Network fundamentals
Network components
Clients (user devices), servers (provide resources), hubs (legacy, repeat everything), switches (smarter hubs, better security and bandwidth use), WAPs (radio bridge to the wired LAN), routers (connect networks, forward on IP), firewalls (traffic barrier), load balancers, proxy servers (intermediary for security and privacy), IDS (detects) vs IPS (detects and blocks), SDN controllers, NAS (file-level storage), SAN (block-level storage network), media (copper, fiber), and WAN links.
Resource models
Client/server uses a dedicated central server: centralized admin, easier backup, scalable. It costs more and needs specialized hardware and skills. The standard for business networks.
Peer-to-peer shares directly between peers: cheap, no infrastructure, but decentralized management and poor scalability. Fine for tiny setups only.
Network geography
- PAN: about 10 feet. Bluetooth, USB.
- LAN: about 100 m. Office, school, home (802.3 Ethernet, 802.11 Wi-Fi).
- CAN: several miles. Campus, business park, military base.
- MAN: up to about 25 miles. City departments.
- WAN: states to global. The internet, leased lines, VPNs.
Wired topologies
Physical topology is the actual cabling layout; logical topology is how data flows.
- Point-to-point: a direct link. Simple, not scalable (WAN links to remote offices).
- Ring: a circular unidirectional path. No collisions, but a single point of failure without redundancy (FDDI).
- Bus: one shared cable. Easy install, cable failure kills everything, collisions grow with device count. Legacy.
- Star: everything into a central switch; central point failure takes the network down. The standard for homes.
- Hub-and-spoke: a star variant where spokes transit a hub (airlines, telecom); cheaper at scale.
- Mesh: point-to-point everywhere. Full mesh links = n(n-1)/2. Partial mesh interconnects only some nodes. Redundant but complex and costly.
Wireless topologies
Infrastructure mode centralizes on a WAP, like a wireless star, and supports security controls. The standard at home.
Ad hoc is peer-to-peer with no AP; devices join and leave dynamically.
Wireless mesh mixes Bluetooth, Wi-Fi, microwave, cellular, and satellite for redundant coverage: satellite for long haul, microwave for medium, Wi-Fi for short. Used in disaster response and humanitarian missions.
Datacenter topologies
The three-tier hierarchy: core (high-performance backbone routers), distribution/aggregation (policy, ACLs, Layer 3 switches routing between subnets and VLANs), and access/edge (switches to endpoints). The layered design helps performance, management, scalability, redundancy, and fault isolation.
A collapsed core merges core and distribution into one layer, fine for small and medium datacenters.
Spine and leaf: leaf switches aggregate server traffic, and spine switches full-mesh the leaves. Lower latency, pairs well with SDN, and can hang off the core of a three-tier design.
Traffic flows: north-south enters and leaves the datacenter; east-west moves between servers inside it (dominant with SDN and virtualization).