Iptables

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iptables is the standard firewall software. The syntax is a little bit difficult, but luckily, lots of it can be reproduced very easily since the firewall behavior is very similar for each port. iptables is installed by default with the following rules, but you must use these steps to manually add any other different ports (at least the add and save functions).

MineOS Turnkey comes with 22 (ssh), 8443 (webui) and 25565 (default minecraft) open by default. Any additional ports (for additional servers or alternative ports) must be opened up manually. Only MineOS Turnkey can be released with pre-configured firewalls; other distributions (such as Ubuntu, CentOS, etc.) typically operate unsecured upon fresh installation (no rules in place); it is recommended to then add these rules to secure the server.

Contents

Establishing iptables rules

Checking iptables rules

Your actual rules may differ slightly.


Chain INPUT (policy DROP)
target     prot opt source               destination
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:ssh
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:8080
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:25565
 
Chain FORWARD (policy ACCEPT)
target     prot opt source               destination
 
Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

Default iptables-rules

A not-yet configured iptables policy is to ACCEPT all input, output, and forward packets. This is an unsecured state. The proper way to secure a server is to lock out ALL inbound contact, and individually add only that which you need. I have determined the following rules to be useful for all MineOS deployments. You should review each port to see if this is the case.

Note: if you are completing this step via PuTTY, it is essential you 'ACCEPT' ssh before you change the default policy to 'DROP'. The order these are listed in is significant.

command inbound outbound port action behavior
iptables -P INPUT ACCEPT matched unaffected * ACCEPT All unmatched packets are ACCEPTED (policy change)
iptables -A INPUT -p tcp -m tcp --dport 22 -j ACCEPT matched unaffected 22 (SSH) ACCEPT Allow SSH inbound
iptables -A INPUT -p tcp -m tcp --dport 8080 -j ACCEPT matched unaffected 8080 ACCEPT Allow webui on HTTPS (python webui only)
iptables -A INPUT -p tcp -m tcp --dport 8443 -j ACCEPT matched unaffected 8443 ACCEPT Allow webui on HTTPS (nodes webui only)
iptables -A INPUT -p tcp -m tcp --dport 25565 -j ACCEPT matched unaffected 25565 ACCEPT Allow MC clients inbound
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT matched unaffected * ACCEPT Permit packets in to firewall itself that are part of existing and related connections.
iptables -P INPUT DROP matched unaffected * DROP All unmatched packets are dropped (policy change)

Modifying iptables rules

Adding iptables-rules

The above listed rules are applied by default. Most of the time you will only need to add additional rules and commit them to disk. For example, to open up an additional Minecraft server port, you might type:

You can then test the connectivity, and if all works as expected, save iptables-rules.


Deleting iptables-rules

Removing individual rules can be done by replacing the -A (append) with -D (delete).

Alternatively, you can list each of the rules by number using --line-numbers and remove it by its number iptables -D INPUT 5:

root@mineos ~# iptables --list --line-numbers
Chain INPUT (policy DROP)
num  target     prot opt source               destination
1    ACCEPT     all  --  anywhere             anywhere
2    ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:ssh
3    ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:8443
4    ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:25565
5    ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:25566
6    ACCEPT     all  --  anywhere             anywhere             state RELATED,ESTABLISHED
root@mineos ~# iptables -D INPUT 5
root@mineos ~# iptables --list --line-numbers
Chain INPUT (policy DROP)
num  target     prot opt source               destination
1    ACCEPT     all  --  anywhere             anywhere
2    ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:ssh
3    ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:8443
4    ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:25565
5    ACCEPT     all  --  anywhere             anywhere             state RELATED,ESTABLISHED

Making changes permanent

Saving iptables-rules

Once you have a working set of rules you are happy with, save them to ensure they persist through reboots.

Applying saved rules

To apply the set of rules generated by iptables-save, execute the following line:

Applying rules on startup

/etc/rc.local is the boot-up script. Any user-specified commands may be entered here, such as iptables. iptables is already autostarted by default.

  1. vi /etc/rc.local
  2. Add iptables-restore < /etc/iptables-rules
  3. Save and quit; reboot

Permitting all traffic

Permitting all traffic by turning off all firewall rules is not advised, but is sometimes useful temporarily in order to better troubleshoot an issue, such as starting Minecraft servers on non-standard ports or using any addons (such as connecting through MySQL remotely or voip apps). These steps are temporary and will be reverted on server reboot:

  1. Accept all traffic by default
  2. Flush all existing rules