Which type of attack uses a botnet to reflect requests off of an NTP server...

A Distributed Denial of Service (DDoS) attack involves multiple compromised devices (botnet) sending a large number of requests to a target server to overwhelm it.

In a specific type of DDoS attack known as an NTP amplification attack, the attacker exploits the Network Time Protocol (NTP) servers by sending small queries with a spoofed source IP address (the target’s IP).

The NTP server responds with a much larger reply to the target’s IP address, thereby amplifying the traffic directed at the target.

This reflection and amplification technique significantly increases the volume of traffic sent to the target, causing denial of service.

References

OWASP DDoS Attack Overview

NTP Amplification Attack Explained

Understanding Botnets and Distributed Attacks