# Proxmox 4.x enabling IP forwarding
Published on 21-05-2016

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
        address  192.168.10.2
        netmask  255.255.255.0
        gateway  192.168.10.1

auto vmbr0
#private sub network
iface vmbr0 inet static
        address  10.10.10.1
        netmask  255.255.255.0
        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 '10.10.10.0/24' -o eth0 -j MASQUERADE
        post-down iptables -t nat -D POSTROUTING -s '10.10.10.0/24' -o eth0 -j MASQUERADE