Hey, does anyone know of an SFP28 capable of rate-adapting down from 25G on the cage side down to 1G on the line side? Can be copper or fiber on the line side, I don’t care, my interest is in the chip inside.
Thanks,
-Bill
Hi Bill,
I did that a few months ago with SFP+. Purchased few with copper (different vendors), few with fiber (from Solid Optics, they provide a very nice USB interface to configure them if needed), and used them at different speeds, depending on the equipment on both sides.
The copper ones also work at 2.5 and 5 Gbit/s, not sure
For example, an old 1 Gbit/s SFP-only switch works fine connecting it to a newer switch that has SFP+ (10 Gbit/s). Of course, the speed goes down to 1 Gbit/s only. In this specific case, just for fun, I tried both copper and optical, and both worked.
Some DAC and AOC also work the same as I know.
Note that it may depend on the specific vendor/model, and some of them you may need to "program" them to support multispeed or a fixed speed.
SFP28 is just an enhanced SFP+, an in fact SFP28 work in SFP+ interfaces. So it should be the same, as the electrical signals are the same.
Regards,
Jordi
@jordipalet
El 31/1/22 19:07, "NANOG en nombre de Bill Woodcock" <nanog-bounces+jordi.palet=consulintel.es@nanog.org en nombre de woody@pch.net> escribió:
Hey, does anyone know of an SFP28 capable of rate-adapting down from 25G on the cage side down to 1G on the line side? Can be copper or fiber on the line side, I don’t care, my interest is in the chip inside.
Thanks,
-Bill
I meant:
The copper ones also work at 2.5 and 5 Gbit/s, not sure the fiber ones can do. I think those are restricted to 1, 10 and 25 Gbit/s.
Saludos,
Jordi
@jordipalet
El 31/1/22 19:44, "NANOG en nombre de JORDI PALET MARTINEZ via NANOG" <nanog-bounces+jordi.palet=consulintel.es@nanog.org en nombre de nanog@nanog.org> escribió:
Hi Bill,
I did that a few months ago with SFP+. Purchased few with copper (different vendors), few with fiber (from Solid Optics, they provide a very nice USB interface to configure them if needed), and used them at different speeds, depending on the equipment on both sides.
The copper ones also work at 2.5 and 5 Gbit/s, not sure
For example, an old 1 Gbit/s SFP-only switch works fine connecting it to a newer switch that has SFP+ (10 Gbit/s). Of course, the speed goes down to 1 Gbit/s only. In this specific case, just for fun, I tried both copper and optical, and both worked.
Some DAC and AOC also work the same as I know.
Note that it may depend on the specific vendor/model, and some of them you may need to "program" them to support multispeed or a fixed speed.
SFP28 is just an enhanced SFP+, an in fact SFP28 work in SFP+ interfaces. So it should be the same, as the electrical signals are the same.
Regards,
Jordi
@jordipalet
El 31/1/22 19:07, "NANOG en nombre de Bill Woodcock" <nanog-bounces+jordi.palet=consulintel.es@nanog.org en nombre de woody@pch.net> escribió:
Hey, does anyone know of an SFP28 capable of rate-adapting down from 25G on the cage side down to 1G on the line side? Can be copper or fiber on the line side, I don’t care, my interest is in the chip inside.
Thanks,
-Bill
Are you talking about an SFP28 module that can link at 25Gb, but also 1Gb?
We just put 1Gb SFPs in the SFP28 ports and they work fine. I have not seen a single module that does both, but admittedly, I have not looked too hard, as the 1Gb modules are so cheap.
Or, are you talking about a module that presents as 25Gb to the switch, but 1Gb to the client device?
thanks,
-Randy
We have done that with a CVR and 1g sfp.
The latter.
I remember there were two kinds of copper SFPs: cheap ones, which would talk 1G on both sides, and expensive ones which would talk 1G on the switch/router side, and 10M/100M/1G on the client side.
There seem to be similar kids of copper SFP+, though I haven’t actually tested them:
MikroTik RJ45 SFP+ 10/100/1000M/2.5G/5G/10G copper module | Discomp - networking solutions
SFP-1000-RJ45 - 10GBase-T , 5GBase-T, 2.5GBase-T and 1000Base-T RJ45 coopper SFP+ transceiver module
Dell® SFP-10G-T Compatible TAA Compliant 100/1000/10000Base-TX SFP+ Transceiver (Copper, 30m, RJ-45) | Your Fiber Optic Solution | Proline
LSP443, SFP+, 10-Gbps, RJ-45 - Black Box
https://www.bestbuy.ca/en-ca/product/startech-hp-jl563a-compatible-sfp-module-10-100-1000-10000-copper-transceiver-jl563a-st/14208481
Those seem like they might talk 10G on the switch/router side, and 10M/100M/1G/2.5G/5G/10G on the client side. Or it might be that they establish whatever link speed they can on the client side, and then try to signal the switch/router side to adapt to that rate; which seems possible but improbable. Or it might be that they accept whatever speed the swich/router side tells them it’s running at, and then only provide link at that rate on the client side; again, possible but seems improbable. I haven’t actually taken any of these into the lab to test them, anyway. And those are 10G on the switch/router side, and I’m curious whether anybody knows of one that goes 25G/10G/1G on the switch/router side, and 1G (specifically) on the client side.
I don’t actually want the SFP28, I just need to find a chip that does that in the size/power budget of an SFP, and it seemed like the easiest way to do that would be to find an SFP28 that did what I needed and bust it open to see what chip they were using.
I’m sure you can guess why, given recent threads. 
-Bill