Which of the following firewalls are used to track the state of active connections and determine the
network packets allowed to enter through the firewall?Each correct answer represents a complete
solution. Choose all that apply.

A.
Circuit-level gateway

B.
Stateful

C.
Proxy server

D.
Dynamic packet-filtering

Explanation:

A dynamic packet-filtering firewall is a fourth generation firewall technology. It is also known as a
stateful firewall. It tracks the state of active connections and determines which network packets
are allowed to enter through the firewall. It records session information, such as IP addresses and
port numbers to implement a more secure network. The dynamic packet-filtering firewall operates
at Layer3, Layer4, and Layer5.
Answer option A is incorrect. A circuit-level gateway is a type of firewall that works at the session

layer of the OSI model between the application layer and the transport layer of the TCP/IP stack.
They monitor TCP handshaking between packets to determine whether a requested session is
legitimate. Information passed to a remote computer through a circuit level gateway appears to
have originated from the gateway. This is useful for hiding information about protected networks.
Circuit-level gateways are relatively inexpensive and have the advantage of hiding information
about the private network they protect.
Answer option C is incorrect. A proxy server firewall intercepts all messages entering and leaving
the network. The proxy server effectively hides the true network addresses.