About Cluster Interfaces
You can configure data interfaces as either Spanned EtherChannels or as Individual interfaces. All data interfaces in the cluster must be one type only. You cannot configure Ethernet 1/1 as a Spanned EtherChannel and configure Ethernet 1/2 as an Individual interface within the same cluster, for example.
For Spanned EtherChannels: You can use regular firewall interfaces or IPS-only interfaces (inline sets or passive interfaces). For Individual interfaces: IPS-only interfaces are not supported.
Each unit must also dedicate at least one hardware interface as the cluster control link.