I'm curious what did this guy connect to several 100 GbE ports and how does the upstream connections he mentions look like, and from which provider. The device is second hand, so the likely use-case is a Home(?)Lab type of setup.
They have 100GBASE-PLR4 optics in them, that allow the 100G ports to be split up into 4x25G ports (or actually in this switch, 2x25G ports due to a hardware limitation with this switch)
> how does the upstream connections he mentions look like, and from which provider
They are just normal 10G-LR Single mode optics, in a data center.
> The device is second hand, so the likely use-case is a Home(?)Lab type of setup.
The high speed (25G+) does not have good solutions for multimode, and the length limits that physics enforces with multimode mean that it's not "no-brainer" applicable for going any more than between the same rack row.
So if you are dealing with datacenter cross connects that can exceed the max distance for MultiMode then you might spend hours debugging broken stuff for no real gain. MultiMode is slightly cheaper, but it's a false economy the moment stuff does not work correctly. I've spoken to people with DC cross connects that go into the 5km+ of cable distance. So it's easier to just stock one kind of optic per speed, and call it a day.
I stopped dealing with large data center providers in 2014. By that point we had switched to using single mode within our colocation spaces and most of the colocation data center providers we dealt with had stopped providing any multimode cross connects prior to that.
For them unfamiliar with fiber optics. Single mode fiber is better than multi mode in nearly every category. The only advantage multimode has is when terminating it. The looser tolerances and large fibers make it easier to attach an end.
Single-mode fiber is future-proof. Utilities bury that stuff and depreciate it over a 30-year lifetime. There has been like one spec change since the 1970s.
