DNS and Propagation explained

When you have a new website built or your existing site rebuilt and hosting transferred. Domain Name System (DNS) and Propagation come into play. The net result of this is that your website can go down ( not show on the internet ) for a period of time. This can be concerning for those who don’t normally get involved in websites, but is totally normal. In this article we will look at DNA and Propagation and explore what happens when you make that initial search request.

How does DNS work?

When you type an address into your browser and press return there are those couple of seconds where your computer has a think before it starts to download the web page you are looking for.

It is in these couple of seconds where DNS comes in to play. Let’s use the following example to explain this.

If you type in a web address such as https://bdolphin.co.uk and your computer doesn’t know where to find the web page. It does exactly what we would do, it asks.

But Who does it ask?

The answer lies in the fact that with every internet provider there are DNS resolvers.

The start of the process is that your computer asks the DNS resolvers “where is bdolphin.co.uk?”

If the resolver knows it will respond with the location

Your computer will go to the location and if by magic ( it isn’t magic) the web page bdolphin.co.uk appears

The DNS Resolver Process

1. From the above image you can see above, the computer asks the DNS resolver for the location of bdolphin.co.uk,
2. The DNS resolver returns the answer of 8185.151.30.178.
3. Now your computer has the location (IP Address), it goes to the web server to retrieve the webpage

But, what happens in the situation if the DNS resolvers don’t know where to find bdolphin.co.uk

If this situation occurs the DNS Resolver goes looking for the answer

DNS and Propagation The above diagram explained

1. As in the first example, the computer asks the DNS resolver for the location of bdolphin.co.uk, but as the DNS resolver does not know where bdolphin.co.uk is located, it has to find out.
2. The DNS resolver starts by reading the address from right to left, starting with .co.uk. The reason being all .co.uk domains are managed through Nominet this will be the first stop. Nominet UK is currently delegated by IANA to be the manager of the .uk domain names
3. The DNS resolver goes to Nominet and asks, What are the nameservers for bdolphins.co.uk?. (Nameservers are servers that store the DNS for a domain.) The Nominet servers will tell the DNS resolver what the nameservers are for bdolphin.co.uk.
4. In this case the nameservers for bdolphin.co.uk are ns1.stackdns.com, ns2.stackdns.com, ns3.stackdns.com, ns4.stackdns.com – these are the servers that store the DNS for bdolphin.co.uk.
5. With this new information the DNS resolver then asks ns1.stackdns.com for the location of bdolphin.co.uk.co.uk.
6. The nameservers tell the DNS resolver that bdolphin.co.uk is at 185.151.30.178, and the information is passed back to your computer.
7. Your computer will go to that location, and once again the web page will appear.

After this, the DNS resolver will store the answer for 24 hours in case anyone else asks for that particular website.

All of this happens in a couple of seconds, and now that the DNS resolver has stored the information it has found, the website will appear even faster should we search for it again.

Propagation explained and how it can affect you

Once your Internet Service Providers (ISP) 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,

This is really important as this will increase the speed at which that website is found in future. As we now all know the speed at which a site is found and loads is of critical importance. The other advantage is that it reduces the strain on other servers being constantly asked where a particular website is.

The downside is that it can’t keep that record for too long. 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 – a great question with an “it depends answer”?

1. 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.
2. If in that time you view your website your DNS resolver will search for the website and find the old location.
3. On top of this it will store the old location for up to 24 hours, so any subsequent searches will return the old website.
4. Worst Case Scenario
   • So in a worst case scenario a new DNS record update can take 24 hours,
   • 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,
   • Therefore you should allow up to 48 hours for DNS propagation to complete.
5. I have changed my DNS today, and my colleague can see my new site but I can’t….. why?
   • This is a frustrating and 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.
   • Hence the reason I mentioned that “it depends” because there are so many variables
   • In this situation your DNS resolver still has a stored record of your websites old location, but your colleagues DNS resolver has recently cleared it’s stored record and has now found the new location.

Whilst 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. For more information on all aspects of website design and technical optimisation click here