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IPTABLES complete cheatlist

Please note that the iptables rules are stored in the /etc/sysconfig/iptables file. If you view this file, you’ll see all the default rules.

1. Delete Existing Rules

Before you start building new set of rules, you might want to clean-up all the default rules, and existing rules. Use the iptables flush command as shown below to do this.

iptables -F
(or)
iptables –flush
service iptables save

2. Set Default Chain Policies

The default chain policy is ACCEPT. Change this to DROP for all INPUT, FORWARD, and OUTPUT chains as shown below.

iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -P OUTPUT DROP

When you make both INPUT, and OUTPUT chain’s default policy as DROP, for every firewall rule requirement you have, you should define two rules. i.e one for incoming andone for outgoing.
Change default policy for INPUT/OUTPUT/FORWARD to ACCEPT. All inbound connections will be allowed

iptables -P INPUT ACCEPT
iptables -P OUTPUT ACCEPT
iptables -P FORWARD ACCEPT

3.Block an IP for inbound connection

iptables -A INPUT -s 192.168.1.5 -j DROP
iptables -A INPUT -i eth0 -p tcp -s “$BLOCK_THIS_IP” -j DROP
4.Allow an IP for inbound connection

iptables -A INPUT -s 192.168.1.5 -j ACCEPT

5.Block outbound IP address

iptables -A OUTPUT -d <IP> -j DROP

6.Block outbound PORT

iptables -A OUTPUT -p tcp –dport <PORT> -j DROP

7.Block outbound IP:PORT

iptables -A OUTPUT -p tcp -d <IP> –dport <PORT> -j DROP

8.Allow port 2222 for inbound tcp connections

iptables -A INPUT -p tcp –dport 2222 -j ACCEPT

9.White list an IP

iptables -A INPUT -i eth0 -s <IP> -j ACCEPT

10.Open port 5666

iptables -I INPUT -p tcp -m tcp –dport 5666 -j ACCEPT
11.Allow ALL Incoming SSH

The following rules allow ALL incoming ssh connections on eth0 interface.

iptables -A INPUT -i eth0 -p tcp –dport 22 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 22 -m state –state ESTABLISHED -j ACCEPT

12.Allow Incoming SSH only from a Sepcific Network

The following rules allow incoming ssh connections only from 192.168.100.X network.

iptables -A INPUT -i eth0 -p tcp -s 192.168.100.0/24 –dport 22 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 22 -m state –state ESTABLISHED -j ACCEPT

In the above example, instead of /24, you can also use the full subnet mask. i.e “192.168.100.0/255.255.255.0″.

13. Allow Incoming HTTP and HTTPS

The following rules allow all incoming web traffic. i.e HTTP traffic to port 80.

iptables -A INPUT -i eth0 -p tcp –dport 80 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 80 -m state –state ESTABLISHED -j ACCEPT

The following rules allow all incoming secure web traffic. i.e HTTPS traffic to port 443.

iptables -A INPUT -i eth0 -p tcp –dport 443 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 443 -m state –state ESTABLISHED -j ACCEPT

14.Combine Multiple Rules Together using MultiPorts

When you are allowing incoming connections from outside world to multiple ports, instead of writing individual rules for each and every port, you can combine them together using the multiport extension as shown below.

The following example allows all incoming SSH, HTTP and HTTPS traffic.

iptables -A INPUT -i eth0 -p tcp -m multiport –dports 22,80,443 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp -m multiport –sports 22,80,443 -m state –state ESTABLISHED -j ACCEPT

15.Allow Outgoing SSH

The following rules allow outgoing ssh connection. i.e When you ssh from inside to an outside server.

iptables -A OUTPUT -o eth0 -p tcp –dport 22 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -i eth0 -p tcp –sport 22 -m state –state ESTABLISHED -j ACCEPT

Please note that this is slightly different than the incoming rule. i.e We allow both the NEW and ESTABLISHED state on the OUTPUT chain, and only ESTABLISHED state on  the INPUT chain. For the incoming rule, it is vice versa.

16.Allow Outgoing SSH only to a Specific Network

The following rules allow outgoing ssh connection only to a specific network. i.e You an ssh only to 192.168.100.0/24 network from the inside.

iptables -A OUTPUT -o eth0 -p tcp -d 192.168.100.0/24 –dport 22 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -i eth0 -p tcp –sport 22 -m state –state ESTABLISHED -j ACCEPT

17.Allow Ping from Outside to Inside

The following rules allow outside users to be able to ping your servers.
iptables -A OUTPUT -p icmp –icmp-type echo-request -j ACCEPT
iptables -A INPUT -p icmp –icmp-type echo-reply -j ACCEPT
19.Allow Loopback Access

You should allow full loopback access on your servers. i.e access using 127.0.0.1

iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT

20. Allow MySQL connection only from a specific network

iptables -A INPUT -i eth0 -p tcp -s 192.168.100.0/24 –dport 3306 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp –sport 3306 -m state –state ESTABLISHED -j ACCEPT

21.Prevent DoS Attack

The following iptables rule will help you prevent the Denial of Service (DoS) attack on your webserver.

iptables -A INPUT -p tcp –dport 80 -m limit –limit 25/minute –limit-burst 1000 -j ACCEPT
In the above example:
-m limit: This uses the limit iptables extension

–limit 25/minute: This limits only maximum of 25 connection per minute. Change this value based on your specific requirement
–limit-burst 1000: This value indicates that the limit/minute will be enforced only after the total number of connection have reached the limit-burst level.

22.Port forwarding using IPTables

Forward port 80 from IP address to another IP

iptables -t nat -A PREROUTING -i eth0 -p tcp –dport 80 -j DNAT –to <DESTIP>:80
iptables -t nat -A POSTROUTING -p tcp –dst <DESTIP> –dport 80 -j SNAT –to <SRCIP>
iptables -t nat -A OUTPUT –dst <SRC> -p tcp –dport 80 -j DNAT –to <DESTIP>:80

Removing the above rules
iptables -t nat -D PREROUTING -i eth0 -p tcp –dport 80 -j DNAT –to <DESTIP>:80
iptables -t nat -D POSTROUTING -p tcp –dst <DESTIP> –dport 80 -j SNAT –to <SRCIP>
iptables -t nat -d OUTPUT –dst <SRC> -p tcp –dport 80 -j DNAT –to <DESTIP>:80

23.List all the rules in the iptables

iptables  -L

24.Check an IP in the rule

iptables -nL | grep <IP>

25.Save the current iptables rules

iptables-save >  File_name

26.Restore iptable rules from the file

iptables-restore <  File_name

Joomla jos_session table crashed

You may come across the following error sometime if you are working joomla site.
jtablesession::Store Failed
DB function failed with error number 145
Table ‘./eilmccco_cmsicdc/jos_session’ is marked as crashed and should be repaired SQL=INSERT INTO jos_session ( `session_id`,`time`,`username`,`gid`,`guest`,`clie nt_id` ) VALUES ( ‘ca7331cb8a008d79e24df425257229ea’,’1227636484′,” ,’0′,’1′,’0′ )

This is a very common error. The problem with this error is that you cannot access your site nor the admin page.
The error messages means that the table “jos_session” is crashed or damaged. This table stores your session information.

This issue can be easily fixed by repairing the session table. For doing this the first thing you should do is find out your joomla database. This can be done by checking your joomla configuration.php file.
Now we can try  repairing the table in following ways.

Cpanel
If you are using the Cpanel, then you can repair you joomla database by clicking the “Repair DB” option in the Mysql section of the Cpanel.

phpMyAdmin

If you can access your database though phpMyAdmin, then on the phpMyAdmin interface, select the joomla database and look for the table “jos_session”. Once you selected the “jos_session” (tick the checkbox) and choose “Repair table” from the drop-down you find at the bottom of the list of tables.

SSH access

If you have shell access of your server, the database can be repaired within the Mysql.
Login to the mysql with necessary privileges
#mysql -u <dbuser> -p
mysql> use joomla1;                              [Assume your joomla database name is joomla1]
mysql> REPAIR TABLE jos_session;

If all the above tricks failed, then you must recreate the “jos_session” table

First of all, please take a complete backup of the joomla database.

phpMyAdmin

1 – Go to MySQL phpMyadmin Control Panel

2 – Go and click on “SQL” near the top left corner of the page, and paste the following lines (below) into the empty text area :

DROP TABLE IF EXISTS `jos_session`;
CREATE TABLE `jos_session` (
`username` varchar(150) default ”,
`time` varchar(14) default ”,
`session_id` varchar(200) NOT NULL default ‘0’,
`guest` tinyint(4) default ‘1’,
`userid` int(11) default ‘0’,
`usertype` varchar(50) default ”,
`gid` tinyint(3) unsigned NOT NULL default ‘0’,
`client_id` tinyint(3) unsigned NOT NULL default ‘0’,
`data` longtext,
PRIMARY KEY (`session_id`(64)),
KEY `whosonline` (`guest`,`usertype`),
KEY `userid` (`userid`),
KEY `time` (`time`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

3 – Click on “Execute” or “Go” to execute the command.

Thats it. This must fix your concern…

Please let me know your feedback and also if you have any other easy workaround

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