Unit 11.4C · Term 4

URL & Domain Name System

Every website has an address you type in your browser — a URL. Behind the scenes, the Domain Name System (DNS) translates human-readable names into IP addresses that computers understand to route traffic.

Learning Objectives

11.6.2.1 Explain the structure and purpose of URL and DNS.

Lesson Presentation

11.4C-url-dns.pdf · Slides for classroom use

View Download

Conceptual Anchor

The Phone Book Analogy

You remember your friend's name but not their phone number. A phone book maps names to numbers. DNS is the internet's decentralized phone book: you type google.com (name) and DNS looks up 142.250.74.46 (IP address) so your browser knows exactly which server to connect to globally.

Visualizing DNS

Animated explanation of the DNS resolution process.

Rules & Theory

1. URL Structure & FQDN

A URL (Uniform Resource Locator) is a reference to a web resource that specifies its location on a computer network and a mechanism for retrieving it. The domain part of a URL is often referred to as an FQDN (Fully Qualified Domain Name), which specifies the exact location in the tree hierarchy of the DNS.

   
  Protocol  – https:// (secure) or http:// (not secure)
  Subdomain – www (optional prefix, identifies a specific server)
  Domain    – example.com (registered FQDN)
  TLD       – .com, .org, .kz, .edu (Top-Level Domain)
  Port      – 443 (HTTPS default) or 80 (HTTP default) — usually hidden
  Path      – /courses/cs11/index.html (specific file or directory)
  Query     – ?page=2 (parameters sent to the server database)
  Fragment  – #section3 (client-side anchor, jumps to a section on the page)

2. How DNS Resolution Works

When you enter a URL, the DNS process uses a mix of Recursive queries (your ISP asking servers on your behalf) and Iterative queries (servers referring your ISP to other servers down the hierarchy).

The step-by-step lookup process of translating a domain name to an IP address.

You type: https://geeksforgeeks.org

Step 1: Browser checks LOCAL CACHE (browser, OS, and router cache).
Step 2: If not cached → OS asks the DNS RESOLVER.
Step 3: DNS Resolver asks ROOT SERVER → "Who handles .org domains?"
Step 4: Root replies iteratively → "Ask the .org TLD server."
Step 5: DNS Resolver asks TLD SERVER → "Who handles geeksforgeeks.org?"
Step 6: TLD server replies → "Ask the authoritative nameserver."
Step 7: DNS Resolver asks AUTHORITATIVE SERVER for geeksforgeeks.org.
Step 8: Authoritative server replies → Returns the exact IP address.
Step 9: IP address is returned to browser, cached, and connection to REAL SERVER is established!

3. DNS Hierarchy & Server Types

Level	Server Role	Example
Root	The top of the hierarchy. Directs queries to the appropriate TLD server. 13 logical root servers worldwide (labeled A–M).	a.root-servers.net
TLD (Top-Level Domain)	Stores information for all domain names that share a common extension.	.com, .org, .kz, .uk
Authoritative	The final server that holds the actual IP records for a specific domain.	ns1.amazon.com

4. Types of DNS Records

Record	Purpose	Example
A	Maps domain → IPv4 address. (Most common)	example.com → 93.184.216.34
AAAA	Maps domain → IPv6 address.	example.com → 2606:2800:…
CNAME	Canonical Name. Alias that points one domain to another domain name.	www.example.com → example.com
MX	Mail Exchange. Directs email to a mail server.	mail.example.com

DNS Caching & TTL

To prevent overloading root servers, DNS results are cached at every level (browser, OS, ISP). Each record has a TTL (Time To Live) value — after this expires in seconds, the cache is refreshed. This is why migrating a website to a new server IP can take up to 48 hours to propagate globally.

Common Pitfalls

URL vs Domain Name

A domain name is only ONE PART of the URL. The full URL includes the protocol, domain, path, and query. google.com is a domain; https://www.google.com/search?q=DNS is a URL.

Tasks

Remember

Label all parts of this URL: https://www.school.edu.kz/students/grades.html?term=4#math

Create / Model

Cisco Packet Tracer Lab: Add a Server-PT to your network and activate the DNS Service. Create an "A Record" mapping www.nis.edu.kz to the IP address of another Web Server in your network. On a PC-PT, set its DNS Server IP to your new DNS server. Open the PC web browser and type the URL to verify resolution.

Understand

Explain the difference between a Root Server and an Authoritative Server in the DNS resolution process.

Apply

A company changes its web server hardware and gets a new IP address. They update their 'A Record', but some users still see the old offline website. Explain why this happens and what role TTL plays in the solution.

Self-Check Quiz

Q1: What does DNS stand for, and what is its primary function?

Domain Name System — it translates human-readable domain names (FQDNs) into machine-routable IP addresses.

Q2: What is the TLD of the domain "portal.school.edu.kz"?

.kz (the top-level domain). "edu.kz" is a second-level domain, "school" is the domain, and "portal" is the subdomain.

Q3: What specific DNS record type is required to map a domain to an IPv6 address?

AAAA record.