1. AP CSP: Making a reliable Internet & DNS

2. Introduction:
Your friend sent you a message on the Internet, but you never received it. Based on what you already know about routers and the physical Internet, list what reasons might explain this fact.

3. Dropped Messages: Some reasons for dropped messages:
Wires are cut
Interference on a radio channel
Router malfunctions or cannot keep up with traffic being directed to it
When we communicate on the Internet, we are not just sending short text messages as we did yesterday. We also use the Internet to exchange documents, videos, music, and scientific data, and these files can easily grow to enormous size.
It turns out that splitting up a message into packets provides many benefits. If a faster route opens up halfway through transmitting a large file, it is easy to reroute later packets in the transmission through that route.
Splitting up a message into smaller chunks doesn’t solve all the problems of unreliability on the Internet. Packets can still be dropped or arrive out of order.

4. Unplugged Activity:
We will form into groups of 6. You will create a drawing or message of some sort that you will break into 4 equal pieces.
You will then find another partner on the other side of the room and exchange addresses with them.
You will then write your partners address on the back of the four pieces of paper you have created.
You will then send your message one piece at a time to your partner across the classroom.
You cannot get out of your seat! You can only pass it to people that are next to you!

5. Unplugged Discussion:
For a student who was able to get the whole drawing - did the pieces of paper come to you in order?  (Probably not) Why not?
How did you know how to reconstruct the message or image? (if it was a drawing, the correct order was probably pretty obvious, but what if your message was a word like “dear”, which could also be reconstructed as “read”? How do you know which word the sender intended?)
Did anyone not get all the pieces intended for them?  What happened?
Packets may get dropped because of over-congestion, nature (power outage, etc), or even malicious acts.
What happened at the table in the middle - what was that like? (lots of congestion?)
The interesting question is: if you receive some but not all of the pieces of a message, what can you as the recipient do to fix it?  What should the protocol be?

6. Creating an Reliable Packet Network:
Today’s challenge is to develop a protocol to reliably send messages even though the network itself is unreliable.
You will only be allowed to send packets containing 8 characters of text!
You may construct multiple packets prior to sending them, by clicking "Add Packet", and then send them all with one click of the "Send" button.
Every message has a small chance of being dropped on each “hop” it makes between routers.
You will group up into parties of 2 or 3 but all group members will be on different routers!

7. Practice Simulator:
Exchange messages across routers. Try to construct a multi-packet message and send multiple packets at once to someone else
View the router logs to examine the result of these transmissions.
Think about how you might be able to send Images
 The wider the drawing is, the more challenging the protocol will be
Some things to be aware of:
Packets are dropped with some frequency
Packets of more than 8 characters are always truncated to just the first 8 characters
Packets sometimes arrive out of order.

8. Guidelines for Protocol:
All communication can only be done through the Internet Simulator.
The full message sent will be at least 80 characters long - broken into at least 10 packets - and might be entirely random (i.e. there’s no way to use human intuition to reconstruct the message).
The sender and receiver must be confident the full message was successfully transmitted and reconstructed.
Develop your protocol!
TEST it TOO!!

9. Transmission Control Protocol:
The Internet: Packets, Routing, and Reliability Video:
Transmission Control Protocol, or more simply, TCP divides larger messages into smaller packets which have ordering information added to their header.
When a packet arrives at a destination computer, an acknowledgement is sent to the sender, letting them know they don’t need to resend that packet.
Once all the packets have arrived, the ordering information in the headers of the packets allows them to be reordered to create the original message.

10. DNS Unplugged:
When you walked in, I handed you a slip of paper with an IP address on it.
You also should have a Names and Addresses - Worksheet.
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!

11. Unplugged Discussion:
Why did I keep taking your IP addresses?
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?
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.
“Code.org” vs

12. DNS Internet Simulator:
Now each router in the Internet Simulator contains a DNS server. We no longer can see anybody’s IP address. To get an IP address, we have “ask” the DNS server using a text- based protocol.
GET madeline4 : you will type this to get the IP address of your partner
After the DNS has returned an IP address, you can type that IP address into the “To” field, enter a message, and then press “send.”
You are going to interview/have a conversation with a classmate using only the Internet Simulator. HOWEVER….As you’re working, if tap you and your partner, you both MUST disconnect and reconnect from the simulation
Your Hostname will remain the same!

13. DNS Protocol: Video: IP and DNS: Starts at 4:12
The DNS is the large-scale system that translates human-readable web addresses into their numeric IP addresses so that computers can communicate.
This system however was not designed to be secure and that has resulted in some major security incidents over time.
You're now going to learn about some of them and how they work.

14. DNS and DDoS Attacks:
Group up into groups between 4-6 people to complete their readings.
You will be assigned and article to read and answer questions
You will have minutes to read and make sense of the content
When you are done with your article. Talk to another individual who read a different article and jot done some key information from that article.
Do this with at least two individuals!

15. DNS Wrap-Up: DNS Questions: Security Questions:
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?
Security Questions:
What is one vulnerability of DNS and how is that vulnerability attacked?
What are the implications of an attack on a DNS server (or severs) - how does this affect your life?