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Does using a straight through cable between two similar network devices (switch to switch, router to router, PC to PC, etc) cause any damage to the switch or the router that you are connecting? I understand that you must use a crossover cable to connect two similar network devices together.

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No, it wouldn't cause any damage.

But all modern Ethernet cards support automatic crossover (Auto-MDIX), which means you can (and in many cases, should) simply use a straight-through cable and the two adapters will automatically decide how to use each pair. This feature is present in practically all Gigabit Ethernet adapters as well as huge majority of 100 Mbps "Fast Ethernet" adapters.

(Gigabit Ethernet actually uses all pairs in both directions at the same time, so if your idea of a 'crossover cable' is to just swap 2 pairs, that no longer makes sense anyway.)

What can cause damage is connecting a cable from a proprietary "Passive PoE" adapter to a device that isn't expecting PoE.

  • Oh ok, thank you. I wasn't aware of automatic crossover. I always heard that if you are connecting like network devices, you MUST use a crossover cable. – thecomputerguru Dec 6 '19 at 17:37
  • That was true in the early days with 10 Mbps twisted-pair Ethernet, and especially in "shared medium" (hub) Ethernet where many devices almost literally share the same wires. But with "point-to-point" (switched) Ethernet taking over, manufacturers started introducing auto-crossover features in high-end switches and over time it became quite widespread even in cheap hardware. Eventually Gigabit Ethernet pretty much made it mandatory by design. – user1686 Dec 6 '19 at 18:41

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