Thunderbolt Bridge not working on macos 15.5

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Level 1

14 points

Thunderbolt Bridge not working on macos 15.5

Dear Apple Community:

I have not been able to make a Thunderbolt connection between my Mac Mini M4 Pro using the Thunderbolt 5 rear port #3 and a M3 Air laptop, with an Apple Thunderbolt 3 cable. In system report, both computers show the presence of the other machine. I also have Internet Sharing with default settings. The Network -> Set Service Order is giving the Thunderbolt Bridge the highest priority.

I have tried all of the steps given by ChatGPT, including messing with pfctl, to no avail. In Settings -> Network the Thunderbolt Bridge is listed with a yellow dot as "Self-assigned IP." netstat -ib shows 0 for bridge0 Ipkts and Ibytes. Both show non-zero Opkts. ifconfig shows bridge0 is "active" on both computers.

My understanding is that the Apple Thunderbolt 3 cable, 0.8 m, is fine with Thunderbolt 4.

I had difficulty turning on Internet Sharing, had to select en7 to enable, and then "Ethernet". A bug.

My Intego NetBarrier is set to off on both machines. My pf routing is on. I have also tried it off, to no avail.

ping does not work to the IP address displayed by ifconfig bridge0 in either direction.

Please let me know any additional steps I might take. I had hoped that this would simply work and greatly speed up my file transfer from machine to machine, not to mention providing Internet connectivity for my laptop.

-- Alex G

Mac mini, macOS 15.5

Posted on Jun 10, 2025 9:58 PM

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Answer 1

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agascoig Author

Level 1

14 points

Jun 11, 2025 8:25 PM in response to Luis Sequeira1

Thank you for your prompt response. I tried another Thunderbolt cable.

It turns out that Intego NetBarrier was the problem, even though it was set to off on both the host and client. I uninstalled it and now everything is working.

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Answer 2

Jun 11, 2025 11:12 AM in response to agascoig

It seems to me that your problem may be one of configuration.

When I did use Thunderbolt Bridge it was just as way to quickly share files between two macs.

It seems that you are trying to use it in order to do Internet Sharing from one to the other.

I have to wonder why you'd do it, since it would be far easier just to connect both to the same wifi network, but still:

I will assume that you have your Mini connected to the internet (maybe via Ethernet), and you want to share its connection to the Air. If it is the other way around, then adapt the following accordingly.

1) On the Mini: you do NOT want Thunderbolt Bridge to be the first in service order! You want whatever it should be using (presumably, Ethernet) to be first

2) On the Air, you want Thunderbolt Bridge to be first.

3) On the Mini, System Settings->Sharing, turn on Internet Sharing, and activate "To devices using Thunderbolt Bridge".

4) On the Air, you will want to make sure that in System Settings->Network, Thunderbolt Bridge is set to use DHCP and that the address for its server is whatever address the Mini has for its own Thunderbolt Bridge.

NOTE: I can't test further right now for lack of a Thunderbolt cable. I do have two macs at my desk, but alas no cable. Anyway, unless your purpose is to copy files between the two, and you have a very poor Wifi, you'd be better off just letting them use Wifi or Ethernet. Less setup, and less things that can fail.

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Answer 3

BDAqua

Level 10

250,873 points

Jun 11, 2025 8:53 PM in response to agascoig

Thanks for filling us in!👍🏽

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