>i am looking to open vpn remote page now do you know where could i set client's sites that allow to connect or not ?
I can't remember if there are other controls, but AFAIK the primary method of saying who is allowed is via certificates that you create when setting it up.
It is still unclear to me what you are trying to achieve.
Is it that you have three sites...
A <-> B <-> C
where <-> represents the VPN link? Is it that A needs to talk to B, B to C, but you don't want A to talk to C? If that is the case, I think it needs to be solved with a combination of VPN's as described and Iptables to stop the A to C conversation..