Which statement reflects the likely need for external coordination in defending against DoS as described in the material?

• A. External coordination with ISPs is often necessary.
• B. External coordination is never needed.
• C. External coordination is only for private networks.
• D. External coordination is irrelevant.

Answer: (A)

When defending against DoS, external coordination with the networks that carry your traffic is often necessary. Large or distributed attacks can saturate your upstream links long before you can filter everything at your own edge. Upstream providers—like ISPs and transit providers—can implement filters or redirects at their points of presence, drop attack traffic through scrubbing services, or route bad traffic away from your network using techniques like BGP blackholing or traffic diversion to dedicated scrubbing centers. This helps protect your bandwidth and keeps legitimate users connected, something you typically can’t achieve by working in isolation on your own devices.

As a result, the idea that coordination with ISPs isn’t needed, or is only relevant for private networks, or is irrelevant, doesn’t fit real-world defenses. DoS traffic can originate from anywhere and traverse multiple networks, so getting the involvement of external networks is a common and practical part of effective mitigation.