🌐 06-01: DNS Infrastructure¶

📌 What is DNS?¶

DNS (Domain Name System) is a distributed system that translates:

Domain Names → IP Addresses

Example¶

Human-friendly: www.google.com
Machine-friendly: 142.250.xxx.xxx

💡 Without DNS, users would need to remember IP addresses instead of domain names.

🧱 DNS Infrastructure Overview¶

DNS uses a hierarchical and distributed architecture.

Main Components:¶

DNS Resolver (Recursive Resolver)
Root Name Server
Top-Level Domain (TLD) Server
Authoritative Name Server

🌳 DNS Domain Hierarchy¶

DNS namespace is organized as a tree-like structure.

The top is the ROOT, denoted as .
Each node is a domain or subdomain

Hierarchy Example¶

DNS Domain Hierarchy

Explanation¶

TLD: .com
Second-Level Domain: google
Subdomains: www, mail

🧾 DNS Root Servers¶

There are 13 logical root servers (a to m)

Hostname	IP Addresses	Manager
a.root-servers.net	198.41.0.4, 2001:503:ba3e::2:30	VeriSign, Inc.
b.root-servers.net	192.228.79.201	University of Southern California (ISI)
c.root-servers.net	192.33.4.12	Cogent Communications
d.root-servers.net	199.7.91.13, 2001:500:2d::d	University of Maryland
e.root-servers.net	192.203.230.10	NASA (Ames Research Center)
f.root-servers.net	192.5.5.241, 2001:500:2f::f	Internet Systems Consortium, Inc.
g.root-servers.net	192.112.36.4	US Department of Defense (NIC)
h.root-servers.net	128.63.2.53, 2001:500:1::803f:235	US Army (Research Lab)
i.root-servers.net	192.36.148.17, 2001:7fe::53	Netnod
j.root-servers.net	192.58.128.30, 2001:503:c27::2:30	VeriSign, Inc.
k.root-servers.net	193.0.14.129, 2001:7fd::1	RIPE NCC
l.root-servers.net	199.7.83.42, 2001:500:3::42	ICANN
m.root-servers.net	202.12.27.33, 2001:dc3::35	WIDE Project

👉 Root servers do NOT store full records — they redirect queries to TLD servers

🌐 Top-Level Domains (TLD)¶

Types of TLDs:¶

Type	Function	Example
Infrastructure TLD	Used for DNS infrastructure	`.arpa`
Generic TLD (gTLD)	General-purpose domains	`.com`, `.net`, `.org`
Sponsored TLD (sTLD)	Restricted domains managed by organizations	`.edu`, `.gov`, `.mil`, `.travel`, `.jobs`
Country Code TLD (ccTLD)	Represents specific countries	`.bd`, `.au`, `.fr`
Reserved TLD	Reserved for testing and special use	`.example`, `.test`, `.localhost`, `.invalid`

🔹 Subdomain¶

A subdomain is a subdivision of a main domain.

Example¶

Domain: google.com
Subdomains:
www.google.com
mail.google.com
maps.google.com

💡 Subdomains are used to: - Organize services
- Separate applications
- Structure large systems

🗂️ DNS Zones¶

A DNS zone is a portion of the domain namespace managed by a DNS server.

Example¶

example.com → Main zone
usa.example.com → Delegated zone
uk.example.com → Delegated zone

💡 Zones enable: - Delegation
- Distributed management
- Scalability

⚖️ Subdomain vs DNS Zone¶

Feature	Subdomain	DNS Zone
Definition	Logical subdivision of a domain	Administrative portion of DNS
Purpose	Organization	Management & delegation
Example	`blog.example.com`	Zone for `example.com` or `usa.example.com`
Dependency	Always part of a domain	May be managed independently

💡 Key Idea: - Every DNS zone is a domain - A subdomain becomes a separate zone only when delegated

🌍 DNS Server Types¶

1️⃣ Recursive Resolver (DNS Resolver)¶

First contact point for the client
Performs the full lookup process

2️⃣ Root Server¶

Directs queries to TLD servers

3️⃣ TLD Server¶

Directs queries to authoritative servers

4️⃣ Authoritative Server¶

Stores DNS records
Provides the final IP address

🌍 Public DNS Servers¶

Google DNS → 8.8.8.8
Cloudflare → 1.1.1.1
OpenDNS → 208.67.222.222

📌 Key Takeaways¶

DNS is a hierarchical distributed system
Query flow: Root → TLD → Authoritative
Domains follow a tree structure
Subdomains organize services logically
DNS zones enable delegation and scalability
A subdomain becomes a zone only when delegated
Root servers guide queries globally