sqlnet.ora question

Can anyone tell me when sqlnet.ora is read? Oracle support says
"Each time a SQL*Net connection is established." My testing seems
to show that I have to shutdown the database and start it up again.

I've tried stopping and re-starting the TNS listener but that doesn't seem to do it.

I'm experimenting with the Dead Connection Detection parameter
"sqlnet.expire_time"

I'm running Oracle7 Server 7.1.4.1.0 and TNSLSNR 2.1.4.1.0 on an HP 9000/800 HP-UX 9.04

Thanks

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   |  \/  |(_)| |__ ___                                   __o
   | |\/| || || / // -_)      Mike Moritz               _ \<._
   |_|  |_||_||_\_\\___|      mmoritz_at_netcom.com   ____(_)/ (_)____