ASID Working Group                                            Y. Yaacovi

INTERNET-DRAFT                                                 Microsoft
                                                                 M. Wahl
                                                     Critical Angle Inc.
                                                               K. Settle
                                                             T. Genovese

Expires in six months from                              10 September                               14 October 1996
Intended Category: Standards Track

                   Lightweight Directory Access Protocol:
                  Extensions for Dynamic Directory Services

1. Status of this Memo

   This document is an Internet-Draft.  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."

   To learn the current status of any Internet-Draft, please check the
   "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow
   Directories on (US East Coast),
   (Europe), (US West Coast), or (Pacific Rim).

2.  Abstract

   This document defines the requirements for dynamic directory services
   and specifies the format of request and response extended operations
   for supporting client-server interoperation in a dynamic directories

   The Lightweight Directory Access Protocol (LDAP) [1] supports
   lightweight access to static directory services, allowing relatively
   fast search and update access.  Static directory services store
   information about people that persists in its accuracy and value over
   a long period of time.

   Dynamic directory services are different in that they store
   information about people that only persists in its accuracy and value
   while people are online.  Though the protocol operations and
   attributes used by dynamic directory services are similar to the ones
   used for static directory services, clients that are bound to a
   dynamic directory service need to periodically refresh their presence
   at the server to keep directory entries from getting stale in the
   presence of client application crashes.

   In addition, static directories may include dynamic information, in
   the form of dynamic attributes in an otherwise static entry.  Such
   information needs to be refreshed periodically in the same manner.

   A flow control mechanism from the server is also described that
   allows a server to inform clients how often they should refresh
   their presence.

3. Requirements

   The protocol extensions must allow accessing dynamic directories in a
   standard LDAP manner, to allow clients to access static and dynamic
   directories in the same way.

   By nature of definition, dynamic directories, entries or dynamic attributes are not
   persistent and clients may go away gracefully or not.  The proposed
   extensions must offer a way for a server to tell if entries or
   attributes are still valid, and to do this in a way that will scale
   for a relatively large number of users.  There also must be a
   mechanism for clients to reestablish their entry or attributes with
   the server.

   Finally, to allow clients to broadly use the dynamic extensions, they
   the extensions need to be registered as standard LDAP extended

4. Description of Approach

   The Lightweight Directory Access Protocol (LDAP) [1] permits
   additional operation requests and responses to be added to the
   protocol.  The support for dynamic directories takes advantage of
   these to establish a mechanism to support dynamic directories
   which is fully integrated with LDAP.

   The approach described in this proposal defines dynamic entries and
   dynamic attributes in order to allow implementing directories with
   dynamic information.  An implementation of dynamic directories, must
   be able to support both dynamic directory entries and dynamic

4.1. Dynamic Entries and the dynamicObject object class

   A dynamic entry is an object in the directory tree which has a
   time-to-live associated with it.  This time-to-live is set when the
   entry is created.  The time-to-live is automatically decremented, and
   when it expires the dynamic entry disappears.  By invoking the
   refresh extended operation (defined below) to re-set the time-to-live, a
   client can cause the entry to remain present a while longer.

   A dynamic entry is created by including the objectClass value given
   in section 6 in the list of attributes when adding an entry.  This
   method is subject to standard access control restrictions.

   The extended operation covered here, allows a client to refresh a
   dynamic entry by invoking at intervals refresh operations containing
   that entry's name.  Dynamic entries will be treated the same as
   non-dynamic entries when processing search, compare, add, delete,
   modify and modifydn operations.  However if clients stop sending
   refresh operations for an entry, then the server will automatically
   and without notification remove that entry from the directory.  This
   removal will be treated the same as if the client entry had issued a
delete operation on that entry. been deleted by
   an LDAP protocol operation.

   There is no way to change a static entry into a dynamic one and vice-
   versa.  If the client is using Modify with an objectClass of
   dynamicObject on a static entry, the server must return a service
   error either "objectClassModsProhibited" (if the server does not
   allow objectClass modifications at all) or "objectClassViolation"
   (if the server does allow objectClass modifications in general).

   A dynamic entry may be removed by the client using the delete
   operation.  This operation will be subject to access control

   A non-dynamic entry cannot be added subordinate to a dynamic entry:
   the server must return an appropriate update or service error if this
   is attempted.

5. Protocol Additions

5.1 Refresh Request


4.2. Dynamic Attributes

   A similar concept is a protocol operation sent by a client to tell dynamic attributes.  These attributes behave the server
   same as ordinary user attributes to Search, Compare and Modify
   requests, except that if they time out they disappear from the client is still alive and entry
   in which they are located.  (Unlike the dynamicObject class, the directory
   entry is still accurate itself does not disappear, and
valuable. The client sends non-dynamic attributes are
   unaffected).  Like dynamic entries, a Refresh request periodically based on static entry with dynamic
   attributes must have the
value entryTtl attribute which is described
   in section 6 below.

   Dynamic attributes do not necessarily introduce a new set of
   attributes in the client refresh period (CRP). The server can request that
the client change this value. As long as schema.  Any static attribute in the server receives a Refresh
request within schema can be
   made dynamic by including the timeout period, ;dynamic attribute modifier with the directory entry
   typename.  It is guaranteed allowed to persist on introduce new dynamic attributes which
   are not useful in the server. Clients implementors should be aware that
since static domain.  Such attributes will still require
   including the intervening network between ;dynamic attribute modifier with the client and server is
unreliable, a Refresh request typename to define
   them as dynamic.

   A dynamic attribute may be a subtype of a non-dynamic attribute, ]
   but a non-dynamic attribute must not be a subtype of a dynamic attribute.
   Operational attributes and collective attributes must not be dynamic.
   All dynamic attributes are considered to be user attributes, however
   they are not guaranteed to be present in shadow copies of entries.

   A client may introduce dynamic attributes into an entry by using a
   Modify request to add them, or by including them in the attribute
   list of an Add Request.  If the attribute type is permitted in the entry
   then the dynamic attribute is also permitted.  The client would
   specify that the attribute is dynamic by including the tag ";dynamic"
   with the typename.  Dynamic values may be changed, and the attributes
   removed, by using the Modify request as normal.  If the entry is
   deleted, dynamic attributes disappear immediately along with all the
   non-dynamic.  A ;dynamic modifier on an attribute may not be used in
   a compare request, or in a search request (either in the filter or
   attributes requested for return).  This is in keeping with the
   philosophy that dynamic attributes be indistinguishable from static
   attributes as much as possible.

   The granularity of a dynamic attribute is the entire attribute
   including all values.  Dynamic and static values may not be mixed
   within a single attribute.  For example, suppose an existing static
   entry had an attribute called "ipAddress" with the value "".
   A modification of the entry to add the value "" to the attribute
   "ipAddress;dynamic" would fail with a "constraintViolation" error.

   The addition and modification of dynamic attributes are subject to
   schema and access control restrictions, as with non-dynamic
   attributes.  Thus unless the extensibleObject object class is
   present, generally an object class or content rule must be defined
   to permit those attributes to be present in an entry.  If their presence
   is controlled by an object class, then just as with non-dynamic
   attributes, the object class value must have already been added
   before the attributes are added.  The dynamicObject object class
   described in section 4.1 does not itself permit any particular
   dynamic attributes.

   Dynamic attributes in a particular entry are refreshed using the
   Refresh extended operation.  All of the entry's dynamic attributes
   are refreshed by a single refresh request.  The TTL given in the refresh
   response applies to all of the entry's dynamic attributes.  There is
   no way to refresh particular dynamic attributes within an entry at
   different times, or to have different TTLs apply to different dynamic

   If not refreshed, all dynamic attributes in an entry time out
   simultaneously.  All the attributes which are dynamic with all their
   values disappear atomically, as if the server had done a ModifyEntry
   specifying that all the dynamic types were to be deleted from that
   entry.  The client must not expect any dynamic attributes to be
   present in an entry after the time-to-live for that entry has reached
   zero.  However the attributes may not disappear immediately as
   servers may only process timing out attributes at intervals
   (e.g.  every few minutes).

   Note that if an object class definition references a dynamic
   attribute as a mandatory attribute, the entry will still time out,
   but a schema inconsistency will be present in that entry.
   (The objectClass attribute and its values always remain
   since objectClass is not a dynamic attribute.) Thus it is
   strongly recommended that designers not specify dynamic
   attributes as anything other than optional attributes
   of auxiliary classes.

   Dynamic attributes may be used within dynamic entries (i.e., entries
   containing object class "dynamicObject", defined below), but since
   all of such an entry's attributes are implicitly dynamic, such use
   is superfluous.

5. Protocol Additions

5.1 Refresh Request

   Refresh is a protocol operation sent by a client to tell the server
   that the client is still alive and the dynamic directory entry or the
   dynamic attributes of the entry are still accurate and valuable.  The
   client sends a Refresh request periodically based on the value of the
   client refresh period (CRP).  The server can request that the client
   change this value.  As long as the server receives a Refresh request
   within the timeout period, the directory entry is guaranteed to
   persist on the server.  Clients implementers should be aware that
   since the intervening network between the client and server is
   unreliable, a Refresh request packet may be delayed or lost while in
   transit.  If this occurs, the entry or the dynamic attributes may
   disappear, and the client will need to detect this and re-add the entry.
   entry or the attributes.

   A client may request this operation by transmitting an LDAP PDU
   containing an ExtendedRequest.  An LDAP ExtendedRequest is defined as

         ExtendedRequest ::= [APPLICATION 23] SEQUENCE {
                 requestName             [0] LDAPOID,
                 requestValue            [1] OCTET STRING }

   The requestName field must be set to the string

   The requestValue field will contain as a value the DER-encoding of
   the following ASN.1 data type:

        SEQUENCE {
                entryName  [0] LDAPDN,
                requestTtl [1] INTEGER

   The entryName field is the UTF-8 string representation of the name of
   the dynamic entry or the entry containing dynamic attributes [3].
   This entry must already exist.

   The requestTtl is a time in seconds (between 1 and 31557600) that the
   client requests that the entry or the dynamic attributes exists in
   the directory before it is being automatically removed.  Servers are not
   required to accept this value and might return a different TTL value
   to the client.  Clients must be able to use this server-dictated
   value as their CRP.

5.2 Refresh Response

   If a server implements this extension, then when the request is made
   it will return an LDAP PDU containing an ExtendedResponse.  An LDAP
   ExtendedResponse is defined as follows:

        ExtendedResponse ::= [APPLICATION 24] SEQUENCE {
                responseName            [0] LDAPOID OPTIONAL,
                response                [1] OCTET STRING OPTIONAL,
                standardResponse        [2] LDAPResult }

   The responseName field contains the same string as that present in
   the request.

   The response field will contain as a value the DER-encoding of the
   following ASN.1 data type:

        SEQUENCE {
                responseTtl [1] INTEGER

   The responseTtl field is the time in seconds which the server chooses
   to have as the time-to-live field for that entry.  It must not be any
   smaller than that which the client requested, and it may be larger.
   Please note that for the case of a static entry with dynamic
   attributes, this time-to-live applies to all the dynamic attributes
   in this entry.

   If the operation was successful, the errorCode field in the
   standardResponse part of an ExtendedResponse will be set to success.

   In case of an error, the responseTtl field will have the value 0, and
   the errorCode field will contain an appropriate value, as follows: If
   the entry named by entryName could not be located, the errorCode
   field will contain "noSuchObject".  If the entry is not dynamic, or
   does not have dynamic attributes, the errorCode field will contain
   "objectClassViolation".  If the requestor requester does not have permission to
   refresh the entry, the errorCode field will contain
   "insufficientAccessRights".  If the requestTtl field is too large,
   the errorCode field will contain "sizeLimitExceeded".

   If a server does not implement this extension, it will return an LDAP
   PDU containing an ExtendedResponse, which contains only the
   standardResponse element (the responseName and response elements will
   be absent).  The LDAPResult element will indicate the protocolError
   result code.

   This request is permitted to be invoked when LDAP is carried by a
   connectionless transport.

   When using a connection-oriented transport, there is no requirement
   that this operation be on the same particular connection as any
   other.  A client may open multiple connections, or close and then
   reopen a connection.

6. Schema Additions

   All dynamic entries must have the dynamicObject value in their
   objectClass attribute. This object class is defined as follows
   (using the ObjectClassDescription notation of [2]):

   ( NAME 'dynamicObject'
     DESC 'This class, if present in an entry, indicates that this entry
           has a limited lifetime and may disappear automatically when
           its time-to-live has reached 0.  There are no mandatory
           attributes of this class, however if the client has not
           supplied a value for the entryTtl attribute, the server will
           provide one.'
     SUP top AUXILIARY )

   Furthermore, the dynamic entry or the static entry with dynamic
   attributes must have the following operational attribute.  It is
   described using the AttributeTypeDescription notation of [2]:

   ( NAME 'entryTtl'
     DESC 'This operational attribute is maintained by the server and
           appears to be present in every dynamic entry. entry or an entry that
           contains dynamic attributes.  The attribute is not present
           when the entry does not contain the dynamicObject object class.
           class or dynamic attributes.  The value of this attribute is the
           time in seconds that the entry or the dynamic attributes in a
           static entry will continue to exist before it disappears disappearing from
           the directory.  In the absence of intervening refresh
           operations, the values returned by reading the attribute in
           two successive searches are guaranteed to be nonincreasing.
           The smallest permissible value is 0, indicating that the
           entry may disappear without warning.  The attribute is marked
           NO-USER-MODIFICATION since it may only be changed using the
           refresh operation.'

7. Client and Server Requirements

7.1 Client Requirements

   Once a dynamic entry has been created, clients are responsible for
   invoking the refresh extended operation, in order to keep that entry
   present in the directory.  The same holds true for keeping dynamic
   attributes present on a static entry.

   Clients must not expect that the a dynamic entry will be present in the
   DIT after it has timed out, however it must not either require that
   the server remove the entry immediately (some servers may only
   process timing out entries at intervals).  If the client wishes to
   ensure the entry does not exist it should issue a RemoveRequest for
   that entry.  Again, dynamic attributes behave the same: they will not
   be present in the DIT after they timed out, but the client should not
   require their immediate removal.

   Initially, a client needs to know how often it should send refresh
   requests to the server.  This value is defined as the CRP (Client
   Refresh Period) and is set by the server based on the entryTtl.
   Since the AddRequest is left unchanged and is not modified in this
   proposal to return this value, a client must issue a Refresh extended
   operation immediately after an Add that created a dynamic entry.
   The Refresh Response will return the CRP (in responseTtl) to the client.

   Clients must not issue the refresh request for dynamic entries which
   they have not created. created or for static entries to which they did not add
   dynamic attributes.  Please note that when a client refreshes a
   static entry to which it added dynamic attribute(s), it refreshes ALL
   the dynamic attributes in this entry, including ones added by other
   clients.  Also note that servers which allow anonymous clients to
   create and refresh dynamic entries and attributes will not be able to
   enforce the above.

   Clients should always be ready to handle the case in which their
   entry or dynamic attributes timed out.  In such a case, the Refresh
   operation will fail with an error code such as noSuchObject, and the
   client is expected to re-create its entry. entry or re-add the dynamic

   Clients should be prepared to experience refresh operations failing
   with protocolError, even though the add and any previous refresh
   requests succeeded.  This might happen if a proxy between the client
   and the server goes down, and another proxy is used which does not
   support the Refresh extended operation.

7.2 Server Requirements

   Servers are responsible for removing dynamic entries and dynamic
   attributes when they time out.
Server  Servers are not required to do this

   Servers must enforce the structural rules listed in above section 4.

   Servers must ensure that the operational attribute described in
   section 6 is present in dynamic entries. entries or in static entries that
   contain dynamic attributes.

   Servers are permitted to check the authentication of the client
   invoking a refresh extended operation, and only permit the operation
   if it matches that of the client which created the dynamic entry. entry or
   added dynamic attributes to this entry (please see a note about that
   in section 7.1).  Servers may permit anonymous users to refresh

   Servers may require that a client which attempts to create a dynamic
   entry have a remove permission for that entry.

   Servers which implement this extension must have the OBJECT
   IDENTIFIERs, described above in section 5 for the request and
   response, present as values of the supportedExtension field in the
   root DSE.  They must also have as values in the attributeTypes and
   objectClasses attributes of their subschema subentries, the
   AttributeTypeDescription and ObjectClassDescription from section 6.

   An implementation of dynamic directories, must be able to support
   both dynamic directory entries and dynamic attributes.

8. Implementation issues

8.1 Storage of dynamic information

   Dynamic information is expected to change very often.  In addition,
   Refresh requests are expected to arrive at the server very often.
   Disk-based databases that static directory services often use are
   likely inappropriate for storing dynamic information.  We recommend
   that server implementations store dynamic entries in memory
   sufficient to avoid paging.  This is not a requirement.

   We expect LDAP servers to be able to store static and dynamic
   entries.  If an LDAP server does not support dynamic entries,
   it should respond with an error code such as objectClassViolation objectClassViolation.
   Such a server might still support setting dynamic attributes
   on a static entry.

8.2 Client refresh behavior

   In some cases, the client might not get a Refresh response.  This may
   happen as a result of a server crash after receiving the Refresh
   request, the TCP/IP socket timing out in the connection case, or the
   UDP packet getting lost in the connection-less case.

   It is recommended that in such a case, the client will retry the
   Refresh operation immediately, and if this Refresh request does not
   get a response as well, it will resort to its original Refresh cycle,
   i.e.  send a Refresh request at its Client Refresh Period (CRP).

9. Localization

   The are no localization issues for this extended operation.

10. Security Considerations

   Security issues are not addressed in this document.  Please note,
   though, that anonymous clients are able to refresh entries which they
   did not create.

   Also, Care should be taken in making use of information obtained from
   directory servers that has been supplied by client, as it may now be
   out of date.  In many networks, for example, IP addresses are
   automatically assigned when a host connects to the network, and may
   be reassigned if that host later disconnects.  An IP address obtained
   from the directory may no longer be assigned to the host that placed
   the address in the directory.  This issue is not specific to LDAP or
   dynamic directories.

11. Acknowledgements Acknowledgments

   Design ideas included in this document are based on those discussed
   in ASID and other IETF Working Groups.

12. Authors Addresses

       Yoram Yaacovi
       One Microsoft way
       Redmond, WA 98052

       Phone:  +1 206-936-9629

       Mark Wahl
       Critical Angle Inc.
       4815 W. Braker Lane #502-385
       Austin, TX 78759


       Kent Settle
       One Microsoft way
       Redmond, WA 98052

       Phone:  +1 206-936-3027

       Tony Genovese
       One Microsoft way
       Redmond, WA 98052

       Phone:  +1 206-703-0852

13. Bibliography

   [1] M.Wahl, T.  Howes, S.  Kille, "Lightweight Directory Access
       Protocol (Version 3)".  INTERNET DRAFT

   [2] M.Wahl, A.Coulbeck, T.  Howes, S.  Kille, "Lightweight Directory
       Access Protocol Standard and Pilot Attributes".  INTERNET DRAFT

   [3] M.Wahl, S.Kille, "Lightweight Directory Access Protocol UTF-8
       String Representation of Distinguished Names".  INTERNET DRAFT

   Expires on 10 March 1996. six months from the post date (see top).