1. Vocabulary
Prototype: A preliminary sketch of an idea or model for something new. It’s the original drawing from which something real might be built or created.
Binary - A way of representing information using only two options.
Bit - A contraction of "Binary Digit". A bit is the single unit of information in a computer, typically represented as a 0 or 1.
Bandwidth - Transmission capacity measure by bit rate
Bit rate - (sometimes written bitrate) the number of bits that are conveyed or processed per unit of time. e.g. 8 bits/sec.
Latency - Time it takes for a bit to travel from its sender to its receiver.
Protocol - A set of rules governing the exchange or transmission of data between devices.
ASCII - ASCII - American Standard Code for Information Interchange. ASCII is the universally recognized raw text format that any computer can understand.
code - (v) to write code, or to write instructions for a computer.
IETF - Internet Engineering Task Force - develops and promotes voluntary Internet standards and protocols, in particular the standards that comprise the Internet protocol suite (TCP/IP).
Internet - A group of computers and servers that are connected to each other.
Net Neutrality - the principle that all Internet traffic should be treated equally by Internet Service Providers. To / From Address: Like an IP address, included on every message sent over the Internet.
Dropped Messages: Poorly formed messages cannot be delivered and so are dropped, just like a letter with a bad address on it. Tomorrow you’ll discuss more technical reasons messages are dropped.
Multiple Hops: A message travelling across the Internet will visit many routers as each tries to forward it along the most efficient path to its destination.
Different Paths: Routers respond to traffic on the Internet in real time. The best path at one moment might be backed up a few seconds later. Routers choose the current best path to get the message through
Router: a computer designed to receive and redirect packets of information based upon the addressing information (e.g. an IP address) contained in the packet.
Packets - Small chunks of information that have been carefully formed from larger chunks of information.
TCP - Transmission Control Protocol - provides reliable, ordered, and error-checked delivery of a stream of packets on the internet. TCP is tightly linked with IP and usually seen as TCP/IP in writing.
DNS - The service that translates URLs to IP addresses.

2. CS Principles
U1L12 The Need For DNS

3. U1L12 The Need For DNS Objectives
SWBAT:
Give a high level description of DNS as a name-to-IP-address mapping system used on the Internet
Give a few reasons why DNS is useful and necessary
Describe at least one vulnerability of DNS and how an attack on it works

4. U1L12 Vocab
DNS – Domain Name Service; the service that translates URLs to IP addresses.

5. U1L12 Content: DNS
At its core, the DNS is "simply" a hierarchical system of computers and databases, that maps IP addresses to domain names.
It enables Internet users to connect human-language locations on the Internet with numeric addresses used by IP.
While distributed and hierarchical, it can be treated in the abstract as a centralized registry of locations on the Internet, allowing users to quickly find locations they are looking for and register themselves so that others may find them.

6. U1L12 Prompt? Prompt1: Why did I keep taking your IP addresses?
Prompt2: 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?

7. U1L12 Prompt? Prompt: Why did I keep taking your IP addresses?
This simulates the fact that a computer’s IP address does not stay the same. For example, a person’s IP address on their phone changes quite frequently as they move around throughout their day and their phone tries to connect to the Internet from different locations.
Prompt: 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?
A central list would be better, and the Internet has a system for that

8. U1L12 Activity 1
Transition to the Internet Simulator (see Code Studio):
Open DNS Partner Questionnaire - Activity Guide.
The new configuration of the simulator includes a DNS server:
A DNS server now appears attached to every router.
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.
Demonstrates how to send a request to the DNS for someone’s address. Let students try the DNS protocol to get the address of someone who is attached to their router.

9. U1L12 Activity 1
When you go to the Internet Simulator now, you will see a "DNS server" attached to the router. In order to communicate with someone else, you must first find their IP address by asking the DNS.
1. To begin, click over to the “DNS” tab to see all the hostnames of people on the router. You will see the address of the DNS (always 15) but will not see an address for anyone else on the router.
2. The DNS server responds to a text protocol that will give you someone’s IP address. The protocol is:
3. 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.”
GET <hostnameOfPerson>

10. Directions (from activity guide)
You are going to interview/have a conversation with a classmate using only the Internet Simulator. We’ve created a list of interview questions (on the next page) and you should both jot down each other’s responses.
To find the person, you will have to ask the DNS for her IP address. When you have retrieved the IP address, start the interview.
HOWEVER….As you’re working, if your teacher taps you and your partner, you both MUST disconnect and reconnect from the simulation. This is to simulate changing IP addresses.
Even though your IP address will change, your hostname will stay the same, so 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!

11. VIDEO: DNS
You may remember (from the IP/DNS video that we saw several lessons ago) that you learned about the Internet system (v DNS) for sharing names and IP addresses. Let's watch that section again!

12. U1L12 Reflection
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?