This adds the route immediately to the Kernel IP routing table (after reboot it will be erased).
# route add -net 172.31.0.0 netmask 255.255.0.0 gw 192.168.1.1
to print the Kernel IP Routing table:
# netstat -rn
To keep the Static Route persistent you need to edit the file: /etc/network/interfaces
and the static routes in the following format:
up route add [-net/-host] <host/net>/<mask> gw <host/ip> dev <interface>
up route add -net 172.31.0.0/16 gw 192.168.1.1 dev eno1