--- title: "Names and addresses" subtitle: "Security and privacy · How systems are kept safe · Lesson 2" --- # Names and addresses **Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}} > **Key question:** 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? :::teacher-note **In one sentence:** 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). **Students should be able to say:** I can explain what DNS and IP addresses do. I can describe how a router uses an address. I can spot a lookalike name. **Width:** the unmarked parts are the floor every student does (predict, run, investigate and make). Typical adds the modify practice; wider adds the real-world contexts. They add contexts, not difficulty. Students work in the online tutorial alongside this sheet. ::: ## Predict :::keep-together **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?** ☐ Nowhere: the name is invalid ☐ To the school, because it ends in .edu.au ☐ To the school, because DNS fixes small typos ☐ To whatever computer schoo1.edu.au points to: a different one My prediction, and why: {{lines-3}} ::: :::teacher-note **What happens:** 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. ::: ## Run Try it on the board in the tutorial. Was your prediction right? What was different? {{lines-2}} ## Worked example: following a name :::keep-together ### school.edu.au 1. $\text{school.edu.au} \to \text{DNS}$ — Your laptop asks a DNS server for the name's address. 2. $\text{answer: } 203.0.113.10$ — The IP address of the school's web server. 3. $\text{packet: to } 203.0.113.10$ — Every packet carries that address (and where it came from). 4. $\text{router table: } 203.0.113.x \to \text{row 1}$ — The router matches the start of the address to choose a way. 5. $\text{schoo1.edu.au} \to 198.51.100.66$ — A different name has a different address: a different computer. Now say what DNS does. **What does DNS do?** ☐ Turns a name like school.edu.au into an IP address ☐ Checks the website is safe ☐ Speeds up the internet ☐ Encrypts the web page ::: :::teacher-note **Answer:** Turns a name like school.edu.au into an IP address DNS is the internet's address book: name in, IP address out. ::: :::keep-together ### Find the mistake **Sam decides an email link is safe. Click the line where it first goes wrong.** ``` 1 An email says: reset your school password at schoo1.edu.au. 2 The name looks like the school's website. 3 So DNS will send me to the school's computer. 4 So it is safe to type my password there. ``` Line: {{field-15}} Why is it wrong? {{lines-2}} ::: :::teacher-note **Answer:** 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. ::: :::keep-together ### Private and public **Your laptop at home is 192.168.1.23, but websites see 198.51.100.7. Why?** ☐ The laptop has two network cards ☐ 192.168… is a private address used only inside your home; your router uses one public address for the internet ☐ Websites can't read addresses ☐ The laptop changes its address for each website ::: :::teacher-note **Answer:** 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. ::: :::typical ## Vary: one name at a time **Part of the school.** **Another site.** **No such name.** **Reading the table.** Work in the tutorial. Plan first: what will you change, and how will you test it? {{box-4}} ::: ## Names and addresses :::keep-together ### Real or not? **Which link goes to the real school site **school.edu.au**?** ☐ https://school-edu-au.example ☐ https://school.edu.au/login ☐ https://school.edu.au.login-help.example ☐ https://schooI.edu.au (capital I) ::: :::teacher-note **Answer:** https://school.edu.au/login Only the first ends in exactly school.edu.au. The others are other people's names dressed up. ::: :::keep-together ### IP addresses **What does an IP address identify?** ☐ A website's owner ☐ A device (or a network's router) on the internet ☐ A password ☐ A person ::: :::teacher-note **Answer:** A device (or a network's router) on the internet It is the address packets are delivered to. ::: :::keep-together ### Review: HTTPS **Review: where does HTTPS encrypt your data?** ☐ At the website only ☐ On your device, before it is sent ☐ At the router ☐ At the DNS server ::: :::teacher-note **Answer:** On your device, before it is sent Encrypted on your device, decrypted by the website. ::: ## Make: check before you click Then: write one rule for checking a link before you click it. Work in the tutorial. Plan first: what will you change, and how will you test it? {{box-4}} ## Exit ticket :::keep-together **What does DNS do? Why is schoo1.edu.au not the school?** {{lines-3}} ::: :::teacher-note **Answer:** Turns a name into an IP address. It is a different name, so DNS gives a different address: someone else's computer. :::