I have a 48 port Cisco 2960-X running IOS Version 15.0(2)EX5.

I'm trying to connect it to a Ubiquiti EdgeRouter4 using a Ubiquiti DAC Twinax cable..

I'm aware that this is technically not recommended, however:

It's for a homelab environment. I wouldn't do this for a production enterprise network, and I'm aware that Cisco do not recommend this, however - Cisco DACs are expensive.

When I plug the DAC in, I see the port come up in the logs, and them immediately go into an error state. Something to the effect of:

Jul  6 00:30:02.214: %GBIC_SECURITY_CRYPT-4-VN_DATA_CRC_ERROR: GBIC in port Gi1/0/50 has bad crc
Jul  6 00:30:02.218: %PM-4-ERR_DISABLE: gbic-invalid error detected on Gi1/0/50, putting Gi1/0/50 in err-disable state

I've tried running following this guide which suggests running:

  • no errdisable detect cause gbic-invalid followed by:
  • service unsupported-transceiver

As well as running service internal which I found here.

to disable CRC checks and enable the use of third-party transceivers in the switch. However, I'm still getting CRC errors. It feels like there's something else I need to do to enable third party SFP transceivers.

Is there something I'm missing? Or something else I can try?

  • 2
    What's the exact model? (not all of them support SFP+) If you're seeing "bad crc" then there's something wrong with the module, or it's fundamentally incompatible with the switch. I've had this happen several times, the only fix is a different module. (and for the record, I've had HP switches refuse HP's own optics. The equation for signing them changed at some point.)
    – Ricky
    Commented Jul 6, 2021 at 2:59
  • @Ricky The model is WS-C2960X-48TS-L. To save you the bother of looking it up, this one does not support SFP+, just SFP. However - I can't seem to find any reasonably priced SFP DACs, just SFP+. I was kinda hoping to bring the interface up, then hard set the port speed to 1G
    – robertmain
    Commented Jul 6, 2021 at 5:05

1 Answer 1


The giveaway is the port name Gi1/0/50. An SFP+ DAC generally requires an SFP+ (10G) port. There are very few SFP ports (1G) that accept SFP+ modules.

There are no SFP DACs, so you could use either a simple twisted-pair port (1000BASE-T), or SFP with multi-mode fiber (1000BASE-SX), or single-mode fiber (1000BASE-LX). If you do require 10G you'll need a 10G switch.

  • Ah, so you can't manually set it to do so, I take it...
    – robertmain
    Commented Jul 6, 2021 at 17:06

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