When two Macs are connected using a Thunderbolt data cable, a high-speed direct network connection is established. While this may seem like an ideal way to provide network access to or between VMs on the Macs, current limitations in macOS virtualization prevent this setup from working as expected.
Summary of the Limitation
The vmnet component of Apple’s virtualization framework, which handles VM networking, does not support bridging to interfaces that it doesn’t recognize as valid network devices. This includes the Thunderbolt-based network connection, even though it functions similarly to Ethernet.
Even though macOS may show a Thunderbolt Bridge (typically bridge0) when using a Thunderbolt cable, this is a logical interface and does not qualify as a physical Ethernet connection for bridging purposes. Removing or reconfiguring individual member interfaces doesn’t change their classification in the eyes of vmnet.
Workarounds and Alternatives
If you need to provide network access to a VM while using a Thunderbolt data cable connection between Macs, consider these alternatives:
- Shared Internet Connection: Configure one Mac to share its internet connection (via Wi-Fi or Ethernet) and have the other Mac connect to it as a client. You can then bridge the shared connection to the VM.
- External Ethernet Adapter: Connect one of the Macs to an external Ethernet adapter (using Thunderbolt or USB) and bridge that physical Ethernet connection to the VM.
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