home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Internet Info 1997 December
/
Internet_Info_CD-ROM_Walnut_Creek_December_1997.iso
/
drafts
/
draft_ietf_a_c
/
draft-ietf-asid-ldapv3ext-02.txt
< prev
next >
Wrap
Text File
|
1996-10-17
|
26KB
|
560 lines
ASID Working Group Y. Yaacovi
INTERNET-DRAFT Microsoft
M. Wahl
Critical Angle Inc.
K. Settle
Microsoft
T. Genovese
Microsoft
Expires in six months from 14 October 1996
Intended Category: Standards Track
Lightweight Directory Access Protocol:
Extensions for Dynamic Directory Services
<draft-ietf-asid-ldapv3ext-02.txt>
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 ds.internic.net (US East Coast), nic.nordu.net
(Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (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
environment.
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 definition, dynamic 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,
the extensions need to be registered as standard LDAP extended
operations.
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
attributes.
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 entry had 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
restrictions.
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.
4.2. Dynamic Attributes
A similar concept is dynamic attributes. These attributes behave the
same as ordinary user attributes to Search, Compare and Modify
requests, except that if they time out they disappear from the entry
in which they are located. (Unlike the dynamicObject class, the
entry itself does not disappear, and non-dynamic attributes are
unaffected). Like dynamic entries, a static entry with dynamic
attributes must have the entryTtl attribute which is described
in section 6 below.
Dynamic attributes do not necessarily introduce a new set of
attributes in the schema. Any static attribute in the schema can be
made dynamic by including the ;dynamic attribute modifier with the
typename. It is allowed to introduce new dynamic attributes which
are not useful in the static domain. Such attributes will still require
including the ;dynamic attribute modifier with the 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 "1.2.3.4".
A modification of the entry to add the value "5.4.3.2" 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
attributes.
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 or the attributes.
A client may request this operation by transmitting an LDAP PDU
containing an ExtendedRequest. An LDAP ExtendedRequest is defined as
follows:
ExtendedRequest ::= [APPLICATION 23] SEQUENCE {
requestName [0] LDAPOID,
requestValue [1] OCTET STRING }
The requestName field must be set to the string
"1.3.6.1.4.1.1466.101.119.1".
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 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 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]):
( 1.3.6.1.4.1.1466.101.119.2 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]:
( 1.3.6.1.4.1.1466.101.119.3 NAME 'entryTtl'
DESC 'This operational attribute is maintained by the server and
appears to be present in every dynamic entry or an entry that
contains dynamic attributes. The attribute is not present
when the entry does not contain the dynamicObject object
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 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.'
SYNTAX 'Integer' SINGLE-VALUE NO-USER-MODIFICATION USAGE dSAOperation )
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 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 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 or re-add the dynamic
attributes.
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. Servers are not required to do this
immediately.
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 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 or
added dynamic attributes to this entry (please see a note about that
in section 7.1). Servers may permit anonymous users to refresh
entries.
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.
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. Acknowledgments
Design ideas included in this document are based on those discussed
in ASID and other IETF Working Groups.
12. Authors Addresses
Yoram Yaacovi
Microsoft
One Microsoft way
Redmond, WA 98052
USA
Phone: +1 206-936-9629
EMail: yoramy@microsoft.com
Mark Wahl
Critical Angle Inc.
4815 W. Braker Lane #502-385
Austin, TX 78759
USA
EMail: M.Wahl@critical-angle.com
Kent Settle
Microsoft
One Microsoft way
Redmond, WA 98052
USA
Phone: +1 206-936-3027
EMail: kentse@microsoft.com
Tony Genovese
Microsoft
One Microsoft way
Redmond, WA 98052
USA
Phone: +1 206-703-0852
EMail: tonyg@microsoft.com
13. Bibliography
[1] M.Wahl, T. Howes, S. Kille, "Lightweight Directory Access
Protocol (Version 3)". INTERNET DRAFT
<draft-ietf-asid-ldapv3-protocol-01.txt>
[2] M.Wahl, A.Coulbeck, T. Howes, S. Kille, "Lightweight Directory
Access Protocol Standard and Pilot Attributes". INTERNET DRAFT
<draft-ietf-asid-ldapv3-attributes-02.txt>
[3] M.Wahl, S.Kille, "Lightweight Directory Access Protocol UTF-8
String Representation of Distinguished Names". INTERNET DRAFT
<draft-ietf-asid-ldapv3-dn-00.txt>
Expires on six months from the post date (see top).