Amplification and reflection attacks
termsecurityISP & telecom
Sending small forged requests to public servers so their much larger replies are delivered to a victim - reflection provides the disguise, amplification provides the volume.
Two conditions are required: a protocol whose answer is far larger than its question, usually over UDP, and a network that permits source address forgery. Only the second is fixable at scale, which is why the defence lives at other people's edges rather than at the victim's. The property that makes it hard to answer at the destination is that the arriving traffic comes from legitimate servers behaving correctly - there is nothing malicious to identify, only volume, so the response is capacity rather than filtering.
Also known as: reflection, amplification factor, udp reflection, booter