DAC Transceiver odd behavior

Question

I'm trying to connect a pair of S5212F-ON VxRail TOR switches to a new pair of Cisco C9500-48Y4C-A using FS sfp28 DAC cables. I have a 5M Cisco/Dell custom programmed DAC that show serial and mac on both ends Line Up, Protocol down. Switched to a 2m Cisco/Cisco sfp28 and the link comes up. without issue. Ordered 3m because the 2M is a little short to manage and they won't come up. Clone the config from the 2m to the 3m still not working. Everything seems to be a problem on the Dell side as I can loop interfaced on the 9500's and the link will come up with everything except the Cisco/Dell custom programmed. If I program the Dell end of the 5m to Cisco it works fine in a loop.  My question is there a power requirement on the SFP port to see a link? because currently it looks like the only real difference is the length of cable. Of course, I don't want to loop the Dell interfaces as that pair of switches is in productions. Any ideas?

DELL-Chris H · Answer

SJ003,   I believe the issue isn't with the ports power requirement, I think it is downt ot he cable/cable type you're using. I say that as I see there are 3m DAC cables listed for the S5212 switch, but they are QSFP28 (part# D9YM8), not straight SFP28s. I am not certain that is the issue, and will research the issue further, but I think this may be playing a part.    Let me know if this helps.

SJ003 · Answer

@DELL-Chris H​ Thank you for the response. Not sure why I didn't get a notification. The issue turned out to be the FS DAC interface chip relaying connection status to the Dell switch with a cable length over 2M.  Being a third-party DAC not a Dell part since it needed to be cross manufacture compatible. I'm going to use SFP28 optical transceivers for now.

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