iface eth0 inet manual

auto eth0.0
iface eth0.0 inet manual
    vlan-raw-device eth0

interface eth0
  static ip_address=192.168.3.50/24
  static routers=192.168.3.3
  static domain_name_servers=8.8.8.8 8.8.4.4

interface eth0.0
  static ip_address=192.168.3.51/24
  static routers=192.168.3.50
  static domain_name_servers=8.8.8.8 8.8.4.4

Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         192.168.3.3     0.0.0.0         UG    202    0        0 eth0
default         192.168.3.50    0.0.0.0         UG    204    0        0 eth0.0

192.168.66.0/24 (prefix mask 255.255.255.0)
192.168.0.0/16  (prefix mask 255.255.0.0)
0.0.0.0/0       (prefix mask 0.0.0.0)