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  • Angelie Soto thinks this is interesting:

If you change the allocation method to static, you as the administrator cannot specify the actual IP address assigned to the Public IP address resource. Azure assigns the IP address from a pool of IP addresses in the Azure region where the resource is located.

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Cover of Exam Ref 70-533 Implementing Microsoft Azure Infrastructure Solutions

Note

That is correct. It has happened to me. Azure has pool of Public IPs per region that can't he assigned by the administrator. Azure chooses one from there.