DNS Cache and your
ISP:
There is also the issue of DNS cache, which is something we won't go into
great detail about here, but here's the short version.
Every time you access a site from your ISP, they cache the
URL, as well as its associated IP number.
If their network is properly setup, these DNS cache
records should "Expire" at least every 24-hours.
If they did not (which is often the case), you'll
experience this:
You enter your http://www.mydomain.com/ URL, and it keeps
taking you back to your old server account.
In a large number of cases, it's the result of an ISP who "Did Not"
configure their servers to "Expire" the DNS cache records at the
appropriate intervals.
Unfortunately, this adds additional confusion to their
clients, and especially the ones whom are trying to point their domain
name to a new server.
The DNS propagation process is not limited
to ISP's!
The Internet itself must update/clear its DNS cache as well.
When we say the Internet, we mean the numerous
intermediate "points of access" you're routed through before reaching your
final destination.
For the most part, these intermediate points of access
consist of "Internet Routers" and "Internet Caching Engines."
These too, maintain their own DNS cache, which assists
them in routing traffic/resolving URL's to the correct destination IP's.
Don't worry though, as Internet routers are usually faster
at clearing their DNS cache than ISP's are.
What to expect during this 2 to 4 day
propagation period:
In most cases, the propagation process will take at least 48 hours to
complete.
The first thing that happens is the "World Root Name
Servers" will check all of the various "Domain Registers for updates.
Ok, so now the Root Name Servers have done their job. The
rest of it is up to the many ISP providers who "should be" updating their
DNS records (at least every 24 hours), but a number of them will not.
