One thing that you have to to consider when installing ISE in an organization is complete ISE failure. In this scenario ISE has failed because of complete power outage or network access to ISE has been removed and no access can be granted to end devices. This could in effect shut down your entire company. This is a very big problem when dealing with a multi-site business with a singular data center.
On your switch ports, add the following command to your standard 802.1x config:
authentication event server dead action authorize vlan X
This command will grant access and dump all traffic on the specified VLAN in the event of total ISE failure/unreachability.
