/etc/network/interfaces file for Linux router

interfaces

# This file describes how to configure a Linux computer as a router for GoogleFiber.
# References:
#  https://wiki.debian.org/NetworkConfiguration#Bridges_and_VLANs
#  https://wiki.debian.org/BridgeNetworkConnections#Configuring_bridging_in_.2Fetc.2Fnetwork.2Finterfaces
#  http://flyovercountry.org/2014/02/google-fiber-gigabit-speeds-your-router-part-2-qos/

source /etc/network/interfaces.d/*

# The loopback network interface
auto lo
iface lo inet loopback

#This is the standard NAT setup
pre-up iptables-restore < /etc/iptables.rules

#This interface connects to Google's GPON Fiber<->Ethernet converter. Also spoof the Google Fiber router's MAC
auto enp3s0f0
iface enp3s0f0 inet manual
        hwaddress ether 00:11:22:33:44:55

#This creates a VLAN
auto enp3s0f0.2
iface enp3s0f0.2 inet manual
        hwaddress ether 00:11:22:33:44:55
        #By default, route all traffic to priority 3. This is not strictly correct, but close enough.
        up vconfig set_egress_map "$IFACE" 0 3

#Create a bridge to support hosting virtual machines on the internet.
#You could also configure enp3s0f0.2 directly with DHCP 
auto br_external
iface br_external inet dhcp
        bridge_ports enp3s0f0.2
        bridge_stp off
        up ip link set dev enp3s0f0 up

#Create a bridge to support hosting virtual machines on the LAN and VPN bridging.
auto br_internal
iface br_internal inet static
        bridge_ports enp3s0f1
        bridge_stp off
        address 192.168.9.1
        broadcast 192.168.9.255
        netmask 255.255.255.0