Siri does not work with encrypted DNS when VPN is default gateway (Apple bug)

[BetaMatrixCompositor]

Setting custom DNS (either DoH or DoT) through Passepartout causes Siri to display a message that Siri is unavailable (stating the iPhone is not connected to the internet.)

Using cleartext DNS or the VPN’s DNS does not cause this issue. I am not sure more Apple services are affected, and whether some connectivity check is failing. Verified this behaviour on both an iPhone and an iPad with iOS 14.4.2.

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EDIT

Known bug? https://developer.apple.com/forums/thread/677812

Basic test:

• Configuration
  • DNS over HTTPS
  • Servers
  • 1.1.1.1
  • 1.0.0.1
  • URL
  • https://1.1.1.1/dns-query

Confirmed to be correctly configured on https://1.1.1.1/help/

Test:

• Connect to the VPN
• Try "Hey Siri"
• "Siri is not available. iPhone is not connected to the Internet"

Test DOES work when using CloudFlare 1.1.1.1 app though (in fact, it's not the default gateway).

[JGitHubB]

Same issue there. Are you planning a fix? @keeshux

[keeshux]

A quick test revealed that the issue DOES NOT happen when the VPN is not the default gateway.

[keeshux]

https://developer.apple.com/forums/thread/677812

[keeshux]

You can tell from the forum thread that this is an Apple issue. Siri has never worked with encrypted DNS since iOS 14 released the feature.