Which two types of firewalls work at Layer 4 and above? (Choose two.)

Which two types of firewalls work at Layer 4 and above? (Choose two.)
A . application-level firewall
B . static packet filter
C . stateful inspection
D . Network Address Translation
E . circuit-level gateway

View Answer

Answer: BC

Explanation:

Dynamic or Stateful Packet-Filtering Firewalls

Stateful inspection is a firewall architecture classified at the network layer; although, for some applications it can analyze traffic at Layers 4 and 5, too.

Unlike static packet filtering, stateful inspection tracks each connection traversing all interfaces of the firewall and confirms that they are valid. Stateful packet filtering maintains a state table and allows modification to the security rules dynamically. The state table is part of the internal structure of the firewall. It tracks all sessions and inspects all packets passing through the firewall. Although this is the primary Cisco Firewall technology, it has some limitations: http://www.ciscopress.com/articles/article.asp?p=1888110