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.

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

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Conceptual Anchor

The Phone Book Analogy

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

Rules & Theory

URL Structure

    https://www.example.com:443/courses/cs11/index.html?page=2#section3
    ──┬───  ─┬─ ────┬──── ─┬─ ─┬─ ──────────┬──────── ───┬─── ───┬────
      │      │      │      │   │             │            │       │
  Protocol  Sub  Domain  Port  │           Path         Query  Fragment
           domain  name        │                        String
                          TLD (.com)

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

How DNS Resolution Works

You type: www.example.com

Step 1: Browser checks its LOCAL CACHE (already visited?)
Step 2: If not cached → asks the OS resolver
Step 3: OS asks the RECURSIVE DNS SERVER (usually your ISP)
Step 4: Recursive server asks ROOT DNS SERVER → "Who handles .com?"
Step 5: Root says → "Ask the .com TLD server"
Step 6: TLD server says → "example.com is handled by ns1.example.com"
Step 7: Authoritative server for example.com → "IP is 93.184.216.34"
Step 8: IP address returned to browser → connection established!

DNS Hierarchy

Level	Server	Example
Root	13 root servers worldwide (labeled A–M)	a.root-servers.net
TLD	Handles top-level domains	.com, .org, .kz, .edu
Authoritative	Knows the IP of a specific domain	ns1.example.com

Types of DNS Records

Record	Purpose	Example
A	Maps domain → IPv4 address	example.com → 93.184.216.34
AAAA	Maps domain → IPv6 address	example.com → 2606:2800:…
CNAME	Alias — points to another domain	www.example.com → example.com
MX	Mail server for the domain	mail.example.com

DNS Caching

DNS results are cached at every level (browser, OS, ISP) to speed up future lookups. Each record has a TTL (Time To Live) — after this expires, the cache is refreshed. This is why domain changes can take hours to propagate globally.

Common Pitfalls

URL = Domain Name

The domain name is only PART of the URL. The full URL includes protocol, subdomain, domain, path, query, and fragment. 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

Understand

Explain the DNS resolution process in your own words using a real-world analogy.

Apply

You changed your website's IP address but users still see the old version. Explain why this happens and how it will resolve.

Self-Check Quiz

Q1: What does DNS stand for?

Domain Name System — translates human-readable domain names into IP addresses.

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

.kz (the country-code TLD for Kazakhstan)

Q3: What DNS record type maps a domain to an IPv4 address?

A record