I thought the below was an interesting presentation by Cloudflare. Those who read the  cnna's by Todd Lammle back in the days, it is time to clean up your network, otherwise you are using someone's IP range if you are doing such on the core links :-)

https://www.afpif.org/wp-content/uploads/sites/26/2018/08/02_1.1.1.1-…-cleanup-and-privacy-–-Martin-J.-Levy.pdf​

Regards,

Simon Mayoye