Try to add these in the up/down scripts
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
...
iptables -t nat -D POSTROUTING -o eth0 -j MASQUERADE
Try to add these in the up/down scripts
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
...
iptables -t nat -D POSTROUTING -o eth0 -j MASQUERADE