Add the DNS entry for the new Cisco ISE node into the DNS server. This is because the fully qualified domain name (FQDN) of the new Cisco ISE node, for example, ise1.cisco.com, must be DNS-resolvable from the primary Administration ISE node. Otherwise, node registration will fail. The DNS server must contain the IP addresses and FQDNs of the ISE nodes that are part of the distributed deployment1.
The other options are incorrect because:
* Changing the IP address of the new Cisco ISE node to the same network as the others is not necessary, as long as the nodes can communicate with each other over the network.
* Making the new Cisco ISE node a secondary PAN before registering it with the primary is not possible, as the node must be registered first before changing its persona or role.
* Opening port 8905 on the firewall between the Cisco ISE nodes is not required, as this port is used for communication between the primary and secondary Monitoring ISE nodes, not for node registration.
References:
* Setting Up Cisco ISE in a Distributed Environment
* ISE node registering after change domain-name
* FQDN IN ISE