Computer Networks and the Internet
What this domain tests
The domain covers network types, topologies, transmission media, networking devices, protocols and IPv4 addressing. Expect classification questions, device comparisons and a small addressing calculation.
Core rules
- By span: PAN, LAN, MAN, WAN; the Internet is a network of networks.
- Topologies: bus (one backbone, cheap, collisions), star (central switch, one point of failure), ring (token passing), mesh (redundant, costly).
- Media: twisted pair, coaxial cable, optical fibre (high bandwidth, immune to electromagnetic interference); unguided media are radio, microwave and satellite.
- Devices: hub broadcasts to all ports, switch forwards by MAC address, router forwards packets between networks by IP address, repeater regenerates signals, gateway connects dissimilar systems, modem converts digital and analog signals, NIC attaches a host.
- TCP is connection-oriented and reliable; UDP is connectionless and faster. Common ports: 80 HTTP, 443 HTTPS, 21 FTP, 25 SMTP, 110 POP3, 53 DNS.
- IPv4 is 32-bit dotted decimal. Class A starts 1-126, B 128-191, C 192-223, D multicast.
Worked example
Take 192.168.10.5. The first octet 192 lies in 192-223, so it is Class C with default mask 255.255.255.0. The first three octets identify the network, 192.168.10.0; the host part is the last octet, so the broadcast address is 192.168.10.255 and usable host addresses run from .1 to .254, that is 254 hosts.
Traps that cost marks
- Saying a hub forwards only to the destination port; it broadcasts.
- Confusing MAC (physical, hardware) with IP (logical) addressing.
- Choosing UDP where guaranteed delivery is required.
- Saying DNS sends mail; it resolves names to IP addresses.
- Counting all 256 addresses in a Class C host range as usable.