- Packet-Filtering Firewalls (Layer 3/4)
- Function: Analyze packets based on source, destination, port, and other basic information to determine whether to allow them into the network.
- Advantages: Fast, simple, and effective for basic filtering.
- Limitations: Does not inspect the actual content of the packets.
- Stateful Packet Filtering Firewalls (Layer 7)
- Function: Monitors the state of active connections and makes decisions based on the state and context of packets, such as conversations.
- Advantages: Provides better security by understanding the state of network traffic.
- Limitations: More complex and resource-intensive than packet-filtering firewalls.
- Application Proxy Firewalls (Layer 7, but spans 3-7)
- Function: Inspects the content of the traffic and can involve authentication and encryption. Acts as an intermediary for requests between users and the destination server.
- Advantages: Offers detailed control over traffic, higher security, and can inspect application data.
- Limitations: Slower due to deep inspection and processing overhead.
- Circuit-Level Proxy Firewalls (Layer 5)
- Function: Inspects the headers of packets to determine whether a session (circuit) should be allowed, then tunnels all traffic between the parties once the session is established.
- Advantages: Protects a broad range of protocols and services with less overhead than application proxies.
- Limitations: Less granular control compared to application-level firewalls.
- SPF (Static Packet Firewall, Layer 3)
- Function: Filters packets based on static rules, such as IP address, port, and protocol type.
- Advantages: Simple to configure and fast in operation.
- Limitations: Does not consider the state or context of network traffic.
Firewalls are crucial for network security, offering various levels of protection based on the type of firewall and the specific needs of the network. Proper configuration is essential to ensure they effectively protect against threats while allowing legitimate traffic.