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Computer Science Paper 2 > The internet > Flashcards

The internet Flashcards

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1
Q

What is the internet

A

A network of networks that are Inter-Connected networks

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2
Q

how are devices on the internet uniquely identified

A

an ip address

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2
Q

Describe IPV4

A

IP version 4, addresses are made up of four octet values ( numerical values described by 8 bits) separated by a full stop

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3
Q

What is A FQDN

A

A fully qualified domain name can be broken down into constituent parts including a host name, and the domain name itself.

www.example.com

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4
Q

what is bbc.co.uk

A

the domain name

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5
Q

what does URL stand for

A

Uniform resource locator

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5
Q

what does www. do

A

specifies the host

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6
Q

what would be the FQDN for the bbc

A

www.bbc.co.uk

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7
Q

what is the url made up of

A

the protocol and the domain name of the resource together form the URL.

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8
Q

what does DNS servers mean

A

Domain Name System- servers are dedicated computers with an index of domain names and their corresponding ip addresses.

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9
Q

Describe the process of resolving an ip address (7 steps)

A

1st URL request by browser from a user
2nd Browser extracts the FQDN and sends it to a dns server
3rd Local dns server maps the FQDN to ip address and returns it to browser
4. If local DNS doesnt have the request is moved to the Regional DNS. (has a much larger look up table)
5. Unlikely event Regional DNS doesnt have it it mvoed to NSP (network service provider)
6. Ip is sent to browser and GET request is sent to web server.
7. File is returned to web browser

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10
Q

what is the purpose of the dns system

A

domain name system resolves names to ip addresses

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11
Q

Why do websites have both domain names and ip addresses

A

hard to remember ip
IP address required for computer to access the site.

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12
Q

Describe the process of packet switching (6 steps)

A

Messages are split into packets
Each packet is given a destination and source address
Packets are given a sequence number
Each packet in independently dispatched to the Internet through a router gateway
Routers forward packets to other nodes on the network until they reach destination
Packets reassembled at the destination

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13
Q

What is a router

A

Connects two networks together
Determines which node to send a packet to next

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14
Q

Describe the process of Routing (3)

A

Routers forward data packets from one network to another
Each router stores data about the available routes to the destination node
Routers are organised in a hierarchy

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15
Q

What does the header of a packet contain (4)

A

the destination’s (recipient’s) address so that it can be directed appropriately across the network

the source (sender’s) address

the packet (sequence) number and number of packets

the Time To Live (TTL) or hop limit is also included

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16
Q

What are the 3 parts of the data packet

A

Trailer payload header

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17
Q

What does the payload contain

A

At its core, a data packet is a segment of data that needs to be sent, often referred to as the payload
This part of the packet will often vary in size from 500 to
1,500 bytes

Payload refers to the actual data being sent in the packet

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18
Q

What does the Trailer/Footer contain

A

A packet trailer / footer contains error checking components that verify the data received in the payload has not been corrupted on transfer
Techniques such as checksums are used to check the data by the receiving host
The same checksum is recalculated at the destination
If they do not match, the data has become corrupted and is refused and a new copy is requested to be sent again

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19
Q

What is a gateway when is it required (2)

A

A gateway is required where data is travelling from one network to another that use different protocols

Networks using different transmission media can require this

A router and gateway can often be combined into one integrated device

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20
Q

Describe how a gateway operates

A

Header data are removed and reapplied using the correct format of the new network

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21
Q

Describe what is meant by the Time To Live data in a data packet.

A

a maximum number of hops a packet can take to reach its destination

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22
Q

why are packets a certain size

A

small enough to ensure individual packets do not take excessive time to transfer

However, they should not be too small as the additional data added makes data transfer inefficient as unnecessary headers and trailers would be required each time

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23
Q

Example gateways

A

Examples include connecting a LAN to the Internet, or connecting different types of internal networks

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24
Q

describe what happens to the data packet at a gateway

A

header is removed and reapplied using the correct format of the new newtork.

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25
Q

What is the point of the application layer of the TCP/IP Layer (2)

A

Used to provide services for applications that want to communicate across a network, often the internet

Uses high level protocols that set an agreed standard between the communicating end points.

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26
Q

How is the transport layer of the TCP/IP Model used

A

Uses the transmission control protocol to establish an end to end connection with the recipient computer,

splits data into packets and numbers then sequentially

adds the ports number to be used based on HTTP protocol

At the receiving end this layer confirms that packets have been received and requests any missing packets be resent.

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27
Q

How is the network layer of the tcp/ip layer used

A

Uses the internet protocol (IP) to address packets with the source and destination IP addresses

Adds source IP destination IP addressses to packets

Performs routing, selects the next host to transmit a packet to

Creates checksum for the packet.

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28
Q

How is the link layer of the TCP/IP used

A

The link layer operates across a physical connection

Adds the mac address of the physical NIC that packets
should be sent to based on the destination IP address

MAC addresses change with each hop

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29
Q

Describe the process of receiving data

A

At the destination, the message is passed back up through the layers

THe link layer removes the MAC addressfrom each packet and passes it to the network layer

The network layer removes the ip address from each packet and passes it to the internet

The transport layer removes the port number from each packet, reassembles the packets in correct order and passes them to the application layer.

The application layer presents the image data for the user in a browser.

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30
Q

Describe how a port number is used

A

A port is used to alert a specific application to deal with data sent to a computer

These are used by protocols to specify what data is being sent

The combination of an IP address and a port number, separated by acolon is known as a socket.

31
Q

What are the two types of port numbers

A

Well known port numbers - A reserved port number that has a specific purpose assigned by the Internet Assigned Numbers Authority (IANA)

Client port numbers - Temporary port numbers are assigned by the transport layer to the network application on the client computer.

32
Q

What is Secure Shell

A

An encrypted protocol that allows secure communication between nodes across a network.

33
Q

What protocols are used for sending an receiving emails

A

SMTP
POP3
IMAP

34
Q

Explain SMTP

A

Used to send emails and forward them between mail servers to their destination

35
Q

Explain POP3

A

Downloads emails stored on a remote server to a local client(removed after download)

36
Q

Explain IMAP

A

Manages emails on a server so multiple clients can access the same email account in synchronicity

37
Q

What is a firewall

A

A firewall is either software or hardware that controls access to and from a network

38
Q

How does a firewall operate

A

A firewall is either software or hardware that controls access to and from a network
Data packets from specific IP addresses can be filtered
Data packets also have ports which can be used to only allow traffic through from certain port numbers.

39
Q

Describe packet filtering

A

Packets of data are inspected by the firewall to check their source IP address and which port they are attempting to access
Different network protocols use different port numbers for example, HTTP traffic, used to transfer web page data, uses port 80 or 8080
If this traffic is to be allowed through, the port must be opened for the duration of the connection, otherwise the firewall will automatically reject it

40
Q

What is a proxy server

A

A proxy server makes a web request on behalf of your own computer, hiding the true request IP addresses from the recipient

41
Q

What are the functions of a proxy server

A

Enables anonymous surfing

Can be used to filter undesirable online content

Logs user data with their requests

Provides a cache of previously visited sites to speed up access

42
Q

four different ways that a firewall can protect computers on a LAN

A

Block/allow traffic on specific ports

Block/allow traffic from specific IP addresses

Block/allow certain types of packet

Firewall maintains information about current connections and only allows packets relevant to these connections through

43
Q

Definition of encryption

A

The act of encoding a plaintext message so that it cannot be deciphered unless you have a numerical key to decrypt it.

44
Q

What is meant by symmetric encryption

A

Symmetric encryption uses the same key to encrypt and decrypt the data being transferred

45
Q

What is asymmetric encryption

A

Uses two separate, but related keys

46
Q

Describe the steps of asymettric encryption

A

recipients public key is made available
The recipient’s public key is then used to encrypt the data before sending
The encrypted message is sent
The recipient’s private key is used to decrypt the message

47
Q

What are worms

A

A worm is a standalone program that does not require a user to run it in order for it to spread.

They exploit vulnerabilities in the destination system and spread automatically.

48
Q

What is trojan horse

A

Trojans are malicious are pieces of software that masquerade as something seemingly innocuous or useful

They cannot self replicate

Often they server to open up back doors in your computer to the internet so that the processing power, internet bandwidth and data can be exploited remotely.

49
Q

How can we reduce threats from malware,

A

improve code quality
Monitoring attempts, protection
Guarding against buffer overflow attack
Use of strong passwords for login credentials.
2FA

50
Q

What is buffer overflow

A

Buffer overflow occurs when a program accidentally writes data to a location too small to handle it.

51
Q

What is sql injection

A

A malicious user can enter SQL commands via online database forms to change the processing.

52
Q

What is a ip address

A

a unique numerical address which identifies a host computer of network.

53
Q

Describe IPv4 makeup

A

Uses four octets each octect made up of a byte.

54
Q

what is the last address in a network used for

A

is reserved as the broadcast address on that network for sending data simultaneously to all host on that network

55
Q

What is a host

A

any computer on a network that can use the internet

56
Q

What is 127.x.y.z

A

is reserved for loopback in which a hosts ip software treats an outgoing packet as incoming

57
Q

what are the address range of IP’s that are private addresses for LANS or private WANS

A

10.x.y.z, 172.16.0.1 to 172.31.255.255 and 192.168.y.z

58
Q

How many devices does IPv4 provide for

A

2^32 4.3 billion addresses

59
Q

What are the two parts that make up IP’s

A

Network identifier

Host identifier

60
Q

Describe the host identifier

A

Right hand bits of 32 bit number used to identify seperate nodes on the network

61
Q

Describe the network identifier

A

left hand bits of 32 bits number used to define the network where the nodes are communicating.

62
Q

What is classless ip addressing

A

The use of a suffix such as /24 enables IP addresses to be used with varying proportions of network ID and host ID

63
Q

what is a subnet mask

A

a number that identifies the network and host portions of an IP address

64
Q

How is a subnet mask

A

The subnet mask is used together with an IP address.

The subnet mask has all network id bits set to 1 and all host ID bits set to - so that, when compared to the IP address using a bitwise and operation, the network is identified.

65
Q

How do computers with private ips address receive and send data on the internet

A

They must communicate via another network device that provides a network address translation, this allows a single public ip address

66
Q

describe the operation of the NAT

A

This allows a single public IP address e.g. 12.65.42.1 to be shared by any number of hosts with private IP addresses
This system is normally part of the router.
It keeps track of which private host is making requests on the internet
It then makes sure that when it receives the response from the internet, it sends it back to the private host that made the request.

The translation device records the source and destination socket addresses for each request
It then communicates on the host’s behalf with the destination IP address
When a response returns, it is passed back to the host that made the original request

67
Q

What is port forwarding

A

Routers can be programmed so that requests with a particular port number can be automatically forwarded on to a device with a specific IP address within the network

68
Q

Describe port forwarding

A

Servers accessible to the public can be given a non-routable
IP address within a private network
A public request reaches the external router of the private network using a given port
The data packets are forwarded internally to the correct device
This also provides additional filtering

69
Q

What is the DHCP

A

Dynamic host configuration protocol is used to automatially allocate ip addressses and other network configuration information

70
Q

What does the DHCP allow

A

Allows limited pools of dynamic ip addresses to be shared out between hosts and freed up when not needed

allows hosts to reconfigure themseleves when moving between networks and reduces the number of ip addressses required locally as not all hosts.

71
Q

What are the 4 steps involved in the DHCP

A

DHCPDISCOER - request ip
DHCPOFFER -
DHCP REQUEST - Broadcast confirm ip request
DHCPACK - acknowledgment and assignment

72
Q

What is the purpose of the DHCP

A

To automate the configuration of hosts connecting to a (TCP/IP) network
To allocate IP addresses to hosts

73
Q

What are internet registers

A

These are five global organisations governed by the internet corporation for assigned names and numbers.

74
Q

How is the domain name hierarchy ordered by

A

Generic Top level domains, Country TLD’s, 2nd Level Domains, 3rd level domains

75
Q

What are the functions of a router

A

Uses the most efficient path to the destination
Monitors the network and updates its routing table to reflect congestion/network changes
Modifies the MAC addresses for the next hop (not actually contained in the packet)

76
Q

how are client ports and well known ports used when retrieving a web page

A

client port allocated to web browser by transport layer

Web servers use well known ports so that client is able to contact it to initiate.

77
Q
A

Computer Science Paper 2 (7 decks)

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