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INTERNET-DRAFT S. Legg
draft-ietf-ldup-urp-03.txt Adacel Technologies
A. Payne
Telstra
June 29, 2000
LDUP Update Reconciliation Procedures
Copyright (C) The Internet Society (2000). All Rights Reserved.
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.
This draft is published by the IETF LDUP Working Group. Distribution
of this document is unlimited. Comments should be sent to the LDUP
Replication mailing list <ldup@imc.org> or to the authors.
This Internet-Draft expires on 29 December 2000.
1. Abstract
This document describes the procedures used by LDAP [LDAPv3] or X.500
[X500] directory servers to reconcile updates performed by
autonomously operating directory servers in a distributed, replicated
directory service.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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document are to be interpreted as described in RFC 2119 [RFC2119].
2. Table of Contents
1. Abstract 1
2. Table of Contents 2
3. Introduction 2
4. Model Extensions 3
4.1 Unique Identifier 3
4.2 Timestamps & Existence 3
4.3 Replication Primitives 4
4.4 Lost & Found 5
5. Replication Procedures 6
5.1 Processing LDAP, DAP or DSP Operations on the DIT 6
5.1.1 Add Entry 7
5.1.2 Remove Entry 8
5.1.3 Modify Entry 8
5.1.4 Modify DN 10
5.2 Generating Replication Primitives 10
5.3 Processing Replication Primitives on the DIT 12
5.3.1 Saving Deletion Records 13
5.3.2 Glue Entries 14
5.3.3 Generating Change Sequence Numbers 14
5.3.4 Comparison of Attribute Values 15
5.3.5 Entry Naming 15
5.3.6 Processing Add Attribute Value Primitive 18
5.3.7 Processing Remove Attribute Value Primitive 19
5.3.8 Processing Remove Attribute Primitive 20
5.3.9 Processing Add Entry Primitive 20
5.3.10 Processing Remove Entry Primitive 21
5.3.11 Processing Move Entry Primitive 22
5.3.12 Processing Rename Entry Primitive 23
6. Security Considerations 24
7. Acknowledgements 25
8. References 25
9. Intellectual Property Notice 26
10. Copyright Notice 26
11. Authors' Addresses 27
3. Introduction
Each DAP, LDAP or DSP operation successfully performed by a directory
server is subsequently reported to other directory servers with which
it has a replication agreement as a set of one or more simple
timestamped replication primitives. These primitives reflect the
intended final state of an update operation rather than the specific
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changes required to achieve that state.
A directory server will receive replication primitives from its
various agreement partners according to the agreement schedules.
Those primitives MUST be reconciled with the current directory server
contents. In broad outline, received replication primitives are
compared to the timestamp information associated with the directory
data item being operated on. If the primitive has a more recent
timestamp a change in the directory contents is made (which may
involve only the revision of the timestamp). If the directory server
has other replication agreements then the change will be reflected in
primitives sent during replication sessions for those other
agreements. If the primitive has an older timestamp it is no longer
relevant and is simply ignored.
The Update Reconciliation Procedures are designed to produce a
consistent outcome at all participating directory servers regardless
of the order in which the primitives are received and processed. The
primitives can also be safely replayed in the event that an exchange
of replication information with another directory server is
interrupted. This greatly simplifies the recovery mechanisms
required in the replication protocol.
4. Model Extensions
This section describes the extensions to the data model required to
effect multi-master replication.
4.1 Unique Identifier
A Unique Identifier is associated with each entry in the global DIT.
This Unique Identifier MUST be globally unique for all time in the
Directory. This can be achieved by defining a unique prefix for each
directory server and then ensuring that the suffix of the Unique
Identifier is locally unique.
The Unique Identifier for an entry is held in the entryUUID
operational attribute.
Some pre-allocated global Unique Identifier values are used to
indicate the X.500 global root entry, and the Lost & Found entry (see
Section 4.4).
4.2 Timestamps & Existence
The timestamp for a replication primitive or directory data item is
in the form of a Change Sequence Number (CSN). The components of the
CSN are, from most significant to least significant, a time in
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seconds, a change count, a Replica Identifier and a modification
number. Notionally a CSN is associated with an entry's Relative
Distinguished Name (the Name CSN), the reference to its superior
entry (the Parent CSN) and each of its attribute values (including
the distinguished values and operational attribute values), to record
the time of the most recent action on that part of the entry.
The entry itself has a CSN (the Entry CSN) asserting the most recent
time at which the entry was added. An entry is permitted to be
removed and then re-added at one or more directory servers. In this
context re-adding an entry means reusing the Unique Identifier of a
removed entry and does not refer to the case of reusing the RDN of a
removed entry. The reuse of a Unique Identifier can arise by the
explicit action of a directory administrator to restore an entry that
was mistakenly removed. The mechanism by which an administrator adds
an entry with a reused Unique Identifier is outside the scope of the
X.500 and LDAP standards since the Unique Identifier of an entry is
not a user modifiable attribute. Note that from the perspective of a
consumer directory server of a partial area of replication, an entry
may appear to be removed and added several times because
modifications to the entry change whether the entry satisfies the
replication agreement specification for the area of replication.
Additionally, a deletion record is kept for each of the recently
deleted entries (entry deletion records), attributes (attribute
deletion records), or attribute values (value deletion records). A
deletion record contains a CSN and asserts that the associated
directory object no longer existed at the particular time.
4.3 Replication Primitives
Each update operation performed on an entry in a part of the DIT
subject to one or more replication agreements MUST be subsequently
reported as replication primitives to the replication partner
directory servers of those agreements. The collection of primitives
sent by a directory server to a replication partner will reflect both
the results of locally processed user update requests and also of
replicated updates received from other directory servers. A single
update operation will decompose into one or more primitives.
Common to all update primitives is an entry identifier argument, uid,
containing the Unique Identifier of the target entry of the change,
and a CSN argument, csn, to indicate the time of the change. In the
case of adding a new entry, the Unique Identifier for the entry is
allocated by the directory server in the course of processing the
operation. Additional arguments are present depending on the type of
replication primitive.
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The p-add-entry(uid, csn, superior, rdn) primitive is used to
describe the addition of a new entry with minimal contents. The
superior argument contains the Unique Identifier of the immediate
superior entry of the added entry. The rdn argument contains the
Relative Distinguished Name of the added entry.
The p-move-entry(uid, csn, superior) primitive is used to describe
the moving of an entry to a new immediate superior in the DIT. The
superior argument contains the Unique Identifier of the new superior
entry.
The p-rename-entry(uid, csn, rdn) primitive is used to describe a
change to the Relative Distinguished Name of an entry. The rdn
argument contains the new RDN for the entry.
The p-remove-entry(uid, csn) primitive is used to describe the
removal of an entry.
The p-add-attribute-value(uid, csn, type, value) primitive is used to
describe the addition of a single attribute value to an entry. The
type argument contains the attribute type of the value and the value
argument contains the attribute value.
The p-remove-attribute-value(uid, csn, type, value) primitive is used
to describe the removal of a single attribute value from an entry.
The type argument contains the attribute type of the value and the
value argument contains the attribute value.
The p-remove-attribute(uid, csn, type) primitive is used to describe
the removal of all values of an attribute from an entry. The type
argument contains the removed attribute type.
These primitives reflect the intended final state of an update
operation rather than the specific changes required to achieve that
state.
4.4 Lost & Found
As a result of conflicting updates at two or more master directory
servers, an entry may be left with a reference to a non-existent
superior entry. Such an entry is called an orphaned entry. When
this situation arises, the directory server creates a glue entry for
the missing superior entry. This glue entry is made a subordinate of
the specially nominated Lost & Found entry and the orphaned entry
becomes a subordinate of the glue superior entry (see Section 5.3.2).
Entries that exist in the Lost & Found subtree can still be modified
by actions of the replication protocol since entries are identified
by Unique Identifiers in the protocol, independent of their
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positioning in the global DIT.
Entries will also be explicitly moved to become immediate
subordinates of the Lost & Found entry to prevent the formation of a
loop in the superior-subordinate relationships in the DIT. This
situation can only arise through conflicting move entry operations at
two or more master directory servers.
Entries that exist under the Lost & Found entry are able to be
returned to a suitable position in the DIT by an administrator or
user with appropriate access rights.
5. Replication Procedures
The procedures defined in this section ensure the consistent and
correct application of the results of DAP, LDAP or DSP operations
across all replicating directory servers.
5.1 Processing LDAP, DAP or DSP Operations on the DIT
A successful DAP, LDAP or DSP operation applied to a part of the DIT
subject to a replication agreement will create or replace one or more
CSNs on an entry or its contents, and create zero, one or more
deletion records referencing the entry or its contents. The CSNs and
deletion records generated from an operation are atomic with that
operation. That is, either the operation succeeds, the CSNs are
revised and the deletion records are stored, or the operation fails,
no CSNs are revised and no deletion records are stored. In all
cases, all current error conditions (i.e. reasons for rejecting an
LDAP, DAP or DSP update operation) remain.
At some later time, possibly immediately following the update or
concurrently with it, the CSNs on entry contents and deletion records
are used to generate the replication primitives that will report the
update to other directory servers via a replication session.
All the CSNs generated from a single update operation MUST use the
same time, change count and Replica Identifier. The modification
number is permitted to vary but MUST be assigned such that when the
CSNs resulting from the operation, including those in the deletion
records, are compared to the CSNs resulting from any other operation
they are all strictly greater than or all strictly less than those
other CSNs (i.e. in a global CSN ordering of the primitives
resulting from all operations the primitives of each operation MUST
be contiguous in that ordering). In order for the update to be
consistently applied when replicated to other directory servers the
CSNs generated during that update must generally be greater than any
pre-existing CSNs on the updated entry's contents. It is expected
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that directory servers will normally use the current time according
to their system clocks in generating the CSNs for an operation.
However in an environment where directory server clocks are not
necessarily synchronized the current time may be older than existing
CSNs on entry contents. The constraints the new CSNs MUST satisfy
with respect to pre-existing CSNs on entry data are covered in the
sections on each type of update operation. The Update Reconciliation
Procedures allow a directory server to generate CSNs in advance of
its current time to satisfy the constraints and proceed with the
update.
The LDUP Update Vector mechanism imposes the additional constraint
that the CSN generated for an update operation MUST also be greater
than the highest CSN generated by the directory server that has
already been seen by any other directory server. An implementation
that generates successively greater CSNs for each operation will
satisfy this constraint.
The following sections describe the additional actions carried out in
processing each standard type of update operation in order to support
replication. If a directory server implementation supports other
non-standard update operations or alternative non-directory update
protocols then, in so far as these operations alter replicated
directory data, the implementation MUST generate and apply CSNs and
deletion records that accurately reflect any change.
A directory server implementation may also perform implicit updates
in response to user update requests, e.g. to maintain the referential
integrity of distinguished names. Appropriate CSNs and deletion
records for these changes MUST also be generated.
A detailed description of the replication processing for these other
types of update is beyond the scope of this document.
5.1.1 Add Entry
The LDAP Add operation [LDAPv3] or DAP addEntry operation [X511] is
used to add a leaf entry to the DIT. A successful request will
generate a CSN for the entry. The CSN on the entry's RDN, the CSN on
the entry's superior reference, and the CSN on each distinguished and
non-distinguished value added to the entry by the add entry operation
are set to this same value. The affected values include any
operational attribute values automatically generated by the directory
server, e.g. creatorsName and createTimestamp. Note that the value
of the createTimestamp attribute does not necessarily correspond to
the time component of the CSN associated with that value.
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The Unique Identifier generated for an entry created by a user
request is required to be globally unique for all time, so there
ought not be a pre-existing entry deletion record for the same Unique
Identifier. However it is recognized that, in practice, directory
administrators may need to restore a deleted entry using its original
Unique Identifier (the mechanism used to achieve this is undefined
and outside the scope of this specification). In this case the CSN
for the entry MUST be generated such that it is greater than or equal
to the CSN of any existing entry, attribute or value deletion
records, and greater than any of the CSNs contained in an existing
glue entry, for the same Unique Identifier.
5.1.2 Remove Entry
The LDAP Delete operation [LDAPv3] or DAP removeEntry operation
[X511] is used to remove a leaf entry from the DIT. If the request
succeeds then an entry deletion record is stored containing the
Unique Identifier of the removed entry. The CSN for the entry
deletion record MUST be generated such that it is greater than the
entry CSN of the removed entry.
5.1.3 Modify Entry
The LDAP Modify operation (ModifyRequest) [LDAPv3] or DAP modifyEntry
operation [X511] is used to perform a series of one or more
modifications to an entry. If the request succeeds then zero, one or
more new values with CSNs are added to the entry contents, and zero,
one or more value or attribute deletion records are stored.
The modifications described by the modification argument of the LDAP
ModifyRequest have the following additional effects:
a) The add alternative associates a CSN with each of the added
attribute values.
b) The delete alternative with no listed values generates an
attribute deletion record for the removed attribute type.
c) The delete alternative with listed values generates a value
deletion record for each of the removed values.
d) The replace alternative first generates an attribute deletion
record for the removed attribute type. A CSN is then associated
with each of the added values.
The modifications described by the changes argument of the X.500
modifyEntry operation have the following additional effects:
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a) The addAttribute and addValues alternatives associate a CSN
with each of the added attribute values. These two alternatives
are equivalent from the point of view of URP since there is no CSN
associated specifically with the attribute type.
b) The removeAttribute alternative generates an attribute deletion
record for the removed attribute type.
c) The removeValues alternative generates a value deletion record
for each of the removed values.
d) The alterValues alternative first generates a value deletion
record for each of the old values. Secondly, a CSN is associated
with each of the new values.
e) The resetValues alternative generates a value deletion record
for each value actually removed.
A successful ModifyRequest or modifyEntry operation will also result
in changes to operational attributes of the entry. Like the explicit
modifications to user attributes, CSNs are given to new operational
attribute values and deletion records are stored for operational
attribute values that are removed. The processing in each case
depends on the semantics of the particular operational attribute type
and can be deduced by considering an equivalent explicit modification
request. In particular, the revision of the modifyTimestamp and
modifiersName attributes is treated like the ModifyRequest replace
alternative. Note that the value of the modifyTimestamp attribute
does not necessarily correspond to the time component of the CSN
associated with that value. The entryUUID operational attribute
SHALL NOT be modified. Consequently attribute and value deletion
records for the entryUUID attribute type are never generated.
The CSNs generated by a modify operation MUST be greater than the CSN
of any pre-existing attribute value that is removed, greater than or
equal to the CSN of any pre-existing attribute deletion record or
value deletion record applying to an added attribute value, and
greater than or equal to the CSN of the entry.
A further constraint applies to the modification number component of
the CSNs generated by a single modify operation. The CSN generated
for an added attribute value MUST be greater than or equal to the CSN
on any applicable value deletion record or attribute deletion record
already created by this same operation. This constraint is satisfied
if the same modification number is used in all the CSNs generated by
a single modify operation, or if the CSNs generated as the sequence
of modifications in the operation are applied in order use
monotonically increasing modification numbers. The modification
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numbers need not be consecutive in this case.
Whenever a new value is added to the entry contents any value
deletion record for the same entry, attribute type and attribute
value MAY be discarded.
5.1.4 Modify DN
The LDAP Modify DN operation [LDAPv3] and DAP modifyDN operation
[X511] are used to change the Relative Distinguished Name of an entry
and/or to move an entry to a new superior in the DIT. If the entry
is moved to a new superior in the DIT then the CSN on the entry's
superior reference is replaced. If the entry's RDN is changed then
the CSN on the entry's RDN is replaced. A value deletion record is
stored for each of the formally distinguished attribute values
removed from the entry as a consequence of the deleteOldRDN parameter
(modifyDN) or deleteoldrdn parameter (ModifyDNRequest) being set to
true. An entryUUID attribute value that is made non-distinguished
SHALL NOT be removed from the entry regardless of the deleteOldRDN or
deleteoldrdn flag and SHALL NOT have a corresponding value deletion
record.
If the CSN on the entry's superior reference is revised then the new
value MUST be greater than the previous value. If the CSN on the
entry's RDN is revised then the new value MUST be greater than the
previous value of the CSN on the RDN. The CSNs for any value
deletion records MUST be greater than the CSNs on the removed
attribute values.
5.2 Generating Replication Primitives
Each time a replication session is invoked, the supplier directory
server generates and sends replication primitives for updates known
to the supplier but not yet known to the consumer directory server.
The supplier uses the Update Vector of the consumer to determine what
to send. Conceptually, the supplier scans all the glue and non-glue
entries and deletion records covered by the replication agreement
with the consumer and generates primitives where the CSNs held by the
supplier are greater than the CSN for the corresponding identified
replica in the consumer's Update Vector. No replication primitives
are generated for entries or entry contents that are outside the
scope of the replication agreement.
A p-add-entry primitive is generated for each entry whose entry CSN
is greater than the Update Vector CSN for the same replica. The
superior argument of the p-add-entry primitive contains the Unique
Identifier of the immediate superior entry of the added entry. The
rdn argument of the p-add-entry primitive contains the Relative
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Distinguished Name of the created entry except that the value of the
entryUUID attribute, if distinguished, is always omitted from the
RDN. The superior and rdn arguments are provided even if the CSN on
the superior reference or the RDN are greater than the CSN on the
entry.
A p-add-attribute-value primitive is generated for each distinguished
value that has a CSN greater than the Update Vector CSN for the same
replica and greater than the CSN on the RDN of its entry. A p-add-
attribute-value primitive is generated for each non-distinguished
value that has a CSN greater than the Update Vector CSN for the same
replica. The values of operational attributes are treated in the
same way as the values of user attributes. The p-add-attribute-value
primitive uses the CSN of the corresponding value. There are no
separate primitives generated for the distinguished values that have
the same CSN as the CSN on their entry's RDN.
If the CSN on an entry's RDN is greater than the Update Vector CSN
for the same replica and greater than the CSN on the entry then a p-
rename-entry primitive is generated. The CSN for this primitive is
the CSN on the entry's RDN and the rdn argument contains the Relative
Distinguished Name of the entry.
If the CSN on the entry's superior reference is greater than the
Update Vector CSN for the same replica and greater than the CSN on
the entry then a p-move-entry primitive is generated. The CSN for
this primitive is the CSN on the entry's superior reference and the
superior argument contains the Unique Identifier of the immediate
superior entry.
A p-remove-attribute-value primitive is generated for each value
deletion record having a CSN greater than the Update Vector CSN for
the same replica. The primitive uses exactly the same arguments as
the value deletion record.
A p-remove-attribute primitive is generated for each attribute
deletion record having a CSN greater than the Update Vector CSN for
the same replica. The primitive uses exactly the same arguments as
the attribute deletion record.
A p-remove-entry primitive is generated for each entry deletion
record having a CSN greater than the Update Vector CSN for the same
replica. The primitive uses exactly the same arguments as the entry
deletion record.
Rather than scanning the DIT, an implementation MAY choose to
generate replication primitives as the user update requests are being
processed and put these primitives into a replication log in
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preparation for sending during the next replication session. Any
replication primitives generated from an operation in this way MUST
be atomic with that operation. That is, either the operation
succeeds, and primitives are added to the replication log, or the
operation fails, and no primitives are added to the log. The
replication log MAY be filtered prior to sending to eliminate any
primitives that are superseded by later primitives in the log, and to
eliminate any primitives having CSNs less than or equal to the
relevant CSNs contained in a consumer directory server's Update
Vector.
In a log based implementation, the p-add-attribute-value primitive
supersedes a p-remove-attribute-value primitive for the same entry,
attribute type, attribute value and equal or older CSN. It
supersedes another p-add-attribute-value primitive for the same
entry, attribute type, attribute value and older CSN.
The p-remove-attribute-value primitive supersedes a p-add-attribute-
value primitive for the same entry, attribute type, attribute value
and older CSN. It supersedes another p-remove-attribute-value
primitive for the same entry, attribute type, attribute value and
equal or older CSN.
The p-remove-attribute primitive supersedes a p-add-attribute-value
primitive for the same entry, attribute type and older CSN. It
supersedes a p-remove-attribute-value or another p-remove-attribute
primitive for the same entry, attribute type and equal or older CSN.
The p-remove-entry primitive supersedes a p-add-attribute-value, p-
add-entry, p-move-entry or p-rename-entry primitive for the same
entry and older CSN. It supersedes a p-remove-attribute-value or p-
remove-attribute or another p-remove-entry primitive for the same
entry and equal or older CSN.
The p-move-entry primitive supersedes another p-move-entry primitive
for the same entry and older CSN.
5.3 Processing Replication Primitives on the DIT
Each replication primitive received from another directory server
during a replication session that is within the scope of the
replication agreement is processed against the DIT. Replication
primitives outside the scope of the replication agreement are
rejected.
This section defines some commonly used sub-procedures and the
algorithms for processing each of the primitives. These algorithms
are not intended to be implemented verbatim but instead describe the
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behaviour an LDUP implementation MUST exhibit externally.
Alternative equivalent processing logic is permitted.
Components of primitives, entries, attributes and values are
referenced with the `.' operator. In particular the notation X.csn
refers to the CSN of the directory object X. The operators, < and >
when applied to CSNs, use the convention of CSNs becoming greater
with the progression of time, so older CSNs are less than younger
CSNs. In the case where the CSN for object X has been discarded
through the purging mechanism, X.csn is assumed to have the least
possible CSN value. In some of the procedures a CSN will be
explicitly purged. An implementation MAY instead keep the CSN but
set it to some value that is old enough for it to be eligible for
purging (e.g. the least possible CSN value) without affecting the
correctness of the procedures.
For an entry, E, the notation E.rdn refers to the entry's Relative
Distinguished Name, E.dn refers to the entry's Distinguished Name,
and E.superior refers to the Unique Identifier of the entry's
superior in the DIT.
5.3.1 Saving Deletion Records
It is necessary for a directory server to store deletion records to
remember that some entry, attribute or attribute value has been
deleted, for a period after the processing of the update operation or
replication primitive causing the deletion.
Value deletion records have the same parameters as the p-remove-
attribute-value primitive. The StoreValueDeletion procedure creates
a value deletion record from the actual arguments and stores it for
later access by the various primitive processing procedures. When an
attribute value is added to an entry, a value deletion record for the
same entry, attribute type and value, and with an older CSN, MAY be
discarded.
Attribute deletion records have the same parameters as the p-remove-
attribute primitive. The StoreAttributeDeletion procedure creates an
attribute deletion record from the actual arguments and stores it for
later access. When an attribute deletion record is stored any value
deletion records for the same entry and attribute type, and with
equal or older CSNs, MAY be discarded.
Entry deletion records have the same parameters as the p-remove-entry
primitive. The StoreEntryDeletion procedure creates an entry
deletion record from the actual arguments and stores it for later
access. When an entry deletion record is stored any value deletion
records and attribute deletion records for the same entry, and with
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equal or older CSNs, MAY be discarded.
Since the deletion records have the same components as their
associated remove primitives an implementation MAY choose to use the
same internal structures for both.
5.3.2 Glue Entries
Entries are permitted to be re-added and this can lead to situations
where applicable primitives are received in the period after an entry
is removed but before the arrival of the notification of it being
re-added. In these cases a glue entry is created for the Unique
Identifier to preserve relevant updates in the event that a p-add-
entry primitive with an older CSN is later received for the same
entry. A glue entry is upgraded to a normal entry by a subsequent
p-add-entry primitive.
A glue entry with no subordinate entries and containing only CSNs (on
itself or its component parts) that are eligible to be purged MAY be
removed. A glue entry is discarded if its contents are completely
superseded by another p-remove-entry primitive.
The CreateGlueEntry function is called when required to create a glue
entry as a subordinate of Lost & Found. CreateGlueEntry takes a
single parameter which is the Unique Identifier for the glue entry.
The Unique Identifier, in the form of the entryUUID attribute, also
becomes the RDN for the glue entry. No CSNs are associated with the
entry, the entry's superior reference, or the entry's name (or
equivalently they are set to the least possible CSN value).
5.3.3 Generating Change Sequence Numbers
There are circumstances where conflicts arise in the processing of a
replication primitive. It is necessary in these cases for the
directory server processing the primitives to make corrective changes
and emit additional primitives to ensure that all other directory
servers reach the same consistent state. The GenerateNextCSN
function is used to obtain a CSN for the corrective change. An
implementation that generates replication primitives as the user
update requests are being processed and puts them into a replication
log MUST take the additional step of creating a primitive to convey
the corrective change to other directory servers. Implementations
that generate primitives by scanning entries will pick up the
corrective change automatically.
As is the case for CSNs generated from DAP, DSP or LDAP operations,
the CSN for the corrective change is typically generated from the
current clock time of the directory server. The conditions imposed
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for the correct operation of the LDUP Update Vector MUST also be
satisfied.
GenerateNextCSN takes a single CSN parameter. In addition to all
other conditions, the CSN generated by the function MUST be greater
than this parameter. Since the CSN parameter passed to
GenerateNextCSN is always an actual CSN from some directory object
stored in the local directory server, an implementation MAY choose to
allocate CSNs from an incrementing internal CSN register that is
reset after each replication session to a value greater than the
largest CSN seen so far, and thereby be safely able to disregard the
parameter to GenerateNextCSN.
5.3.4 Comparison of Attribute Values
Values in primitives, in deletion records or in entries are compared
using the equality matching rule for the associated attribute type
where that type is permitted to be multi-valued. This means that two
values that are considered equal may nonetheless have minor
differences. For example, two commonName values may be equal, but
use different letter case and have different numbers of leading or
trailing spaces. Whenever a CSN for some value is refreshed the
value is also refreshed using the exact value from the primitive so
that all directory servers use exactly the same representation for
the value.
Compared values for a single-valued attribute type are all considered
to be equal even though they may be significantly different according
to that attribute type's equality matching rule. In effect the
equality operator, `=', in the following procedures is
unconditionally true when used to compare values of a single-valued
attribute type. Whenever a CSN for the value of a single-valued
attribute is refreshed the value is also refreshed using the value
from the primitive. One significant consequence is that an entry
whose RDN contains a value of a single-valued attribute type is
effectively renamed by a p-add-attribute-value primitive with a more
recent value for the attribute type.
A value in an entry that is replaced by the exact representation from
a primitive retains its distinguished or non-distinguished status.
This includes replaced values of single-valued attribute types.
5.3.5 Entry Naming
Independent changes at two or more directory servers can lead to the
situation of two distinct entries having the same name. The
procedure, CheckUniqueness(E, S, R), takes an entry and determines
whether it is uniquely named. If not, it disambiguates the names of
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the entries by adding the Unique Identifier (i.e. the entryUUID
attribute) of each of the conflicting entries to their own RDN.
The procedure CheckUniqueness is called in each circumstance where
the Relative Distinguished Name of an entry might conflict with
another entry, either because the entry has been renamed or because
it has been moved to a new superior. An entry can be renamed
directly by a p-rename-entry primitive, or as a side-effect of other
primitives causing changes to distinguished values. While each move
or rename of an entry potentially causes a conflict with some other
entry already having the new Distinguished Name, it also potentially
removes a previous conflict on the old Distinguished Name. To enable
the CheckUniqueness function to remove the Unique Identifier from an
entry's RDN when it is no longer needed, the old name for an entry is
passed through the second and third parameters. The parameter, S, is
the Unique Identifier of the old superior entry of E, and the
parameter, R, is the old RDN of E. CheckUniqueness ignores
distinguished entryUUID values when comparing entry RDNs. The
function BaseRDN(rdn) returns its argument minus any distinguished
entryUUID values, to support these comparisons.
CheckUniqueness(E, S, R)
{
make E.uid non-distinguished
IF there exists exactly one subordinate entry, C, of S
where BaseRDN(C.rdn) = BaseRDN(R)
make C.uid non-distinguished
IF E.rdn is empty
make C.uid distinguished
ELSE IF there exists a subordinate entry, C, of E.superior
where E <> C AND BaseRDN(C.rdn) = BaseRDN(E.rdn)
{
make C.uid distinguished
make E.uid distinguished
}
}
Because updates are performed in isolation at multiple directory
servers in a multimaster configuration it is possible to encounter a
situation where there is a request to delete a distinguished value in
an entry. The recommended practice in these circumstances is to
remove the distinguished value and call CheckUniqueness to correct
any resulting name conflicts. An implementation MAY instead reassert
the existence of the distinguished value with a more recent CSN to
avoid altering the entry's RDN. This option is only available to
updatable replicas. Read-only replicas MUST remove the distinguished
value. The function ProtectDistinguished() returns true for an
updatable part of the DIT in a directory server that implements this
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option, and false otherwise. directory servers exercising this
option MUST generate a p-add-attribute-value primitive so that other
directory servers are guaranteed to also reassert the distinguished
value. Directory servers that implement the option will correctly
interwork with servers that do not.
The primitives p-add-entry and p-rename-entry contain common elements
that are applied to the Relative Distinguished Name of an entry in
the same way. This common processing is described in the RenameEntry
procedure. The parameters to this procedure are the entry, E, and
the p-add-entry or p-rename-entry primitive specifying the new RDN.
The procedure assumes that the entry does not currently contain any
distinguished values. It is the responsibility of the calling
procedure to first reset any pre-existing distinguished values to
non-distinguished. The procedure then resets the CSNs and sets the
distinguished flags for existing values and adds distinguished values
if necessary. The CSN for the entry's RDN, as distinct from the CSNs
on each of the distinguished values making up the RDN, is also set.
RenameEntry(E, P)
{
FOREACH AttributeTypeAndValue, N, in P.rdn
IF there exists an attribute value, V, in E of type N.type
where V = N.value
{
IF P.csn > V.csn
{
replace V with N.value if they are not identical
V.csn := P.csn
}
make V distinguished
}
ELSE IF ProtectDistinguished()
{
V := N.value
add V to E as a distinguished value
V.csn := P.csn
FOREACH attribute deletion record (uid, type, csn)
where (uid = P.uid AND type = N.type)
IF csn > V.csn
V.csn := csn
FOREACH value deletion record (uid, type, value, csn)
where (uid = P.uid AND type = N.type AND value = N.value)
IF csn > V.csn
V.csn := csn
V.csn := GenerateNextCSN(V.csn)
}
ELSE IF no attribute deletion record (uid, type, csn) exists
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where (uid = P.uid AND type = N.type AND csn > P.csn)
AND no value deletion record (uid, type, value, csn) exists
where (uid = P.uid AND type = N.type AND
value = N.value AND csn > P.csn)
{
V := N.value
add V to E as a distinguished value
V.csn := P.csn
}
E.rdn.csn := P.csn
}
5.3.6 Processing Add Attribute Value Primitive
This section details the algorithm for processing the p-add-
attribute-value (P.uid, P.type, P.value, P.csn) primitive, which
describes the addition of a single attribute value. If P.type is the
entryUUID attribute type then the primitive MUST be rejected.
IF no value deletion record (uid, type, value, csn) exists where
(uid = P.uid AND type = P.type
AND value = P.value AND csn > P.csn)
AND no attribute deletion record (uid, type, csn) exists where
(uid = P.uid and type = P.type AND csn > P.csn)
AND no entry deletion record (uid, csn) exists where
(uid = P.uid AND csn > P.csn)
{
IF entry, E, with uid = P.uid does not exist
E := CreateGlueEntry(P.uid)
IF P.csn >= E.csn
IF attribute value V, of type P.type
where V = P.value exists in E
{
IF P.csn > V.csn
{
V.csn := P.csn
R := E.rdn
replace V with P.value if they are not identical
IF V is distinguished
AND P.type is a single-valued attribute type
CheckUniqueness(E, E.superior, R)
}
}
ELSE
{
V := P.value
Add V to E as a non-distinguished attribute value
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V.csn := P.csn
}
}
5.3.7 Processing Remove Attribute Value Primitive
This section details the algorithm for processing the p-remove-
attribute-value (P.uid, P.type, P.value, P.csn) primitive, which
describes the removal of a single attribute value. If P.type is the
entryUUID attribute type then the primitive MUST be rejected.
IF no value deletion record (uid, type, value, csn) exists
where (uid = P.uid AND type = P.type AND
value = P.value AND csn >= P.csn)
AND
no attribute deletion record (uid, type, csn) exists
where (uid = P.uid AND type = P.type AND csn >= P.csn)
AND
no entry deletion record (uid, csn) exists
where (uid = P.uid AND csn >= P.csn)
IF entry, E, with uid = P.uid exists
{
IF P.csn > E.csn
IF attribute value, V, of P.type
where V = P.value, exists in E
{
IF P.csn > V.csn
IF V is distinguished
IF ProtectDistinguished()
V.csn := GenerateNextCSN(P.csn)
ELSE
{
R := E.rdn
remove value V
CheckUniqueness(E, E.superior, R)
StoreValueDeletion (P.uid, P.type, P.value, P.csn)
}
ELSE
{
remove value V
StoreValueDeletion (P.uid, P.type, P.value, P.csn)
}
}
ELSE
StoreValueDeletion (P.uid, P.type, P.value, P.csn)
}
ELSE
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StoreValueDeletion (P.uid, P.type, P.value, P.csn)
The presence of a younger deletion record for the entry, attribute or
value provides a convenient test for whether the p-remove-attribute-
value primitive needs to be processed at all. If the value exists to
be removed then there cannot be a deletion record affecting it that
has a younger CSN. If there is a younger deletion record than the
primitive then there cannot be an older value to remove.
5.3.8 Processing Remove Attribute Primitive
This section details the algorithm for processing the p-remove-
attribute (P.uid, P.type, P.csn) primitive, which describes the
removal of all attribute values of P.type. If P.type is the
entryUUID attribute type then the primitive MUST be rejected.
IF no attribute deletion record (uid, type, csn) exists
where (uid = P.uid AND type = P.type AND csn >= P.csn)
AND no entry deletion record (uid, csn) exists where
(uid = P.uid AND csn >= P.csn)
IF entry, E, with uid = P.uid exists
{
IF P.csn > E.csn
{
FOREACH attribute value, V, of type P.type in E (if any)
IF P.csn > V.csn
IF V is distinguished
IF ProtectDistinguished()
V.csn := GenerateNextCSN(P.csn)
ELSE
{
R := E.rdn
remove value V
CheckUniqueness(E, E.superior, R)
}
ELSE
remove value V
StoreAttributeDeletion (P.uid, P.type, P.csn)
}
}
ELSE
StoreAttributeDeletion (P.uid, P.type, P.csn)
5.3.9 Processing Add Entry Primitive
This section details the algorithm for processing the p-add-entry
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(P.uid, P.superior, P.rdn, P.csn) primitive, which describes the
addition of an entry. The CSN on an entry records the time of the
latest p-add-entry primitive for the Unique Identifier. In normal
circumstances there will only ever be one p-add-entry primitive
associated with an entry. The entry CSN MAY be discarded when it
becomes eligible to be purged according to the Purge Vector.
IF no entry deletion record (uid, csn) exists where
(uid = P.uid AND csn > P.csn)
IF entry, E, with uid = P.uid exists
{
IF P.csn > E.csn
{
R := E.rdn
S := E.superior
E.csn := P.csn
FOREACH attribute type, T, in E, except entryUUID
FOREACH attribute value, V, of type T
IF V.csn < P.csn
remove value V
CheckUniqueness(E, S, R)
process P according to
p-rename-entry(P.uid, P.rdn, P.csn)
process P according to
p-move-entry(P.uid, P.superior, P.csn)
}
}
ELSE
{
create entry E
E.csn := P.csn
E.uid := P.uid
E.uid.csn := P.csn
IF an entry with uid = P.superior does not exist
CreateGlueEntry(P.superior)
E.superior = P.superior
E.superior.csn := P.csn
RenameEntry(E, P)
CheckUniqueness(E, E.superior, E.rdn)
}
5.3.10 Processing Remove Entry Primitive
This section details the algorithm for processing the p-remove-entry
(P.uid, P.csn) primitive, which describes the removal of an entry.
If the target entry has attribute values with CSNs greater than the
primitive's CSN, a superior reference with a greater CSN, or if it
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has any subordinate entries, it becomes a glue entry instead of being
removed. It is also moved to Lost & Found, unless it has a CSN for
its superior reference that is greater than the CSN of the p-remove-
entry.
IF no entry deletion record (uid, csn) exists
where (uid = P.uid AND csn >= P.csn)
IF entry, E, with uid = P.uid exists
{
IF P.csn > E.csn
{
IF E.superior.csn >= P.csn
OR any value, V, with csn >= P.csn exists
OR E has subordinates
{
R := E.rdn
S := E.superior
make E a glue entry
purge E.csn
IF E.superior.csn < P.csn
{
E.superior := LOST_AND_FOUND
purge E.superior.csn
}
IF E.rdn.csn < P.csn
purge E.rdn.csn
FOREACH attribute type, T, in E, except entryUUID
FOREACH attribute value, V, of type T
IF V.csn < P.csn
remove value V
CheckUniqueness(E, S, R)
}
ELSE
remove entry E
StoreEntryDeletion (P.uid, P.csn)
}
}
ELSE
StoreEntryDeletion (P.uid, P.csn)
5.3.11 Processing Move Entry Primitive
This section details the algorithm for processing the p-move-entry
(P.uid, P.superior, P.csn) primitive, which describes the moving of
an entry to a new immediate superior in the DIT. If the new superior
specified by the primitive does not exist, or is a direct or indirect
subordinate of the entry being moved, then the entry is moved to Lost
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& Found instead.
IF no entry deletion record (uid, csn) exists
where (uid = P.uid AND csn > P.csn)
{
IF entry, E, with uid = P.uid does not exist
E := CreateGlueEntry(P.uid)
IF P.csn > E.superior.csn
{
R := E.rdn
O := E.superior
IF entry, S, with uid = P.superior does not exist
S := CreateGlueEntry(P.superior)
IF S is not in the subtree of E
{
E.superior := P.superior
E.superior.csn = P.csn
}
ELSE
{
E.superior := LOST_AND_FOUND;
E.superior.csn := GenerateNextCSN(P.csn)
}
CheckUniqueness(E, O, R)
}
}
5.3.12 Processing Rename Entry Primitive
This section details the algorithm for processing the p-rename-entry
(P.uid, P.rdn, P.csn) primitive, which describes a change to the
Relative Distinguished Name of an entry. A p-rename-entry primitive
that is older than current name of an entry is not simply ignored
since it may contain attribute values that would have been added to
the entry had the primitives arrived in CSN order. These extra
values would now be non-distinguished.
IF no entry deletion record (uid, csn) exists
where (uid = P.uid AND csn >= P.csn)
{
IF entry, E, with uid = P.uid does not exist
E := CreateGlueEntry(P.uid)
IF P.csn > E.rdn.csn
{
R := E.rdn
FOREACH distinguished attribute value, V, in entry E
make V non-distinguished
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RenameEntry(E, P)
CheckUniqueness(E, E.superior, R)
}
ELSE
FOREACH AttributeTypeAndValue, N, in P.rdn
{
IF there exists an attribute value, V, in E of type
N.type AND V = N.value
{
IF P.csn > V.csn
{
replace V with N.value if they are not identical
V.csn := P.csn
}
}
ELSE
{
IF no value deletion record (uid, type, value, csn)
exists where (uid = P.uid AND type = N.type AND
value = N.value AND csn > P.csn)
AND
no attribute deletion record (uid, type, csn)
exists where (uid = P.uid AND type = N.type AND
csn > P.csn)
{
V := N.value
Add V to E
V.csn := P.csn
}
}
}
}
6. Security Considerations
The procedures described in this document are not subject to access
controls on the directory data items being modified. Specifically,
the update primitives received from a peer replica are applied
without regard for access controls. This is necessary so that access
control information can also be replicated. An LDUP enabled server
entering into a multi-master replication agreement with a peer server
is enabling joint authority and responsibility for some part of the
directory data. A replica must trust that the other replicas are
properly enforcing access controls on user update requests, but this
trust extends only as far as described by the replication agreements
currently in place. The replication agreement acts as a surrogate
for access controls between peer replicas. Replication primitives
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that are outside the scope of the agreement are rejected.
Authentication of peer replica LDUP sessions and the security of the
exchange of replication primitives through the LDUP protocol are
outside the scope of this document and are described elsewhere.
Simultaneous updates at different replicas can result in two entries,
corresponding to two different real world entities, having the same
distinguished name. The Update Reconciliation Procedures
disambiguate these two names by appending the respective Unique
Identifiers to the entries' RDNs. This action will disable any
access controls based on an entry's specific DN or RDN. Disabling
such an access control may have the effect of granting a permission
that was explicitly denied. Since a Unique Identifier is required to
be globally unique for all time, appending a Unique Identifier to the
RDN cannot unintentionally enable access controls applying to a
different real world entity.
It is sufficient when disambiguating entry RDNs to append the UID to
only one of a pair of entries ending up with the same name. The
Update Reconciliation Procedures require both entries to have their
UID appended to minimize the chance that either entry will gain
permissions intended for the other. This is based on the assumption
that most access controls will grant permissions rather than deny
permissions.
7. Acknowledgements
The authors would like to thank Suellen Faulks and Tony Robertson
from Telstra and Mark Ennis from Adacel Technologies who contributed
to the design and verification of the procedures described in this
document.
The authors would also like to thank the members of the LDUP
architecture group for their input into the refinement of the design.
8. References
[RFC2119] - S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119.
[LDAPv3] - M. Wahl, S. Kille, T. Howes, "Lightweight Directory Access
Protocol (v3)", RFC 2251, December 1997.
[X500] - ITU-T Recommendation X.500 (08/97) | ISO/IEC 9594-1:1998,
Information Technology - Open Systems Interconnection - The
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Directory: Overview of concepts, models and services
[X511] - ITU-T Recommendation X.511 (08/97) | ISO/IEC 9594-3:1998,
Information Technology - Open Systems Interconnection - The
Directory: Abstract service definition
[BCP-11] - R. Hovey, S. Bradner, "The Organizations Involved in the
IETF Standards Process", BCP 11, RFC 2028, October 1996.
9. Intellectual Property Notice
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. [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 implementors or users of this
specification can be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
10. Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
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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.
11. Authors' Addresses
Steven Legg
Adacel Technologies Ltd.
250 Bay Street
Brighton, Victoria 3186
AUSTRALIA
Phone: +61 3 8530 7808
Fax: +61 3 9596 2960
EMail: steven.legg@adacel.com.au
Alison Payne
Telstra
21/242 Exhibition Street
Melbourne, Victoria 3000
AUSTRALIA
Phone: +61 3 9634 4628
EMail: alison.payne@team.telstra.com
12. Appendix A - Changes From Previous Drafts
12.1 Changes in Draft 01
Some of the terminology has been changed to better align with the
terminology used in the LDUP architecture draft.
Descriptions on the usage of CSNs have been revised to account for
the extra modification number component.
The semantics of re-added entries has been simplified so that only
changes after the latest re-add are preserved instead of all those
after the earliest re-add. This eliminates the need for Addition
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CSNs in the entry. It is anticipated that new replication primitives
will be introduced to manage entries that come and go from partial
replicas instead of using p-add-entry and p-remove-entry.
Orphaned entries are no longer moved directly to Lost & Found.
Instead a glue entry is created in Lost & Found for the missing
superior and the orphaned entry becomes a subordinate of that. This
change eliminates the need for explicit propagated primitives for
moving orphaned entries to Lost & Found.
Glue entries have also been used as the mechanism for saving
primitives. There are no longer any references to saved primitives
though the functionality is still present.
The procedures for processing received replication primitives have
been rearranged to follow a more consistent pattern where the
presence of deletion records is tested first.
12.2 Changes in Draft 02
Multimaster replication has been dropped as a work item for the next
edition of X.500 so references to the proposed X.500 multimaster
replication protocol have been removed.
The treatment of distinguished values has been simplified.
Previously an attempt to remove a distinguished value caused the
value to be tagged distinguished-not-present. Now the distinguished
value is removed, and if necessary, the Unique Identifier is made
distinguished to avoid an empty RDN. Optionally, the value to be
removed can be reasserted by emitting an explicit p-add-attribute-
value primitive.
The current draft is more implementation neutral. A replication log
no longer figures prominently in the specification. The previous
descriptions had the user updates generating replication primitives,
which in turn were used to determine the CSNs and deletion records.
The new descriptions have user updates generating CSNs and deletion
records and the primitives are subsequently generated from them.
12.3 Changes in Draft 03
The draft has been edited to make use of the key words "MUST",
"SHOULD", "MAY", etc.
The treatment of server maintained operational attributes has been
clarified.
An extra CheckUniqueness call has been added to the procedure for
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processing the p-add-entry primitive (Section 5.3.9) to cover the
case where an entry is re-added. A loop through all of the values of
an entry in the p-add-entry and p-remove-entry processing has been
altered to explicitly skip the entryUUID operational attribute. No
other changes have been made to the behaviour of the Update
Reconciliation Procedures from Draft 02.
The list of references has been expanded.
The Security Considerations section has been added.
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