I have the following topology: LAN Users:192.168.1.2 - 254 (192.168.1.0/24) gateway1: 192.168.2.2/24 used for all outgoing connections of LAN users (default gateway) gateway2: 192.168.3.2/24 used for incoming services (destination NAT, ports 80,443 are forwarded to 192.168.2.1) linux router-server R eth0 192.168.1.1/24: LAN eth1 192.168.2.1/24: WWAN1 eth2 192.168.3.1/24: WWAN2 I want to: route all outgoing traffic coming from LAN and R via 192.168.2.2 route the responses to incoming connections via 192.168.3.2 My config: ifconfig eth0 up 192.168.1.1 netmask 255.255.255.0 ifconfig eth1 up 192.168.2.1 netmask 255.255.255.0 ifconfig eth2 up 192.168.3.1 netmask 255.255.255.0 echo 0 >/proc/sys/net/ipv4/ip_forward route add default gw 192.168.2.2 iptables -t nat -A POSTROUTING -d !192.168.0.0/16 -j MASQUERADE I want to add iptables rule to mark incoming traffic from WWAN2 and send back the responses to WWAN2, while keeping default gateway on WWAN1