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I have a Laptop with a Thunderbolt port (ROG GU603HM on Arch) that I would like to bridge to another device (2018 iPad Pro) using IP over Thunderbolt technology. However, the second device does not support Thunderbolt, and instead has a 10gbps capable USB-C port.

My question is, is it possible to have my laptop's Thunderbolt port to act as a Network Interface (USB gadget) to the second device? In other words, I would like to make my laptop a "Device", and the second device a "Host", and have an IP link over this connection (similar to USB OTG with a Raspberry Pi, for example).

I am not too sure how IP over Thunderbolt is implemented, but this sort of connection seems deceivingly possible if two Thunderbolt capable devices are able to communicate in this way. Is this sort of connection possible? Or does IP over Thunderbolt require hardware that simply doesn't exist in my configuration?

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  • To begin with, if you're wanting to use IP over Thunderbolt the other system will also have to support Thunderbolt. While it MAY be possible for one computer to emulate USB device mode and offer services to another host, that doesn't grant that other host Thunderbolt IF that host doesn't already support Thunderbolt. Commented Jun 10, 2024 at 21:16
  • Yes - I am aware of that. I guess a clarification to the question could be that instead of using IP over Thunderbolt itself, I want to do something similar (IP over USB-C?) by having the laptop present itself to the second device as a network interface. Commented Jun 10, 2024 at 21:18
  • So get rid of the Thunderbolt part of your question, give us all the OSes and hardware involve, and focus on asking just about using one computer to pretend to be a USB NIC for a second computer. Commented Jun 10, 2024 at 21:26
  • unix.stackexchange.com/questions/120368/… and superuser.com/questions/1645341/… Commented Jun 10, 2024 at 21:27
  • I have searched and read through both these posts and many similar ones, all of which state that something like this is not possible with USB A without a USB Device controller/USB OTG technology. USB-C and especially thunderbolt, have dual role device/host capabilities that seemingly contradict this claim, yet there has been no clear answers on whether it is possible to use these new technologies to achieve this. I bring up IP over thunderbolt specifically as it is closest to the functionality I am trying to achieve. Commented Jun 10, 2024 at 21:37

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I am not too sure how IP over Thunderbolt is implemented, but this sort of connection seems deceivingly possible if two Thunderbolt capable devices are able to communicate in this way. Is this sort of connection possible? Or does IP over Thunderbolt require hardware that simply doesn't exist in my configuration?

It requires hardware that simply doesn't exist. Thunderbolt is not USB – it only shares the connector but is otherwise a completely separate "mode" that gets routed over the same data lines. The physical layer (i.e. the electrical signalling) is different from what a USB host controller would recognize, and the communication protocol is also completely unlike USB. (Thunderbolt devices form a kind of a network which can then tunnel PCI-Express packets, DisplayPort packets, USB packets, etc. between any two nodes in the network – apparently the ability to carry Ethernet is implemented through PCIe.)

(Though, confusingly, there is now USB4 which is also "not USB" in this regard – it's pretty much a Thunderbolt connection that then tunnels USB3 packets inside a TB channel – but since you mentioned 10 Gbps, I'm assuming your laptop only has traditional USB3.)

In other words, you don't have two Thunderbolt capable devices, so what two Thunderbolt capable devices can achieve does not really apply here – since one end only has a USB host controller, the other end also needs to remain in USB mode; its TB capabilities are not useful.

Your laptop's type-C port can probably be either role for power supply, but this other answer talks about it being unlikely that it would be capable of switching roles for the data communications – it needs additional hardware to be anything other than a host, just like with OTG in older USB: https://superuser.com/a/1213301

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While not completely the same, I managed to figure out a similar solution with the same functionality, going the other way. While the laptop doesn't have a USB Device Controller, the iPad does.

Using usbmuxd and an undocumented feature, I was able to get the iDevice to show up as a network interface for the laptop. By "sharing my connection" to the interface, I was able to get a ~2.5 Gbps IP over USB connection between my two devices.

To support this alternate usbmuxd mode set USBMUXD_DEFAULT_DEVICE_MODE=3 as an environment variable (in usbmuxd's systemd config, for example).

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It is interesting that it doesn't work. I mean, no surprise there - if all your information is correct, then of course this will not be possible. But from what I know your information is INCORRECT in some details.

iPad Pro (Gen 3, Oct 2018) is a device that is - according to Apple - equipped with Thunderbolt 3 technology. Asus claims that 2021 ROG ROG GU603HM laptop is equipped with Thunderbolt 4. So nominally it should work.

That it doesn't may be due to one or more of the three problems below:

  1. Apple claims it T3 port, but it isn't, really. I mean, it may actually be a T3 port and it supports DisplayPort, Power Delivery and data transfer, but not network. Thunderbolt mode does not require availability of full spectrum capabilities all the time, as per specification.
  2. Cable you use is USB, and not Thunderbolt. USB-C is just a connector/port standard, it's not the actual technology.
  3. Asus Laptop drivers are Microsoft supplied and they may not support the network feature of the device's Thunderbolt. Happens more often than not, especially when laptop originally comes with Windows 10, but it runs Windows 11. In this case drivers are basic, not supporting full range of capabilities of the equipped components.

It is important to note that Thunderbolt 3 supports only peer-2-peer connectivity, of 2 or more devices in a star/daisy-chain configuration, up to the limit. While it supports power sharing, file sharing and video connectivity, it will not work as an Ethernet adapter (even though it creates virtual one for that purpose). Duh.

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