Network Working Group J. Strassner
Internet-draft Cisco Systems
Category: Standards Track E. Ellesson
B. Moore
IBM Corporation
May 1999
Policy Framework Core Information Model
draft-ietf-policy-core-schema-03.txt
May 17, 1999 15:02
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Abstract
This document takes as its starting point the object-oriented
information model for representing policy information currently under
development as part of the Common Information Model (CIM) activity in
the Desktop Management Task Force (DMTF). This CIM model defines two
hierarchies of object classes: structural classes representing
policy information and control of policies, and relationship classes
that indicate how instances of the structural classes are related to
each other. In general, both of these class hierarchies will need to
be mapped to a particular data store.
This draft defines the mapping of these DMTF-defined CIM classes to a
directory that uses LDAPv3 as its access protocol. When mapping to an
LDAP schema, the structural classes can be mapped more or less
directly. The relationship hierarchy, however, must be mapped to a
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form suitable for directory implementation. Since this mapping of the
relationship classes could be done in a number of different ways,
there is the risk of non-interoperable implementations. To avoid
this possibility, this document provides a single mapping that all
implementations using an LDAP directory as their policy repository
SHALL use.
Classes are also added to the LDAP schema to improve the performance
of a client's interactions with an LDAP server when the client is
retrieving large amounts of policy-related information. These
classes exist only to optimize LDAP retrievals: there are no classes
in the CIM model that correspond to them.
The LDAP schema described in this document consists of six very
general classes: policy (an abstract class), policyGroup, policyRule,
policyCondition, policyTimePeriodCondition, and policyAction. The
schema also contains two less general classes: vendorPolicyCondition
and vendorPolicyAction. To achieve the mapping of the CIM
relationships, the schema contains two auxiliary classes:
policyGroupContainmentAuxClass and policyRuleContainmentAuxClass.
Finally, the schema includes two classes policySubtreesPtrAuxClass
and policyElement for optimizing LDAP retrievals, and a structural
class policyInstance for attaching auxiliary classes representing
policy conditions and policy actions. In all, therefore, the schema
contains 13 classes.
Within the context of this document, the term "Core [Policy] Schema"
is used to refer to the LDAP class definitions it contains.
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Table of Contents
1. Introduction.....................................................4
2. Modeling Policies................................................6
2.1. Policy Scope................................................8
3. Overview of the Schema...........................................8
3.1. Relationships...............................................9
3.2. Associations...............................................10
3.3. Aggregations...............................................10
3.4. Key Relationships in the CIM Policy Model..................10
4. Inheritance Hierarchy for the LDAP Core Policy Schema...........12
5. General Discussion of the CIM-to-LDAP Mapping...................13
5.1. Summary of Class and Relationship Mappings.................13
5.2. Naming Attributes in the Core Schema.......................15
5.3. Flexibility Gained through Auxiliary Classes...............16
5.4. Location and Retrieval of Policy Objects in the Directory..17
5.4.1. Aliases..................................................19
6. Class Definitions...............................................20
6.1. The Abstract Class policy..................................20
6.1.1. The Attribute commonName (cn)............................21
6.1.2. The Attribute caption....................................21
6.1.3. The Attribute description................................21
6.1.4. The Attribute policyKeywords.............................22
6.2. The Class policyGroup......................................22
6.2.1. The Attribute policyGroupName............................24
6.3. The Class policyRule.......................................24
6.3.1. The Attribute policyRuleName.............................26
6.3.2. The Attribute policyRuleEnabled..........................26
6.3.3. The Attribute policyRuleConditionListType................27
6.3.4. The Attribute policyRuleConditionList....................27
6.3.5. The Attribute policyRuleActionList.......................29
6.3.6. The Attribute policyRuleValidityPeriodList...............30
6.3.7. The Attribute policyRuleUsage............................30
6.3.8. The Attribute policyRulePriority.........................31
6.3.9. The Attribute policyRuleMandatory........................31
6.3.10. The Attribute policyRuleSequencedActions................32
6.4. The Class policyCondition..................................32
6.4.1. The Attribute policyConditionName........................34
6.5. The Class policyTimePeriodCondition........................34
6.5.1. The Attribute ptpConditionTime...........................36
6.5.2. The Attribute ptpConditionMonthOfYearMask................36
6.5.3. The Attribute ptpConditionDayOfMonthMask.................37
6.5.4. The Attribute ptpConditionDayOfWeekMask..................37
6.5.5. The Attribute ptpConditionTimeOfDayMask..................38
6.5.6. The Attribute ptpConditionTimeZone.......................39
6.6. The Class vendorPolicyCondition............................39
6.6.1. The Attribute vendorPolicyConstraintData.................40
6.6.2. The Attribute vendorPolicyConstraintEncoding.............41
6.7. The Class policyAction.....................................41
6.7.1. The Attribute policyActionName...........................41
6.8. The Class vendorPolicyAction...............................42
6.8.1. The Attribute vendorPolicyActionData.....................42
6.8.2. The Attribute vendorPolicyActionEncoding.................43
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6.9. The Class policyInstance...................................43
6.10. The Auxiliary Class policyElement.........................44
6.11. The Auxiliary Class policySubtreesPtrAuxClass.............44
6.11.1. The Attribute policySubtreesAuxContainedSet.............45
6.12. The Auxiliary Class policyGroupContainmentAuxClass........46
6.12.1. The Attribute policyGroupsAuxContainedSet...............46
6.13. The Auxiliary Class policyRuleContainmentAuxClass.........46
6.13.1. The Attribute policyRulesAuxContainedSet................47
7. Extending the Core Schema.......................................48
7.1. Subclassing policyCondition and policyAction...............48
7.2. Using the Vendor Policy Encoding Attributes................48
7.3. Using Time Validity Periods................................49
8. Security Considerations.........................................49
9. Intellectual Property...........................................49
10. Acknowledgments................................................50
11. References.....................................................50
12. Authors' Addresses.............................................51
13. Full Copyright Statement.......................................51
14. Appendix A - Guidelines for Construction of DNs................52
1. Introduction
This document takes as its starting point the object-oriented
information model for representing policy information currently under
development as part of the Common Information Model (CIM) activity in
the Desktop Management Task Force (DMTF). This CIM model defines two
hierarchies of object classes: structural classes representing policy
information and control of policies, and relationship classes that
indicate how instances of the structural classes are related to each
other. In general, both of these class hierarchies will need to be
mapped to a particular data store.
This draft defines the mapping of these DMTF-defined CIM classes to a
directory that uses LDAPv3 as its access protocol. Two types of
mappings are involved:
o For the structural classes in the CIM model, the mapping is
basically one-for-one: CIM classes map to LDAP classes, CIM
properties map to LDAP attributes.
o For the relationship classes in the CIM model, different mappings
are possible. In this document the CIM relationship classes and
their properties are mapped in three ways: to LDAP auxiliary
classes, to attributes representing DN pointers, and to "composite"
attributes representing DN pointers with additional data elements.
Implementations that use an LDAP directory as their policy repository
SHALL use the LDAP policy schema defined in this document. The use
of the CIM information model as the starting point enables the schema
and the relationship class hierarchy to be extensible, such that
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other types of policy repositories, such as relational databases, can
also use this information.
These policy classes and their relationships are sufficiently generic
to allow them to represent policies related to anything. However, it
is expected that their initial application will be for representing
policies related to QoS (DiffServ and IntServ) and to IPSec. Policy
models for application-specific areas such as these may extend the
Core Schema in several ways. The preferred way is to use the
policyGroup, policyRule, and policyTimePeriodCondition classes
directly, as a foundation for representing and communicating policy
information. Then, specific subclasses derived from policyCondition
and policyAction can capture application-specific definitions of
conditions and actions of policies. These subclasses of
policyCondition and policyAction MUST be defined as auxiliary
classes, so that they can be used to form both simple and complex
policy rules, as described below in Section 5.3.
Two subclasses, vendorPolicyCondition and vendorPolicyAction, are
also included in this document, to provide a standard escape
mechanism for vendor-specific extensions to the Core Policy Schema.
This document fits into the overall framework for representing,
deploying, and managing policies being developed by the Policy
Framework Working Group. The initial work to define this framework
is in reference [1]. More specifically, this document builds on the
core policy classes first introduced in references [2] and [3]. It
also draws on the work done for the Directory-enabled Networks (DEN)
specification, reference [4]. Work on the DEN specification by the
DEN Ad-Hoc Working Group itself has been completed. Further work to
standardize the models contained in it will be the responsibility of
selected working groups of the CIM effort in the Desktop Management
Task Force (DMTF). Standardization of the core policy model is the
responsibility of the SLA Policy working group.
This document is organized in the following manner:
o Section 2 provides a general overview of policies and how they are
modeled.
o Section 3 takes a brief look at the DMTF's CIM policy classes and
relationships. The complete CIM policy definitions are available
on the DMTF's web site; see reference [9].
o The remainder of the document presents the mapping of the CIM
policy classes and relationships into an LDAP schema.
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 RFC 2119, reference
[5].
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2. Modeling Policies
The classes comprising the Core Policy Schema are intended to serve
as an extensible class hierarchy (through specialization) for
defining policy objects that enable application developers, network
administrators, and policy administrators to represent policies of
different types.
One way to think of a policy-controlled network is to first model the
network as a state machine and then use policy to control which state
a policy-controlled device should be in or is allowed to be in at any
given time. Given this approach, policy is applied using a set of
policy rules. Each policy rule consists of a set of conditions and a
set of actions. Policy rules may be aggregated into policy groups.
These groups may be nested, to represent a hierarchy of policies.
The set of conditions associated with a policy rule specifies when
the policy rule is applicable. The set of conditions can be expressed
as either an ORed set of ANDed sets of condition statements or an
ANDed set of ORed sets of statements. Individual condition statements
can also be negated. These combinations are termed, respectively,
Disjunctive Normal Form (DNF) and Conjunctive Normal Form (CNF) for
the conditions. Please note that it is explicitly NOT a goal of this
specification to represent more complicated conditions (such as those
that may be found in a procedural language) at this time.
If the set of conditions associated with a policy rule evaluates to
TRUE, then a set of actions that either maintain the current state of
the object or transition the object to a new state may be executed.
For the set of actions associated with a policy rule, it is possible
to specify an order of execution, as well as an indication of whether
the order is required or merely recommended. It is also possible to
indicate that the order in which the actions are executed does not
matter.
Policy rules themselves can be prioritized. One common reason for
doing this is to express an overall policy that has a general case
with a few specific exceptions.
For example, a general QoS policy rule might specify that traffic
originating from members of the engineering group is to get Bronze
Service. A second policy rule might express an exception: traffic
originating from John, a specific member of the engineering group, is
to get Gold Service. Since traffic originating from John satisfies
the conditions of both policy rules, and since the actions associated
with the two rules are incompatible, a priority needs to be
established. By giving the second rule (the exception) a higher
priority than the first rule (the general case), a policy
administrator can get the desired effect: traffic originating from
John gets Gold Service, and traffic originating from all the other
members of the engineering group gets Bronze Service.
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Policies can either be used in a stand-alone fashion or aggregated
into policy groups to perform more elaborate functions. Stand-alone
policies are called policy rules. Policy groups are aggregations of
policy rules, or aggregations of policy groups, but not both. Policy
groups can model intricate interactions between objects that have
complex interdependencies. Examples of this include a sophisticated
user logon policy that sets up application access, security, and
reconfigures network connections based on a combination of user
identity, network location, logon method and time of day. A policy
group represents a unit of reusability and manageability in that its
management is handled by an identifiable group of administrators and
its policy rules apply equally to the scope of the policy group.
Stand-alone policies are those that can be expressed in a simple
statement. They can be represented effectively in schemata or MIBs.
Examples of this are VLAN assignments, simple YES/NO QoS requests,
and IP address allocations. A specific design goal of this schema is
to support both stand-alone and aggregated policies.
Policy groups and rules can be classified by their purpose and
intent. This classification is useful in querying or grouping policy
rules. It indicates whether the policy is used to motivate when or
how an action occurs, or to characterize services (that can then be
used, for example, to bind clients to network services). Describing
each of these concepts in more detail,
o Motivational Policies are solely targeted at whether or how a
policy's goal is accomplished. Configuration and Usage Policies
are specific kinds of Motivational Policies. Another example is
the scheduling of file backup based on disk write activity from
8am to 3pm, M-F.
o Configuration Policies define the default (or generic) setup of a
managed entity (for example, a network service). Examples of
Configuration Policies are the setup of a network forwarding
service or a network-hosted print queue.
o Installation Policies define what can and cannot be put on a
system or component, as well as the configuration of the
mechanisms that perform the install. Installation policies
typically represent specific administrative permissions, and can
also represent dependencies between different components (e.g.,
to complete the installation of component A, components B and C
must be previously successfully installed or uninstalled).
o Error and Event Policies. For example, if a device fails between
8am and 9pm, call the system administrator, else call the Help
Desk.
o Usage Policies control the selection and configuration of
entities based on specific "usage" data. Configuration Policies
can be modified or simply re-applied by Usage Policies. Examples
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of Usage Policies include upgrading network forwarding services
after a user is verified to be a member of a "gold" service
group, or reconfiguring a printer to be able to handle the next
job in its queue.
o Security Policies deal with verifying that the client is actually
who the client purports to be, permitting or denying access to
resources, selecting and applying appropriate authentication
mechanisms, and performing accounting and auditing of resources.
o Service Policies characterize network and other services (not use
them). For example, all wide-area backbone interfaces shall use a
specific type of queuing.
Service policies describe services available in the network.
Usage policies describe the particular binding of a client of the
network to services available in the network.
These categories are represented in the Core Schema by special values
defined for the policyKeywords attribute of the abstract class
policy.
2.1. Policy Scope
Policies represent business goals and objectives. A translation must
be made between these goals and objectives and their realization in
the network. An example of this could be a Service Level Agreement
(SLA), and its objectives and metrics (Service Level Objectives, or
SLOs), that are used to specify services that the network will
provide for a given client [8]. The SLA will usually be written in
high-level business terminology. SLOs address more specific metrics
in support of the SLA. These high-level descriptions of network
services and metrics must be translated into lower-level, but also
vendor- and device-independent specifications. The Core Schema
classes are intended to serve as the foundation for these vendor- and
device-independent specifications.
It is envisioned that the definition of policy in this draft is
generic in nature and is applicable to Quality of Service (QoS), to
non-QoS networking applications (e.g., DHCP and IPSEC), and to non-
networking applications (e.g., backup policies, auditing access,
etc.).
3. Overview of the Schema
The following diagram provides an overview of the five central
classes comprising the CIM core policy schema, and their
relationships to each other. Note that the abstract class Policy and
the two extension classes VendorPolicyCondition and
VendorPolicyAction are not shown.
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(various other CIM classes)
^ 0..n ^ 0..n
* *
* RuleJurisdiction * GroupJurisdiction
* *
* ********************
* *
* * **************
* * * *
* * 0..n * * ContainedPolicyGroup
* * +------v------+ *
* ****> PolicyGroup <******
* 0..n| | 0..n
* +------^------+
* 0..n *
* * ContainedPolicyRule
* 0..n *
* +------v------+
* | |
* | PolicyRule |
* | | ContainedPolicyCondition
*******> <****************************
0..n | | 0..n *
| | * 0..n
| | +---------v------------+
| | | PolicyCondition |
| | +----------------------+
| | PolicyRuleValidityPeriod ^
| <****************** I
| | 0..n * I
| | * 0..n ^
| | +----v----------------------+
| | | PolicyTimePeriodCondition |
| | +---------------------------+
| |
| | ContainedPolicyAction
| <*****************************
| | 0..n *
| | * 0..n
| | +----------v-----------+
| | | PolicyAction |
+-------------+ +----------------------+
Figure 1. Overview of the CIM Policy Classes and Their
Relationships
3.1. Relationships
Relationships are a central feature of information models. A
relationship represents a physical or conceptual connection between
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objects. CIM and DEN define the general concept of an association
between two (or more) objects. Two types of associations are
aggregations (which express whole-part relationships) and other
relationships, such as those that express dependency. Both are used
in this model.
3.2. Associations
An association is a class that contains two or more references, where
each reference identifies another object. An association is defined
using a class. Associations can be defined between classes without
affecting any of the related classes. That is, addition of an
association does not affect the interface of the related classes.
3.3. Aggregations
An aggregation is a strong form of an association. An aggregation is
usually used to represent a "whole-part" relationship. This type of
relationship defines the containment relationship between a system
and the components that make up the system. Aggregation often
implies, but does not require, that the aggregated objects have
mutual dependencies.
3.4. Key Relationships in the CIM Policy Model
The following relationships are shown in the preceding figure:
o The ContainedPolicyGroup relationship enables policy groups to be
nested. This is critical for scalability and manageability, as it
enables complex policies to be constructed from multiple simpler
policies for administrative convenience. For example, a policy
group representing policies for the US might have nested within
it policy groups for the Eastern and Western US.
In the LDAP schema, the ContainedPolicyGroup relationship is
mapped to the policyGroupsAuxContainedSet attribute in the
auxiliary class policyGroupContainmentAuxClass. (Other data
stores may define a different mapping). This attribute enables a
policyGroup to identify another policyGroup as its offspring.
o A policy group may aggregate one or more policy rules, via the
ContainedPolicyRule relationship. Grouping of policy rules into a
policy group is again for administrative convenience; a policy
rule may also be used by itself, without belonging to a policy
group. In the LDAP schema, the ContainedPolicyRule relationship
is mapped to the policyRulesAuxContainedSet attribute in the
auxiliary class policyRuleContainmentAuxClass.
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o A policy group or policy rule may also be aggregated by an
instance of any class to which the policyGroupContainmentAuxClass
or policyRuleContainmentAuxClass class has been attached. Again,
this is for administrative convenience. If the directory entry
to which the policyGroupContainmentAuxClass or
policyRuleContainmentAuxClass has been attached is a policy
group, then the pointer in the auxiliary class realizes one of
the relationships discussed above; a separate attribute is not
needed in the policyGroup class. If the directory entry is
something other than a policy group, then the pointer in the
auxiliary class realizes a Jurisdiction relationship from the CIM
model.
o A policy rule aggregates zero or more instances of the
PolicyCondition class, via the ContainedPolicyCondition
association. A policy rule that aggregates zero policy
conditions is not a valid rule -- it may, for example, be in the
process of being entered into the policy repository. A policy
rule has no effect until it is valid. The conditions aggregated
by a policy rule are grouped into two levels of lists: either an
ORed set of ANDed sets of conditions (DNF, the default) or an
ANDed set of ORed sets of conditions (CNF). Individual
conditions in these lists may be negated. The attribute
PolicyRuleConditionListType specifies which of these two grouping
schemes applies to a particular PolicyRule.
Since conditions may be defined explicitly in a subclass of
PolicyRule, the AND/OR mechanism to combine these conditions with
other (associated) PolicyConditions MUST be specified by the
PolicyRule's subclass.
In either case, the conditions are used to determine whether to
perform the actions associated with the PolicyRule.
o One or more policy time periods may be among the conditions
associated with a policy rule via the ContainedPolicyCondition
association. In this case, the time periods are simply
additional conditions to be evaluated along with any other
conditions specified for the rule.
o A different relationship between a policy rule and a policy time
period is represented by the PolicyRuleValidityPeriod
association: scheduled activation and deactivation of the policy
rule. If a policy rule is associated with multiple policy time
periods via this association, then the rule is active if at least
one of the time periods indicates that it is active. (In other
words, the time periods are ORed to determine whether the rule is
active.) A policy time period may be aggregated by multiple
policy rules. A rule that does not point to a policy time period
via this association is, from the point of view of scheduling,
always active. It may, however, be inactive for other reasons.
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Time periods are a general concept that can be used in other
applications. However, they are mentioned explicitly here in this
specification since they are frequently used in policy
applications.
o A policy rule may aggregate zero or more policy actions. A
policy rule that aggregates zero policy actions is not a valid
rule -- it may, for example, be in the process of being entered
into the policy repository. A policy rule has no effect until it
is valid. The actions associated with a PolicyRule may be given
a required order, a recommended order, or no order at all. For
actions represented as separate objects, the
ContainedPolicyAction aggregation can be used to express an
order. For actions defined explicitly in a subclass of
PolicyRule, the ordering mechanism must be specified in the
subclass definition.
4. Inheritance Hierarchy for the LDAP Core Policy Schema
The following diagram illustrates the class hierarchy for the LDAP
policy schema classes:
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top
|
+--policy (abstract)
| |
| +---policyGroup (structural)
| |
| +---policyRule (structural)
| |
| +---policyCondition (auxiliary)
| | |
| | +---policyTimePeriodCondition (auxiliary)
| | |
| | +---vendorPolicyCondition (auxiliary)
| |
| +---policyAction (auxiliary)
| | |
| | +---vendorPolicyAction (auxiliary)
| |
| +--policyInstance (structural)
| |
| +--policyElement (auxiliary)
|
+--policySubtreesPtrAuxClass (auxiliary)
|
+--policyGroupContainmentAuxClass (auxiliary)
|
+--policyRuleContainmentAuxClass (auxiliary)
Figure 2. LDAP Class Inheritance Hierarchy for the Core Policy
Schema
5. General Discussion of the CIM-to-LDAP Mapping
The classes described in Section 6 below contain certain
optimizations for a directory that uses LDAP as its access protocol.
One example of this is the use of auxiliary classes to represent CIM
relationships. Other data stores might need to implement these
relationships differently. A second example is the introduction of
classes specifically designed to optimize retrieval of large amounts
of policy-related data from a directory. This section discusses some
general topics related to the mapping from CIM to LDAP.
5.1. Summary of Class and Relationship Mappings
Eight of the classes in the LDAP Core Policy Schema come directly
from corresponding CIM classes. Note that names of classes begin
with an upper case character in CIM, but with a lower case character
in LDAP.
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+---------------------------+---------------------------+
| CIM Class | LDAP Class |
+---------------------------+---------------------------+
+---------------------------+---------------------------+
| Policy | policy |
+---------------------------+---------------------------+
| PolicyGroup | policyGroup |
+---------------------------+---------------------------+
| PolicyRule | policyRule |
+---------------------------+---------------------------+
| PolicyCondition | policyCondition |
+---------------------------+---------------------------+
| PolicyAction | policyAction |
+---------------------------+---------------------------+
| VendorPolicyCondition | vendorPolicyCondition |
+---------------------------+---------------------------+
| VendorPolicyAction | vendorPolicyAction |
+---------------------------+---------------------------+
| PolicyTimePeriodCondition | policyTimePeriodCondition |
+---------------------------+---------------------------+
Figure 3. Mapping of CIM Structural Classes to LDAP
The relationships in the CIM model map to pointer attributes in LDAP.
Two of these attributes appear in auxiliary classes, which allows
each of them to represent several CIM associations.
+--------------------------+---------------------------------+
| CIM Relationship | LDAP Attribute / Class |
+--------------------------+---------------------------------+
+--------------------------+---------------------------------+
| GroupJurisdiction | policyGroupsAuxContainedSet in |
| | policyGroupContainmentAuxClass |
+--------------------------+---------------------------------+
| ContainedPolicyGroup | policyGroupsAuxContainedSet in |
| | policyGroupContainmentAuxClass |
+--------------------------+---------------------------------+
| RuleJurisdiction | policyRulesAuxContainedSet in |
| | policyRuleContainmentAuxClass |
+--------------------------+---------------------------------+
| ContainedPolicyRule | policyRulesAuxContainedSet in |
| | policyRuleContainmentAuxClass |
+--------------------------+---------------------------------+
| ContainedPolicyCondition | policyRuleConditionList in |
| | policyRule |
+--------------------------+---------------------------------+
| ContainedPolicyAction | policyRuleActionList in |
| | policyRule |
+--------------------------+---------------------------------+
| PolicyRuleValidityPeriod | policyRuleValidityPeriodList in |
| | policyRule |
+--------------------------+---------------------------------+
Figure 4. Mapping of CIM Relationships to LDAP
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The remaining classes in the LDAP Core Schema (policyInstance,
policyElement, and policySubtreesPtrAuxClass) are all included to
make navigation through the Directory Information Tree (DIT) and
retrieval of the entries found there more efficient. This topic is
discussed in Section 5.4 below.
5.2. Naming Attributes in the Core Schema
Instances in a directory are identified by distinguished names (DNs),
which provide the same type of hierarchical organization that a file
system provides in a computer system. A distinguished name is a
sequence of relative distinguished names (RDNs), where an RDN
provides a unique identifier for an instance within the context of
its immediate superior, in the same way that a filename provides a
unique identifier for a file within the context of the folder in
which it resides.
To preserve maximum naming flexibility for policy administrators,
each of the structural classes defined in this schema has its own
naming attribute. (The structural class policyInstance gets its
naming attribute from one of two auxiliary classes defined in the
schema: either policyConditionName from the auxiliary class
policyCondition, or policyActionName from the auxiliary class
policyAction.) Since the naming attributes are different, a policy
administrator can, by using these attributes, guarantee that there
will be no name collisions between instances of different classes,
even if the same VALUE is assigned to the instances' respective
naming attributes.
The X.500 attribute commonName (cn) is included as a MAY attribute in
the abstract class policy, and thus by inheritance in policyGroup,
policyRule, policyCondition, policyAction, policyInstance,
policyElement, and all of their subclasses. In X.500 commonName
typically functions as an RDN attribute, for naming instances of such
classes as X.500's person. It has a different role in the Core
Schema, however: to hold a short, human-friendly text string to be
displayed on a user interface.
To avoid the interoperability problems that could arise if different
implementations took different approaches to naming their policy-
related instances, the following constraints apply:
o A management tool or other entity that creates policy-related
instances SHOULD NOT use the commonName (cn) attribute for naming
these instances, that is, SHOULD NOT use cn as the attribute for an
instance's final RDN.
o A PDP or other entity that retrieves policy-related instances
SHOULD NOT take any action that presupposes these instances are
named with the commonName (cn) attribute.
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5.3. Flexibility Gained through Auxiliary Classes
A key feature of the Core Schema is the use of auxiliary classes for
modeling policy conditions and policy actions. These auxiliary
classes make it possible to model a policy rule in two different
ways:
o Simple Policy Rule: The conditions and/or the actions for the rule
are attached to the rule object itself.
o Complex Policy Rule: The conditions and/or the actions for the
rule are attached to instances of the structural class
policyInstance, and these instances are pointed to by one of three
attributes in the policy rule object - policyRuleConditionList,
policyRuleActionList, or policyRuleValidityPeriodList (for the
special case of a policyTimePeriodCondition object).
The simple/complex distinction for a policy rule is not all or
nothing. A policy rule may have its conditions attached to itself
and its actions attached to instances of policyInstance, or it may
have its actions attached to itself and its conditions attached to
instances of policyInstance. However, it SHALL NOT have either its
conditions or its actions attached both to itself and to instances of
policyInstance, with one exception: a policy rule may point to its
validity periods with the policyRuleValidityPeriodList attribute, but
have its other conditions attached to itself.
The tradeoffs between simple and complex policy rules are between the
efficiency of simple rules and the flexibility and greater potential
for reuse of complex rules. With a simple policy rule, the semantic
options are limited:
o All conditions are ANDed together. This combination can be
represented in two ways in the DNF / CNF expressions
characteristic of policy conditions: as a DNF expression with a
single AND group, or as a CNF expression with multiple single-
condition OR groups. The first of these is arbitrarily chosen as
the representation for the ANDed conditions in a simple policy
rule.
o If multiple actions are included, no order can be specified for
them.
Thus if a policy administrator needs to combine conditions in some
other way, or if there is a set of actions that must be ordered, then
the only option is to use a complex policy rule. The cost of a
complex rule lies in the overhead of following DN pointers from the
rule object to condition and/or action objects. Section 5.4 below
describes a technique for minimizing this overhead, by making the
following of these pointers a local operation for a PDP.
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Note that whether a policy condition or policy action is represented
as simple or complex has no effect on the relationship cardinality
between the condition or action and the policy rule that aggregates
it.
The classes policyCondition and policyAction do not themselves
represent actual conditions and actions: these are introduced in
subclasses of policyCondition and policyAction. What policyCondition
and policyAction do introduce, in addition to the naming attributes
policyConditionName and policyActionName, are the semantics of being
a policy condition or a policy action. These are the semantics that
all the subclasses of policyCondition and policyAction inherit.
Among these semantics are those of being an object to which,
respectively, the policyRuleConditionList and policyRuleActionList
attributes may point.
In order to preserve the flexibility of attaching either to
policyRule or to policyInstance, all the subclasses of
policyCondition and policyAction MUST also be auxiliary classes.
5.4. Location and Retrieval of Policy Objects in the Directory
When a PDP goes to an LDAP directory to retrieve the policy object
instances relevant to the PEPs it serves, it is faced with two
related problems:
o How does it locate and retrieve the directory entries that apply to
its PEPs? These entries may include instances of the Core Schema
classes, instances of domain-specific subclasses of these classes,
and instances of other classes modeling such resources as user
groups, interfaces, and address ranges.
o How does it retrieve the directory entries it needs in an efficient
manner, so that retrieval of policy information from the directory
does not become a roadblock to scaleability? There are two facets
to this efficiency: retrieving only the relevant directory
entries, and retrieving these entries using as few LDAP calls as
possible.
The placement of objects in the Directory Information Tree (DIT)
involves considerations other than how the policy-related objects
will be retrieved by a PDP. Consequently, all that the Core Schema
can do is to provide a "toolkit" of classes to assist the policy
administrator as the DIT is being designed and built. A PDP must be
able to take advantage of any tools that the policy administrator is
able to build into the DIT, but also able to use a less efficient
means of retrieval if that is all it has available to it.
The basic idea behind the LDAP optimization classes is a simple one:
make it possible for a PDP to retrieve all the policy-related objects
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it needs, and only those objects, using as few LDAP calls as
possible. Figure 5 illustrates how these goals can be accomplished.
+-----+
---------------->| A |
DN pointer to | | DN pointers to subtrees +---+
starting object +-----+ +------------------------->| C |
| o--+----+ +---+ +---+
| o--+------------->| B | / \
+-----+ +---+ / \
/ \ / ... \
/ \
/ ... \
Figure 5. Using a policyContainer Object to Scope Policies
The PDP is configured initially with a DN pointer to some entry in
the DIT. The structural class of this entry is not important; the
PDP is interested only in the policySubtreesPtrAuxClass attached to
it. This auxiliary class contains a multi-valued attribute with DN
pointers to objects that anchor subtrees containing policy-related
objects of interest to the PDP. Since policySubtreesPtrAuxClass is
an auxiliary class, it can be attached to an entry that the PDP would
need to access anyway - perhaps an entry containing initial
configuration settings for the PDP, or for a PEP that uses the PDP.
Once it has retrieved the DN pointers, the PDP will direct to each of
the objects identified by them an LDAP request that all entries in
its subtree be evaluated against the selection criteria specified in
the request. The LDAP-enabled directory then,returns all entries in
that subtree that satisfy the specified criteria.
The selection criteria always specify that object class = "policy".
Since all classes representing policy rules, policy conditions, and
policy actions, both in the Core Schema and in any domain-specific
schema derived from it, are subclasses of the abstract class policy,
this criterion evaluates to TRUE for all instances of these classes.
To accommodate special cases where a PDP needs to retrieve objects
that are not inherently policy-related (for example, an IP address
range object pointed to by a subclass of policyAction representing
the DHCP action "assign from this address range), the auxiliary class
policyElement can be used to "tag" an entry, so that it will be found
by the selection criterion "object class = policy".
The approach described in the preceding paragraph will not work for
certain directory implementations, because these implementations do
not support matching of auxiliary classes in the objectClass
attribute. For environments where these implementations are expected
to be present, the "tagging" of entries as relevant to policy can be
accomplished by inserting the special value "POLICY" into the list of
values contained in the policyKeywords attribute.
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In a PDP needs only a subset of the policy-related objects in the
indicated subtrees, then it can be configured with additional
selection criteria based on the policyKeywords attribute defined in
the policy class. This attribute supports both standardized and
administrator-defined values. Thus a PDP could be configured to
request only those policy-related objects containing the keywords
"DHCP" and "Eastern US".
Returning to the example in Figure 5, we see that in the best case, a
PDP can get all the policy-related objects it needs, and only these
objects, with exactly three LDAP requests: one to its starting
object to get the pointers to B and C, and then one each to B and C
to get all the policy-related objects that pass the selection
criteria with which it was configured. Once it has retrieved all of
these objects, the PDP can then traverse their various DN pointers
locally to understand the semantic relationships among them. The PDP
must also be prepared to find a pointer to another subtree attached
to any of the objects it retrieves, and to follow this pointer first,
before it follows any of the semantically significant pointers it has
received. This recursion permits a structured approach to
identifying related policies. In Figure 5, for example, if the
subtree under B includes departmental policies and the one under C
includes divisional policies, then there might be a pointer from the
subtree under C to an object D that roots the subtree of corporate-
level policies.
Since a PDP has no guarantee that the entity that populates the
directory won't use the policySubtreesPtrAuxClass, a PDP MUST
understand this class, MUST be capable of retrieving and processing
the entries in the subtrees it points to, and MUST be capable of
doing all of this recursively. The same requirements apply to any
other entity needing to retrieve policy information from the
directory. Thus a Policy Management Tool that retrieves policy
entries from the directory in order to perform validation and
conflict detection MUST also understand and be capable of using the
policySubtreesPtrAuxClass.
When it is serving as a tool for creating policy entries in the
directory, a Policy Management Tool SHOULD support creation of
policySubtreePrtAuxClass entries and their DN pointers.
5.4.1. Aliases
Additional flexibility in DIT structure is available to the policy
administrator via LDAP aliasing. Figure 6 illustrates this
flexibility.
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+-----+
---------------->| A |
DN pointer to | | DN pointers to subtrees +---+
starting object +-----+ +------------------------->| C |
| o--+----+ +---+ +---+
| o--+------------->| B | / \
+-----+ +---+ / \
/ \ / ... \
/ \
/ \
+---+ / +------+ \
| X |<********|aliasX|
+---+ +------+
Figure 6. Addition of an Alias Object
Even if it is necessary to store a policy entry X in a directory
location separate from the other policy entries, batch retrieval
using policy subtrees can still be done. The administrator simply
inserts into one of the subtrees of policy entries an alias entry
aliasX pointing to the outlying entry X. When the PDP requests all
entries in the subtree under B, a response will be returned for entry
X, just as responses are returned for all the (non-alias) entries
that actually are in the subtree.
Since resolution of an alias to its true entry is handled entirely by
the LDAP directory, and is invisible to directory clients, PDPs need
not do anything extra to support aliases. A Policy Management Tool
MAY make available to a policy administrator the ability to create
alias entries like the one in Figure 6.
6. Class Definitions
6.1. The Abstract Class policy
The abstract class policy collects four attributes that may be
included in instances of any of the Core Policy classes (or their
subclasses). The class value "policy" is also used as the mechanism
for identifying policy-related instances in the Directory Information
Tree. An instance of any class may be "tagged" with this class value
by attaching to it the auxiliary class policyElement.
The class definition is as follows:
NAME policy
DESCRIPTION An abstract class with four attributes for
describing a policy-related instance.
DERIVED FROM top
TYPE abstract
AUXILIARY CLASSES none
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OID <to be assigned>
MAY cn caption description policyKeywords
6.1.1. The Attribute commonName (cn)
The cn, or commonName, attribute is an X.500 attribute. It specifies
one or more user-friendly names (typically only one name) by which an
object is commonly known, names that conform to the naming
conventions of the country or culture with which the object is
associated. A commonName may be ambiguous by itself, so it is
typically used in a limited scope (such as an organization).
Unlike X.500, the Core Policy Schema specifies that the commonName
attribute SHOULD NOT be used for forming the final RDN in the
Distinguished Name of a policy-related instance.
NAME cn
DESCRIPTION A user-friendly name of a policy-related object.
SYNTAX DirectoryString
OID 2.4.5.3
EQUALITY caseIgnoreMatch
MULTI-VALUED
6.1.2. The Attribute caption
This attribute corresponds to the Caption attribute defined in CIM.
It provides a place for a one-line description of an entry.
NAME caption
DESCRIPTION A one-line description of this policy-related
object.
SYNTAX IA5String
OID <to be assigned>
EQUALITY caseExactIA5Match
SINGLE-VALUED
6.1.3. The Attribute description
This attribute corresponds to the Description attribute defined in
CIM. It provides a place for a longer description than that provided
by the caption attribute.
NAME description
DESCRIPTION A long description of this policy-related object.
SYNTAX IA5String
OID <to be assigned>
EQUALITY caseExactIA5Match
SINGLE-VALUED
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6.1.4. The Attribute policyKeywords
This attribute provides a set of one or more keywords that a policy
administrator may define to assist directory clients in locating the
policy objects applicable to them. Keywords are of one of two types:
Keywords defined in this document, or in documents that define
subclasses of the classes defined in this document. These keywords
provide a vendor-independent, installation-independent way of
identifying and locating policy objects.
Installation-dependent keywords for identifying and locating policy
objects. Examples include "Engineering", "Billing", and "Review in
December 1999".
This document defines the following keywords for identifying policy
objects: "UNKNOWN", "CONFIGURATION", "USAGE", "SECURITY", "SERVICE",
"MOTIVATIONAL", "INSTALLATION", and "EVENT". These concepts were
defined in Section 2. In addition to these, the keyword "POLICY" is
defined, to serve as a tag for policy-related entries when a
directory implementation does not support matching on auxiliary
classes in the objectClass attribute.
Documents that define subclasses of the Core Schema classes should
define additional keywords to identify policy objects associated with
instances of these subclasses. By convention, keywords defined in
conjunction with class definitions are in uppercase. Installation-
defined keywords can be in any case.
The attribute definition is as follows:
NAME policyKeywords
DESCRIPTION A set of keywords to assist directory clients in
locating the policy objects applicable to them.
SYNTAX IA5String
OID <to be assigned>
EQUALITY caseExactIA5Match
MULTI-VALUED
6.2. The Class policyGroup
This class is a generalized aggregation container. It enables either
policyRules or policyGroups, but not both, to be aggregated in a
single container. Loops, including the degenerate case of a
policyGroup that contains itself, are not allowed when policyGroups
contain other policyGroups.
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PolicyGroups and their nesting capabilities are shown in Figure 7
below. Note that a policyGroup can nest other policyGroups, and there
is no restriction on the depth of the nesting in sibling
policyGroups.
+---------------------------------------------------+
| policyGroup |
| |
| +--------------------+ +-----------------+ |
| | policyGroup A | | policyGroup X | |
| | | | | |
| | +----------------+ | ooo | | |
| | | policyGroup A1 | | | | |
| | +----------------+ | | | |
| +--------------------+ +-----------------+ |
+---------------------------------------------------+
Figure 7. Overview of the policyGroup class
As a simple example, think of the highest level policyGroup shown in
Figure 7 above as a logon policy for US employees of a company. This
policyGroup may be called USEmployeeLogonPolicy, and may aggregate
several policyGroups that provide specialized rules per location.
Hence, policyGroup A in Figure 5 above may define logon rules for
employees on the West Coast, while another policyGroup might define
logon rules for the Midwest (e.g., policyGroup X), and so forth.
Note also that the depth of each policyGroup does not need to be the
same. Thus, the WestCoast policyGroup might have several additional
layers of policyGroups defined for any of several reasons (different
locales, number of subnets, etc.). The policyRules are therefore
contained at n levels from the USEmployeeLogonPolicyGroup. Compare
this to the Midwest policyGroup (policyGroup X), which might directly
contain policyRules.
The class definition for policyGroup is as follows. Note that this
class definition does not include attributes to realize the
ContainedPolicyRule and ContainedPolicyGroup associations from the
object model, since a policyGroup object points to instances of
policyGroup and policyRule via, respectively, the pointer in
policyGroupContainmentAuxClass and the pointer in
policyRuleContainmentAuxClass.
NAME policyGroup
DESCRIPTION A container for either a set of related
policyRules or a set of related policyGroups.
DERIVED FROM top
TYPE structural
AUXILIARY CLASSES policyGroupContainmentAuxClass,
policyRuleContainmentAuxClass
POSSIBLE SUPERIORS container, organization, organizationalUnit,
policyGroup
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OID <to be assigned>
MUST policyGroupName
6.2.1. The Attribute policyGroupName
This attribute provides a user-friendly name for a policy group, and
is normally what will be displayed to the end-user as the name of
this class. It is defined as follows:
NAME policyGroupName
DESCRIPTION The user-friendly name of this policy group.
SYNTAX IA5String
OID <to be assigned>
EQUALITY caseExactIA5Match
SINGLE-VALUED
6.3. The Class policyRule
This class represents the "If Condition then Action" semantics
associated with a policy. A policyRule condition, in the most
general sense, is represented as either an ORed set of ANDed
conditions (Disjunctive Normal Form, or DNF) or an ANDed set of ORed
conditions (Conjunctive Normal Form, or CNF). Individual conditions
may either be negated (NOT C) or unnegated (C). The actions
specified by a policyRule are to be performed if and only if the
policyRule condition (whether it is represented in DNF or CNF)
evaluates to TRUE.
The conditions and actions associated with a policy rule are modeled,
respectively, with auxiliary subclasses of the classes
policyCondition and policyAction. These auxiliary classes are
attached either to an instance of policyRule itself, or to an
instance of the structural class policyInstance identified by a DN
pointer in an instance of policyRule.
As discussed above in section 3, a policy rule may also be associated
with one or more policy time periods, indicating the schedule
according to which the policy rule is active and inactive.
A policy rule is illustrated conceptually in Figure 8. below.
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+------------------------------------------------+
| policyRule |
| |
| +--------------------+ +-----------------+ |
| | policyCondition(s) | | policyAction(s) | |
| +--------------------+ +-----------------+ |
| |
| +------------------------------+ |
| | policyTimePeriodCondition(s) | |
| +------------------------------+ |
+------------------------------------------------+
Figure 8. Overview of the policyRule Class
The policyRule class uses the attribute policyRuleConditionListType,
to indicate whether the conditions for the rule are in DNF or CNF.
The DN pointers from a policyRule to its associated policyConditions
also contain an integer to partition the referenced conditions into
one or more sets, and a plus ('+') or minus ('-') character to
indicate whether the referenced condition is negated. An example
shows how the attribute, the grouping integer, and the '+' / '-'
provide a unique representation of a set of conditions in either DNF
or CNF.
Suppose we have pointers to five policyConditions from an instance of
policyRule, grouped as follows:
(C1: groupNumber = 1: unnegated,
C2: groupNumber = 1: negated,
C3: groupNumber = 1: unnegated,
C4: groupNumber = 2: unnegated,
C5: groupNumber = 2: unnegated)
If policyRuleConditionListType = DNF, then the overall condition for
the policyRule is:
(C1 AND (NOT C2) AND C3) OR (C4 AND C5)
On the other hand, if policyRuleConditionListType = CNF, then the
overall condition for the policyRule is:
(C1 OR (NOT C2) OR C3) AND (C4 OR C5)
In both cases, there is an unambiguous specification of the overall
condition that is tested to determine whether to perform the actions
associated with the policyRule. This class also contains several
attributes designed to help directory clients locate the policy rules
applicable to them. The class definition is as follows:
NAME policyRule
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DESCRIPTION The central class for representing the "If
Condition then Action" semantics associated with a
policy rule.
DERIVED FROM top
TYPE structural
AUXILIARY CLASSES none
POSSIBLE SUPERIORS policyGroup
OID <to be assigned>
MUST policyRuleName
MAY policyRuleEnabled policyRuleConditionListType
policyRuleConditionList policyRuleActionList
policyRuleValidityPeriodList policyRuleUsage
policyRulePriority policyRuleMandatory
policyRuleSequencedActions
6.3.1. The Attribute policyRuleName
This attribute provides a user-friendly name for a policy rule. The
attribute definition is as follows:
NAME policyRuleName
DESCRIPTION The user-friendly name of this policy rule.
SYNTAX IA5String
OID <to be assigned>
EQUALITY caseExactIA5Match
SINGLE-VALUED
6.3.2. The Attribute policyRuleEnabled
This attribute indicates whether a policy rule is currently enabled,
from an ADMINISTRATIVE point of view. Its purpose is to allow a
policy administrator to enable or disable a policy rule without
having to add it to, or remove it from, the directory.
The attribute also supports the value 'enabledForDebug'. When the
attribute has this value, the Policy Decision Point is being told to
evaluate the conditions for the policy rule, but not to perform the
actions if the conditions evaluate to TRUE. This value serves as a
debug vehicle when attempting to determine what policies would
execute in a particular scenario, without taking any actions to
change state during the debugging.
The attribute definition is as follows:
NAME policyRuleEnabled
DESCRIPTION A flag indicating whether this policy rule is
enabled from an administrative point of view.
SYNTAX INTEGER
OID <to be assigned>
EQUALITY integerMatch
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SINGLE-VALUED
DEFAULT VALUE enabled(1)
The defined values for this attribute are enabled(1), disabled(2),
and enabledForDebug(3).
6.3.3. The Attribute policyRuleConditionListType
This attribute is used to specify whether the list of policy
conditions associated with this policy rule is in disjunctive normal
form (DNF) or conjunctive normal form (CNF). If this attribute is
not present, the list type defaults to DNF. The attribute definition
is as follows:
NAME policyRuleConditionListType
DESCRIPTION Indicates whether the list of policy conditions
associated with this policy rule is in disjunctive
normal form (DNF) or conjunctive normal form
(CNF). Defined values are 'DNF (1)' and 'CNF
(2)'.
SYNTAX INTEGER
OID <to be assigned>
EQUALITY integerMatch
SINGLE-VALUED
DEFAULT VALUE 1 (DNF)
6.3.4. The Attribute policyRuleConditionList
This attribute provides an unordered list of DN pointers that
identify a set of policy conditions associated with this policy rule.
There is an integer associated with each pointer, to provide the
grouping of the conditions into first-level groups for the DNF or CNF
representation of the overall policyRule condition. In addition,
each pointer has associated with it a plus ('+') or minus ('-') to
indicate whether the condition is negated: the '+' indicates that
the condition is not negated, and the '-' indicates that it is
negated. To accommodate this grouping, the syntax of this attribute
is a string of the form 'groupNumber:+|-:DN'.
Existing matching rules are built to operate on a single data type.
This attribute is conceptually composed of three data types, an
Integer (groupNumber), an enumeration ('+' or '-'), and a
DistinguishedName (DN). There are three ways to address this.
Collapse the three attribute types into a single structured
DirectoryString with the format 'groupNumber:+|-:DN'. This approach
has the advantage of not requiring any new support in the directory
server implementations, since these servers already support a
DirectoryString matching rule. Its disadvantage is that a
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DirectoryString match works somewhat differently from a DN match with
respect to subtleties such as preserving versus ignoring versus
removing repeated whitespace characters. Thus DNs that would match
with the distinguishedNameMatch matching rule might fail to be found
as substrings of 'groupNumber:+|-:DN' strings by the DirectoryString
matching rules, or vice versa.
Define a new syntax '<integer>:<+|->:<DN>', with its own matching
rules. With this approach, the matching problems introduced by the
DirectoryString could be avoided, since the new type would have its
own matching rules. The disadvantage of defining a new type in this
way is that a directory server must add new code that recognizes the
type and implements its matching rules. A directory server would
thus be unable to support the Core Policy Schema until it had added
this new code.
Use three objects in the directory to represent the three data types,
and relate the objects with the Families of Entries model currently
being discussed in the LDAP Extensions working group. This approach
has the same problem as the previous one: without the addition of new
code to support Families of Entries, a directory server would be
unable to support the Core Policy Schema at all. There is also the
additional complication here, that the Families of Entries model
itself may take some time to reach approved status in the LDAP
Extensions (LDAPEXT) working group.
For now, this document will move forward with the 'groupNumber:+|-
:DN' structured DirectoryString approach for mapping
ContainedPolicyCondition, as well as with an analogous 'n:DN'
approach for mapping ContainedPolicyAction. To minimize problems
arising from differences in matching rules, this document will
provide a series of guidelines for constructing DNs that behave
identically with respect to the DirectoryString matching rules and
the distinguishedNameMatch. These guidelines are in Appendix A. Note
that even if the DNs are chosen so that the matching rules behave the
same, automatic processes such as "Modify RDN" that count on finding
objects with the DistinguishedName syntax will not find attributes
with the structured-string syntaxes.
The attribute definition is as follows:
NAME policyRuleConditionList
DESCRIPTION An unordered list of strings of the form
'groupNumber:+|-:DN', indicating a set of policy
conditions that determine when the policyRule is
applicable.
SYNTAX DirectoryString
OID <to be assigned>
EQUALITY caseIgnoreSubstringsMatch
MULTI-VALUED
FORMAT groupNumber:+|-:DN
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6.3.5. The Attribute policyRuleActionList
This attribute provides an unordered list of strings of the form
'n:DN' that identify a set of policy actions associated with this
policy rule. (See section 6.3.4 for a discussion of the issues
surrounding the use of a syntax of this type.) When 'n' is a
positive integer, it indicates a place in the sequence of actions to
be performed, with smaller integers indicating earlier positions in
the sequence. The special value '0' indicates "don't care". If two
or more actions have the same non-zero sequence number, they may be
performed in any order, but they must all be performed at the
appropriate place in the overall action sequence.
A series of examples will make ordering of actions clearer:
o If all actions have the same sequence number, regardless of
whether it is '0' or non-zero, any order is acceptable.
o The values
1:DN-A
2:DN-B
1:DN-C
3:DN-D
indicate two acceptable orders: A,C,B,D or C,A,B,D, since A and
C can be performed in either order, but only at the '1' position.
o The values
0:DN-A
2:DN-B
3:DN-C
3:DN-D
require that B,C, and D occur either as B,C,D or as B,D,C.
Action A may appear at any point relative to B,C, and D. Thus
the complete set of acceptable orders is: A,B,C,D; B,A,C,D;
B,C,A,D; B,C,D,A; A,B,D,C; B,A,D,C; B,D,A,C; B,D,C,A.
o Note that the non-zero sequence numbers need not start with '1',
and they need not be consecutive. All that matters is their
relative magnitude.
This attribute indicates the actions of a policyRule and their order
(or absence of order). However, another attribute,
policyRuleSequencedActions, indicates whether the indicated order is
required, recommended, or not to be used at all.
All actions specified in the policyRuleActionList will be executed as
long as the overall policy condition as defined by the
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policyRuleConditionListType and policyRuleConditionList attributes
evaluates to TRUE.
The attribute definition is as follows:
NAME policyRuleActionList
DESCRIPTION An unordered list of strings of the form 'n:DN',
indicating an ordered set of policy actions to be
performed if the associated condition(s) of the
policyRule evaluates to true.
SYNTAX DirectoryString
OID <to be assigned>
EQUALITY caseIgnoreSubstringsMatch
MULTI-VALUED
FORMAT n:DN
6.3.6. The Attribute policyRuleValidityPeriodList
This attribute provides an unordered set of DN pointers to one or
more policyTimePeriodConditions, indicating when the policy rule is
scheduled to be active and when it is scheduled to be inactive. The
rule is scheduled to be active if it is active according to AT LEAST
ONE of the policyTimePeriodConditions pointed to by this attribute.
The attribute definition is:
NAME policyRuleValidityPeriodList
DESCRIPTION Distinguished names of policyTimePeriodConditions
that determine when the policyRule is scheduled to
be active / inactive. No order is implied.
SYNTAX DN
OID <to be assigned>
EQUALITY distinguishedNameMatch
MULTI-VALUED
6.3.7. The Attribute policyRuleUsage
This attribute is a free-form string that recommends how this policy
should be used. The attribute definition is as follows:
NAME policyRuleUsage
DESCRIPTION This attribute is used to provide guidelines on
how this policy should be used.
SYNTAX DirectoryString
OID <to be assigned>
EQUALITY caseIgnoreMatch
SINGLE-VALUED
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6.3.8. The Attribute policyRulePriority
This attribute provides a non-negative integer for prioritizing
policy rules relative to each other. For policy rules that have this
attribute, larger integer values indicate higher priority. Since one
purpose of this attribute is to allow specific, ad hoc policy rules
to temporarily override established policy rules, an instance that
has this attribute set has a higher priority than all instances that
lack it.
Prioritization among policy rules provides a simple and efficient
mechanism for resolving policy conflicts.
The attribute definition is as follows:
NAME policyRulePriority
DESCRIPTION A non-negative integer for prioritizing this
policyRule relative to other policyRules. A
larger value indicates a higher priority.
SYNTAX INTEGER
OID <to be assigned>
EQUALITY integerMatch
SINGLE-VALUED
DEFAULT VALUE 0
6.3.9. The Attribute policyRuleMandatory
This attribute indicates whether evaluation (and possibly action
execution) of a policyRule is mandatory or not. Its concept is
similar to the ability to mark packets for delivery or possible
discard, based on network traffic and device load.
The evaluation of a policyRule MUST be attempted if the
policyRuleMandatory attribute value is True. If the
policyRuleMandatory attribute value of a policyRule is False, then
the evaluation of the rule is "best effort" and MAY be ignored.
The attribute definition is as follows:
NAME policyRuleMandatory
DESCRIPTION A flag indicating that the evaluation of the
policyConditions and execution of policyActions
(if the condition list evaluates to True) is
required.
SYNTAX Boolean
OID <to be assigned>
EQUALITY booleanMatch
SINGLE-VALUED
DEFAULT VALUE TRUE
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6.3.10. The Attribute policyRuleSequencedActions
This attribute gives a policy administrator a way of specifying how
the ordering of the policy actions associated with this policyRule is
to be interpreted. Three values are supported:
o mandatory (1): Do the actions in the indicated order, or don't
do them at all.
o recommended (2): Do the actions in the indicated order if you
can, but if you can't do them in this order, do them in another
order if you can.
o dontCare (3): Do them -- I don't care about the order.
When error / event reporting is addressed for the Policy Framework,
suitable codes will be defined for reporting that a set of actions
could not be performed in an order specified as mandatory (and thus
were not performed at all), that a set of actions could not be
performed in a recommended order (and moreover could not be performed
in any order), or that a set of actions could not be performed in a
recommended order (but were performed in a different order). The
attribute definition is as follows:
NAME policyRuleSequencedActions
DESCRIPTION An enumeration indicating how to interpret the
action ordering indicated via the
policyRuleActionList attribute.
SYNTAX INTEGER
OID <to be assigned>
EQUALITY integerMatch
SINGLE-VALUED
DEFAULT VALUE 3
The defined values for this attribute are mandatory(1),
recommended(2), and dontCare(3).
6.4. The Class policyCondition
The purpose of a policy condition is to determine whether or not the
set of actions (contained in the policyRule that the condition
applies to) should be executed or not. For the purposes of the Core
Policy Schema, all that matters about an individual policyCondition
is that it evaluates to TRUE or FALSE. (The individual
policyConditions associated with a policyRule are combined to form a
compound expression in either DNF or CNF, but this is accomplished
via the groupNumber component of the policyRuleConditionList string
and by the policyRuleConditionListType attribute, both of which are
discussed above.) A logical structure WITHIN an individual
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policyCondition may also be introduced, but this would have to be
done in a subclass of policyCondition.
+---------------------------------------------------------------+
| Policy Conditions in DNF |
| +-------------------------+ +-----------------------+ |
| | AND list | | AND list | |
| | +-------------------+ | | +-----------------+ | |
| | | policyCondition | | | | policyCondition | | |
| | +-------------------+ | | +-----------------+ | |
| | +-------------------+ | | +-----------------+ | |
| | | policyCondition | | ... | | policyCondition | | |
| | +-------------------+ | ORed | +-----------------+ | |
| | ... | | ... | |
| | ANDed | | ANDed | |
| | +-------------------+ | | +-----------------+ | |
| | | policyCondition | | | | policyCondition | | |
| | +-------------------+ | | +-----------------+ | |
| +-------------------------+ +-----------------------+ |
+---------------------------------------------------------------+
Figure 9. Overview of Policy Conditions in DNF
This figure illustrates that when policy conditions are in DNF, there
are one or more sets of conditions that are ANDed together to form
AND lists. An AND list evaluates to TRUE if and only if all of its
constituent conditions evaluate to TRUE. The overall condition then
evaluates to TRUE if and only if at least one of its constituent AND
lists evaluates to TRUE.
+---------------------------------------------------------------+
| Policy Conditions in CNF |
| +-------------------------+ +-----------------------+ |
| | OR list | | OR list | |
| | +-------------------+ | | +-----------------+ | |
| | | policyCondition | | | | policyCondition | | |
| | +-------------------+ | | +-----------------+ | |
| | +-------------------+ | | +-----------------+ | |
| | | policyCondition | | ... | | policyCondition | | |
| | +-------------------+ | ANDed | +-----------------+ | |
| | ... | | ... | |
| | ORed | | ORed | |
| | +-------------------+ | | +-----------------+ | |
| | | policyCondition | | | | policyCondition | | |
| | +-------------------+ | | +-----------------+ | |
| +-------------------------+ +-----------------------+ |
+---------------------------------------------------------------+
Figure 10. Overview of Policy Conditions in CNF
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In this figure, the policy conditions are in CNF. Consequently,
there are one or more OR lists, each of which evaluates to TRUE if
and only if at least one of its constituent conditions evaluates to
TRUE. The overall condition then evaluates to TRUE if and only if
ALL of its constituent OR lists evaluate to TRUE. The class
definition is as follows:
NAME policyCondition
DESCRIPTION A class representing a condition to be evaluated
in conjunction with a policy rule.
DERIVED FROM top
TYPE auxiliary
AUXILIARY CLASSES none
POSSIBLE SUPERIORS policyRule
OID <to be assigned>
MUST policyConditionName
MAY
6.4.1. The Attribute policyConditionName
This attribute provides a user-friendly name for a policy condition.
The attribute definition is as follows:
NAME policyConditionName
DESCRIPTION The user-friendly name of this policy condition.
SYNTAX IA5String
OID <to be assigned>
EQUALITY caseExactIA5Match
SINGLE-VALUED
6.5. The Class policyTimePeriodCondition
This class provides a means of representing the time periods during
which a policy rule is valid, i.e., active. At all times that fall
outside these time periods, the policy rule has no effect. A policy
rule is treated as valid at all times if it does not specify a
policyTimePeriodCondition.
In some cases a PDP may need to perform certain setup / cleanup
actions when a policy rule becomes active / inactive. For example,
sessions that were established while a policy rule was active might
need to be taken down when the rule becomes inactive. In other
cases, however, such sessions might be left up: in this case, the
effect of deactivating the policy rule would just be to prevent the
establishment of new sessions. Any such setup / cleanup behaviors on
validity period transitions must be specified in a subclass of
policyRule. If such behaviors need to be under the control of the
policy administrator, then a mechanism to allow this control must
also be specified in the subclass.
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policyTimePeriodCondition is defined as a subclass of
policyCondition. This is to allow the inclusion of time-based
criteria in the AND/OR condition definitions for a policyRule.
Instances of this class may have up to five attributes identifying
time periods at different levels. The values of all the attributes
present in an instance are ANDed together to determine the validity
period(s) for the instance. For example, an instance with an overall
validity range of January 1, 1999 through December 31, 1999; a month
mask of "001100000000" (March and April); a day-of-the-week mask of
"0000100" (Fridays); and a time of day range of 0800 through 1600
would represent the following time periods:
Friday, March 5, 1999, from 0800 through 1600;
Friday, March 12, 1999, from 0800 through 1600;
Friday, March 19, 1999, from 0800 through 1600;
Friday, March 26, 1999, from 0800 through 1600;
Friday, April 2, 1999, from 0800 through 1600;
Friday, April 9, 1999, from 0800 through 1600;
Friday, April 16, 1999, from 0800 through 1600;
Friday, April 23, 1999, from 0800 through 1600;
Friday, April 30, 1999, from 0800 through 1600.
Attributes not present in an instance of policyTimePeriodCondition
are implicitly treated as having their value "always enabled". Thus,
in the example above, the day-of-the-month mask is not present, and
so the validity period for the instance implicitly includes a day-of-
the-month mask containing 31 1's. If we apply this "missing
attribute" rule to its fullest, we see that there is a second way to
indicate that a policy rule is always enabled: have it point to an
instance of policyTimePeriodCondition whose only attributes are its
naming attributes.
The class definition is as follows. Note that instances of this
class are named with the attributes cn and policyConditionName that
they inherit from policyCondition.
NAME policyTimePeriodCondition
DESCRIPTION A class that provides the capability of enabling /
disabling a policy rule according to a pre-
determined schedule.
DERIVED FROM policyCondition
TYPE auxiliary
AUXILIARY CLASSES none
POSSIBLE SUPERIORS policyRule
OID <to be assigned>
MUST
MAY ptpConditionTime ptpConditionMonthOfYearMask
ptpConditionDayOfMonthMask
ptpConditionDayOfWeekMask
ptpConditionTimeOfDayMask ptpConditionTimeZone
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6.5.1. The Attribute ptpConditionTime
This attribute identifies an overall range of calendar dates and
times over which a policy rule is valid. It is formatted as a string
consisting of a start date and time, then a colon (':'), and followed
by an end date and time. The first date indicates the beginning of
the range, while the second date indicates the end. Thus, the second
date and time must be later than the first. Dates are expressed as
substrings of the form "yyyymmddhhmmss". For example:
19990101080000:19990131120000
January 1, 1999, 0800 through January 31, 1999, noon
The attribute definition is as follows:
NAME ptpConditionTime
DESCRIPTION The range of calendar dates on which a policy rule
is valid.
SYNTAX PrintableString
OID <to be assigned>
EQUALITY caseIgnoreMatch
SINGLE-VALUED
FORMAT yyyymmddhhmmss:yyyymmddhhmmss
6.5.2. The Attribute ptpConditionMonthOfYearMask
The purpose of this attribute is to refine the definition of the
valid time period that is defined by the ptpConditionTime attribute
by explicitly specifying which months the policy is valid for. These
attributes work together, with the ptpConditionTime used to specify
the overall time period that the policy is valid for, and the
ptpConditionMonthOfYearMask used to pick out which months of that
time period the policy is valid for.
This attribute is formatted as a string containing 12 ASCII '0's and
'1's, where the '1's identify the months (beginning with January) in
which the policy rule is valid. The value "000010010000", for
example, indicates that a policy rule is valid only in the months May
and August.
If this attribute is omitted, then the policy assumes that it is
valid for all twelve months. The attribute definition is as follows:
NAME ptpConditionMonthOfYearMask
DESCRIPTION A mask identifying the months of the year in which
a policy rule is valid.
SYNTAX Printable String
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OID <to be assigned>
EQUALITY caseIgnoreMatch
SINGLE-VALUED
FORMAT A string of 12 ASCII '0's and '1's.
6.5.3. The Attribute ptpConditionDayOfMonthMask
The purpose of this attribute is to refine the definition of the
valid time period that is defined by the ptpConditionTime attribute
by explicitly specifying which days of the month the policy is valid
for. These attributes work together, with the ptpConditionTime used
to specify the overall time period that the policy is valid for, and
the ptpConditionDayOfMonthMask used to pick out which days of the
month that time period the policy is valid for.
This attribute is formatted as a string containing 31 ASCII '0's and
'1's, where the '1's identify the days of the month (beginning with
day 1 and going up through day 31) on which the policy rule is valid.
The value "1110000000000000000000000000000", for example, indicates
that a policy rule is valid only on the first three days of each
month. For months with fewer than 31 days, the digits corresponding
to days that the months do not have are ignored. The attribute
definition is as follows:
NAME ptpConditionDayOfMonthMask
DESCRIPTION A mask identifying the days of the month on which
a policy rule is valid.
SYNTAX PrintableString
OID <to be assigned>
EQUALITY caseIgnoreMatch
SINGLE-VALUED
FORMAT A string of 31 ASCII '0's and '1's.
6.5.4. The Attribute ptpConditionDayOfWeekMask
The purpose of this attribute is to refine the definition of the
valid time period that is defined by the ptpConditionTime attribute
by explicitly specifying which days of the week the policy is valid
for. These attributes work together, with the ptpConditionTime used
to specify the overall time period that the policy is valid for, and
the ptpConditionDayOfWeekMask used to pick out which days of the week
of that time period the policy is valid for.
This attribute is formatted as a string containing 7 ASCII '0's and
'1's, where the '1's identify the days of the week (beginning with
Monday and going up through Sunday) on which the policy rule is
valid. The value "1111100", for example, indicates that a policy rule
is valid Monday through Friday.
The attribute definition is as follows:
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NAME ptpConditionDayOfWeekMask
DESCRIPTION A mask identifying the days of the week on which a
policy rule is valid.
SYNTAX PrintableString
OID <to be assigned>
EQUALITY caseIgnoreMatch
SINGLE-VALUED
FORMAT A string of 7 ASCII '0's and '1's.
6.5.5. The Attribute ptpConditionTimeOfDayMask
The purpose of this attribute is to refine the definition of the
valid time period that is defined by the ptpConditionTime attribute
by explicitly specifying a range of times in a day the policy is
valid for. These attributes work together, with the ptpConditionTime
used to specify the overall time period that the policy is valid for,
and the ptpConditionTimeOfDayMask used to pick out which range of
time periods in a given day of the week of that time period the
policy is valid for.
This attribute is formatted as a string containing two times,
separated by a colon (':'). The first time indicates the beginning
of the range, while the second time indicates the end. Times are
expressed as substrings of the form "hhmmss".
The second substring always identifies a later time than the first
substring. To allow for ranges that span midnight, however, the
value of the second string may be smaller than the value of the first
substring. Thus, "080000:210000" identifies the range from 0800
until 2100, while "210000:080000" identifies the range from 2100
until 0800 of the following day.
When a range spans midnight, it by definition includes parts of two
successive days. When one of these days is also selected by either
the ptpConditionMonthOfYearMask, ptpConditionDayOfMonthMask, and/or
ptpConditionDayOfWeekMask, but the other day is not, then the policy
is active only during the portion of the range that falls on the
selected day. For example, if the range extends from 2100 until
0800, and the day of week mask selects Monday and Tuesday, then the
policy is active during the following three intervals:
From midnight Sunday until 0800 Monday;
From 2100 Monday until 0800 Tuesday;
From 2100 Tuesday until 21:59:59 Tuesday.
The attribute definition is as follows:
NAME ptpConditionTimeOfDayMask
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DESCRIPTION The range of times at which a policy rule is
valid. If the second time is earlier than the
first, then the interval spans midnight.
SYNTAX Printable String
OID <to be assigned>
EQUALITY caseIgnoreMatch
SINGLE-VALUED
FORMAT hhmmss:hhmmss[:<UTC offset>]
6.5.6. The Attribute ptpConditionTimeZone
This attribute is used to explicitly define a time zone for use by
the ptpConditionTime and the various Mask attributes. If this
attribute is NULL, then local time (at the location where the
policyRule is enforced -- in other words, at the Policy Enforcement
Point) is assumed.
This attribute specifies time in UTC, using an offset indicator. The
UTC offset indicator is either a 'Z', indicating UTC, or a substring
of the following form:
'+' or '-' direction from UTC: '+' = east, '-' = west
hh hours from UTC (00..13)
mm minutes from UTC (00..59)
The attribute definition is as follows:
NAME ptpConditionTimeZone
DESCRIPTION The definition of the time zone for the
policyTimePeriodCondition.
SYNTAX PrintableString
OID <to be assigned>
EQUALITY caseIgnoreMatch
SINGLE-VALUED
FORMAT either 'Z' (UTC) or {'+' | '-'}'hhmm'
6.6. The Class vendorPolicyCondition
The purpose of this class is to provide a general escape mechanism
for representing policy conditions that have not been modeled with
specific attributes. Instead, the two attributes
vendorPolicyConstraintData and vendorPolicyConstraintEncoding are
used to define the content and format of the condition, as explained
below.
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As its name suggests, this class is intended for vendor-specific
extensions to the Core Policy Schema. Standardized extensions are
not expected to use this class.
The class definition is as follows:
NAME vendorPolicyCondition
DESCRIPTION A class that defines a registered means to
describe a policy condition.
DERIVED FROM policyCondition
TYPE auxiliary
AUXILIARY CLASSES none
POSSIBLE SUPERIORS policyRule
OID <to be assigned>
MUST vendorPolicyConstraintData
vendorPolicyConstraintEncoding
MAY
6.6.1. The Attribute vendorPolicyConstraintData
This attribute provides a general escape mechanism for representing
policy conditions that have not been modeled with specific
attributes. The format of the OctetString is left unspecified in
this definition. It is determined by the OID value stored in the
attribute vendorPolicyConstraintEncoding. Since
vendorPolicyConstraintEncoding is single-valued, all the values of
vendorPolicyConstraintData share the same format and semantics.
A policy decision point can readily determine whether it supports the
values stored in an instance of vendorPolicyConstraintData by
checking the OID value from vendorPolicyConstraintEncoding against
the set of OIDs it recognizes. The action for the policy decision
point to take in case it does not recognize the format of this data
could itself be modeled as a policy rule, governing the behavior of
the policy decision point.
The attribute definition is as follows:
NAME vendorPolicyConstraintData
DESCRIPTION Escape mechanism for representing constraints that
have not been modeled as specific attributes. The
format of the values is identified by the OID
stored in the attribute
vendorPolicyConstraintEncoding.
SYNTAX OctetString
OID <to be assigned>
EQUALITY octetStringMatch
MULTI-VALUED
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6.6.2. The Attribute vendorPolicyConstraintEncoding
This attribute identifies the encoding and semantics of the values of
vendorPolicyConstraintData in this instance. The value of this
attribute is a single OID.
The attribute definition is as follows:
NAME vendorPolicyConstraintEncoding
DESCRIPTION An OID identifying the format and semantics for
this instance's vendorPolicyConstraintData
attribute.
SYNTAX OID
OID <to be assigned>
EQUALITY objectIdentifierMatch
SINGLE-VALUED
6.7. The Class policyAction
The purpose of a policy action is to execute one or more operations
that will affect network traffic and/or systems, devices, etc. in
order to achieve a desired policy state. This (new) policy state
provides one or more (new) behaviors. A policy action ordinarily
changes the configuration of one or more elements.
A policyRule contains one or more policy actions. Unlike a condition,
however, only one list of policy actions is contained in a
policyRule. A policy administrator can assign an order to the actions
associated with a policyRule, complete with an indication of whether
the indicated order is mandatory, recommended, or of no significance.
The actions associated with a policyRule are executed if and only if
the overall condition(s) of the policyRule evaluates to TRUE.
The class definition is as follows:
NAME policyAction
DESCRIPTION A class representing an action to be performed as
a result of a policy rule.
DERIVED FROM top
TYPE auxiliary
AUXILIARY CLASSES none
POSSIBLE SUPERIORS policyRule
OID <to be assigned>
MUST policyActionName
MAY
6.7.1. The Attribute policyActionName
This attribute provides a user-friendly name for a policy action.
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The attribute definition is as follows:
NAME policyActionName
DESCRIPTION The user-friendly name of this policy action.
SYNTAX IA5String
OID <to be assigned>
EQUALITY caseExactIA5Match
SINGLE-VALUED
6.8. The Class vendorPolicyAction
The purpose of this class is to provide a general escape mechanism
for representing policy actions that have not been modeled with
specific attributes. Instead, the two attributes
vendorPolicyActionData and vendorPolicyActionEncoding are used to
define the content and format of the condition, as explained below.
As its name suggests, this class is intended for vendor-specific
extensions to the Core Policy Schema. Standardized extensions are
not expected to use this class.
The class definition is as follows:
NAME vendorPolicyAction
DESCRIPTION A class that defines a registered means to
describe a policy action.
DERIVED FROM policyAction
TYPE auxiliary
AUXILIARY CLASSES none
POSSIBLE SUPERIORS policyRule
OID <to be assigned>
MUST vendorPolicyActionData vendorPolicyActionEncoding
MAY
6.8.1. The Attribute vendorPolicyActionData
This attribute provides a general escape mechanism for representing
policy actions that have not been modeled with specific attributes.
The format of the OctetString is left unspecified in this definition.
It is determined by the OID value stored in the attribute
vendorPolicyActionEncoding. Since vendorPolicyActionEncoding is
single-valued, all the values of vendorPolicyActionData share the
same format and semantics.
A policy decision point can readily determine whether it supports the
values stored in an instance of vendorPolicyActionData, by checking
the OID value from vendorPolicyActionEncoding against the set of OIDs
it recognizes. The action for the policy decision point to take in
case it does not recognize the format of this data could itself be
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modeled as a policy rule, governing the behavior of the policy
decision point.
The attribute definition is as follows:
NAME vendorPolicyActionData
DESCRIPTION Escape mechanism for representing actions that
have not been modeled as specific attributes. The
format of the values is identified by the OID
stored in the attribute
vendorPolicyActionEncoding.
SYNTAX OctetString
OID <to be assigned>
EQUALITY octetStringMatch
MULTI-VALUED
6.8.2. The Attribute vendorPolicyActionEncoding
This attribute identifies the encoding and semantics of the values of
vendorPolicyActionData in this instance. The value of this attribute
is a single OID.
The attribute definition is as follows:
NAME vendorPolicyActionEncoding
DESCRIPTION An OID identifying the format and semantics for
this instance's vendorPolicyActionData attribute.
SYNTAX OID
OID <to be assigned>
EQUALITY objectIdentifierMatch
SINGLE-VALUED
6.9. The Class policyInstance
This class introduces no additional attributes, beyond those defined
in the class policy from which it is derived. Its role in the Core
Schema is to serve as the structural class to which the auxiliary
classes policyCondition and policyAction may be attached when the
complex policy rule structure is required. With its attached
auxiliary class, an instance of policyInstance represents a single
policy condition or a single policy action, but not both.
An instance of this class is named by an attribute it acquires via an
attached auxiliary class. In the Core Schema, the naming attributes
available for this purpose are policyConditionName and
policyActionName.
The class definition is as follows:
NAME policyInstance
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DESCRIPTION A structural class to which the auxiliary classes
policyCondition and policyAction may be attached,
when the complex policy rule structure is
required.
DERIVED FROM policy
TYPE structural
AUXILIARY CLASSES policyCondition, policyAction
OID <to be assigned>
6.10. The Auxiliary Class policyElement
Like policyInstance, this class also introduces no additional
attributes, beyond those defined in the class policy from which it is
derived. Its role is to "tag" an instance of a class defined outside
the realm of policy as being nevertheless relevant to a policy
specification. This tagging can potentially take place at two
levels:
o Every instance to which policyElement is attached becomes an
instance of the class policy, since policyElement is a subclass of
policy. Thus a DIT search with the filter "objectClass=policy"
will return the instance. (As noted earlier, this approach does
not work for some directory implementations. To accommodate these
implementations, policy-related entries SHOULD be tagged with the
keyword "POLICY".)
o With the policyKeywords attribute that it inherits from policy, an
instance to which policyElement is attached can be tagged as being
relevant to a particular type or category of policy, using standard
keywords, administrator-defined keywords, or both.
The class definition is as follows:
NAME policyElement
DESCRIPTION An auxiliary class used to tag instances of
classes defined outside the realm of policy as
relevant to a particular policy specification.
DERIVED FROM policy
TYPE auxiliary
AUXILIARY CLASSES none
OID <to be assigned>
6.11. The Auxiliary Class policySubtreesPtrAuxClass
This auxiliary class provides a single, multi-valued attribute that
points to a set of objects that are at the root of DIT subtrees
containing policy-related information. By attaching this attribute
to instances of various other classes, a policy administrator has a
flexible way of providing an entry point into the directory that
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allows a client to locate and retrieve the policy information
relevant to it.
This object does not provide the semantic linkages between individual
policy objects, such as those between a policy group and the policy
rules that belong to it. Its only role is to enable efficient bulk
retrieval of policy-related objects, as described in Section 5.4.
Once the objects have been retrieved, a directory client can
determine the semantic linkages by following DN pointers such as
policyRulesAuxContainedSet locally.
Since policy-related objects may or may not be included in the DIT
subtree beneath an object to which this auxiliary class is attached,
there is no automatic presumption that this subtree should be
searched by a directory client. If this subtree does contain policy-
related objects, this is indicated by including a DN pointer to this
object itself in the policySubtreesAuxContainedSet attribute.
The class definition is as follows:
NAME policySubtreesPtrAuxClass
DESCRIPTION An auxiliary class providing a DN pointer to roots
of DIT subtrees contained policy-related objects.
DERIVED FROM top
TYPE auxiliary
AUXILIARY CLASSES none
OID <to be assigned>
MUST policySubtreesAuxContainedSet
6.11.1. The Attribute policySubtreesAuxContainedSet
This attribute provides an unordered set of DN pointers to one or
more objects under which policy-related information is present. The
objects pointed to may or may not themselves contain policy-related
information.
The attribute definition is as follows:
NAME policySubtreesAuxContainedSet
DESCRIPTION Distinguished names of objects that serve as roots
for DIT subtrees containing policy-related
objects. No order is implied.
SYNTAX DN
OID <to be assigned>
EQUALITY distinguishedNameMatch
MULTI-VALUED
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6.12. The Auxiliary Class policyGroupContainmentAuxClass
This auxiliary class provides a single, multi-valued attribute that
points to a set of policyGroups. By attaching this attribute to
instances of various other classes, a policy administrator has a
flexible way of providing an entry point into the directory that
allows a client to locate and retrieve the policyGroups relevant to
it.
As is the case with policyRules, a policy administrator might have
several different pointers to a policyGroup in the overall directory
structure. The policyGroupContainmentAuxClass is the mechanism that
makes it possible for the policy administrator to define all these
pointers.
The class definition is as follows:
NAME policyGroupContainmentAuxClass
DESCRIPTION An auxiliary class used to bind policyGroups
to an appropriate container object.
DERIVED FROM top
TYPE auxiliary
AUXILIARY CLASSES none
OID <to be assigned>
MUST policyGroupsAuxContainedSet
6.12.1. The Attribute policyGroupsAuxContainedSet
This attribute provides an unordered set of DN pointers to one or
more policyGroups associated with the instance of a structural class
to which this attribute has been appended. The attribute definition
is as follows:
NAME policyGroupsAuxContainedSet
DESCRIPTION Distinguished names of policyGroups associated in
some way with the instance to which this attribute
has been appended. No order is implied.
SYNTAX DN
OID <to be assigned>
EQUALITY distinguishedNameMatch
MULTI-VALUED
6.13. The Auxiliary Class policyRuleContainmentAuxClass
This auxiliary class provides a single, multi-valued attribute that
points to a set of policyRules. By attaching this attribute to
instances of various other classes, a policy administrator has a
flexible way of providing an entry point into the directory that
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allows a client to locate and retrieve the policyRules relevant to
it.
A policy administrator might have several different pointers to a
policyRule in the overall directory structure. For example, there
might be pointers to all policyRules for traffic originating in a
particular subnet from a directory entry that represents that subnet.
At the same time, there might be pointers to all policyRules related
to a particular DiffServ setting from an instance of a policyGroup
explicitly introduced as a container for DiffServ-related
policyRules. The policyRuleContainmentAuxClass is the mechanism that
makes it possible for the policy administrator to define all these
pointers.
Note that the cn attribute does NOT need to be defined for this
class. This is because an auxiliary class is used as a means to
collect common attributes and treat them as properties of an object.
A good analogy is a #include file, except that since an auxiliary
class is a class, all the benefits of a class (e.g., inheritance) can
be applied to an auxiliary class.
The class definition is as follows:
NAME policyRuleContainmentAuxClass
DESCRIPTION An auxiliary class used to bind policyRules to an
appropriate container object.
DERIVED FROM top
TYPE auxiliary
AUXILIARY CLASSES none
OID <to be assigned>
MUST policyRulesAuxContainedSet
6.13.1. The Attribute policyRulesAuxContainedSet
This attribute provides an unordered set of DN pointers to one or
more policyRules associated with the instance of a structural class
to which this attribute has been appended. The attribute definition
is:
NAME policyRulesAuxContainedSet
DESCRIPTION Distinguished names of policyRules associated in
some way with the instance to which this attribute
has been appended. No order is implied.
SYNTAX DN
OID <to be assigned>
EQUALITY distinguishedNameMatch
MULTI-VALUED
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7. Extending the Core Schema
The following subsections provide general guidance on how to create a
domain-specific schema derived from the Core Schema, discuss how the
vendor classes in the Core Schema should be used, and explain how
policyTimePeriodConditions are related to other policy conditions.
7.1. Subclassing policyCondition and policyAction
In Section 5.3 above, there is a discussion of how, by representing
policy conditions and policy actions as auxiliary classes in a
schema, the flexibility is retained to instantiate a particular
policy as either a simple policy rule or a complex one. This
flexibility is lost if a schema takes either of two "hard-coded"
paths:
o If the schema subclasses policyRule to add domain-specific
characteristics that implicitly express a policy condition, a
policy action, or both, then the schema supports only the simple
policy rule form.
o If the schema introduces structural subclasses of
policyCondition, policyAction, or both, then the schema supports
only the complex policy rule form.
Even if the authors of a domain-specific schema can only envision one
of these forms of policy rules being used when the schema is
instantiated, it costs nothing extra to express the schema as
auxiliary subclasses of policyCondition and policyAction. For
standardized schemata, this document specifies that domain-specific
information MUST be expressed in auxiliary subclasses of
policyCondition and policyAction. It is RECOMMENDED that non-
standardized schemata follow this practice as well.
7.2. Using the Vendor Policy Encoding Attributes
As discussed Section 6.6 "The Class vendorPolicyCondition", the
attributes vendorPolicyConstraintData and
vendorPolicyConstraintEncoding are included in the
vendorPolicyCondition to provide an escape mechanism for representing
"exceptional" policy conditions. The attributes
vendorPolicyActionData and vendorPolicyActionEncoding in the
vendorPolicyAction class play the same role with respect to actions.
This enables interoperability between different vendors.
For example, imagine a network composed of access devices from vendor
A, edge and core devices from vendor B, and a policy server from
vendor C. It is desirable for this policy server to be able to
configure and manage all of the devices from vendors A and B.
Unfortunately, these devices will in general have little in common
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(e.g., different mechanisms, different ways for controlling those
mechanisms, different operating systems, different commands, and so
forth). The escape conditions provide a way for vendor-specific
commands to be encoded as OctetStrings, so that devices from
different vendors can be commonly managed by a single policy server.
7.3. Using Time Validity Periods
Time validity periods are defined as a subclass of policyCondition,
called policyTimePeriodCondition. This is to allow their inclusion
in the AND/OR condition definitions for a policyRule. Care should be
taken not to subclass policyTimePeriodCondition to add domain-
specific condition properties. For example, it would be incorrect to
add IPSec- or QoS-specific condition properties to the
policyTimePeriodCondition class, just because IPSec or QoS includes
time in its condition definition. The correct subclassing would be to
create IPSec or QoS-specific subclasses of policyCondition and then
combine instances of these domain-specific condition classes with the
validity period criteria. This is accomplished using the AND/OR
aggregation capabilities for policyConditions in policyRules.
8. Security Considerations
Security and denial of service considerations are not explicitly
considered in this memo, as they are appropriate for the underlying
policy architecture. However, the policy architecture must be secure
as far as the following aspects are concerned. First, the mechanisms
proposed under the framework must minimize theft and denial of
service threats. Second, it must be ensured that the entities (such
as PEPs and PDPs) involved in policy control can verify each other's
identity and establish necessary trust before communicating. The
schema defined in this document MUST not compromise either of these
goals.
9. Intellectual Property
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11.
Copies of claims of rights made available for publication and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
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such proprietary rights by implementers or users of this
specification can be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
10. Acknowledgments
This document is closely aligned with the work being done in the
Desktop Management Task Force (DMTF) Service Level Agreements and
Networks working groups. As noted, the Core Schema described here
was initially defined in references [2] and [3]. We would especially
like to thank Raju Rajan, Sanjay Kamat, Andrea Westerinen, Lee
Rafalow, Raj Yavatkar, Glenn Waters, David Black, Michael Richardson,
Mark Stevens, David Jones, and Hugh Mahon for their helpful comments.
11. References
[1] J. Strassner and E. Ellesson, "Terminology for describing network
policy and services", draft-strassner-policy-terms-00.txt, August
1998.
[2] Bhattacharya, P., and R. Adams, W. Dixon, R. Pereira, R. Rajan,
"An LDAP Schema for Configuration and Administration of IPSec
based Virtual Private Networks (VPNs)", Internet-Draft work in
progress, October 1998
[3] Rajan, R., and J. C. Martin, S. Kamat, M. See, R. Chaudhury, D.
Verma, G. Powers, R. Yavatkar, "Schema for Differentiated Services
and Integrated Services in Networks", Internet-Draft work in
progress, October 1998
[4] J. Strassner and S. Judd, "Directory-Enabled Networks", version
3.0c5 (August 1998).
[5] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[6] Hovey, R., and S. Bradner, "The Organizations Involved in the IETF
Standards Process", BCP 11, RFC 2028, October 1996.
[7] Wahl, M., and S. Kille, T. Howes, "Lightweight Directory Access
Protocol (v3): UTF-8 String Representation of Distinguished
Names", RFC 2253, December 1997.
[8] J. Strassner, policy architecture BOF presentation, 42nd IETF
Meeting, Chicago, Illinois, October, 1998
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[9] DMTF web site, http://www.dmtf.org.
12. Authors' Addresses
John Strassner
Cisco Systems, Bldg 1
170 West Tasman Drive
San Jose, CA 95134
Phone: +1 408-527-1069
Fax: +1 408-527-1722
E-mail: johns@cisco.com
Ed Ellesson
IBM Corporation, JDGA/501
4205 S. Miami Blvd.
Research Triangle Park, NC 27709
Phone: +1 919-254-4115
Fax: +1 919-254-6243
E-mail: ellesson@raleigh.ibm.com
Bob Moore
IBM Corporation, JDGA/501
4205 S. Miami Blvd.
Research Triangle Park, NC 27709
Phone: +1 919-254-4436
Fax: +1 919-254-6243
E-mail: remoore@us.ibm.com
13. Full Copyright Statement
Copyright (C) The Internet Society (1999). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
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TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
14. Appendix A - Guidelines for Construction of DNs
To Be Provided
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