allowed-group>
         <allowed-group>guest</allowed-group>
         <nacm-action>deny</nacm-action>
         <comment>
           Do not allow the monitor or guest group
           to kill another session.
         </comment>
       </rpc-rule>

       <rpc-rule>
         <module-name>ietf-netconf</module-name>
         <rpc-name>delete-config</rpc-name>
         <rule-name>rpc-2</rule-name>
         <allowed-group>monitor</allowed-group>
         <allowed-group>guest</allowed-group>
         <nacm-action>deny</nacm-action>
         <comment>
           Do not allow monitor or guest group
           to delete any configurations.
         </comment>
       </rpc-rule>

       <rpc-rule>
         <module-name>ietf-netconf</module-name>
         <rpc-name>edit-config</rpc-name>
         <rule-name>rpc-3</rule-name>
         <allowed-group>monitor</allowed-group>
         <nacm-action>permit</nacm-action>
         <comment>
           Allow the monitor group to edit the configuration.
         </comment>
       </rpc-rule>
     </rules>
   </nacm>



   This example shows 3 protocol operation rules:







Bierman & Bjorklund    Expires September 12, 2011              [Page 48]


Internet-Draft                    NACM                        March 2011


   rpc-1:  This rule prevents the monitor or guest groups from invoking
      the NETCONF <kill-session> protocol operation.

   rpc-2:  This rule prevents the monitor or guest groups from invoking
      the NETCONF <delete-config> protocol operation.

   rpc-3:  This rule allows the monitor group to invoke the NETCONF
      <edit-config> protocol operation.  This rule will have no real
      affect 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">
     <rules>
       <data-rule>
         <rule-name>data-1</rule-name>
         <path>/nacm</path>
         <allowed-rights>*</allowed-rights>
         <allowed-group>guest</allowed-group>
         <nacm-action>deny</nacm-action>
         <comment>
           Deny the guest group any access to the /nacm data.
         </comment>
       </data-rule>

       <data-rule>
         <rule-name>data-acme-config</rule-name>
         <path xmlns:acme="http://example.com/ns/netconf">
           /acme:acme-netconf/acme:config-parameters
         </path>
         <allowed-rights>read create update delete</allowed-rights>
         <allowed-group>monitor</allowed-group>
         <nacm-action>permit</nacm-action>
         <comment>
           Allow the monitor group complete access to the acme
           netconf configuration parameters.  Showing long form
           of 'allowed-rights' instead of shorthand.
         </comment>
       </data-rule>

       <data-rule>
         <rule-name>dummy-itf</rule-name>
         <path xmlns:acme="http://example.com/ns/itf">
           /acme:interfaces/acme:interface[acme:name='dummy']



Bierman & Bjorklund    Expires September 12, 2011              [Page 49]


Internet-Draft                    NACM                        March 2011


         </path>
         <allowed-rights>read update</allowed-rights>
         <allowed-group>monitor</allowed-group>
         <allowed-group>guest</allowed-group>
         <nacm-action>permit</nacm-action>
         <comment>
           Allow the monitor and guest groups read
           and update access to the dummy interface.
         </comment>
       </data-rule>

       <data-rule>
         <rule-name>admin-itf</rule-name>
         <path xmlns:acme="http://example.com/ns/itf">
           /acme:interfaces/acme:interface
         </path>
         <allowed-rights>*</allowed-rights>
         <allowed-group>admin</allowed-group>
         <nacm-action>permit</nacm-action>
         <comment>
           Allow admin full access to all acme interfaces.
           This is an example of an unreachable rule,
           because the admin group already has full access
           to all modules (see rule 'mod-4').
           All 'module-rule' entries will be checked
           before this 'data-rule' entry is checked.
         </comment>
       </data-rule>
     </rules>
   </nacm>



   This example shows 4 data rules:

   data-1:  This rule denies the guest group any access to the <nacm>
      sub-tree.  Note that the default namespace is only applicable
      because this sub-tree is defined in the same namespace as the
      <data-rule> element.

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

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





Bierman & Bjorklund    Expires September 12, 2011              [Page 50]


Internet-Draft                    NACM                        March 2011


   admin-itf:  This rule gives the 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 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">
     <rules>
       <notification-rule>
         <module-name>acme-system</module-name>
         <notification-name>sys-config-change</notification-name>
         <rule-name>notif-1</rule-name>
         <allowed-group>monitor</allowed-group>
         <allowed-group>guest</allowed-group>
         <nacm-action>deny</nacm-action>
         <comment>
           Do not allow the guest or monitor groups
           to receive config change events.
         </comment>
       </notification-rule>
     </rules>
   </nacm>



   This example shows 1 notification rule:

   notif-1:  This rule prevents the monitor or guest groups from
      receiving the acme <sys-config-change> event type.

















Bierman & Bjorklund    Expires September 12, 2011              [Page 51]


Internet-Draft                    NACM                        March 2011


Appendix B.  Change Log

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

B.1.  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.2.  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.3.  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.4.  00

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












Bierman & Bjorklund    Expires September 12, 2011              [Page 52]


Internet-Draft                    NACM                        March 2011


Authors' Addresses

   Andy Bierman
   Brocade

   Email: andy.bierman@brocade.com


   Martin Bjorklund
   Tail-f Systems

   Email: mbj@tail-f.com







































Bierman & Bjorklund    Expires September 12, 2011              [Page 53]


Html markup produced by rfcmarkup 1.129b, available from https://tools.ietf.org/tools/rfcmarkup/