All the nodes of a NetScaler cluster must be running the same software version. Therefore, to upgrade or downgrade the cluster, you must upgrade or downgrade each NetScaler appliance of the cluster, one node at a time.
A node that is being upgraded or downgraded is not removed from the cluster. The node continues to be a part of the cluster and serves traffic uninterrupted, except for the down-time when the node reboots after it is upgraded or downgraded.
However, due to software version mismatch among the cluster nodes, configuration propagation is disabled on the cluster and is enabled only after all the cluster nodes are of the same version. Since configuration propagation is disabled during upgrading on downgrading a cluster, you cannot perform any configurations through the cluster IP address during this time.