thanks ilario!
the lime-report is very useful, I didn't know it.
this command worked to see the rules:
iptables -nvL -t nat
but the forwarding didn't work. i added two rules on the gateway router (by gui's suggestion)
iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j DNAT --to-destination 10.74.135.155
iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 443 -j DNAT --to-destination 10.74.135.155
but when I try the public ip of my network, what I get is the lime-app menu.
Does anyone have other suggestions?