Introduction to Networking

Quizzes @net-intro.com
1. Introduction
Q: What did early telephone operators do?
A: Connected pairs of wires to allow people to talk
Q: What is a leased line?
A: An "always on" telephone connection
Q: How long might a message be stored in an intermediate computer for a store-and-forward network?
A: possibly as long as several hours
Q: What is a packet?
A: A portion of a larger message that is sent across a network
Q: Which of these is most like a router?
A: A mail sorting facility
Q: What was the name given to early network routers?
A: Interface Message Processors
Q: In addition to breaking large messages into smaller segments to be sent, what else was needed to properly route each message segment?
A: A source and destination address on each message segment
Q: Why is it virtually free to send messages around the world using the Internet?
A: Because so many people share all the resources

2. Network Architecture
Q: Why do engineers use a "model" to organize their approach to solving a large and complex problem?
A: Because they can break a problem down into a set of smaller problems that can be solved independently
Q: Which is the top layer of the network model used by TCP/IP networks?
A: Application
Q: Which of the layers concerns itself with getting a packet of data across a single physical connection?
A: Link
Q: What does CSMA/CD stand for?
A: Carrier Sense Multiple Access with Collision Detection
Q: What is the goal of the Internetwork layer?
A: Get a packet of data moved across multiple networks from its source to its destination
Q: In addition to the data, source, and destination addresses, what else is needed to make sure that a message can be reassembled when it reaches its destination?
A: An offset of where the packet belongs relative to the beginning of the message
Q: What is "window size"?
A: The maximum amount of data a computer can send before receiving an acknowledgement
Q: In a typical networked client/server application, where does the client application run?
A: On your laptop, desktop, or mobile computer
Q: What does URL stand for?
A: Uniform Resource Locator

3. Link Layer
Q: When using a WiFi network to talk to the Internet, where does your computer send its packets?
A: A gateway
Q: How is the link/physical address for a network device assigned?
A: By the manufacturer of the link equipment
Q: Which of these is a link address?
A: 0f:2a:b3:1f:b3:1a
Q: How does your computer find the gateway on a WiFi network?
A: It broadcasts a request for the address of the gateway
Q: When your computer wants to send data across WiFi, what is the first thing it must do?
A: Listen to see if other computers are sending data
Q: What does a WiFi-connected workstation do when it tries to send data and senses a collision has happened?
A: Stop transmitting and wait a random amount of time before restarting
Q: When a station wants to send data across a "token"-style network, what is the first thing it must do?
A: Wait until informed that it is your turn to transmit

4. Internetworking Layer (IP)
Q: What is the goal of the Internetworking layer?
A: Move packets across multiple hops from a source to destination computer
Q: How many different physical links does a typical packet cross from its source to its destination on the Internet?
A: 15
Q: Which of these is an IP address?
A: 192.168.3.14
Q: Why is it necessary to move from IPv4 to IPv6?
A: Because we are running out of IPv4 addresses
Q: What is a network number?
A: A group of IP addresses with the same prefix
Q: How many computers can have addresses within network number "218.78"?
A: 65000
Q: How do routers determine the path taken by a packet across the Internet?
A: Each router looks at a packet and forwards it based on its best guess as to the correct outbound link
Q: What is a routing table?
A: A list of network numbers mapped to outbound links from the router
Q: How does a newly connected router fill its routing tables?
A: By asking neighboring routers how they route packets
Q: What does a router do when a physical link goes down?
A: Throws away all of the routing table entries for that link
Q: Why is it good to have at least a "two-connected" network?
A: Because it continues to function even when a single link goes down
Q: Do all packets from a message take the same route across the Internet?
A: No
Q: How do routers discover new routes and improve their routing tables?
A: They periodically ask neighboring routers for their network tables
Q: What is the purpose of the "Time to Live" field in a packet?
A: To make sure that packets do not end up in an "infinite loop"
Q: How does the "traceroute" command work?
A: It sends a series of packets with low TTL values so it can get a picture of where the packets get dropped
Q: About how long does it take for a packet to cross the Pacific Ocean via an undersea fiber optic cable?
A: 0.025 Seconds
Q: On a WiFi network, how does a computer get an Internetworking (IP) address?
A: Using the DHCP protocol
Q: What is Network Address Translation (NAT)?
A: It reuses special network numbers like "192.168" across multiple network gateways at multiple locations
Q: How are IP addresses and network numbers managed globally?
A: There are five top-level registries that manage network numbers in five geographic areas
Q: How much larger are IPv6 addresses than IPv4 addresses?
A: IPv6 addresses are twice as large as IPv4 addresses
Q: What does it mean when your computer receives an IP address that starts with "169.."?
A: The gateway is mapping your local address to a global address using NAT
Q: If you were starting an Internet Service Provider in Poland, which Regional Internet Registry (RIR) would assign you a block of IP addresses.
A: RIPE NCC

5. The Domain Name System
Q: What does the Domain Name System accomplish?
A: It allows network-connected computers to use a textual name for a computer and look up its IP address
Q: What organization assigns top-level domains like ".com", ".org", and ".club"?
A: ICANN - International Corporation for Assigned Network Names
Q: Which of these is a domain address?
A: www.khanacademy.org
Q: Which of these is *not* something a domain owner can do with their domain?
A: Create new top-level domains

6. Transport Layer
Q: What is the primary problem the Transport (TCP) layer is supposed to solve?
A: Deal with lost and out-of-order packets
Q: What is in the TCP header?
A: Port number and offset
Q: Why is "window size" important for the proper functioning of the network?
A: It prevents a fast computer from sending too much data on a slow connection
Q: What happens when a sending computer receives an acknowledgement from the receiving computer?
A: The sending computer sends more data up to the window size
Q: Which of these detects and takes action when packets are lost?
A: Receiving computer
Q: Which of these retains data packets so they can be retransmitted if a packets lost?
A: Sending computer
Q: Which of these is most similar to a TCP port?
A: Apartment number
Q: Which half of the client/server application must start first?
A: Client
Q: What is the port number for the Domain Name System?
A: 53
Q: What is the port number for the IMAP mail retrieval protocol?
A: 143

7. Application Layer
Q: Which layer is right below the Application layer?
A: Transport
Q: What kind of document is used to describe widely used Application layer protocols?
A: RFC
Q: Which of these is an idea that was invented in the Application layer?
A: http://www.dr-chuck.com/
Q: Which of the following is *not* something that the Application layer worries about?
A: How the window size changes as data is sent across a socket
Q: Which of these is an Application layer protocol?
A: HTTP
Q: What port would typically be used to talk to a web server?
A: 80
Q: What is the command that a web browser sends to a web server to retrieve an web document?
A: GET
Q: What is the purpose of the "Content-type:" header when you retrieve a document over the web protocol?
A: Tells the browser how to display the retrieved document
Q: What common UNIX command can be used to send simple commands to a web server?
A: telnet
Q: What does an HTTP status code of "404" mean?
A: Document not found
Q: What characters are used to mark up HTML documents?
A: Less-than and greater-than signs < >
Q: What is a common application protocol for retrieving mail?
A: IMAP
Q: What application protocol does RFC15 describe?
A: telnet
Q: What happens to a server application that is sending a large file when the TCP layer has sent enough data to fill the window size and has not yet received an acknowledgement?
A: The application is paused until the remote computer acknowledges that it has received some of the data
Q: What is a "socket" on the Internet?
A: A two-way data connection between a pair of client and server applications
Q: What must an application know to make a socket connection in software?
A: The address of the server and the port number on the server

8. Secure Transport Layer
Q: How do we indicate that we want a secure connection when using a web browser?
A: Use https:// in the URL
Q: Why is a shared-secret approach not suitable for use on the Internet?
A: It is difficult to distribute the secrets
Q: What is the underlying mathematical concept that makes public/private key encryption secure?
A: Prime numbers
Q: Which of the keys can be sent across the Internet in plain text without compromising security?
A: Encryption key
Q: Where does the Secure Sockets Layer (SSL) fit in the four-layer Internet architecture?
A: Between the Transport and Application layers
Q: If you were properly using https in a browser over WiFi in a cafe, which of the following is the greatest risk to your losing credit card information when making an online purchase?
A: You have a virus on your computer that is capturing keystrokes
Q: With the Secure Sockets Layer, where are packets encrypted and decrypted?
A: They are encrypted in your computer and decrypted in the server
Q: What changes to the IP layer were needed to make secure socket layer (SSL) work?
A: No changes were needed
Q: If a rogue element was able to monitor all packets going through an undersea cable and you were using public/private key encryption properly, which of the following would be the most difficult for them to obtain?
A: Which documents you retrieved from the servers
Q: What is the purpose of a Certificate Authority in public/private key encryption?
A: To assure us that a public key comes from the organization it claims to be from
Q: The ARPANET network was in operation starting in the 1960s. Secure Sockets Layer (SSL) was not invented util the 1980s. How did the ARPANET insure the security of the data on its network?
A: By making sure no one could access the physical links
Q: Which of these answers is "Security is fun" encrypted with a Caesar Cipher shift of 1.
A: Tfdvsjuz jt gvo
Q: What Caesar Cipher shift was used to encrypt "V yvxr frphevgl"?
A: 13

9. The OSI Model
Q: What is the primary value of the OSI network model?
A: The OSI approach can be use to analyze many different network models
Q: How many layers does the OSI model have?
A: Seven
Q: Which of the OSI layers deals with the shape of connectors for network connections?
A: Physical
Q: Which of the layers is most similar between the OSI and TCP network models?
A: TCP Internetwork Layer and OSI Network Layer
Q: What layer does the TCP/IP Secure Sockets Layer map to in the OSI network model?
A: Session and Presentation Layers
Q: Why does the TCP model combine the OSI Data Link and Physical layers into a single Link layer?
A: Because quite often the design of Data Link and Physical layers are tightly connected for a particular technology