When Facebook withdrew all their routes to their DNS gear in Oct 2021 because their DNS restarts/fix scripts depending on DNS - every major university and large enterprise started having DNS issues with all domains because of the recursion load due to Facebook no longer being in cache.

https://blog.cloudflare.com/october-2021-facebook-outage/

https://www.cisa.gov/sites/default/files/publications/Factsheet_SCS%20Mitigations%20and%20Phishing%20Analysis%20Guidance%209.2021_FINAL_508c.pdf

https://www.cisa.gov/resources-tools/programs/shared-cybersecurity-services-scs