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I need to verify something. If you have a Gig-E network, and you connect a 100Mbp device to this network, and the network is completely switched, the network still functions at Gig-E for all Gig-E devices, and 100Mbp for the 100Mbp device, correct?

What I am trying to ask is, a 100Mbp device, plugged into a switched Gig-E network will not drop every other device down to 100Mbps, right?

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up vote 2 down vote accepted

Yes, that is correct. Each port works independently. This is what switched networks were invented for.

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Ok, just making sure I am not losing my mind. – user978122 Jul 30 '13 at 16:25

Correct. Each port should independently decide on its own speed.

Usually this is the highest supported speed by both sides, but this can be lower if:

  • One side does not support gbit speeds (then the port falls back to 10 or 100)
  • Or if the [managed] switch has configured that port for lower speeds. (Usually SoHO devices are plain dumb switches, not managed switches where you can log in on the switch and change the port settings).
  • Or when the other side is configured for a lower speed (e.g. a NIC on a attached computer could be set to a lower speed)
  • Or when the cable if not good enough to support Gbit speeds. (gbit Ethernet uses all 8 wires, 10 and 100 mbit only used 4 wires, so there are cables which will work fine with 100 mbit networks but not at Gbit speeds).

So, before you loose your mind, check all four scenarios. :-)

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aside from using 8 vs. 4 conductors in some Cat5 wiring, the number of twists on each pair is greater in Cat 5e or 6 vs. Cat 5 this reduces crosstalk and allows for gigabit speeds. Over a short enough distance, Cat 5 might be able to support gigabit with good equipment on either end, but to be certain you should make sure it is 5e or 6. My house is wiried with mostly cat5 as i did it back in 1999, and it works ok for Gigabit, but at work anywhere we see cat5 (not 5e) we rip it out. 99% of the time when our workstations are having network issues, it is the wire. – Rod MacPherson Aug 6 '13 at 17:14

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