Computer Networks and Security Basics
Tested: network types and topologies, the device that does what, transmission media, and the vocabulary of threats and safeguards.
Types and topologies
PAN (a few metres, Bluetooth), LAN (a room or building), MAN (a city), WAN (countries; the Internet is the largest). Topologies: bus (single backbone, cheap, one break kills the network), star (central switch, easy fault isolation, central failure is fatal), ring (token passing, one direction), mesh (every node linked, most reliable, most cabling). Client-server centralises control; peer-to-peer shares directly between machines.
Devices
Hub repeats signals to every port with no intelligence (Layer 1). Switch forwards frames by MAC address to the correct port (Layer 2). Router joins different networks and chooses paths by IP address (Layer 3). Modem converts digital to analogue and back for the line. Gateway connects dissimilar protocols. NIC is the interface inside each machine. Media: twisted pair (UTP/STP, RJ-45), coaxial, optical fibre (highest bandwidth, immune to electromagnetic interference), radio/Wi-Fi.
Security vocabulary
Malware: virus (needs a host file), worm (self-replicating across networks), Trojan (disguised as useful), ransomware (encrypts data and demands payment), spyware and keyloggers. Attacks: phishing, pharming, social engineering. Safeguards: firewall (filters traffic but does not remove viruses), updated antivirus, strong unique passwords with 2FA, encryption, offline backups, digital signatures for authenticity.
Worked example
Two labs on different floors must share one broadband line but keep their internal traffic separate. Reasoning: a router connects the LAN to the ISP and joins the two lab subnets; each lab gets its own switch for its nodes. A hub would broadcast every frame to every port and waste bandwidth, and it cannot separate the two subnets.
Traps
- Claiming a firewall removes viruses, or that antivirus replaces a firewall.
- Describing a worm as needing a host file.
- Mixing up switch (MAC, Layer 2) and router (IP, Layer 3).
- Calling a copy on the same hard disk a backup.