source /etc/network/interfaces.d/*

auto lo
iface lo inet loopback

auto wan0
iface wan0 inet dhcp

auto eth0.11
iface eth0.11 inet static
     address 10.1.0.1
     network 10.1.0.0
     netmask 255.255.0.0
     broadcast 10.1.255.255
     vlan-raw-device eth0

auto eth1.22
iface eth1.22 inet static
     address 10.2.0.1
     network 10.2.0.0
     netmask 255.255.0.0
     broadcast 10.2.255.255
     vlan-raw-device eth1

auto eth1.33
iface eth1.33 inet static
     address 10.3.0.1
     network 10.3.0.0
     netmask 255.255.0.0
     broadcast 10.3.255.255
     vlan-raw-device eth1

auto dsl-provider
iface dsl-provider inet ppp
pre-up /bin/ip link set wan0 up # line maintained by pppoeconf
provider dsl-provider

$IPTABLES -N privnet_as_source_accept
$IPTABLES -A privnet_as_source_accept -i eth0.11 -j ACCEPT
$IPTABLES -A privnet_as_source_accept -i eth1.22 -j ACCEPT
$IPTABLES -A privnet_as_source_accept -i eth1.33 -j ACCEPT
$IPTABLES -A privnet_as_source_accept -j DROP

.
.
.

# Allow everything which is related to an earlier action
$IPTABLES -A FORWARD -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT

# ICMP forward all subtype from private network to internet
$IPTABLES -A FORWARD -o ppp0 -p icmp -j privnet_as_source_accept

# SSH
$IPTABLES -A FORWARD -o ppp0 -p tcp --dport 22   -m conntrack --ctstate NEW -j privnet_as_source_accept

# whois
$IPTABLES -A FORWARD -o ppp0 -p udp --dport 43   -m conntrack --ctstate NEW -j privnet_as_source_accept
$IPTABLES -A FORWARD -o ppp0 -p tcp --dport 43   -m conntrack --ctstate NEW -j privnet_as_source_accept

# DNS
$IPTABLES -A FORWARD -o ppp0 -p udp --dport 53   -m conntrack --ctstate NEW -j privnet_as_source_accept
$IPTABLES -A FORWARD -o ppp0 -p tcp --dport 53   -m conntrack --ctstate NEW -j privnet_as_source_accept

# HTTP
$IPTABLES -A FORWARD -o ppp0 -p tcp --dport 80   -m conntrack --ctstate NEW -j privnet_as_source_accept

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         10.0.0.1        0.0.0.0         UG    0      0        0 ppp0
10.0.0.1        0.0.0.0         255.255.255.255 UH    0      0        0 ppp0
10.1.0.0        0.0.0.0         255.255.0.0     U     0      0        0 eth0.111
10.2.0.0        0.0.0.0         255.255.0.0     U     0      0        0 eth1.222
10.3.0.0        0.0.0.0         255.255.0.0     U     0      0        0 eth1.333