1. 3. 3 Networks Flashcards
Characteristics of a Network
- 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)
Advantages of Networks
- 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)
Disadvantages of Networks
- 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
LANs and WANs
- 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
Protocols
- 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
The Internet Structure
- Internet is network of networks, allows communication of computers across the globe
- Continents connected with international backbone cables (usually underwater)
TCP/IP Stack and Protocol Layering
Stack of networking protocols work together passing packets during communication, consists of 4 layers, Application Layer, Transport Layer, Network Layer and Link Layer
Application Layer
- 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
Transport Layer
- 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
Network Layer
- 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
Link Layer
- 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
Recipients Computer
- 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
MAC Address Vs IP Address
- 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
DNS
- 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
DNS process
- 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
Network Communication- Data Packets
- 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
Network Communication- Circuit Switching
- 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
Network Communication- Packet Switching
- 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
Network Security and Threats
- Network security we look at Firewalls, Proxies, Encryption and Other Preventions
- Network threats we look at a variety looked at in another flashcard
Firewalls
- 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
Proxies
- 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
Encryption
- 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
Other Preventions
- Up to date security and anti-virus
- Trained staff, levels of access, strong passwords created
- Policies created that must be followed
Threats
- 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
Network Hardware
Network Hardware we look at are NIC, Modem, Switch, WAP, Routers, Hub, Gateway and Cables.
Network Interface Card (NIC)
- 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)
Modem
- 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
Switch
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.
Wireless Access Point (WAP)
Allows device to connect to network, commonly combined with router/modem or hub to enable internet access
Routers
Connect two or more networks together, allow private home networks to connect to the internet
Hub
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.
Gateway
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.
Cables
- 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
Client-server
- 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
Advantages and Disadvantages of Client-server
- 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
Peer-to-peer
- 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
Advantages and Disadvantages of Peer-to-peer
- 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)