Topic 9.4 TCP/IP

Question 1

Describe the role of the Application Layer

Answer 1

Selects the correct protocol to transmit the data.
Interacts with user using application software like a web browser

Question 2

Describe the role of the Transport Layer

Answer 2

Establishes end to end connection between the sender and recipient

Splits the transmission into packets

Each packet will have a sequence number which identifies the position of the packet in relation to the others.

The port number is also contained in these packets which identifies the protocol being used.

Question 3

Describe the role of the Network Layer

Answer 3

Provides correct IP addresses for each packets source and destination

Routers work within the network layer, using the IP addresses to send to its destination

Question 4

Describe the role of the Link Layer

Answer 4

Controls the physical connections between hardware in a network.

Receives MAC Addresses from network layer and adds them to the packets.

Question 5

What is the role of MAC Addresses

Answer 5

They are assigned to every device that can connect to a network or internet and are unique.

They identify the hardware to which a packet should be sent.

They change everytime packets hop from one router to another.

Question 6

What is the role of Sockets in the TCP/IP stack

Answer 6

A socket address is where the IP address is combined with the port number. E.G. :
114.26.20.199:443

This identifies which of the applications on the recipient device the packets should be sent to

Question 7

What is a well-known port

Answer 7

A port number that is assigned to a specific protocol or service like HTTPS or SSH

They are used by servers and are easily recognisable

Question 8

What is a client port used for

Answer 8

A temporary port used by the client that specifies which application is going to send and receive data across a network.

Question 9

Differences between well-known ports and client ports

Answer 9

Client ports are temporary
Well known ports are fixed

Client ports are randomly assigned

Well known ports are for servers to understand what service is being used
Client ports are for clients to start temporary connections

Question 10

What are the 2 parts of an IP Address

Answer 10

A network identifier
A host identifier

Each computer in a network has the same network identifier but a different host identifier

Question 11

What is a subnet

Answer 11

When a network divides, these are called subnets
Each subnet has a different network identifier.

Question 12

What and How does a Subnet Mask work

Answer 12

A subnet mask determines the network part of an IP address

1) Convert IP Address of device to binary
2) Convert IP Address of subnet mask to binary
3) AND the binary numbers together
4) Convert back to IP Address (denary)
4) The result is the network identifier

Question 13

What are the two standards of IP Address

Answer 13

IPv4
IPv6

Question 14

Why was IPv6 introduced

Answer 14

IPv4 has 2^32 unique addresses
Number of devidces rapidly increasing so IPv^ introduced
IPv6 uses 8 blocks of 4 hex characters which have 2^128

Question 15

What is a routable (public) IP Address

Answer 15

Globally unique as these are public IP addresses.
Each home or business only has a small number of routable (public) IP Addresses.
Global Authorities issue routable IP addresses to ensure they are not repeated

Question 16

What is a non-routable (private) IP address

Answer 16

A Private IP Address.
If every device had a routable IP Address, there would not be enough IP addresses.
Only works withing a private network like a school or office.
Cannot be used across the public internet.

Question 17

What is the purpose of the Dynamic Host Configuration Protocol (DHCP)

Answer 17

The number of Private IP Addresses in a private network is limited
Assigning each device a private IP Address is not sensible since a device may leave and not join back
SO DHCP prevents these IP addresses being wasted

Question 18

How does Dynamic Host Configuration Protocol work

Answer 18

DHCP is used to assign IP addresses to devices as they join a network.
There is a pool of available IP addresses.
DHCP assigns the device an available IP address
DHCP returns the IP address to the pool after device leaves.
Ensures no IP address are wasted

Question 19

How does Network Address Translation (NAT) work

Answer 19

1) Private device sends packets to the router
2) Routers makes a record of the packet
3) Router replaces the private IP Address with its own IP address
4) Router forwards response to the corresponding private device using the record it made previously

Question 20

Why is Network Address Translation Used

Answer 20

When a device on a private network needs to communicate to a device across the internet, NAT gets around this problem.

Question 21

Why is Port Forwarding used

Answer 21

Used when a device needs to communicate with a server that is connected to a private network.

Question 22

How does Port Forwarding work

Answer 22

1) The device sends packets to the public IP address of the router that belongs to the server’s private network

2) These packets contain the port number of the application the device wishes to access

3) The private network’s router forwards the packets to the server using NAT