DNS Definition

The Domain Name System (DNS) turns domain names into IP addresses, which browsers use to load internet pages. Every device connected to the internet has its own IP address, which is used by other devices to locate the device. DNS servers make it possible for people to input normal words into their browsers, such as Fortinet.com, without having to keep track of the IP address for every website.

What is a DNS Server?�

• A DNS server is a computer with a database containing the public IP addresses associated with the names of the websites an IP address brings a user to. DNS acts like a phonebook for the internet. Whenever people type domain names, like Fortinet.com or Yahoo.com, into the address bar of web browsers, the DNS finds the right IP address. The site’s IP address is what directs the device to go to the correct place to access the site’s data.
• Once the DNS server finds the correct IP address, browsers take the address and use it to send data to content delivery network (CDN) edge servers or origin servers. Once this is done, the information on the website can be accessed by the user. The DNS server starts the process by finding the corresponding IP address for a website’s uniform resource locator (URL).

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How Does DNS Work?�

• In a usual DNS query, the URL typed in by the user has to go through four servers for the IP address to be provided. The four servers work with each other to get the correct IP address to the client, and they include:
• DNS recursor: The DNS recursor, which is also referred to as a DNS resolver, receives the query from the DNS client. Then it communicates with other DNS servers to find the right IP address. After the resolver retrieves the request from the client, the resolver acts like a client itself. As it does this, it makes queries that get sent to the other three DNS servers: root nameservers, top-level domain (TLD) nameservers, and authoritative nameservers.
• Root nameservers: The root nameserver is designated for the internet's DNS root zone. Its job is to answer requests sent to it for records in the root zone. It answers requests by sending back a list of the authoritative nameservers that go with the correct TLD.
• TLD nameservers: A TLD nameserver keeps the IP address of the second-level domain contained within the TLD name. It then releases the website’s IP address and sends the query to the domain’s nameserver.
• Authoritative nameservers: An authoritative nameserver is what gives you the real answer to your DNS query. There are two types of authoritative nameservers: a master server or primary nameserver and a slave server or secondary nameserver. The master server keeps the original copies of the zone records, while the slave server is an exact copy of the master server. It shares the DNS server load and acts as a backup if the master server fails.

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Authoritative DNS Servers vs. Recursive DNS Servers: What’s the Difference?�

• Authoritative nameservers keep information of the DNS records. A recursive server acts as a middleman, positioned between the authoritative server and the end-user. To reach the nameserver, the recursive server has to “recurse” through the DNS tree to access the domain’s records.
• Authoritative DNS Server
• To use the phone book analogy, think of the IP address as the phone number and the person’s name as the website’s URL. Authoritative DNS servers have a copy of the “phone book” that connects these IP addresses with their corresponding domain names. They provide answers to the queries sent by recursive DNS nameservers, providing information on where to find specific websites. The answers provided have the IP addresses of the domains involved in the query.
• Authoritative DNS servers are responsible for specific regions, such as a country, an organization, or a local area. Regardless of which region is covered, an authoritative DNS server does two important jobs. First, the server keeps lists of domain names and the IP addresses that go with them. Next, the server responds to requests from the recursive DNS server regarding the IP address that corresponds with a domain name. 
• Once the recursive DNS server gets the answer, it sends that information back to the computer that requested it. The computer then uses that information to connect to the IP address, and the user gets to see the website.

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• Recursive DNS Server
• After a user types in a URL in their web browser, that URL is given to the recursive DNS server. The recursive DNS server then examines its cache memory to see whether the IP address for the URL is already stored. If the IP address information already exists, the recursive DNS server will send the IP address to the browser. The user is then able to see the website for which they typed in the URL.
• On the other hand, if the recursive DNS server does not find the IP address when it searches its memory, it will proceed through the process of getting the IP address for the user. The recursive DNS server's next step is to store the IP address for a specific amount of time. This period of time is defined by the person who owns the domain using a setting referred to as time to live (TTL).

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DNS Servers and IP Addresses�

• Computers and various devices that use the internet depend on IP addresses to send a user's request to the website they are attempting to reach. Without DNS, you would have to keep track of the IP addresses of all the websites you visit, similar to carrying around a phone book of websites all the time. The DNS server allows you to type in the name of the website. It then goes out and gets the right IP address for you. Armed with the IP address, your computer (or browser) can bring you to the site.
• For instance, if you input www.fortinet.com in your web browser, that URL, on its own, cannot bring you to the website. Those letters cannot be “read” by the servers that connect you with the site. However, the servers are able to read IP addresses. The DNS server figures out which IP address corresponds with www.fortinet.com and sends it to your browser. Then the website appears on your device’s screen because the browser now knows where to take your device.

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DNS Server Not Responding? What Does That Mean?�

• You may get a message that says “DNS server isn’t responding” after entering a domain name in the URL bar of your browser. This means there was an attempt to communicate with the DNS server, but the server failed to return a result. This could be due to a few different things:
• Your internet connection is weak or unstable, making it hard for your browser to communicate with the DNS server
• Your DNS settings or browser need to be updated
• There is an issue with the DNS server, such as a loss of power at the data center where it is housed

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Best DNS Servers�

• Here are some of the top DNS servers available:
• Cloudflare 1.1.1.1. This is a simple-to-use DNS service that comes with tutorials for all of the most popular operating systems, such as Mac, Windows, Android, iOS, and Linux. Users can also use Cloudflare’s service to block adult content.
• Google Public DNS. The Google Public DNS service is different from Cloudflare’s in that it is designed for more technically adept users. But you can find tutorials if needed.
• Quad9. Quad9’s DNS service is renowned for its fast performance. It also claims to block malicious sites using threat intelligence data.

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Browser DNS Caching�

• The operating system (OS) used by your device stores DNS resource records through the use of caching. Caching prevents redundancy when someone tries to go to a site. This, in turn, reduces the amount of time it takes to get to the website. If the device you are using recently went to the page it is trying to access, the IP address can be supplied by the cache. In this way, the website request can be completed without involving the DNS server.
• The DNS cache, therefore, helps streamline the DNS lookup process that would otherwise be necessary to link a domain name to an IP address. This makes the process of getting to the website much faster.
• OS DNS Caching
• The operating systems of many devices are capable of maintaining a local copy of DNS lookups. This makes it possible for the OS to quickly get the information it needs to resolve the URL to the correct IP address.

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How to Perform a DNS Lookup�

• Each domain has DNS records, and these are pulled by nameservers. You can check the status of the DNS records associated with your domain. You can also examine the nameservers to ascertain which records are being pulled by the servers. On a Windows computer, for example, this is done using the NSLOOKUP command. Here’s how to do it:
• Access the Windows command prompt by going to Start >> command prompt. You can also get to it via Run >> CMD.
• Type NSLOOKUP and then hit Enter. The default server gets set to your local DNS, and the address will be your local IP address.
• You then set the type of DNS record you want to look up by typing "set type=##" where "##" is the record type, then hit Enter. You can also use A, AAAA, A+AAAA, ANY, CNAME, MX, NS, PTR, SOA, or SRV as the record type.
• Enter the domain name you want to query. Hit Enter.
• At this point, the NSLOOKUP returns the record entries for the domain you entered.

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What is a DNS Revolver?�

• A DNS resolver is also referred to as a recursive resolver. It is designed to take DNS queries sent by web browsers and applications. The resolver receives the website URL, and it then retrieves the IP address that goes with that URL.
• What are the Types of DNS Queries?
• During the DNS lookup process, three different kinds of queries are performed. The queries are combined to optimize the resolution of the DNS, saving time.
• Recursive query
• Iterative query
• Non-recursive query

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Free vs. Paid DNS Servers: What is the Difference?�

• In some cases, a regular user may not need a paid DNS server. However, there are significant benefits of paying for a premium DNS.
• Dynamic DNS (DDNS): A DDNS maps internet domains, matching them to IP addresses. This enables you to get into your home computer no matter where you are in the world. DDNS is different from a regular DNS because it works with changing or dynamic IP addresses, making them a good choice for home networks.
• Secondary DNS: A secondary DNS nameserver makes sure that your domain does not go offline. It provides you with a redundancy or backup that can be accessed in the event of a complication.
• Management interface: Many paid DNS servers offer users a dashboard they can use to manage their service and tweak it according to their needs.
• Two-factor authentication: You can provide protection for your domain with an extra level of authentication.
• More security: When you make use of a paid DNS server, you get another protective level of security. This helps shield your website from attackers.
• Better, faster performance: A paid DNS server comes with a service-level agreement (SLA). Each SLA guarantees a high rate of DNS resolution, often between 99% and 100%.
• Customer service: With a paid DNS server, you get the additional advantage of customer service that can answer questions and troubleshoot any issues.

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What is DNS Cache Poisoning?�

• DNS cache poisoning, also called DNS spoofing, involves the introduction of corrupt DNS data into the resolving device’s cache. This results in the nameserver returning the wrong IP address.
• The operating systems of many devices are capable of maintaining a local copy of DNS lookups. This makes it possible for the OS to quickly get the information it needs to resolve the URL to the correct IP address.

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