[ SOLVED? NOPE? MAYBE? ] Do QSFP28 optics work in QSFP+ ports? (Obviously at lower speed)[SX6036][CX3]

[Prophes0r]

[EDIT] After 2+ more hours I think I have found an answer. Nope.

Every article I see talks about compatibility of using older 40Gbit QSFP+ optics in 100Gbit QSFP28 switches.

Does the opposite work?
I doubt it, but it would be good to know.

I'm on a shoestring budget and I'm encountering problems finding cheap 40G-LR optics.

I already have the OS2 LC/LC fiber.
I already have an SX6036.
I already have a stack of CX3 NICs.

If I can broaden my search and use whatever optics are the cheapest, it would be easier to find something.

 

[DaveLTX]

Sadly no, I was in the same boat because I wanted to use cheap QSFP28 optics for my QSFP+ hp flom nics but no, it won't work because QSFP28 transceivers doesn't support 4x10G mode
While switches and nics do
(As that would increase die area on the transceiver and thus power consumption)

Which is very odd because SFP+ transceivers support 1G mode. Not sure about SFP28

 

[klui]

The optics just need to support 40G then they will work. I've tried inexpensive Intel CWDM4 (LR4L) transceivers and a bit more expensive Arista ones directly in CX3s and SX6012 and they link at 40G.

The "cheapest" optics may not support them and the only way to find out before purchase is to look at their data sheet. If you can find them, or believe them. But the Intel ones are $5 unless you're looking for bottom of the barrel less than $1 but I'm not sure you can get any 100G transceivers for $1.

 

[DaveLTX]

The optics just need to support 40G then they will work. I've tried inexpensive Intel CWDM4 (LR4L) transceivers and a bit more expensive Arista ones directly in CX3s and SX6012 and they link at 40G.

The "cheapest" optics may not support them and the only way to find out before purchase is to look at their data sheet. If you can find them, or believe them. But the Intel ones are $5 unless you're looking for bottom of the barrel less than $1 but I'm not sure you can get any 100G transceivers for $1.

So they work? I was told they don't after digging into the CWDM4 when STH mentioned they were 5$

 

[DavidWJohnston]

So I decided to test this in my lab because I was curious. To my astonishment, IT WORKS, by setting 100G ports to 40G on my DX010, $5 Intel and "ColorChip" transceivers successfully get link lights.

I did have to set the FEC mode to "none" for it to work. (Also tried "rs" and "fc" but those did not work) But when I set it to "none" the link came right up.

The Intel ones are the same $5 transceivers I posted a few month back in the good deals. The ColorChip ones were an impulse buy and very cheap as well. Both of them are duplex LC CWDM4s.



Interestingly, they don't say anything about 40G compatibility in the EEPROM data. I don't know, maybe this only works in a 100G switch hard-set to 40G, and won't work on a real 40G switch/NIC? I do not own any 40G gear anymore. Also my test was link light only, I didn't try to send any traffic across it. But for $5 each, just try it!!

Intel EEPROM Data:

Ethernet12: SFP EEPROM detected
        Application Advertisement: N/A
        Connector: LC
        Encoding: 64B66B
        Extended Identifier: Power Class 4(3.5W max), CDR present in Rx Tx
        Extended RateSelect Compliance: Unknown
        Identifier: QSFP28 or later
        Length Cable Assembly(m): 0
        Nominal Bit Rate(100Mbs): 255
        Specification compliance:
                Extended Specification compliance: 100G CWDM4
        Vendor Date Code(YYYY-MM-DD Lot): 2019-09-19 00
        Vendor Name: INTEL CORP
        Vendor OUI: 00-02-b3
        Vendor PN: SPTSBP2CLCKS
        Vendor Rev: 02
        Vendor SN: CRCL19220GJVP

ColorChip EEPROM Data:

Ethernet116: SFP EEPROM detected
        Application Advertisement: N/A
        Connector: LC
        Encoding: NRZ
        Extended Identifier: Power Class 4(3.5W max), CDR present in Rx Tx
        Extended RateSelect Compliance: Unknown
        Identifier: QSFP28 or later
        Length Cable Assembly(m): 0
        Nominal Bit Rate(100Mbs): 255
        Specification compliance:
                Extended Specification compliance: 100G CWDM4
        Vendor Date Code(YYYY-MM-DD Lot): 2017-11-07
        Vendor Name: ColorChip ltd
        Vendor OUI: e4-25-e9
        Vendor PN: C100QSFPCWDM400B
        Vendor Rev: 00
        Vendor SN: 17464850

 

[DaveLTX]

Sadly the only way I can get them at 5USD is to get a friend of mine who's going back to US in a week to buy it for me and send it across the globe to where I am

I tried looking for a datasheet for intel's 100G-CWDM4 and i got nothing either

 

[Prophes0r]

But for $5 each, just try it!!

I ended up finding 40Gbit Transceivers for $3 each. Seller has a bad rep here but it's worth a try.
I'll pick up some of those 100Gbit Intel ones too and try them when I get the chance.

Right now I'm working on the fiber part of the conundrum though.