Understanding what happens during the 3 - 4 days propagation period
Where do the Root Name Servers receive their information from ?
The root name server will query "domain registrars" several times a day.The root name server will gather this information from the many registrars now in existence and update their master records accordingly.Now your ISP must access their Root Name servers and update their DNS records which resides on their local DNS server.The process is fully automated and most ISP's will check the Root Name servers for updates every 24 hours.Beware however that some lame ISP's will delay this process for as much as 2 to 4 days in some cases. If that happens, it will no doubt cause additional confusion as everyone else will be reaching your new account on our server except you.This is because your ISP has not updated their DNS records and or have not cleared their DNS cache which means they'll still be pointing your domain name to your old server.If it's a new domain you've registered , then you'll receive a blank 'Site Not Found Page'.
DNS cache and your ISP
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.domain.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 "point 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 lof the various "Domain Registrars for updates".After the root name server has done this processing, 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.
Site effect that can be expected during the propagation time frame
It's perfectly normal for strange things to happen within the 48 hours propagation period ,but sometimes longer.While we could provide a full list of all the anomalies that can occur during the DNS propagation period, we'll stick to some of the most common scenarios that most people experience.
Help ! My friends can reach my website, but I'm still being redirected to the OLD ONE !
This is a classic case of your friends ISP ( who did update their DNS records ) but yours unfortunately did not.As a result,your ISP is still pointing your domain name to the old DNS record, which is your old hosting account.Wait a couple of more days and it if appears that everyone but you can access your new account,then contact yours ISP and tell them to expire their old DNS cache records.
WOW! http://www.mydomain.com is taking me to my new account just a minute ago but when I try it now ,I'm being taken back to my old hosting account - what's up with this?
In all likelihood,your ISP may be in the process of cleaning their DNS cache and or updating their local DNS server records.During this small interval,it's normal to fluctuate between the new and old web site as the old DNS records may not have completely expired from their cache yet.Give it another several hours and it should be fine.
What's going on with my email?When I try to access it , I receive "host does not exist" or a "cannot authenticate" error message.
This can happen for a number of reasons but in most cases , it's because your new DNS records have not fully completed the propagation process yet.Consequently,you may be trying to access your old email account on your "old server" which you may have already cancelled , or it's in a state of DNS flux ,which means it points to the new server one moment ,and the next ,points back to the old server.Give it some more time and it will eventually settle down.