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Network Working Group D. Chadwick
Request for Comments: 2120 University of Salford
Category: Experimental March 1997


Managing the X.500 Root Naming Context

Status of this Memo

This memo defines an Experimental Protocol for the Internet
community. This memo does not specify an Internet standard of any
kind. Discussion and suggestions for improvement are requested.
Distribution of this memo is unlimited.

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 X.500 Standard.

The NameFLOW-Paradise 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 X.500 Standard.

The NameFLOW-Paradise project is moving towards 1993 ISO X.500
Standard replication protocols and wants to standardise the protocol
and procedure for managing the root naming context which will be
based on 1993 X.500 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 ISO X.500 Standard protocols
for managing the root context. Whilst the ASN.1 is compatible with
that of the X.500 Standard, the actual settings of the parameters are
supplementary to that of the X.500 Standard.




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Table of Contents

1 Introduction............................................. 2
2 Migration Plan........................................... 3
3 Technical Solutions...................................... 3
4 The Fast Track Solution.................................. 4
5 The Slower Track Solution................................ 6
6 The Long Term Solution................................... 7
7 Security Considerations.................................. 8
8 Acknowledgments.......................................... 9
9 References............................................... 9
10 Author's Address........................................ 10
Annex 1 Solution Text of Defect Reports submitted to ISO/ITU-
T by the UK........................................... 11
Annex 2 Defect Report on 1993 X.500 Standard for Adding
full ACIs to DISP for Subordinate References, so that
Secure List Operation can be performed in Shadow DSAs. 12
Annex 3 Defect Report on 1997 X.500 Standard Proposing
an Enhancement to the Shadowing Agreement in order to
support 1 Level Searches in Shadow DSAs............... 14

1 Introduction

The NameFLOW-Paradise 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 and other DSAs by Quipu replication [RFC 1276] from
the root DSA. In June 1996 there were 770 DSAs replicating this
information over the Internet. 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 X.500 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 an insecure List
operation, but not a one-level Search operation. When access controls
were added to the 1993 X.500 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 X.500 Standard restricted its use to
the List operation, in order to remain compatible with the 1988
edition of the X.500 Standard.



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2 Migration Plan

The NameFLOW-Paradise service is now migrating to X.500 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 NameFLOW-Paradise service to have
one master root DSA. This root DSA will not support user Directory
operations via the LDAP, 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 ISO X.500
Standard. In the X.500 Standard 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 X.500 Standard conforming
system.)

3 Technical Solutions

3.1 The solution at first appears to be relatively straight forward,
and involves two steps. Firstly, create a root DSA, and establish
hierarchical operational bindings using the DOP, between it and each
master first level DSA. Secondly, 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.





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3.2 Unfortunately there are a number of complications that inhibit a
quick implementation of this solution. Firstly, few DSA suppliers
have implemented the DOP. Secondly there are several defects in the
X.500 Standard that currently stop the above solution from working.

3.3 At a meeting chaired by DANTE in the UK on 18 June 1996[Mins], at
which several DSA suppliers were present, the following pragmatic
technical solution was proposed. This comprises a fast track partial
solution and a slower track fuller solution. Both the fast and slower
tracks use the shadowing protocol (DISP) for both steps of the
solution, and do not rely on the DOP to establish HOBs. The fast
track solution, described in section 4, will support knowledge
distribution of the root context, and the (insecure) List operation
of the root's subordinates. The List operation will be insecure
because access control information will not be present in the shadow
DSEs. (However, since it is generally thought that first level
entries, in particular country entries, are publicly accessible, this
is not considered to be a serious problem.) Suppliers expect to have
the fast track solution available before the end of 1996. The slower
track solution, described in section 5, will in addition support
fully secure one level Search and List operations of the root
(without the need to chain to the master DSAs). Suppliers at the
DANTE meeting did not realistically expect this to be in their
products much sooner than mid 1998.

3.4 The long term solution, which relies on the DOP to establish
HOBs, is described in section 6 of this document.

(Note. 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 X.500 Standard
[ENV 41215] and the NADF standing document [NADF 7]. It is also
preferred by the International X.500 Standardized Profile [ISP
10615-6].)

4 The Fast Track Solution

4.1 The fast track solution provides root knowledge collection and
insecure List operations for first level DSAs, and will be of use to
systems which do not yet support the DOP for managing hierarchical
operational bindings. The fast track solution relies upon the DISP
with very few changes to the 1993 edition of the X.500 Standard.









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4.2 Each master first level DSA administrator will make available to
the administrator of the root DSA, sufficient information to allow
the root DSA to configure a subordinate reference to their DSA. In
the simplest case, this can be via a telephone call, and the
information comprises the access point of their DSA and the RDNs of
the first level entries that they master.

4.3 Each master first level DSA enters into a shadowing agreement
with the root DSA, for the purpose of shadowing the root naming
context.

The 1993 edition of the X.500 Standard explicitly recognises that
there can be master and shadow first level DSAs (X.501 Section 18.5).
(The 1988 edition of the X.500 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 X.500
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).





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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 that are held in the root DSA excluding
the DSEs that the first level DSA already masters, plus a complete
set of subordinate reference."

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.

5 The Slower Track Solution

5.1 The slower track solution provides support for fully secure one
level Search and List operations of the root in first level DSAs, and
comprises of two steps for HOB establishment between the root DSA and
master first level DSAs, using the DISP instead of the DOP. Step one,
described in 5.3, allows the root DSA to shadow first level entries
from a master first level DSA. Step two, described in 5.4, 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 4.3 above.

5.2 This solution requires two significant defects in the ISO X.500
Standard to be corrected. Firstly, access control information needs
to be added to subordinate references in the DISP to allow the List
operation to work securely in a shadowed DSA. (The ACI are held in
both the subr DSE and in its subentry.) This requires a defect report
on the 93 X.500 Standard to be submitted. The text of this defect
report (that has been submitted to ISO) is given in Annex 2.

Secondly, a new type of shadowing agreement will need to be
established between the supplier and consumer DSAs, to copy
subordinate entries rather than simply subordinate references, so
that one level Search operations can work in the shadowing DSA. This
procedure should have been part of the 1997 edition of the X.500
Standard, but due to an omission is not. Consequently a defect
report on the 1997 X.500 Standard has been submitted. The text of
this defect report is given in Annex 3.











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5.3 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.

5.4 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.

6 The Long Term Solution

6.1 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).








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Whilst hierarchical agreements are standardised, this particular
novel use of a HOB is not specifically recognised in the X.500
Standard. Although the ASN.1 will support it, there is no supporting
text in the X.500 Standard. The following text supplements that in
the X.500 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 (i.e. first
level DSEs), one for each first level naming context in the domain,
and their corresponding subentries. The first level DSEs and their
subentries will contain, in addition to specific knowledge attribute
values of category master and shadow, sufficient attributes and
collective 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."

6.2 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 1993 edition of the X.500 Standard limits this
to those which are required to perform a List operation. In the 1997
edition of the X.500 Standard [DAM User] this restriction has been
removed, so that the attributes may also be used for a one-level
Search operation.

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

7 Security Considerations

Security considerations are discussed in this memo in relation to
List and one-level Search operations. Each DSE has access control
information associated with it, and these must be adhered to when the
operations are performed.










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8 Acknowledgments

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 first
version of this document in detail and provided valuable comments,
and who first suggested the use of the DISP as a pragmatic solution
for HOB establishment until the DOP becomes widely implemented.

The author would also like to thank John Farrell from the ISODE
Consortium, Andrew Palk from Digital and Keith Richardson from ICL
who attended the DANTE meeting, and contributed to the technical
contents of the defect reports in Annexes 2 and 3.

9 References

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

[ENV 41215] "Behaviour of DSAs for Distributed Operations",
European X.500 Pre-Standard, Dec 1992

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

[Mins] "Notes of DANTE meeting to discuss Managing the Root Naming
Context. 18 June 1996." D W Chadwick, circulated to IDS mailing
list

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

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














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

[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

10 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


























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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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Annex 2 Defect Report on 1993 X.500 Standard for Adding full ACIs to
DISP for Subordinate References, so that Secure List Operation can
be performed in Shadow DSAs

Nature of Defect:

The List operation may be carried out in a superior DSA using
subordinate reference information, providing that the fromEntry flag
is set to false in the response. However, in order to do this
securely, complete access control information is needed for the RDN
of the subordinate entry. The existing text assumes that this is held
in entry ACI (e.g. see 9.2.4.1 c) or in prescriptive ACI held in
subentries above the DSE (e.g. see 9.2.4.1 b). In the case of a
subordinate reference, the prescriptive ACI may be held below the
DSE, if the subordinate reference points to a new administrative
point. The shadowing document needs to make it clear that this can be
the case, and needs to allow for this additional access control
information to be shadowed.

A related defect report (140) has already suggested that this same
omission should be added to operational bindings.

Solution Proposed by the Source:

All the following changes are to X.525|ISO 9594-9.

I) Insert the following text into 7.2.2.3, at the end of both the
second paragraph and the first sentence of the third paragraph (after
"appropriate knowledge"): "and access control information."

II) Insert a new third paragraph into 7.2.2.3: "If subordinate
knowledge is supplied, and the supplying DSE (of type subr) is also
of type admPoint, then the SDSE shall additionally be of type
admPoint and the administrativeRole attribute shall be supplied. If
such a DSE has any immediately subordinate subentries containing
PrescriptiveACI relating to the administrative point, then they shall
also be supplied as SDSEs in the shadowed information.

Note. A DSE can be of type subr and admPoint in a superior DSA, when
the naming context in the subordinate DSA is the start of a new
administrative area."

III) Update figure 3 to show a subentry immediately below a
subordinate reference. The subentry contains prescriptiveACI and is
part of the shadowed information.






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.
Etc. / \
/ \
/ o \
/ / \ \
Replicated / / \ \
Area --------------/--/-> \ \
/ / \ \
/ / \ \
/ / \ \
Subordinate /__/_____________\__\
knowledge--------/-> o o o \
/ / \ \
Prescriptive---/-> o o \
ACI Subentries/ \
Unit of Replication


Etc.
o
/ \
/ \
/ \
/ \
/ \
/ \
/_____________\
o o o
/ \
o o
Shadowed Information

ADDITIONS TO FIGURE 3, SECTION 7.2, X.525

IV) Add supporting text to section 7.2 in the paragraph after Figure
3. Insert after the sentence "Subordinate knowledge may also be
replicated" the following sentences "Implicit in the Add supporting
text to section 7.2 in the paragraph after Figure 3. Insert after
the sentence subordinate knowledge is the access control information
which governs access to the RDN of the subordinate knowledge. When
the subordinate entry is an administrative point in another DSA, then
part of this access control information may be held in
prescriptiveACI subentries beneath the subordinate knowledge."

v) Add a new point d) to 9.2.4.1: "if subordinate knowledge (not
extended knowledge) is shadowed then any prescriptiveACI in
subordinate subentries shall also be copied."




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Annex 3 Defect Report on 1997 X.500 Standard Proposing an Enhancement to
the Shadowing Agreement in order to support 1 Level Searches in Shadow
DSAs.

Nature of Defect:

The 1997 edition of the X.500 Standard has allowed, for reasons of
operational efficiency, one level Searches to be carried out in the
superior DSA, when the actual entries are context prefixes in
subordinate DSAs. The HOBs have been extended to allow this entry
information to be carried up to the superior DSA. Unfortunately, we
forgot to add the corresponding text to Part 9, so that shadow DSAs
are able to copy this additional information from the supplier DSA.
This defect report proposes the additional text for Part 9.

Solution Proposed by the Source:

All the following changes are to X.525|ISO 9594-9.

I) Section 9.2, add a new subordinates parameter to
UnitOfReplication, viz:

UnitOfReplication ::= SEQUENCE{
area AreaSpecification,
attributes AttributeSelection,
knowledge Knowledge OPTIONAL,
subordinates BOOLEAN DEFAULT FALSE }

subordinates is used to indicate that subordinate entries, rather
than simply subordinate references, are to be copied to the
consumer DSA. subordinates may only be TRUE if knowledge is
requested and extendedKnowledge is FALSE.

II) Insert a new fourth paragraph (assuming previous defect for
List was accepted) into 7.2.2.3:

"If subordinates is specified, then the supplier shall send
subordinate entries rather than subordinate references, and the
SDSEs will be of type subr, entry and cp. The subordinate entries
will contain attributes according to the attribute selection.

In addition, if the supplying DSE is of type admPoint, then the
SDSE shall additionally be of type admPoint and the
administrativeRole attribute shall be supplied. All appropriate
subentries below the admPoint DSE shall also be supplied as SDSEs
in the shadowed information."





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