Computer Networking and Internet Basics
What this domain covers
Expect questions on network sizes and topologies, cabling and connectors, IP addressing basics, network devices, protocols, and simple command-line checks such as ping and ipconfig.
Core rules
- PAN, then LAN, then MAN, then WAN; the Internet is the largest WAN.
- Star topology is standard in labs: one failed cable affects only one node, but a failed central switch takes the segment down.
- UTP with RJ-45 connectors, Cat5e or Cat6, 100 m maximum run; fibre for long distance and EMI-prone routes.
- A hub broadcasts to all ports, a switch forwards by MAC address, and a router forwards between networks by IP address.
- Private ranges: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16. APIPA 169.254.x.x means no DHCP server was reached.
- Ports to remember: HTTP 80, HTTPS 443, FTP 20/21, SMTP 25, POP3 110, IMAP 143.
Worked example
A workstation shows IP 169.254.18.7 and cannot browse, while its neighbour works. Reasoning: 169.254.x.x is self-assigned, so the machine never got a DHCP lease. Check the link light and cable, confirm DHCP is enabled, then check whether the DHCP service or router is running. A static IP in the correct subnet is a valid temporary fix.
Traps
- Confusing MAC (48-bit hardware address) with IP (logical address).
- Saying ping measures speed; it tests reachability and round-trip time.
- Mixing up switch and router roles.
- Forgetting the subnet mask and default gateway when setting a static IP.