Which type of firewall is most likely to prevent SYN floods?

Which type of firewall is most likely to prevent SYN floods?

• A. Stateless Packet Filtering
• B. Stateful Packet Inspection
• C. Application Firewall
• D. Proxy Firewall

Answer: (B)

SYN floods exploit TCP by sending a flood of connection initiation requests and leaving many half-open connections, which ties up the server’s resources in the backlog. A firewall that performs stateful packet inspection monitors the progression of TCP connections and understands when a handshake is not completing as expected. Because it tracks connection state, it can recognize an abnormal surge of half-open connections and intervene by dropping those packets, enforcing rate limits, or applying techniques like SYN cookies to prevent resource exhaustion. This direct awareness of the TCP state makes it the most effective at mitigating this type of attack. Stateless packet filtering looks at individual packets without regard to connection state, so it cannot reliably distinguish normal from malicious half-open attempts under flood conditions. An application firewall focuses on inspecting data at higher layers, not on the handshake process itself, so it won’t address the flood at the TCP level. A proxy firewall can help by terminating client connections at the proxy, but the core protection against floods comes from understanding and controlling the underlying TCP state, which is what Stateful Packet Inspection provides.

SYN floods exploit TCP by sending a flood of connection initiation requests and leaving many half-open connections, which ties up the server’s resources in the backlog. A firewall that performs stateful packet inspection monitors the progression of TCP connections and understands when a handshake is not completing as expected. Because it tracks connection state, it can recognize an abnormal surge of half-open connections and intervene by dropping those packets, enforcing rate limits, or applying techniques like SYN cookies to prevent resource exhaustion. This direct awareness of the TCP state makes it the most effective at mitigating this type of attack.

Stateless packet filtering looks at individual packets without regard to connection state, so it cannot reliably distinguish normal from malicious half-open attempts under flood conditions. An application firewall focuses on inspecting data at higher layers, not on the handshake process itself, so it won’t address the flood at the TCP level. A proxy firewall can help by terminating client connections at the proxy, but the core protection against floods comes from understanding and controlling the underlying TCP state, which is what Stateful Packet Inspection provides.