DNS

what is DNS
DNS is a global system for translating IP address to human-readable domain names. the DNS server takes the hostname and resolves it into a numeric IP address which the web browser can connect to. 

purpose 
it manages to translate all the inquiries into IP addresses, and like this, it can identify different devices that are connected to the network.


 DNS queries

A DNS query (also known as a DNS request) is a demand for information sent from a user's computer (DNS client) to a DNS server. In most cases a DNS request is sent, to ask for the IP address associated with a domain name. An attempt to reach a domain is actually a DNS client querying the DNS servers to get the IP address, related to that domain.


1. recursive query 
- A recursive query is a kind of query, in which the DNS server, who received your query will do all the job of fetching the answer, and giving it back to you. During this process, the DNS server might also query other DNS servers on the internet on your behalf, for the answer.



2. iterative / non-Recursive query 
It either immediately returns a DNS record because it already stores it in the local cache, or queries a DNS Name Server which is authoritative for the record, meaning it definitely holds the correct IP for that hostname.


describe DNS servers 

1. DNS resolver 
- is a server, designed to receive DNS queries, which include a human-readable hostname such as “www.example.com”, and is responsible for tracking the IP address for that hostname.

2. root server 
- A root server is part of the supporting infrastructure of the Internet and facilitates Internet use by acting as the backbone of online access.

3. Authoritative  Name server 



Describe 3 types of common DNS record 

Address Mapping record (A Record)
also known as a DNS host record, stores a hostname and its corresponding IPv4 address.

IP Version 6 Address record (MX Record)
stores a hostname and its corresponding IPv6 address.

Mail exchanger record 
specifies an SMTP email server for the domain, used to route outgoing emails to an email server.





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