We are going for a 30 sites networking with our head office via some ISP's VPN. Can all experts pls suggest me what firewall and IDS should I use to protect my network to maximum extent. We have Windows 2000 advanced server with Exchange 2000 as mail server. We will expose our server for ERP and mail access to all our sites as well as for external internet users. (To note we are taking a leased connectivity with ISP for internet exposure). We will be using 3600 series CISCO routers at central location.