Computers communicate using IP addresses (such as 142.250.182.14), not domain names. DNS exists to map domain names → IP addresses.

However, DNS is not a single database. Instead, it is:

• Distributed across thousands of servers

• Hierarchical in structure

• Highly cached for performance and resilience

• 

This design avoids central bottlenecks and allows the internet to scale to billions of devices and domains.

Introducing dig: Inspecting DNS Internals

dig (Domain Information Groper) is a command-line utility used to:

• Query DNS records directly

• Inspect which servers respond at each layer and get theirn addresses

• Debug DNS configuration and propagation issues

• Understand how resolution actually happens

Unlike browsers or operating systems—which hide DNS behind caching and abstraction—dig shows raw DNS responses.

The DNS Hierarchy: Resolution in Layers

DNS resolution happens through a strict hierarchy:

ff

Root Name Servers

↓

Top-Level Domain (TLD) Servers (.com, .org, .in)

↓

Authoritative Name Servers (e.g., google.com)

Each layer only knows where to find the next layer—never the final answer directly (except the authoritative servers).

Querying the Root Zone: dig . NS

» dig . NS

This command asks:

“Who are the name servers for the DNS root?”

What the response shows

A list of root name servers, such as:

• a.root-servers.net

• b.root-servers.net

• … ETC

Or can show Error

• Many DNS resolvers (especially ISP, router, or enterprise DNS servers):

  • Do not allow direct root (.) queries

  • Treat them as unnecessary or suspicious

• Private / ISP / Router DNS Resolver

  • Such resolvers:

    • Answer normal domain queries (google.com)

    • Refuse infrastructure-level queries like dig . NS

• Security and Abuse Prevention

  • Root-level queries can be used for:

    • DNS amplification attacks, Reconnaissance, Traffic analysis

  • As a result, many resolvers:

    • Allow them internally

    • Block them for clients

Key characteristics of root servers

• They do not store IP addresses for websites .

• They only delegate to TLD servers.

• They are globally distributed and heavily cached.

• DNS governance and coordination is handled by organizations such as ICANN.

Root servers are the starting point for all DNS resolution.

Querying a TLD: dig com NS

» dig com NS

This asks:

“Which name servers manage the .com domain?”

What TLD servers do

• Maintain delegation information for all .com domains

• Point resolvers to the authoritative servers for each registered domain

• Do not store A/AAAA records for individual websites

This separation allows millions of domains to exist under a single TLD without overload.

Finding Authoritative Servers: dig google.com NS

» dig google.com NS

This query returns the authoritative name servers for google.com.

Authoritative servers

• Are controlled by the domain owner (e.g., Google)

• Store final DNS records such as:

  • A / AAAA (IP addresses)

  • MX (mail servers)

  • TXT (verification, security)

  • CNAME (aliases)

Only authoritative servers can give final, trusted answers for a domain.

Full DNS Resolution: dig google.com

» dig google.com

Although this looks like a single query, the recursive resolver performs multiple steps internally:

1. Check local and upstream caches

2. Query a root server for .com

3. Query a .com TLD server for google.com

4. Query Google’s authoritative server

5. Return the resolved IP address

The client sees only the final answer, but the resolver walks the hierarchy on its behalf.

Understanding NS Records

NS (Name Server) records answer one critical question:

“Which servers are authoritative for this zone?”

They enable:

• Delegation between DNS layers

• Domain ownership and registrar changes

• Load balancing and redundancy

• Failover and disaster recovery

Incorrect NS records can cause complete domain outages—even if all other systems are healthy.

How Browsers Use DNS in Practice

When a user enters a URL in a browser:

1. DNS resolution occurs first

2. A TCP connection is established

3. TLS handshake secures the connection

4. HTTP request/response begins

DNS is therefore step zero of every web request.

Mapping dig Commands to DNS Layers

System Design Perspective

DNS succeeds at internet scale because it is:

• Hierarchical instead of flat

• Decentralized instead of centralized

• Cached aggressively

• Delegated cleanly using NS records

Tools like dig are invaluable for understanding, debugging, and designing reliable internet-facing systems

• THE END …

How DNS Works :

1. When you type a website name in your browser its called a domain name , but computer dont recognize these domain names , it recognizes numbers and numeric ip address.

2. Suppose you type google.com on browser, the request is sent from browser to the DNS server, which finds the ip address from its records for that domain name

3. response is sent back to user and we are connected to google.com to ip address given by dns server eg. 142.250.196.110 .

Why DNS records Are needed:

DNS Servers maps domain names to specific IP addresses (eg. A records for IPv4 , AAAA for IPv6) so that we dont have to remember long numbers.

What an NS Record is (who is responsible for a domain):

NS is a record in DNS Server that tells which Authoritative server is responsible for that Domain names TLD

it directes queries to the correct place to find other DNS records (like A, MX, CNAME) for that domain

Reocrds (like A, MX, CNAME) for that domain, ensures websites and services load properly.

It points to the DNS servers that manage a domain's records, acting like a pointer to the right "phone book" for that domain's information.

Multiple NS records can be added (primary and secondary)which provide redundancy for reliability and changing them is necessary when switching hosting providers.

Example Structure

example.com. NS ns1.exampleserver.com. (TTL 21600) [1, 3]

example.com.: The domain name.

NS: The record type (Name Server).

ns1.exampleserver.com.: The authoritative nameserver.

21600: Time to Live (TTL) in seconds, how long caches store the record.

1. What an A Record is (domain → IPv4 address)

   An A Record (Address Record) is a fundamental Domain Name System (DNS) record that maps a human-readable domain name (like www.example.com) directly to its corresponding numerical IPv4 address, acting as the internet's phonebook to find the server hosting a website or service, allowing your browser to connect to the right computer. The "A" stands for Address, distinguishing it from AAAA records (for IPv6) and other types like MX (mail) or CNAME (alias).

2. What an AAAA Record is (domain → IPv6 address)

   An AAAA (Quad-A) record is a type of DNS record that maps a human-readable domain name (like www.example.com) to a specific IPv6 address, serving the same function as an A record but for the newer, longer IPv6 format instead of IPv4. It tells your browser the IPv6 location of a website, enabling communication over the IPv6 internet as adoption grows.

3. What a CNAME Record is (one name pointing to another name)

   A CNAME (Canonical Name) Record is a Domain Name System (DNS) record that acts as an alias, pointing one domain name (like blog.example.com) to another canonical domain name (like example.com), not directly to an IP address, it says "This name is another name for that name". When someone requests the alias, the DNS resolver follows the CNAME to the target domain, performs another lookup for the target's IP address, and returns it, streamlining management by pointing multiple subdomains to a single service or server.

   WORKING :

   • User Request: A user types blog.example.com into their browser.

   • DNS Lookup: The DNS resolver finds the CNAME record for blog.example.com.

   • Alias Followed: The CNAME tells the resolver that blog.example.com is an alias for example.com (the canonical name).

   • Second Lookup: The resolver then looks up the A (or AAAA) record for example.com to get its IP address.

   • Connection: The browser connects to the IP address found for example.com

   • USES :

   • Subdomains: you can set up your DNS to direct queries from blogs.jayworks.dev (personal domain ) to blogname.hashnode.com using a CNAME record.

   • Third-Party Services: Directing subdomains (eg. shop.yourdomain.com) to platforms like Shopify or GitHub Pages (eg. your-store.myshopify.com).

   • CDN Integration: Routing traffic through a Content Delivery Network (CDN) by pointing a subdomain to the CDN's domain.

4. What an MX Record is (how emails find your mail server)

   An MX record is a simple map in the Domain Name System (DNS) that tells email servers exactly where to deliver messages for your domain.

   How Emails Find Your Mail Server

   When an email is sent, the following process occurs:

   1. Email Submission: Your email client (like Outlook or Gmails web interface) sends the email to your email provider's outgoing mail server (a Mail Transfer Agent or MTA).

   2. DNS Query: The sending MTA performs a DNS query for the recipient's domain name to retrieve its MX records.

   3. MX Record Identification: The DNS server responds with a list of MX records for that domain. Each record contains a priority value and the hostname of a mail server responsible for handling the email.

   4. SMTP Connection: The sending MTA attempts to connect to the mail server with the lowest priority number (highest priority) first.

   5. Email Delivery: Once a connection is established, the email is transferred via SMTP to the recipient's mail server, where it is placed in the recipient's mailbox to be accessed later by their email client (via IMAP or POP).

5. What a TXT Record is (extra information and verification)

   A TXT record is a small , customizable note you pin to your domains official record book (DNS).

   Its just plain text, but other internet services read these notes to verify that you own the domain or to check your policies.

A single domain name (like example.com) functions much like a single street address for multiple services within a building. Just as a building needs separate suites for a doctor, a lawyer, and an accountant, a single domain uses multiple DNS record types to direct different kinds of network traffic to the correct destination.

Here’s how different records work together under one domain:

The Domain's Directory

Think of the domain name as the main entrance to a complex. The DNS records are the directory in the lobby, pointing visitors (traffic) to specific suites (servers).