What is DNS propagation? DNS propagation is the time delay between the time
you make DNS changes on your authoritative DNS servers, usually at your
hosting provider, and the time it takes for these changes to be seen by your
end users and customers. The time it takes to propagate is going to be
based on your current time to live (TTL) settings for the resource record
your changing. These TTL values must expire from the recursive DNS servers
around the Internet. Meaning the recursive DNS servers at ISP around the
world. Once the TTL value reaches zero the recursive DNS server will then
need to ask the authoritative DNS server for the new answer. The higher the
TTL value the longer it takes changes to propagate because it will take
longer for the cached value to expire. This tools will query several recursive
DNS servers at random ISP's around the world to report on what IP address
they are currently returning to their end users DNS queries for your domain.
This will help you gauge if the changes you have made are being propagated
in a timely manner.