multihome routing setup

#setup the route table per wan
ip route add 0/0 via <gw1> dev <wan1> table 11
ip route add 0/0 via <gw2> dev <wan2> table 12

#reply from right local addresses
ip rule add from <wan1_ip> table 11 pref 91
ip rule add from <wan2_ip> table 12 pref 92

#route by mark
ip rule add fwmark 11 table 11 pref 101
ip rule add fwmark 12 table 12 pref 102

#setup the dnat
iptables -t nat -A PREROUTING -i <wan1> --dst <wan1_ip> -p <proto> --dport <service-port> -j DNAT --to <int_server_ip>
iptables -t nat -A PREROUTING -i <wan2> --dst <wan2_ip> -p <proto> --dport <service-port> -j DNAT --to <int_server_ip>

#mark the incoming connections with CONNMARK
iptables -t mangle -A PREROUTING -i <wan1> -m conntrack --ctstatus DNAT --ctstatus NEW -j CONNMARK --set-mark 11
iptables -t mangle -A PREROUTING -i <wan2> -m conntrack --ctstatus DNAT --ctstatus NEW -j CONNMARK --set-mark 12

#reflect the connmark to firewall mark in reply packets
iptables -t mangle -A PREROUTING -i <lan> --src <int_server_ip> -j CONNMARK --restore-mark