sorry for the post, it seems in some case my code can't correct find the utun ifindex, this plan actually works.

Yes, mess around with UTUN interface is hard but joyful:) Here is the answers for the question, the platform is iOS, it's a packet tunnel provider. Will also consider to release a macOS app later if we have more time.

Thanks a lot for the msg, I was noticed virtualInterface property, but sadyly found it's only avalable on iOS 18+, may be in the future we'd better migrate to use this for reliably get the bsd interface and index.

Hi, Thanks for the suggestion, I think that's resonable and I modify my app code to follow the guideline. Actually I do find some issue because my quirks sometimes find a stale ifindex due to previous utun interface seems does not cleanup, in iOS 18 its quite easy to get the correct index, below iOS 18 I have to fix the logic to make it's more stable...