Internet Engineering Task Force A. Bierman
Internet-Draft Brocade
Intended status: Standards Track M. Bjorklund
Expires: March 6, 2011 Tail-f Systems
September 2, 2010
Network Configuration Protocol Access Control Model
draft-ietf-netconf-access-control-00
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
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provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 6, 2011.
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carefully, as they describe your rights and restrictions with respect
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.1.1. Requirements Notation . . . . . . . . . . . . . . . . 5
1.1.2. NETCONF Terms . . . . . . . . . . . . . . . . . . . . 5
1.1.3. NACM Terms . . . . . . . . . . . . . . . . . . . . . . 6
2. Authentication Requirements . . . . . . . . . . . . . . . . . 7
3. Access Control Requirements . . . . . . . . . . . . . . . . . 8
3.1. Protocol Control Points . . . . . . . . . . . . . . . . . 8
3.2. Simplicity . . . . . . . . . . . . . . . . . . . . . . . . 9
3.3. Procedural Interface . . . . . . . . . . . . . . . . . . . 9
3.4. Database Access . . . . . . . . . . . . . . . . . . . . . 9
3.4.1. Access Rights . . . . . . . . . . . . . . . . . . . . 10
3.4.2. <get> and <get-config> Operations . . . . . . . . . . 10
3.4.3. <edit-config> Operation . . . . . . . . . . . . . . . 10
3.4.4. <copy-config> Operation . . . . . . . . . . . . . . . 11
3.5. Users and Groups . . . . . . . . . . . . . . . . . . . . . 12
3.6. Maintenance . . . . . . . . . . . . . . . . . . . . . . . 12
3.7. Configuration Capabilities . . . . . . . . . . . . . . . . 12
3.8. Identifying Security Holes . . . . . . . . . . . . . . . . 13
3.9. Data Shadowing . . . . . . . . . . . . . . . . . . . . . . 13
3.10. NETCONF Specific Requirements . . . . . . . . . . . . . . 14
4. NETCONF Authentication and Authorization Model . . . . . . . . 15
4.1. SSH Public Key Authentication . . . . . . . . . . . . . . 15
4.2. Local User Password Authentication . . . . . . . . . . . . 16
4.3. RADIUS Password Authentication and Service
Authorization . . . . . . . . . . . . . . . . . . . . . . 16
4.3.1. Operation . . . . . . . . . . . . . . . . . . . . . . 16
5. NETCONF Access Control Model (NACM) . . . . . . . . . . . . . 18
5.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 18
5.1.1. Features . . . . . . . . . . . . . . . . . . . . . . . 18
5.1.2. External Dependencies . . . . . . . . . . . . . . . . 19
5.1.3. Message Processing Model . . . . . . . . . . . . . . . 19
5.2. Model Components . . . . . . . . . . . . . . . . . . . . . 21
5.2.1. Users . . . . . . . . . . . . . . . . . . . . . . . . 21
5.2.2. Groups . . . . . . . . . . . . . . . . . . . . . . . . 22
5.2.3. Sessions . . . . . . . . . . . . . . . . . . . . . . . 22
5.2.4. Access Permissions . . . . . . . . . . . . . . . . . . 22
5.2.5. Global Enforcement Controls . . . . . . . . . . . . . 23
5.2.6. Access Control Rules . . . . . . . . . . . . . . . . . 23
5.3. Access Control Enforcement Procedures . . . . . . . . . . 23
5.3.1. Initial Operation . . . . . . . . . . . . . . . . . . 24
5.3.2. Session Establishment . . . . . . . . . . . . . . . . 24
5.3.3. 'access-denied' Error Handling . . . . . . . . . . . . 24
5.3.4. Incoming RPC Message Validation . . . . . . . . . . . 24
5.3.5. Data Node Access Validation . . . . . . . . . . . . . 27
5.3.6. Outgoing <rpc-reply> Authorization . . . . . . . . . . 29
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5.3.7. Outgoing <notification> Authorization . . . . . . . . 30
5.4. Data Model Definitions . . . . . . . . . . . . . . . . . . 33
5.4.1. High Level Procedures . . . . . . . . . . . . . . . . 33
5.4.2. Data Organization . . . . . . . . . . . . . . . . . . 33
5.4.3. YANG Module . . . . . . . . . . . . . . . . . . . . . 34
5.5. IANA Considerations . . . . . . . . . . . . . . . . . . . 49
5.6. Security Considerations . . . . . . . . . . . . . . . . . 49
6. Normative References . . . . . . . . . . . . . . . . . . . . . 51
Appendix A. Usage Examples . . . . . . . . . . . . . . . . . . . 52
A.1. <groups> Example . . . . . . . . . . . . . . . . . . . . . 52
A.2. <module-rule> Example . . . . . . . . . . . . . . . . . . 53
A.3. <rpc-rule> Example . . . . . . . . . . . . . . . . . . . . 54
A.4. <data-rule> Example . . . . . . . . . . . . . . . . . . . 56
A.5. <notification-rule> Example . . . . . . . . . . . . . . . 58
Appendix B. Open Issues . . . . . . . . . . . . . . . . . . . . . 59
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 60
C.1. 00 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 61
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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 NETCONF protocol authentication and access
control mechanisms for the Operation and Content layers, as defined
in [RFC4741], and [RFC5277]. It contains five main sections:
1. Authentication Requirements
2. Access Control Requirements
3. NETCONF Authentication and Authorization Model
4. NETCONF Access Control Model (NACM)
5. YANG Data Model (nacm.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 RFC 4741 and are not redefined
here:
o client
o operation
o RPC operation
o server
o session
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o user
1.1.3. 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 should 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.
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2. Authentication Requirements
The authentication mechanism must support password authentication
over RADIUS, to support deployment scenarios with centralized
authentication servers. Additionally, local users must be supported,
for scenarios when no centralized authentication server exists, or
for situations where the centralized authentication server cannot be
reached from the device.
Since the mandatory transport protocol for NETCONF is SSH NETCONF
Over SSH [RFC4742], the authentication model must support SSH's
"publickey" and "password" authentication methods [RFC4252]
The model for authentication configuration should be flexible enough
to support authentication methods defined by other standard documents
or by vendors.
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3. Access Control Requirements
3.1. 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 must be protected at several
conceptual control points.
+-------------+ +-------------+
client | RPC | | prune | client
request --> | operation | | restricted | ---> reply
| allowed? | | <rpc-reply> |
+-------------+ | nodes? |
| +-------------+
| if any database 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:
RPC operation: Configurable permission to invoke specific RPC
operations is required. Wildcard or multiple target mechanisms to
reduce configuration and effort are also required.
NETCONF database: Configurable permission to read and/or alter
specific data nodes within any conceptual database 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.
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Notification Content: Configurable permission to receive specific
notification event types is required.
3.2. 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
should be easy to do simple things, and hard to do complex things,
instead of hard to do everything.
Configuration of the access control system must be simple to use.
Simple and common tasks should be easy to configure, and require
little expertise or domain-specific knowledge. Complex tasks should
be 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 RPC operation invocation, all conceptual database
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 database
access.
Access control does not need to be applied to NETCONF <hello>
messages.
3.3. 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 RPC operations is not required.
3.4. Database Access
It must be possible control access to specific nodes and sub-trees
within the conceptual NETCONF database.
In order for a user to obtain access to a particular database node,
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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 databases. For
example, the candidate configuration or the running configuration.
Only the standard NETCONF databases (candidate, running, and startup)
are controlled by the ACM. Local or remote files or databases
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.
Only a privileged user should be able to alter the factory-default
access control rules.
3.4.1. Access Rights
A small set of hard-wired database access rights is needed to control
access to all possible NETCONF database 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
database.
o Read: Allows the client to read a data node instance from a
database, or receive the notification event type.
o Update: Allows the client to update an existing data node instance
in a database.
o Delete: Allows the client to delete a data node instance from a
database.
o eXec: Allows the client to execute the protocol operation.
3.4.2. <get> and <get-config> Operations
Read operations for restricted configuration data, either directly or
via wildcard access, are silently omitted from the <rpc-reply>
message.
3.4.3. <edit-config> Operation
The NACM access rights are not directly coupled to the NETCONF
operation attribute, although they are similar. Instead, a NACM
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access right applies to all operations which would result in a
particular access operation to the target database. This section
describes how these access rights apply to the specific database
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 database 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 database 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' or 'delete' operation on a database 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 database. For example, a container or list
nodes may be present for naming purposes, which do not actually alter
the corresponding database 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 database. 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 database nodes must not be
exposed in any <rpc-error> elements within the reply.
3.4.4. <copy-config> Operation
Access control for the <copy-config> operation requires special
consideration because the operator is replacing the entire target
database. Write access to the entire database is needed for this
operation to succeed.
A client must have access to every database node, even ones that are
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not present in the source configuration data.
For example, consider a common use-case such as a simple backup and
restore procedure. The operator must have full read access to the
database 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 database, the server
will interpret the missing nodes as a request to delete those nodes,
and return an error.
3.5. 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 is needed which bypasses all access
control rules. This is needed in case the access control rules are
mis-configured, and all access is denied.
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.
3.6. 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.
3.7. Configuration Capabilities
Suitable control and monitoring mechanisms are needed to allow an
operator to easily manage all aspects of the ACM behavior. A
standard data model, suitable for use with the <edit-config>
operation must be available for this purpose.
Access control rules to restrict operations on specific sub-trees
within the configuration database must be supported. Existing
mechanisms should be used to identify the sub-tree(s) for this
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purpose.
3.8. 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 customary 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 must study
some more RFC text, and determine how to close the security
hole(s).
o The ACM on each server must 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 should be able to use machine-readable
statements to identity NETCONF content which should 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.
3.9. 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
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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 insure than unauthorized access to its
conceptual databases 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 must
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.
3.10. 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 database access request, even
for proprietary operations.
A session must always be authorized to invoke the <close-session>
operation, defined in [RFC4741].
A session must always be authorized to receive the <replayComplete>
and <notificationComplete> notification events, defined in [RFC5277]
The set of module name strings used within one particular server must
be unique.
Within a single server, the module namespace URI associated with a
specific module name string must persist across a reboot, and never
change, once assigned.
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4. NETCONF Authentication and Authorization Model
This document defines three authentication methods for use with
NETCONF:
publickey for local users over SSH
password for local users over any transport
password for RADIUS users over any transport
Additional methods may be defined by other standard documents or by
vendors.
Conceptually, the NETCONF transport subsystem authenticates the user,
and passes the name of the authenticated user to the NETCONF server.
The NETCONF server authorizes the user by mapping it to one or more
groups. Access to specific operations and content is then controlled
by access control rules as described in Section 5.
Some protocols, such as RADIUS, performs both authentication and
authorization, and has a mechanism to report authorization attributes
to the client. These attributes are made available to the NETCONF
server in an implementation specific manner.
This document defines two optional YANG features, 'local-users' and
'radius', which the server advertises to indicate support for
configuring local users on the device, and for configuring RADIUS
access, respectively.
4.1. SSH Public Key Authentication
If the NETCONF server advertises the 'local-users' feature,
configuration of local users and their SSH public keys is supported
in the /nacm/authentication/user list.
Public key authentication is requested by the SSH client. The SSH
server looks up the user name provided by the client in the /nacm/
authentication/user list, and verifies the key as described in
[RFC4253].
If the 'local-users' feature is supported, then when a NETCONF client
starts an SSH session towards the server, using the "publickey"
authentication 'method name' [RFC4252], the SSH server looks up the
user name given in the SSH authentication request in the /nacm/
authentication/user list,
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4.2. Local User Password Authentication
If the NETCONF server advertises the 'local-users' feature,
configuration of local users and their passwords is supported in the
/nacm/authentication/user list.
For NETCONF transport protocols that support password authentication,
the leaf-list 'user-authentication-order' is used to control if local
user password authentication should be used.
In SSH, password authentication is requested by the client. Other
NETCONF transport protocols may also support password authentication.
When local user password authentication is requested, the NETCONF
transport looks up the user name provided by the client in the /nacm/
authentication/user list, and verifies the password.
4.3. RADIUS Password Authentication and Service Authorization
If the NETCONF server advertises the 'radius' feature, it supports
user authentication and service authorization with RADIUS, as
described in this section.
For NETCONF transport protocols that support password authentication,
the leaf-list 'user-authentication-order' is used to control if
RADIUS password authentication should be used.
In SSH, password authentication is requested by the client. Other
NETCONF transport protocols may also support password authentication.
4.3.1. Operation
[Editor's Note: I prefer to keep this section short, and just refer
to the relevant rfcs which have detailed information on radius usage,
instead of duplicating this info here...]
When RADIUS user authentication is requested, the NETCONF transport
subsystem acts as a RADIUS client. In the Access-Request request
[RFC2865], the following RADIUS attributes SHOULD be sent by the
client [RFC5607]:
o Service-Type with the value Framed-Management
o Framed-Management-Protocol with the value NETCONF
o Management-Transport-Protection with the value Integrity-
Confidentiality-Protection
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As described in RFC 5607, if an Access-Accept message is received
which does not authorize the requested service, access MUST be
denied.
If any Management-Policy-Id attributes are present in the Access-
Accept message, they are treated as group names in the access control
procedure, as described in Section 5.
The following RADIUS attributes MAY be sent by the RADIUS server:
o Session-Timeout
o Idle-Timeout
See [RFC2865] for a description of these attributes. These timeout
values MUST be enforced by the NETCONF server.
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5. NETCONF Access Control Model (NACM)
5.1. 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.
5.1.1. 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. The server must be able to determine if a superuser
account is available, and if so, 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 database 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 RPC operation requests and denied database
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, or child
nodes within specific RPC input, RPC output, and notification
event type content.
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5.1.2. External Dependencies
The NETCONF [RFC4741] protocol is used for all management purposes
within this document. The server must support the features
identified by the 'NETCONF-base' capability. It is expected that the
mandatory transport mapping NETCONF Over SSH [RFC4742] 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 [I-D.ietf-netmod-yang] is used to
define the NETCONF data models specified in this document. The YANG
instance-identifier data type can be used to configure data-node-
specific access control rules.
5.1.3. 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.
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+-------------------------+
| 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 |
| database | | 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 user identity for the session is the
'superuser'.
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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 database or conceptual state data is accessed
by the RPC operation, then the configuration access must be
authorized first. 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.
5.2. Model Components
This section defines the conceptual components related to access
control model.
5.2.1. Users
A 'user' is the conceptual identity, 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.
The user name string is usually derived from the transport layer
during session establishment. A server is required to have an
authenticated user name for a session before <rpc> requests will be
accepted. Otherwise all write requests must be rejected with an
'access-denied' error-tag value. If a read operation is not
authorized, then the requested data is silently dropped from the
reply.
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.
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5.2.2. 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.
The server should support the 3 default group identities defined in
this document (admin, monitor, guest), however these roles are just
unique identities, provided for operator convenience. There is no
standard behavior defined for each group identity. That is up to the
operator who configures the groups.
5.2.3. 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.
5.2.4. Access Permissions
The access permissions are the NETCONF protocol specific set of
permissions that have been assigned to a particular session role or
group.
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 RPC operation execution separately
from configuration database access and outgoing messages:
create: Permission to create conceptual server data.
read: Read access to conceptual server data, <rpc-reply> and
<notification> content.
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update: Permission to modify existing conceptual server data.
delete: Permission to delete existing conceptual server data.
exec: Permission to invoke an RPC operation.
5.2.5. 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 RPC 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.
5.2.6. 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.
RPC operation rule: Controls access for a specific RPC 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.
5.3. Access Control Enforcement Procedures
There are seven separate phases that must 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 must
also be considered.
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5.3.1. 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
should 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
into the running configuration.
5.3.2. 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, a NETCONF server will enforce the access control
rules, based on the supplied user identity and the configuration data
stored on the server.
5.3.3. 'access-denied' Error Handling
The 'access-denied' error-tag is generated when the access control
system denies access to either a request to invoke an RPC operation
or a request to perform a particular operation on the configuration
database.
A server must not include any sensitive information in any <error-
info> elements within the <rpc-error> response.
5.3.4. 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.
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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 |
| database |
+----------------------+
Figure 3
Access control begins with the message dispatcher. Only well-formed
XML messages should be processed by the server.
After the server validates the <rpc> element, and determines the
namespace URI and the element name of the RPC operation being
requested, the RPC access control enforcer verifies that the session
is authorized to invoke the RPC operation.
The RPC operation is authorized by following these steps:
1. If the <enable-nacm> parameter is set to 'false', then the RPC
operation is permitted.
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2. If the session is associated with the 'superuser' account, then
the RPC operation is permitted.
3. If the requested operation is the NETCONF <close-session>
operation, then the RPC 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.
5. If no groups are found:
* If the requested RPC 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 RPC operation is denied.
* If the <exec-default> parameter is set to 'permit', then
permit the RPC operation, otherwise deny the request.
6. Check if there are any matching <rpc-rule> entries for the
requested RPC operation. Any matching rules are processed in
user-defined order, in case there are multiple <rpc-rule>
entries for the requested RPC 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, the the 'nacm-
action' leaf is checked. If is equal to 'permit', then the RPC
operation is permitted, otherwise it is denied.
9. Check if there are any matching <module-rule> entries for the
same module as the requested RPC operation. Any matching rules
are processed in user-defined order, in case there are multiple
<module-rule> entries for the module containing the requested
RPC 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.
11. If the <module-rule> entry is considered a match, the the 'nacm-
action' leaf is checked. If is equal to 'permit', then the RPC
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operation is permitted, otherwise it is denied.
12. If the requested operation is identified an a nacm:secure or
nacm:very-secure RPC operation, then the RPC operation is
denied.
13. If the <exec-default> parameter is set to 'permit', then permit
the RPC operation, otherwise the RPC operation is denied.
If the session is not authorized to invoke the RPC 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 RPC operation name. For example,
'/rpc/edit-config' represents the <edit-config> operation in the
NETCONF base namespace.
If the configuration database is accessed, either directly or as a
side effect of the RPC operation, then the server must intercept the
operation and make sure the session is authorized to perform the
requested operation on the specified data.
5.3.5. Data Node Access Validation
If a data node within a configuration database 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.
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
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definition statements (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, the 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.
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.
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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, the 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 inlcude 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.
5.3.6. Outgoing <rpc-reply> Authorization
The <rpc-reply> message should 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.
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For RPC operations which do not access any data nodes, then any
client authorized to invoke the RPC operation is also authorized to
receive the <rpc-reply> for that RPC operation.
5.3.7. Outgoing <notification> Authorization
The <notification> message should 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.
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NETCONF server
+------------+
| XML |
| message |
| generator |
+------------+
^
|
+----------------+
| <notification> |
| generator |
+----------------+
^
|
+=================+
| <notification> |
| access control |
| <eventType> |
+=================+
^
|
+------------------------+
| server instrumentation |
+------------------------+
| ^
V |
+----------------------+
| configuration |
| database |
+----------------------+
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.
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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.
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.
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5.4. Data Model Definitions
This section defines the semantics of the conceptual data structures
found in the data model in Section 5.4.
5.4.1. 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 RPC
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.
5.4.2. Data Organization
The top-level element is called <nacm>, and it is defined in the
'nacm' 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.
container <authentication>: Configuration of the NETCONF server user
authentication mechanisms.
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 RPC
operation execution requests.
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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.
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 RPC
operation invocation.
list <data-rule>: Configures the access control rules for
configuration database access.
list <notification-rule>: Configures the access control rules for
controlling delivery of <notification> events.
5.4.3. YANG Module
The following YANG module is provided to specify the normative
NETCONF content that must by supported by the server.
<CODE BEGINS> file="nacm@2010-06-29.yang"
module nacm {
namespace "file://draft-bierman-netconf-access-control-02.txt";
prefix "nacm";
import ietf-yang-types {
prefix yang;
}
import ietf-inet-types {
prefix inet;
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}
organization
"IETF";
contact
"Andy Bierman <andy.bierman@brocade.com>
Martin Bjorklund <mbj@tail-f.com>";
description
"NETCONF Server Access Control Model";
revision 2010-09-02 {
description
"Initial version (work-in-progress).";
}
/*
* Extension statements
*/
extension secure {
description
"Used to indicate that the data model node
represents a sensitive security system parameter.
If present, the NETCONF server will only allow
the designated '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, 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
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otherwise.";
}
/*
* Features
*/
feature authentication {
description
"Indicates that the NETCONF server can be configured
to do authentication of users.";
}
feature radius {
if-feature authentication;
description
"Indicates that the NETCONF server can be
configured to act as a NAS and authenticate users
with RADIUS.";
reference
"RFC 2865: Remote Authentication Dial In User Service (RADIUS)
RFC 5607: Remote Authentication Dial-In User Service (RADIUS)
Authorization for Network Access Server (NAS)
Management";
}
feature local-users {
if-feature authentication;
description
"Indicates that the NETCONF server supports
local user authentication.";
}
/*
* Identities
*/
identity authentication-method {
description
"Base identity for NETCONF authentication methods.";
}
identity radius {
base authentication-method;
description
"Indicates NETCONF authentication using RADIUS.";
reference
"RFC 2865: Remote Authentication Dial In User Service (RADIUS)
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RFC 5607: Remote Authentication Dial-In User Service (RADIUS)
Authorization for Network Access Server (NAS)
Management";
}
identity local-users {
base authentication-method;
description
"Indicates password-based NETCONF authentication using locally
configured users.";
}
/*
* Derived types
*/
typedef nacm-user-name-type {
type string {
length "1..max";
}
description
"General Purpose User Name string.";
}
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
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"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 database
node instance is a delete operation.";
}
bit exec {
description
"Execution access to the specified RPC operation.
Any RPC operation invocation is an exec operation.";
}
}
}
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.";
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}
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.
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.";
}
typedef md5-crypt {
type string {
pattern "$0$.* | $1$[a-zA-Z0-9./]{2,8}$.*";
}
description
"The md5-crypt type is used to store a password hash based on the
MD5 message digest algorithm. When a clear text value is set to
a leaf of this type, the server calculates a MD5 password hash,
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and stores the result in the datastore. Thus, the password is
never stored in clear text.
When a leaf of this type is read, the stored password hash is
returned.
A value of this type matches one of the forms:
$0$<clear text password>
$1$<salt>$<password hash>
The '$0$' prefix signals that the value is clear text. When
such a value is received by the server, an MD5 digest is
calculated, and the string '$1$<salt>$' is prepended to the
result, where <salt> is a random 2-8 characters long salt used
to generate the digest. This value is stored in the
configuration data store.
If a value starting with '$1$<salt>$' is received, the server
knows that the value already represents an MD5 digest, and
stores it as is in the data store.
When a server needs to verify a password given by a user, it
finds the stored password hash string for that user, extracts
the salt, and calculates the hash with the salt and given
password as input. If the calculated hash value is the same as
the stored value, the password given by the client is correct.
The digest algorithm is the md5 crypt function used for
encrypting passwords for various UNIX systems.";
reference
"RFC 1321: The MD5 Message-Digest Algorithm
http://en.wikipedia.org/wiki/Crypt_(Unix)";
// FIXME: ref to wikipedia ok??
}
container nacm {
nacm:very-secure;
presence
"An empty nacm container indicates that the
NACM service is running, and using
all default parameters.";
description
"Parameters for NETCONF Access Control Model.";
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container authentication {
nacm:very-secure;
if-feature authentication;
description
"The authentication configuration for the
NETCONF server.";
leaf-list user-authentication-order {
type identityref {
base authentication-method;
}
must '(. = "nacm:radius" and ../radius/server) or'
+ '(. != "nacm:radius")' {
error-message
"When 'radius' is used, a radius server
must be configured.";
}
ordered-by user;
description
"When the NETCONF server authenticates a user with
a password, it tries the authentication methods in this
leaf-list in order. If authentication with one method
fails, the next method is used. If no method succeeds,
the user is denied access.
If the 'radius' feature is advertised by the NETCONF
server, the 'radius' identity can be added to this
list.
If the 'local-users' feature is advertised by the
NETCONF server, the 'local-users' identity can be
added to this list.";
}
container radius {
if-feature radius;
description
"The radius configuration for the NETCONF server.";
list server {
key address;
description
"The radius server configuration used by
the NETCONF server.";
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leaf address {
type inet:host;
description
"The address of the radius server.";
}
leaf port {
type inet:port-number;
default "1812";
description
"The port number of the radius server.";
}
leaf shared-secret {
type string; // FIXME
/*
We're using a special type aes-cfb-128-encrypted-string which works
like the md5-crypt string, but encrypts the clear text value using a
pre-provisioned password (not part of the config db!).
We use $0$ for cleartext and $4$ for the encrypted value.
(we also have a des-version which uses $3$).
But I was thinking that maybe we could define a type for encrypted
values without specifying the encryption algorithm, just specifying
the format. $0$<clear text> | $x$<encrypted value>, and how it is
encrypted is implementation specific.
One alternative is to store this shared secret in clear text. It is
transmitted over a secure transport, and marked as very-secure. (The
same argument could be made for user passwords, but these are
personal and not even root should be able to read my passwd in clear
text, so it makes more sense to keep them hidden.)
*/
description
"The shared secret which is known to both the RADIUS
client and server.";
reference
"RFC 2865: Remote Authentication Dial In User Service";
}
/*
How about configuration of number of retransmits
and timeout?
*/
}
}
list user {
if-feature local-users;
key name;
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description
"The list of local users configured on this device.";
leaf name {
type nacm-user-name-type;
description
"The user name string identifying this entry.";
}
leaf password {
type md5-crypt;
description
"The password for this entry.";
}
leaf ssh-dsa {
type binary;
description
"The public DSA key for this entry.";
}
leaf ssh-rsa {
type binary;
description
"The public RSA key for this entry.";
}
}
}
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";
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description
"Controls whether create, update, or delete access
is granted if no appropriate rule is found for a
particular write request.";
}
leaf exec-default {
type 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 {
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
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"Each entry identifies the user name of
a member of the group associated with
this entry.";
}
}
}
container rules {
description
"NETCONF Access Control Rules.";
grouping common-rule-parms {
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;
mandatory true;
description
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"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";
ordered-by user;
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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
database, 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;
description
"Schema Instance Identifier associated with the data node
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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 database
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
"Name of the notification event.";
}
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uses common-rule-parms;
}
}
}
}
<CODE ENDS>
Figure 5
5.5. IANA Considerations
There are two actions that are requested of IANA:
1. register data model schema namespace URI (TBD)
2. register data model name ('nacm')
5.6. 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,
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 RPC operations will
have undocumented side effects. An administrator should construct
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access control rules such that the configuration database is
protected from such side effects. Also, such RPC operations should
never be invoked by a session using the 'superuser' administrative
user.
There is a risk that non-standard RPC 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 should avoid
using data models which use this practice.
An administrator should 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 must be taken not to disrupt the access control
enforcement.
An administrator should 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
o write-default
o exec-default
o groups
o rules
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6. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000.
[RFC4252] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
Authentication Protocol", RFC 4252, January 2006.
[RFC4253] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
Transport Layer Protocol", RFC 4253, January 2006.
[RFC4741] Enns, R., "NETCONF Configuration Protocol", RFC 4741,
December 2006.
[RFC4742] Wasserman, M. and T. Goddard, "Using the NETCONF
Configuration Protocol over Secure SHell (SSH)", RFC 4742,
December 2006.
[RFC5277] Chisholm, S. and H. Trevino, "NETCONF Event
Notifications", RFC 5277, July 2008.
[RFC5607] Nelson, D. and G. Weber, "Remote Authentication Dial-In
User Service (RADIUS) Authorization for Network Access
Server (NAS) Management", RFC 5607, July 2009.
[W3C.REC-xml]
Bray, T., Paoli, J., Sperberg-McQueen, C., and E. Maler,
"Extensible Markup Language (XML) 1.0 (2nd ed)", W3C REC-
xml, October 2000, <http://www.w3.org/TR/REC-xml>.
[I-D.ietf-netmod-yang]
Bjorklund, M., "YANG - A data modeling language for the
Network Configuration Protocol (NETCONF)",
draft-ietf-netmod-yang-13 (work in progress), June 2010.
[I-D.ietf-netmod-yang-types]
Schoenwaelder, J., "Common YANG Data Types",
draft-ietf-netmod-yang-types-09 (work in progress),
April 2010.
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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 must 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="file://draft-bierman-netconf-access-control-02.txt">
<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'.
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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="file://draft-bierman-netconf-access-control-02.txt">
<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>
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<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 RPC
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 RPC operation.
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<nacm xmlns="file://draft-bierman-netconf-access-control-02.txt">
<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 RPC operation rules:
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rpc-1: This rule prevents the monitor or guest groups from invoking
the NETCONF <kill-session> RPC operation.
rpc-2: This rule prevents the monitor or guest groups from invoking
the NETCONF <delete-config> RPC operation.
rpc-3: This rule allows the monitor group to invoke the NETCONF
<edit-config> RPC 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="file://draft-bierman-netconf-access-control-02.txt">
<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']
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</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.
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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="file://draft-bierman-netconf-access-control-02.txt">
<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.
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Appendix B. Open Issues
-- RFC Ed.: remove this section before publication.
1. Do modules need to be identified by their XML namespace URI, or
is the module name good enough?
2. Are any more wildcard mechanisms needed to specify the scope of
an access control rule?
3. Should regular expressions (module='foo-*') be allowed in schema-
instance-identifier strings?
4. Should XPath be allowed for specifying access control rules for
data nodes?
5. Are any 'access-denied' notifications needed?
6. Should data rules support nodes that would not be eligible for
retrieval with the <get> operation? If so, should schema nodes
such as rpc 'input' or 'output' be in the path expression? How
would notification content be identified?
7. Do any external access control models need to be supported
somehow? For example, should the <groups> configuration be
optionally read-only, so it can just mirror the internal
(external or proprietary) group configuration?
8. Should the nacm:secure and nacm:very-secure extensions be
optional to support, via a YANG feature?
9. Should the default access levels (e.g., read-default) be more
restrictive by default? Shiuld these defaults be a vendor
decision? An operator decision? It is important that the server
be able to install a factory default <nacm> container if needed.
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Appendix C. Change Log
-- RFC Ed.: remove this section before publication.
C.1. 00
Initial version cloned from
draft-bierman-netconf-access-control-02.txt.
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Authors' Addresses
Andy Bierman
Brocade
Email: andy.bierman@brocade.com
Martin Bjorklund
Tail-f Systems
Email: mbj@tail-f.com
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