LDAP URI scheme that specify alternative transport protocols

["Kurt D. Zeilenga" <kurt@boolean.net>]

One of the problems facing LDAP (and other application protocols)
is how to specify URIs that indicate use of an alternative transport
protocol.  This problem stems from the need to represent LDAP knowledge
references which indicate the transport to use when the referred to
server supports/requires alternative transport protocols.

For example, LDAP can be utilized over TCP or over TLS (versus
StartTLS).  In fact, LDAP can be utilized over any transport
which provides a reliable byte stream.

We (and I believe other vendors) are currently extending our LDAP
implementation to support a number of other transport protocols
such as Local IPC and TLS.  The current approach is to define a
URI scheme per transport protocol, ie:
	ldap://host:port/
	ldaps://tlshost:port/
	ldapi:///

[Note: StartTLS could be handled using the ldap: scheme
with an extension <ldap://host/dc=openldap,dc=com????tls>.
Maybe we should document a URL format for StartTLS in the
TLS draft?]

This problem is not unique to LDAP.  Numerous application protocols
support multiple transports.  Though this can be handled by adding
additional URI scheme for each transport protocol supported by each
application protocol, an extensible mechanism is desirable.

I have two approaches that might be workable that I would like to
discuss:
	ldap://host:port/
	ldap+transport:://host:port/

or
	ldap://host:port/
	ldap[transport]:://host:port/

where transport is tcp, tls, ipc or other transport protocol
identifier.

As this could be extended to support other application protocols,
it may be appropriate to move this discussion into another forum.