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Networking - DNS

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Lesson Description


Lession - #1382 DNS Look Up


There are 232 ip Addresses (approximately four, 294, 967, 296>
. With growth of internet at a speedy pace came issue of remembering websites with their information processing Address (not a difficulty if powerful or bot pretending to be human>
. This issue was resolved using DNS. domain name System is method of resolving human-understandable URLs into their respective ip addresses. whereas you enter uniform resource locator (this url is understood as FQDN – fully Qualified Domain Name>
into browser, DNS takes care of looking at actual ip address related to web site.

DNS Look-Up :

To resolve such DNS queries, there area unit domain name Servers built across world that takes your DNS look-up request and resolve it. There are five types of Name Servers –


Caching Name Servers.
Recursive Name Servers.
Root Name Servers.
Top Level Domain (TLD>
Name Servers.
Authorative Name Servers.
Caching and algorithmic Name Servers are generally provided by internet Service providers. Purpose of Caching Name Server is to store known domain names surely amount of time (similar to caching in data storage>
. recursive Name Server performs Full Name Resolution. There are thirteen Root Name Servers across globe, responsible for directing requests to appropriate TLD Server.

DNS Look-up



When you sort FQDN in your browser, it checks host files already available in your system. a number file has entries as follows –

Example –

127.0.0.1 localhost
216.58.203.36 www.google.com




If the ip Address is not found in Host files, then DNS look-up is carried to Caching Name Server, which stores domain names for certain amount of time.

If caching name server doesn't resolve look-up, it's then transmitted to recursive Name Server. algorithmic name servers are responsible to perform full DNS Resolution requests.

The request from recursive Name Server is transmitted to 13 Root Name Servers using Anycast (It is technique that's used to route traffic to completely different destinations depending on factors like location, link health and congestion>
.

Root Name Server responds to DNS Look-up with name of TLD Name Server that should be queried.

For each top Level Domain in name (A superior domain is an element of domain that comes when the dot, as an example, com, org or net>
there's top Level Domain (TLD>
Name Server. TLD server responds to DNS Look-up with redirect, informing your system regarding that Authorative Name Server to contact.

Finally, DNS Look-up is redirected to Authorative Name Server for resolving web site name and it provides actual ip Address of the server.

This strict hierarchy maintains stability of net by resolution each lookup in correct manner. This protects against malicious redirecting traffic. nowadays devices have built-in local cache servers to stop performing DNS lookup for every new TCP connection.