Which of the following would be MOST effective in reducing the impact of a distributed denial of service (DDoS) attack?

Imposing state limits on servers can help mitigate some types of application-layer attacks by limiting resource consumption but is generally insufficient against volumetric DDoS attacks designed to saturate network links.

Spreading a site across multiple ISPs provides geographical distribution and increased bandwidth capacity, making it significantly harder for a DDoS attack to overwhelm all ingress points simultaneously. This multi-homing strategy allows traffic to be rerouted and absorbed by different networks, thereby maintaining service availability even under attack.

Hardening network security (e.g., firewalls, IDS/IPS) helps defend against various attacks but may not prevent network saturation from a large-scale DDoS attack without external scrubbing services or distributed infrastructure.

Blocking the attack at the source is often impractical due to IP spoofing, botnets, and the distributed nature of DDoS attacks, making it a reactive and often unfeasible solution.