1. 3. 3 Networks Flashcards
1
Q
Characteristics of a Network
A
- Network, two or more computers are connected together allowing them to transmit data between each other and share peripherals
- Two types, Local Area Networks (LAN) and Wide Area Network (WAN)
2
Q
Advantages of Networks
A
- Users can share files, peripherals, and connections to other networks (internet)
- Users can access files from any computer on the network
- Servers can control security, central updates and central backups
- Allows communication with other people (emailing)
3
Q
Disadvantages of Networks
A
- Increased security risks to data
- Malware and viruses spread easier on networks; one computer affected rest at risk
- If server fails, computers connected may not work
- Computers may run slower if large amounts of data is travelling across the network
4
Q
LANs and WANs
A
- LAN, small geographical area, Infrastructure/equipment owned (school or home)
- WAN, large geographical area, Infrastructure/equipment hired from third parties (offices or the internet)
- Largest WAN is the Internet, this is made up of a series of smaller networks
5
Q
Protocols
A
- Set of rules/instructions defining how two computers communicate over a network
- They are a standard; all devices have designated method of communication with each other no matter the manufacturer
- Standards are a set of hardware and software specifications that allow manufactures to produce products and services that are compatible with each other
- Devices must share same protocol in order to exchange information (Same as languages)
- HTTP (Hyper Text Transfer Protocol), used for web page rendering
- HTTPS (Hyper Text Transfer Protocol Secure), same as HTTP but encrypted
- TCP/IP (Transmission Control Protocol/Internet Protocol), networking protocol used in routing packets through networks (Used between two routers for error-free transmission)
- POP3 (Post Office Protocol) & IMAP (Internet Message Access Protocol), mailing protocols, used for email access
- FTP (File Transfer Protocol), used for transmission of files over a network
- SMTP (Simple Mail Transfer Protocol), transfers outgoing emails between servers, also from email clients to servers
6
Q
The Internet Structure
A
- Internet is network of networks, allows communication of computers across the globe
- Continents connected with international backbone cables (usually underwater)
7
Q
TCP/IP Stack and Protocol Layering
A
Stack of networking protocols work together passing packets during communication, consists of 4 layers, Application Layer, Transport Layer, Network Layer and Link Layer
8
Q
Application Layer
A
- Top of stack, specifies protocol to be used, to relate the application being sent
- For example, if app is browser, selects HTTP, POP3 or FTP
9
Q
Transport Layer
A
- Uses TCP to establish end to end communication between source and recipient computer
- This layer splits data into packets, labelled with packet number, total num of packets and port number being used for communication
- If packets get lost, this layer on recipient computer requests retransmissions of lost packets
10
Q
Network Layer
A
- Adds source and destination IP addresses (IP address + Port Number = Socket address)
- Routers operate on this layer; it uses IP address to forward the packets
- Sockets used to specify device the packets sent to, and application being used on device
11
Q
Link Layer
A
- Connection between network devices, adds MAC addresses identifying Network Interface Cards of source and destination computer
- Device on same network, destination MAC address is address of recipient computer
- Device on different network, destination MAC address is address of the router
12
Q
Recipients Computer
A
- The TCP/IP is a stack keep in mind, on recipient’s computer layers go from bottom to top
- Once destination been reached following occurs
- MAC addresses are removed by the Link Layer
- IP Addresses are removed by the Network Layer
- Port Number is removed, and packets are reassembled at the Transport layer
- Data presented to recipient in form it was requested in at the Application Layer
13
Q
MAC Address Vs IP Address
A
- MAC address unique to every physical device
- Your MAC address tells me who you are
- Used in LAN to identify a computer system
- IP address is an address used to identify a single computer or a network of computers
- Your IP address tells me where you are
- Used in WAN to identify “roughly” the location of the target computer system
14
Q
DNS
A
- Domain Name System, used to name and organise internet resources
- Hierarchy, smaller domain separate larger domain with full stop (leeds.gov.uk)
- TLD stands for Top Level Domain 2LD stands for 2nd Level Domain
- Domain names easier to remember than IP addresses
- Used to link servers across the world, domain name system server (DNS server) translates domain names into IP addresses when accessing a website
15
Q
DNS process
A
- User requests a URL via a browser (www.bbc.co.uk)
- Browser sends domain name to DNS
- DNS matches domain name to an IP address, returns this to browser
- GET request for webpage sent to web server using IP address
- Requested web page returned to client’s web browser
16
Q
Network Communication- Data Packets
A
- Packets are segments or data that are made up of a Header, Payload and Trailer
- Header which contains IP addresses, Protocol, Order of packets and TTL
- Sender and recipient IP addresses, allows packet to be delivered to correct destination as well as allowing recipient to trace where packet came from
- Protocol being used, allows recipient computer to understand how to interpret data
- Order of packets, packets reconstructed on arrival in appropriate order specified here
- Time To Live (TTL) / Hop Limit, tells packet when to expire so does not travel forever
- Payload is the raw data to be transmitted
- Trailer contains a checksum to detect if any errors occurred during transmission
17
Q
Network Communication- Circuit Switching
A
- Method of communication, direct link between two devices, maintained for duration of conversation between devices
- Data arrives in logical order, quicker reconstruction of data
- Two users hold a call without delay in speech
- Bandwidth (Max capacity data can be transmitted, 40mbps for example) wasted in periods where data not being sent
- Devices must transfer and receive data at same rate
- Electrical interference, may produce corrupt or destroy data
- Sections of network cannot be used till transmission complete
- Telephone for example
18
Q
Network Communication- Packet Switching
A
- Method of communication, packets sent across network through most efficient route (varies between packets)
- Checksum ensures data arrives intact
- Multiple routes, one breaks another used
- Packets can be transferred over large network, global communication
- Time spent constructing reconstructing packets (delay)
- Must wait for all packets to arrive before data can be received
- Sending an email for example
19
Q
Network Security and Threats
A
- Network security we look at Firewalls, Proxies, Encryption and Other Preventions
- Network threats we look at a variety looked at in another flashcard
20
Q
Firewalls
A
- Application that uses packet filters (rules) to prevent unauthorised access to a network
- Packet filtering limits access in accordance to administrator rules and policies
- When access denied, packet dropped or rejected
- Rejected packet sends alert to sender, notify them of error
- Dropped packet does not send alert to sender
21
Q
Proxies
A
- Application that acts as an intermediary, collects and send data on behalf of the user
- Privacy of user is protected, remain anonymous
- Can cache frequently visited websites, faster load times
- Can reduce overall web traffic
- Used by administrators to prevent access to sensitive or irrelevant info at school or work
22
Q
Encryption
A
- Way of keeping data secure when it is being sent across a network
- Makes data unreadable if intercepted, encrypted and decrypted with keys
- Without keys, data is useless to hackers
23
Q
Other Preventions
A
- Up to date security and anti-virus
- Trained staff, levels of access, strong passwords created
- Policies created that must be followed
24
Q
Threats
A
- Malware such as Viruses, Worms, Keyloggers, Trojan, SQL injections
- Spyware, adware
- Social engineering such as Pharming, Phishing, Baiting, Weak passwords
- Hackers, Denial of service, Data interception
25
Q
Network Hardware
A
Network Hardware we look at are NIC, Modem, Switch, WAP, Routers, Hub, Gateway and Cables.
26
Q
Network Interface Card (NIC)
A
- Required to connect device to network, usually built into device, assigns MAC address to each device
- 48-bit value coded into device, usually written as 12-digit hex number
- Allows both wired and wireless communications between computers on a LAN or a large-scale network using the Internet Protocol (IP)
27
Q
Modem
A
- Transforms digital info from computer into analogue signals (can be transmitted through wires)
- Can also do vice versa (Analogue signals to digital data that computer understands)
- Does this by modulating and demodulating electrical signals from phone lines, coaxial cables or other types of wiring
28
Q
Switch
A
Allows multiple devices to connect to a network, directs flow of data across a network, data received from sender device directly transmitted to target device. Switches typically faster than hubs.
29
Q
Wireless Access Point (WAP)
A
Allows device to connect to network, commonly combined with router/modem or hub to enable internet access
30
Q
Routers
A
Connect two or more networks together, allow private home networks to connect to the internet
31
Q
Hub
A
Allows multiple devices to connect to a network, broadcasts transmissions it receives to all devices connected, can make network susceptible to traffic, slower than switches.
32
Q
Gateway
A
Used when protocols not the same between networks, translates protocols so networks can communicate with each other, removes header from packets before adding data to packets using new protocol.
33
Q
Cables
A
- Main methods of connectivity are wired and wireless
- Choices of wired cable are twisted pair, coaxial and fibre optic
- Twisted pair cable made up of pair of insulated copper wires
- Affected by magnetic fields but more affordable than other two, low bandwidth (used for telephone networks)
- Coaxial cables, made up of solid conductor wire, layer of insulation, grounding conduction and a layer of exterior insulation, affected by magnetic field but to lesser extent than twisted pair
- Moderate bandwidth fair price, used for computer network connections, digital audio and cable television
- Fibre optic, made up of optical fibres bundled together into single cable (either glass or plastic fibres)
- Use light rays, high bandwidth, most expensive, used in long distance connections between cities and countries as well as organisations transmitting large volumes of data
34
Q
Client-server
A
- Terminals (clients) connected to a server
- Server is a powerful, central computer, stores all info and resources, better processing power than terminal
- Client makes a request to a server for data, connections and other services
35
Q
Advantages and Disadvantages of Client-server
A
- More secure, data only in one location
- Central backups and updates, no need for individual backups and updates
- Data and resources can be shared between clients (Files, Printer etc)
- Relatively expensive to set up
- Terminal’s server dependent (server is single point of failure if it fails users lose network access)
- Trained staff required to maintain the server
- Suited for organisations with large number of computers that may need access to same info
36
Q
Peer-to-peer
A
- Computers (peers) connected to each other, can share files
- Each device acts as a client and server, can request and provide resources
- Peer is equal to all other peers
- Used in piracy since it is almost impossible to trace the origins of the files
37
Q
Advantages and Disadvantages of Peer-to-peer
A
- Cheaper to setup compared to client-server
- Allows the sharing of resources, easy to maintain
- Not dependent on central server (One terminal breaks rest fine)
- Specialist staff not required
- Impossible to trace origins of files
- Backups must be done individually, poorer security
- May be difficult to locate resources (Difficult to maintain well-ordered file store)
