Question

Describe the functions of the following:
(a) Packet Filtering Firewalls
(b) Stateful Inspection Firewalls
(c) Application-Level Gateways

Hint:

Firewalls secure networks at multiple layers: packet filtering controls traffic basics, stateful inspection tracks sessions, and application gateways filter content deeply.

Answer 1

(a) Packet Filtering Firewalls:
Packet filtering firewalls are security devices that monitor and control network traffic based on predefined security rules. They operate at the network layer by inspecting each packet’s header information such as source and destination IP addresses, port numbers, and protocol type. Based on these parameters, the firewall either allows the packet to pass or blocks it. Packet filtering firewalls are efficient and fast but provide only basic security since they do not inspect the packet contents or maintain any information about connection states. They are primarily used to create a basic barrier between trusted and untrusted networks. (b) Stateful Inspection Firewalls:
Stateful inspection firewalls enhance the functionality of packet filtering firewalls by tracking the state of active connections. Instead of examining packets in isolation, they monitor the full context of the network session, such as the TCP handshake and ongoing data flow. This allows them to determine whether incoming packets are part of an existing legitimate connection or are unsolicited and potentially harmful. Stateful firewalls can block packets that do not conform to the expected state and are more effective at preventing attacks compared to simple packet filtering firewalls.
(c) Application-Level Gateways (Proxy Firewalls):
Application-level gateways, also known as proxy firewalls, operate at the application layer of the OSI model. They act as intermediaries between clients and servers by receiving client requests and forwarding them to the destination server after inspection. These firewalls examine the actual data payload and can enforce policies based on application-specific protocols such as HTTP, FTP, or SMTP. They provide detailed filtering, user authentication, and content filtering, making them highly secure. However, because of their thorough inspection, they may introduce latency and require more processing power.