Networking and Communications
Domain scope
Networking and communications covers models, media, addressing, protocols and devices. STPM 958 frequently examines OSI and TCP/IP layers, IP addressing and subnetting, LAN and WAN technologies, and basic troubleshooting.
Core rules
- OSI seven layers: Physical, Data Link, Network, Transport, Session, Presentation and Application. TCP/IP collapses these into Network Access, Internet, Transport and Application.
- An IPv4 address is 32 bits; a /n prefix leaves 32−n host bits. Usable hosts per subnet = 2^(host bits) − 2, subtracting network and broadcast addresses.
- A router forwards between networks using IP addresses; a switch forwards within a LAN using MAC addresses.
- TCP is connection-oriented and reliable; UDP is connectionless and lower overhead.
Worked example
Subnet 192.168.10.0/26. Find the subnet mask, number of subnets and usable hosts per subnet. Reasoning: /26 means 26 network bits and 6 host bits. The mask is 255.255.255.192, because 128 + 64 = 192 in the last octet. Hosts per subnet = 2^6 − 2 = 62. The 192.168.10.0/24 space is divided into 2^2 = 4 subnets of /26: .0, .64, .128 and .192. The first subnet's usable range is .1 to .62; .63 is broadcast.
Traps
- Using 2^n instead of 2^n − 2 for usable hosts.
- Assigning a network or broadcast address to a host.
- Placing switches at the Network layer; basic switches are Layer 2.
- Saying UDP is unreliable because it is broken; it is deliberately best-effort.