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DNS. Three letters that can make or break your website. A fault with DNS and your website can go down for 24 to 48 hours. What is DNS? From where does this 48 hour delay come from in the age of super fast Internet and high-speed technology? Why hasn’t the ever evolving technology replaced the age-old DNS and the frightening 48 hours delay? This discussion will shed some light on most of the queries about DNS. I hope that you will see DNS from a completely different perspective after this writeup.
That is the customary question that we got to answer when we are discussing something as vast as DNS. Basically, DNS (Domain Name System) is responsible for translating human friendly website URLs like www.1stwebdesigner.com to computer readable IP addresses like 22.214.171.124 (just an example). You know, our mind cannot remember combination of such digits so we devised a system which helps convert these IP addresses to English names and vice versa.
Please understand that DNS isn’t a localized system where all the IP addresses corresponding to every website present on this planet is stored. If that was the case then an unimaginable amount of care would be required to keep such a huge database working. Also, having a localized DNS would be against the distributed character of the Internet.
Rather, DNS is a distributed service which is actually a collective group of name servers (which we call as “nameserver” in Internet lingo). These nameservers constantly refer to each other in order to stay updated with the changes that are rolled out every now and then. The process sounds simple but it is quite complex.
Well, technically speaking, yes! Though it’s a different case that one nameserver will be used for multiple websites. Otherwise, we would end up having 100 million nameservers for 100 million domains – which makes no sense. Like, I host a domain of mine on DreamHost.com. So, they give me nameservers like ns1.dreamhost.com, ns2.dreamhost.com and ns3.dreamhost.com. Now, DreamHost is giving these nameservers to almost every client that they have. So, these three nameservers basically have almost all the IP address to URL details of every DreamHost client.
When you type Google.com in your browser then a lot of stuff happens behind the scenes before you get to see the Google homepage. The image below tries to explain the flow of request.
Let me try to make it bit more clearer:
Usually, when you are about to change the nameservers for your domain or when you are hosting a fresh domain then your hosting company will tell you that it might take up to 48 hours for the information to be updated. Technically speaking, they are correct. It might take up to 48 hours for all nameservers on this planet to connect with every other nameserver and keep themselves in sync. You see, it’s a huge virtual world out there. But, my personal experience says that it usually takes less than 24 hours for the global update to complete. Still, you should consider the 48 hour delay in your time plan before you make any changes.
The below image via Wikipedia will give you an idea of hierarchical DNS, organized into zones, each served by a nameserver.
Nice question. You got the information for Google.com request that you had sent some time back. Now, that information is saved in the local ISP’s nameservers so that next time your request isn’t sent to third-party nameservers. But, after a stipulated time period these nameservers contact other nameservers so that their information isn’t outdated. This is where the term TTL comes into play.
TTL (or Time To Live) is the time period that comes in along with the IP address info. This time period information is sent by the third-party nameserver along with the IP address. The value is usually in seconds and it is more like a suggestion from the third-party nameserver that you can stay away from me for X seconds and still stay updated. Come back after X seconds and I will pass on the latest information.
Usually the TTL value is 12 hours or 24 hours. This can be set to a custom number as and when required to reduce traffic.
Once DNS started to serve the IP address lookup (as discussed above), then it was time to expand. DNS was later on used for other type of lookups, two of which we will discuss below:
Other then the three lookups that I discussed above, DNS can be used for many other functions like:
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Salman Siddiqui is an alpha geek, design guru and seasoned WordPress critic. Writing, for him, started out of ego but it has become the most luring and enlightening career option of his life. He is walking that extra mile for his freelancing dream.