Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
0.0.0.0         172.21.0.1      0.0.0.0         UG        0 0          0 eth1
172.21.0.0      0.0.0.0         255.255.0.0     U         0 0          0 eth0
172.21.0.0      0.0.0.0         255.255.0.0     U         0 0          0 eth1

/etc/network/interfaces
"# interfaces(5) file used by ifup(8) and ifdown(8)"
"#auto lo"
"#iface lo inet loopback"
auto lo eth0
iface lo inet loopback
iface eth0 inet static
address 172.21.3.42
netmask 255.255.0.0
gateway 172.21.0.1
"#       dns-search www.google.com"
dns-nameservers 172.21.3.1