My understanding of the core functionality of DNS is to provide a naming/mapping service between domain names (e.g.
blah-whatever.com) and IP addresses (e.g. 18.104.22.168).
Furthermore, my understanding of how Internet DNS servers work is that when a domain/IP mapping record is changed (say, changing
blah-whatever.com to now point to 22.214.171.124, etc.), this change needs to be propagated over every DNS server in the world before the change can be said to be "complete". This propagation period can sometimes last up to 24 hours.
So to begin with, if anything I have said so far is misguided or incorrect, please begin by correcting me!
Assuming I'm more or less correct, I don't understand how companies like CloudFlare or DynamicDNS can offer "instant rollover"-type services whereby you change your DNS record with them and - boom - the change takes affect instantly.
I understand there is something called "TTL" (time to live, I presume ?!?) that plays a role in this instant rollover capability, but since I'm already fuzzy on the capability to begin with it's hard to make sense of what this TTL is or what purpose it serves.
So I ask: what is it about Dynamic DNS and its competitors that allows them to change DNS mappings instantly (without taking 24 hours to propagate DNS changes like everybody else), and how does TTL fit into this process? Thanks in advance.