Firewall on Oracle virtual machines

Oracle virtual machines, at least those running on Ubuntu, come with a restrictive firewall which doesn’t allow any incoming TCP traffic. Check before and after state using:

sudo iptables -L

Flush these rules:

sudo iptables --flush

And, to make this stick on instance reboots, copy-paste the output of iptables -L into the /etc/iptables/rules.v4 file.

Also: