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 and routing of packets across a network.
- Split into layers - division of network functionality (abstraction)
- Is a stack - pops back up on recipient computer.
Advantages :
- Protocols belong to different layers - smaller and simpler to change.
- Layers are self-contained - can be removed, changed and tested individually.
- Layers can be developed independently and by specialized programmers
- Layers hide data from other layers and grouped together - abstraction by generalisation
- Complex networking tasks divided into smaller simpler manageable tasks that have defined role
- Improved troubleshooting - see which layer error is in
- Each layer deals with different hardware
TCP/IP Stack Layers
Application Layer : Specifies protocols needed relating to application.
- Encodes / decodes message.
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 retransmission sent if any packets lost.
Internet Layer : IP routes packets across network.
- Source and destination IP addresses added to packets.
- 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.
- Adds MAC address to identify NIC of source and destination computers.
- Destination MAC address will be router or recipient computer if devices on same network.
LAN’s and WAN’s
LAN : Local area network that spans a small geographical area.
- often using own hardware
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 TDL (top domain level) name server which checks cache and returns answer or passes on to the authoritative name server
- IP address returned back up to the requesting client
- 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
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 Servers
- Server does processing and holds data (Provides network functionality) - central point
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)
