Many hosting networks do not support IP multicast, the default method for Proxmox VE 2.x cluster communication (based on corosync).
This wiki article explains multicast and the alternative, unicast.
http://pve.proxmox.com/wiki/Multicast_notes
This wiki article explains multicast and the alternative, unicast.
http://pve.proxmox.com/wiki/Multicast_notes