thanks Udo,
i decided to use network:
20-bit block 172.16.0.0 – 172.31.255.255 1,048,576 16 contiguous class Bs 172.16.0.0/12 (255.240.0.0) 20 bits
based on this:
http://en.wikipedia.org/wiki/Private_network#Private_IPv4_address_spaces
and set IPs for the proxmox nodes in this network as well...