For some reason, iptables isn’t blocking ports on a droplet, when the exact same rules work fine on a VirtualBox VM. The output from iptables -S is:
root@public:~# iptables -S
-P INPUT ACCEPT
-P FORWARD ACCEPT
-P OUTPUT ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -p tcp -m tcp --dport 22 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 80 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 443 -j ACCEPT
-A INPUT -j DROP
This is modelled exactly on the tutorial at https://www.digitalocean.com/community/tutorials/how-to-set-up-a-firewall-using-iptables-on-ubuntu-14-04, with a small change to the conntrack line due to Ansible’s iptables module kind of doing that whether I liked it or not.
But that’s not a helpful explanation, since the behaviour of the exact same rule set on Debian 8 is so very different.
Any ideas why this doesn’t block on a droplet, i.e., even with these iptables in place, a telnet command to port 554 will connect.
This textbox defaults to using Markdown to format your answer.
You can type !ref in this text area to quickly search our full set of tutorials, documentation & marketplace offerings and insert the link!
These answers are provided by our Community. If you find them useful, show some love by clicking the heart. If you run into issues leave a comment, or add your own answer to help others.
Get our biweekly newsletter
Sign up for Infrastructure as a Newsletter.
Hollie's Hub for Good
Working on improving health and education, reducing inequality, and spurring economic growth? We'd like to help.
Become a contributor
Get paid to write technical tutorials and select a tech-focused charity to receive a matching donation.
@stuart250691
I’ve ran in to cases where not setting a default policy results in some connections being allowed.
When I setup
iptablesorufw, I always set the default policy todenythat way it’s the first rule in my set. That basically says deny everything except what I explicitly allow.With
iptablesyou can do this by running:Though you’d need to remove that last rule in your set first (i.e.
-A INPUT -j DROP).With
ufw, it’d be:I tend to prefer
ufwover directly usingiptablesas the commands and arguments are a little more straight-forward than they are withiptables(and it’s available on both Ubuntu and Debian).For example, allowing connections on ports 22, 80, and 443, with
ufw, is achieved using:or by setting the default policy first:
My main reason for using
ufw, other than the fact that it’s faster to set rules, is the fact that the rules are not ephemeral as they are withiptables(unless you install another package to make them stick).So when the web server is restarted,
ufwwill maintain my rules, whereas without another package,iptableswill not.