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Topologies & Architecture
How nodes are wired together, and how enterprise/data-center networks are layered.
// three-tier campus
CORE
Core-1Core-2
DISTRIBUTION
Dist-1Dist-2
ACCESS
Acc-1Acc-2Acc-3
Access = endpoints & PoE · Distribution = routing & policy · Core = high-speed switching. Redundant links between layers.
// physical topologies
| Star | All nodes to a central switch — the common LAN |
| Mesh | Nodes interconnected — resilient (full or partial), costly |
| Bus | Single shared backbone — legacy |
| Ring | Each node to two neighbours — token / SONET |
| Hybrid | A mix of the above |
// architectures
| Three-tier | Core → Distribution → Access (campus) |
| Collapsed core | Core + distribution merged (smaller sites) |
| Spine-leaf | Every leaf to every spine — low-latency DC fabric |
// topology trade-offs
| Topology | Fault tolerance | Cabling cost | Typical use |
|---|
| Star | Low — hub is SPOF | Low | Standard LAN |
| Full mesh | High — many paths | Very high (n(n-1)/2 links) | Core / WAN backbone |
| Partial mesh | Medium-high | Medium | Distribution / hybrid WAN |
| Ring | Medium (dual-ring) | Medium | Metro / SONET |
| Bus | Low — one break kills it | Very low | Legacy only |
// facts
- Access layer = endpoints & PoE · Distribution = policy/routing · Core = fast switching
- North-south = client↔server out; East-west = server↔server inside
- Spine-leaf optimises east-west traffic in data centers