Does ISA Server support stateful inspection?
Yes. ISA Server supports three layers of filtering for complete comprehensive security: packet-level filtering, circuit-level filtering, and application-level filtering. Circuit-level filtering, commonly referred to as "stateful inspection," is the process of inspecting packets as they reach the firewall, keeping state information, and allowing or disallowing them to pass the firewall based on the access policy. ISA Server adds application filters that provide filtering at a higher communication layer, based on "smart" inspection of specific application commands. This allows the blocking of specific SMTP commands, filtering RPC access based on requested interfaces.