gateway:
on eth0 address is 10.0.0.1/24
on eth1 address is 10.0.1.1/24
ip route list
10.0.0.0/24 dev eth0  proto kernel  scope link  src 10.0.0.1
10.0.1.0/24 dev eth1  proto kernel  scope link  src 10.0.1.1

machine connected to gateway's eth0
on eth0 address is 10.0.0.5/24
ip route list
10.0.0.0/24 dev eth0 proto kernel scope link src 10.0.0.5
10.0.1.0/24 via 10.0.0.1 dev eth0 proto kernel scope global src 10.0.0.5

machine connected to gateway's eth1
on eth0 address is 10.0.1.5/24
10.0.1.0/24 dev eth0 proto kernel scope link src 10.0.1.5
10.0.0.0/24 via 10.0.1.1 dev eth0 proto kernel scope global src 10.0.1.5