What is propagation and how does it affect me?

If you have read the above articles regarding What DNS is and how it works, you will be aware that it involves a DNS resolver finding the location of a domain name for you. If not I recommend reading them to get an idea how how DNS works.

Once your Internet Service Providers DNS resolver finds where a domain name is it will store the DNS information it has found so it doesn’t have to search for it again, the main advantage of this is it will increase the speed at which that website is found in future, the other advantage is it reduces the strain on other servers being constantly asked where a particular website is.

However it cannot keep that record for too long, so the majority of servers will only keep a record of what it has found for 24 hours. This means the DNS resolver will only actively look for a website once ever 24 hours.

So how does DNS propagation effect me?

Well if a DNS change is made to move your website to another server, it can take up to 24 hours for that change to go live.

If in that time you view your website your DNS resolver will search for the website and find the old location.
On top of this it will store the old location for up to 24 hours, so any subsequent searches will return the old website.

So in a worst case scenario a new DNS record update can take 24 hours, and on top of this it can take a further to 24 hours for the DNS resolver to clear it’s memory and find this latest update, hence we have to allow up to 48 hours for DNS propagation to complete.

I have changed my DNS today, and my friend can see my new site but I can’t….. why?

This is a common occurrence and is mainly caused by the fact that there are many different Internet Service Providers, who have many different DNS resolvers around the country.

In this situation your DNS resolver still has a stored record of your websites old location, but your friends DNS resolver has recently cleared it’s stored record and has now found the new location.

Although this can be frustrating it should be seen as a good situation as it reassures us that the change has been successful and it is only a matter of time until the change completely propagates.