1.3.3 Networks Flashcards
Network Characteristics
Network : Two or more computers with the ability to transmit data between each other.
Logical Topology : Layout In which data flows around network.
Physical Topology : Physical layout of wires and components that form network.
Protocols
Protocol : Set of rules defining how computers communicate across network
- Ensure successful transfer of data between devices
- So all devices have designated communication method and interpret data in same way.
- Used to standardize transmission of data (may specify format/ error checking etc)
- Allow for communication of data as all computers follow same rules so interpret data in the same way.
Examples of Protocols
FTP(File transfer protocol) - used for transmission of files across network
HTTP (hypertext transfer protocol) - used for web page rendering
HTTPS (hypertext transfer protocol secure) - encrypted version
TCP/IP (Transmission control protocol/ Internet protocol) - Used in routing packets through networks and packaging data into packets
POP3 (Post office protocol) - Downloads email from server and deletes it
IMAP (internet message access protocol) - Stores email on server and syncs across multiple devices – for accessing emails
SMTP – (simple mail transfer protocol) - for sending emails
Standards
Standards : Formalised protocol - set of rules needed for data communication
De Facto - Accepted as best standard for purpose - proven track record
De Jure - Approved by formal authority - assessed critically
TCP/IP Stack and Advantages
TCP/IP Stack : Transmission control protocol / Internet protocol - stack of protocols that work together to ensure error free transmission / communication and routing of packets across the Internet.
- Split into layers - division of network functionality (abstraction)
- Is a stack - pops back up on recipient computer.
Advantages :
- Complex networking tasks divided into smaller simpler manageable tasks that have defined role (Modularity)
- Layers are self-contained - can be removed, updated and tested individually.
- Layers can be developed independently and by specialized programmers
- Protocols belong to different layers - smaller and simpler to change.
- Improved troubleshooting - see which layer error is in
- Layers hide data from other layers and grouped together
- Each layer deals with different hardware
TCP/IP Stack Layers
Application Layer : Specifies protocols needed relating to application. e.g. HTTPS for web based application
- Encodes / decodes message.
- Passes data onto Transport layer to send (Can be said for all layers)
- Gets data from transport layer when Recieving (can be said for all layers)
Transport Layer : TCP establishes end to end connection between source and recipient.
- Data split up into packets (Label with numbers and port number used in header)
- Adds error checking value (checksum) to packets.
- Packets reassembled and re-transmission sent if any packets lost.
Internet Layer : IP routes packets across network.
- Source and destination IP addresses added to packet header.
- Routers use IP to forward packets between routers until find specific network, port number and IP specifies device being sent to.
Link Layer : Connection between network devices - receives data from internet layer and prepares them for transmission over the physical network.
- Adds MAC address to packets to identify NIC of source and destination computers.
- Receives data from Internet layer to send
- Passes data back up to Internet layer when Receiving
LAN’s and WAN’s
LAN : Local area network that spans a small geographical area.
- often using own hardware owned by owner of network
WAN : Wide area network that spans a large geographical area.
- Usually requires extra, expensive telecommunications hardware.
DNS
Domain Name System : System to organise internet recourses.
- Domain names easier to remember than IP addresses.
- DNS server converts domain names/ URL’s to IP addresses - has database of URL’s and corresponding IP’s.
- Consists of many Domain Name Servers.
- If address cannot be found search reaches out to other DNS servers.
Process :
- Request sent to DNS server from browser
- DNS Resolver server checks cache – if no URL it passes it into TLD (top level domain) name server which checks cache and returns answer or passes on to the authoritative name server (gives IP for authoritative name server)
- IP address returned back up to the requesting client from authoritative name server if found
- IP used to retrieve web pages from web server
- Or error if no resolution can be found
IP and MAC addresses
IP address : Identifies the device globally
- 4 bytes / 0-255 numbers
- Logical identifier (Can change)
MAC address : Identifies device on local network - Physical address
- 12 Hex Digits
- Doesn’t change
Packet switching
Packet Switching : Data sent as packets across network through most efficient route (IP and packet number added to packet header)
- Paths may vary so arrive in different order (reorder at destination).
- No physical path - hardware can deal with multiple connections of network.
Advantages :
- More secure - If data intercepted not all packets will be intercepted
- Multiple routes can be taken if one breaks
- No Bandwidth reserved
- Packets can be sent across large networks
- Only need to resend individual packets if transmission error
Disadvantages :
- Time deconstructing packets
- Must wait for all packets to arrive before get data
Circuit Switching
Circuit Switching : Direct link created between two devices (Physical path)
- Direct link maintained throughout, dedicated hardware needed
Advantages :
- Data arrives in logical order - quick reconstruction
- No delay in speech in conversation
Disadvantages:
- Reserves and wastes bandwidth when no data sent
- Devices must transfer and receive data at same rate
- Ties up sections of the network
- decreased security
Network Threats
DDOS (Distributed Denial of Service attack) : Repeatedly sends requests sent to system to overload and slow servers.
- Uses botnet of infected computers.
- Firewall to prevent.
Virus : Can Replicate itself and spread by attaching to infected files.
- Can change or corrupt system when opening file - destroy files.
- Antivirus to prevent.
SQL Injection : Malicious SQL query entered into input to gain unauthorised access to website database.
- Clean inputs of SQL commands to prevent.
Brute Force attack : Attempt every possible combination of password to break and gain access.
- Firewall to prevent
Social Engineering : Using humans as vulnerability to gain unauthorised access to computer system.
- Training to prevent
Network Security : Firewalls
Firewall : Software that monitors packets leaving / entering network.
- Validates packets against administrator rules.
Advantages :
- Prevents unauthorised access to a network (Hackers)
- Restrict Applications and Websites that waste time / inappropriate
- Protect Company data / Intellectual property
Network Security : Proxies
Proxies : Server that manages all packets sent and retrieved by network.
- Intermediatory - collects and sends data for user
- Hides IP address for network
Advantages:
- Privacy protected (user anonymous)
- More secure from hackers (Don’t have IP)
- Prevent access to sensitive or irrelevant information
- Caches frequently used data - reduces web traffic
Client - Server Network
Client - Server Network : Consists of Clients connected to central Servers
- Server does processing and holds data (Provides network functionality) - central point
- Server provides resources and files to connected client devices
Advantages :
- Centralised Security - more secure
- Centralised Updates / installations
- Central Backups
- Clients can share files and recourses
- Can control access levels and monitor activity
Disadvantages :
- Expensive to setup
- Specialist staff needed to maintain server
- Central point of failure
- Harder to add device (Install and setup software and OS policies)
