Nothing, different DNS names for the same server.
derpibooru.org
www.derpibooru.org
derpiboo.ru
www.derpiboo.ru
trixiebooru.org
www.trixiebooru.org
All resolve to the same 2 IP addresses (178.33.231.189, 2001:41d0:8:28bd::1). You’re always being served by the same celestia. (derpicdn load-balances across different endpoints by design of Cloudflare)
Help fund the $15 daily operational cost of Derpibooru - support us financially!