= How to edit iptables rules

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In this how-to, we will illustrate three ways to edit iptables Rules :

* *CLI :* iptables command line interface and system configuration file
/etc/sysconfig/iptables.
* *TUI (text-based) interface :* setup or system-config-firewall-tui
* *GUI :* system-config-firewall

NOTE: This how-to illustrates editing existing iptables Rules, not the
initial creation of Rules chains.

__TOC__

[[cli-command-line-interface]]
== CLI (command line interface)

[[hot-changes-to-iptables-rules]]
=== Hot changes to iptables Rules

The following procedures allow changes in the behaviour of the firewall
while it is running.

Read the man pages for iptables (man iptables) for further explanations
and more sophisticated Rules examples.

[[listing-rules]]
==== Listing Rules

Current running iptables Rules can be viewed with the command

....
iptables -L
....

.

Example of iptables Rules allowing any connections already established
or related, icmp requests, all local traffic, and ssh communication:

....
[root@server ~]# iptables -L
Chain INPUT (policy DROP)
target     prot opt source               destination
ACCEPT     all  --  anywhere             anywhere             state RELATED,ESTABLISHED
ACCEPT     icmp --  anywhere             anywhere
ACCEPT     all  --  anywhere             anywhere
ACCEPT     tcp  --  anywhere             anywhere             state NEW tcp dpt:ssh

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination
....

Note that Rules are applied in order of appearance, and the inspection
ends immediately when there is a match. Therefore, for example, if a
Rule rejecting ssh connections is created, and afterward another Rule is
specified allowing ssh, the Rule to reject is applied and the later Rule
to accept the ssh connection is not.

[[appending-rules]]
==== Appending Rules

The following adds a Rule at the end of the specified chain of iptables:

....
[root@server ~]# iptables -A INPUT -p tcp --dport 80 -j ACCEPT
[root@server ~]# iptables -L
Chain INPUT (policy DROP)
target     prot opt source               destination
ACCEPT     all  --  anywhere             anywhere             state RELATED,ESTABLISHED
ACCEPT     icmp --  anywhere             anywhere
ACCEPT     all  --  anywhere             anywhere
ACCEPT     tcp  --  anywhere             anywhere             state NEW tcp dpt:ssh
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:http

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination
....

Notice the last line in chain INPUT. There are now five Rules in that
chain.

[[deleting-rules]]
==== Deleting Rules

To delete a Rule, you must know its position in the chain. The following
example deletes an existing Rule created earlier that is currently in
the fifth position:

....
[root@server ~]# iptables -D INPUT 5
[root@server ~]# iptables -L
Chain INPUT (policy DROP)
target     prot opt source               destination
ACCEPT     all  --  anywhere             anywhere             state RELATED,ESTABLISHED
ACCEPT     icmp --  anywhere             anywhere
ACCEPT     all  --  anywhere             anywhere
ACCEPT     tcp  --  anywhere             anywhere             state NEW tcp dpt:ssh

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination
....

[[inserting-rules]]
==== Inserting Rules

Create a Rule at the top (first) position:

....
[root@server ~]# iptables -I INPUT 1 -p tcp --dport 80 -j ACCEPT
[root@server ~]# iptables -L
Chain INPUT (policy DROP)
target     prot opt source               destination
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:http
ACCEPT     all  --  anywhere             anywhere             state RELATED,ESTABLISHED
ACCEPT     icmp --  anywhere             anywhere
ACCEPT     all  --  anywhere             anywhere
ACCEPT     tcp  --  anywhere             anywhere             state NEW tcp dpt:ssh

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination
....

The number given after the chain name indicates the position *before* an
existing Rule. So, for example, if you want to insert a Rule *before*
the third rule you specify the number 3. Afterward, the existing Rule
will then be in the fourth position in the chain.

[[replacing-rules]]
==== Replacing Rules

Rules may be specified to replace existing Rules in the chain.

In the example shown previously, the first Rule given allows connections
to the http port (port 80) from anywhere. The following replaces this
Rule, restricting connections to the standard http port (port 80) only
from the network address range 192.168.0.0/24:

....
[root@server ~]# iptables -R INPUT 1 -p tcp -s 192.168.0.0/24 --dport 80 -j ACCEPT
[root@server ~]# iptables -L
Chain INPUT (policy DROP)
target     prot opt source               destination
ACCEPT     tcp  --  192.168.0.0/24       anywhere             tcp dpt:http
ACCEPT     all  --  anywhere             anywhere             state RELATED,ESTABLISHED
ACCEPT     icmp --  anywhere             anywhere
ACCEPT     all  --  anywhere             anywhere
ACCEPT     tcp  --  anywhere             anywhere             state NEW tcp dpt:ssh

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination
....

[[flushing-rules]]
==== Flushing Rules

To flush or clear iptables Rules, use the *--flush*, *-F* option :

....
iptables -F <chain>
....

Specifying a ** is optional; without a chain specification, all chains
are flushed.

Example to flush Rules in the *OUTPUT* chain :

....
[root@server ~]# iptables -F OUTPUT
....

[[making-changes-persistent]]
=== Making changes persistent

The iptables Rules changes using CLI commands will be lost upon system
reboot. However, iptables comes with two useful utilities:
*iptables-save* and *iptables-restore*.

* *iptables-save* prints a dump of current iptables rules to *stdout*.
These may be redirected to a file:

....
[root@server ~]# iptables-save > iptables.dump
[root@server ~]# cat iptables.dump
# Generated by iptables-save v1.4.12 on Wed Dec  7 20:10:49 2011
*filter
:INPUT DROP [45:2307]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [1571:4260654]
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -p icmp -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT
COMMIT
# Completed on Wed Dec  7 20:10:49 2011
....

* iptables-restore : restore a dump of rules made by iptables-save.

....
[root@server ~]# iptables-restore < iptables.dump
[root@server ~]# iptables -L
Chain INPUT (policy DROP)
target     prot opt source               destination
ACCEPT     all  --  anywhere             anywhere             state RELATED,ESTABLISHED
ACCEPT     icmp --  anywhere             anywhere
ACCEPT     all  --  anywhere             anywhere
ACCEPT     tcp  --  anywhere             anywhere             state NEW tcp dpt:ssh

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination
....

In the default configuration, stopping or restarting the iptables
service will discard the running configuration. This behavior can be
changed by setting IPTABLES_SAVE_ON_STOP="yes" or
IPTABLES_SAVE_ON_RESTART="yes" in /etc/sysconfig/iptables-config. If
these values are set, the affected files are:

* ....
/etc/sysconfig/iptables
....
+
for IPv4
* ....
/etc/sysconfig/ip6tables
....
+
for IPv6

If preferred, these files may be edited directly, and iptables service
restarted to commit the changes. The format is similar to that of the
iptables CLI commands:

....
# Generated by iptables-save v1.4.12 on Wed Dec  7 20:22:39 2011
*filter <--------------------------------------------------------- Specify the table of the next rules
:INPUT DROP [157:36334] <----------------------------------------- This is the three chain belong to filter table, then the policy of the chain
:FORWARD ACCEPT [0:0] <------------------------------------------- and between brackets [<packet-counter>:<byte-counter>] numbers is for
:OUTPUT ACCEPT [48876:76493439] <--------------------------------- debug/informations purpose only. Leave them at their current value.
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT <--------- A rule.
-A INPUT -p icmp -j ACCEPT <-------------------------------------- You just have to take all arguments
-A INPUT -i lo -j ACCEPT <---------------------------------------- of an iptables command.
-A INPUT -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT
COMMIT <---------------------------------------------------------- Needed at each end of table definition. Commit rules in that table.
# Completed on Wed Dec  7 20:22:39 2011
....

If needed, to reset packet and byte counters, use *-Z*, *--zero* :

....
iptables -Z <chain> <rule_number>
....

It is possible to reset only reset a single rule counter. It can be
useful, if you want to know how many packets were captured for a
specific rule.

[[tui-text-based-user-interface]]
== TUI (text-based user interface)

There is two ways to managing iptables rules with a text-based user
interface, either using *setup* or *system-config-firewall-tui*. Using
*system-config-firewall-tui* takes you directly to editing the rules.
Using *setup* you need to select *firewall configuration* and then you
can edit rules. Starting with *setup* looks like this:

image:Firewall-tui.PNG[setup menu
utility,title="setup menu utility",width=700]

On the next screen, which is where you start with
*system-config-firewall-tui*, make sure that "Firewall" is enabled, or
you cannot edit the settings. Then select *Customize* :

image:First_menu_firewall_tui.PNG[Firewall Configuration by TUI. First
screen.,title="Firewall Configuration by TUI. First screen.",width=700]

There is good chance that a service you want to modify is part of the
list of standard "Trusted" services. Select the services you want to
trust (ports to open) and press *Forward* (which means 'next', it is not
port forwarding):

image:Firewall_TUI_Trusted_services.PNG[Editing trusted service with
firewall tui
interface.,title="Editing trusted service with firewall tui interface.",width=700]

The Other Ports menu lets you open additional ports not in the list of
standard Trusted Services, or to edit an existing list of additional
ports :

image:Firewall_TUI_other_ports.PNG[Editing Other ports on firewall
configuration by TUI
interface.,title="Editing Other ports on firewall configuration by TUI interface.",width=700]

To add other ports, specify one port or a port range, and choose between
*tcp* or *udp* for the protocol. The port range format is _beginningPort
- endingPort_.

image:Firewall_TUI_adding_other_ports.PNG[Adding other ports on firewall
configuration by TUI
interface.,title="Adding other ports on firewall configuration by TUI interface.",width=700]

The trusted interfaces menu allows you to trust all traffic on a network
interface. All traffic will be allowed and the port filtering rules will
never match. You should only select an interface that faces a private
network, never an interface that directly faces the Internet.

image:Firewall_TUI_trusted_interfaces.PNG[Trusted
interfaces.,title="Trusted interfaces.",width=700]

The Masquerading menu lets you select an interface to be masqueraded.
Masquerading is better known as
*http://en.wikipedia.org/wiki/Network_address_translation[NAT]* (Network
Address Translation), and it is useful for example when your computer is
used as gateway to access the internet:

image:Firewall_TUI_masquerading.PNG[Firewall TUI interface :
masquerading.,title="Firewall TUI interface : masquerading.",width=700]

Port forwarding, also known as
*http://en.wikipedia.org/wiki/Network_address_translation#Port_address_translation[PAT]*,
permits traffic from one port to be rerouted to another port.

image:Firewall_TUI_Port_Forwarding.PNG[Firewall TUI interface :
configuring Port
Forwarding.,title="Firewall TUI interface : configuring Port Forwarding.",width=700]

For example:

image:Firewall_TUI_Port_Forwarding_Adding.PNG[Firewall TUI : adding port
forwarding
rules.,title="Firewall TUI : adding port forwarding rules.",width=700]

The ICMP Filter menu lets you reject various types of ICMP packets. By
default, no limitations are made, but you can define rules to reject
ICMP traffic, define the return error to an ICMP request, etc.

image:Firewall_TUI_ICMP_Filter.PNG[Firewall TUI: configuring ICMP
behaviour.,title="Firewall TUI: configuring ICMP behaviour.",width=700]

Finally, you can add custom firewall rules. These must be prepared ahead
of time in files that use the same format as the iptables file.

image:Firewall_TUI_Custom_Rules.PNG[Firewall TUI: create custom
rules.,title="Firewall TUI: create custom rules.",width=700]

For adding custom rules you have specify the protocol between *ipv4* or
*ipv6* and on what table add the custom rules *filter*, *mangle* or
*nat* then the path to the file containing rules to add :

image:Firewall_TUI_Custom_Rules_Adding.PNG[Firewall TUI: adding a custom
rules.,title="Firewall TUI: adding a custom rules.",width=700]

When you have completed all menus, *Close* the interface, which brings
you back to the first screen of firewall configuration. Select *OK* and
a warning message appear :

image:Firewall_TUI_Warning.PNG[Firewall TUI
warning.,title="Firewall TUI warning.",width=700]

Select *Yes* if the configuration you made fits to you and exit
interface, or *No* to go back to the firewall configuration screen.

[[gui]]
== GUI

[[red-hat-gui-configuration-tool]]
=== Red Hat GUI configuration tool

GUI interface allow you exactly the same thing that TUI interface, but
it is more friendly usable.

First time you start GUI, you have a welcome message that warning you
that if you have existing manual rules then this rules will be
overwritten. image:Firewall_GUI_First_Time_Startup.PNG[First time
startup message,title="fig:First time startup message"]

Before all, you need to *Enable* your firewall to use Firewall
Configuration utility.

image:FireWwall_GUI_startup.PNG[Firewall Gui startup
screen,title="Firewall Gui startup screen"]

Then utility warn you that you don't have any existing configuration and
want you execute the wizard. Click on *Start wizard*:

image:No_configuration.PNG[No firewall
configuration,title="No firewall configuration"]

Click on forward :

image:Firewall_Wizard.PNG[Firewall Wizard : welcome
screen,title="Firewall Wizard : welcome screen"]

_System with network access_ enable Firewall and _System without network
access_ disable Firewall, so select _System with network access_ :

image:Firewall_Wizard_2.PNG[Firewall Wizard : network
access?,title="Firewall Wizard : network access?"]

Beginner allow you to modify only _Trusted Services_, it's fine if you
use only known services like ftp, dns, http, etc but don't allow you to
configure customs ports range, select _Expert_ to have full featured
Firewall Configuration utility, you can change this option later in the
*Options* menu Main windows, in *User Skill Level* :

image:Firewall_Wizard_3.PNG[Firewall Wizard :
skill?,title="Firewall Wizard : skill?"]

*Server* template enable only ssh port on firewall configuration
_Desktop_ template enable additional ports for _IPsec_, _Multicast DNS_,
_Network Printing Client_ and _SSH_. For convenience select Desktop, and
*OK* :

image:Firewall_Wizard_4.PNG[Firewall Wizard : configuration
base?,title="Firewall Wizard : configuration base?"]

As described earlier _Desktop_ template enable 4 services _IPsec_,
_mDNS_, _IPP_ and _SSH_. If you have services listed in *Trusted
Services* section that you want to enabled, you just have to click on
it, that's all. It is possible to change template by using the *Options*
menu, in *Load Default Configuration*.

image:Firewall_Wizard_5.PNG[Firewall Main interface :
enabled,title="Firewall Main interface : enabled"]

*Other Ports* allow you to edit custom rules if your service port wasn't
in *Trusted service*. To begin, just click on *Add* button. Then either
you choose in services list the right service or you tick *User Defined*
and fill requested information about *Port / Port Range* and *Protocol*.

image:Firewall_GUI_other_ports.PNG[Firewall GUI : edit other ports
rules.,title="Firewall GUI : edit other ports rules."]

*Trusted Interfaces*, *Masquerading*, *Port Forwarding*, *ICMP Filter*
and _Custom Rules_' have exactly the same effect than in TUI interface.

When configuration fits to you, just click on the *Apply* button.

[[others-gui]]
=== Others GUI

There are others GUI available to configure iptables rules.

* http://www.fwbuilder.org/_fwbuilder[http://www.fwbuilder.org/
fwbuilder] : very complete gui tools to configure iptables.
* http://shorewall.net/_Shorewall[http://shorewall.net/ Shorewall] :
another very complete gui like fwbuilder.
* http://www.turtlefirewall.com/_Turtle_firewall_project[http://www.turtlefirewall.com/
Turtle firewall project] : web interface and integrated to webmin. Fits
to basic usage of Iptables, can not handle all iptables options like
fwbuilder
* http://users.telenet.be/stes/ipmenu.html_IPmenu[http://users.telenet.be/stes/ipmenu.html
IPmenu] : console based interface that allow you all iptables
functionalities.
'''

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