Network Working Group J. Strassner
Internet-draft Cisco Systems
Category: Standards Track E. Ellesson
IBM
February 1999
Policy Framework Core Information Model
draft-ietf-policy-core-schema-01.txt
February 11, 1999 21:40
Status of this Memo
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Copyright Notice
Copyright (C) The Internet Society (1999). All Rights Reserved.
Abstract
This document defines an object-oriented information model for
representing policy information. This model defines structural
information of objects that comprise and control policy (the
"schema", or class inheritance hierarchy) as well as information that
describes how different objects are related to other objects (the
relationship hierarchy). In general, both of these class hierarchies
will need to be mapped to a particular data store.
This draft targets a directory that uses LDAP as its access protocol.
As such, the class inheritance hierarchy can be directly mapped, but
the relationship hierarchy will in general need to be mapped to a
form suitable for directory implementation. This is because it
contains concepts that are usually not directly translatable to the
underlying data store. This document defines a schema and one such
mapping of relationships for implementation in directories using
LDAPv3 as their access protocol.
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The information model described in this document consists of five
very general classes: policyGroup, policyRule, policyCondition,
policyValidityPeriodCondition, and policyAction. While structural
information is represented very well in LDAP schemas, relationships
between objects are not. This document also defines how to map more
abstract concepts, such as relationships, into LDAP schemas. One
mechanism to do this mapping is to use auxiliary classes. This
document defines one such class, the policyRuleContainmentAuxClass.
While these classes are general, they are not abstract: they can all
be directly instantiated. Policy solutions for specific areas, such
as DiffServ and IPSec, may use the policyGroup, policyRule,
policyValidityPeriodCondition, and policyRuleContainmentAuxClass
classes directly, while creating their own subclasses derived from
policyCondition and policyAction in order to represent their own
application-specific needs.
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Table of Contents
1. Introduction....................................................4
2. Modeling Policies...............................................5
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 of the Policy Framework Core Information Model
...................................................................10
4. Inheritance Hierarchy for the LDAP Schema......................11
5. Class Definitions for the LDAP Schema..........................12
5.1. Naming Attributes in the Core Schema.........................12
5.2. The Class policyGroup........................................12
5.2.1. The attribute cn...........................................14
5.2.2. The Attribute policyGroupName..............................14
5.2.3. The Attribute containedPolicyGroups........................14
5.2.4. The Attribute policyGroupType..............................15
5.3. The Class policyRuleContainmentAuxClass......................15
5.3.1. The Attribute policyRulesAuxContainedSet...................16
5.4. The Class policyRule.........................................16
5.4.1. The Attribute cn...........................................18
5.4.2. The Attribute policyRuleName...............................18
5.4.3. The Attribute policyRuleEnabled............................18
5.4.4. The Attribute policyRuleConditionListType..................18
5.4.5. The Attribute policyRuleConditionList......................19
5.4.6. The Attribute policyRuleActionList.........................20
5.4.7. The Attribute policyRuleKeywords...........................21
5.4.8. The Attribute policyRuleType...............................21
5.4.9. The Attribute policyRuleUsage..............................22
5.4.10. The Attribute policyRulePriority..........................22
5.4.11. The Attribute policyRuleMandatory.........................23
5.4.12. The Attribute policyRuleDebugMode.........................23
5.4.13. The Attribute policyRuleSequencedActions..................24
5.5. The Class policyValidityPeriodCondition......................24
5.5.1. The Attribute pvpConditionTime.............................25
5.5.2. The Attribute pvpConditionMonthOfYearMask..................26
5.5.3. The Attribute pvpConditionDayOfMonthMask...................26
5.5.4. The Attribute pvpConditionDayOfWeekMask....................27
5.5.5. The Attribute pvpConditionTimeOfDayMask....................28
5.5.6. The Attribute pvpConditionTimeZone.........................29
5.6. The Class policyCondition....................................29
5.6.1. The Attribute cn...........................................31
5.6.2. The Attribute policyConditionName..........................31
5.7. The Class vendorPolicyCondition..............................31
5.7.1. The Attribute vendorPolicyConditionConstraint..............32
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5.7.2. The Attribute vendorPolicyConditionEncoding................32
5.8. The Class policyAction.......................................33
5.8.1. The Attribute cn...........................................33
5.8.2. The Attribute policyActionName.............................33
5.9. The Class vendorPolicyAction.................................34
5.9.1. The Attribute vendorPolicyActionData.......................34
5.9.2. The Attribute vendorPolicyActionEncoding...................35
6. Extending the Core Schema......................................35
6.1. Subclassing policyCondition and policyAction.................35
6.2. Subclassing policyRule.......................................36
6.2.1. Refining the semantics of policyRule.......................36
6.2.2. Optimizing the computation of a policyRule.................36
6.3. Using the Vendor Policy Encoding Attributes..................36
6.4. Using Time Validity Periods..................................37
7. Security Considerations........................................37
8. Intellectual Property..........................................37
9. Acknowledgments................................................38
10. References....................................................38
11. Authors' Addresses............................................39
12. Full Copyright Statement......................................39
13. Appendix A - Guidelines for Construction of DNs...............39
1. Introduction
This document defines an information model, containing a schema
(represented as a class inheritance hierarchy) and a relationship
model. The schema contains five core classes for representing
policies: policyGroup, policyRule, policyCondtion, policyAction, and
policyValidityPeriodCondition.
This schema can be mapped to many different data store
implementations. This document concentrates on a mapping of the data
store to a directory that uses LDAP as its access protocol. However,
the relationship class hierarchy needs to be mapped to a specific
data store implementation. This document defines a mapping for the
relationships of this information model to a directory that uses
LDAPv3 as its access protocol. A sixth core class,
policyRuleContainmentAuxClass, is used as part of this mapping. The
use of an information model enables the schema and the relationship
class hierarchy to be extensible, such that other types of policy
repositories, such as relational databases, can use this information.
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These six classes and their relationships are sufficiently generic to
allow them to represent policies related to anything. However, 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,
policyValidityPeriodCondition, and policyRuleContainmentAuxClass
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
will then fit naturally within the policy framework of the above four
classes. This will be explored more thoroughly in Section 6.0,
"Extending the Core Schema".
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 (Common Information Model) effort
in the Desktop Management Task Force (DMTF). Standardization of the
core policy model is the responsibility of the SLA Policy working
group.
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].
2. Modeling Policies
The classes comprising the Policy Framework Core Information Model
Class Hierarchy 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.
The simplest 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
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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. 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.
Actions can be prioritized so as to avoid conflicts. However, this
release of the core schema draft does not specify conditional
handling of the actions to be executed, nor does it specify the
handling of generalized error conditions. This is because if this
feature is implemented, then policies immediately become much more
complex. It is considered better to gain implementation experience
with simpler policies and use this experience to then build more
complex policies.
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 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.
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
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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 policyRules apply equally to the scope of the policyGroup.
Stand-alone policies are those that can be expressed in a simple
statement. They can be represented effectively in schemas 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 can't 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 of
Usage Policies include upgrading network forwarding services after
a user is verified to be a member of a "gold" service group, or
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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.
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 policy schema
classes are intended to be used as part of the definition of this
specification.
This translation is domain-independent. That is, it applies equally
to Quality of Service (QoS) as defined in the Differentiated Services
working group of the IETF) as it does to signaled QoS, as specified
in the Integrated Services working group of the IETF.
Furthermore, it is envisioned that the definition of policy in this
draft is generic in nature and is suitable for non-QoS networking
applications (e.g., DHCP and IPSEC) as well as non-networking
applications (e.g., backup policies, auditing access, etc.).
3. Overview of the Schema
The following diagram provides an overview of the five classes that
comprise the CIM core schema, and their relationships to each other.
Note that the two extension classes vendorPolicyCondition and
vendorPolicyAction are not shown.
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**************
* *
0..n * * ContainedPolicyGroups
+------v------+ *
| policyGroup <******
| | 0..n
+------^------+
0..n *
* ContainedPolicyRules
0..n *
+-----v-------+
| |
| policyRule |
| | ContainedPolicyConditions (ORed set of
ANDed
| <************************* conditions, or
| | 0..n * vice-versa)
| | * 0..n
| | +---------v------------+
| | | policyCondition |
| | +----------------------+
| | ^
| | I
| | I
| | ^
| | +------------------------------ +
| | | policyValidityPeriodCondition |
| | +------------------------------ +
| |
| | ContainedPolicyActions
| <*************************
| | 0..n *
| | * 0..n
| | +---------v------------+
| | | policyAction |
+-------------+ +----------------------+
Figure 1. An 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
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.
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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 of the Policy Framework Core Information Model
The following relationships are shown in the preceding figure:
o The ContainedPolicyGroups relationship enables policyGroups 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
policyGroup representing policies for the US might have nested
within it policy groups for the Eastern and Western US.
For LDAP schemata, the ContainedPolicyGroups relation is mapped to
the containedPolicyGroups attribute (note that 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 also aggregate one or more policy rules.
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.
o A policyRule may also be aggregated by an instance of any class to
which the policyRuleContainmentAuxClass class has been attached.
Once again, this is for administrative convenience. If the
directory entry to which the policyRuleContainmentAuxClass has
been attached is a policy group, then the pointer in the
policyRuleContainmentAuxClass realizes the relationship discussed
above between the group and a policyRule; a separate attribute is
not needed in the policyGroup class.
o A condition of a policyRule may specify one or more time validity
periods. This can be used for several purposes. Two important uses
include representing time as an additional condition (e.g., use
one policy in the morning and use a different policy in the
afternoon) and to enable scheduled activation and deactivation of
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the policyRule. A policy validity period may be aggregated by
multiple policyRules. A rule that does not point to a policy
validity period is, from the point of view of scheduling, always
active. It may, however, be inactive for other reasons.
Time validity 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 policyRule aggregates zero or more instances of the
policyCondition class. For all policy rules, at least one
condition MUST be specified, either via the
containedPolicyConditions aggregation, or defined explicitly
within a subclass of policyRule. These conditions 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). 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. For LDAP
schemata, pointers to PolicyCondition objects (or subclasses of
this class) are used.
o A policyRule may aggregate zero or more policy actions. For all
policy rules, at least one action MUST be specified, either via
the containedPolicyActions aggregation, or defined explicitly
within a subclass of policyRule. 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
containedPolicyActions 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 Schema
The following diagram illustrates the class hierarchy for the LDAP
policy schema classes:
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top
|
+---policyGroup
|
+---policyRuleContainmentAuxClass
|
+---policyRule
|
+---policyCondition
| |
| +---policyValidityPeriodCondition
| |
| +---vendorPolicyCondition
|
+---policyAction
|
+---vendorPolicyAction
5. Class Definitions for the LDAP Schema
The classes described below contain certain optimizations for a
directory that uses LDAP as its access protocol. One example of this
is the use of an auxiliary class to represent CIM relationships.
Other data stores might need to implement these relationships
differently.
5.1. 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 classes defined in this schema has its own naming
attribute. Since the naming attributes are different, the policy
administrator is guaranteed 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. To fit in
with existing directory practice, each of the classes uses the
commonName (cn) attribute as its naming attribute.
5.2. 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
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policyGroup that contains itself, are not allowed when policyGroups
contain other policyGroups.
PolicyGroups and their nesting capabilities are shown in Figure 2
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 2. Overview of the policyGroup class
As a simple example, think of the highest level policyGroup shown in
Figure 2 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, policyGroupA in Figure 2 above may define logon rules for
employees on the West Coast, while another policyGroup might define
logon rules for the Midwest (e.g., policyGroupX), 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 (policyGroupX), which might directly
contain policyRules.
The class definition for policyGroup is as follows. Note that this
class definition does not include an attribute to realize the
ContainedPolicyRules association from the object model, since a
policyGroup object points to instances of policyRule via 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 policyRuleContainmentAuxClass
POSSIBLE SUPERIORS container, organization, organizationalUnit,
policyGroup
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OID <to be assigned>
MUST cn, policyGroupName
MAY containedPolicyGroups, policyGroupType
5.2.1. The attribute cn
The cn, or commonName, attribute is an X.500 attribute. It stands for
commonName. It specifies a user-friendly name by which the object is
commonly known. This name may be ambiguous by itself. This name is
used in a limited scope (such as an organization). It conforms to the
naming conventions of the country or culture with which it is
associated. CN is used universally in DEN as the naming attribute for
a class.
NAME cn
DESCRIPTION Naming attribute of this class
SYNTAX DirectoryString
OID 2.4.5.3
EQUALITY caseExactMatch
SINGLE-VALUED
5.2.2. 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
5.2.3. The Attribute containedPolicyGroups
This attribute provides an unordered set of DN pointers to zero or
more other policyGroup objects, representing nested policyGroups
contained by this policyGroup. The attribute definition is as
follows:
NAME containedPolicyGroups
DESCRIPTION Distinguished names of other policyGroup objects
aggregated by this policy group. There is no
order implied among the members of the set.
SYNTAX DN
OID <to be assigned>
EQUALITY distinguishedNameMatch
MULTI-VALUED
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5.2.4. The Attribute policyGroupType
This attribute is used to specify the type of policy that this
policyGroup represents. This can be used for classification (for
example, service policy or usage policy) or categorization (the type
of service or usage policy that this policy is). The attribute
definition is as follows:
NAME policyGroupType
DESCRIPTION Defines a policyGroup classification and
categorization. When multiple classifications are
possible, the one that "best" describes the
policyGroup's type should be used.
SYNTAX INTEGER
OID <to be assigned>
EQUALITY integerMatch
SINGLE-VALUED
DEFAULT VALUE 0
The defined values for this attribute are: Unknown (0), Configuration
(1), Usage (2), Security (3), Service (4), Motivational (5),
Installation (6), and Event (7). These concepts were defined in
Section 2.0.
5.3. The 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
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:
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NAME policyRuleContainmentAuxClass
DESCRIPTION An auxiliary class used to bind policyRules to an
appropriate container object.
DERIVED FROM top
TYPE auxiliary
AUXILIARY CLASSES none
POSSIBLE SUPERIORS container, organization, organizationalUnit,
policyGroup
OID <to be assigned>
MUST policyRulesAuxContainedSet
5.3.1. 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
5.4. 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). 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. Both the conditions and the actions are identified by DN
pointers and/or by specific attributes introduced in subclasses of
policyRule.
This is illustrated conceptually in Figure 3 below.
+------------------------------------------------+
| PolicyRule |
| |
| +--------------------+ +-----------------+ |
| | PolicyCondition(s)| | PolicyAction(s) | |
| +--------------------+ +-----------------+ |
| |
+------------------------------------------------+
Figure 3. Overview of the PolicyRule Class
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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. An example shows how the attribute and the
grouping integer 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,
C2: groupNumber = 1,
C3: groupNumber = 1,
C4: groupNumber = 2,
C5: groupNumber = 2)
If policyRuleConditionListType = DNF, then the overall condition = for
the policyRule is:
(C1 AND C2 AND C3) OR (C4 AND C5)
On the other hand, if policyRuleConditionListType = CNF, then the
overall condition for the policyRule is:
(C1 OR 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
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 cn policyRuleName
MAY policyRuleEnabled policyRuleConditionListType
policyRuleConditionList policyRuleActionList
policyRuleKeywords policyRuleType policyRuleUsage
policyRulePriority policyRuleMandatory
policyRuleDebugMode policyRuleSequencedActions
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5.4.1. The Attribute cn
This is the exact same definition as in Section 5.2.1. It is included
in this class for the reasons enumerated there.
5.4.2. 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
5.4.3. The Attribute policyRuleEnabled
This flag 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 definition
is as follows:
NAME policyRuleEnabled
DESCRIPTION A flag indicating whether this policy rule is
enabled from an administrative point of view.
SYNTAX Boolean
OID <to be assigned>
EQUALITY booleanMatch
SINGLE-VALUED
DEFAULT VALUE TRUE
5.4.4. 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
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DEFAULT VALUE 1 (DNF)
5.4.5. 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. 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 comprised of two data types, an
Integer (groupNumber) and DistinguishedName (DN). There are three
ways to address this.
1. Collapse the two attribute types into a single structured IA5
string 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 an IA5 string
matching rule. Its disadvantage is that an IA5 string 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 IA% matching rules,
or vice versa.
2. Define a new syntax '<integer>:<DN>', with its own matching rules.
With this approach the matching problems introduced by the IA5
string 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.
3. Use two objects in the directory to represent the two 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 IA5 string approach for containedPolicyConditions, as well
as with an analogous 'n:DN' approach for containedPolicyActions. To
minimize problems arising from differences in matching rules, this
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document will provide a series of guidelines for constructing DNs
that behave identically with respect to the IA5 matching rules and
the distinguishedNameMatch. These guidelines are in Appendix A.
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 OctetString
OID <to be assigned>
EQUALITY TBD
MULTI-VALUED
FORMAT groupNumber:DN
5.4.6. 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 5.4.5 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," with one
exception: all actions with positive sequence numbers are to be
performed before any actions with sequence number '0'. Finally, 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
0:DN-C
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3:DN-D
indicate either B,D,A,C or B,D,C,A, since the '0' actions A and C
must be performed after the non-zero ones. 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
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 Octet String
OID <to be assigned>
EQUALITY TBD
MULTI-VALUED
FORMAT n:DN
5.4.7. The Attribute policyRuleKeywords
This attribute provides a set of one or more ad hoc keywords that a
policy administrator may define to assist directory clients in
locating the policy rules applicable to them. Values for this
attribute are installation dependent, and thus are not specified in
any schema document. The attribute definition is as follows:
NAME policyRuleKeywords
DESCRIPTION A set of ad hoc keywords to assist directory
clients in locating the policy rules applicable to
them.
SYNTAX IA5String
OID <to be assigned>
EQUALITY caseExactIA5Match
MULTI-VALUED
5.4.8. The Attribute policyRuleType
This attribute is used to specify the type of policy that this policy
rule represents. This can be used for classification (for example,
service policy or usage policy) or categorization (the type of
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service or usage policy that this policy is). The attribute
definition is as follows:
NAME policyRuleType
DESCRIPTION Defines a policy classification and
categorization. When multiple classifications are
possible, the one that "best" describes the
policy's type should be used.
SYNTAX INTEGER
OID <to be assigned>
EQUALITY integerMatch
SINGLE-VALUED
DEFAULT VALUE 0
The defined values for this attribute are: Unknown (0), Configuration
(1), Usage (2), Security (3), Service (4), Motivational (5),
Installation (6), and Event (7). These concepts were defined in
Section 2.0.
5.4.9. 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
5.4.10. The Attribute policyRulePriority
This attribute provides a positive integer for prioritizing policy
rules relative to each other. For policy rules that have this
attribute, smaller 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 positive integer for prioritizing this
policyRule relative to other policyRules. A
smaller value indicates a higher priority.
SYNTAX INTEGER
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OID <to be assigned>
EQUALITY integerMatch
SINGLE-VALUED
DEFAULT VALUE 0
5.4.11. 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 evaulation 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
5.4.12. The Attribute policyRuleDebugMode
This attribute indicates that the policyRule should be evaluated, but
no actions taken. It serves as a debug vehicle when attempting to
determine what policies would execute in a particular scenario, but
not to take any actions to change state due to that scenario.
The attribute definition is as follows:
NAME policyRuleDebugMode
DESCRIPTION A flag indicating that the evaluation of the
policyRule's policyConditions should occur, but
the set of actions specified for the rule should
not be executed.
SYNTAX Boolean
OID <to be assigned>
EQUALITY booleanMatch
SINGLE-VALUED
DEFAULT VALUE FALSE
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5.4.13. The Attribute policyRuleSequencedActions
This attrribute 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).
5.5. The Class policyValidityPeriodCondition
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
policyValidityPeriodCondition.
PolicyValidityPeriodCondition 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
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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 8 AM through 4 PM
would represent the following validity periods:
Friday, March 5, 1999, from 8 AM through 4 PM;
Friday, March 12, 1999, from 8 AM through 4 PM;
Friday, March 19, 1999, from 8 AM through 4 PM;
Friday, March 26, 1999, from 8 AM through 4 PM;
Friday, April 2, 1999, from 8 AM through 4 PM;
Friday, April 9, 1999, from 8 AM through 4 PM;
Friday, April 16, 1999, from 8 AM through 4 PM;
Friday, April 23, 1999, from 8 AM through 4 PM;
Friday, April 30, 1999, from 8 AM through 4 PM.
Attributes not present in an instance of
policyValidityPeriodCondition 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
policyValidityPeriodCondition 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 policyValidityPeriodCondition
DESCRIPTION A class that provides the capability of enabling /
disabling a policy rule according to a pre-
determined schedule.
DERIVED FROM policyCondition
TYPE structural
AUXILIARY CLASSES none
POSSIBLE SUPERIORS policyRule
OID <to be assigned>
MUST
MAY pvpConditionTime pvpConditionMonthOfYearMask
pvpConditionDayOfMonthMask
pvpConditionDayOfWeekMask
pvpConditionTimeOfDayMask pvpConditionTimeZone
5.5.1. The Attribute pvpConditionTime
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
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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, 8 AM through January 31, 1999, noon
The attribute definition is as follows:
NAME pvpConditionTime
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
5.5.2. The Attribute pvpConditionMonthOfYearMask
The purpose of this attribute is to refine the definition of the
valid time period that is defined by the pvpConditionTime attribute
by explicitly specifying which months the policy is valid for. These
attributes work together, with the pvpConditionTime used to specify
the overall time period that the policy is valid for, and the
pvpConditionMonthOfYearMask 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 pvpConditionMonthOfYearMask
DESCRIPTION A mask identifying the months of the year in which
a policy rule is valid.
SYNTAX Printable String
OID <to be assigned>
EQUALITY caseIgnoreMatch
SINGLE-VALUED
FORMAT A string of 12 ASCII '0's and '1's.
5.5.3. The Attribute pvpConditionDayOfMonthMask
The purpose of this attribute is to refine the definition of the
valid time period that is defined by the pvpConditionTime attribute
by explicitly specifying which days of the month the policy is valid
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for. These attributes work together, with the pvpConditionTime used
to specify the overall time period that the policy is valid for, and
the pvpConditionDayOfMonthMask 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 pvpConditionDayOfMonthMask
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.
5.5.4. The Attribute pvpConditionDayOfWeekMask
The purpose of this attribute is to refine the definition of the
valid time period that is defined by the pvpConditionTime attribute
by explicitly specifying which days of the week the policy is valid
for. These attributes work together, with the pvpConditionTime used
to specify the overall time period that the policy is valid for, and
the pvpConditionDayOfWeekMask 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:
NAME pvpConditionDayOfWeekMask
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.
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5.5.5. The Attribute pvpConditionTimeOfDayMask
The purpose of this attribute is to refine the definition of the
valid time period that is defined by the pvpConditionTime attribute
by explicitly specifying a range of times in a day the policy is
valid for. These attributes work together, with the pvpConditionTime
used to specify the overall time period that the policy is valid for,
and the pvpConditionTimeOfDayMask 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 8 AM until
9 PM, while "210000:080000" identifies the range from 9 PM until 8 AM
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 policyValidityMonthMask, policyValidityDayOfMonthMask, and/or
policyValidityDayOfWeekMask, 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 9 PM until
8 AM, and the day of week mask selects Monday and Tuesday, then the
policy is active during the following three intervals:
From midnight Sunday until 8 AM Monday; From 9 PM Monday until 8
AM
Tuesday; From 9 PM Tuesday until 11:59:59 Tuesday.
The attribute definition is as follows:
NAME pvpConditionTimeOfDayMask
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>]
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5.5.6. The Attribute pvpConditionTimeZone
This attribute is used to explicitly define a time zone for use by
the pvpConditionTime and the various Mask attributes. If this
attribute is NULL, then local time 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 = plus:
hh hours from UTC (00..13)
mm minutes from UTC (00..59)
The attribute definition is as follows:
NAME pvpConditionTimeZone
DESCRIPTION The definition of the time zone for use by the
PolicyValidityCOndition.
SYNTAX PrintableString
OID <to be assigned>
EQUALITY caseIgnoreMatch
SINGLE-VALUED
FORMAT either 'Z' (UTC) or {'+' | '-'}'hhmm'
5.6. 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 Framework, all that matters about an individual
policyCondition is that it evaluate 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 policyCondition may also be introduced, but this
would have to be done in a suclass of policyCondition.
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+---------------------------------------------------------------+
| Policy Conditions in DNF |
| +-------------------------+ +-----------------------+ |
| | AND list | | AND list | |
| | +-------------------+ | | +-----------------+ | |
| | | policyCondition | | | | policyCondition | | |
| | +-------------------+ | | +-----------------+ | |
| | +-------------------+ | | +-----------------+ | |
| | | policyCondition | | ... | | policyCondition | | |
| | +-------------------+ | ORed | +-----------------+ | |
| | ... | | ... | |
| | ANDed | | ANDed | |
| | +-------------------+ | | +-----------------+ | |
| | | policyCondition | | | | policyCondition | | |
| | +-------------------+ | | +-----------------+ | |
| +-------------------------+ +-----------------------+ |
+---------------------------------------------------------------+
Figure 4. 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 5. Overview of Policy Conditions in CNF
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
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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 structural
AUXILIARY CLASSES none
POSSIBLE SUPERIORS policyRule
OID <to be assigned>
MUST cn PolicyConditionName
MAY
5.6.1. The Attribute cn
This is the exact same definition as in Section 5.2.1. It is included
in this class for the reasons enumerated there.
5.6.2. 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
5.7. 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 policyConstraintData
and policyConstraintEncoding 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 vendorPolicyCondition
DESCRIPTION A class that defines a registered means to
describe a policy condition.
DERIVED FROM policyCondition
TYPE structural
AUXILIARY CLASSES none
POSSIBLE SUPERIORS policyRule
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OID <to be assigned>
MUST vendorPolicyConditionConstraint
vendorPolicyConditionEncoding
MAY
5.7.1. The Attribute vendorPolicyConditionConstraint
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 vendorPolicyConditionEncoding. Since
vendorPolicyConditionEncoding is single-valued, all the values of
vendorPolicyConditionData share the same format and semantics.
A policy decision point can readily determine whether it supports the
values stored in an instance of vendorPolicyConditionData by checking
the OID value from vendorPolicyConditionEncoding 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 vendorPolicyConditionConstraint
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
vendorPolicyConditionEncoding.
SYNTAX OctetString
OID <to be assigned>
EQUALITY octetStringMatch
MULTI-VALUED
5.7.2. The Attribute vendorPolicyConditionEncoding
This attribute identifies the encoding and semantics of the values of
vendorPolicyConditionConstraint in this instance. The value of this
attribute is a single OID.
The attribute definition is as follows:
NAME vendorPolicyConditionEncoding
DESCRIPTION An OID identifying the format and semantics for
this instance's vendorPolicyConditionConstraint
attribute.
SYNTAX OID
OID <to be assigned>
EQUALITY objectIdentifierMatch
SINGLE-VALUED
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5.8. 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 structural
AUXILIARY CLASSES none
POSSIBLE SUPERIORS policyRule
OID <to be assigned>
MUST cn PolicyActionName
MAY
5.8.1. The Attribute cn
This is the exact same definition as in Section 5.2.1. It is included
in this class for the reasons enumerated there.
5.8.2. The Attribute policyActionName
This attribute provides a user-friendly name for a policy action.
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
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5.9. 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 structural
AUXILIARY CLASSES none
POSSIBLE SUPERIORS policyRule
OID <to be assigned>
MUST vendorPolicyActionData vendorPolicyActionEncoding
MAY
5.9.1. 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
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>
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EQUALITY octetStringMatch
MULTI-VALUED
5.9.2. 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. Extending the Core Schema
There are three fundamental ways to extend the core schema. These are
detailed in sections 6.1 through 6.3 below. A guideline for using the
policyValidityPeriod class is discussed in Section 6.4. Each of
these methods may be used separately or in conjunction with other
methods.
6.1. Subclassing policyCondition and policyAction
The simplest way of extending the core schema is to use the first
four classes as they are, and simply subclass policyCondition and
policyAction. An instance of policyRule ties everything together,
with its very simple, invariant semantics:
If the policyRule is active, then evaluate, possibly in a
specified order, all conditions pointed to by
policyConditionList. If all conditions evaluate to TRUE, then
perform, possibly in a specified order, all actions pointed to by
policyActionList.
With this approach a new schema specifies the conditions it needs in
subclasses of policyCondition (or, better still, reuses conditions
that have already been specified in subclasses of policyCondition),
and it specifies (or reuses) the actions it needs in subclasses of
policyAction.
PolicyRules are used to aggregate policy conditions and actions, and
policyGroups are used to aggregate policyRules. Of course, the
policyRuleContainmentAuxClass and policyValidityPeriodCondition
classes can still be used as previously described. Note that the
subclassing of policyCondition and policyAction can also be used in
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combination with the other methods (discussed below) to extend the
schema.
6.2. Subclassing policyRule
There are two possible ways to subclass policyRule, as described
below.
6.2.1. Refining the semantics of policyRule
This approach refines the structural and possibly behavioral
semantics of what it means to be a policy rule. For example,
additional attributes and relationships could be defined in a
subclass of policyRule. These attributes and relationships could
provide extra meaning for how to interpret the set of conditions and
actions that a policyRule aggregates.
This method can be used in a stand-alone fashion by keeping the
semantics of policyCondition and policyAction as specified and adding
semantics to policyRule. These policyRule semantics can explicitly
specify policyConditions and/or policyActions, or dictate how
policyConditions and policyActions are used and interpreted.
Finally, these methods can be used with the other methods discussed
in this subsection to extend the schema.
6.2.2. Optimizing the computation of a policyRule
All preceding mechanisms for extending the core schema will work in
all cases, but they come at a price: in order to fully understand a
policy rule, a client must retrieve at least three objects: a policy
rule, at least one policy condition, and at least one policy action.
A future version of this specification may define how to optimize the
evaluation of a policy rule so as to reduce the number of classes
that must be instantiated to define a policy.
6.3. Using the Vendor Policy Encoding Attributes
As discussed in 5.7, "The Class vendorPolicyCondition", the
attributes vendorPolicyConditionConstraint and
vendorPolicyConditionEncoding are included in the
vendorPolicyCondition to provide an escape mechanism for representing
"exceptional" policy conditions. The attributes
vendorPolicyActionData and vendorPolicyActionEncoding of the
vendorPolicyAction class play the same role with respect to actions.
This enables interoperability between different vendors.
For example, imagine a network comprised of access devices from
vendor A, edge and core devices from vendor B, and a policy server
from vendor C. It is desirable for the 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
(e.g., different mechanisms, different ways for controlling those
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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.
6.4. Using Time Validity Periods
Time validity periods are defined as a subclass of policyCondition,
called policyValidityPeriodCondition. This is to allow their
inclusion in the AND/OR condition definitions for a policyRule. Care
should be taken to not subclass policyValidityPeriodCondition to add
domain-specific condition properties. For example, it would be
incorrect to add IPSec- or QoS-specific condition properties to the
policyValidityPeriodCondition 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.
7. 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.
8. 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
such proprietary rights by implementers or users of this
specification can be obtained from the IETF Secretariat.
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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.
9. 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 Bob Moore, Raju Rajan, Sanjay Kamat, Andrea Westerinen,
Lee Rafalow, Raj Yavatkar, Glenn Waters, David Black, Michael
Richardson, Mark Stevens, and David Jones for their helpful comments.
10. 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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11. 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
12. 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
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.
13. Appendix A - Guidelines for Construction of DNs
To Be Provided
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