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Comment by roomey | Hacker News Reader

I recently had to set up a new laptop (xubuntu).

Previously I cloned but I this time I wanted to refresh some of the configs.

Using a usb-c cable to transfer at 10gb/s is so useful (as my only other option was WiFi).

When you plug the computers together they form an ad-hoc network and you can just rsync across. As far as I could tell the link was saturated so using anything else (other protocols) would be pointless. Well not pointless, it's really good to learn new stuff, maybe just not when you are cloning your laptop (joke)!

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Did it ‘just work’?

Serious question since last time I tried a direct non-Ethernet connection was sometime in the 90s ;)

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.

If both ends got APIPA addresses would they be able to talk to each other?

I was under the impression you have to set up the devices as each other's default gateway, but maybe I'm the one not up to modern standards this time.

Their randomly chosen addresses are within the same /16 subnetwork.

Therefore they can talk directly, without using a gateway.

Their corresponding Ethernet MAC addresses will be resolved by ARP.

The problem is that in many cases you would have to look at the autoconfigured addresses and introduce manually the peer address in each computer.

For file sharing, either in Windows or using Samba on Linux, you could autodiscover the other computer and just use the name of the shared resource.

There's https://en.wikipedia.org/wiki/Multicast_DNS though I'll admit I never properly tried it.

I did this also, but had to buy a ~$30+ Thunderbolt 4 cable to get the networking to work. Just a USB3-C cable was not enough.

The transfer itself screamed and I had a terabyte over in a few mins. Also I didn't bother with encryption on this one, so that simplified things a lot.

Were you transferring the entire filesystem, after booting from a live disk, or were you transferring files over after having set up a base system?

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