Networks Flashcards
Network
Set of interconnected devices that exchange data and resources with each other
Internet
The largest public network (WAN), a network of interconnected networks. Contains a backbone, and a set of dedicated connections that connect large networks at various points in the world. Each point is connected to another regional network controlled by ISP’s.
WiFi
Wireless networking tech providing high speed internet and network connection. A family of wireless network protocols.
Station
Consists of NIC and computer
Wireless Access Point
Point where devices connect to a wireless network. Requires connection to a router.
Network switch
Connects devices on a LAN, receives and sends packets.
IP Address
A unique identifier for every device on the internet. Made up of 4 or 6 octet values.
URL
Used to specify the means of accessing a resource across a network and its location. Consists of protocol and domain name
Web search procedure
DNS server maps domain to an IP address.
If it cannot resolve, it passes the request to the root DNS.
DNS server sends the IP address to the requested web browser.
DNS servers
Domain Name system; dedicated computers with an index of domain names and their IP addresses.
When computers query a DNS server to domain, it returns an IP address for the computer to send a message to it.
Topology
Arrangement of devices that make up a network
Bus topology
Devices connected by a single cable(backbone).
Devices can be easily added, good for small networks.
Unidirectional,only one computer can transmit at a time,main cable is point of failure, performance lowers with heavy use due to collisions, poor security.
Star Topology
Contains central hub which acts as connection point for devices. Computers connected to central node. Switch communicates to specific computer intended.
Good performance, easy to isolate problems, more secure
Expensive to set up, central device is point of failure.
Physical vs logical topology
Physical: Defines how devices are physically connected
Logical: Defines how devices communicate across physical topology
5 internet global registries
Allocate IP addresses to specific domain names, which must be unique.
Protocols
Set of rules that define how data is transmitted across a network (i.e TCP/IP stack)
Must be standard across all devices for communication to work
TCP/IP stack
Transmission control protocol/internet protocol consists of 4 layers:
Application
Transport
Internet
Link
Application layer
Provides services for applications that want to communicate across a network. Uses high level protocols like SMTP, FTP,HTTP that set an agreed standard between end points.
Presents image data for user at destination
Transport layer
Uses the TCP to establish end to end connection with receiver. Splits data into packets, numbers them sequentially, adds port number to be used based on HTTP. At receiving end, confirms if packets have been received, requests for missing packets to be resent.
Internet layer
Uses the IP to address packet with source and destination IP address. Router forwards each packet to an endpoint, defined by combination of IP addresses and port numbers. Router uses routing table to instruct next hop
Link Layer
Operates across a physical connection. Adds MAC address of physical NIC that packets should be sent to.
FTP, SMTP, IMAP,POP3
FTP - used to transfer files
SMTP - send and receive emails
IMAP- manages emails
POP3- downloads emails
Firewalls
Hardware/software that controls access to and from a network. Ports are opened to allow specific traffic (packets) to pass
Packet filtering
Packets inspected by a firewall to see which port they are trying to access, if allowed through, port opened for duration of communication, otherwise firewall rejects.
Proxy servers
Make a web request on behalf of users device, hiding true request’s IP address from receiver.
Enables anonymous surfing, can be used to filter undesirable online content, logs user data with their requests. Provides a cache of previously visited sites to speed access.
Phishing
Using fake emails to manipulate victims into visiting a fake website to give away personal information.
Measures:
2fa,strong passwords, use of access rights, guard against SQL injection and buffer overflow, improving code quality.
Malware
Malicious software, annoys users and damages their data.
Examples: trojans, viruses, worms
Virus
Infects other programs ans data by self replicating. Need a user to spread
Worms
Do not need a user to spread
Trojans
Pretends to be harmless application. Cannot self replicate.
Gateways
Alternative to routers.
Required when data is travelling from one network to another that use different protocols.
Required by networks using different transmission media.
Header data removed and reapplied using correct format of new network.
Can combine with router to create one integrated device.
Routers
Forward data packets from one network to another
Shares data about available routes to destination
Looks up destination IP address in routing table to find best router to forward packets to,
Each transfer between routers=hop.
Data packets
A segment of data that needs to be sent (size ~ 500-1500 bytes)
Kept small to ensure individual packets do not take time to transfer preventing other packets from moving.
Should not be too small as additional data makes transfer inefficient.
Data packet format
Header- holds sender and receivers ip address, time to live/hop limit
Payload - holds data and protocol used as well as packet number
Trailer - Contains a checksum/CRC to detect transmission error. (done by obtaining a hash total calculated by adding number of 1’s in transmission)
Packet switching
Packets sent across separate routes, determined by least congested route. Easily reassemble when reaching receiver. Packets that do not make it are resent.
Circuit switching
Creates direct link between devices for duration of communication, even when data is not transmitted (a waste of bandwidth)
Very device specific as two devices need to transmit and receive at the same time.
Data segments are sent in order of arrival so simplification of restructuring packets at the receiving end.
Switches connecting and disconnecting circuits causes electrical interference, producing corrupt data.
