Network Topologies — Bus, Ring, Star, Mesh, Hybrid, Hub-and-Spoke

The one-sentence mental model

Topology = the shape connections make. N10-009 splits it two ways: the physical shape (where the cables run) and the logical shape (how data actually flows). They can differ — a star-cabled network with a hub in the middle behaves logically like a bus.

The six topologies you must know cold

Topology	Shape	What breaks when a link fails	Real-world use
Bus	One shared cable, all hosts tap in	The whole segment	Legacy 10BASE-2/5 coax. Effectively dead.
Ring	Each host connected to two neighbours in a loop	The ring — unless dual-ring (FDDI, SONET)	Token Ring (dead in the enterprise). SONET/SDH in carriers.
Star	Every host has its own cable to a central switch/AP	Only that one host	Every modern LAN.
Mesh (full)	Every node connects to every other node	Nothing user-visible — traffic reroutes	High-availability WAN cores.
Mesh (partial)	Some nodes fully connected, some only to a few	Depends on which link	Enterprise WANs balancing cost vs redundancy.
Hub-and-spoke	One hub site, many branch spokes	If a spoke fails, only that branch. If the hub fails, everything.	Classic MPLS WAN, Fortinet SD-WAN dial-up VPN.

Physical vs logical — the gotcha question

The Network+ exam loves this:

• Ethernet on a switch is physically a star (every cable goes to the switch) but logically a bus (originally — one shared collision domain). Modern switched Ethernet is now logical star too.
• Token Ring on a MAU is physically a star (cables to the MAU) but logically a ring (token passes host-to-host inside the MAU).

If a question says “logical topology” — it’s asking about the traffic path, not the cabling.

Data-center topologies you’ll see on N10-009

• Three-tier — Access → Distribution → Core. Classic campus. Blocking at STP.
• Collapsed-core — Distribution + Core merged. Small enterprise.
• Spine-leaf — Every leaf connects to every spine. No traditional Access/Dist/Core. Uses ECMP + VXLAN. The topology modern DCs use — no oversubscription, predictable latency.
• Point-to-multipoint (PMP) — One transmitter, many receivers. Wireless bridging.
• Point-to-point (P2P) — Just two ends. E.g., a fiber leased line between two buildings.

The exam heuristic

• “Which topology has no single point of failure?” → Full mesh (or dual ring).
• “Which topology is cheapest to cable at scale?” → Star.
• “Modern data-center fabric?” → Spine-leaf.
• “Classic branch WAN?” → Hub-and-spoke.
• “Central management, but branch-to-branch traffic goes direct?” → Partial mesh (or SD-WAN full-mesh overlay).

Common mistakes

1. Confusing full mesh cable count. For N nodes, a full mesh has N × (N − 1) / 2 links. Six nodes = 15 cables. That’s why full mesh doesn’t scale.
2. Assuming Wi-Fi is star. Wireless is logically PMP — the AP is one transmitter, all clients are receivers on the same channel.
3. Missing that spine-leaf is not the same as three-tier. Spine-leaf has no distribution layer. Every leaf is one hop from every other leaf.

Cheat strip

Physical vs logical: cabling shape vs traffic path — can differ.
Star:     modern LAN. Cheap at scale. One host fails = one host.
Full mesh: no SPOF, but N(N-1)/2 links. WAN core only.
Hub-spoke: classic branch WAN. Hub fails = everything down.
Spine-leaf: modern DC. Every leaf ↔ every spine via ECMP + VXLAN.
Three-tier: Access / Distribution / Core. Classic campus.
Ring:     dead in the LAN. Alive in carriers (SONET dual-ring).
Bus:      dead. Old coax segments.