← IGCSE Computer Science Paper 1

From URL to web page: the full sequence

The ordered steps after you enter a URL: the browser asks DNS for the IP address, sends a request to the web server, gets HTML back, then renders the page.

Part of: IGCSE Computer Science 0478 — 5.1 The Internet and the World Wide Web — Module 33, ACARA Digital Technologies Years 9–10 — Networked Systems and Access Control — Module 58, QCE Digital Solutions Unit 3 — Interactions Between Users, Data and Digital Systems — Module 38, QCE Digital Solutions Unit 4 — Digital Methods for Exchanging Data — Module 126, WA Computer Science ATAR Year 11 — Network Communications — Module 62

Understanding From URL to web page: the full sequence in IGCSE Computer Science Paper 1

What it does: After the HTML arrives, the browser renders it as a visible web page, which completes the sequence. The named website shows the order: domain name first, then DNS lookup, then the IP address, then the request to the server. The browser cannot contact the web server until DNS has given it the IP address, so DNS comes before the server.

Common mistakes: The URL is text, so it must be written as a string in quotes: url = 'www.bbc.co.uk'. Without quotes it is not a valid value. The request to the web server is sent using the IP address that DNS returned, not the URL. It should be send_request(ip).

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This module's key terms are also in a printable crossword (Modules 477–489) and word search (Modules 464–489).

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Learning

Duo

Which step comes FIRST after you type a URL into the browser?

The browser asks a DNS server for the IP addressThe web server sends the HTML back

Matches

URL -> web server -> DNS -> HTML

↓

DNS is in the wrong place. The DNS lookup must come before the request to the web server, because the browser needs the IP address first

Applying

Meanings

Term

URL -> DNS -> IP -> server -> HTML -> render

Meaning

The ordered steps after you enter a URL: the browser asks DNS for the IP address, sends a request to the web server, gets HTML back, then renders the page.

Practice

1. Browser: user enters www.bbc.co.uk

Testing

Gaps

2. lookup finds the IP address

Check Answer

Spots

1url = www.bbc.co.uk

2ip = dns_lookup(url)

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Quick Questions

1. Which step comes FIRST after you type a URL into the browser?

A. The web server sends the HTML back

B. The browser asks a DNS server for the IP address ✓

The browser needs the IP address of the web server before it can send a request, so the DNS lookup comes first.

2. What does the DNS server return to the browser?

A. The IP address that matches the domain name ✓

B. The HTML code of the web page

DNS only translates the domain name into an IP address. The web server is the one that sends the HTML.

3. Which is the correct order of steps?

A. DNS lookup, then request to the web server, then HTML returned ✓

B. Request to the web server, then DNS lookup, then HTML returned

The browser must know the IP address (from DNS) before it can send a request to the web server.

4. Who sends the HTTP request to the web server?

A. The DNS server

B. The web browser ✓

The browser, acting as the client, uses the IP address from DNS to send the request. The DNS server only answers the lookup.

5. Worked example: you enter www.bbc.co.uk. After DNS gives the IP address, what happens next?

A. The browser sends a request to the BBC web server at that IP address ✓

B. The browser renders the BBC home page

The page can only be rendered after the web server has received the request and returned the HTML.

Match the Pairs

URL -> DNS -> IP address → The browser sends the domain name to a DNS server, which looks it up and returns the matching IP address

IP address -> web server -> HTML → The browser sends an HTTP request to the web server at that IP address, and the server sends back the HTML for the page

The last step of the sequence is the browser turning the HTML it received into the page you see on screen → HTML -> browser -> render page

Worked example: typing www.bbc.co.uk makes the browser ask DNS for the IP address before contacting the web server → www.bbc.co.uk -> DNS -> IP -> server

URL -> web server -> DNS -> HTML → DNS is in the wrong place. The DNS lookup must come before the request to the web server, because the browser needs the IP address first

URL -> DNS -> IP -> render -> server → The page cannot be rendered before the web server sends back the HTML. Rendering is the last step, not before the server

Key Term

URL -> DNS -> IP -> server -> HTML -> render

The ordered steps after you enter a URL: the browser asks DNS for the IP address, sends a request to the web server, gets HTML back, then renders the page.

Fill in the Blanks

1. 1. Browser reads the URL 2. DNS lookup finds the IP address

Hint: Type the abbreviation for the service that matches a domain name to an IP address.

2. URL -> DNS -> IP -> server -> HTML -> render

Hint: Type the abbreviation for the address that DNS gives back to the browser.

3. 3. Browser sends a request to the web server

Hint: Type the computer that stores the site and receives the browser's request.

4. 4. Server sends back HTML for the page

Hint: Type the name of the markup language file that the server returns.

5. 1. Type www.bbc.co.uk in the address bar 2. DNS finds the IP for bbc.co.uk 3. Browser renders the HTML as a page

Hint: Type the verb for the final step, where the browser turns HTML into the visible page.

Spot the Error

Question 1

A url = www.bbc.co.uk

B ip = dns_lookup(url)

C page = request(ip)

D render(page)

Line A — The URL is text, so it must be written as a string in quotes: url = 'www.bbc.co.uk'. Without quotes it is not a valid value.

Question 2

A url = 'www.bbc.co.uk'

B ip = dns_lookup(url)

C html = send_request(url)

D render(html)

Line C — The request to the web server is sent using the IP address that DNS returned, not the URL. It should be send_request(ip).

Question 3

A url = 'www.bbc.co.uk'

B ip = dns_lookup(url)

C html = request(ip)

D render(ip)

Line D — The browser renders the HTML that the web server returned, not the IP address. It should be render(html).

Question 4

A # 1 Browser gets the URL

B # 2 DNS finds the IP address

C # 3 Browser requests the page

D # 4 DNS server sends back HTML

E # 5 Browser renders the page

Line D — The web server sends back the HTML, not the DNS server. The DNS server only returns the IP address. Step 4 should say Web server.

Question 5

A # 1 Enter URL in the browser

B # 2 DNS finds the IP address

C # 3 Browser renders the page

D # 4 Web server sends back HTML

E # 5 Browser renders the page

Line C — The steps are out of order. The browser can only render the page after it has requested it and received the HTML. Step 3 should be the browser requesting the page.

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