# Linux Routing

# read the kernel routing table
   route
   route -n
   ip route show
   ip route list

# set default route
   route add default gw 192.168.0.1 eth0
   ip route add default via <GatewayIP>
   ip route delete default

# there is a difference between host and network routing.
# a route to a host is a route to only this one host
# and a route to a network reaches all devices in a network segment

# set an additional network route
   route add -net 192.168.0.0 netmask 255.255.255.0 dev eth0
   route add -net 192.168.0.0/24 dev eth0
   ip route add <network/mask> via <GatewayIP> dev <device>
   ip route add <network/mask> dev <device>
   ip route add <network/mask> dev <device>

# set a route to a certain host
   route add -host 192.168.1.1 dev eth0

# delete a route
   route del -net  192.168.0.0/24
   route del -host 192.168.1.2
   ip route delete network/mask dev <device>

# the route / gateway is written in the following files:
CentOS
   /etc/sysconfig/network
or
   /etc/sysconfig/network-scripts/ifcfg-enp5s0
or
   /etc/sysconfig/network-scripts/route-enp5s0:
   GATEWAY=192.168.0.1

Debian
   /etc/network/interfaces
   gateway 192.168.0.1

openSUSE
   /etc/sysconfig/network/ifroute-eth0