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Versions: 00 01                                                         
IETF ASID Working Group                                      Sanjay Jain
Internet Draft                                        Oracle Corporation
                                                       Uppili Srinivasan
                                                      Oracle Corporation
                                                             Gordon Good
                                     Netscape Communications Corporation
                                                               July 1997

                     Schema for Replication Information

I. Status of this Memo

This document is an Internet-Draft.  Internet-Drafts are working docume-
nts of the Internet Engineering Task Force (IETF), its areas, and its
working groups.  Note that other groups may also distribute working doc-
uments 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.''

To learn the current status of any Internet-Draft, please check the
``1id-abstracts.txt'' listing contained in the Internet- Drafts Shadow
Directories on ds.internic.net (US East Coast), nic.nordu.net (Europe),
ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim).

Distribution of this memo is unlimited. Editorial comments should be
sent to skjain@us.oracle.com. Technical discussion should take place on
the IETF ASID mailing list (ietf-asid@umich.edu).

This Internet Draft expires February 1st, 1998.

II. Abstract

This document defines a new attribute syntax and an operational attribu-
te type to store replication agreements within the directory.  In addit-
ion it defines a framework to detect whether an entry is a master or

The replication agreement structure defined here includes a placeholder
to specify the replication protocol associated with an agreement.  This
document itself does not define any replication protocol.  Replication
protocols and replication agreements are seen as orthogonal issues.

III. Definition Of Terms

Consumer          An LDAP server which receives replica updates.

Master            An LDAP server holding a master copy of an entry.

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Master Entry      The copy of an entry where all direct LDAP
                  modifications are performed. In a multi-master
                  environment, there could exist multiple master copies
                  for an entry.

Replication Agreement
                   An agreement between a supplier and a consumer
                   regarding replication of a full/partial naming
                   context. The main components of a replication
                   agreement are:
                       . Reference to the supplier
                       . Reference to the consumer
                       . Specification of the directory information to
                         be replicated.
                       . Schedule for updating the replicas.

Replica            A copy of an entry where modifications are allowed
                   only through replication updates. I.e. direct LDAP
                   modifications are not allowed on a replica of an
                   entry. A replica will typically issue a referral to a
                   supplier if a client attempts an update operation.

Supplier           An LDAP server which supplies replica updates.

IV. Introduction

The broadening of interest in LDAP directories beyond their use as front
ends to X.500 and proliferation of stand alone LDAP implementations has
created a need to define standards that would facilitate deployment of
distributed and replicated directory involving multi-vendor implementat-

The "referrals" draft (Ref[4]) defines ways to create and use knowledge
references.  It lays the foundation for distributed directories by defi-
ning mechanisms that can be used to "glue" the parts of directory infor-
mation tree (DIT) together.  The framework defined here is a step in the
direction to standardize the directory replication process.  Together,
these proposals establish the infrastructure to distribute and replicate
the directory information.

This document defines a new attribute syntax and an operational attribu-
te type to store replication agreements within the directory.  The attr-
ibute is a root DSE attribute.

A replication agreement is established between a consumer and a
supplier.  Establishment of an agreement is expected to precede any rep-
lication. An agreement specifies, among other things, the replication
area and the update frequency.  It also identifies the replication prot-
ocol and the parameters that are specific to that protocol.

While it is desirable for a single LDAP replication protocol to be defi-
ned and standardized, this draft accommodates the possibility of variat-

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ions and versions to be specified in the agreement through a replication
protocol identifier (oid) and associated parameters.  Some of the possi-
ble variations include characteristics such as supplier initiated (push)
, consumer initiated (pull) etc.

Proprietary replication protocols already exist and LDAP directories
will be rolled out into these environments.  Replication protocol oids
can be registered for such protocols as well.  The intent is not to pro-
mote proprietary protocols, but to facilitate painless roll-out of stan-
dards based implementations within pre-existing directory environments.
It is believed that this accommodation in the replication agreements
would ease adoption of the standards.

V. Replication Agreement Establishment and Usage Model

Creation of a replication agreement would either be initiated by a human
administrator or by a consumer.  Identical copies of an agreement would
exist on the supplier and the consumer.  A replication agreement has to
exist before replication can take place.  The servers will enforce  rep-
lication exchanges per the terms of an agreement.

The replication agreements should be added, deleted or modified using
LDAP "modify" operation on the root DSE. The server should check the
consistency and acceptability of an agreement  based on local administr-
ative policies. An agreement is considered to be in effect when both the
supplier and consumer have identical copies of the agreement in their
root DSEs. Two agreements are deemed identical when they match according
to the replBindingMatch matching rule defined in this document.

It is possible to achieve the effect of the above administrative actions
(creation of replication agreements) through protocol exchanges between
servers, equivalent of the X.500 DOP.  Such protocols may get standardi-
zed in the future.  This draft does not define such a protocol.  It only
defines a standard for the structure and semantics of resulting replica-
tion agreement information.

A supplier can maintain different replication agreements with different
consumer servers for a single naming context.  It is also possible for a
consumer to have multiple agreements with one or more suppliers for same
or different naming contexts.

VI. Attribute Definitions

A. replAgreement

( < ora_onldap_replica_oid1> NAME 'replAgreement' DESC 'describes a rep-
lication agreement between 2 servers' EQUALITY replBindingMatch SYNTAX
'replBinding' USAGE distributedOperation )

'replAgreement' attribute stores the information about a replication
agreement reached between two servers (consumer and supplier). It is a
multi-valued attribute.  It is a root DSE attribute.

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A replication agreement specifies, among other details, the user entries
and attributes to be replicated from the supplier LDAP server to the
consumer LDAP server.  Normally, the administrative information (Schema,
ACLs etc.), associated with the selected user entries, would also be re-
plicated along with the user entries.

B. supportedReplProtocols

( < ora_onldap_replica_oid2> NAME 'supportedReplProtocols' DESC 'Stores
the OIDS of the supported replication protocols" SYNTAX 'OID' USAGE dis-

'supportedReplProtocols' attribute stores the OIDS of the supported rep-
lication protocols.  It is a multi-valued attribute.   It is a root DSE

C. myRef

( < ora_onldap_replica_oid3> NAME 'myRef' DESC 'LDAP URI without any DN
part. Reference to self.' EQUALITY caseExactIA5Match SYNTAX 'IA5String'

'myRef' is a root DSE attribute .  It is a single valued attribute.  It
contains the LDAP reference (without the DN part) to the server itself.

D. masterRef

( < ora_onldap_replica_oid4> NAME 'masterRef' DESC 'LDAP URI without any
DN part' EQUALITY caseExactIA5Match SYNTAX 'IA5String' USAGE dSAOperati-
on )

'masterRef' is an operational attribute for every entry (except the DSE
root entry) in the LDAP directory.  It is a multi-valued attribute.  The
values of this attribute refer to the servers which master this entry.

By comparing 'myRef' attribute value and the 'masterRef' attribute valu-
es for an entry,  a server and a directory user can determine whether
the particular copy is a master copy or a replica. When an LDAP client
tries a modify operation on a replica then the server by looking at the
'masterRef' attribute can return a referral to the master LDAP server.

VII. replBinding Syntax

( < ora_onldap_replica_oid5> DESC 'Replication Agreement Syntax' )

Attribute values with 'replBinding' syntax are written according to
following BNF:

<replBinding>     ::= "("
                      "AGREEMENTID"            <NumericString>
                      "NAMINGCONTEXT"          <DirectoryString>
                      "SUPPLIER_REFERENCE"     <IA5STRING>

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                      "CONSUMER_REFERENCE"     <IA5STRING>
                      ["SUPPLIER_IDENTITY"     <DirectoryString>]
                      ["CONSUMER_IDENTITY"     <DirectoryString>]
                      ["BASEDN"                <DirectoryString>]
                      ["FILTER"                <DirectoryString>]
                      ["SCOPE"                 <0|1|2>]
                      ["ATTRIBUTE_SELECTION    <AttributeSelectionList>]
                      "UPDATE_SCHEDULE"        <UpdateSchedule>
                      ["REPLICATION_PROTOCOL"  <ReplProtocol>]

AGREEMENTID is local to the supplier. The server must verify that the
combination of AGREEMENTID and SUPPLIER_REFERENCE is unique.  Otherwise
the LDAP "modify" operation to enter an agreement should fail with an

NAMINGCONTEXT is the DN of the root of the naming context with which the
replication agreement is associated.

SUPPLIER_REFERENCE is an LDAP URI [6] (without the DN part) to the supp-

CONSUMER_REFERENCE is an LDAP URI [6] (without the DN part) to the cons-

SUPPLIER_IDENTITY is the identity which the supplier must use to authen-
ticate itself to the consumer for replica update exchanges.  This param-
eter would be most useful in the push model.

CONSUMER_IDENTITY is the identity which the consumer must use to authen-
ticate itself to the supplier for replica update exchanges.  This param-
eter would be most useful in the pull model.

Note: For security reasons, bind credentials MUST NOT be stored in the
replication agreement attribute.

SUPPLIER_IDENTITY, CONSUMER_IDENTITY and associated credentials may not
actually exist in the directory.  When binding for sending/receiving
replication updates,  the target server would recognize the
SUPPLIER_IDENTITY /CONSUMER_IDENTITY and adjust its semantics appropria-

SUPPLIER_IDENTITY and CONSUMER_IDENTITY are both optional parameters of
a replication agreement.

BASEDN, FILTER and SCOPE have same semantics as in a LDAP search request
. Default value for BASEDN is the root of the naming context. Default
value for SCOPE is 2 (whole subtree).

Through ATTRIBUTE_SELECTION one can specify the list of attributes of a
particular object class which should be included/excluded in the replic-

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AttributeSelectionList       ::=     <AttributeSelection> |

AttributeSelectionList       ::=     <AttributeSelectionList> '$'
                                     <AttributeSelection> |

AttributeSelection           ::=     "(" [<ldapFilter>]

<ldap-Filter>                ::=     An LDAP filter as described in [5]

If the filter is absent, then the attribute list selection applies to
all replicated entries.

<AttributeSelectionSpec>     ::=      <IncludeList> |

<IncludeList>                ::=      "INCLUDE"  <AttributeList>

<ExcludeList>                ::=      "EXCLUDE"  <AttributeList>
<AttributeList>              ::=      <AttributeType> |
                                      '(' <AttributeList> ')'

 <AttributeList>             ::=      <AttributeList> '$'
                                      <AttributeType> |

UPDATE_SCHEDULE specifies the schedule for updating the replica.

<UpdateSchedule>             ::=       <ScheduleList>

<ScheduleList>               ::=       <ScheduleItem> |

<ScheduleList>               ::=       < ScheduleList> '$'
                                       <ScheduleItem> |

<ScheduleItem>               ::=       <minute> <hour> <day_of_month>
                                       <month_of_year> <day_of_week>

<ScheduleItem> has UNIX crontab style syntax and semantics.  The schedu-
le is specified using five fields separated by spaces.  The fields are
integer patterns that specify the following:

            minute (0-59)
            hour (0-23)
            day of the month (1-31)
            month of the year (1-12)
            day of the week (0-6 with 0=Sunday)

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Each of these five patterns may be either an asterisk (meaning all legal
values) or a list of elements separated by commas.  An element is either
a number or two numbers separated by a minus sign (meaning an inclusive
range).  Note that the specification of days may be made by two fields
(day of the month and day of the week).  Both are adhered to if specifi-
ed as a list of elements.  Times are always interpreted as Greenwich
Mean Time.


1.Always keep replicas updated immediately:
            UPDATE_SCHEDULE  * * * * *

2. Update replicas at 1 am every day:
            UPDATE_SCHEDULE  * 1 * * *

3. Update replicas every hour between 8am and 5 pm on weekdays, and at
1am on weekends:
            UPDATE_SCHEDULE  (* 8-17 * * 1-5 $ * 1 * * 0, 6)
4. Update replicas every 30 minutes:
            UPDATE_SCHEDULE  0,30 * * * *

5. Update replicas on first and fifteenth of each month as well as on
every Monday (Example of using two fields for the specification of days)
            UPDATE_SCHEDULE  * * 1,15 * 1

REPLICATION_PROTOCOL is the protocol to be used to exchange replica upd-

ReplProtocol       ::=        "("
                                "OID"                <oid>
                                ["PROTOCOL_SPECIFIC" <DirectoryString>]

VIII. replBindingMatch definition

( < ora_onldap_shadow_oid6> NAME ' replBindingMatch' SYNTAX 'replBinding
' )

Two replication agreements are equal if and only if the AGREEMENTID and
SUPPLIER_REFERENCE match for equality, as determined by the NumericStri-
ngMatch and CaseExactIA5Match matching rules defined in X.520 (1993).

IX. Relationship To X.500 Shadowing Agreements

LDAP replication agreements are independent of X.500 shadowing agreemen-
ts, although terminology has been borrowed from X.500 and, in general,
the meaning of these terms is equivalent.

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It is anticipated that LDAP servers which front-end and X.500 server
will advertise the fact that they support X.500 DISP by placing in the
'supportedReplProtocols' attribute of the root DSE the OID which repres-
ents X.500 DISP (this OID has not been defined at this time).

X. Examples

Following are examples of attribute values for replAgreement attribute:

1.  This is an example of a replication agreement between two cooperati-
ng organizations, "ABC Inc." and "XYZ AG".  ABC's LDAP server runs on
the host "ldap.abc.com" while XYZ's LDAP server runs on the host
"ldap.mch.xyz.de".  The objective is for both organizations to have a
copy of the subtree "ou=Sales, o=ABC, c=US". The server "ldap.mch.xyz.de
", then, is a consumer for the subtree "ou=Sales, o=ABC, c=US", which is
part of the "c=US" naming context held by the supplier. The server "ldap
.abc.com" is the supplier for that subtree. The replica is updated by
the supplier (since only supplier identity isthere in the agreement)
continuously, using the replication protocol identified by the OID '1.2.
3'.  When connecting to the consumer, the supplier will bind as "cn=rep-
lAdmin,dc=replTree,dc=ldap,dc=mch,dc=xyz,dc=de".  The following replAgr-
eement attribute describes this agreement:

            'ldap://ldap.abc.com' CONSUMER_REFERENCE
            'ldap://ldap.mch.xyz.de' SUPPLIER_IDENTITY
            BASEDN 'ou=Sales, o=ABC, c=US' SCOPE 2 UPDATE_SCHEDULE * * *
            * * REPLICATION_PROTOCOL 1.2.3 )

2. This example is a refinement of the above agreement.  In addition to
the parameters described above, entries are only replicated if they
match the filter "(objetclass=person)".  Furthermore, only the attribut-
es cn, sn, telephoneNumber, and mail are replicated, and replication may
only occur between 1 am and 2 am GMT.

            'ldap://ldap.abc.com' CONSUMER_REFERENCE
            'ldap://ldap.mch.xyz.de' SUPPLIER_IDENTITY
            BASEDN 'ou=Sales, o=ABC, c=US' FILTER '(objectlass=person)'
            ATTRIBUTE_SELECTION '(objectclass=*) INCLUDE cn $ sn $
            telephoneNumber $ mail)' SCOPE 2 UPDATE_SCHEDULE * 1-2 * * *
            REPLICATION_PROTOCOL 1.2.3 )

XI. Security Considerations

This document defines a mechanism that can be used to describe the repl-
ication agreements between suppliers and consumers.  The replication pr-
ocess would rely on this information to schedule and control the replica
updates.  Hence the replication agreement attribute should be protected
from unauthorized access.  If the identity of consumers and/or the natu-
re of their subscription to directory information is not public informa-

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tion, the relevant directory information should be protected from unaut-
horized access as well.

Servers will generally need to persistently store authentication creden-
tials used to bind to consumer or supplier servers when performing repl-
ica updates.  These credentials MUST be adequately protected from unaut-
horized access.

XII. References

[1]  Good, G., "The LDAP Data Interchange Format (LDIF) - Technical Spe-
cification", INTERNET-DRAFT draft-ietf-asid-ldif-01.txt, Netscape Commu-
nications Corp.,

[2]  Good, G., "Definition of an Object Class to Hold LDAP Change Recor-
ds", INTERNET-DRAFT draft-ietf-asid-changelog-01.txt, Netscape Communic-
ations Corp.,

[3]  C. Weider, J. Strassner, "LDAP Multi-master Replication Protocol",
INTERNET-DRAFT draft-ietf-asid-ldap-mult-mast-rep-00.txt, Microsoft Cor-
poration, Cisco Systems Corporation,

[4]  T. Howes, M. Wahl, "Referrals and Knowledge References in LDAP Dir-
ectories", INTERNET-DRAFT draft-ietf-asid-ldapv3-referral-00.txt,
Netscape Communications Corp., Critical-Angle, Inc., <URL:ftp://ietf.org

[5]  T. Howes, "The String Representation of LDAP Search Filters",
INTERNET-DRAFT draft-ietf-asid-ldapv3-filter-02.txt, Netscape Communica-
tions Corp.,

[6] T. Howes, M. Smith, "The LDAP URL Format", INTERNET-DRAFT
draft-ietf-asid-ldapv3-url-03.txt, Netscape Communications Corp.,

XIII. Authors' Addresses

Sanjay Jain
Oracle Corporation
200 Oracle Parkway
Box 659210
Redwood Shores, CA 94065
Phone: +1 415-506-9325
E-mail: skjain@us.oracle.com

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Uppili Srinivasan
Oracle Corporation
200 Oracle Parkway
Box 659210
Redwood Shores, CA 94065
Phone: +1 415-506-3039
E-mail: usriniva@us.oracle.com

Gordon Good
Netscape Communications Corporation
501 E. Middlefield Rd.
Mail Stop MV068
Mountain View, CA 94043
Phone: +1 415 937 3825
E-mail: ggood@netscape.com

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