According to NIST SP800-61, the incident response phase called "Containment, Eradication, and Recovery" involves containing the incident, eradicating the threat, and recovering from the incident2. In the scenario described, the engineer worked on containing the DDoS attack by identifying the attacker and the technique used, which is part of the containment process. The recommendation to implement Blackhole filtering is part of the eradication process, where measures are taken to prevent the attack from happening again. Finally, restoring the server is part of the recovery process, where normal operations are resumed. Therefore, the engineer finished work during the "Containment, Eradication, and Recovery" phase. Reference:: NIST SP800-61 Computer Security Incident Handling Guide2.