Define packet filtering, session filtering, proxy gateway (both circuit and application level).
The correct answer and explanation is:
Correct Answer:
- Packet Filtering is a firewall technique that examines each packet’s header information to allow or block it based on predefined rules.
- Session Filtering involves tracking the state of active connections and making decisions based on the context of the traffic flow.
- Proxy Gateway (Circuit-Level) establishes a virtual circuit between client and server, relaying packets without inspecting their content.
- Proxy Gateway (Application-Level) acts as an intermediary that understands and filters traffic at the application protocol level (e.g., HTTP, FTP).
Explanation (300 words):
Packet filtering is a network security mechanism used in firewalls to control the flow of data based on information found in packet headers. Each packet that passes through the firewall is evaluated individually against a set of rules. These rules can be based on IP addresses, port numbers, and protocols. If a packet matches an allowed rule, it is forwarded; otherwise, it is blocked. This method is fast and efficient, but it does not track connection state or inspect the data payload, making it vulnerable to certain attacks.
Session filtering, also known as stateful packet inspection, builds upon packet filtering by keeping track of the state of active connections. Instead of treating each packet in isolation, it understands whether a packet is part of an existing session. For instance, if a request is sent from an internal device to a web server, the firewall remembers this connection and allows return traffic that is part of the same session. This increases security because unauthorized packets that do not match an existing session are denied.
A circuit-level proxy gateway operates at the session layer of the OSI model. It creates a secure and transparent connection between the internal user and the external server. It does not analyze the content of the traffic, but it hides the internal network structure and manages session establishment, making it useful for enforcing policies without deep inspection.
An application-level proxy gateway goes a step further by inspecting the actual data in the application layer. For example, it can understand and filter HTTP requests or FTP commands. This type of proxy provides the highest level of control and security, as it can block specific operations or malicious payloads based on protocol rules, but it is slower and requires more processing power.