Re: RFC 2251 considered harmful

[Steve Kille <S.Kille@isode.com>]

Ed,

This is an interesting point.

The "critical extension mechanism" was originally developed for X.400,
and I think has proved to work quite well.   It enables new protocols
and services to be delvelped over an existing infrastructure.   In
general, extensions which respect the installed base are a good thing.

Some extensions can safely be ignored without loss of service.
Others will simply not work if they are not understood and need to be
rejected.   The criticality mechanism allows this to be communicated.
This is particularly important in a store and forward messaging
environment, or where directory requests are chained.

For a client/server only system, negotiating capabilities at bind time
also works.

I think that the critical extension mechanism is a sound choice for LDAPv3.

As you point out, use of critical extensions does allow vendors a
mechanism to lock in server choice.  However, such vendors would
simply do the same using propietary mechanisms in any event.  All
vendors like to achieve customer lock in, to increase sales.  Although
I think that the mechanism is good, it will help some marketing
departments to promote proprietary extensions as "open".

A good way for organizations deploying directory services to minimize
this problem, is to require (as a matter or principle, which is clear
to all suppliers) that client and server products are always procured
from different vendors.



Steve Kille