Hello,
NAC Posture Assessment licenses come in multiple flavors:
IA-PA-1K - Health Results for 1,000 end systems
IA-PA-3K Health Results for 3,000 end systems
IA-PA-6K Health Results for 6,000 end systems
IA-PA-12K Health Results for 12,000 end systems
A license is taken up as long an an end system exists with a health result, by default end systems are aged out after 90 days of inactivity.
If you're looking for more information on deployment and capabilities of Posture Assessment Check out this guide starting on page 133:
https://documentation.extremenetworks.com/netsight/8.0/9035081__EMC_8.0_NAC_Manager.pdf
Assessment is not currently supported in Extreme Management Center web GUI, it will need to be configure though the Java NAC Manager application.
Thanks
-Ryan
