DNS by default and through 1.1.1.1/8.8.8.8?

Question

Computer networks

Good afternoon, tell me please, I ran into a trace. situation:
sites lagged, then rebooted, then did not enter at all, contacting the ISP,
they said to register 1.1.1.1 and 8.8.8.8 DNS`s in the router configs.
Everything started working, but what happened/changed?

Answer 1

dns servers automatically offered by ISP via DHCP are crappy or buggy.
1.1.1.1 - dns server from the CloudFlare
Internet service 8.8.8.8 - dns server from Google
there is also Yandex.dns and a little more for every taste and color

Answer 2

If I understand correctly, then your new DNS servers are faster than the old ones :)

Answer 3

Apparently your ISP is not able to set up its own DNS servers, and told you to use public