No internet connection on wan Interface of a virtual pfsense Firewall using Proxmox

I created an virtual environment using proxmox for virtualisation with one VM for testing purposes and a pfsense vm. The pfsense has two network adapters. One for the WAN Interface and one for the LAN interface. I connected the VM and pfsense with an bridge vmbr1. That is working fine.

On the WAN interface I have another bridge vmbr1 which is connected to eth0. The bridges are configured as follows:

/etc/network/interfaces

auto lo
iface lo inet loopback

iface lo inet6 loopback

auto eth0
iface eth0 inet manual


auto vmbr0
iface vmbr0 inet static
    address  public_ip
    netmask  255.255.255.224
    gateway  inet_gateway
    bridge_ports eth0
    bridge_stp off
    bridge_fd 0
  # route public_ip/27 via inet_gateway
  up route add -net inet_getway netmask 255.255.255.224 gw inet_gateway dev eth0

auto vmbr1
iface vmbr1 inet static
        address  192.168.18.1
        netmask  255.255.255.0
        bridge_ports none
        bridge_stp off
        bridge_fd 0

What I want is an internet connection for the VMs with the pfsense firewall between internet and VMs. But I wasn't able to connect the pfsense with the internet with the public IP.

Do you have some suggestion to solve this problem?

Thanks in advance!