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I have a few general questions about this passive breakout cable which I plan to use with an Mellanox ConnectX-3 40Gb Adapter (MCX314A-BCCT) and some basic SFP+ 10Gb adapters:

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  1. Can I leave some of the 10G SFP+ ports not connected or do they all have to be terminated?
  2. Does the QSFP+ side need to be specifically configurated for a breakout or should that work out of the box?
  3. Somewhat related to question 2: does the 40Gb side have one IP address and all traffic is mirrored on the four 10Gb ports or does it have four IP addresses? And, lastly:
  4. Are QSFP+ cables often vendor-specific or are they interchangeable? (A good answer for me would be a mix 10%/90% or 50%/50% in your experience...)

Thank you!

Related:

Passive Copper Breakout Direct Attach Cable Specs

About 4x10G SFP+ <--> QSFP breakout cable

Connecting Intel X722 SFP+ to Mellanox SX1012 QSFP via 4-split breakout

sdittmar
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1 Answers1

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  1. You can leave them unconnected, there is no way to terminate SFP module.

  2. If your 40Gb hardware is PC with Mellanox ConnectX-3 then it depends on software, usually it need some configuration to split 40Gb port to four 10Gb. Switches have support and may detect split ports automatically.

  3. If your software treat 40Gb port as one port - you would not be able to use more than one device on the other end. They both treat it as one port or both treat them as 4 ports. If you need to have 40Gb link between devices with breakout cable you have to split 40Gb to 4x10Gb and then join them into one virtual aggregated port on both sides. This depend on what protocols you plan to use on this cable.

  4. All brand switches do not like using 3rd party SFP modules as well as SFP direct cables. Many switches would not accept foreign modules and need some configuration. This is also can void the warranty.

On the other side, generic cables and modules vendors used to imitate brand modules so the hardware do not feel the difference. FS is the company known to imitate proper module response so you will not get an error in your switch.

However, there are still some cases when 3rd party module imitating original module will bring you to hell. I have the only experience of Cisco Nexus switches were filled by 3rd party 10G modules and worked for a year, but then they all went to error and huge network was down till switches restart. They did not investigate, they just replaced all modules so noone know the real cause of the problem.

kab00m
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  • Thank you! I read that the Mellanox ConnectX-3 does not support breakout. Only one 10Gb Link would be active, like you say. – sdittmar Jul 11 '22 at 20:19