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 ********************************************** IPv4 is over Are you ready for the new Internet ? http://www.theipv6company.com The IPv6 Company This electronic message contains information which may be privileged or confidential. The information is intended to be for the exclusive use of the individual(s) named above and further non-explicilty authorized disclosure, copying, distribution or use of the contents of this information, even if partially, including attached files, is strictly prohibited and will be considered a criminal offense. If you are not the intended recipient be aware that any disclosure, copying, distribution or use of the contents of this information, even if partially, including attached files, is strictly prohibited, will be considered a criminal offense, so you must reply to the original sender to inform about this communication and delete it. ********************************************** IPv4 is over Are you ready for the new Internet ? http://www.theipv6company.com The IPv6 Company This electronic message contains information which may be privileged or confidential. The information is intended to be for the exclusive use of the individual(s) named above and further non-explicilty authorized disclosure, copying, distribution or use of the contents of this information, even if partially, including attached files, is strictly prohibited and will be considered a criminal offense. If you are not the intended recipient be aware that any disclosure, copying, distribution or use of the contents of this information, even if partially, including attached files, is strictly prohibited, will be considered a criminal offense, so you must reply to the original sender to inform about this communication and delete it.

On Jan 31, 2022, at 8:02 PM, Randy Carpenter <rcarpen@network1.net> wrote:

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?

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: https://www.discomp.eu/mikrotik-rj45-sfp-10-100-1000m-2-5g-5g-10g-metalicky-... https://datainterfaces.com/sfp-1000-rj45-10gbase-t-copper-sfp-transceiver-mo... https://www.prolineoptions.com/dell-sfp-10g-t-de-pro-100-1000-10000base-tx-s... https://www.blackbox.be/en-be/i/14164/SFP+,10-Gbps,RJ-45/ https://www.bestbuy.ca/en-ca/product/startech-hp-jl563a-compatible-sfp-modul... 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