Secure Your OpenSUSE 42.1 Server With Iptables


Hi all.

Today we will come to know how we can secure our OpenSUSE 42.1 Server with the help of iptables. Now a days, security is the prime concern for servers. Every now and then, you will face problems with your LIVE or Production server’s security. If your server security is not high enough, then you will face real problem losing your data over internet.

Let’s get started then.

What is iptables?

First, we need to know what is iptables. Iptables is an application that allows a user to configure the firewall security tables provided by the Linux kernel firewall and the chains so that a user can add / remove firewall rules to it accordingly to meet his / her requirements. Iptables uses different kernel modules and different protocols so that user can take the best out of it. As for example, iptables is used for IPv4 ( IP version 4/32 bit ) and ip6tables for IPv6 ( IP version 6/64 bit ). Normally, iptables rules are configured by System Administrator.  You must have root privileges to execute iptables rules. On openSUSE 42.1 Linux system, iptables can be found as preinstalled on /usr/sbin/iptables location. Every iptables rules are directly handled by the Linux Kernel itself and it is known as kernel duty. Whatever GUI tools or other security tools you are using to configure your server’s firewall security, at the end of the day, it is converted into iptables rules and supplied to the kernel to perform the operation.

Linux Kernel uses the Netfilter framework so that it can provide various networking-related operations which can be performed by using iptables. We will not cover those though.

Previously, ipchains was used in most of the Linux distributions for the same purpose. But, now a days, every Linux Kernel comes with iptables instead of ipchains.

Why OpenSUSE?

OpenSUSE is a very famous Linux distribution. It is widely used by System Admins now a days and too good for development purpose and for production environment. You can install this on your Laptop and enjoy the beauty of OpenSUSE. Beyond the distribution, the openSUSE Project provides a web portal for community involvement. It is built for software developers and system administrators, also has a user-friendly desktop, and feature-rich server environment. It has both KDE & GNOME Desktop environment.

Iptables version

To know your iptables version, type the following command in your terminal.

sudo iptables --version

Start & Stopping your firewall

To start or stop your iptables firewall on your OpenSUSE 42.1, type the following

sudo /sbin/rcSuSEfirewall2 stop

To start it again

sudo /sbin/rcSuSEfirewall2 start

Getting all iptables rules lists

To know all the rules that is currently present & active in your iprables, simply open a terminal and type the following.

sudo iptables -L

If there are no rules exits on the iptables means if there are no rules added so far in your iptables firewall, you will see something like the below image.


In this above picture, you can see that , there are three (3) chains and they are INPUT, FORWARD, OUTPUT and there are no rules exists. Actually I haven’t add one yet.

Type the following to know the status of the chains of your iptables firewall.

sudo iptables -S

With the above command, you can learn whether your chains are accepting or not.

Clear all iptables rules

To clear all the rules from your iptables firewall, please type the following. This is normally known as flushing your iptables rules.

sudo iptables -F

If you want to flush the INPUT chain only, or any individual chains, issue the below commands as per your requirements.

sudo iptables -F INPUT
sudo iptables -F OUTPUT
sudo iptables -F FORWARD


To accept or drop a particular chain, issue any of the following command on your terminal to meet your requirements.

iptables --policy INPUT DROP

The above rule will not accept anything that is incoming to that server. To revert it again back to ACCEPT, do the following

iptables --policy INPUT ACCEPT

Same goes for other chains as well like

iptables --policy OUTPUT DROP
iptables --policy FORWARD DROP

Note: By default, all chains of iptables ( INPUT, OUTPUT, FORWARD ) are in ACCEPT mode. This is known as Policy Chain Default Behavior.

Allowing any port

If you are running any web server on your host, then you must allow your iptables firewall so that your server listen or respond to port 80. By default web server runs on port 80. Let’s do that then.

sudo iptables -A INPUT -p tcp --dport 80 -j ACCEPT

On the above line, A stands for append means we are adding a new rule to the iptables list. INPUT stands for the INPUT chain. P stands for protocol and dport stands for destination port. By default any web server runs on port 80. Similarly, you can allow SSH port as well.

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

By default, SSH runs on port 22. But it’s good practise not to run SSH on port 22. Always run SSH on a different port. To run SSH on a different port, open /etc/ssh/sshd_config file on your favorite editor and change the port 22 to a other port.

Blocking any port

Say we want to block port 135. We can do it by

sudo iptables -A INPUT -p tcp --dport 135 -j DROP


if you want to block your server to initiate any SSH connection from the server to another host/server, issue the following command

sudo iptables -A OUTPUT -p tcp --dport 22 -j DROP

By doing so, no one can use your sever to initiate a SSH connection from the server. The OUPUT chain will filter and DROP any outgoing tcp connection towards another hosts.

Allowing specific IP with Port

sudo iptables -A INPUT -p tcp -s 0/0 --dport 22  -j ACCEPT

Here -s 0/0 stand for any incoming source with any IP addresses. So, there is no way your server is going to respond for a tcp packet which destination port is 22. If you want to allow only any particular IP then use the following one.

sudo iptables -A INPUT -p tcp -s --dport 22  -j ACCEPT

On the above example, you are only allowing IP address to connect to port SSH. Rest IP addresses will not be able to connect to port 22. Similarly you can allow by using CIDR values. Such as

sudo iptables -A INPUT -p tcp -s --dport 22  -j ACCEPT

The above example show how you can allow a whole IP block for accepting connection on port 22. It will accept IP starting from to

If you want to block such IP addresses range, do the reverse by replacing ACCEPT by DROP like the following

sudo iptables -A INPUT -p tcp -s --dport 22  -j DROP

So, it will not allow to get a connection on port 22 from from to IP addresses.

Blocking ICMP

If you want to block ICMP (ping) request to and from on your server, you can try the following. The first one will block not to send ICMP ping echo request to another host.

sudo iptables -A OUTPUT -p icmp --icmp-type 8 -j DROP

Now, try to ping Your OpenSUSE server will not be able to ping

If you want block the incoming ICMP (ping) echo request for your server, just type the following on your terminal.

sudo iptables -I INPUT -p icmp --icmp-type 8 -j DROP

Now, It will not reply to any ICMP ping echo request. Say, your server IP address is And if you ping ping that IP of your server then you will see that your server is not responding for that ping request.

Blocking MySql / MariaDB Port

As Mysql is holding your database so you must protect your database from outside attach. Allow your trusted application server IP addresses only to connect with your MySQL server. To block other

sudo iptables -A INPUT -p tcp -s --dport 3306 -m state --state NEW,ESTABLISHED -j ACCEPT

So, it will not take any MySql connection except IP block. By default MySql runs on 3306 port.

Blocking SMTP

If you not running any mail server on your host server or if your server is not configured to act like a mail server, you must block SMTP so that your server is not sending any spam or any mail towards any domain. You must do this to block any outgoing mail from your server. To do so,

sudo iptables -A OUTPUT -p tcp --dport 25 -j DROP

Block DDoS

We all are familiar with the term DDoS. To get rid of it, issue the following command in your terminal.

iptables -A INPUT -p tcp --dport 80 -m limit --limit 20/minute --limit-burst 100 -j ACCEPT

You need to configure the numerical value to meet your requirements. This is just a standard to maintain.

You can protect more by

echo 1 > /proc/sys/net/ipv4/ip_forward
echo 1 > /proc/sys/net/ipv4/tcp_syncookies
echo 0 > /proc/sys/net/ipv4/conf/all/accept_redirects
echo 0 > /proc/sys/net/ipv4/conf/all/accept_source_route
echo 1 > /proc/sys/net/ipv4/conf/all/rp_filter
echo 1 > /proc/sys/net/ipv4/conf/lo/rp_filter
echo 1 > /proc/sys/net/ipv4/conf/lo/arp_ignore
echo 2 > /proc/sys/net/ipv4/conf/lo/arp_announce
echo 1 > /proc/sys/net/ipv4/conf/all/arp_ignore
echo 2 > /proc/sys/net/ipv4/conf/all/arp_announce
echo 0 > /proc/sys/net/ipv4/icmp_echo_ignore_all
echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
echo 30 > /proc/sys/net/ipv4/tcp_fin_timeout
echo 1800 > /proc/sys/net/ipv4/tcp_keepalive_time
echo 1 > /proc/sys/net/ipv4/tcp_window_scaling 
echo 0 > /proc/sys/net/ipv4/tcp_sack
echo 1280 > /proc/sys/net/ipv4/tcp_max_syn_backlog

Blocking Port Scanning

There are hundred of people out there to scan your open ports of your server and try to break down your server security. To block it

sudo iptables -N block-scan
sudo iptables -A block-scan -p tcp —tcp-flags SYN,ACK,FIN,RST RST -m limit —limit 1/s -j RETURN
sudo iptables -A block-scan -j DROP

Here, block-scan is a name of a new chain.

Blocking Bad Ports

You may need to block some bad ports for your server as well. Here is how you can do this.

sudo iptables -A INPUT -p tcp -m multiport --dport $badport -j DROP
sudo iptables -A INPUT -p udp -m multiport --dport $badport -j DROP

You can add more ports according to your needs.

That’s all for today. Thank you. Hope you enjoy it.

  • cybernard

    NO,NO,NO!!!! This is not how you set up iptables correctly. The commands are valid, at least. However, you NEVER block individual ports, you allow the 0-5 (approx) you need and just drop all the rest of it. You don’t even have an ACCEPT of RELATED,ESTABLISHED traffic. The article fails to mention any help for those with multiple ethernet interfaces such as eth0,eth1,eth2,eth3. There is no mention even of intergrating ipset with this solution.

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