Khan Academy The Internet Study List

In the Internet Protocol (IP), computers send messages to each other through a network of routers, with each message split up into packets. How do routers figure out where a packet needs to go?

Routers look at the IP packet header and use the destination address field.

Noemi works out of an office in San Francisco that recently got an upgrade to a 1 Gigabit Fiber internet connection. Ammar works at a company in Pakistan with a 500 Kbps internet connection. How much faster is the SF office connection than the Pakistan office connection?

2000x

TCP/IP are the protocols that route data around the internet. What are they each responsible for? 👁️Note that there are 2 answers to this question.

IP is responsible for routing of packets from source to destination across the internet. TCP is responsible for reliable transmission of packets.

Each IP packet contains a destination address. What is the primary purpose of the destination address?

It helps the router know where to send the packet.

DevFest is a conference that wants to make sure it has a reliable connection to the internet. The conference partners with two internet providers, Comcast and Sonic, just in case one of them goes down. The ISP routers then connect to the rest of the internet. Unfortunately, this network is not fault tolerant: there's still a single point of failure. Which router needs to stay available for DevFest to have a working connection to the internet?

Router A

GameCon is a multiplayer gaming tournament that wants to make sure its connection to the internet is reliable. The conference partners with three internet providers (AT&T, Sonic, and Verizon) just in case one of them goes down. The ISP routers then connect to the rest of the internet. Unfortunately, this network is not fault tolerant: there's still a single point of failure. Which router needs to stay available for GameCon to have a working connection to the internet?

Router A

We use modems to connect our home network to the larger network provided by our internet provider (and ultimately the whole internet). Here's a sampling of modems from the last 80 years: Image source: Pratyeka, Wikipedia They look similar, but the bandwidth has been steadily increasing as engineers develop new technologies. Sort this list of historical modems from lowest to highest bandwidth, with the lowest on the top and the highest on the bottom:

"Bell 101" @ 110 bits/s "Bell 103" @ 300 bits/s "Modem 1200" @ 1.2 kbit/s "Modem 2400" @ 2.4 kbit/s "VDSL" @ 52 Mbit/s "MDSL" @ 2.32 Gbit/s

Over the years, engineers have invented many networking technologies for LANs (local area networks). Many are still in use, and many of the very slow ones were abandoned long ago. The following is a sampling of LAN technologies and their bandwidths. Sort the technologies from lowest to highest bandwidth, with the lowest on the top and the highest on the bottom: "LocalTalk" @ 230 kbit/s "Econet" @ 800 kbit/s "Omninet" @ 1 Mbit/s "FireWire" @ 400 Mbit/s "Gigabit Ethernet" @ 1 Gbit/s "Omni-Path" @ 100 Gbit/s

"LocalTalk" @ 230 kbit/s "Econet" @ 800 kbit/s "Omninet" @ 1 Mbit/s "FireWire" @ 400 Mbit/s "Gigabit Ethernet" @ 1 Gbit/s "Omni-Path" @ 100 Gbit/s

Jelani is a student in a Somalia school, where their internet download speed is 400 kbps. He visits relatives in Oakland, California, and stays at a home where the download speed is 60 Mbps. How much faster is the Oakland home's download speed than the Somalian school's download speed?

150x

NSFNET was an early internet connecting the computer science departments of universities. In 1986, NSFNET connected 6 departments across the US: Redundancy in a network makes it more fault-tolerant. When two computers in a network are connected by multiple routes, that adds redundancy. Assuming any connection can go down, how many routes are there between NCAR and JVNC?

3 routes

NSFNET was an early internet connecting the computer science departments of universities. In 1986, NSFNET connected 6 departments across the US: Redundancy in a network makes it more fault-tolerant. When two computers in a network are connected by multiple routes, that adds redundancy. Assuming any connection can go down, how many routes are there between San Diego and Illinois?

3 routes

The Mozilla Firefox browser gives users three different ways they can disable cookies. The most restrictive option to "disable all cookies" includes a note that it will cause websites to break. What features on websites are likely to break if a user disables all cookies?

A login that works across multiple pages of the website.

Arthur clicks a link from a chat with his friend that opens "https://www.charitywater.org/". He sees this website load: Which of these best describes how the website loaded?

Arthur's browser sent an HTTP request to the web server that hosts "charitywater.org". The web server sent back an HTTP response with the HTML for the webpage.

Computer A wants to send data to Computer B using the TCP/IP protocols. What's the best description of how Computer A sends the data?

Computer A splits the data into packets. It does a three-way handshake with Computer B to establish the connection, then sends each packet to the nearest router. If it detects packet loss, it re-sends the missing packets.

Computer A wants to send data securely to Computer B using public key encryption. What information do they need from Computer B before Computer A can send the data?

Computer B's public key

Reina navigates to her bank's website: She notices it looks different from usual - strange fonts and layout, plus it doesn't show how much money is in her banking accounts. Reina checks Twitter and sees reports of a DNS spoofing attack on the banking site: What is a good explanation of this DNS spoofing attack?

Cyber criminals hacked into a DNS server and redirected the mapping for the "banksrus.com" domain name to an IP address that they control.

When packets are routed on the internet, the route for a particular packet is not pre-determined. Instead, the next hop is decided by each router along the way. How does that increase the fault tolerance of routing?

Each router can pick a connection that's currently working and available.

Emily is trying to use her home computer as a server. She told the IP address to her friend Kolby, and he was able to send messages from his computer to hers. Emily's home just had a power outage, and after a few minutes, the power came back and the internet started working again. However, Kolby can't send messages to Emily's server anymore. Which explanation is the most likely?

Emily's ISP assigned a different IP address to her computer after the power came back on.

In the modern age of computers, we cannot use the same symmetric encryption schemes that were used 1000 years ago or even a 100 years ago. What is the best explanation for why we can't use them?

Older encryption schemes are easy to crack with computers, since a computer can quickly perform frequency analysis and try out many keys.

What is the Transmission Control Protocol (TCP) responsible for? What is the Internet Protocol (IP) responsible for?

TCP is responsible for reliable transmission of packets. IP is responsible for routing of packets from source to destination across the internet.

Public key encryption is considered "asymmetric" encryption due to its use of two keys for encryption and decryption while the Caesar Cipher is considered "symmetric" since it uses the same key for both. Which of these describes how the two keys are used in public key encryption?

The recipient's public key is used to encrypt the data; the recipient's private key is used to decrypt the data.

The most time-intensive part of public key encryption is the generation of the key pair. Why does key generation take so long?

Processing power: the computer has to do a series of difficult mathematical operations on very large numbers, like generating randomness and checking for prime-ness.

Startuppr is a web company that's running their servers out of their garage. Uptime is important to them, so they pay for two internet service providers, Xfinity & Wave. The ISP routers then send their server's packets to the rest of the internet. Unfortunately, this network is not fault tolerant: there's still a single point of failure. Which router needs to stay available for Startuppr servers to stay connected to the internet?

Router A

Why does each IP packet contain a destination address?

Routers use the destination address to decide where to send a packet

The Transmission Control Protocol (TCP) splits each message into multiple packets. It's possible for packets from the same message to arrive out of order. Which field in the IP packet helps computers put the packets in the original order?

Sequence number

A new internet provider ZoomyZoomy is creating advertising for their fast upload speed. Which of these has the correct unit?

Sign up now for an upload speed of 50 Mbps

TCP/IP are the protocols that route data around the internet. What are they responsible for?

TCP is responsible for reliable transmission of packets. IP is responsible for routing of packets from source to destination across the internet.

Jay is playing BigBalloon, an online multiplayer balloon popping game, and is trying to help his team win during a rumble with another team. However, his attempts to pop balloons aren't working. He's clicking the balloons as soon as he sees them, but the other team's clicks are counting instead. What's the most likely explanation for why that might be happening?

Jay's on an internet connection with too high latency.

The administration of a high school decides to install antivirus software on all of the school computers. What can the antivirus software protect the computers from?

The antivirus software can protect the computers from any malware that it is able to successfully detect.

In 2000, a 15-year-old launched a DDoS attack against the servers of the Yahoo search engine, resulting in users being unable to use Yahoo for an entire hour. Which of these is the most likely explanation for how the DDoS attack brought down Yahoo?

The attack used a large number of compromised computers to send requests to the Yahoo servers, rendering them unable to answer legitimate requests.

Rosa is trying to explain to a classmate that IP addresses are hierarchical. Which of these explanations are the best?

The first part of an IP address specifies the network, the next part specifies the individual node in the network.

Processing power: the computer has to do a series of difficult mathematical operations on very large numbers, like generating randomness and checking for prime-ness.

Verifying a computer has a trusted certificate Establishing an encrypted communication channel between 2 computers

In 2012, cyber criminals launched DDoS attacks on 6 popular US banking websites. They hijacked hundreds of computers and sent traffic that peaked at 60 Gbps. What was the likely effect of the attacks?

Visitors to the websites were unable to use the websites during the attack.

Consider the website: blog.gardeningknowhow.com That URL leads to the blog of a gardening tips & tricks website. Which of these statements are true? 👁️Note that there are 2 answers to this question.

blog is a subdomain of gardeningknowhow.com blog is a third-level domain

Consider the website: help.donorschoose.org That website hosts the help center for DonorsChoose, a site where teachers can fundraise for classrooms. Which of these statements are true? 👁️Note that there are 2 answers to this question.

help is a subdomain of donorschoose.org org is a top-level domain

An online ads distributor AddTheAds claims that its server has lower latency than other ad servers. Which of these claims makes sense?

"Our ad server has a latency of just 40 ms"

Nadia is at an internet cafe in Paraguay, where the download speed is 600 kbps. She's chatting with her friend Jun in Singapore, where the download speed is 60 Mbps. How much faster is Jun's speed than Nadia's?

100x

NSFNET was an early internet connecting the computer science departments of universities. In 1986, NSFNET connected 6 departments across the US: Redundancy in a network makes it more fault-tolerant. When two computers in a network are connected by multiple routes, that adds redundancy. In this network, how many routes are between San Diego and Cornell?

4 routes

There is a large difference in IP v6 adoption across the world. These are the IP v6 adoption rates of the top 5 most populated countries, as of October 2018: Country Adoption % China 2.9% India 34% US 34% Indonesia 0.2% Brazil 25.7% Why is it important to encourage countries and their Internet Service Providers to upgrade to IP v6?

If a country's ISPs don't adopt IP v6, they may run out of addresses when too many devices want to use the internet in their country.

Jewel is playing Agar, a multiplayer online game where cells gain mass by eating other cells in a petri dish. She's experiencing "lag": it feels like she doesn't have enough time to move before another cell eats her cell. An online article recommends reducing lag by connecting to a regional Agar server closer to her home. What's the best explanation for why that might help?

If she connects to a regional server, her connection will be lower latency than before.

Each IP packet contains a sequence number. What is the primary purpose of the sequence number?

It helps the receiving computer reassemble the packets.

An office receives a copyright infringement notice from their ISP. The notice claims they have evidence that someone in the office illegally downloaded a copyrighted movie on a particular day. The office manager asks around and finds out that, yes, one of the employees did download that movie. How did the ISP likely know about the illegal downloading?

The ISP monitored the internet traffic coming from each of the computers using the office's connection.

Which of these could be a valid IP v4 or IP v6 address? 👁️Note that there may be multiple answers to this question.

a90f:712c:c81d:eeb1:42b8:64e7:f336:31fd 92.169.42.163

Why does each IP packet contain a sequence number?

Computers use the sequence number to determine the original order of the packets.

Eliott came up with a scheme for encrypting messages to send to his friend in class. He wanted to use the Caesar Cipher, but his classmates already knew it, so he added a twist on top of it. For each word in the message, he first swaps the first letter of the word with the third letter of the word (if it's long enough), switches the As and the Es, and finally he applies a Caesar Cipher of 14. Demonstration of encryption algorithm, in 3 steps. The first line shows message "MEET_ME_AT_THE_LOCKERS_AT_THREE". "TAMT_ET_AHT_COLKARS_ET_RHTAA". "HOAH_SH_OVH_QCZYOFG_SH_FVHOO". He needs to share an encryption key with his friend before they can decrypt his messages. What would be the best key for this symmetric encryption scheme?

A 3-step explanation of how he encrypted the message (the in-word letter swap, the A and E swap, and the Caesar shift of 14).

Which of these is an accurate description of how the TCP/IP protocols send data around the internet?

Computers split messages into packets, and send them through routers to their final destination. The destination computer acknowledges the receipt of each packet, so that the sending computer can ensure every packet is delivered.

Keung types in the URL for an online email service and sees this in the browser bar: He decides to bypass the error and log into his email anyway, as he's expecting a very important email. What are some consequences of visiting the website with a non-secured HTTP connection? 👁️Note that there are 2 answers to this question.

His ISP can inject advertisements into the emails. A cybercriminal can steal his password.

Bailey decides to make their own version of the internet. To map domains to IP addresses, he sets up a single computer that stores every mapping. What are the flaws in this system that affect its scalability? 👁️Note that there are 2 answers to this question.

If the computer turns off, no other computer will be able to find out how to map domain names to IP addresses. Once many computers join their internet, the computer may be overwhelmed by requests and not be able to handle all of them in a reasonable amount of time.

An intranet is a private network set up for an organization like a company or university. Here's an intranet with 5 routers labeled A-E: An intranet is more secure, because computers can communicate without using the public internet, but it is often not as fault-tolerant. Imagine that router C needs to send a message to router E. Which of these situations will lead to the message failing to arrive? 👁️Note that there may be multiple answers to this question.

If these 2 connections go down: B to C, C to D. If the connection between D and E goes down.

What types of encryption are used in the TLS protocol to ensure secure communication between a client and server?

It starts with public key encryption and then uses symmetric encryption.

Which of these users has the strongest password?

Marjorie combines 5 random words and alternates the casing: "scarves-TOKYO-theme-TEAMWORK-trulia".

Which are the primary aspects of the domain name system (DNS) that help it scale? 👁️Note that there are 2 answers to this question.

Scalability in the DNS is helped by caching of domain ↔ IP mappings on multiple machines. Scalability in the DNS is helped by the division of labor between root name servers, TLD name servers, and host name servers.

Mr. Jones bought a server where his students can upload their homework assignments, and mapped it to the domain "writing302.org". He then acquired a digital certificate for "writing302.org" from a certificate authority and installed it on the server. What does the certificate prove?

The certificate proves that "writing302.org" and its associated encryption key are both owned by the same entity.

Imagine you're trying to explain the domain name system (DNS) to a 5 year old. Which of these metaphors are the most fitting?

The domain name system is like a phone book for the internet.

Which of these best describes the fault tolerance of routing on the internet?

There are multiple routes for each IP packet to follow. A packet can be re-routed if a path becomes unavailable.

IP v4 addresses currently cost more to lease than in the past. What's the most likely explanation for why people are willing to pay more for IP v4 addresses now?

There are very few available IP v4 addresses in the world, and the scarcity increases the demand.

The most recent big DNS cache poisoning attacks have been on the cryptocurrency websites MyEtherWallet and Trezor. Those websites help users keep track of their cryptocurrency investments, and they store user credentials that are used for buying and selling. Why would cyber criminals want to DNS spoof a cryptocurrency website?

They can direct those websites to fake websites that ask users for secure information that they can then use on the real website.

Mason receives an email from a law firm called "Baker & McKenzie". The email states that they are scheduled to appear in court and includes a link to view the court notice. Mason is suspicious that this may be a phishing attack, since this is the first they've heard about a court appearance.

They can email

Taylor switched WiFi networks from an AT&T network to a Verizon network. He noticed his IP address changed. What's the best explanation for the change?

Verizon has a different set of IP addresses to allocate than AT&T, so Verizon had to give Taylor's computer a different IP address than the AT&T address.

Imagine an internet without the domain name system (DNS). What would that internet be like?

Without the domain name system, we would not be able to use nice URLs like "facebook.com" to visit websites on the internet.

Over the years, engineers have invented many networking technologies for WANs (wide area networks), connecting large geographic regions like cities and states. The slower technologies are mostly obsolete, but may still be used in developing nations. The following is a sampling of WAN technologies and their bandwidths. Sort the technologies from lowest to highest bandwidth, with the lowest on the top and the highest on the bottom:

"56k line" @ 56 kbit/s "DS0" @ 64 kbit/s "T1" @ 1.544 Mbit/s "VDSL" @ 100 Mbit/s "10 Gigabit Ethernet" @ 9.953 Gbit/s "OC-256" @ 13.271 Gbit/s

These are screenshots of URLs loaded in the Firefox web browser, which uses visual indicators to indicate the security of a web connection. Which of these URLs were successfully loaded over a secure HTTP connection? 👁️Note that there may be multiple answers to this question.

(Locked) https://www.bbc.com

Which of these could be a valid IP v4 or IP v6 address? 👁️Note that there may be multiple answers to this question.

192.168.17.43 2001:0db8:85a3:03eF:7cb3:8a2e:0370:7334

Tiffany is helping a family member learn how to use Gmail. She notices the website is using a different font and logo, and that the emails are suspiciously worded: Tiffany suspects that gmail.com has been compromised by a DNS spoofing attack. Which of these are good next steps? 👁️Note that there are 2 answers to this question.

Contact the Gmail team via social media or phone Close the Gmail tab

HTTPS is a combination of multiple internet protocols that provides secure browsing on the web. What's the best description of how HTTPS combines multiple protocols?

HTTPS retrieves webpages using the HTTP protocol, and uses the TLS protocol to wrap the HTTP requests and responses in a layer of security.

Devon navigates to "https://www.kidsalive.org/" in his browser and sees this on the front page:

The HTML of the webpage The logo The JavaScript code for the map pop-ups Each graphic file The custom font file

Which of these is the best description of the domain name system (DNS)?

The domain name system associates domain names with IP addresses, like "www.youtube.com" with 208.65.153.251.

The University of California at Davis has many IP addresses that it can assign to its campus computers. One IP address is 169.237.121.44. Which explanation best describes the hierarchical nature of that address?

The first part of the address (169.237) identifies the network (UC Davis) and the second part (121.44) identifies the campus computer.

Comcast, an Internet Service Provider in the US, has many IP addresses that it can assign to its customer's computers. One IP address is 24.128.139.211. Which explanation best describes the hierarchical nature of that address?

The first part of the address (24.128) identifies the network (Comcast) and the second part (139.211) identifies the individual customer.

D'Andre is riding a train with wireless internet service. When he logs online, he sees a warning that the wireless network has limited bandwidth. Which online activities are most likely to be affected by limited bandwidth? 👁️Note that there are 2 answers to this question.

Watching online movies Downloading a large application

Consider the website: eecs.berkeley.edu That website leads to the Electrical Engineering & Computer Science department of UC Berkeley. Which of these statements are true? 👁️Note that there are 2 answers to this question.

eecs is a subdomain of berkeley.edu edu is a top-level domain

Logan types this URL in his browser's address bar: http://wolverinefoundation.org/ After a few seconds, the browser loads the webpage: Which of these protocols are used by the browser in fetching and loading the webpage? 👁️Note that there may be multiple answers to this question.

HTTP IP TCP

In 2016, the ACLU reported that a company called Geofeedia analyzed data from social media websites like Twitter and Instagram to find users involved in local protests and sold that data to police forces. The data included usernames and their approximate geographic locations. Geofeedia claims the data was all publicly available data. For a user that does not want to risk making their geolocation public, which of these actions would NOT reduce the risk?

Cookies

What is the main advantage of the IP v6 addressing protocol?

IP v6 allows for more addresses than IP v4.

An intranet is a private network set up for an organization like a company or university. Here's an intranet with 5 routers labeled A-E: An intranet is more secure, because computers can communicate without using the public internet, but it is often not as fault-tolerant. Imagine that router A needs to send a message to router E. What situations will lead to the message failing to arrive? 👁️Note that there may be multiple answers to this question.

If these 2 connections go down: D to E, and B to C. If these 2 connections go down: D to E, and C to E.

Jaime received an email from his favorite movie streaming service. The email stated that all customers were being asked to reset their passwords (due to a security breach) and linked to a webpage with a password reset form. The webpage asks him to confirm his old password and then enter a new password. At that point, Jaime wonders if the email and webpage are part of a phishing scam. He searches the internet and finds other reports of the scam, so he closes the webpage and marks the email as spam. What could have happened if he had filled out the form? 👁️Note that there are 2 answers to this question.

The attackers could try using the "old password" and "new password" to login to Jaime's accounts on other sites. The attackers could use Jaime's "old password" to login to the actual movie streaming website.