How DNS Resolution Works

What is DNS and why name resolution exists?

DNS stands for domain name system. DNS is used to convert browser url to IP address. Forward lookup resolves domain names to IP addresses, reverse lookup does the opposite, and name resolution commonly refers to the forward process.

Why name resolution exists?

1. Humans remember names, not numbers
   1. People understand google.com
   2. Computers need IP addresses like 142.250.195.46

2. IP addresses change frequently
1. Servers are replaced
2. Load balancing is added
3. Cloud scaling happens
4. Regions change

3. Names stay stable, IPs can change
1. Domain name remains the same
2. IP address can change behind the scenes

4. Avoids hard-coding IPs in applications
1. Without name resolution, apps depend directly on IPs
2. IP change = code change + redeploy

5. Removes tight coupling between app and server
   1. App talks to a name, not a server
   2. Infrastructure changes do not break applications

6. Enables scalability
   1. One name can map to multiple IPs
   2. Load balancing and CDNs become possible

7. Improves reliability
   1. If one server fails, traffic can go to another
   2. Reduces downtime

8. Provides operational flexibility
   1. Easy server migration
   2. Disaster recovery
   3. Infrastructure upgrades without impact

Name: Stable IP: Flexible

Why is Dig command?

Browser hides DNS and with dig commands reveals below information:

1. Who is responsible

2. Who you are talking to

3. How resolution actually works

   Root of the internet→ dig .NS

   Command

   dig .NS

   Who runs the ROOT of the internet

   Answer

   a.root-servers.net`[b.root-servers.net](http://b.root-servers.net) ... [m.root-servers.net`](http://m.root-servers.net)

   I don’t know Google.
   But I know who handles .com, .in, .org.

   → Root servers never give IP addresses. They only give directions.

   .com Level — dig com NS

   Command

   dig com NS

   Who manages all .com websites?

Answer
a.gtld-servers.net
b.gtld-servers.net
...

TLD servers says:
1. I don’t know Google’s IP.
2. But I know who owns google.com.

Google’s Own Servers — dig google.com NS

Command
dig google.com NS

Who is the official authority for google.com?

Answer
ns1.google.com`[ns2.google.com](http://ns2.google.com) ...`

These servers are authoritative.

I am Google. I know everything about google.com.

Finally Getting the IP — dig google.com

dig google.com

What happens:
1. Ask Root

Who handles .com?

2. Ask .com

Who handles google.com?

3. Ask Google’s DNS

What is the IP of google.com?

4. Google replies

   142.250.195.46