This is just to keep a trace for myself on how to create a Vserver with Internet connectivity.
Create the network interface
Edit /etc/network/interfaces and add:
auto dummy0
iface dummy0 inet static
address 192.168.50.1
netmask 255.255.255.0
Restart the network
/etc/init.d/networking restart
Turns the NAT on
echo 1 > /proc/sys/net/ipv4/ip_forward
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
eth0 here is the network interface you use for your network access.
Create the VM
sudo vserver build build -n cyrus2.3 -m debootstrap --netdev dummy0 --interface 192.168.50.2/24 -- -d lenny
Enter the VM
sudo vserver cyrus2.3 start
sudo vserver cyrus2.3 enter
Ansible, VMware and a bit more 
What’s the goal of this?
Does it allow iptables in guest?