Before you can test for your MCSE: Core Infrastructure, you must first earn your MSCA in either Windows Server 2016 or Windows Server 2012. With your MCSA in hand, you can sit for one of the required exams to earn this certification. As with all Microsoft Certifications, you cannot sit for an MCSE exam that you used to earn your MCSA.
Microsoft provides two re-certification options for those who want to demonstrate continues competence in these areas. You can demonstrate that you're staying current in the technology by either taking a re-certification exam or stay-current course within two years of earning your certification. As soon as you pass either the course or the exam, the expiration date on your certification will be extended two years from that date. For more information, please check out the FAQ on Microsoft's Certification Exam Policies page.