DNS Concepts

Some notes for myself as I familiarize myself with networking. I used Digital Ocean's informative article as a resource.

Terminology

Domain Name System (DNS): A system that resolves human friendly names to addresses
Domain Name: Human friendly name that is associated to a resource.

Ex: google.com

IP Address: "Network addressable location". IP addresses must be unique within its network. IPv4 is the most common form of addresses, and is written with 4 sets of numbers, each having up to 3 digits.

192.198.1.10

Top Level Domain (TLD): The most general portion of the domain.

Ex: com, org, io

ICANN (Internet Corporation for Assigned Names and Numbers) give control to these TLD to specific parties, which then distributes domains under the TLD.

Hosts: Computers/Services accessible through domain

Domain owners often expose their webserveres through their bare domain e.g. google.com and also through the host definition www, e.g. www.google.com. There can also be other host definitions, such as api (api.google.com) for API's or files (files.google.com) for ftp.

SubDomain: A domain that is a part of a larger domain

google.com is a subdomain of com.

It looks similar to hosts, but www.google.com points to a resource/computer/service, and does not divide the google.com domain (which is what subdomains do).

Fully Qualified Domain Name: Absolute domain name. Ends with a dot to indicate the root of the DNS heirarchy.

mail.google.com.

Name Server: A computer that translates domain names to IP addresses.

Can be authorative, giving the answer to a domain they own. Else, they point to another server, serve cached, or other server's data.

Zone File: A text file that holds the mappings between domain names and IP addresses. Stored in name servers, it defines resources for the subdomain (or where to go to see the definition)
Records: A single mapping between a resource and a name residing in a zone file. This can map a domain to an IP address, define the name server for a domain, etc.
Root Servers: The top servers of the DNS heirarchical structure. These are controlled by various organizations, delegated by ICANN. There are only a handful of these root servers, but are mirrored due to the high traffic flow to resolve names. Each mirror share the same IP address. These servers