I am currently designing a network, and there are 2 fibers between 2 switches. Can I use a 40Gbit QSFP+ module to achieve this speed or is 10Gbit SFP the best possible without adding more fibers?

  • 4
    You can run up to 100G on one single OS2 singlemode fiber.
    – user36472
    Dec 11, 2018 at 12:33
  • You should make this an answer, @Cown, so it can be accepted and the answer can be closed.
    – Teun Vink
    Dec 11, 2018 at 16:01
  • @TeunVink thanks, i can see Zac67 made a good answer. :-)
    – user36472
    Dec 11, 2018 at 18:21

1 Answer 1


QSFP+ is just the transceiver interface. Medium compatibility and reach is defined by the PHY used by the fitted transceiver.

While the short-range 40GBASE-SR4 PHY requires four separate multi-mode fibers per direction (OM3 or OM4), 40GBASE-LR4 (CWDM) or -FR (single-lane) use only one fiber per direction - both require single-mode fiber, however. Both will work on short MMF runs as well - unspecified though.

Beyond the official IEEE 802.3 PHYs there's a range of other types available - many from third-party vendors.

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