After experiencing a large-scale distributed denial-of-service (DDoS) attack that caused service outages, a national telecom...

Comprehensive and Detailed Explanation (ECIH-aligned):

This question focuses on post-incident recovery and resilience, a key ECIH concept. After restoring services, organizations must strengthen defenses to prevent recurrence.

Option B is correct because Content Delivery Networks (CDNs) distribute traffic and absorb volumetric attacks, while blackhole routing discards malicious traffic upstream. ECIH identifies these as industry-standard controls for DDoS resilience.

Options A, C, and D weaken security or increase attack surface and contradict ECIH guidance.

ECIH stresses that recovery is not complete until preventive measures are implemented. CDN deployment and upstream traffic control significantly improve availability during future attacks.