What I'm looking for is a solution to connect workstations with RJ-45 Ethernet NICs with a workstation with SFP/SFP+ NIC.

I found that many switches have both RJ-45 and SFP/SFP+ ports available, however, normally the SFP/SFP+ ports are uplinks used for switch-to-switch connection. From the definition of "uplink" (from http://www.linfo.org/uplink_port.html and https://stackoverflow.com/questions/954396/why-do-some-switches-have-uplink-ports), it seems that the only difference between a uplink port and normal "downlink" port is whether the TX/RX is crossed-over or not. So for RJ-45 based uplinks, if proper twist-cables are provided, I take that a uplink can be used to connect to a workstation (rather than another switch) just like other "downlink" ports.

Now here is my question, when the uplinks are SFP/SFP+ ports, do I need to use special "twisted" (probably not physically...) fiber cable to connect to a workstation with SFP/SFP+ NIC? Or, if direct attach cable (copper one) is used, do I need to cross-over the transmit and receive pair(s)?

1 Answer 1


Dedicate uplink ports are an anarchism from when MDI/MDI-X was not detected and account for by the switch software. In some cases you had a physical switch you needed to flip on the switch to turn it on or off.

That said, I don't think i've seen a switch that didn't have auto MDI/MDI-X capabilities (or it was controllable in software ) in about 8 years. You should be able to connect you workstation to an "Uplink" port and it'll work just fine. You may have to make software configuration adjustments in the switch config, you documentation should tell you if you need to and how to do it.

  • +1... pretty much anything with a GigE or 10GE PHY is going to Auto MDIX if the PHY vendor had a clue Nov 8, 2011 at 9:41
  • Thanks, Zypher and Mike. This pretty much cleared my doubt.
    – imxiaozhu
    Nov 8, 2011 at 14:43

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