The official Cisco documentation says that you can be out of compliance for up to 45 days in a 60 day time window. The time window of 60 days allows ISE to dip in and out of compliance. But once you have "collected" 45 days of non-compliance in that window, you will be locked out of the Admin GUI and constrained to the licensing page.
I have never experienced this scenario myself, but I have seen customers who occasionally dip into and out of compliance. Recently I even saw a case where a customer had a particular license type out of compliance for more than 30 days and the warning popped up that I should please get more licenses to regain access to the system. But it was a warning shot, and not serious:
But I could Accept and close and all was well again.
Then after a few days, a different warning appeared to tell me "Out of compliance for 2 days". What about the previous 30 days of violation???
I don't understand how one goes from 30 days, to 2 days in such a short space of time. Either way, nothing bad has happened so far.
My biggest complaint with Smart Licensing in ISE is that Cisco has not provided any historical utilisation trending - I have no idea how the license usage is trending over a 24 hour, 7 day, 14 day, or 1 month period. In pre-Smart License days, ISE had a simple but useful histogram that showed peak utilisation trends.
In summary. I think ISE Smart Licensing is a half-baked attempt and not very accurate or predictable. Just do your best to try and keep the right amount of licenses in your Smart Account to not cause yourself any headaches. But don't over purchase either - you have to check at PEAK times in the day to see what your license numbers should be.
