Beginning taxonomy for finding LDAP servers.

[Ryan Moats <jayhawk@att.com>]

Since the mailing list seems to have come back today, I am resending
this...

Hi all-

Since I've been thinking on and off about this problem for a good long
while now, I thought I'd kick off the discussion by listing the ways that
I know of for finding LDAP servers.  I'm beginning to envision the
work item on the LDAPEXT charter resulting in an informational level
document
(which I am volunteering to author or co-author as the case may be).

So...


For LDAP clients finding Servers there are several different methods.
This list is not complete, but should be considered the beginning of
a taxonomy.

Method: Client configuration

In this case, the client administrator configures it with a list of known
LDAP servers
to send queries to.  This list will be right (initially), but modification
to the list
requires client updates and doesn't scale real well.

Method: WK DNS alias

If the DIT uses the "dc-naming scheme", then it is possible to construct the
DNS names of potential servers using well known DNS aliases.  Without the
use of
the dc-naming scheme, it is possible to construct potential names based on
the client's
DNS name.  This has the shortcoming of being inexact and not supporting
client roaming
well when tunneling is not used.

Method: Service Location Protocol

A client that supports the service location protcol could do a SLP query for
LDAP servers.
This requires that the network be using SLP and and that the servers
announce themselves.
This method has the scaling drawbacks of SLP since it depends on that
method.

Method: "discovery"

Besides using other methods, this method involves storing either the DN or
related URL
in the DNS in some way.  This method requires an administrator to configure
the DNS with the
information and the idea of storing either a DN or a URL in the DNS is a
controversial one.
The i-d that expounds this idea will not be renewed and is being taken off
the service location
WG's workplan.  This method would require persuation of the IESG to even
reach
experimental status.

Method: DHCP extensions

An expired internet-draft proposed using DHCP to deliver information about
LDAP servers to a
DHCP client. This requires that (a) the information be configured into the
DHCP server and that
the client both support DHCP and this extension.  Such a method would
require resubmitting the
DHCP and getting approval for it.

Method: CIP index objects

If LDAP servers are exchanging CIP index objects, then they can also
exchange URL information for
providing referalls to clients.  This would help by allowing a client to
query a local server
(that it discovered by one of the previous methods) and receive a referal to
a non-local LDAP server
which it could then query.

Comments are welcome as well as additional method brainstorming.

Ryan Moats