Types of Firewalls
¨Circuit-level firewall
–verifies TCP 3-way handshake on behalf of inside
hosts
¨Proxy server firewalls
–application aware
–Proxies TCP connections on behalf of clients
–not transparent to end-users
¨Non-stateful packet filters
¨Stateful packet filters
–Maintains source/destination TCP/UDP port numbers, TCP sequence numbers, TCP flags, TCP session state, and UDP traffic timing based on timers
–Application aware
¨Personal firewalls