checkrad and db based simultaneous use checks

[Bill Schoolfield]

Hello All

A client of mine just asked that we limit active sessions per user to 1 
(e.g simultaneous use checking). Radutmp was already configured but I 
disabled it in favor of the checks via the SQL module. Things look to be 
working but I'm concerned as the radacct table has lots of (possibly 
old/bogus) records with no stop info that I assume will cause the check 
to return false negatives.

We also configured checkrad and it is working. My question is this: how 
exactly is checkrad used? Is it used exclusively or in concert with the 
SQL module checks? Will I need to cleanup the radacct table or will 
checkrad "save" me? I have reviewed all the documents and configuration 
I can find but checkrad use is still a bit of a mystery to me.

Bill