The internet phone book to convert .coms to ip addresses only scales up to the load level of hte internet because results are cached at multiple layers.

your browser asks your computer which asks your router which asks your isp which asks .com's dns servers which ask facebook's dns servers for facebook's ip address.

each layer will cache the results so say, even if 100,000 people in seattle want to know facebook.com's ip address, only the 5 or isps who provide internet in seattle have to ask for facebook.com's ip address, so 100,000 requests, but only 5 actual requests.

even the per-device and per-home cache is helpful, because 500 page loads in 15 minutes still only results in 1 actual dns request.

Here's the issue:

Failures aren't cached.

so while 100,000 people in 1 second trying to get facebook's ip only resulted in 5 requests going to the core dns servers, now results in 100,000 requests in 1 second trying going to the core servers.

BGP is like the mail service.

DNS is a translation from human readable addresses to machine addresses.

BGP determines how to find those addresses from your server to theirs.