Fundamentals
The core concepts every IT professional must know.
Key Concepts
OSI Model
7 layers: Physical → Data Link → Network → Transport → Session → Presentation → Application.
TCP/IP Model
4 layers: Network Access → Internet → Transport → Application. The practical model the internet uses.
Subnetting
CIDR notation, subnet masks, IP addressing. The hardest topic for beginners — but essential.
Routing & Switching
Switches forward within networks. Routers forward between networks. VLANs, STP, OSPF, BGP.
Common Protocols
HTTP(80), HTTPS(443), DNS(53), DHCP(67/68), SSH(22), FTP(21), SMTP(25) — know the ports.
Network Security Basics
Firewalls, ACLs, VLAN segmentation, port security, 802.1X — security starts at the network layer.