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Last I knew Google Fiber used PON. With PON a provider would not allow a subscriber to use their own equipment.

The above is important because PON is essentialy one bidirectional fiber from a central office serving dozens of customers in the field. If you plug in with something on the same wavelength you could interrupt all the other customers on your PON. In PON since your fiber is not dedicated all the way back to the CO, they would have no way to know what device was trying to connect to their access node. They would need to configure your devices Mac address similar to how DOCSIS cable internet works.

If they ARE using dedicated fibers back to the CO then that would more likely be Active Ethernet, a slightly different technology. They would probably still tell you no because of how the CPE (the box at your house) needs to be remotely configured by the access node for shapers etc.

Is it possible that you have a power issue at your house that is causing the failures?

Have a look at the Mikrotik switches (the ones that can run routerOS like the CSS610-8P-2S+IN). I don't know much about fiber and up to now I didn't even know that the 10Gbps SFP+ transceivers couldn't work at 2.5Gbps, but have a look at the Optcore Sober transceivers. I've just found them doing a rapid searche, I don't know them.

But if you could go the OPNsense route that @ostsjoe suggested, that would be better!

I use a mikrotik RB5009 for my 2.5gb routing. It technically can hit 10gbps via routing.

Switching you can try https://mikrotik.com/product/crs305_1g_4s_in

I have no way to test this with the equipment I have, but what about opnsense on an x86-64 box and throw an sfp+ pcie card in there. You could then in theory turn off auto negotiation and set it to 2.5g. Has anyone out there tried this?

I've been running opnsense with my CenturyLink 1g setup, though I'm still using their ont to convert to copper, and been very happy with it.

Check out https://www.fs.com/c/25g-smb-switches-4247

FS have inexpensive switching and SFPs. Even if you get another brand switch I still recommend FS SFPs which can be ordered for compatibility with various vendor equipment.

Be wary of the unifi ones. I just got the Unifi enterprise 8-poe and the SFP overheats constantly. There's a bug in the firmware where the fan doesn't kick on, from the forums I read it's because "users don't like fan noise", but uh, I also don't like my switch crashing and freezing to where I have to do a full power cycle to get it back on. If you go unifi read reviews first, get something with active cooling.

If it's just on the first bit of your network, could you do a pfsense/opensense box with a 2.5gig card? Then everything after that could be whatever you need

Maybe look at HORACO, maybe they have something. I grabbed a few 2.5gbit switches with 10gbit uplink that have so far worked perfectly.

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:

3 acronyms in this thread; the most compressed thread commented on today has 6 acronyms.

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I don't have an exact answer for you but went through this a few years ago with the help of a thread on DSLReports

There's a lot of info there and can be a bit tough to follow but it should get you what you need.

10G SFP+ devices should be able to negotiate down to 2.5G. It’s 10G SFP devices that aren’t able to negotiate lower speeds, as 10G actually came a generation before 2.5 & 5G. I think it was something like it was realised that it was overkill in many cases.

SODOLA 8 Port 2.5G Ethernet Switch with 10G SFP,60Gbps Switching Capacity,Plug & Play/Wall Mountable/Fanless Metal Multi-Gig Unmanaged Network Switch https://a.co/d/deBM8O9