topic QSFP functionality & compatibility in ExtremeSwitching (EXOS/Switch Engine)

QSFP functionality & compatibility

nixcraft — Thu, 02 May 2024 20:11:32 GMT

Up to now I've only dealt with SFP & SFP+ ports and I'm not familiar with QSFP yet. So a few questions.

If connecting a QSFP port to a 10 Gb device with a breakout cable, can a lane be bonded with LACP with another lane and port from a different switch in the stack?
Are all the lanes usable as separate ports for separate devices, or will for example the LACP bond reserve all the lanes. Are there any limitations or do the lanes behave like any traditional switch port?
Would an adapter like QSFP-SFPP-ADPT be better for connecting 10 Gb devices and forming LAGs? At least it costs less if the other lanes are not needed.
Are the Extreme DAC cables compatible with generic server hardware or is it better to use optical modules certified for the specific hardware and skip DAC's unless connecting to other Extreme gear?

I'm looking at the X870 series as a future proofed server rack switch for hardware that is currently 10 Gb but could be upgraded to 25 Gb, 40 Gb or 100 Gb in the future.

Re: QSFP functionality & compatibility

Stefan_K_ — Thu, 02 May 2024 23:29:51 GMT

These breakout cables act like individual ports and you can do what you want with them.

QSFP-SFPP-ADPT is working fine, used it a few times.

you have higher chances that your Server DACs are working with your Extreme Switch than the other way round. Of course the truely supported way would be Transceivers, but EXOS is quite open to third party DACs.

Re: QSFP functionality & compatibility

nixcraft — Fri, 03 May 2024 05:53:18 GMT

Thanks. Sounds like it works how one would expect then. And probably better to use a compatible transceivers for peace of mind.

Re: QSFP functionality & compatibility

FredrikB-NN2 — Fri, 03 May 2024 14:54:05 GMT

The switches may be, but not the TAC, believe me!!!

QSFP-SFPP-ADPT will use only one lane and of course waste the other three. If you have separate SFP+ ports, use those instead. In the X870 and 7720, you may need an occasional QSFP-SFPP-ADPT (or the newer 10506 which is identical at first glance, but will support both 40/10 and 100/25 breakout).

Breakout cables come in DAC style but you can also breakout 4x25G in a QSFP28 transceiver with MPO, like the 10405. You'll need a patch that splits the MPO connector to 8 x LC connectors, though.

Do NOT buy the X870 as it is at it's end when it comes to EXOS releases. It will never be supported by anything newer than EXOS 31.7!!! The 7720 would be your alternative here. The problem is that neither QSFP-SFPP-ADPT or 10506 are supported in them (yet at least).

Re: QSFP functionality & compatibility

Stefan_K_ — Fri, 03 May 2024 23:55:41 GMT

What do you mean it wastes lanes? What do you want to use these lanes for anyways, if an SFP+ is plugged? Makes no sense.

Re: QSFP functionality & compatibility

FredrikB-NN2 — Sat, 04 May 2024 15:24:42 GMT

What I mean is that if you use only one lane out of four, the three remaining are wasted. With a QSFP suitable for breakout they could be used. I was merely trying to point out (for OP that claims not to be so familiar with QSFPs) that it may be a good idea to investigate breakout options if lots of ports need SFP+/SFP28. Having said that, I have a customer that has a 24 port QSFP+ switch with only QSFP/SFP adapters in it except for uplink, so there are certainly cases where this is the most economical option.

Also, sometimes breakout is not possible, as with CWDM plugs or LR for more than 2 km with supported optics, and then you have to "waste" those three lanes.