INTERNET-DRAFT S. Legg
draft-ietf-ldup-urp-08.txt Adacel Technologies
Category: Experimental A. Payne
Telstra
October 24, 2003
LDUP Update Reconciliation Procedures
Copyright (C) The Internet Society (2003). 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.
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Abstract
This document describes the procedures used by Lightweight Directory
Access Protocol (LDAP) directory servers or X.500 directory servers
to reconcile updates performed by autonomously operating directory
servers in a distributed, replicated directory service, using the
LDAP Duplication/Replication/Update protocols.
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Table of Contents
1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Model Extensions. . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Universally Unique Identifier . . . . . . . . . . . . . . 3
3.2. Timestamps & Existence. . . . . . . . . . . . . . . . . . 4
3.3. Replication Primitives. . . . . . . . . . . . . . . . . . 4
3.4. Lost & Found. . . . . . . . . . . . . . . . . . . . . . . 6
4. Replication Procedures . . . . . . . . . . . . . . . . . . . . . 6
4.1. Processing LDAP, DAP or DSP Operations on the DIT . . . . 6
4.1.1. Add Entry . . . . . . . . . . . . . . . . . . . . 8
4.1.2. Remove Entry. . . . . . . . . . . . . . . . . . . 8
4.1.3. Modify Entry. . . . . . . . . . . . . . . . . . . 9
4.1.4. Modify DN . . . . . . . . . . . . . . . . . . . . 11
4.2. Sending Replication Primitives. . . . . . . . . . . . . . 12
4.3. Processing Replication Primitives on the DIT. . . . . . . 12
4.3.1. Saving Deletion Records . . . . . . . . . . . . . 13
4.3.2. Glue Entries. . . . . . . . . . . . . . . . . . . 14
4.3.3. Generating Change Sequence Numbers. . . . . . . . 14
4.3.4. Comparison of Attribute Descriptions and Values . 15
4.3.5. Entry Naming. . . . . . . . . . . . . . . . . . . 16
4.3.6. Processing Add Attribute Value Primitive. . . . . 19
4.3.7. Processing Remove Attribute Value Primitive . . . 20
4.3.8. Processing Remove Attribute Primitive . . . . . . 21
4.3.9. Processing Add Entry Primitive. . . . . . . . . . 22
4.3.10. Processing Remove Entry Primitive . . . . . . . . 23
4.3.11. Processing Move Entry Primitive . . . . . . . . . 24
4.3.12. Processing Rename Entry Primitive . . . . . . . . 24
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 26
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 26
7. References. . . . . . . . . . . . . . . . . . . . . . . . . . . 27
7.1. Normative References. . . . . . . . . . . . . . . . . . . 27
7.2. Informative References. . . . . . . . . . . . . . . . . . 27
8. Intellectual Property Notice. . . . . . . . . . . . . . . . . . 27
9. Authors' Addresses. . . . . . . . . . . . . . . . . . . . . . . 28
10. Full Copyright Statement. . . . . . . . . . . . . . . . . . . . 28
1. Introduction
This document describes the procedures used by Lightweight Directory
Access Protocol (LDAP) [LDAP] or X.500 [X500] directory servers to
reconcile updates performed by autonomously operating directory
servers in a distributed, replicated directory service using the LDUP
Replication Update Protocol [PROT].
Each DAP, LDAP or DSP operation successfully performed by a directory
server is subsequently reported to other directory servers with which
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it has an LDUP Replication Agreement [ARCH], 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 changes required to achieve that state.
A directory server will receive replication primitives from its
various agreement partners according to the agreement's Replication
Schedule [ARCH]. 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 primitive is retained for forwarding 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 (URP) 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.
2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, RFC 2119
[RFC2119].
3. Model Extensions
This section describes the extensions to the data model required to
support multi-master replication.
3.1. Universally Unique Identifier
A Unique Identifier [ARCH] is associated with each entry in the
global Directory Information Tree (DIT). This Unique Identifier MUST
be globally unique for all time in the Directory. This can be
achieved, for example, 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
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operational attribute [ARCH].
3.2. Timestamps & Existence
The timestamp for a replication primitive or directory data item is
in the form of a Change Sequence Number (CSN) [ARCH]. The components
of the CSN are, from most significant to least significant, a time in
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 Relative
Distinguished Name (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's 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.
3.3. 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. A single update operation
will decompose into one or more primitives.
Each directory server maintains a replication log, in which are
stored the replication primitives resulting from user updates
performed locally and the replication primitives received from other
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directory servers during replication sessions. 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.
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.
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 RDN
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 RDN 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, desc, value) primitive is used to
describe the addition of a single attribute value to an entry. The
desc argument is an AttributeDescription containing the attribute
type of the value and zero, one or more attribute options. The value
argument contains the attribute value.
The p-remove-attribute-value(uid, csn, desc, value) primitive is used
to describe the removal of a single attribute value from an entry.
The desc argument is an AttributeDescription containing the attribute
type of the value and zero, one or more attribute options. The value
argument contains the attribute value.
The p-remove-attribute(uid, csn, desc) primitive is used to describe
the removal of all values of an attribute with specific attribute
options from an entry. The desc argument is an AttributeDescription
containing the attribute type of the removed attribute with zero, one
or more attribute options.
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These primitives reflect the intended final state of an update
operation rather than the specific changes required to achieve that
state.
3.4. 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 [ARCH] and the orphaned
entry becomes a subordinate of the glue superior entry (see Section
4.3.2). 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 position 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.
4. 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.
4.1. 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, create zero, one or more deletion
records referencing the entry or its contents, and put one or more
replication primitives into the replication log in preparation for
sending during subsequent replication sessions. The CSNs, deletion
records and replication primitives generated from an operation MUST
be atomic with that operation. That is, either the operation
succeeds, CSNs are revised, deletion records are stored and
replication primitives are added to the replication log, or the
operation fails, no CSNs are revised, no deletion records are stored
and no replication primitives are added to the replication log. In
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all cases, all current error conditions (i.e., reasons for rejecting
an LDAP, DAP or DSP update operation) remain.
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
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 [ARCH] 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,
deletion records and replication primitives 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 (DNs). Appropriate
CSNs, deletion records and replication primitives for these changes
MUST also be generated.
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A detailed description of the replication processing for these other
types of update is beyond the scope of this document.
4.1.1. Add Entry
The LDAP Add operation [LDAPOP] or DAP addEntry operation [X511] is
used to add a leaf entry to the DIT. A successful request will
generate a CSN for the added 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 of the added entry are set
to this same value. A successful request will also generate and add
to the replication log, a p-add-entry primitive, and a
p-add-attribute-value primitive for each of the non-distinguished
attribute values of the added entry. There are no separate
p-add-attribute-value primitives generated for the distinguished
values of the entry. The generated primitives use the CSN of the
added entry.
The applicable attribute values include any operational attribute
values automatically generated by the directory server, e.g., for
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.
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 RDN of the
created entry except that the value of the entryUUID attribute, if
distinguished, is omitted from the rdn argument.
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.
4.1.2. Remove Entry
The LDAP Delete operation [LDAPOP] or DAP removeEntry operation
[X511] is used to remove a leaf entry from the DIT. If the request
succeeds then an entry deletion record containing the Unique
Identifier of the removed entry is stored and a p-remove-entry
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primitive is generated and added to the replication log. The
primitive uses the same arguments as the entry deletion record.
The CSN for the entry deletion record MUST be generated such that it
is greater than the entry CSN of the removed entry.
4.1.3. Modify Entry
The LDAP Modify operation (ModifyRequest) [LDAPOP] 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, zero, one
or more value or attribute deletion records are stored, and zero, one
or more p-add-attribute-value, p-remove-attribute-value or
p-remove-attribute primitives are generated and added to the
replication log.
As the sequence of modifications in the modify operation are applied
in order, the primitives they generate are assigned CSNs with
strictly increasing modification numbers. The modification numbers
need not be consecutive.
The modifications described by the modification argument of the LDAP
ModifyRequest generate replication primitives as follows:
1) The add alternative generates a p-add-attribute-value primitive,
including any attribute options, for each of the added attribute
values
2) The delete alternative with no listed values generates a
p-remove-attribute primitive for the removed attribute type,
including any attribute options.
3) The delete alternative with listed values generates a
p-remove-attribute-value primitive, including any attribute
options, for each of the removed values.
4) The replace alternative first generates a p-remove-attribute
primitive for the removed attribute type, including any attribute
options. A p-add-attribute-value primitive is then generated,
including any attribute options, for each of the added values.
The replace alternative with no attribute values generates only
the p-remove-attribute primitive.
For cases 2) and 4), it is not necessary to generate a
p-remove-attribute-value primitive for each of the values actually
removed because the p-remove-attribute primitive implicitly includes
the effects of any such p-remove-attribute-value primitives (it
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applies to all possible values).
The modifications described by the changes argument of the X.500
modifyEntry operation generate replication primitives as follows:
5) The addAttribute and addValues alternatives generate a
p-add-attribute-value primitive for 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.
6) The removeAttribute alternative generates a p-remove-attribute
primitive for the removed attribute type. It is not necessary to
generate a p-remove-attribute-value primitive for each of the
values actually removed because the p-remove-attribute primitive
implicitly includes the effects of any such
p-remove-attribute-value primitives (it applies to all possible
values).
7) The removeValues alternative generates a p-remove-attribute-value
primitive for each of the removed values.
8) The alterValues alternative first generates a
p-remove-attribute-value primitive for each of the old values.
Secondly, a p-add-attribute-value primitive is generated for each
of the new values.
9) The resetValues alternative generates a p-remove-attribute-value
primitive for each value actually removed.
The following additional actions apply to each of the cases 1) to 9)
above.
a) Each generated primitive is added to the replication log.
b) Each time a p-remove-attribute-value primitive is generated a
value deletion record with the same arguments is stored.
c) Each time a p-remove-attribute primitive is generated an attribute
deletion record with the same arguments is stored.
d) Each time a p-add-attribute-value primitive is generated the CSN
from the primitive is associated with the corresponding value
added to the entry.
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
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attribute values, deletion records are stored for operational
attribute values that are removed, and in both cases appropriate
replication primitives are generated and added to the replication
log. 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, and
p-remove-attribute and p-remove-attribute-value primitives are never
generated for the entryUUID attribute type.
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.
Whenever a new value is added to the entry contents any value
deletion record for the same entry, AttributeDescription and
attribute value MAY be discarded.
4.1.4. Modify DN
The LDAP Modify DN operation [LDAPOP] and DAP modifyDN operation
[X511] are used to change the RDN of an entry and/or to move an entry
to a new superior in the DIT.
If the entry is successfully moved to a new superior in the DIT then
the CSN on the entry's superior reference is replaced and a
p-move-entry primitive is generated and added to the replication log.
The CSN for this primitive is the new CSN on the entry's superior
reference and the superior argument contains the Unique Identifier of
the new immediate superior entry.
If the entry's RDN is successfully changed then the CSN on the
entry's RDN is replaced and a p-rename-entry primitive is generated
and added to the replication log. The CSN for this primitive is the
new CSN on the entry's RDN and the rdn argument contains the new RDN
of the entry. A p-remove-attribute-value primitive is generated and
added to the replication log, and a value deletion record with the
same arguments 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
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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 or a
p-remove-attribute-value primitive.
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
p-remove-attribute-value primitives MUST be greater than the CSNs on
the attribute values removed.
4.2. Sending Replication Primitives
Each time a replication session is invoked, the supplier directory
server 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 the replication log and sends those
primitives that are within the scope of the Replication Agreement
with the consumer, and which have a CSN that is greater than the CSN
for the corresponding identified replica in the consumer's Update
Vector. Replication primitives that apply to entries or entry
contents which are outside the scope of the Replication Agreement
MUST NOT be sent.
The consumer's Update Vector has a CSN for each replica of the
Replication Context [ARCH]. Each CSN held by the supplier contains a
Replica Identifier. When a CSN from a replication primitive held by
the supplier is compared to the consumer's Update Vector it is
compared to the single CSN in the consumer's Update Vector that has
the same Replica Identifier as the CSN from the replication
primitive.
4.3. 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
behaviour an LDUP implementation MUST exhibit externally.
Alternative equivalent processing logic is permitted.
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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 RDN, E.dn
refers to the entry's DN, and E.superior refers to the Unique
Identifier of the entry's immediate superior in the DIT.
4.3.1. 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, AttributeDescription 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
AttributeDescription, 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
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
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same internal structures for both.
4.3.2. 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 [ARCH] 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.
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).
4.3.3. 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 primitive 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 a corrective change. The
AddToLog procedure is used to add a replication primitive for the
corrective change to the replication log.
As is the case for CSNs generated from LDAP, DAP or DSP operations,
the CSN for the corrective change is typically generated from the
current clock time of the directory server. The conditions imposed
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
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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.
The AddToLog procedure adds the replication primitive described by
its argument to the replication log.
4.3.4. Comparison of Attribute Descriptions and Values
Two AttributeDescription arguments are equal if they have the same
attribute type and the same set of subtyping attribute options.
Attribute options that specify a transfer encoding (e.g., ";binary")
are ignored in the comparison of AttributeDescription arguments. An
attribute type that is a subtype of another attribute type in an
attribute hierarchy as defined in [X501] is treated as an unrelated
and distinct type by the procedures in this document.
For example, "cn" and "cn;binary" are equal, "cn" and "cn;lang-en"
are not equal, and "cn" and "name" are not equal.
In some procedures an AttributeDescription from a replication
primitive or deletion record is compared to the attribute type from
an AttributeTypeAndValue. In these cases, the two arguments are
equal if and only if the attribute types are the same and the
AttributeDescription contains no subtyping attribute options.
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 stored value is refreshed,
the stored value itself is also refreshed using the value from the
primitive, if the stored value and primitive value are not identical.
For the purposes of the procedures described in this document, two
values are considered identical if they compare TRUE according to the
allComponentsMatch matching rule [CMR]. The purpose of refreshing
stored values is so that all directory servers converge to the exact
same abstract value. Each server is, of course, free to represent
the value using any transfer encoding defined for the attribute's
syntax.
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
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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 stored value that is replaced by the value from a primitive retains
its distinguished or non-distinguished status. This includes
replaced values of single-valued attribute types.
Compared values for an attribute type that does not have an equality
matching rule are all considered to be not equal. In effect, the
equality operator is unconditionally false when used to compare
values of an attribute type without an equality matching rule. This
means that stored values and values in a primitive are never
considered equal for such an attribute type, so duplicate values with
different CSNs could accumulate in the attribute and the
p-remove-attribute-value primitive will be ineffectual. However, the
only permitted changes to an attribute without an equality matching
rule are to add, remove or replace the entire attribute. Therefore,
except when values are first added to an attribute, there will be a
p-remove-attribute primitive immediately prior to the
p-add-attribute-value primitives for the added values, and only the
values of the latest (by CSN) add or replace will appear in the
attribute. It is possible that values could be simultaneously
initially added to the previously non-existent attribute at two
separate replicas. If the clients choose to add the attribute using
the add alternative of the modification argument of the LDAP
ModifyRequest then both sets of values (potentially including
duplicates) will eventually appear in the attribute. If the clients
choose to add the attribute using the replace alternative of the
modification argument then only the values from the client update
with the latest CSN will eventually appear in the attribute.
Note that values of an attribute type without an equality matching
rule cannot be distinguished values.
4.3.5. 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
the entries by adding each conflicting entry's Unique Identifier to
its RDN (i.e., making the value of its entryUUID attribute
distinguished).
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The procedure CheckUniqueness is called in each circumstance where
the RDN 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 DN, it also potentially removes a previous conflict on the
old DN. 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 E.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
updateable replicas. Read-only replicas MUST remove the
distinguished value. The function ProtectDistinguished() returns
true for an updateable part of the DIT in a directory server that
implements this option, and false otherwise. Directory servers
exercising this option MUST generate a p-rename-entry primitive (as
shown in the procedures) so that other directory servers are
guaranteed to also reassert the distinguished value. Directory
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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 RDN 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 P, 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)
{
IF ProtectDistinguished()
C := P.csn
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 no attribute deletion record (uid, csn, desc) exists
where (uid = P.uid AND desc = N.type AND csn > P.csn)
AND no value deletion record (uid, csn, desc, value) exists
where (uid = P.uid AND desc = 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
}
ELSE IF ProtectDistinguished()
{
FOREACH attribute deletion record (uid, csn, desc)
where (uid = P.uid AND desc = N.type)
IF csn > C
C := csn
FOREACH value deletion record (uid, csn, desc, value)
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where (uid = P.uid AND desc = N.type AND
value = N.value)
IF csn > C
C := csn
}
E.rdn.csn := P.csn
IF ProtectDistinguished() AND C > P.csn
{
csn := GenerateNextCSN(C)
AddToLog(p-rename-entry(P.uid, csn, P.rdn))
RenameEntry(E, p-rename-entry(P.uid, csn, P.rdn))
}
}
4.3.6. Processing Add Attribute Value Primitive
This section details the algorithm for processing the
p-add-attribute-value (P.uid, P.csn, P.desc, P.value) primitive,
which describes the addition of a single attribute value. If the
attribute type of P.desc is the entryUUID attribute type then the
primitive MUST be rejected.
IF no value deletion record (uid, csn, desc, value) exists where
(uid = P.uid AND desc = P.desc
AND value = P.value AND csn > P.csn)
AND no attribute deletion record (uid, csn, desc) exists where
(uid = P.uid and desc = P.desc 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 attribute P.desc
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.desc is a single-valued attribute
CheckUniqueness(E, E.superior, R)
}
}
ELSE
{
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V := P.value
Add V to E as a non-distinguished attribute value
V.csn := P.csn
}
}
4.3.7. Processing Remove Attribute Value Primitive
This section details the algorithm for processing the
p-remove-attribute-value (P.uid, P.csn, P.desc, P.value) primitive,
which describes the removal of a single attribute value. If the
attribute type of P.desc is the entryUUID attribute type then the
primitive MUST be rejected.
IF no value deletion record (uid, csn, desc, value) exists
where (uid = P.uid AND desc = P.desc AND
value = P.value AND csn >= P.csn)
AND
no attribute deletion record (uid, csn, desc) exists
where (uid = P.uid AND desc = P.desc 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 attribute P.desc
where V = P.value, exists in E
{
IF P.csn > V.csn
IF V is distinguished
IF ProtectDistinguished()
{
csn := GenerateNextCSN(P.csn)
AddToLog(p-rename-entry(P.uid, csn, E.rdn))
RenameEntry(E,
p-rename-entry(P.uid, csn, E.rdn))
}
ELSE
{
R := E.rdn
remove value V
CheckUniqueness(E, E.superior, R)
StoreValueDeletion
(P.uid, P.desc, P.value, P.csn)
}
ELSE
{
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remove value V
StoreValueDeletion
(P.uid, P.desc, P.value, P.csn)
}
}
ELSE
StoreValueDeletion (P.uid, P.desc, P.value, P.csn)
}
ELSE
StoreValueDeletion (P.uid, P.desc, 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.
4.3.8. Processing Remove Attribute Primitive
This section details the algorithm for processing the
p-remove-attribute (P.uid, P.csn, P.desc) primitive, which describes
the removal of all attribute values of attribute P.desc. If the
attribute type of P.desc is the entryUUID attribute type then the
primitive MUST be rejected.
IF no attribute deletion record (uid, csn, desc) exists
where (uid = P.uid AND desc = P.desc 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 attribute P.desc
in E (if any)
IF P.csn > V.csn
IF V is distinguished
IF ProtectDistinguished()
{
csn := GenerateNextCSN(P.csn)
AddToLog(p-rename-entry(P.uid, csn, E.rdn))
RenameEntry(E,
p-rename-entry(P.uid, csn, E.rdn))
}
ELSE
{
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R := E.rdn
remove value V
CheckUniqueness(E, E.superior, R)
}
ELSE
remove value V
StoreAttributeDeletion (P.uid, P.desc, P.csn)
}
}
ELSE
StoreAttributeDeletion (P.uid, P.desc, P.csn)
4.3.9. Processing Add Entry Primitive
This section details the algorithm for processing the p-add-entry
(P.uid, P.csn, P.superior, P.rdn) 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, A, in E, except entryUUID
FOREACH attribute value, V, of A
IF V.csn < P.csn
remove value V
CheckUniqueness(E, S, R)
process P according to
p-rename-entry(P.uid, P.csn, P.rdn)
process P according to
p-move-entry(P.uid, P.csn, P.superior)
}
}
ELSE
{
create entry E
E.csn := P.csn
E.uid := P.uid
E.uid.csn := P.csn
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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)
}
4.3.10. 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
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, A, in E, except entryUUID
FOREACH attribute value, V, of A
IF V.csn < P.csn
remove value V
CheckUniqueness(E, S, R)
}
ELSE
remove entry E
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StoreEntryDeletion (P.uid, P.csn)
}
}
ELSE
StoreEntryDeletion (P.uid, P.csn)
4.3.11. Processing Move Entry Primitive
This section details the algorithm for processing the p-move-entry
(P.uid, P.csn, P.superior) 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, the entry being moved
becomes a subordinate of a glue entry subordinate to Lost & Found.
If the new superior specified by the primitive is a direct or
indirect subordinate of the entry being moved, the entry is moved to
Lost & 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)
AddToLog(p-move-entry
(P.uid, E.superior.csn, LOST_AND_FOUND))
}
CheckUniqueness(E, O, R)
}
}
4.3.12. Processing Rename Entry Primitive
This section details the algorithm for processing the p-rename-entry
(P.uid, P.csn, P.rdn) primitive, which describes a change to the RDN
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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
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, csn, desc, value)
exists where (uid = P.uid AND desc = N.type AND
value = N.value AND csn > P.csn)
AND
no attribute deletion record (uid, csn, desc)
exists where (uid = P.uid AND desc = N.type AND
csn > P.csn)
{
V := N.value
Add V to E
V.csn := P.csn
}
}
}
}
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5. 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
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 Replication
Update 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
DN. 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 Unique
Identifier to only one of a pair of entries ending up with the same
name. The Update Reconciliation Procedures require both entries to
have their Unique Identifier 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.
6. Acknowledgments
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
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architecture group for their input into the refinement of the design.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[LDAPOP] M. Wahl, M., Kille, S. and T. Howes, "Lightweight
Directory Access Protocol (v3)", RFC 2251, December 1997.
[LDAP] Hodges, J. and R. Morgan, "Lightweight Directory Access
Protocol (v3): Technical Specification", RFC 3377,
September 2002.
[ARCH] Merrells, J., Srinivasan, U. and E. Reed, "LDAP
Replication Architecture", draft-ietf-ldup-model-xx.txt, a
work in progress, October 2003.
[PROT] McMeeking, J., "The LDUP Replication Update Protocol",
draft-ietf-ldup-protocol-xx.txt, a work in progress, March
2003.
[CMR] Legg, S., "LDAP & X.500 Component Matching Rules",
draft-legg-ldapext-component-matching-xx.txt, a work in
progress, June 2003.
[X501] ITU-T Recommendation X.501 (08/97) | ISO/IEC 9594-2:1998,
Information technology - Open Systems Interconnection -
The Directory: Models
[X511] ITU-T Recommendation X.511 (08/97) | ISO/IEC 9594-3:1998,
Information technology - Open Systems Interconnection -
The Directory: Abstract service definition
7.2. Informative References
[X500] ITU-T Recommendation X.500 (08/97) | ISO/IEC 9594-1:1998,
Information technology - Open Systems Interconnection -
The Directory: Overview of concepts, models and services
8. 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
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might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by 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.
9. Authors' Addresses
Steven Legg
Adacel Technologies Ltd.
250 Bay Street
Brighton, Victoria 3186
AUSTRALIA
Phone: +61 3 8530 7710
Fax: +61 3 8530 7888
EMail: steven.legg@adacel.com.au
Alison Payne
Telstra
19/242 Exhibition Street
Melbourne, Victoria 3000
AUSTRALIA
Phone: +61 3 9634 3947
EMail: alison.payne@team.telstra.com
10. Full Copyright Statement
Copyright (C) The Internet Society (2003). 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
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INTERNET-DRAFT Update Reconciliation Procedures October 24, 2003
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assignees.
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.
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