An administrator is attempting to join a new node to the primary Cisco ISE node, but receives the error message "Node is Unreachable". What is causing this error?

The fact that the second node could potentially become a PAN node is not a cause for an "Unreachable" error; it's a potential role after a successful join.

When attempting to join a new Cisco ISE node to a deployment, a crucial step involves establishing trust via certificates. If there is no valid administrative certificate available or properly configured on the new node, the primary node will not be able to establish a secure connection and will report the node as "unreachable" due to a trust or secure communication failure.

A new node is typically in standalone mode before joining a deployment, so this is an expected state and not an error cause for "Unreachable".

Lack of admin privileges on the second node might prevent successful configuration changes on that node, but the "Unreachable" error typically refers to the primary node's inability to communicate securely with the secondary, which is often certificate-related.