Policy Framework Working Group J. Strassner
Internet-draft Cisco Systems
Category: Standards Track E. Ellesson
B. Moore
IBM Corporation
June 1999
Policy Framework LDAP Core Schema
draft-ietf-policy-core-schema-04.txt
June 25, 1999 13:39
Status of this Memo
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Task
Force (IETF), its areas, and its working groups. Note that other
groups may also distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
Copyright Notice
Copyright (C) The Internet Society (1999). All Rights Reserved.
Abstract
This document takes as its starting point the object-oriented
information model for representing policy information currently under
joint development in the Service Level Agreements (SLA) Policy working
group of the Distributed Management Task Force (DMTF) and in the
IETF's Policy Framework working group. The IETF document defining
this information model is the "Policy Framework Core Information
Model" [10]. This 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 information model classes to a
directory that uses LDAPv3 as its access protocol. When mapping to an
Strassner, et. al. Expires: December 25, 1999 [Page 1]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
LDAP schema, the structural classes can be mapped more or less
directly. The relationship hierarchy, however, must be mapped to a
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
information 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 information
model's 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.
Strassner, et. al. Expires: December 25, 1999 [Page 2]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
Table of Contents
1. Introduction......................................................3
2. The Policy Core Information Model.................................4
3. Inheritance Hierarchy for the LDAP Core Policy Schema.............5
4. General Discussion of Mapping the Information Model to LDAP.......5
4.1. Summary of Class and Relationship Mappings...................6
4.2. Naming Attributes in the Core Schema.........................7
4.3. Flexibility Gained through Auxiliary Classes.................8
4.4. Location and Retrieval of Policy Objects in the Directory....9
4.4.1. Aliases...................................................12
5. Class Definitions................................................13
5.1. The Abstract Class "policy".................................13
5.2. The Class policyGroup.......................................14
5.3. The Class policyRule........................................14
5.4. The Class policyCondition...................................19
5.5. The Class policyTimePeriodCondition.........................19
5.6. The Class vendorPolicyCondition.............................21
5.7. The Class policyAction......................................22
5.8. The Class vendorPolicyAction................................22
5.9. The Class policyInstance....................................23
5.10. The Auxiliary Class policyElement..........................23
5.11. The Auxiliary Class policySubtreesPtrAuxClass..............24
5.11.1. The Attribute policySubtreesAuxContainedSet..............25
5.12. The Auxiliary Class policyGroupContainmentAuxClass.........25
5.12.1. The Attribute policyGroupsAuxContainedSet................26
5.13. The Auxiliary Class policyRuleContainmentAuxClass..........26
5.13.1. The Attribute policyRulesAuxContainedSet.................27
6. Extending the Core Schema........................................27
6.1. Subclassing policyCondition and policyAction................27
6.2. Using the Vendor Policy Encoding Attributes.................28
6.3. Using Time Validity Periods.................................28
7. Security Considerations..........................................29
8. Intellectual Property............................................31
9. Acknowledgments..................................................31
10. References......................................................31
11. Authors' Addresses..............................................32
12. Full Copyright Statement........................................32
1. Introduction
This document takes as its starting point the object-oriented
information model for representing policy information currently under
joint development in the Service Level Agreements working group of the
Distributed Management Task Force (DMTF) and in the IETF's Policy
Framework working group. The IETF document defining this information
model is the "Policy Framework Core Information Model" [10]. This
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
Strassner, et. al. Expires: December 25, 1999 [Page 3]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
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 information model classes to a
directory that uses LDAPv3 as its access protocol. Two types of
mappings are involved:
o For the structural classes in the information model, the mapping is
basically one-for-one: information model classes map to LDAP
classes, information model properties map to LDAP attributes.
o For the relationship classes in the information model, different
mappings are possible. In this document the information model's
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 information model defined in reference [10] as the starting point
enables the schema and the relationship class hierarchy to be
extensible, such that other types of policy repositories, such as
relational databases, can also use this information.
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 Common Information Model (CIM) effort
in the Distributed 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. The Policy Core Information Model
This document contains an LDAP schema representing the Policy Core
Information Model, which is defined in the companion document "Policy
Framework Core Information Model" [10]. Other documents may
subsequently be produced, with mappings of this same Core Information
Model to other storage technologies. Since the detailed semantics of
Strassner, et. al. Expires: December 25, 1999 [Page 4]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
the Core Policy classes appear only in reference [10], that document
is a prerequisite for reading and understanding this document.
3. Inheritance Hierarchy for the LDAP Core Policy Schema
The following diagram illustrates the class hierarchy for the LDAP
Core Policy Schema classes:
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 1. LDAP Class Inheritance Hierarchy for the Core Policy
Schema
4. General Discussion of Mapping the Information Model to LDAP
The classes described in Section 5 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 some of the
relationships defined in the information model. 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
Strassner, et. al. Expires: December 25, 1999 [Page 5]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
directory. This section discusses some general topics related to the
mapping from the information model to LDAP.
4.1. Summary of Class and Relationship Mappings
Eight of the classes in the LDAP Core Policy Schema come directly from
corresponding classes in the information model. Note that names of
classes begin with an upper case character in the information model
(although for CIM in particular, case is not significant in class and
property names), but with a lower case character in LDAP.
+---------------------------+---------------------------+
| Information Model | LDAP Class |
+---------------------------+---------------------------+
+---------------------------+---------------------------+
| Policy | policy |
+---------------------------+---------------------------+
| PolicyGroup | policyGroup |
+---------------------------+---------------------------+
| PolicyRule | policyRule |
+---------------------------+---------------------------+
| PolicyCondition | policyCondition |
+---------------------------+---------------------------+
| PolicyAction | policyAction |
+---------------------------+---------------------------+
| VendorPolicyCondition | vendorPolicyCondition |
+---------------------------+---------------------------+
| VendorPolicyAction | vendorPolicyAction |
+---------------------------+---------------------------+
| PolicyTimePeriodCondition | policyTimePeriodCondition |
+---------------------------+---------------------------+
Figure 2. Mapping of Information Model Classes to LDAP
The relationships in the information model map to pointer attributes
in LDAP. Two of these attributes appear in auxiliary classes, which
allows each of them to represent several associations from the
information model.
Strassner, et. al. Expires: December 25, 1999 [Page 6]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
+--------------------------------+---------------------------------+
| Information Model 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 3. Mapping of Information Model Relationships to LDAP
Of the remaining classes in the LDAP Core Schema, two (policyElement,
and policySubtreesPtrAuxClass) are 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 4.4
below.
The final class in the LDAP Core Schema, policyInstance, plays the
role of a structural class to which the auxiliary classes
policyCondition and policyAction (and their subclasses) may be
attached. This topic is discussed in Section 4.3 below.
4.2. 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
Strassner, et. al. Expires: December 25, 1999 [Page 7]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
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.
Each of the Core Schema classes thus has two attributes suitable for
naming: cn and its own class-specific attribute. Either of these
attributes MAY be used for naming an instance of a Core Schema class.
Consequently, implementations MUST be able to accommodate instances
named in either of these ways.
4.3. 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:
Strassner, et. al. Expires: December 25, 1999 [Page 8]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
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 4.4 below
describes a technique for minimizing this overhead, by making the
following of these pointers a local operation for a PDP.
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.
4.4. 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.
Strassner, et. al. Expires: December 25, 1999 [Page 9]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
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 SHOULD be
able to take advantage of any tools that the policy administrator is
able to build into the DIT, but it MUST be 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
it needs, and only those objects, using as few LDAP calls as possible.
Figure 4 illustrates how these goals can be accomplished.
+-----+
---------------->| A |
DN pointer to | | DN pointers to subtrees +---+
starting object +-----+ +------------------------->| C |
| o--+----+ +---+ +---+
| o--+------------->| B | / \
+-----+ +---+ / \
/ \ / \ / ... \
/ \ / \
/ \ / ... \
Figure 4. 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
Strassner, et. al. Expires: December 25, 1999 [Page 10]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
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.
If 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".
To optimize what is expected to be a typical case, the initial request
from the client includes not only the object to which its "seed" DN
pointer points, but also the subtree contained under this object. The
filter for searching this subtree is whatever the client is going to
use later to search the other subtrees: "object class = policy",
presence of the keyword "POLICY", or presence of a more specific
policyKeyword.
Returning to the example in Figure 4, 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
A to get the pointers to B and C, as well as the policy-related
objects it needs from the subtree under A, 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
should 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 4, 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 SHOULD
understand this class, SHOULD be capable of retrieving and processing
the entries in the subtrees it points to, and SHOULD 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
Strassner, et. al. Expires: December 25, 1999 [Page 11]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
entries from the directory in order to perform validation and conflict
detection SHOULD also understand and be capable of using the
policySubtreesPtrAuxClass. All of these requirements are "SHOULD"s
rather than "MUST"s because an LDAP client that doesn't implement them
can still access and retrieve the directory entries it needs . The
process of doing so will just be less efficient than it would have
been if the client had implemented these optimizations.
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.
4.4.1. Aliases
Additional flexibility in DIT structure is available to the policy
administrator via LDAP aliasing. Figure 5 illustrates this
flexibility.
+-----+
---------------->| A |
DN pointer to | | DN pointers to subtrees +---+
starting object +-----+ +------------------------->| C |
| o--+----+ +---+ +---+
| o--+------------->| B | / \
+-----+ +---+ / \
/ \ / \ / ... \
/ \ / \
/ \ / \
+---+ / +------+ \
| X |<***************************|aliasX|
+---+ +------+
Figure 5. 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 5.
Strassner, et. al. Expires: December 25, 1999 [Page 12]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
5. Class Definitions
The semantics for the LDAP classes mapped directly from the
information model are detailed in reference [10]. Consequently, all
that this document presents for these classes is a bare specification
of the LDAP classes and attributes. More details are provided for the
attributes listed above in Figure 3, which realize in LDAP the
relationships defined in the information model. Finally, the classes
that exist only in the LDAP Core Schema are documented fully in this
document.
5.1. The Abstract Class "policy"
The abstract class policy is a direct mapping of the abstract class
Policy from the Core Information Model. The property
CreationClassName maps to the LDAP attribute objectClass, which is
inherited from "top". The remaining properties in Policy map directly
to attributes in the class policy.
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
OID <to be assigned>
MAY cn caption description policyKeywords
The attributes are defined as:
NAME commonName (cn)
DESCRIPTION A user-friendly name of a policy-related object.
SYNTAX DirectoryString
OID 2.4.5.3
EQUALITY caseIgnoreMatch
MULTI-VALUED
NAME caption
DESCRIPTION A one-line description of this policy-related
object.
SYNTAX IA5String
OID <to be assigned>
EQUALITY caseExactIA5Match
SINGLE-VALUED
Strassner, et. al. Expires: December 25, 1999 [Page 13]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
NAME description
DESCRIPTION A long description of this policy-related object.
SYNTAX IA5String
OID <to be assigned>
EQUALITY caseExactIA5Match
SINGLE-VALUED
NAME policyKeywords
DESCRIPTION A set of keywords to assist directory clients in
locating the policy objects applicable to them.
Standard keyword values are listed in the Policy
Core Information Model document.
SYNTAX IA5String
OID <to be assigned>
EQUALITY caseExactIA5Match
MULTI-VALUED
5.2. The Class policyGroup
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
OID <to be assigned>
MUST policyGroupName
The one attribute of PolicyGroup is defined as:
NAME policyGroupName
DESCRIPTION The user-friendly name of this policy group.
SYNTAX IA5String
OID <to be assigned>
EQUALITY caseExactIA5Match
SINGLE-VALUED
5.3. The Class policyRule
This class represents the "If Condition then Action" semantics
associated with a policy. The conditions and actions associated with
Strassner, et. al. Expires: December 25, 1999 [Page 14]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
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.
Of the ten attributes in the policyRule class, seven are mapped
directly from corresponding properties in the information model. The
remaining three attributes realize three of the aggregations in the
information model. Since the PolicyRuleValidityPeriod aggregation has
no "extra" properties (besides those that tie the aggregation to the
aggregating and aggregated objects), the attribute
policyRuleValidityPeriodList is simply a multi-valued DN pointer.
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 ContainedPolicyCondition and ContainedPolicyAction aggregations,
however, have additional properties: ContainedPolicyAction has an
integer to sequence the actions, and ContainedPolicyCondition has an
integer to group the conditions, and a boolean to specify whether a
condition is to be negated. To represent these additional properties,
the attributes policyRuleConditionList and policyRuleActionList are
defined as "structured DN pointers." A structured DN pointer is, from
the point of view of an LDAP directory implementation, a
DirectoryString. These DirectoryStrings, however, have embedded in
them both a DN pointer and elements to represent the additional
properties from the aggregations being mapped. Figures 6 and 7
illustrate the mappings:
Contained Condition ------------------+
Condition Negated --------------+ |
Group Number ---------+ | |
| | |
V V V
<integer>:<+|->:<DN> policyRuleConditionList
Figure 6. Mapping of ContainedPolicyCondition Properties
There is one subtlety here. In the element "<+|->", the '+' indicates
that the condition is not negated, and the '-' indicates that it is
negated. In the information model, however, this information is
represented by the boolean-valued property ConditionNegated in the
ContainedPolicyCondition aggregation. The mapping between the
information model and the LDAP Core Schema is thus:
o If ConditionNegated = TRUE (i.e., it's true that the condition is
negated), use '-'.
Strassner, et. al. Expires: December 25, 1999 [Page 15]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
o If ConditionNegated = FALSE (i.e., it's false that the condition is
negated), use '+'.
For example, the Directory String "1:+:DN-C" points to the condition
named by DN-C, places it in Group 1, and indicates that it is not
negated.
Contained Action ---------------+
Action Order ---------+ |
| |
V V
<integer>:<DN> policyRuleActionList
Figure 7. Mapping of ContainedPolicyAction Properties
For example, the DirectoryString "2:DN-A" points to the action named
by DN-A, and indicates that it is to be performed second.
Since these structured DN pointers appear as DirectoryStrings to a
directory implementation, the implementation does not apply DN-
oriented operations to them. In particular, if a condition or action
pointed to by a DN pointer embedded in one of these strings has its
name changed, the ModifyDN operation will NOT update the embedded DN
pointer.
The class definition of policyRule 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 policyRuleName
MAY policyRuleEnabled policyRuleConditionListType
policyRuleConditionList policyRuleActionList
policyRuleValidityPeriodList policyRuleUsage
policyRulePriority policyRuleMandatory
policyRuleSequencedActions
The attributes of policyRule are as follows:
NAME policyRuleName
DESCRIPTION The user-friendly name of this policy rule.
SYNTAX IA5String
OID <to be assigned>
EQUALITY caseExactIA5Match
SINGLE-VALUED
Strassner, et. al. Expires: December 25, 1999 [Page 16]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
NAME policyRuleEnabled
DESCRIPTION An enumeration indicating whether a policy rule is
administratively enabled, administratively
disabled, or enabled for debug mode. The defined
values for this attribute are enabled(1),
disabled(2), and enabledForDebug(3).
SYNTAX INTEGER
OID <to be assigned>
EQUALITY integerMatch
SINGLE-VALUED
DEFAULT VALUE enabled(1)
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 DNF(1)
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>
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
NAME policyRuleValidityPeriodList
Strassner, et. al. Expires: December 25, 1999 [Page 17]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
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
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
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
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
NAME policyRuleSequencedActions
DESCRIPTION An enumeration indicating how to interpret the
action ordering indicated via the
policyRuleActionList attribute. The defined values
for this attribute are mandatory(1),
recommended(2), and dontCare(3).
SYNTAX INTEGER
OID <to be assigned>
EQUALITY integerMatch
SINGLE-VALUED
DEFAULT VALUE dontCare(3)
Strassner, et. al. Expires: December 25, 1999 [Page 18]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
5.4. 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.
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
The one 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
5.5. The Class policyTimePeriodCondition
This class provides a means of representing the time periods during
which a policy rule is valid, i.e., active. The class definition is
as follows. Note that instances of this class are named with the
attributes cn and policyConditionName that they inherit, respectively,
from policy and 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
Strassner, et. al. Expires: December 25, 1999 [Page 19]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
ptpConditionDayOfWeekMask ptpConditionTimeOfDayMask
ptpConditionTimeZone
The attributes of policyTimePeriodCondition are defined 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]
NAME ptpConditionMonthOfYearMask
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.
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.
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.
NAME ptpConditionTimeOfDayMask
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
Strassner, et. al. Expires: December 25, 1999 [Page 20]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
SINGLE-VALUED
FORMAT hhmmss:hhmmss
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>
5.6. The Class vendorPolicyCondition
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
The attribute definitions for vendorPolicyCondition are 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
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
Strassner, et. al. Expires: December 25, 1999 [Page 21]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
5.7. 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.
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
The one 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
5.8. The Class vendorPolicyAction
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
The attribute definitions for vendorPolicyAction are 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.
Strassner, et. al. Expires: December 25, 1999 [Page 22]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
SYNTAX OctetString
OID <to be assigned>
EQUALITY octetStringMatch
MULTI-VALUED
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
5.9. 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
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>
5.10. 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
Strassner, et. al. Expires: December 25, 1999 [Page 23]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
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>
5.11. 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
allows a client to locate and retrieve the policy information relevant
to it.
These entries may be placed in the DIT such that a well-known DN can
be used by placing the structural entry (e.g. container) with the
policySubtreesPtrAuxClass attached thereto in the root of the
directory suffix. In this case, the subtree entry point can contain
and/or point to all related policy entries for any well-known policy
disciplines. Similarly, the subtree entry point may be placed in the
DIT such that the PDPs starting point is a subtree with policy-related
entries that are dependent on a hierarchically-related set of subtrees
(e.g., region, division, corporate). In this latter case, DNs may be
provided to the PDPs via SNMP or other techniques.
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 4.4.
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 will often be included in the DIT subtree
beneath an object to which this auxiliary class is attached, a client
SHOULD request the policy-related objects from the subtree under the
Strassner, et. al. Expires: December 25, 1999 [Page 24]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
object with these pointers at the same time that it requests the
pointers themselves. Since policySubtreesPtrAuxClass is a subclass of
the abstract class "policy", this can be accomplished with a single
search operation with scope set to subtree and a filter set to select
policy-related objects.
Since clients are expected to behave in this way, the policy
administrator SHOULD make sure that this subtree does not contain so
many objects unrelated to policy that an initial search done in this
way results in a performance problem. For example,
policySubtreesPtrAuxClass SHOULD NOT be attached to the partition root
for a large directory partition containing a relatively few policy-
related objects along with a large number of objects unrelated to
policy. A better approach would be to introduce a container object
immediately below the partition root, attach policySubtreesPtrAuxClass
to this container object, and then place the policy-related objects in
the subtree under it.
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
5.11.1. 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
5.12. 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
Strassner, et. al. Expires: December 25, 1999 [Page 25]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
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
5.12.1. 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
5.13. 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
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
Strassner, et. al. Expires: December 25, 1999 [Page 26]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
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
5.13.1. 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
6. 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.
6.1. Subclassing policyCondition and policyAction
In Section 4.3 above, there is a discussion of how, by representing
policy conditions and policy actions as auxiliary classes in a schema,
Strassner, et. al. Expires: December 25, 1999 [Page 27]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
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.
6.2. Using the Vendor Policy Encoding Attributes
As discussed Section 5.6 "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
(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.
6.3. 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
Strassner, et. al. Expires: December 25, 1999 [Page 28]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
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.
7. Security Considerations
o General: See reference [10].
o Users: See reference [10].
o Administrators of Schema: In general, most LDAP-accessible
directories do not permit old or out-of-date schemas, or schema
elements to be deleted. Instead, they are rendered inactive. This
makes it that much more important to get it right the first time on
an operational system, in order to avoid complex inactive schema
artifacts from lying about in the operational directory. The good
news is that it is expected that large network operators will
change schema design infrequently, and, when they do, the schema
creation changes will be tested on an off-line copy of the
directory before the operational directory is updated. Typically,
a small group of directory schema administrators will be authorized
to make these changes in a service provider or enterprise
environment. The ability to maintain audit trails is also required
here.
o Administrators of Schema Content (Directory Entries): This group
requires authorization to load values (entries) into a policy
repository directory schema, i.e. read/write access. An audit
trail capability is also required here.
o Applications and PDPs: These entities must be authorized for read-
only access to the policy repository directory, so that they may
acquire policy for the purposes of passing it to their respective
enforcement entities.
o Security Disciplines:
o Audit Trail (Non-repudiation): In general, standardizing
mechanisms for non-repudiation is outside the scope of the IETF;
however, we can certainly document the need for this function in
systems which maintain and distribute policy. The dependency for
support of this function is on the implementers of these systems,
and not on any specific standards for implementation. The
requirement for a policy system is that a minimum level of
auditing via an auditing facility must be provided. Logging
should be enabled. This working group will not specify what this
minimal auditing function consists of.
Strassner, et. al. Expires: December 25, 1999 [Page 29]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
o Access Control/Authorization: Access Control List (ACL)
functionality must be provided. Standards for directories which
use LDAPv3 as an access mechanism are still being worked on in
the LDAPext working group, as of this writing. The two
administrative sets of users documented above will form the basis
for two administrative use cases which require support.
o Authentication: In the LDAP-accessible directory case, both TLS
and Kerboros are acceptable for authentication. Existing LDAP
implementations provide these functions within the context of the
BIND request, which is adequate. We advise against using weaker
mechanisms, such as clear text and HTTP Digest. Mutual
authentication is recommended. The LDAPv3 protocol supports
this, but implementations vary in the functionality that they
support.
o Integrity/Privacy: In the LDAP-accessible directory case, TLS
is acceptable for encryption and data integrity on the wire. If
physical or virtual access to the policy repository is in
question, it may also be necessary to encrypt the policy data as
it is stored on the file system; however, specification of
mechanisms for this purpose are outside the scope of this
working group. In any case, we recommend that the physical
server be located in a physically secure environment.
In the case of PDP-to-PEP communications, the use of IPSEC is
recommended for providing confidentiality, data origin
authentication, integrity and replay prevention. See [RAPFRAME]
reference.
o Denial of Service: We recommend the use of multiple policy
repository directories, such that a denial of service attack on any
one directory server will not make all policy data inaccessible to
legitimate users. However, this still leaves a denial of service
attack exposure. Our belief is that the use of a policy schema, in
a centrally administered but physically distributed policy
directory, does not increase the risk of denial of service attacks;
however, such attacks are still possible. If executed
successfully, such an attack could prevent PDPÆs from accessing a
policy repository, and thus prevent them from acquiring new policy.
In such a case, the
PDPÆs, and associated PEPÆs would continue operating under the
policies in force before the denial of service attack was launched.
Note that exposure of policy systems to denial of service attacks
is not any greater than the exposure of DNS with DNSSEC in place.
o Other LDAP-accessible Directory Schema Considerations:
o Replication: Replication among directory copies across servers
should also be protected. Replicating over connections secured
by SSL or IPSEC is recommended.
Strassner, et. al. Expires: December 25, 1999 [Page 30]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
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.
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
Distributed 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.
10. References
[1] J. Strassner and E. Ellesson, "Terminology for describing network
policy and services", draft-strassner-policy-terms-02.txt, June
1999.
[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
Strassner, et. al. Expires: December 25, 1999 [Page 31]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
[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
[9] DMTF web site, http://www.dmtf.org.
[10] Moore B., and E. Ellesson, J. Strassner, "Policy Framework Core
Information Model", draft-ietf-policy-core-info-model-00.txt, June
1999.
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
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
12. Full Copyright Statement
Copyright (C) The Internet Society (1999). All Rights Reserved.
Strassner, et. al. Expires: December 25, 1999 [Page 32]
Internet Draft draft-ietf-policy-core-schema-04.txt June 1999
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.
Strassner, et. al. Expires: December 25, 1999 [Page 33]