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).
Security and privacy · How systems are kept safe · about 40 minutes · Open the student lesson
Classroom resources
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Students will be able to
I can explain what DNS and IP addresses do.
I can describe how a router uses an address.
I can spot a lookalike name.
Timing
Predict and Try 6 min · Worked example 12 min · Vary 10 min · Practise and Make 12 min
Before class
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
What you will see
A question to ask
The fix
A student trusts schoo1.edu.au (Sam's mistake).
Is that the same name, character by character?
A different name has a different address.
A student thinks the IP address is a person.
How many people use your home's public address?
It identifies a device or network, not a person.
Answers to the checks
one letter different: An email links to **schoo1.edu.au** (a number 1 instead of the letter l). The real site is **school.edu.au**. Where will the link take you? To a different computer. DNS looks up the exact name, and schoo1.edu.au is a separate name with its own address, owned by someone else.
Try: look them up: Press Go for school.edu.au, then look up schoo1.edu.au. Where does each one go?
school.edu.au is 203.0.113.10; schoo1.edu.au is 198.51.100.66, a different computer that is not the school's.
school.edu.au: What does DNS do? Turns a name like school.edu.au into an IP address DNS is the internet's address book: name in, IP address out.
Find the mistake: Sam decides an email link is safe. Click the line where it first goes wrong. line 3 Line 3: DNS looks up the exact name. schoo1.edu.au has its own address, so the link goes to someone else's computer: a phishing site.
Private and public: Your laptop at home is 192.168.1.23, but websites see 198.51.100.7. Why? 192.168… is a private address used only inside your home; your router uses one public address for the internet Private addresses (like 192.168.x.x) are reused in millions of homes; the router shares one public address for all of them.
Part of the school: Look up library.school.edu.au. Which router row sends it?
203.0.113.20 starts 203.0.113, so row 1 sends it to the school network.
Another site: Look up weather.example.
192.0.2.44 matches row 2: it goes out to the internet provider.
No such name: Look up a name that doesn't exist, such as nowhere.example.
DNS has no address for it, so nothing is sent.
Reading the table: Why does the router only look at the start of the address? Addresses are grouped by network, so the start says which way to send it Like a postcode: the start of the address says which network, so a router only needs a row for each group.
Real or not?: Which link goes to the real school site **school.edu.au**? https://school.edu.au/login Only the first ends in exactly school.edu.au. The others are other people's names dressed up.
IP addresses: What does an IP address identify? A device (or a network's router) on the internet It is the address packets are delivered to.
Review: HTTPS: Review: where does HTTPS encrypt your data? On your device, before it is sent Encrypted on your device, decrypted by the website.
check before you click: 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.
Both school.edu.au and library.school.edu.au reach the school (203.0.113.x); schoo1.edu.au does not. Typing the address yourself is safer than clicking.
Solutions
One possible solution for each task. Other correct programs are fine.
Vary: one name at a time › Part of the school
Open task: any program that does what the step asks.
Vary: one name at a time › Another site
Open task: any program that does what the step asks.
Vary: one name at a time › No such name
Open task: any program that does what the step asks.
Vary: one name at a time › Reading the table
Open task: any program that does what the step asks.
check before you click
Open task: any program that does what the step asks.
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.
Exit ticket
What does DNS do? Why is schoo1.edu.au not the school?
Turns a name into an IP address. It is a different name, so DNS gives a different address: someone else's computer.
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.
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.