Why DNS is important?

I wrote this to give a basic idea on DNS and how it works. Let's start from the bottom.

What is DNS?

Did you know, every time when you search for a website on the internet, you are searching on the largest distributed database in the world? This is called DNS :)

People do locate the web name and computers use to identify the websites by the IP address. Therefore DNS is used to map each IP address with the web address.  

Why it is important?

Assume if DNS is not here, Then you can’t visit the blog using the name blingtechs.blogspot.com  :) The only way you can visit us is calling the IP address directly.

Type HTTP://<The IP address>.

By entering the IP address, you can bypass the DNS lookup. But you need to keep in mind that, an IP address can be changed regularly and each domain name can have multiple IP addresses.

When you are looking for a website on the internet, the domain name you are trying to access is checked on a DNS server by your computer. This called as Domain Name Resolution  

Assume, you are at home. Assume you want to check my blog posts by searching www.blingtechs.blogspot.com

When you connect to the wifi or modem and search on the internet, your computer's network address will send some information about few DNS servers that device(wifi or modem) needs to check when translating the name to IP address to your computer. Check below diagram

There are many ways that client can query information from DNS servers. Those are

1. Iterative query - When name server of the host cannot resolve the query it sends a referral to another server to resolve. DNS server is queried and returns an answer without querying other DNS servers, even if it cannot provide a definitive answer. Iterative queries are also called non-recursive queries.

2. Recursive query - When name server of the host cannot resolve the query the server issues a query to resolve the query. when a DNS client requests information from a DNS server that is set to query subsequent DNS servers until a definitive answer is returned to the client.

Recursive queries are vulnerable to DNS cache poisoning, unauthorized use of resources, DOS (denial of service) attacks, and root name server performance degradation. (Ref: DNS & Security by Adams)

Ref:safaribooks online

Okay, now we have basic knowledge of DNS and how it works. Yeyyyy :) Let’s discuss few applications on DNS.

Google Public DNS

This is a free service announced by google on 3rd December 2009. One of the main purposes is to make the web faster. It provides a recursive name server addresses for public use, also it maps to the nearest operational server location.

Google public DNS IP addresses for IPv4 are:

8.8.8.8

8.8.4.4

Google public DNS IP addresses for IPv6 are:

2001:4860:4860::8888

2001:4860:4860::8844

Now we are going to check few DNS tools

UltraTools Free DNS tests provide a robust collection of DNS Tools including DNS Hosting Speed Check, DNS Lookup, DNS Query Estimator, DNS Traversal, Zone File Dump and DNS Root Server Speed.(ref www.ultratools.com)

Finally, you need to keep in mind that whenever a client device connects to any Internet service, a DNS lookup is performed before anything else occurs.

First, the cache of the DNS system resolver is checked. This is usually an operating system function, but some client applications (such as some mobile browsers) make their own arrangements.

Yes, that’s it! These are things I want to discuss. Let’s quickly recap what we have discussed. I started with few questions like what is DNS, why it is important, Iterative query, Recursive query, Vulnerability issues at recursive queries, few use cases on DNS and finally what you need to keep in mind. :) Let’s discuss more information about DNS in next post. Thank you :)