Topic 9.4 TCP/IP Flashcards
Describe the role of the Application Layer
Selects the correct protocol to transmit the data.
Interacts with user using application software like a web browser
Describe the role of the Transport Layer
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.
Describe the role of the Network Layer
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
Describe the role of the Link Layer
Controls the physical connections between hardware in a network.
Receives MAC Addresses from network layer and adds them to the packets.
What is the role of MAC Addresses
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.
What is the role of Sockets in the TCP/IP stack
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
What is a well-known port
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
What is a client port used for
A temporary port used by the client that specifies which application is going to send and receive data across a network.
Differences between well-known ports and client ports
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
What are the 2 parts of an IP Address
A network identifier
A host identifier
Each computer in a network has the same network identifier but a different host identifier
What is a subnet
When a network divides, these are called subnets
Each subnet has a different network identifier.
What and How does a Subnet Mask work
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
What are the two standards of IP Address
IPv4
IPv6
Why was IPv6 introduced
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
What is a routable (public) IP Address
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
What is a non-routable (private) IP address
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.
What is the purpose of the Dynamic Host Configuration Protocol (DHCP)
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
How does Dynamic Host Configuration Protocol work
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
How does Network Address Translation (NAT) work
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
Why is Network Address Translation Used
When a device on a private network needs to communicate to a device across the internet, NAT gets around this problem.
Why is Port Forwarding used
Used when a device needs to communicate with a server that is connected to a private network.
How does Port Forwarding work
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
