The Inficloud virtual network is used as private network for the instances in the cluster, For communication between instances with the help of subnet. When you want to communicate between two clusters of different virtual networks. Each virtual network is isolated from other virtual networks.
Take one scenario of having appserver in one cluster and backend operation in another cluster.
In here the 2 clusters are having different virtual networks in order enable communication between them with the help of virtual router.
The cluster is having group of instances in the same virtual network each with independent private ipv4 address or you can modify the subnet by yourself.By default the floating ip(internet ip) is not assigned to any instance in the cluster, unless you specifically assign floating ip it wont communicate with internet.
The backend cluster is also having different virtual network each instance having same as above. In order to establish the connection among clusters a infi-router is used to set up and then configure rules as you desired after proper configuring cluster are able to transfer data within themselves.The virtual-network-1 having subnet-A is assigned a Floating ip and virtual-network-2 not assigned any floating ip, In further if you want floating ip it can be configured.