Extreme Networks X695 to Dell S5148F-ON Switch – 10Gbit SFP+ Intermittent CRC Errors


I recently came across an odd problem with the links from our Extreme Networks X695 switches to some Dell S5148F-ON switches, the X695 was running:, the Dell switch

Essentially what started the oddity was a transceiver failure. The equipment has been in production for a few months, all was working well. Suddenly a transceiver failed in the Extreme Networks switch (nothing particularly odd about that), as these switches are linked with a MLAG everything just carried on working without any issue.

So we replaced the transceiver at the Extreme Networks switch end, the link came up, but starting flapping from time to time, so we assumed well it must be the Dell end, so replaced that, again better but still a problem, so we added a new fibre patch lead, again better, but seeing a number of CRC RX (receive) errors on the Dell end, i.e. seemingly the Extreme Networks switch was putting out traffic with CRC errors.

Well it was possible the new transceivers were faulty or a faulty new cable, but this was unlikely.

So the issue actually turned out to be that the transceiver we swapped in wasn’t quite compatible, below are the results of the transceiver information of first port 23 which was working fine to the same switch and port 24 that was not.

Port :  23

    Media Type            : SF+_SR (Unsupported)
    SKU                   : N/A
    Vendor Name           : Simple
    Vendor Date           : 07/19/21
    Vendor Revision       : 1
    Part Number           : 10301-C
    Serial Number         : N3362081813
    Power Up Counter      : N/A
    Wavelength            : 850 nm
Port :  24

    Media Type            : SF+_SR
    SKU                   : N/A
    Vendor Name           : SOURCEPHOTONICS
    Vendor Date           : 08/08/13
    Vendor Revision       : 10
    Part Number           : SPP10ESRCDFDEX
    Serial Number         : 13323-80657
    Power Up Counter      : N/A
    Wavelength            : 850 nm

So we checked the modules, the first was a working one from port 23:

The second was a faulty one from port 24:

From what we could work out, although the seemingly faulty transceiver was a pukka Extreme Networks one, it appeared it didn’t quite work with the X695 switches which have 10/25 edge ports, i.e. SFP+ but also supporting SFP28 (at 25Gbit). It was like the firmware on the transceiver wasn’t fully compatible with the X695 switch hardware (the module was from 2013), and this manifested as random CRC errors on traffic being sent, traffic did make it through but just some was being dropped for no apparent reason.

Swapping the module with a newer module albeit a third party one, resolved the issue.

One to chalk up to, if you’ve swapped everything and its still not working, compare the old with the new and see what changed…..

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