The physical building blocks that move bits between machines, organized by the OSI layer they operate at.
| Device | OSI Layer | What it does |
|---|---|---|
| Repeater | Physical (L1) | Regenerates a weakened or corrupted signal so it can travel further over the same network, restoring its original strength/shape. |
| Hub | Physical (L1) | A multi-port repeater — receives data on one port and broadcasts it to all connected devices. All hosts share one collision domain. Comes in Active (regenerates signal) and Passive (just splits the signal) variants. |
| Bridge | Data Link (L2) | Filters traffic by reading source/destination MAC addresses, intelligently interconnecting two LAN segments instead of blindly broadcasting like a hub. Comes as transparent bridges (invisible to hosts) and source routing bridges (path chosen by the source). |
| Router | Network (L3) | Forwards packets between different networks based on IP addresses, using routing tables and path-selection algorithms. |
| Gateway | Any / multiple | A passage connecting two networks that may run on entirely different networking models/protocols — translates between them. |
| Brouter | L2/L3 hybrid | A combination device that behaves as both a bridge and a router, depending on the traffic. |