How DNS Resolution Works

1) What is DNS and why name resolution exists

Domain Name Resolution (DNS) , helps to convert your domains into IP address

The above diagram helps you to understand , how websites open when you type www.chaicode.com

Step 1 :

User opens chaicode website in his/her favourite browser

Step 2 :

Request goes to DNS resolver which in return provide the IP of respective website (chaicode.com) in our case.

Step 3:

How DNS provides an IP and shows website in browser?

Inside DNS we have multiple things which helps to provide the IP address , like :

1. Whenever ser open any website it checks cache for loading wesite faster , if not found then goto step 2 , else open the website.

2. Root Server : Checks for the correct Top Level Domain server , like .com , .in and route to correct TLD server.

3. Top Level Domain (TLD server): Routes to correct A record(Authorotative Server) which helps to provide the correct ip address of the respective domain.

4. Authoritative Server: Final place which provides the ip address to the client and clinet can see the website.

dig as a diagnostic tool to inspect DNS resolution

dig = Domain Information Groper , means this tool provides the information related to dns.

It is a command-line tool used to:

• Check DNS records (A, AAAA, MX, TXT, NS, CNAME, etc.)

• Debug DNS issues

• See which DNS server responds

• Trace DNS resolution step-by-step

• Compare DNS across servers

umangpincha@apple ~ % dig google.com

;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 12345

Important Fields:

• status:

  • NOERROR ✅ success

• opcode: QUERY

• id: query ID

;; QUESTION SECTION: ;google.com. IN A

Meaning:

• Asking for A record of google.com

;; ANSWER SECTION:
google.com.        104    IN    A    142.251.223.238

Meaning:

Provides google.com ip address , means if you type 142.251.223.238 in browser, it will open google.com :)

Common dig Use Cases

1. Check A record IP address

dig google.com A

2. Check MX record (Mail Servers)

dig google.com MX

3. Check CNAME (Alias)

 dig google.com CNAME

What NS records represent and why they matter ?

NS = Name Server is a server which tells , which DNS server will handle the DNS request of the particular domain.

dig google.com NS

O/P
google.com.        286115    IN    NS    ns1.google.com.
google.com.        286115    IN    NS    ns3.google.com.
google.com.        286115    IN    NS    ns2.google.com.
google.com.        286115    IN    NS    ns4.google.com.

Meaning:

These servers are responsible for all DNS records of google.com

For eg : If Domain = Company and NS are the customer support , if someone asks where is google.com then it will contact NS like ns1.google.com

Importance

• TLD server contacts with NS , so that it can tell which nameservers are responsible for handling the DNS request of xyz domain.

• If NS don’t exist then its not possible to do the DNS resolution

Why Multiple NS ?

1. High Availability: if ns1 fails ns2 is available

2. Load Balancing: Traffic distributed among the multiple servers.

Thank You 🙏🏻