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Versions: 00 01 RFC 2120

IDS Working Group                            David Chadwick
Internet-Draft                          University of Salford
DANTE IN PRINT 18                            January 21 1996
draft-ietf-ids-root-naming-00.txt       Expires: July 21 1996


              Managing the X.500 Root Naming Context


Status of this Memo

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Abstract

The X.500 Standard [X.500 93] has the concept of first level
DSAs, whose administrators must collectively manage the root
naming context through bi-lateral agreements or other private
means which are outside the scope of the Standard.

The Paradise-NameFLOW X.500 service has an established
procedure for managing the root naming context, which
currently uses Quipu proprietary replication mechanisms and a
root DSA. The benefits that derive from this are twofold:

     - firstly it is much easier to co-ordinate the management
     of the root context information, when there is a central
     point of administration,

     - secondly the performance of one-level Search operations
     is greatly improved because the Quipu distribution and
     replication mechanism does not have a restriction that
     exists in the 1988 and 1993 Standard.

The Paradise-NameFLOW project is moving towards 1993 Standard
replication protocols and wants to standardise the protocol
and procedure for managing the root naming context which will
be based on 1993 Standard protocols. Such a protocol and
procedure will be useful to private X.500 domains as well as
to the Internet X.500 public domain. It is imperative that
overall system performance is not degraded by this transition.

This document describes the use of 1993 Standard protocols for
managing the root context. Whilst the ASN.1 is compatible with
that of the Standard, the actual settings of the parameters
are supplementary to that of the Standard.


Table of Contents

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . .3

2 Migration Plan . . . . . . . . . . . . . . . . . . . . . . . .3

3 Technical Solution . . . . . . . . . . . . . . . . . . . . . .4

4 Interim Solution . . . . . . . . . . . . . . . . . . . . . . .7

5 Security Considerations. . . . . . . . . . . . . . . . . . . .8

6 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .8

References . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Author's Address . . . . . . . . . . . . . . . . . . . . . . . .9

Annex 1 Solution Text of Defect Reports submitted to ISO/ITU-T
     by the UK . . . . . . . . . . . . . . . . . . . . . . . . 10


1 Introduction

The Paradise-NameFLOW service has a proprietary way of
managing the set of first level DSAs and the root naming
context. There is a single root DSA (Giant Tortoise) which
holds all of the country entries, and the country entries are
then replicated to every country (first level) DSA by Quipu
replication [RFC 1276] from the root DSA. The root DSA is not
a feature of the X.500 Standard [X.500 93]. It was introduced
because of the non-standard nature of the original Quipu
knowledge model (also described in RFC 1276). However, it does
have significant advantages both in managing the root naming
context and in the performance of one-level Searches of the
root. Performance is increased because each country DSA holds
all the entry information of every country.

By comparison, the 1988 Standard root context which is
replicated to all the country DSAs, only holds knowledge
information and a boolean (to say if the entry is an alias or
not) for each country entry. This is sufficient to perform a
List operation, but not a one-level Search operation. When
access controls were added to the 1993 Standard, the root
context information was increased (erroneously as it happens -
this is the subject of defect report 140 - see Annex 1) to
hold the access controls for each country entry, but a note in
the Standard restricted its use to the List operation, in
order to remain compatible with the 1988 edition of the
Standard.


2 Migration Plan

The Paradise-NameFLOW service is now migrating to 1993
Standard [X.500 93] conforming products, and it is essential
to replace the Quipu replication protocol with the 1993
shadowing and operational binding protocols, but without
losing the performance improvement that has been gained for
one-level Searches.

It is still the intention of the Paradise-NameFLOW service to
have one master root DSA. This root DSA will not support user
Directory operations via the DAP or the DSP, but each country
(first level) DSA will be able to shadow the root context from
this root DSA, using the DISP. Each first level DSA then only
needs to have one bi-lateral agreement, between itself and the
root DSA. This agreement will ensure that the first level DSA
keeps the root DSA up to date with its country level
information, and in turn, that the root DSA keeps the first
level DSA up to date with the complete root naming context.
When a new first level DSA comes on line, it only needs to
establish a bi-lateral agreement with the root DSA, in order
to obtain the complete root context.

This is a much easier configuration to manage than simply a
set of first level DSAs without a root DSA, as suggested in
the Standard. In this case each first level DSA must have bi-lateral agreements with all of the other first level DSAs.
When a new first level DSA comes on line, it must establish
agreements with all the existing first level DSAs. As the
number of first level DSAs grows, the process becomes
unmanageable.

However, it is also important to increase the amount of
information that is held about every country entry, so that a
one-level Search operation can be performed in each first
level DSA, without it needing to chain or refer the operation
to all the other first level DSAs (as is currently the case
with a Standard conformant system.)


3 Technical Solution

3.1 The solution is three-fold. Firstly, create a root DSA,
and establish hierarchical operational bindings between it and
each master first level DSA (3.2). Secondly, the Standard is
enhanced to allow extra information to be carried to the root
DSA via the HOB, and for this information to be used for one-level Search operations (3.3). Thirdly, each master first
level DSA enters into a shadowing agreement with the root DSA,
to shadow the enlarged root context information. In this way
each first level DSA is then capable of independently
performing List and one-level Search operations, and name
resolving to all other first level DSAs (3.4).

(Note 1. It is strongly recommended that non-specific
subordinate references should not be allowed in the root
context for efficiency reasons. This is directed by the
European functional standard [ENV 41215] and the NADF standing
document [NADF 7]. It is also preferred by the International
Standardized Profile [ISP 10615-6].)

(Note 2. It is recognised that manufacturers are taking a
phased approach to implementing the features of the 1993
Standard, and are usually implementing the DISP prior to the
DOP. For this reason, section 4 details an interim solution
that relies entirely on the DISP for populating the root DSA.)

3.2 Each master first level DSA will have a hierarchical
operational binding with the root DSA of the domain. Each
master first level DSA will master one or more first level
entries. The hierarchical operational binding will keep the
appropriate subordinate reference(s) (of category shadow and
master) up to date, as well as the other entry information
that is needed for one-level Search operations (such as access
controls, and attributes used in filtering).

Whilst hierarchical agreements are standardised, this
particular novel use of a HOB is not specifically recognised
in the Standard. Although the ASN.1 will support it, there is
no supporting text in the Standard. The following text
supplements that in the Standard, and describes how a first
level DSA may have a hierarchical operational binding with the
root DSA of its domain.

"Clause 24 of ISO/IEC 9594-4:1993 shall also apply when a
first level DSA is a subordinate DSA, and the root DSA of the
domain is the superior DSA. The naming context held by the
superior (root) DSA is the root naming context (or root
context - the terms are synonymous) of the domain. The root
context consists of the root entry of the DIT (which is empty)
plus a complete set of subordinate DSEs, one for each first
level naming context in the domain. The subordinate DSEs will
contain, in addition to specific knowledge attribute values of
category master and shadow, sufficient attributes, including
access control information, to allow List and one-level Search
operations to be performed on them.

In clause 24.1.2, the DistinguishedName of the
immediateSuperior component of HierarchicalAgreement shall be
null."


3.3 The ASN.1 of hierarchical operational bindings already
allows any attributes to be passed from the subordinate DSA to
the superior DSA (SubordinateToSuperior parameter in clause
24.1.4.2 of X.518). However, a note in the Standard limits
this to those which are required to perform a List operation.
The UK submitted a ballot comment to the PDAM on Minor
Extensions to OSI Directory Service to support User
Requirements, to remove this restriction, so that the
attributes may also be used for a one-level Search operation.
This amendment has been accepted, and the restriction has been
removed in the current Draft Amendment to the 1996 version of
the Standard [DAM User].

1993 implementations of X.500 conforming to this RFC, shall
also remove this restriction.


3.4 Each master first level DSA will enter into a shadowing
agreement with the root DSA, for the purpose of shadowing the
root naming context.

The 1993 edition of the Standard explicitly recognises that
there can be master and shadow first level DSAs (X.501 Section
18.5). (The 1988 edition of the standard does not explicitly
recognise this, since it does not recognise shadowing.) A
shadow first level DSA holds a copy of the root context,
provided by a master first level DSA. In addition it holds
shadow copies of the (one or more) country entries that the
master first level DSA holds. There is currently an
outstanding defect report [UK 142] on the 1993 Standard to
clarify how a shadowing agreement is established between first
level DSAs. Once this has been ratified, the only additional
text needed in order to establish a shadowing agreement
between the root DSA and a master first level DSA is as
follows:

"When clause 9.2 of ISO/IEC 9594-9:1993 is applied to the
shadowing of the root context by a first level DSA from the
root DSA of a domain, then UnitOfReplication shall be set as
follows:

contextPrefix of AreaSpecification shall be null,

replicationArea of AreaSpecification shall be set to
                    SEQUENCE {
     specificExclusions  [1]  SET OF {
                    chopBefore     [0]  FirstLevelEntry},
     maximum             [3]  1 }

where FirstLevelEntry is the RDN of a first level entry (e.g.
country, locality or international organisation) held by the
master first level DSA. specificExclusions shall contain one
FirstLevelEntry for each first level entry mastered by this
DSA,

attributes of UnitofReplication shall be an empty SET OF
SEQUENCE,

knowledge of UnitofReplication shall be set to both (shadow
and master).

In other words, the information that will be replicated will
be an empty root entry plus all the attributes of the complete
set of subordinate DSEs of the root, excluding the DSEs that
the first level DSA already masters."

Note that the maximum component of replicationArea, although
not strictly necessary, is there for pragmatic reasons, for
example, where a community of users wish to use the root DSA
to hold some country specific entries.


4 Interim Solution

4.1 The interim solution may be of use to systems which do not
yet support the DOP for managing hierarchical operational
bindings. The interim solution comprises of two replacement
steps for HOB establishment between the root DSA and master
first level DSAs. Step one (4.2) allows the root DSA to shadow
first level entries from a master first level DSA. Step two
(4.3) requires either the root DSA administrator or the root
DSA implementation to massage the shadow first level entries
so that they appear to have been created by a HOB. Managing
the root context then continues as in 3.4 above.

4.2 The hierarchical operational binding between the root DSA
and a master first level DSA can be replaced by a set of
"spot" shadowing agreements, in which the first level DSA acts
as the supplier, and the root DSA as the consumer. Each "spot"
shadowing agreement replicates a first level entry which is
mastered by the first level DSA. The UnitOfReplication shall
be set as follows:

contextPrefix of AreaSpecification shall be FirstLevelEntry,

replicationArea of AreaSpecification shall be set to
                    SEQUENCE {
     specificExclusions  [1]  SET OF {
                    chopAfter [1]  {null} } }

where FirstLevelEntry is the Distinguished Name of a first
level entry (e.g. country, locality or international
organisation) held by the master first level DSA.

attributes of UnitofReplication shall be an empty SET OF
SEQUENCE,

knowledge of UnitofReplication shall be absent.


4.3 The root DSA administrator, or the root DSA implementation
(suitably tailored) must then administratively update each
shadowed first level entry, so that they appear to have been
created by a HOB, i.e. it is necessary to add a subordinate
reference to each one of them. The subordinate reference will
point to the respective master first level DSA, and will
comprise of a specific knowledge attribute, and the DSE bit of
type subr being set. The contents of the specific knowledge
attribute can be created from the contents of the supplier
knowledge attribute already present in the first level entry
and created by the "spot" shadowing agreement.


5 Security Considerations

Security considerations are not discussed in this memo.


6 Acknowledgements

The author would like to thank DANTE, without whose funding
this work would not have been possible.

The author would also like to thank Nexor, who reviewed the
document in detail and provided valuable comments, and who
first suggested the Interim Solution as a stop-gap measure
until the DOP is widely implemented.


References

[RFC 1276] Kille, S., "Replication and Distributed Operations
extensions to provide an Internet Directory using X.500", UCL,
November 1991.

[X.500 93] X.500 | 9594.Part 1 Overview of Concepts, Models
and Services
X.501 | 9594.Part 2 Models
X.511 | 9594.Part 3 Abstract Service Definition
X.518 | 9594.Part 4 Procedures for Distributed Operations
X.519 | 9594.Part 5 Protocol Specifications
X.520 | 9594.Part 6 Selected Attribute Types
X.521 | 9594.Part 7 Selected Object Classes
X.509 | 9594.Part 8 Authentication Framework
X.525 | 9594.Part 9 Replication

[ENV 41215] "Behaviour of DSAs for Distributed Operations",
European Pre-Standard, Dec 1992

[ISP 10615-6] "DSA Support of Distributed Operations", 5th
draft pDISP, Oct 1994

[NADF 7] SD-7 "Mapping the North American DIT onto Directory
Management Domains", North American Directory Forum, V 8.0,
Jan 1993

[UK 142] Defect report number 142, submitted by the UK to ISO,
March 1995. (Proposed solution text included in Annex 1)

[DAM User] Draft Amendments on Minor Extensions to OSI
Directory Service to support User Requirements, August 1995.


Author's Address

D W Chadwick
IT Institute
University of Salford
Salford
M5 4WT
England
Phone: +44 161 745 5351
Fax: +44 161 745 8169
E-mail: D.W.Chadwick@iti.salford.ac.uk



Annex 1 Solution Text of Defect Reports submitted to ISO/ITU-T
by the UK


Defect Report 140

Nature of Defect

In section 24.1.4.2 it is defined that the
SubordinateToSuperior parameter of a HOB can pass an entryInfo
parameter. This should contain entryACI which may be used in
the resolution of the List operation.

This is not correct as the prescriptive ACI from the relevant
subentries is also required in the superior DSA.

Solution Proposed by Source

It is proposed that the following is added to the
SubordinateToSuperior SEQUENCE of section 24.1.4.2 of X.518:

     subentries     [2] SET OF SubentryInfo OPTIONAL

This is used to pass the relevant subentries from the
subordinate to the superior. This is similar to the way
subentry information is passed in the SuperiorToSubordinate
parameter defined in 24.1.4.1.


Defect Report 142

Nature of Defect

The text which describes AreaSpecification in clause 9.2 of
X.525 is completely general. However, for the special case of
replicating first level knowledge references between first
level DSAs, a clarifying sentence should be added.

Solution Proposed by Source

In Section 9.2, under the ASN.1, after the description of
area, and before the description of SubtreeSpecification, add
the sentence:

     "For the case where a DSA is shadowing first level
     knowledge from a first level DSA, the contextPrefix
     component is empty."


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