What is DNS propagation.

When a new domain name is registered (or an existing one is transferred to a new DNS), the information must be updated in the entire ISP’s and root servers around the world. This updating process is called as DNS propagation.

DNS propagation time and Problems during the propagation.

Any time that DNS changes are made on any level, you will need to wait for the propagation to complete and this will usually takes 3-4 days (72-96 hours). During propagation, traffic may come to either location. One person may see the new server while the other person sees the old one. Also, your domain name may work and may not too. All of this is normal during propagation. This means that just because you go to the new site when you type in the domain name does not mean that propagation is complete.

Detailed explanation of propagation

DNS stands for Domain Name Service. Every time you go to a web site using a domain name, you are using DNS. Your request for that domain name goes to your local primary or secondary DNS server which is usually administered by your ISP. Your local DNS server check its records to see if it knows what IP address that domain points to. If it does, then it directs you to that IP address. If it does not, then it sends a query to the Root DNS servers.

The Root servers are what make the process work. When a domain is registered, it is added to the Root servers. When a domain is expired, it is removed from the Root servers. The Root servers tell your local DNS server which DNS servers are the authorities for your domain.

Your local DNS server then queries the authorities DNS server, and that server tells your local DNS server what IP address is the domain located. Your local DNS server then caches the information. This process is essential because it does not only does it speed up future queries but also reduces the load on the Root servers.

This process leads to the propagation.
Your local DNS server will not keep that information forever. It will be kept for a certain amount of time, at one point it deletes it. The next time, which is after the information is deleted when you try to visit that domain, the process will start all over again.

DNS Propagation Check

DNS Propagation will usually takes 3-4 days (72-96 hours).   There are a lot of tools available on the web to check DNS propagation. With the DNS propagation checkers you can verify that with a few DNS servers around the world.  Enter in a domain name and it will check what IP it is associated with through several ISP DNS caches.

99% of the time this is completely useless, but if you have just moved a domain name this can be helpful to see how the propagation is going.

How to Speed up DNS Propagation

The well-known way to do this, is to lower your TTL values for a while before making a DNS change.  However, there are three big issues with this:

1) sometimes you don’t know when you’ll be making such a change

2) lots of ISPs set the DNS TTL to several days, and stubbornly refuse to make an exception for you, particularly because you generally ask them when you are leaving as a customer.

3) Various client programs and DNS client modules do their own caching, and do not process DNS TLL anywhere near correctly.

I have now concluded that to be completely safe (i.e., no person or search engine will think your site is missing), you should allow a week overlap – the server at the old IP address should continue to work for that duration.