I assume that those USB-C connectors were USB 4 or Thunderbolt, not USB 3.
With Thunderbolt and operating systems that support Ethernet over Thunderbolt, a virtual network adapter is automatically configured for any Thunderbolt connector, so connecting a USB C cable between 2 such computers should just work, as if they had Ethernet 10 Gb/s connectors.
With USB 3 USB C connectors, you must use USB network adapters (up to 2.5 Gb/s Ethernet).
USB C is perfectly capable of connecting two equals, even with USB-2.
It merely requires one side to be capable of behaving as a device, with the other side behaving as a host.
I.e., unlike PCIe hubs, you won't get P2P bandwidth savings on a USB hub.
It just so happens that most desktop xhci controllers don't support talking "device".
But where you can, you can set up a dumb bidirectional stream fairly easily, over which you can run SLIP or PPP.
It's essentially just a COM port/nullmodem cable. Just as a USB endpoint instead of as a dedicated hardware wire.
Yes, both were modern enough laptops. Although the ideapad didn't advertise thunderbolt in the lspci, connecting that and the dell precision "just worked" (tm).
It's very useful for sending large data using minimal equipment. No need for two cat6 cables and a router for example.
You just need a single Ethernet cable really, if the devices are reasonably modern. With Auto MDI-X the days of needing a crossover cable or a switch are over.
I'm not sure, first off the precision doesn't have an ethernet port at all!
Secondly, I'm not sure if a crossover cable setup will autoconfigure the network, as the poster above says, it has been since the 90s when I bothered trying something like that!
Right, that plan is somewhat foiled by most laptops not having ethernet ports anymore.
You don't need crossover cables anymore. You can just connect a regular patch cable directly between 2 devices. Modern devices can swap RX/TX as needed.
As for auto-configuration, that's up to the OS, but yeah you probably have to set up static IPs.
They would receive APIPA (169.254.0.0/16) address for IPv4 and link-local for IPv6, if the interface would be brought up. Now, that second part is a question; windows would do it, but linux probably not.
With Thunderbolt and operating systems that support Ethernet over Thunderbolt, a virtual network adapter is automatically configured for any Thunderbolt connector, so connecting a USB C cable between 2 such computers should just work, as if they had Ethernet 10 Gb/s connectors.
With USB 3 USB C connectors, you must use USB network adapters (up to 2.5 Gb/s Ethernet).