# Proxmox 4.x enabling IP forwarding
Published on 21 May 2016

If you are upgrading your machine from Debian Wheezy to Jessie, then you will find out that there is no IP forwarding anymore. In my case I was upgrading my Proxmox 3.1 to 4.2 and masqerading with iptables. So having 1 public address for multiple virtual machines.

You have to check your  /etc/network/interfaces and add this line:

post-up echo 1 > /proc/sys/net/ipv4/ip_forward

This enables ip forwarding.

Should look like this:

auto lo
iface lo inet loopback

auto eth0
#real IP adress 
iface eth0 inet static

auto vmbr0
#private sub network
iface vmbr0 inet static
        bridge_ports none
        bridge_stp off
        bridge_fd 0

        post-up echo 1 > /proc/sys/net/ipv4/ip_forward
        post-up   iptables -t nat -A POSTROUTING -s '' -o eth0 -j MASQUERADE
        post-down iptables -t nat -D POSTROUTING -s '' -o eth0 -j MASQUERADE