Stub zone not resolving

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Hi,

I have a server at local network configured as a DC of example.local domain and also another server on the external network. I set secondary zone of the example.local domain on this external server and everything is fine I can ping by name and the external server is resolving the names.
Then I created stub zone and it's also transferred to the external server but it's not resolving and I can't even ping the NS itself.