9.3 The Internet Flashcards
what is The internet?
A network of interconnected computer networks which uses an end-to-end communication protocol.
How is the internet connected?
It is mostly a wired network with cables that pass under oceans to connect the different continents.
What is an internet service provider (ISP)
A company that provides its customers with access to the internet.
What are national internet service companies and what do they do?
The largest internet service providers and provide internet access to smaller regional and local ISPs, from whom homes and businesses can buy access to the internet.
What is a packet in terms of the internet?
A container in which data is transmitted over networks. They’re labelled with addresses for the sender and the recipient and contain information intended for the recipient.
What is a packet switched network?
A network which data is sent in packets. One message is frequently split into multiple packets, each of which is sent to its recipient via the best possible route before being reassembled with packets by its recipient.
How does sending a packet through a network work?
The packet will usually have to pass through a number of routers before reaching its destination. A router uses the recipient address on a packet to determine where to send the packet. Every time that a packet passes through a router, a hop is said to occur.
Explain what a packets time to live (TTL is)?
Each packet can only pass through a finite number of hops. A packet’s time to live is a number that indicates how many hops the packet can partake in and is reduced by one with each hop. When a packet’s TTL expires the is said to be dropped meaning that the packet is deleted. The recipient will notice a missing packet and request that the sender transmits the missing packet again.
What are the primary components of a packet?
Sender’s address, receiver’s address, packet contents, time to live (TTL), sequence number
Explain the purpose of a packet’s sender’s address?
Identifies where the packet was sent from, and therefore where the response should be sent to.
Explain the purpose of a packet’s receiver’s address?
Identifies the packet’s intended recipient, allowing it to be routed to the correct device.
Explain the purpose of a packet’s contents?
Where the packet holds the data that is being transferred
Explain the purpose of a packet’s time to live (TTL)?
Holds the number of hops a packet can go through before being dropped.
Explain the purpose of a packet’s sequence number?
Contains the number of packets in a message and identifies a packet’s position in relation to others. This allows packets to be reassembled in the correct order and allows missing packets to be identified
What are the two types of network device?
Routers and gateways
What do routers and gateways do together?
They connect different networks, allowing packets to reach their destination.
Explain what a router does?
Send packets to their recipient via the fastest possible route. This could be the route that involves the lowest amount of hops or the route that is least congested at the time. They hold tables with information relating to the fastest routes to certain devices which they frequently update to enable maximum performance.
Explain what a gateway does?
As two networks could use different protocols, packets must be modified so they conform to both protocols. Therefore gateways strip away most of the packet’s details, leaving just the packet’s contents. The gateway will then give packets new sender and receiver addresses which comply to the new protocol.
What is a uniform resource locator (URL)?
An address assigned to files on the internet. Different protocols can be used in URL’s to access different types of files in different ways.
In the URL (https://ww.bbc.co.uk/news/technology/index.html) explain the purpose of “https://”?
It is the protocol being used to access the file. HTTPS stands for hypertext transfer protocol secure.
In the URL (https://ww.bbc.co.uk/news/technology/index.html) explain the purpose of “www”?
It is the subdomain for world wide web. It will usually point to the web server hosted at the following domain.
In the URL (https://ww.bbc.co.uk/news/technology/index.html) explain the purpose of “bbc.co.uk”?
It is the domain. BBC is the name of the organisation, .uk is a top level domain (TLD) and .co is a second level domain (2LD)
In the URL (https://ww.bbc.co.uk/news/technology/index.html) explain the purpose of “/news”?
It is the directory of the file being requested.
In the URL (https://ww.bbc.co.uk/news/technology/index.html) explain the purpose of “/technology”?
It is the subdirectory of the file being requested.
In the URL (https://ww.bbc.co.uk/news/technology/index.html) explain the purpose of “/index”?
It is the name of the file being requested.
In the URL (https://ww.bbc.co.uk/news/technology/index.html) explain the purpose of “.html”?
It is the file’s extension. Hypertext markup language (HTML) is frequently used for creating web pages.
What is the purpose of a domain name?
Identifies an organisation or individual on the internet. They use alphanumeric characters which make them easy for humans to remember.
what is a fully qualified domain name (FQDN)?
A domain that specifies an exact resource and can be interpreted in only one way. An FQDN will always include the servers host name. For example “www”.
What uses an internet protocol (IP) address?
Every computer on the internet and every device that communicates on a network.
Explain the purpose of domain names?
As IP addresses are not easy for humans to read, domain names are used. They map to IP addresses, meaning they are a human-friendly representation of an IP address.
Explain the relationship between a domain name and an IP address?
They have a direct relationship with an IP address. When you enter a domain name into your browser’s address bar a domain name server is used to translate the domain name into its corresponding IP address.
Explain the functionality a domain name server (DNS) does?
Stores a table of domain names and their corresponding IP address. If a domain name server does not have a record of the domain that you are trying to access, your request will be passed to another domain name server.
Explain why smaller websites are harder to access than larger websites?
As small websites and rarely visited websites will require numerous changes of servers before a record can be found making them slower to access than larger, more frequently used websites.
What is an internet registry?
An organisation responsible for the allocation of IP addresses. There are only 5 internet registries in operation, each serving different geographical area.
What is the role of an internet registry?
To protect the world’s depleting pool of unallocated IP addresses. When a new IP address is requested an Internet registry will first look for a previously allocated IP address that has become unused rather than allocate a brand new IP address straight away.
What does a firewall do?
Sits between a device and the internet and regulates the packets that pass through it. Firewalls can be software or hardware and work as a proxy server which can perform both packet filtering and stateful inspection.
How does packet filtering work and what does it do?
Firewalls use packet filtering to accept and block packets based on their source IP address or the protocol that they are using (determined by port number). A network’s administrator can specify particular IP addresses or protocols to block or use automatic filtering software that can block suspicious packets.
What is stateful inspection and how does it work?
Stateful inspection actually examine the content of a packet before deciding whether to allow it through the firewall. Some firewalls keep a record of current in a network, allowing them time to filter out packets that aren’t related to activity on the network.
What is a proxy server and what do they do?
A server that sits between a public network and a private network. They manage every packet that passes between the two networks. Firewalls can be said to act as proxy servers when they control the movement of packets between public and private networks.
How do firewalls provide anonymity?
When a device in a private network sends a packet through a firewall and into a public network, the packet’s “sender” address is that of the firewall, rather than the devices private IP address. Providing anonymity as the devices on the private network as their private address is never sent beyond the firewall.
What is symmetric encryption?
Both the sender and receiver share the same private key. This is used to both encrypt and decrypt data sent between the 2 parties.
How does symmetric encryption work?
Before sending any information the sender and receiver must participate in a key exchange to ensure that they both have a copy of their shared key.
What is the disadvantage of symmetric encryption.
If the key exchanged over a network, it is vulnerable to interception.
What is asymmetric encryption?
Four different keys are used. Each device has a pair of mathematically related keys, one of which is kept secret (the private key) and the other shared on the internet (the public key).
How does asymmetric encryption work?
When a message is encrypted with a public key, only the corresponding private key can decrypt it and vice-versa. Before a message is sent, it is encrypted by the send using the recipients public key. This means that the message can only be decrypted by the corresponding private key, the recipient’s private key, which only the recipient has access to. This means that the recipient is the only person who can decrypt the message.
what are digital signatures and when are they used?
When using asymmetric encryption, it can be used to verify the sender of a message and to verify that a message has not been tampered with during transmission.
What are the 4 stages of digital signature encryption?
1) A digest of the message is created, by a hashing or checksum algorithm or else. The value of the digest depends on the content of the message and will not be the same if the message is changed.
2) This digest is encrypted with the sender’s private key (which anyone can decrypt using the sender’s public key)
3) The encrypted digest is appended to the message
4) The message and appended digest are encrypted with the recipient’s public key, meaning that the recipient can decrypt the information.
How does digital signature decryption work?
When the recipient receives the message, they first decrypt it using their private key; leaving them with the decrypted message and the encrypted digest. As the digest was encrypted using the sender’s private key it can be decrypted using the sender’s public key. This verifies that the message was really sent by the sender as only they have access to their private key. The recipient then carries out the same hashing or checksum algorithm on the message and checks whether their result matches the now decrypted digest. If everything matches, the recipient can be certain that the message was sent by the sender and hasn’t been tampered with or corrupted during transmission.
What is a digital certificate and how does it work?
It verifies ownership of a key pair used in asymmetric encryption and can be used to check that a fake key pair isn’t being used by an imposter.
What do digital certificates contain?
They contain: a serial number, the owner’s name, an expiry date, the owner’s public key and the certificate authority’s digital signature.
What links worms, trojans and viruses?
They are all types of malware that can infect computers.
What are worms in computing?
Pieces of malicious software that can self-replicate between computers, either within a network or by users downloading and running a malicious file.
What are Trojans in computing?
A type of malware that is disguised as a benign file that users can be tricked into opening. These are often spread as email attachments or downloaded from malicious websites.
What are viruses in computing?
A type of malware that requires a host file to reside. These files are typically executable files, meaning that viruses can lie dormant in a computer until their host file is opened or run. Viruses can spread between computers over a private network, the internet or the use of physical media.
What are some ways to prevent malware?
Good code quality, antivirus software, up-to-date software, employee training.
Why can good code quality prevent malware?
Malware often exploit bugs in code that enable them to take hold of a computer system.
How can installing antivirus software prevent malware?
They are specialist pieces of software that scan files on a computer and remove any suspicious files.
How can training employees prevent malware?
They can be trained about the risks of opening suspicious email attachment or other methods in order to reduce the risks posed by malware.
