The shape of the lesson
By the end of the lesson, learners can
- The steps in order: Run the lab from start to finish.
- When the DNS does not know: No single DNS holds every domain name in the world.
- Who does what: Questions often ask for the role of one part.
- Browser: sends the domain name to the DNS, requests the page, renders the HTML.
- DNS: looks up the domain name and returns the matching IP address.
- Web server: at that IP address; sends back the HTML files.
- Order: URL, DNS, IP address, request, HTML, render.
One picture every idea returns to
Computers on the internet are found by IP address, not by name. When a URL is entered, the browser sends the domain name to a domain name server (DNS), which looks up and returns the matching IP address. The browser then sends an HTTP request to the web server at that IP address. The web server sends back the page as HTML files, and the browser renders the HTML to display the page.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, From name to page.. You type a URL and a page appears in a fraction of a second. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: The steps in order | Run the lab from start to finish. Project tab 1 of the lab (From URL to web page) and let a student drive it while the class predicts. | Whole class, then pairs |
| 13 to 21 min | Teach and check: When the DNS does not know | No single DNS holds every domain name in the world. Model the worked example Exam-style answer on the board, one line at a time. | Pairs |
| 21 to 30 min | Teach and check: Who does what | Questions often ask for the role of one part. Your turn: Put these in order: web server sends HTML; DNS returns IP address; browser renders page; browser sends domain name to DNS; browser requests page from IP address. | Corners |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 15 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Who does what, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Corners
Put one answer or viewpoint in each corner of the room. Students move to the corner they agree with, justify the choice to a partner there, then hear one voice from each corner before the reveal.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| The DNS does not send the web page. | It only returns the IP address. The web server sends the HTML. Mixing these up loses most of the marks. |
How a web page is located and retrieved: DNS: worksheet
6 questions, 15 marks. Written in the style of the papers; no past paper question is reproduced.
A user enters a URL into a web browser. Describe how the web page is located, retrieved and displayed.
State what is meant by DNS.
Explain why a DNS is needed when a user enters a URL.
A DNS receives a request for a domain name that is not in its database. Describe what happens next.
State the role of the web server and the role of HTML in displaying a web page.
A student writes: "The browser sends the URL to the DNS, which sends back the web page." Identify and correct the error.
Answer key and marking notes
- The browser sends the domain name (from the URL) to a DNS.
- The DNS searches its database for the matching IP address (passing the request to another DNS if it is not found).
- The DNS returns the IP address to the browser.
- The browser sends a request to the web server at that IP address.
- The web server sends the web page files / HTML to the browser.
- The browser renders the HTML and displays the web page.
Domain name server: a server that stores domain names and their matching IP addresses.
- Users enter a text-based domain name, but devices on the internet are located using IP addresses.
- The DNS translates the domain name into the IP address of the web server.
- The DNS passes the request on to another DNS (higher up).
- If that DNS finds it, the IP address is returned to the browser; if no DNS holds it, an error message is returned.
- Web server: stores the web page files and sends them to the browser when requested.
- HTML: the language the page is written in, which the browser renders to display the page.
- The DNS does not send the web page; it sends back the IP address of the web server.
- The browser then requests the page from the web server, which sends the HTML.
6 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
What is the role of a domain name server (DNS)?
- ATo look up a domain name and return the matching IP address
- BTo store the HTML files of websites and send them to browsers
- CTo render HTML so that the page can be displayed
- DTo encrypt the data sent between a browser and a web server
After receiving the browser's request, what does the web server send back?
- AThe web page files, written in HTML
- BThe IP address of the website
- CThe domain name of the DNS
- DA list of other web servers
A user enters https://www.harbour-museum.org/visit.html. Which part of the URL does the browser send to the DNS?
- Awww.harbour-museum.org
- Bhttps
- C/visit.html
- DThe whole URL including the protocol
Which is the correct order of events after a URL is entered?
1: the web server sends the HTML
2: the DNS returns the IP address
3: the browser renders the page
4: the browser sends the domain name to the DNS
5: the browser sends a request to the web server
- A4, 2, 5, 1, 3
- B5, 4, 2, 1, 3
- C4, 5, 2, 1, 3
- D4, 2, 1, 5, 3
A DNS receives a request for a domain name that is not in its own database. What happens next?
- AIt passes the request on to another DNS, which may find the IP address
- BIt immediately tells the browser that the website does not exist
- CIt asks the web server to tell it its own domain name
- DIt sends the browser the IP address of the nearest web server instead
A student writes: "The browser sends the URL to the DNS, and the DNS sends back the web page." What is the error?
- AThe DNS sends back the IP address; the web page is sent by the web server
- BThe browser should send the URL to the web server first, not the DNS
- CThe DNS sends back the web page, but only after encrypting it
- DThe DNS sends the domain name back, and the browser looks up the IP address
Quiz key
A DNS holds domain names with their IP addresses and returns the IP address for the domain name it is sent. Storing and sending HTML is the web server's job, rendering HTML is the browser's job, and encryption is done by SSL/TLS.
The web server responds with the requested page files in HTML (plus images and other files), which the browser renders. The IP address was supplied earlier by the DNS. The web server does not send domain names or lists of servers.
The DNS looks up the domain name, www.harbour-museum.org, to find the IP address of the web server. The protocol (https) and the file name (/visit.html) are used later in the request to the web server, so the DNS does not need them.
The browser sends the domain name to the DNS (4), which returns the IP address (2). Only then can the browser send its request to the web server at that address (5). The server sends the HTML (1), and the browser renders it (3). The other orders contact the server before the IP address is known, or receive the HTML before it has been requested.
The DNS passes the query to another DNS higher up; if one finds it, the IP address is returned to the browser. An error is returned only if no DNS holds the domain name, so the first DNS does not give up straight away. It cannot ask the web server, because it does not know the server's address, and sending a different server's address would load the wrong site.
The DNS only returns the IP address of the web server. The browser then requests the page from the web server, which sends the HTML. The browser cannot contact the web server first because it does not yet know its IP address. The DNS never sends web pages, and it is the DNS, not the browser, that looks up the IP address.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.