Free CompTIA Security+ SY0-601 Practice Question

You are observing an outage of your employers website. While investigating the cause of the outage you learn that there is a large-scale DDOS attack that has caused network outages for large percentages of the internet. The attack is targeting key infrastructure of major web service providers. According to news sources the attackers are sending huge numbers of requests to open DNS servers with spoofed IP addresses. The responses from the DNS servers are sent to the spoofed IP addresses which have resulted in network outages due to overwhelmed infrastructure. What type of attack is being conducted?