ISE versions need to match.
Ensure that the primary Administration node and the standalone node that you are about to register as a secondary node are running the same version of Cisco ISE.
Here is a link that discusses registering a secondary node with a primary node and their versions do need to match.
http://www.cisco.com/c/en/us/td/docs/security/ise/1-3/admin_guide/b_ise_admin_guide_13/b_ise_admin_guide_sample_chapter_011.html
Hope this helps,
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Guidelines for Setting Up a Distributed Deployment
Read the following statements carefully before you set up Cisco ISE in a distributed environment.
Choose a node type, ISE node or Inline Posture node. For Administration, Policy Service, and Monitoring capabilities, you must choose an ISE node. For Inline Posture service, you must choose the Inline Posture node.
Choose the same Network Time Protocol (NTP) server for all the nodes. To avoid timezone issues among the nodes, you must provide the same NTP server name during the setup of each node. This setting ensures that the reports and logs from the various nodes in your deployment are always synchronized with timestamps.
Configure the Cisco ISE Admin password when you install Cisco ISE. The previous Cisco ISE Admin default login credentials (admin/cisco) are no longer valid. Use the username and password that was created during the initial setup or the current password if it was changed later.
Configure the Domain Name System (DNS) server. Enter the IP addresses and fully qualified domain names (FQDNs) of all the Cisco ISE nodes that are part of your distributed deployment in the DNS server. Otherwise, node registration will fail.
- Configure the Reverse DNS lookup for all Cisco ISE nodes in your distributed deployment in the DNS server. Otherwise, you may run into deployment related issues when registering Cisco ISE nodes, and restarting Cisco ISE nodes.
(Optional) Deregister a secondary Cisco ISE node from the primary Administration node to uninstall Cisco ISE from it.
Back up the primary Monitoring node, and restore the data to the new secondary Monitoring node. This ensures that the history of the primary Monitoring node is in sync with the new secondary node as new changes are replicated.
Ensure that the primary Administration node and the standalone node that you are about to register as a secondary node are running the same version of Cisco ISE.
Ensure that the database passwords of the primary and secondary nodes are the same. If these passwords are set differently during node installation, you can modify them using the following commands:
