Ubuntu – Uncomplicated Firewall blocks playing streames in VLC

The problem was using the -p flag on containers.

It turns out that Docker makes changes directly on your iptables, which are not shown with ufw status.

Possible solutions are:

1. Stop using the -p flag. Use docker linking or docker networks instead.

2. Bind containers locally so they are not exposed outside your machine:

   docker run -p 127.0.0.1:8080:8080 ...

3. If you insist on using the -p flag, tell docker not to touch your iptables by disabling them in /etc/docker/daemon.json and restarting:

   { "iptables" : false }

I recommend option 1 or 2. Beware that option 3 has side-effects, like containers becoming unable to connect to the internet.

ufw is an uncomplicated configuration tool for firewalls. It is designed to be usable by people who have no experience with firewalls or want an uncomplicated way to modify the underlying iptables and netfilter rulesets.

For example:

ufw allow all port 22 traffic (UDP and TCP):

ufw allow 22

iptables allow port 22 traffic (UDP and TCP):

iptables -A INPUT -p tcp --dport 22 -j ACCEPT
iptables -A INPUT -p udp --dport 22 -j ACCEPT

Comparatively, ufw permits users to modify the basic firewall needs with limited knowledge of iptables or such.

It in and of itself only modifies iptables / netfilter rules when 'enabled'. It does not run as its own process, in that sense, because the rules it applies are updated on the fly; I am fairly certain it doesn't continue to 'run'.

The only way I would consider ufw to be a service is in that, at boot time, it may be able to restore whatever rules are defined in it. However, iptables-persistent does the same thing, and is not really a service, therefore I do not consider ufw a service, as such, as to determine if ufw (that is, the actual firewall rules) are being enforced is with ufw status.

As per the Community Help Documentation on ufw, it says nothing about ufw being a service, which seems to support this.

And through testing, I have confirmed that ufw is just a less complicated way to 'configure' firewall rules - the real magic of ufw is that it sets up iptables / netfilter rules which you can then see with iptables -L when ufw is enabled.