Lesson 02 — What the Internet Actually Is

DNS, IP, HTTPS, browsers, CDNs — what happens between pressing Enter and the page appearing.

IT Landscape Module 1

The question

We'll answer it in 11 slides.

Step 1: Your computer needs an address

• wikipedia.org is a name.
• Computers talk in numbers — IP addresses like 208.80.154.224.
• Translating names ↔ numbers is what DNS does.

DNS = the phonebook of the internet.

DNS in one diagram

Each step is cached for seconds-to-days — usually you only hit the resolver.

Step 2: Open a connection

• Your computer opens a TCP connection to that IP.
• Port 443 — the standard port for HTTPS.

Step 3: Wrap it in TLS

• HTTPS = HTTP + encryption.
• The browser asks for a certificate.
• The certificate must be signed by a Certificate Authority the browser trusts (Let's Encrypt, DigiCert, …).
• The two sides derive a shared key. Everything after is encrypted.

🔒 Padlock icon = encryption + verified identity.

Step 4: Send the HTTP request

GET / HTTP/2
Host: wikipedia.org
Accept: text/html
User-Agent: Mozilla/5.0 ...

This is — literally — what your browser sends down the encrypted pipe.

Step 5: The server responds

HTTP/2 200 OK
Content-Type: text/html
Content-Length: 84211

<html>...</html>

200 OK = "here you go". Other common ones: 301 redirect, 404 not found, 500 server error.

CDNs: the same page, served from near you

Wikipedia's origin lives in a couple of data centers. You don't.

• A CDN (Content Delivery Network) keeps copies at edge nodes all over the world.
• You talk to the closest copy — maybe 50 ms away, instead of 200 ms.
• Brands: Cloudflare, Akamai, AWS CloudFront, Fastly.

The browser renders

1. Parses the HTML.
2. Fetches CSS, JavaScript, images, fonts — each one is another HTTP request.
3. Runs the JavaScript.
4. Paints pixels.

One "page load" is often hundreds of requests in the background.

Why this matters when something breaks

• DNS issue → this one site unreachable, other sites still work.
• Certificate expired → padlock warning, scary red page.
• Slow page → could be DNS, your network, the CDN, the origin server, or the page's own JavaScript. Any of them.

What this course won't teach you

Honest list of things we're not covering:

• BGP — how ISPs route between each other.
• IPv6 details and dual-stack realities.
• The TLS handshake math.
• TCP congestion control.

They exist, they matter, they're someone's full-time job. See the Reading on list in the theory page.

Recap

• Name → number = DNS.
• Encrypted call = HTTPS (TCP + TLS + HTTP).
• CDN = a "near you" copy of the page.