Reference:

Need 2012 R2 Domain functional level on the forest to use authentication silos/policies

Their are part of the configuration partition (so, at the forest level), replicated on all domain controllers

 

https://github.com/MicrosoftDocs/windowsserverdocs/blob/master/WindowsServerDocs/security/credentials-protection-and-management/authentication-policies-and-authentication-policy-silos.md

 

https://docs.microsoft.com/en-us/windows-server/security/credentials-protection-and-management/authentication-policies-and-authentication-policy-silos#BKMK_HowKerbUsed

 

Videos: