Hello I will briefly draw the situation
Router with one interface eth0 , to local network 10.123.0.0/16
on a local network ADSL modem with IP 10.123.10.11
I want to use 10.123.10.11 as a connection to internet .
Because of that I have created default route "ip route add default via 10.123.10.11 dev eth0"
I do not want my ADSL modem to do NATing , since it shows to be slow. I have configured static route on ADSL modem "10.123.0.0/16 via 10.123.10.11" which ensures traffic comming from internet will ge to my router.
Now i want to configure NATTING. My concern is, how to create iptables rule which will match only the traffic going via 10.123.10.11 and only for this will make SNAT. If I will do iptables -A POSTROUTING -o eth0 --j SNAT --to-source 213.194.242.198 this will not work . I need to add there a magic words that only traffic going via 10.123.10.11 should be SNATted.
Please help,
Thank you in advance.
David