Every device on the internet has an IP address, and every packet carries the address it is going to. DNS turns a name like school.edu.au into that address, and routers use their tables to send each packet the right way. A name that only looks right gets a different address, and a different computer.
You type a website's name, but computers find each other by numbers. Who turns the name into the number, and what happens if one letter is wrong?
On the internet, devices find each other by IP addresses: numbers such as 203.0.113.10. Every packet carries the address it is going to. People use names instead, so a DNS server (the Domain Name System) looks up the address for each name. Routers then read the address on each packet and use their tables to choose where to send it.
Predict: Read the problem and decide what you think before you try anything. A wrong guess is fine: it shows you what to look for.
Try: Try it on the board and compare the result with your prediction.
Investigate: Work out why it happens, one step at a time.
Modify: Change the problem on purpose and see what happens.
Practise: A few on your own, to check you have it.
Make: Make your own problem using what you have learned. Expect a few tries; that is normal.
Make your prediction first. Help opens once you've locked it in.
PredictRead the problem and decide what you think before you try anything. A wrong guess is fine: it shows you what to look for.
One letter different
TryTry it on the board and compare the result with your prediction.
Try: look them up
Was your prediction right? Compare the router table row each one used.
Try it yourselfYour edits are saved in this browser.
Press Go for school.edu.au, then look up schoo1.edu.au. Where does each one go?
Use the board. This ticks when you get there.
InvestigateWork out why it happens, one step at a time.
Worked example: following a name
Worked exampleBefore each step, say what you think comes next.
school.edu.au→DNSYour laptop asks a DNS server for the name's address.
answer: 203.0.113.10The IP address of the school's web server.
packet: to 203.0.113.10Every packet carries that address (and where it came from).
router table: 203.0.113.x→row 1The router matches the start of the address to choose a way.
schoo1.edu.au→198.51.100.66A different name has a different address: a different computer.
Now say what DNS does.
Sam decides an email link is safe. Click the line where it first goes wrong.
ModifyChange the problem on purpose and see what happens.
Vary: one name at a time
Try it yourselfYour edits are saved in this browser.
Look up library.school.edu.au. Which router row sends it?
Use the board. This ticks when you get there.
Look up weather.example.
Use the board. This ticks when you get there.
Look up a name that doesn't exist, such as nowhere.example.
Use the board. This ticks when you get there.
PractiseA few on your own, to check you have it.
Names and addresses
MakeMake your own problem using what you have learned. Expect a few tries; that is normal.
Check before you click
Then: write one rule for checking a link before you click it.
Try it yourselfYour edits are saved in this browser.
Need a hint?
Look up each name and compare its address with the school's.
Another hint
The school's portal is at 203.0.113.10.
Another hint
A name that ends in exactly school.edu.au goes to the school.
An email offers these links: schoo1.edu.au, school.edu.au, library.school.edu.au. Look up all three, and finish on one that reaches the real school portal.
Use the board. This ticks when you get there.
For teachers
Students look up names in a DNS board and follow each packet's address through a router table, to explain how domain names and IP addresses get data to the right computer and why a lookalike name is dangerous (AC9TDI10K01 node 2). About 40 minutes.
Try the board yourself. Every address on it comes from the ranges kept for documentation and examples (192.0.2.x, 198.51.100.x, 203.0.113.x), so none is a real site.
The one idea: names map to addresses through DNS, packets carry addresses, routers forward by the start of the address. Lookalike names (phishing) reach other computers.
Hands-on: on a school computer, nslookup or ping a well-known site to see a real address (check the school network allows it).
Running the lesson
Predict: students who chose "DNS fixes typos" hold Sam's misconception.
Try: ask whose computer 198.51.100.66 might be.
Worked example: compare the router table with postcodes.
Vary: ask why nothing is sent for a name that doesn't exist.
Make: collect students' rules for checking links.
The hard part (on purpose)
The difference between a name looking right and being right. Make students read names character by character, aloud.
When students get stuck
A student trusts schoo1.edu.au (Sam's mistake). Ask: Is that the same name, character by character? Fix: A different name has a different address.
A student thinks the IP address is a person. Ask: How many people use your home's public address? Fix: It identifies a device or network, not a person.
Stretch and support
Stretch: IPv4 addresses have four numbers from 0 to 255. How many is that, and why did the world run out? (About 4.3 billion; look up IPv6.)
Support: Show a name split into parts (library . school . edu . au) and read it right to left.
Where it leads
Next: Who are you, and what may you do? (sign-in and permissions).
Builds on: Networks (packets and routers). Links to Data representation: each part of an IPv4 address is one byte.
What each step is for
one letter different: Committing to where a lookalike name leads tests the new move: DNS maps each exact name to its own address, so a different name reaches a different computer, however similar it looks.
Try: look them up: Looking up both names settles the prediction: two different IP addresses, two different computers.
Worked example: following a name: Tracing one name through DNS, the packet's address and the router's table models the new move. Sam trusts a lookalike name, the misconception planted after the method.
Vary: one name at a time: Each task changes one name: a part of the school site, an outside site, a name that doesn't exist, then reading which router row each used.
names and addresses: Spotting lookalike names, what an IP address identifies, and a review of encryption.
check before you click: Finding the one safe link among lookalikes with the board reverses the process: students start from a list of names and use addresses to decide.