Hi Gennaro
The data network is used to bring up the ND cluster just consider how many nodes you will use. You can use the calculator to review the sizing of the cluster.
https://www.cisco.com/c/dam/en/us/td/docs/dcn/tools/nd-sizing/index.html
If you will create another cluster you can use another /29 subnet if you want. Just a consideration:
The Data interface is used too:
•Used for Apps to communicate with ACI Fabric Inband Mgmt or ACI Fabric Out-of-Band or DCNM Inband à needs to be routable
•ND Data Interface IP subnet must be different from ACI INB IP subnet, when ND is directly connected to an ACI fabric
•Used for cluster internal communication: App and Service Network flows are tunneled between the ND nodes via VXLAN encapsulation managed by ND. MTU needed is 1500 bytes, between ND nodes.
I hope this helps