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Networking - DNS

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Lesson Description


Lession - #1375 DNS Architecture


Root Level Domains
The DNS root level is the highest in the DNS hierarchy tree because it's the first step in resolving a domain name. The root DNS server is the DNS for the root zone. It handles requests for records in the root zone and answers other requests by providing lists of authoritative name servers for the appropriate TLD( top- level domain>
. These are the authoritative nameservers that serve the DNS root zone. These servers contain the global list of the top- level domains. The root zone contains the following

Organizational hierarchy
– such as. com,. net,. org,. edu.
Geographic hierarchy
– such as. ca,. uk,. fr,. pe.

Currently, there are 13 root name servers specified, with logical names in the form “letter.root-servers.net ”, where letter ranges from “ A ” to “ M ” and represent companies like Verisign, University of Maryland, NASA, and The Internet Corporation for Assigned Names and Numbers( ICANN>
.

Root DNS servers
Previously, there were only single servers for each of the 13 IP addresses. Today, there are server clusters for each of them meaning there are hundreds of servers all around the world. They use Anycast DNS routing for load- balancing and better- decentralized performance.

Top- Level Domains
The next level in the DNS hierarchy is Top- Level Domains or TLDs, for short. There are over 1000 TLDs covering everything from “. abb ” to “. zw ” and still growing. As we've seen, the TLDs are classified into two subcategories organizational hierarchy and geographic hierarchy.

The organizational hierarchy is divided into domains for the likes of commercial enterprises( “. com ”>
, government entities( “. gov ”>
, educational institutions( “. edu ”>
, and nonprofit organizations( “. org ”>
.

The geographic hierarchy, meanwhile, represents the country where the domain is hosted. Examples include “. ca ” for Canada, “. uk ” for the United Kingdom, “. au ” for Australia, and even “. aq ” for Antarctica.

Organizations that want to cater to their local customers can opt for TLDs that use both organizational and geographical hierarchies. Examples would be “.com.et ” for an Ethiopian business, “.org.al ” for an organization in Albania, and “.gov.it ” for the Italian government.

Second- Level Domains
A domain is a second- level domain if it's contained within a top- level domain. A second- level domain is a label – usually, a name related to the website or the business that owns it – immediately to the left of the top- level domain, and separated by a dot.

In the Domain Name System( DNS>
hierarchy, a second- level domain( SLD or 2LD>
is a domain that's directly below a top- level domain( TLD>
. For illustration, in “myexample.com ”, “ myexample ” is the second- level domain of the “. com ” TLD.
Subdomains
A subdomain –sometimes referred to as “ third- level domains. ” – is related to the root domain and is denoted on the left as a second- level domain. In the URL “blog.myexample.com ” the subdomain address would be “ blog. ”

Trivia the “ WWW ” inwww.example.com is also asub-domain, although it is n’t always necessary to type it in a domain name.

Hosts
The host part of an FQDN is used to identify an individual device – usually a server. In the FQDN “myserver.example.com ” the hostname would be “ myserver. ”