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Open source router firmware project OpenWrt ships its own entirely repairable hardware
(www.theregister.com)
This is a most excellent place for technology news and articles.
It's just the router, I guess. Provide your own switch for more ports.
Exactly this. With VLAN tagging you can plug that single 2.5Gb connection into a 48-port managed switch and effectively have up to 47 different NICs if that's what floats your boat. They'd all share the 2.5Gb but that's still more than a lot of small networks need.
In a shared 2.5Gb scenario as you describe, would fully pegged upload/download be 1.25Gb each? Could it do 2.5Gb in both directions simultaneously? Assuming no compute bottlenecks.
It's full duplex so it's 2.5Gb each way simultaneosly. Most NICs support half-duplex but I don't know of any good reason to use that. I used to have a BananaPi based router that could comfortably saturate it's gigiabit interface. I assume there's some kind of offloading going on.