1. Lesson 2-9 AP Computer Science Principles
The Need for DNS
Lesson 2-9
AP Computer Science Principles

2. Objectives Students will be able to:
Explain the inefficiencies of everyone managing their own name-to- address table.
Describe the protocols necessary for users to update and utilize DNS to translate a human-readable location on the Internet into a numeric IP address.

3. Names vs. Addresses
When computers talk to one another on the web, they don’t refer to each other by names; they use an IP address to indicate who they are and who they are sending a message to.
Without this system, the packets would be impossible to route across the Internet.
The problem with this system is that, while computers are fine with referring to other computers by numbers, humans are really terrible at remembering long strings of seemingly-random numbers.
We’d prefer to identify a web page by its name, and besides, it makes remembering our favorite locations on the Internet (“Code.org” vs ) much easier!

4. Activity
When you walked in, I handed you a slip of paper with an IP address on it.
You also should have a Worksheet - Names and Addresses.
For the next 5 minutes, your goal is to complete an accurate list of IP addresses and names for all students in the room. You may only talk to one person at a time, but you may exchange as much information with that person as you want.
GO!

5. Activity Why did I keep changing your IP address?
Do you think the system we just simulated is an efficient way of collecting IP addresses? Are there any inefficiencies you observe? How could it be made better?

6. Video
You may remember from the IP/DNS video that we saw several lessons ago) that you learned about the Internet system for sharing names and IP addresses.
Let’s look at the DNS part again…

7. Activity Guide - DNS Partner Questionnaire
You are going to interview (have a conversation with) someone in class whom you don’t know very well, using only the Internet Simulator. We’ve prepared a list of interview questions and you should both jot down each other’s responses.
To find the person, you will have to ask the DNS for his/her IP address.
When you have retrieved the IP address, start the interview.
HOWEVER….As you’re working, if I tap you and your partner, you MUST disconnect and reconnect from the simulation. This is to simulate changing IP addresses.
You’ll need to re-join a router and ask the DNS for your partner’s new IP address in order to continue having your conversation

8. DNS
The challenges we encountered in today’s activity very closely mirror those that exist on the actual Internet.
The response to those challenges was the development of a protocol called the Domain Name System, DNS.
The DNS serves as a localized list of all names and IP addresses, similar to the contacts section of your phone. When a device joins the Internet, it shares its IP address with the DNS. It can then use the agreed-upon protocol to request the IP addresses of others on the network and use those addresses to communicate directly with them.

9. Let’s Review What We Know About Internet Protocols
Why does the Internet use IP addresses?
Why don’t we need to know IP addresses?
Why do we need a Domain Name System?
Why don’t we all maintain our own DNS?
Is there one big DNS for the entire Internet?
How do you think all these DNS servers are maintained?

10. Stage 9
Complete Stage 9