IP

ip addr show
ip route list
ip route replace default via 1.2.3.4
ip route delete default via 1.2.3.4
ip route add default via 1.2.3.4
ip route add 172.1.2.0/21 via 172.1.2.3(gateway of the network) dev eth1
ip route del 172.1.2.0/21 via 172.1.2.3(gateway of the network) dev eth1
ip link set <dev> down
ip link set <dev> up
ip address add 1.2.3.5 dev eth12
ip address delete 1.2.3.5 dev eth12