1.3.3 Flashcards
What is a protocol?
A set of rules to govern communication across a network.
What are some examples of protocols?
TCP
IP
POP
SMTP
IMAP
FTP
What are the benefits of protocols?
Allow networks to communicate by ensuring all devices follow the same rules
This means devices interpret data in the same way
Define and give examples of a standard.
An agreed way of doing things like USB, HTML, MP3
What is the benefit of standards?
Standards make it easier for people to build programs and software that work on different systems in different countries.
What is a DNS, and what is its purpose?
Domain Name System (DNS)
Used to convert a given URL to a corresponding IP address.
What is the process used by a DNS?
URL (www.google.co.uk) is entered and sent to the DNS resolver
DNS servers map this domain to an IP address, by looking up in a lookup table/cache.
If the DNS server cannot find it, it passes the request (recursively) to the top-level domain name server.
If the IP address is found it updates the DNS servers that did not know it.
If it is not found then it will return an error
The original DNS Server sends the IP address to the browser so it can retrieve the website from the server on which it is hosted.
What is an IP address?
Uniquely identifies a device on a network.
An IP address is a logical identifier. (e.g. 192.168.0.1)
State the four layers of the TCP/IP Stack.
Application
Transport
Internet
Link
Describe the application layer and give an example of a protocol used at this layer.
Sits at the top of the stack.
If a browser is used, then it will use HTTP protocols
Describe the transport layer and give an example of a protocol used at this layer.
Uses the Transmission Control Protocol (TCP) to establish an end-to-end connection
Splits the data into packets
Adds the packet number, total, and port.
Describe the internet layer and give an example of a protocol used at this layer.
Routers operate on this layer
Adds the IP address to the packet (to/from)
Describe the link layer of the TCP/IP stack.
Source and destination MAC addresses added.
What are the benefits of protocol layering?
Allows different layers to be worked on independently.
Allows layers to be upgraded without affecting others.
Allows for layers from different providers to be used interchangeably.
What is a LAN?
LAN – Local Area Network
A group of devices connected over a small geographical area.
The equipment is owned by the network owner.
The range could include a building or campus.
What is a WAN?
WAN – Wide Area Network
A group of devices connected over a large geographical area
Often uses third-party communication channels.
Range could include the entire world
Define circuit switching and its associated pros and cons.
Creates a direct link between two devices for the duration of the communication. The public telephone system is an example.
- The connection is set up for the entire duration of the message so
bandwidth is wasted during the periods when no data is being sent. - The two devices must transmit and receive data at the same rate
+ Data packets arrive in the same order that they are sent, simplifying the process of reconstructing the message at the recipient end.
Define packet switching.
Data is split into equal-sized packets.
Each packet has a header of information (including the destination address and the place of the packet in the complete message)
Each packet is placed on the network, each may travel by a different route, meaning they may arrive at different times.
At each node on the network, the destination address is read, and the best route is found.
Packets need to be reordered at the destination.
What are the three benefits of packet switching?
Transmission is safer from interception because it is impossible to intercept all the packets as they use different routes.
Very efficient use of the network as it does not tie up a part of the network.
If there is an error then only a small, identifiable, part of the data is affected, and this can be retransmitted easily.
What is unauthorised access?
Access to a computer system by users who are not authorised to have access.
This could include users with correct usernames and passwords who are not who they say they are.
What is a firewall?
A hardware device or piece of software
Monitors traffic going to and from a network.
Why would a company use a firewall?
Prevent unauthorised access to a network.
To restrict applications that are used internally that have internet access.
To restrict websites that can be accessed from within the company.
To protect the company’s data.
What are the three main purposes of a proxy server?
To Intercept all packets entering and leaving a network, hiding the true network addresses of the source (enables privacy and anonymous surfing)
Can maintain a cache of websites commonly visited, saving resources and multiple requests
Often used to filter requests providing administrative control over content that users can demand.
What is a hacker, and what might they do?
A person who gains unauthorized access to systems or networks in order to commit crimes.
A hacker may, for example, steal information to hurt people via identity theft, damage or bring down systems and, often, hold those systems, hostage, to collect a ransom.
What is a network?
A collection of two or more computers connected in order to exchange information and share resources.
Why might someone use a network?
File and Data Sharing
Resource Sharing (Printers etc..)
Data Protection and Redundancy
Ease of Administration
Distributing Computing Power
Internal Communications
What is phishing?
The fraudulent practice of sending emails claiming to be from trustworthy companies in order to induce individuals to reveal personal information, such as passwords and credit card numbers.
What is a DDoS attack?
Distributed Denial of Service Attack (DDoS)
Any type of attack where the attackers attempt to prevent legitimate users from accessing the service.
In a DoS attack, the attacker usually sends excessive messages asking the network or server to authenticate requests that have invalid return addresses.
This attack can make use of a botnet.
What is a botnet?
A collection of devices injected with a malicious piece of code.
What is SQL injection? Why would it be used?
When malicious SQL statements are added to the end of legitimate code.
This could be done using fields on a form.
This could be used to delete, or extract data.
What is pharming?
The fraudulent practice of directing Internet users to a bogus website that mimics the appearance of a legitimate one, in order to obtain personal information such as passwords, account numbers, etc…
What is a virus, and how can it be protected against?
Code that can self-replicate
Relies on other host files to be opened to spread themselves.
Can be protected against using an up-to-date virus scanner
What is spyware, and how can it be protected against?
Software that enables a 3rd party to obtain covert information about another’s computer activities by transmitting data covertly from their hard drive.
Could be in the form of a key logger
Can be protected against by using an up-to-date anti-spyware program.
What is the purpose of a modem?
Converts between the digital data of a computer and the analogue signal of a telephone line.
What is the purpose of an Ethernet cable?
Required to connect the components to a wired network
What is a router?
A device that passes data between multiple computer networks via either wired or wireless connections.
What is a server? What forms can it take?
A device which provides a central point of control on a network. Comes in many forms including a file server, email server, and application server.
What is a NIC?
Network Interface Card
Allows a computer to connect to a network. May be used for both wired and wireless connections.
What is a Wireless Access Point?
Connects devices wirelessly
Devices connected to the WAP all use the same frequency and are constantly tuned in, listening for signals. Uses an SSID (service set identifier) which is the identifier (the name) for the wireless network.
What is a switch? Why is it said to be more efficient than a hub?
Connects devices on a LAN using packet switching to receive, process, and forward data to the destination device.
Switches are ‘intelligent’ and will inspect packet headers and send packets to the correct port or the specific computer device.
What is a hub and why is it inefficient?
Hubs are inefficient as they do not inspect packets and just broadcast the information to each connected device and then the device decides if it is meant for it.
What is a client-server network?
Client computers connect to and are controlled by a central server
The server provides access to a resource/service (depending on the user)
What are the pros and cons of client-server networks?
+ Centrally administered in one location, including pushing out S/W updates and security patches.
+ One location to back up (file server)
+ Shared resources such as printers are not tied to a single computer
- Has a central point of failure (server)
- Can be expensive to maintain/set up (e.g. cabling costs, specialist staff.)
What are the pros and cons of peer-to-peer networks?
+ Has no central point of failure
+ Cheap to set up and run.
- Multiple locations to back up
- Devices have to maintain their own security.
- Shared resources are lost when the connected computer is offline
What is a peer-to-peer (P2P) network?
A network with no central server where all devices have equal status.
