Unable to make work both private and public ip network on openvz container in Proxmox

Summarising the related forum topic over at the Proxmox site - http://forum.proxmox.com/threads/5008-Network-issue-setting-up-two-networks-(OpenVZ-container)

You need to use VETH (bridged) networking not the default venet(routed) networking.

Create 2 bridged interfaces via the Proxmox gui (one for each bridge interface/network), then you can configure 2 network interfaces inside the container like you would do any other type of server, 1 for each network

for more information on the differences between venet and veth - take a look at the openvz wiki - http://openvz.org/Differences_between_venet_and_veth