Add permanent static routes in Ubuntu

How to add permanent static routes in Ubuntu

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sudo cat /etc/network/interfaces

The output should show something like this

# This file describes the network interfaces available on your system

# and how to activate them. For more information, see interfaces(5).

# The loopback network interface

auto lo

iface lo inet loopback

# The primary network interface

auto eth0 eth1

iface eth0 inet static

address 192.168.1.2

netmask 255.255.255.0

network 192.168.1.0

broadcast 192.168.1.255

gateway 192.168.1.254

# dns-* options are implemented by the resolvconf package, if installed

iface eth1 inet static

address 172.20.10.1

netmask 255.255.255.0

broadcast 172.20.10.255

gateway 172.20.10.254

# static route up route add -net 172.20.11.0/16 gw 172.20.10.254 dev eth1