What is DNS?

What is DNS?

The Domain Name System (aka DNS) is used to resolve human-readable hostnames like www.notesshow.blogspot.in into machine-readable IP addresses like 204.13.248.115. DNS also provides other information about domain names, such as mail services.

But why is DNS important? How does it work? What else should you know?

History of the DNS

When the Internet was still in its infancy when you wanted to visit a website you had to know the IP address of that site. That’s because computers are and were only able to communicate using numbers. It’s long, hard to remember, and we (humans, I presume) are not robots. We needed a way to translate computer-readable information into human-readable. And it had to be fast, lightweight.

DNS

In the early 1980’s, Paul Mockapetris came up with a system that automatically mapped IP addresses to domain names. And the DNS was born. This same system still serves as the backbone of the modern Internet, today. And yet, only a small subset of the world knows that it exists, and an even smaller group understand what it does. The real problem is that the people that need to know how it works and could actually benefit from this knowledge… don’t take the time to learn.

How Does It Work

DNS is a client/server network communication systems: DNS clients send requests to and receive responses from DNS servers. Requests containing a name, that result in an IP address being returned from the server, are called forward DNS lookups. Requests containing an IP address and resulting in a name, called reverse DNS lookups, are also supported. DNS implements a distributed database to store this name and last-known address information for all public hosts on the Internet.

The DNS database resides on a hierarchy of special database servers. When clients like Web browsers issue requests involving Internet host names, a piece of software (usually built into the network operating system) called the DNS resolver first contacts a DNS server to determine the server's IP address. If the DNS server does not contain the needed mapping, it will, in turn, forward the request to a different DNS server at the next higher level in the hierarchy. After potentially several forwarding and delegation messages are sent within the DNS hierarchy, the IP address for the given host eventually arrives at the resolver, that in turn completes the request over Internet Protocol. DNS additionally includes support for caching requests and for redundancy. Most network operating systems support configuration of primary, secondary, and tertiary DNS servers, each of which can service initial requests from clients.

Internet Service Providers (ISPs) maintain their own DNS servers and use DHCP to automatically configure their customer's networks, Automatic DNS server assignment relieves households of the burden of DNS configuration. Home network administrators are not required to keep their ISPs settings, however. Some prefer to use one of the available public Internet DNS services instead. Public DNS services are designed to offer better performance and reliability over what a typical ISP can reasonably offer. Home broadband routers and other network gateway devices store primary, secondary and tertiary DNS server IP addresses for the network and assign them to client devices as needed. Administrators can choose to enter addresses manually or obtain them from DHCP.  Addresses can also be updated on a client device via its operating system configuration menus.Issues with DNS can be intermittent and difficult to troubleshoot given its geographically-distributed nature. Clients can still connect to their local network when DNS is broken, but they will be unable to reach remote devices by their name. When the network settings of a client device show DNS server addresses of 0.0.0.0, it indicates a failure with DNS or with its configuration on the local network.

DNS

The Big Picture

Let’s put that all together. When you query a domain name your first step won’t actually be at the root name servers. Instead, your browser will ask your local resolving name server if they have the DNS records for that domain cached. The resolving name server is typically your ISP (Internet Service Provider), and if it’s a popular website like google.com they will likely have the record in their cache. In this case, you would skip the rest of the DNS lookup process. However, these records are only stored for a short period of time. Whenever you create a record, you have the option to set a TTL (Time to Live). TTL’s tell resolving name servers how long they can store the record information. TTL’s can range anywhere from 30 seconds to a week.

What if the record we are looking for isn’t cached? Then the resolving name server will ask the root name servers for the TLD for that domain, which will point you to the provider authoritative for hosting the records.

Why is DNS important?

DNS is like a phone book for the Internet. If you know a person’s name but don’t know their telephone number, you can simply look it up in a phone book. DNS provides this same service to the Internet.

When you visit http://notesshow.blogspot.in/ in a browser, your computer uses DNS to retrieve the website’s IP address of 204.13.248.115. Without DNS, you would only be able to visit our website (or any website) by visiting its IP address directly, such as http://204.13.248.115.

Malware & DNS Servers 

It's always important to be running an antivirus program. One reason is that malware can attack your computer in a way that changes the DNS server settings, which is definitely something you don't want to happen.

Say as an example that your computer is using Google's DNS servers 8.8.8.8 and 8.8.4.4. Under these DNS servers, accessing your bank website with your bank's URL would load the correct website and let you login to your account.

However, if the malware changed your DNS server settings (which can happen behind the scenes without your knowledge), entering the same URL might take you to a completely different website, or more importantly, to a website that looks like your bank website but really isn't. This fake bank site might look exactly like the real one but instead of letting you log in to your account, it might just record your username and password, giving the scammers all the information they need to access your bank account.

Usually, however, malware that hijacks your DNS servers generally just redirects popular websites to ones that are full of advertisements or fake virus websites that make you think you have to buy a program to clean an infected computer.

There are two things you should do to avoid becoming a victim in this way. The first is to install an antivirus program so that malicious programs are caught before they can do any damage. The second is to be aware of how a website looks. If it's slightly off of what it usually looks like or you're getting an "invalid certificate" message in your browser, it might be a sign that you're on an imitation website.

More Information on DNS Servers 

In most cases, two DNS servers, a primary and a secondary server, are automatically configured on your router and/or computer when connecting to your ISP via DHCP. You can configure two DNS servers in case one of them happens to fail, after which the device will resort to using the secondary server.

While many DNS servers are operated by ISPs and intended to be used only by their customers, several public-access ones are also available. See our Free & Public DNS Servers List for an up-to-date listing and How Do I Change DNS Servers? if you need help making the change.

Some DNS servers may provide faster access times than others but it relies solely on how long it takes your device to reach the DNS server. If your ISP's DNS servers are closer than Google's, for example, then you might find that addresses are resolved quicker using the default servers from your ISP than with a third-party server.

If you're experiencing network issues where it seems as if no website will load, it's possible that there's an issue with the DNS server. If the DNS server isn't able to find the correct IP address that's associated with the hostname you enter, the website won't load. Again, this is because computers communicate via IP addresses and not hostnames–the computer doesn't know what you're trying to reach unless it can use an IP address.

The DNS server settings "closest" to the device are the ones applied to it. For example, while your ISP might use one set of DNS servers that apply to all the routers connected to it, your router could use a different set which would apply the DNS server settings to all the devices connected to the router. However, a computer connected to the router can use it's own DNS server settings to override the ones set by both the router and the ISP; the same can be said for tablets, phones, etc.

We explained above about how malicious programs can take control of your DNS server settings and override them with servers that redirect your website requests elsewhere. While this is definitely something that scammers can do, it's also a feature found in some DNS services like OpenDNS, but it's used in a good way. For example, OpenDNS can redirect adult websites, gambling websites, social media websites and more, to a "Blocked" page, but you have complete control over the redirects.