DNS (Domain Name System) in Computer Networks - Step-by-Step Execution

Concept Flow - DNS (Domain Name System)

User enters website URL

↓

Browser asks DNS resolver

↓

Resolver checks cache

↓

Return IP

↓

Root points to TLD server

↓

TLD points to Authoritative DNS

↓

Authoritative DNS returns IP

↓

Resolver returns IP to Browser

↓

Browser connects to IP

↓

Website loads

This flow shows how a website name is translated into an IP address step-by-step using DNS servers.

Execution Sample

Computer Networks

User types 'example.com'
Browser asks DNS resolver
Resolver checks cache
If no cache, resolver queries root server
Root server directs to .com TLD server
TLD server directs to example.com authoritative server
Authoritative server returns IP
Resolver returns IP to browser
Browser connects to IP

This sequence shows the step-by-step DNS lookup process to find the IP address for a website.

Analysis Table

Step	Action	Query Sent To	Response	Result
1	User enters 'example.com'	Browser	N/A	Start DNS lookup
2	Browser asks DNS resolver	Local DNS Resolver	N/A	Resolver receives query
3	Resolver checks cache	Cache	No IP found	Cache miss, continue lookup
4	Resolver queries Root DNS server	Root DNS Server	Points to .com TLD server	Next query target identified
5	Resolver queries .com TLD server	.com TLD Server	Points to example.com authoritative server	Next query target identified
6	Resolver queries example.com authoritative server	Authoritative DNS Server	Returns IP 93.184.216.34	IP address found
7	Resolver returns IP to browser	Browser	IP 93.184.216.34	Browser can connect
8	Browser connects to IP	Web Server	Website content	Website loads successfully
9	End	N/A	N/A	DNS lookup complete

💡 DNS lookup ends when the authoritative server returns the IP and browser connects to the website.

State Tracker

Variable	Start	After Step 3	After Step 6	Final
Queried Domain	example.com	example.com	example.com	example.com
Cache Result	Empty	No IP found	No change	No change
Current DNS Server	Local Resolver	Root DNS Server	Authoritative DNS Server	Local Resolver
IP Address Found	None	None	93.184.216.34	93.184.216.34

Key Insights - 3 Insights

Why does the resolver ask multiple DNS servers instead of just one?

Because the resolver starts with no direct knowledge of the IP, it asks the root server first, which points to the TLD server, which then points to the authoritative server. This step-by-step process is shown in steps 4 to 6 in the execution_table.

What happens if the IP address is found in the cache?

If the IP is in the cache (step 3), the resolver returns it immediately without querying other servers, speeding up the process. In our example, the cache was empty, so the resolver continued querying.

Why is the authoritative DNS server important?

The authoritative DNS server holds the actual IP address for the domain. Without it, the resolver cannot find the correct IP. This is shown in step 6 where the IP is finally returned.

Visual Quiz - 3 Questions

Look at the execution_table at step 3. What does the resolver find in its cache?

A The IP address for the root server

B The IP address for example.com

C No IP address found

D An error message

💡 Hint

Check the 'Response' column at step 3 in the execution_table.

At which step does the resolver receive the actual IP address for example.com?

A Step 6

B Step 4

C Step 5

D Step 7

💡 Hint

Look for the step where 'Returns IP 93.184.216.34' appears in the Response column.

If the cache had the IP address at step 3, how would the execution_table change?

A Step 2 would be repeated

B Steps 4 to 6 would be skipped

C Step 7 would be removed

D Step 8 would happen earlier

💡 Hint

Refer to the key_moments explanation about cache hits and the execution_table steps.

Concept Snapshot

DNS translates website names into IP addresses.
User's browser asks a DNS resolver.
Resolver checks cache, then queries root, TLD, and authoritative servers stepwise.
Authoritative server returns the IP.
Browser uses IP to connect to website.
This process happens quickly and transparently.

Full Transcript

DNS (Domain Name System) is like the internet's phonebook. When you type a website name, your browser asks a DNS resolver to find the matching IP address. The resolver first checks if it already knows the IP in its cache. If not, it asks the root DNS server, which points to the top-level domain (TLD) server like .com. The TLD server then points to the authoritative DNS server for the website, which finally returns the IP address. The resolver gives this IP to the browser, which connects to the website. This step-by-step lookup ensures that domain names are translated into IP addresses so computers can communicate.