Do the set-up fresh. Reasons; 1) The older set-up might not be completely compatible, and you might not be aware, perhaps even leaving you with a vulnerability. 2) This will guarantee to you the control of the device is again with the proper administrators. 3) If the old device had been compromised with-out being detected, just transferring the 'old' settings might cause the comprise to continue.
Fresh, new, device should give you a fresh start. IMHO, of course. -d
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How to transfer config from Pix 501 to Pix 515E?