OVH Server

When you follow the OVH help:

http://hilfe.ovh.de/proxmox
http://help.ovh.com/proxmox

you will fail because of missing proxyarp support of the bridge and a few other things. The following line does the magic:

Proxmox base system for KVM

Activate procxyarp on vmbr0:

echo 1 > /proc/sys/net/ipv4/conf/vmbr0/proxy_arp

Add this to:

/etc/pve/kvm-networking.sh

to make sure, that everything works again after a reboot.

Add the IP's of you KVM VM's to the file:

/etc/pve/kvm_ips

To activate routing for your freshly installed KVM VM without rebooting do:

ip route add IP_OFF YOU_KVM_VM dev vmbr0

When you've added you IP's to /etc/pve/kvm_ips this command is issued while booting automatically.

On Debian style systemes user your fail over IP with a netmask of 255.255.255.255 without a default gateway. Then add to:

/etc/network/interfaces

at the section for eth0:

post-up ip route add default dev eth0