set -x
tether=enp0s25
#inet=wlp4s0
inet=enp0s20u1c4i2

#ip addr add 192.168.0.1/24 broadcast 192.168.0.255 dev $tether
ip link set up dev $tether
ip addr add 192.168.0.1/24 dev $tether
# run twice and you get the fugly RTNETLINK answers: File exists

# configured in /etc/dhcpd.conf
systemctl start dhcpd4@${tether}.service
echo 1 > /proc/sys/net/ipv4/ip_forward
iptables -t nat -A POSTROUTING -o $inet -j MASQUERADE

iptables -A FORWARD -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -i $tether -o $inet -j ACCEPT