Steps of Name Resolution in DNS

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Steps of Name Resolution in DNS

      DNS is a system that converts domain names into IP addresses. It's the way humans are likely to remember and categorize things resolved into the way computers prefer to think of things. This process of using DNS to turn a domain name into an IP address is known as name resolution. The first thing that's important to know is that DNS servers, are one of the things that need to be specifically configured at a node on a network. 

     There are five primary types of DNS servers:

•  caching name servers
•  recursive name servers
•  root name servers
•  TLD name servers
•  authoritative name servers. 

      It's important to note that any given DNS server can fulfill many of these roles at once. Caching and recursive name servers are generally provided by an ISP or your local network. Their purpose is to store domain name lookups for a certain amount of time. As you'll see in a moment, there are lots of steps in order to perform a fully qualified resolution of a domain name. In order to prevent this from happening every single time a new TCP connection is established, your ISP or local network will generally have a caching name server available. 

     Most caching name servers are also recursive name servers. Recursive name servers are ones that perform full DNS resolution requests. In most cases, your local name server will perform the duties of both, but it's definitely possible for a name server to be either just caching or just recursive. 

     Let's look at what happens when your local recursive server needs to perform a full recursive resolution. The first step is always to contact a root named server, there are 13 total root name servers and they're responsible for directing queries toward the appropriate TLD name server. In the past, these 13 root servers were distributed to very specific geographic regions, but today, they're mostly distributed across the globe via anycast. Anycast is a technique that's used to route traffic to different destinations depending on factors like location, congestion, or link health. Using anycast, a computer can send a data gram to a specific IP but could see it routed to one of many different actual destinations depending on a few factors. 

      The root servers will respond to a DNS lookup with the TLD name server that should be queried. TLD stands for top level domain and represents the top of the hierarchical DNS name resolution system. A TLD is the last part of any domain name, using www.facebook.com as an example again, the dot com portion should be thought of as the TLD. For each TLD in existence, there is a TLD name server, but just like with root servers, this doesn't mean there's only physically one server in question, it's most likely a global distribution of any cast accessible servers responsible for each TLD. The TLD name servers will respond again with a redirect, this time informing the computer performing the name lookup with what authoritative name server to contact. Authoritative name servers are responsible for the last two parts of any domain name which is the resolution at which a single organization may be responsible for DNS lookups.  

     Your computer will blindly send traffic to whatever IP it's told to. So by using a hierarchical system controlled by trusted entities in the way DNS does, we can better ensure that the responses to DNS lookups are accurate.