PROFINET supports several physical topologies: star (via switches), line (daisy-chain through ports integrated in the devices) and ring (with MRP for redundancy), and they may be combined within the same network.

PROFINET is topology-flexible: a star uses switches at the centre with devices on branches (the classical IT pattern); a line uses devices equipped with two or more Ethernet ports daisy-chained together, saving cable and switches; a ring is a closed line combined with MRP (Media Redundancy Protocol), which fails over in under 200 ms after a cable break; and mixed topologies are common, with a star backbone and machine-segment lines branching out. Industrial "managed" switches and devices support all of these modes.

Even on a line topology, always check the maximum number of devices in series quoted by the vendor: each forwarded hop adds latency and the cumulative figure can break your Update Time budget.