ABSTRACT
An intrusion detection/prevention system (IDS/IPS) is another element in the arsenal which is employed to provide deep packet inspection at the entrance of important network. The Intrusion Detection System/Intrusion Prevention System is positioned behind the firewall, as shown in Figure 19.1. VPN is permitted to pass firewall and IDS/IPS since the traffic is usually encrypted and authenticated. The IDS/IPS provides deep packet inspection for the payload, IDS is based on out-of-band detection of intrusions and their reporting, and IPS is in-band filtering to block intrusions.
