13a The Internet Flashcards
What is the internet?
A wide area network connecting smaller networks around the globe together using established protocols.
What is an intranet?
A private network within an organization. Operating using World Wide Web technology.
E.g. the school timetable login
What is an extranet?
Extranets are intranets that can be partially accessed by external organizations allowing closely related businesses access.
What is a URL?
Uniform Resource Locators are strings of characters that refer to the location of an internet source.
How is the domain name (URL) below split up?
http://www.bbc.org.uk/index.html
http - protocol used to transfer information
www - third level/sub domain indicates the type of server being connected to
bbc - second level domain/domain name
org.uk - top level domain indicates country registered to and company type
index.html - page/path
What is an IP address?
When joining a network the device is assigned an IP address not being used in that network. When it leaves, that IP becomes available again.
What are the two different forms of IP?
IPv4 - 4 8 bit digits e.g. 234.57.255.123
IPv6 - 6 8 bit digits
Why is IPv6 needed?
We ran out of combination of IPv4 so an extra 16 bits were added allowing for a possible 2^48 different combinations.
What is a DNS?
A domain name server holds a database of URLs and the corresponding IP.
If the DNS cannot map a domain name what happens?
The domain name is sent to other nearby servers until it is mapped to an IP.
Why aren’t DNS’ always required?
The address may be stored locally if regularly accessed.
If the IP is entered directly.
If the URL refers to a resource stored locally.
What port is used for websites?
Port 80
What is a port?
Ports allow the device to tell which application should handle the data being received. Each port has a unique number to identify it. They are the points at which data is transferred
What do port scanners check?
If the port is open
If the port is filtered
This is done by sending a request to the port and seeing its response
What is SSH?
Secure shell protocol allows remote access to computers
How can hackers abuse port scanning?
Use it check if there are open ports and send malicious data to those ports.
What is a non routable ip?
A private IP that is only used for communicating in a LAN and isn’t used for internet access
How does network address translation work?
All devices in a LAN are connected to a router. When the device tries to access the internet the router replaces its private IP with its own public IP.
What are the advantages of Network address Translation?
Devices don’t all need a unique IP to join the internet.
More secure as the private IPs are not broadcasted.
What is an API?
Allows two software applications to communicate.
E.g. google maps API is integrated into apps such as just eat
What is a socket?
Sockets are the combination of an ip address and a port number.
The socket represents the destination for data.
What is a web socket?
Web sockets are a higher protocol built on top of sockets that are specifically used for real time communication.
They use http/s
What are subnets?
Segmented pieces of larger networks
What are the benefits of web sockets?
Fast
Always open
Real time
What are the types of web socket?
Simplex - one way
Half duplex - both ways
Full duplex - both ways at the same time
What is subnetting?
A network is divided into segments
What is subnet masking?
The process of dividing an ip into two parts. One for identifying the network and one for the host/device.
How does subnet masking work?
A subnet mask is a 32 bit number similar to an ip. When anded with the ip the subnet mask returns the network id.
Give the subnet mask for an ip which has a network number 24 bits large
255.255.255.0
When anded with the subnet IP the ones will return whatever is in the ip but the 0 will return nothing.
What is DHCP
Dynamic host configuration protocol allows IP addresses to be reused by allocating devices on a network dynamic IPs that other devices can use when that device leaves.
What is a gateway?
A gateway connects two different networks together like a router.
It can also connect networks using two different protocols.
What is a router?
Receives packets on a network and forwards them to the correct destination based on the address.
How does packet switching work?
Method for sending data by dividing it into packets.
1. Messages are split into packets
2. Each packet is assigned a destination and sequence number
3. Packets are sent independently through a router
4. Routers forward packets until they reach the destination
5. Packets reassembled in order
How are packets declared lost and what happens to lost packets?
Each packet is assigned a hop count which decrements each time it transferred between routers. If the hop count reaches 0 the packet is declared lost and is resent by the source.
Name two advantages of packet switching
- More secure
- Less stress on cables
What are 3 disadvantages of packet switching?
- Easy to lose packets in high traffic times
- Not good for real time applications as it is slow
- If the file is small it isn’t worth splitting into packets
What do internet registries do?
They are company’s that control the assigning of domains and IPs in certain regions.
Why are internet registries needed?
To ensure each device on the internet has a unique IP address.
