Communications 2 (Internet)

Question 1

What is meant by Packet Switching?

Answer 1

Data to be sent across is split into packets
Each packet is given a destination address and a sequence number
Packets are sent invidually via the fastest possible route across the network
The sequence numbers are used once the packets have been received to reassemble the packets

Question 2

What are the components of a Packet?

Answer 2

Sender’s Address
Receiver’s Address
Packet Contents
Time to Live
Sequence Number

Question 3

What is a router?

Answer 3

A device used to send packets to the recipient via the fastest possibvle route - this may be the fewest number of hops or least congested route

Question 4

What is the Time to Live for a packet?

Answer 4

When a packet is sent through a network, it passes through multiple routers to reach its destination. Every time a packet passes through a router, a hop occurs.

Each packet has a finite number of hops - the time to live indicates how many hops a packet can have.
When the Time to Live expires, the packet is deleted - the recipieint will have to get the packet to be transmitted again

Question 5

What is a gateway?

Answer 5

A device used to convert transmitted data from one protocol to another, when two networks use different protocols.
It does this by stripping the packet so it has just its contents, and then gives it a sender and receiver address which complies with the new protocol

Question 6

https://www.bbc.co.uk/news/technology/index.html

Answer 6

https:// - Protocol used to access the file
bbc.co.uk - Domain Name
/news/technology/index.html - The file path
www - The host name (World Wide Web)

Question 7

What is a fully qualified domain name?

Answer 7

A domain that specifies an exact resource and can only be interpreted in one way - it will always include the server’s host name

e.g. - https://www.bbc.co.uk/news/index.html

Question 8

What is the Domain Name Server System? (DNS)

Answer 8

Each domain name has a direct relationship with an IP address
When you enter a domain name into the search bar, a domain name server will translate is into its corresponding IP address

A DNS stores a table of domain names and their corresponding IP address - if a DNS doesn’t have a record of the domain you are using, the request is passed onto a different DNS.
Smaller websites may take muiltiple changes of server before a record can be found, hence why they are slower to access

Question 9

What is an Internet Registry?

Answer 9

An organisation responsible for the allocation of IP addresses - there are only 5 in operation.

They must protect the depleting pool of unallocated IP addresses. When a new IP address is requested, the registry will look for a previously allocated IP address that is now unused - instead of a new one.

Question 10

What is a firewall?

Answer 10

A firewall sits between a device and the internet and it regulates the packets that pass through it. It acts as a proxy server which can perform both packet filtering and stateful inspectionm

Question 11

What is a proxy server?

Answer 11

A server that sits between a public and a private network - they manage every packet that passes between the networks
When a packet is sent from a private network into a public network, the sender address is the firewall and not the private IP address

Question 12

What is packet filtering?

Answer 12

Firewalls use packet filtering to accept and block packets based on their source IP address or the protocol they use.

Question 13

What is stateful inspection?

Answer 13

Stateful Inspection examines the contents of a packet before allowing it throuugh a firewall - meaning some packets that are unrelated or suispicious are blocked

Question 14

What is symmetric encryption?

Answer 14

Both the sender and receiver share the same private key - this is used to encrypt and decrypt the data swent across the network.
Before sending any information - they need to exchange the private key, this is the flaw of symmetric information as it is vulernable to interception

Question 15

What is aysmmetric encryption?

Answer 15

When using asymmetric encryption, a digital signature can be used to verify if the sender of a message and to verify that a message hasn’t been tampered with during transmission

1) A digest of the message is created using a checksum or hashing algorithm - the value depends on the message and will change if the message is changed
2) The digest is encrypted using the sender’s private key
3) The digest is appended to the message
4) The message and digest are encrypted using the recipient’s public key - meaning only the recipient can decrypt it
5) When the recipient receives it, thety decrypt it using their private key - leaving them with a decrypted message and an encrypted digest
6) They then decrypt the digest using the sender’s public key - this verifies if it was sent by the sender
7) The recipient carries out the same hashing/checksum algorithm to see if the result matches the decrypted digest

Question 16

What are the different types of Malware?

Answer 16

A trojan - A type of malware that is designed as a benign file that users can be tricked into opening - often sent on emails
Worms - A piece of software that can replicate between computers - within a network or by running a malicious file
Viruses - Require a host file, which when opened can lead to it spreading across the computer and even into a private network

Question 17

What does the application layer do?

Answer 17

1) Selects the appropriate protocol for communication
2) Interacts with the user with application software (e.g. Web Browser)

Question 18

What does the Transport Layer do?

Answer 18

1) Establishes an end to end connection between the sender and the receiver
2) Splits the data into packets and assigns the sequence number and a port number - which can route requests to the client application layer or the server
3) Deals with the error checking of packets (checksum) on arrival and reassembles them

Question 19

What does the network layer do?

Answer 19

1) Adds the source and destination IP addresses
2) Routers work within the layer, using the IP addresses to route the packet to its correct destination

Question 20

What does the data link layer do?

Answer 20

1) Controls the physical connections between pieces of hardware on a network
2) Adds MAC Addresses to the packets it receives from the network layer - this identifies the device that has sent the packet
3)

Question 20

What does the data link layer do?

Answer 20

1) Controls the physical connections between pieces of hardware on a network
2) Adds MAC Addresses to the packets it receives from the network layer - this identifies the device that has sent the packet

Question 20

What happens at the receiving end of the TCP/IP stack?

Answer 20

The packet is stripped of its extra information by reversing the TCP/IP stack

1) Data link layer removes the MAC addresses from the packet
2) Network layer removes the IP addresses
3) Transport Layer uses the port number to determine which application to send the packet to. It also uses the packets sequence number to determine if it is in the correct position
4) The application layer receives the packet and displays it to the user

Question 20

How do you perform a subnet mask?

Answer 20

Take the IP address and convert it to binary
Take the subnet mask and perform the binary

Subnet Mask AND IP Address

Question 21

What is the difference between IPv4 and IPv6 IP Addresses?

Answer 21

IPv4 - Can allow 256^4 unique IP addresses (over 4 billion) as it is separate into 3 parts, each assigned a byte
IPV6 allows 128 bits (8 blocks, each contains 4 hexademical characters) - allowing for far more ip address combinations (10^37)

Question 22

What is the DHCP Protocol?

Answer 22

1) There are a finite number of private IP addresses within a private network. Assigning each device on a network its own IP address would lead to IP addresses being wasted - as they could leave and never join again
2) Instead, DHCP assigns IP addresses as soon as they join a network. It uses a pool of available IP addresses to allocate IP addresses to new devices for the duration of their session.
3) Once a device leaves the network, the IP address is returned to the pool for allocation to a new device

Question 23

What is Network Address Translation?

Answer 23

This occurs when a network with private IP addresses want to access the internet - which requires a public IP address
1) The router contains two IP addresses - one public and one private
2) When a private IP address wants to communicate with the internet, it sends packets through the router - which makes a record of the packet before replacing the private IP address with its own public one.
3) When a response is received it is sent to the router’s public IP address - which forwards it to the correct private IP address using the record it made when sending the packet.

Question 24

What is Port Forwarding?

Answer 24

When a client using a public IP address wants to connect to a private network.
1) Client sends packets to the address of the router belonging to the server’s private network
2) Packets sent by the client contain the port number of the application the client wants to access
3) The private network’s router forwards the packets to the server using NAT

Question 25

What is a Thin-Client Network?

Answer 25

The majority of the processing power belongs to the servers which provide services

Question 26

What is a Thick Client Network?

Answer 26

The clients are powerful enough to provide their own processing power and storage - this eliminates the need for a server

Question 27

Compare Thin and Thick Client Networks

Answer 27

1) Thin Clients have greater centralised control as the server controls security
2) Thick Clients require powerful clients, which are expensive to setup - but lacks the need for an expensive server. Whereas thin lacks the need for expensive clients
3) Thick Client Networks have a smaller volume of traffic - meaning there is less likely to be data collisions and corruptions - making them faster and more reliable