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Computer Systems > Computer Networks > Flashcards

Computer Networks Flashcards

1
Q

What is a Network?

A

Multiple computers that are connected together and share information

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2
Q

What is the Internet?

A

The Internet is a network of networks

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3
Q

What is a WAN?

A

A wide area network that extends over a large geographic area

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4
Q

What is a LAN?

A

A local area network that covers a small geographic area

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5
Q

What is a PAN?

A

A personal area network that covers a short-range around a person

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6
Q

What are the two main layered network models?

A
  • OSI model
  • TCP/IP Model
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7
Q

What are the 4 layers in the TCP/IP model?

A
  • Application Layer
  • Transport Layer
  • Internet Layer (Network Layer)
  • Network Access Layer (Link Layer)
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8
Q

Why use a layered model?

A
  • Abstraction
  • Irrespective of underlying hardware and topology, applications and host can talk to each other
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9
Q

What is the End-to-End Concept?

A
  • The network is responsible for providing best-effort connections and should be essentially transparent
  • End hosts are responsible for reliability and security
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10
Q

What is Layer Encapsulation?

A
  • Each layer in the TCP/IP stack adds it’s own header to the data
  • The becomes the payload for the next layer
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11
Q

What does the Network Access Layer do?

A
  • Deals with the local link that a host is connected to
  • Each host has a link-unique address
  • e.g. encapsulation of a packet in an ethernet frame
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12
Q

What is LAN defined by?

A

The IEEE 802 family of standard

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13
Q

What are the basic functions of the Internet Layer?

A
  • Handles next-hop routing
  • Provides unique addressing
  • Passes a received packet’s payload to the transport layer
  • Facilitates connection of different types of network
  • The Internet layer only provides a “best-effort” packet delivery
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14
Q

What are the main protocols of the Internet Layer?

A
  • IPv6
  • IPv4
  • ICMPv6
  • ICMP
  • IPSEC
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15
Q

What is IPv4?

A
  • Internet Protocol version 4
  • Each node has a unique 32-bit IP address
  • Written in octet-grouped dotted decimal notation (152.78.65.112)
  • Variable length header, minimum of 20 bytes
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16
Q

What is IPv4 Exhausion?

A

A 32-bit address space only allows for 4.3 billion addresses so they will eventually run out which has been anticipated since the 1980s

17
Q

What is NAT and NAPT?

A
  • Network Address (and port) Translation is a way to share one IPv4 address between multiple computers
  • A home router shares a public IPv4 address with multiple devices having a private IPv4 address
18
Q

What are the issues with NAT and NAPT?

A
  • NAPT breaks the end-to-end principle & some protocols
  • Gives a false sense of security - NAT is not a replacement for a properly configured firewall
  • Even with NAT, we still have IPv4 exhaustion
19
Q

What is IPv6?

A
  • Internet Protocol version 6
  • Each node has a unique 128-bit IP address, written in colon-delimited hexadecimal e.g. 2001:630:d0:f111:e07a:b1fa:68a1:80eb
  • 40-byte header
20
Q

What is a subnet?

A

A logical subdivision of a network

21
Q

What is routing?

A
  • Occurs where there is a change in IP address spaces at the Internet Layer
  • Each router has an IP address in each address space it routes between
  • Routers can also have other functions: firewalling, dns, dhcp etc
22
Q

What does the Transport layer do?

A

Provides host-to-host communication
- Using two main protocols, TCP (Transmission Control Protocol) and UDP (User Datagram Protocol)

23
Q

What are the characteristics of TCP?

A
  • Connection oriented
  • Handles ACK & retransmissions
  • Guaranteed that it arrives and in the correct order
  • The header is 20-bytes minimum
  • It is good for applications that need high reliability
  • Some example protocols are: HTTP(S), FTP, SMTP, SSH
24
Q

What are the characteristics of UDP?

A
  • Connectionless: “Fire and Forget”
  • Application needs to handle ACK & retransmissions if needed
  • No guarantee that data is received in the order sent
  • The header is 8-bytes
  • It is good for applications that need fast and efficient transmission
  • Example protocols: DHCP. TFTP, RIP
25
Q

What is TCP Flow Control?

A
  • Prevents a fast sender overwhelming a slow receiver
  • TCP uses a sliding window protocol to control the sending rate
  • Sender should only send if the receiver indicates it has buffer space to accept data, the sliding window is the buffer
26
Q

What is TCP Congestion Control?

A
  • Reduces send rate to cope with network congestion
  • Sender starts by sending small packets
  • Sender increases the size of each subsequent packet until there is packet loss (Exponentially up to a threshold then additively)
  • Sender restarts the cycle with a lower threshold
  • Done because congestion leads to packets being dropped
27
Q

What does the Application layer do?

A
  • Software that uses the network
  • Generally, programmers will use pre-made libraries but need to choose appropriate modes
28
Q

What is ICMP/ICMPv6?

A
  • Used for diagnostic and control purposes or generated response to errors in IP operations
  • Used by Ping and Traceroute
29
Q

What Name/Address Type is in the Application Layer?

A

Domain name

30
Q

What Name/Address Type is in the Transport Layer?

A

Port Number

31
Q

What Name/Address Type is in the Network Layer?

A

IP address

32
Q

What Name/Address Type is in the Link Layer?

A

MAC Address

33
Q

What does ARP and NDP do?

A

Address Resolution Protocol (IPv4) and Neighbour Discovery Protocol (IPv6) operate at the Link Layer and translate IP address to MAC addresses

34
Q

What is the DNS?

A
  • The Domain Name Service provides a way to map symbolic domain names to an IPv4 or IPv6 address
  • Highly-reliable and resilient distributed service that operates at the application layer
35
Q

What does a switch do?

A
  • Used to connect multiple devices on one network segment
  • Switches operate at the Network Access layer
  • Switches only forward traffic between the ports it needs to
36
Q

How can you get a working IPv6 on a IPv4?

A

A Tunnelbroker e.g. Hurricane Electrics but it will have high latency than a native IPv6 connection

37
Q

How do you stay anonymous on the internet?

A

VPNs
The Onion Router

38
Q

How do VPNs work

A

Computer Systems (6 decks)

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