IP addresses need not be contiguous, but do need to be on the same network. Although the Aster instance will not manage allocation of IP addresses, it is still best to keep all addresses as part of the same subnet. Also, it is best to limit the number of network devices between nodes and to keep the interconnect as balanced as possible. For example, placing all machines on the same VLAN but having a bridge or router between machines may cause bandwidth skew among nodes, and you may suffer undesirable performance as a result.
Ensure to make a large enough subnet because although it is possible to change the network settings (including IP addresses) of your nodes after installation, it is not recommended.