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A Level Computer Science > The Internet > Flashcards

The Internet Flashcards

1
Q

What is the Internet?

A
  • A network of interconnected computer networks which uses an end-to-end communication protocol
  • Mostly a wired network, underwater cables connect different continents
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2
Q

What are ISPs?

A
  • Stands for Internet Service Provider
  • Companies that provide customers with access to the Internet
  • The largest ISPs / national ISPs provide internet to smaller regional ISPs
  • Homes / businesses can buy access to the Internet from these
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3
Q

What is a packet?

A
  • Containers in which data is transmitted over networks
  • Labelled with addresses for their sender and recipient
  • Contain information intended for the recipient
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4
Q

What are packet switching networks?

A
  • Network in which data is sent in packets
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5
Q

How do packet switching networks work?

A
  • One message is split into multiple packets, each of which is sent to its recipient via the best possible route
  • Packets are reassembled with other packets that form part of the same message by their recipient
  • These pass through a number of routers before the destination, where the router determines where to send them by using the recipient address
  • Every time a packet goes through a router, a hop occurs, only a finite nmber of hops can occur
  • When a packet’s TTL expires, the packet is dropped
  • The recipient notices a missing packet and requests for a retransmission
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6
Q

What is TTL?

A
  • Stands for Time to Live
  • A packet’s TTL is a number that indicates how many hops the packet can partake in
  • Reduced by one with each hop
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7
Q

What are the components of a packet?

A
  • Primary components of a packet:
    • Sender’s address
    • Receiver’s address
    • Packet contents
    • TTL
    • Sequence number
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8
Q

What is the sequence number of a packet?

A
  • Contains the number of packets in a message and identifies a packet’s position in relation to others
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9
Q

What are routers?

A
  • Routers connect different networks
  • They send packets to their recipient via the fastest route
  • Hold tables with info relating to the fastest routes to certain devices
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10
Q

What is a gateway?

A
  • Gateways connect different networks
  • Where two networks use different protocols, packets must be modified by a gateway so as to conform to both protocols
  • Gateways strip away most of the packets details, leaving just the contents, then gives it a new send and receive address to comply with the new protocol
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11
Q

What is a URL?

A
  • Stands for Uniform Resource Locator
  • Addresses assigned to files on the Internet
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12
Q

What is the https:// part of a URL?

A
  • The protocol being used to access a file
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13
Q

What is the www part of a URL?

A
  • Subdomain for the World Wide Web
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14
Q

What is the bbc.co.uk part of a URL?

A
  • Domain
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15
Q

What is the .html part of a URL?

A
  • The file’s extension
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16
Q

What are the different TLDs available for use?

A
  • Stands for Top Level Domain
  • .com or .net or .org
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17
Q

What is a domain name?

A
  • Identifies an organisation or individual on the Internet
  • Easy for humans to remember
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18
Q

What is a FQDN?

A
  • Stands for Fully Qualified Domain Name
  • A domain that specifies an exact resource and always includes the server’s host name (e.g. www)
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19
Q

What is an IP address?

A
  • Stands for Internet Protocol address
  • Assigned to every computer on the Internet and every device that communicates on a network
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20
Q

What is a domain name server?

A
  • Used to translate domain names into their corresponding IP addresses
  • Stores a table of domain names and their corresponding IP addresses
  • If a DNS doesn’t have a record of a domain, the request will be passed onto another DNS
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21
Q

What is an internet registry?

A
  • Organisations responsibe for the allocation of IP addresses
  • Only 5 in operation, each serving a different geographical area
  • When a new IP address is requested, a registry will looked for a previously allocated unused IP address rather than allocated a brand new IP address
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22
Q

What is a firewall?

A
  • These sit between a device and the Internet
  • Regulates the packets that pass through them
  • Either software or hardware
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23
Q

What is packet filtering?

A
  • Firewalls use this to accept or block packets based on their source IP address or the protocol in use
  • Network admins can:
    • Specify particular IP addresses or protocols
    • Use automatic filtering software that can block suspicious packets
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24
Q

What is stateful inspection?

A
  • Examines the contents of a packet before deciding to allow it through the firewall
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25
Q

What is a proxy server?

A
  • Servers that sit between a public and private network
  • Manages every packet that passes between the two
  • Firewalls can be said to act as proxy servers in this scenario
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26
Q

How do firewalls in proxy servers provide anonymity?

A
  • When a device in a private network sends a packet through a firewall and into a public network
  • The packets “sender” address is of the firewall, rather than the private IP address
  • This provides the anonymity
27
Q

What is symmetric encryption?

A
  • Both the sender and receiver share the same private key
  • This key is used to both encrypt and decrypt data sent
28
Q

What is the issue of symmetric encryption?

A
  • Before sending info, the sender and receiver participate in a key exchange
  • If this same key is exchanged over a network, it is vulnerable to interception
29
Q

What is asymmetric encryption?

A
  • Each device has a pair of mathematically related keys
  • One key is kept secret; the private key
  • The other is shared on the Internet; the public key
  • When a message is encrypted with the public key, ONLY the corresponding private key can decrypt it
  • The recipient is the only one with the private key, the sender has the public key
30
Q

What is a digital signature?

A
  • Can be used alongside asymmetric encryption to:
    • Verify the sender of the message
    • Verify any message tampering/corruption during transmission
31
Q

Describe the digital signature process in asymmetric encryption

A
  • A digest of the message is created
  • This is encrypted with the sender’s private key
  • The encrypted digest is appended to the message
  • The message and appended digest are encrypted with the recipient’s public key
  • When the message is received, the recipient:
    • Decrypts the message using their private key
    • Decrypts the digest using the sender’s public key
    • Carry out the same digest algorithm on the message
    • Check whether their result matches the now decrypted digest
32
Q

What is a digital certificate?

A
  • Verifies ownership of a key pair used in asymmetric encryption
  • Can be used to check that a fake key pair isn’t being used by an imposter
  • Issued by certificate authorities, with the files containing the owners details, public key, and the digital signature of the CA
33
Q

What is a worm?

A
  • Piece of malicious software that can self-replicate between computers
  • Either within a network or by users downloading and running malicious files
34
Q

What is a trojan?

A
  • A type of malware that is disguised as a benign file
  • Users can be tricking into opening it
  • Spread as email attachments or downloaded from malicious websites
35
Q

What is a virus?

A
  • Requires a host file in which to reside
  • Files are usually executable files
  • Can lie dormant until their host file is opened
  • Spread between computers over private networks or the Internet
36
Q

What precautions can be taken to avoid malware?

A
  • Good code quality, as malware exploits bugs in code
  • Antivirus software
  • Train employees the risks of opening suspicious files/attachments
37
Q

What is TCP/IP?

A
  • Stands for Transmission Control Protocol / Internet Protocol
  • Used in all parts of the Internet to enable communication between devices
  • Formed from four distinct layers that form the TCP/IP stack:
    • Application
    • Transport
    • Network
    • Link
38
Q

What is the role of the application layer of the TCP/IP stack?

A
  • Selects and uses the correct protocol to transmit data
  • Interacts with the user with application software
39
Q

What is the role of the transport layer of the TCP/IP stack?

A
  • Establishes a virtual path between the sender and receiver
  • Splits the transmission into packets
  • Each packet has a sequence number
  • Also contains a port number which identifies the protocol
40
Q

What is the role of the network layer of the TCP/IP stack?

A
  • Provides the correct IP addresses for each packet’s source and destination
  • Routers work within the network layer, using the IP addresses on a packet to send it to its destination
41
Q

What is the role of the link layer of the TCP/IP stack?

A
  • Controls physical connections between pieces of hardware in a network
  • Adds MAC addresses to packets that are received from the network layer
  • These identify the hardware to where a packet should be sent
  • These change with every hop through a network
42
Q

What happens when a packet has been received?

A
  • It is stripped of extra info by reversing the stack
  • The link layer removes MAC addresses
  • The network layer removes IP addresses
  • The transport layer uses the packet’s port number to determine the correct application to send the packet, but also uses the sequence number
  • The application layer receives the packets and displays the info to the user
43
Q

What two parts are IP addresses split into?

A
  • A network identifier (computers in the same network share these)
  • A host identifier
44
Q

What is a subnet?

A
  • When networks are divided into smaller networks, subnets
  • These have different network identifiers
45
Q

How is a network identifier found?

A
  • It can be determined with a subnet mask
  • To find it:
    • Convert its IP address and subnet mask into binary
    • Perform an AND on both numbers
    • Convert to decimal
46
Q

What are the two types of IP address?

A
  • Version four; IPv4
  • Version six; IPv6
47
Q

What are IPv4 addresses?

A
  • Dotted quad numbers
  • Consists of 4 parts that are separated by dots, each of which is assigned one byte
  • Over 4 billion unique addresses, but are in short supply
48
Q

Why were IPv6 addresses created?

A
  • IPv4 were in short supply, and the number of devices on the Internet that require a routable IP address is increasing rapidly
49
Q

What are IPv6 addresses?

A
  • Formed of eight blocks separated by colons, each of which contains four hex characters
50
Q

What is a routable and non-routable IP address?

A
  • Routable is a public
  • ## Non-routable is a private
51
Q

Why do most homes share the same IP address?

A
  • If every device that is connected to a network had its own IP address, there wouldn’t be enough IP addresses to go around
52
Q

What is DHCP?

A
  • Stands for Dynamic Host Configuration Protocol
  • The number of available private IPs within a private network is limited, DHCP assigns IPs to devices when they join a network, by using a pool of available IPs
  • These are allocated for the duration, once a device leaves, the IP returns to the reallocation pool
53
Q

What is NAT?

A
  • Stands for Network Address Translation
  • When a computer on a private network communicates with a device online, the device cant respond directly to the computer as the computers IP isn’t globally unique
  • NAT sends packets through the router which:
    • Makes a record of the packet
    • Replaces the private IP with its own routable IP
54
Q

What is port forwarding?

A
  • Used when a client communicates with a server that is connected to a private network
  • The client sends packets to the public IP of the router belonging to the server’s private network which contains the port number of the app on the server
  • The packets are forwarded by the private router to the server using NAT
55
Q

What are the steps for a client to connect to a database?

A
  • Client-sever request made by client to web browser
  • Web browser responds with the requested web page
  • The file contains JavaScript which loads an API, which uses REST to enable the database server to be queried by the client using HTTP
  • The database server responds by using JSON or XML
  • The clients browser processes the JSON or XML and displays the response
56
Q

What is XML?

A
  • Stands for Extensible Markup Language
57
Q

What is JSON?

A
  • Stands for JavaScript Object Notation
58
Q

Compare JSON with XML

A
  • JSON is more compact, easier to read, easier to create and faster for computers to process
  • XML is more flexible
59
Q

What is a thin-client network?

A
  • The majority of network’s processing power belongs to servers
  • These provide services and resources
60
Q

What are the advantages of thin-client networking?

A
  • Easy to add new clients
  • Clients are cheap machines
  • Software updates and security are managed from the server, allowing for greater control
61
Q

What are the disadvantages of thin-client networking?

A
  • Requires a powerful server which is expensive and requires expertise to set up and maintain
62
Q

What is a thick-client network?

A
  • The clients are powerful enough to provide their own processing power and services
  • This removes the requirement for a server, although servers can still exist
63
Q

What are the advantages of thick-client networking?

A
  • No high costs and expertise needed as there is no server to set up and maintain
  • Much quieter communication channels which reduces the likelihood of collisions compared to thin-client
64
Q

What are the disadvantages of thick-client networking?

A
  • Require more powerful clients than thin-client networks, so there is some cost in setting up
  • Harder to maintain, no facility to issue updates and manage security from a central server

A Level Computer Science (6 decks)

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