ip addr add 81.82.83.2/24 dev eth1
ip addr add 192.168.173.1/28 dev eth0
ip route add default via 81.82.83.1

iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE
iptables -t nat -A PREROUTING -i eth1 -p tcp --dport 80 -j DNAT --to 192.168.173.2:80
iptables -t nat -A PREROUTING -i eth1 -p udp --dport 53 -j DNAT --to 192.168.173.3:53
iptables -t nat -A PREROUTING -i eth1 -p tcp --dport 53 -j DNAT --to 192.168.173.3:53
iptables -t nat -A PREROUTING -i eth1 -p tcp --dport 25 -j DNAT --to 192.168.173.4:25

touch /var/lib/dhcp/dhcpd.leases
dhcpd