iptables is not always easy to deal with so I prefer to use Uncomplicated firewall (ufw) in Ubuntu, because it simplifies configuring and maintaining my firewall rules.
Unfortunately, ufw does not play nice with OpenVZ containers so I decided to find something else. In the end (after testing various things) I decided to install the package iptables-persistent
which is not as sexy as ufw but gets the job done.
iptables-persistent uses two configuration files /etc/iptables-persistent/rules.v4
and /etc/iptables-persistent/rules.v6
both files can be generated during installation.
The a simple version of /etc/iptables-persistent/rules.v4
may look like this
*filter
# Allows all loopback (lo0) traffic and drop all traffic to 127/8 that doesn't use lo0
-A INPUT -i lo -j ACCEPT
-A INPUT -i ! lo -d 127.0.0.0/8 -j DROP
# Allow all traffic from tun-devices (VPN)
-A INPUT -i tun+ -j ACCEPT
# Accepts all established inbound connections
-A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
# Allows all outbound traffic
# You could modify this to only allow certain traffic
# This is in addition to allowing established and related traffic as listed above
-A OUTPUT -j ACCEPT
# Allows HTTP and HTTPS connections from anywhere (the normal ports for websites)
-A INPUT -p tcp --dport 80 -j ACCEPT
-A INPUT -p tcp --dport 443 -j ACCEPT
# Allows SSH connections from trusted-host only - drop the rest
-A INPUT -p tcp --dport 22 -s 1.2.3.4 -j ACCEPT
# Allow ping
-A INPUT -p icmp -m icmp --icmp-type 8 -j ACCEPT
# log iptables denied calls
-A INPUT -m limit --limit 5/min -j LOG --log-prefix "iptables denied: " --log-level 7
# Drop all other inbound - default deny unless explicitly allowed policy (change to REJECT of you which to reject packets instead of dropping them)
-A INPUT -j DROP
-A FORWARD -j DROP
COMMIT
After making changes to your rules files, apply them by running
$ sudo service iptables-persistent reload