Networks
What the domain tests
Networks tests layered models, addressing and subnetting, protocol behaviour, switching/routing, and wireless/cloud basics. Expect TCP/IP vs OSI, IPv4 subnet calculations, port numbers, DNS/DHCP/HTTP, and choosing TCP or UDP.
Core rules
- OSI layers: physical, data link, network, transport, session, presentation, application. TCP/IP collapses to link, internet, transport, application.
- IPv4 address = network + host bits, set by the prefix/mask. Subnet size = 2^(host bits); usable hosts = that minus 2 (network and broadcast).
- TCP is connection-oriented, reliable, ordered, with flow/congestion control; UDP is connectionless and lower overhead.
- Switches forward by MAC address within a LAN; routers forward by IP address between networks. Default gateway is the router for off-subnet traffic.
- DNS resolves names to IP addresses; DHCP assigns addresses; ARP resolves IPv4 to MAC on a local link.
Worked example
For 192.168.10.0/26, find network, broadcast, usable range and host count. /26 means 32−26 = 6 host bits. Block size = 2^6 = 64. The network is 192.168.10.0; broadcast is 192.168.10.63; usable range is 192.168.10.1–192.168.10.62; usable hosts = 64−2 = 62. Reasoning: the mask 255.255.255.192 fixes the top two bits of the last octet, so addresses step in blocks of 64.
Traps
Do not count the network or broadcast address as usable. Do not confuse /26 with /24. MAC addresses stay local; IP addresses are routed. TCP does not guarantee latency. DNS does not assign addresses. A hub floods; a switch learns MAC addresses. Private addresses (10/8, 172.16/12, 192.168/16) are not globally routable without NAT.