- First Generation (Static) Packet Filtering Firewall
- Also Known As: Screening Router.
- Function: Examines source/destination addresses, protocols, and ports of incoming packets.
- Operation: Based on Access Control Lists (ACLs), it determines whether to deny or accept access.
- OSI Layers: Operates at the Network or Transport layer.
- Second Generation (Application Level Firewall)
- Also Known As: Proxy Server.
- Function: Transfers data streams to another network while masking the data origin.
- Operation: Provides application-level filtering by analyzing traffic at the application layer.
- OSI Layer: Operates at the Application layer.
- Third Generation (Stateful Inspection Firewall)
- Also Known As: Dynamic Firewall.
- Function: Inspects all packets at the Networking layer, examining the state and context of data packets.
- Operation: Tracks connectionless protocols like UDP and RPC, analyzing traffic across all OSI layers.
- OSI Layers: Analyzes at all layers but primarily focuses on the Network layer.
- Fourth Generation (Dynamic Packet Filtering Firewall)
- Function: Allows for the dynamic modification of firewall rules.
- Operation: Provides limited support for UDP by remembering UDP packets across the network.
- Fifth Generation (Kernel Proxy Firewall/Application Level Firewall)
- Function: Runs in a modular, kernel-based environment, typically on Windows NT.
- Operation: Uses dynamic TCP/IP stacks to inspect network packets and enforce security policies.
- Characteristics: Evaluates multi-layer sessions for enhanced security.
These firewall generations represent the evolution of network security mechanisms, each offering different levels of protection and functionality depending on the security needs of the network.