Noob 10G question.

I have a juniper ex4500 10G switch and Qlogic 3242 10G card. I use twinax cables for servers within the rack and they work just fine. But, now we added a new office which has 2 more servers and is about 100ft away from where the racks are and I thought I could run a fiber optic cable. So, I bought cable.

Connected it to the switch and nic using Arista and there are no lights on either end. I'm not sure if I am using the right optical fiber or transceiver?

  • Do you have the pair flipped between the two ends? Rx to Tx and Tx to Rx?
    – Ron Maupin
    Jun 5, 2018 at 2:07
  • Ron's got a fair point - there's no Auto MDI-X for fiber and generally, all patch cables, ... need to be crossover.
    – Zac67
    Jun 5, 2018 at 10:14
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide and accept your own answer.
    – Ron Maupin
    Dec 25, 2018 at 8:35

1 Answer 1


The OM3 fiber you linked to should do nicely, OM3 supports 10GBASE-SR for up to 300 m. As per Ron's comment, you should make sure that the fiber is crossed over - the (left) transmitter side needs to connect to the (right) receiver side and vice versa. There is no Auto MDI-X for fiber.

Generally, you need to check for device compatibility before buying a transceiver or DAC/AOC cable. Many vendors lock out generic SFPs and require you to buy original, branded modules.

Likely, the EX requires a Juniper-branded module and the NIC a Qlogic-branded one. Check the log entries and driver event messages.

However, there's a large market for compatible, 3rd-party transceivers that fake the brand and usually do the job just as well (for sometimes a fraction of the cost). You should use redundant links or have a cold spare stocked anyway. There are even solutions for rebranding stocked transceivers on demand yourself.

Additionally, some switches or routers allow you to deactivate the compatibility check and use generic modules. Check documentation.

With short-wave transceivers (-SR or -SX) you can usually see the transmitter's gleam when looking into the (left) receptacle. The 850 nm wave isn't within the eye's range but the emission isn't that restricted. You can also use a digicam to detect the light. Without light, the transceiver isn't activated.

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