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                       -= Arno's iptables firewall =-
         Single- & multi-homed firewall script with DSL/ADSL support

                      ~ In memory of my dear father ~

Email     : a r n o v a AT r o c k y DOT e l d DOT l e i d e n u n i v DOT n l
            (note: you must remove all spaces and substitute the @ and the .
             at the proper locations!)

# This program is free software; you can redistribute it and/or # modify it under the terms of the GNU General Public License # version 2 as published by the Free Software Foundation.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

A MESSAGE FROM THE AUTHOR:

Almost all my work is distributed under the terms of the GNU GPL License, which means it's free (open-source) software. If you like my work or you want me to implement a certain feature, you are encouraged to donate money. You can (preferably) donate directly to me through my bank account (mail me for my IBAN number (International Bank Account Number). Or you can donate it to one of my favourite charity organisations:
- foundations for cancer research (in The Netherlands: KWF Kanker Bestrijding) and/or
- foundations for CFS (Chronic Fatigue Syndrome) research (in The Netherlands: "ME stichting")

I can also provide paid support (for commercial businesses). For example for firewall customisation, (special) feature requests or other support. Just contact me and we can work something out.

Note that if you directly donate to me, the donation will always go partially (or completely, depending on the amount) to one of the above foundations.

IMPORTANT NOTE:

Before contacting me (by email), in case of problems, questions, etc., please first consult the FAQ's at my website and/or post your message on the mailinglist, for which you can sign up on my website. Please use this way as I'm simply too busy to help everybody out with every (trivial) issue.

An explanation of the files in the package:

arno-iptables-firewall:

        The actual firewall script, core of Arno's iptables firewall. You
        should put this file in eg. /etc/init.d/ or /etc/rc.d/ depending in
        your distribution. Further more you need to make sure it's executable
        (use "chmod 700 or chmod +x).

(/etc/arno-iptables-firewall/)firewall.conf:

        The configuration file used for Arno's iptables firewall script.
        Normally you should put it in /etc/arno-iptables-firewall/ . Make sure root
        is owner/group (with "chown 0:0").

(/etc/arno-iptables-firewall/)firewall.conf.example:

        Example file on how to configure firewall.conf. Only use it as an
        example, do NOT directly use it as your configuration file!

(/etc/arno-iptables-firewall/)custom-rules:

        Put any (iptables) custom rules in this file. The file in this
        package also implements plugin-support for my firewall. This file
        should be put in /etc/arno-iptables-firewall/ . Make sure root
        is owner/group (with "chown 0:0").

(/etc/arno-iptables-firewall/)plugins/:

Put any plugins (& related files) for my firewall in this directory.

*/syslog.conf:

        Example file(s) on how to configure syslogd (/etc/syslog.conf) for
        different distributions to log all firewall messages to a separate
        log-file called /var/log/firewall (instead of /var/log/messages).
        Note that you should also set LOGLEVEL=debug in firewall.conf!

Debian/syslog-ng.conf:

        Example file on how to configure syslogd-ng (/etc/syslog-ng.conf) on
        Debian to log all firewall messages to a separate log-file called
        /var/log/firewall (instead of /var/log/messages). Note that you should
        also set LOGLEVEL=debug in firewall.conf!

arno-fwfilter:

        A pipe filter script to make the firewall-log better readable. It can
        be used for example in conjuction with a tail to log your firewall to
        local tty10 (-12). It can be used for both /var/log/messages and
        /var/log/firewall (or whatever name you configured syslogd), depending
        on the log-level specified in the configuration file. An example on how
        to use it can be found in the beginning of the fwfilter script. Any
        options for fwfilter can be configured within the script itself. You 
        should put this file in for example /usr/local/bin/

/man/arno-iptables-firewall.8:

A man page for the arno-iptables-firewall script.

/man/arno-fwfilter.1:

A man page for the arno-fwfilter script.

| Some IMPORTANT (security) information: |

1) Always first start the firewall before you enable your (ADSL) internet

connection (if possible). For an ppp-interface that doesn't exist yet you can use the wildcard device called "ppp+" (but you can only use ppp+ if there aren't any other ppp interfaces!). 2) Don't change any (security) settings ('EXPERT SETTINGS') if you don't

really understand what they mean. Changing them anyway could have a big impact on the security of your machine. 3) I get a lot of emails from people complaining that their webserver etc.

stopped working after installing my firewall. This is the CORRECT behaviour for a firewall: BLOCKING ALL incoming traffic by default!

| Debian package repository information |

When you are using Debian (or a Debian-flavor: Ubuntu, Kubuntu etc.), you can either use the package from Debian testing/unstable or when running Debian stable (Sarge) use Michael Hanke's package repository. Simply add:

deb http://apsy.gse.uni-magdeburg.de/debian sarge main

to your /etc/apt/sources.list and installing the firewall is then as easy as:

apt-get install arno-iptables-firewall

That way one can automatically profit from any package update. Even if no binary package is available one could build it by adding:

deb-src http://apsy.gse.uni-magdeburg.de/debian/source ./

to /etc/apt/sources.list and execute:

        apt-src install arno-iptables-firewall
        apt-src build arno-iptables-firewall

| Quick setup |

If you want to have it run quickly or are a novice user than this is the part that's important. Remember that my firewall has a lot of other useful features which will NOT be used in this way. On the other hand, various security features are enabled by default to protect you from hostile attacks.

First we've to check whether your Linux setup is OK in order to make the script work correctly:
- It of course requires iptables to be installed. It's recommended to get the latest version (package), if possible. This prevents any incompatibilities or bugs my script might have with older versions and the latest version contains all known (security) fixes, which strengthens the firewall itself.
- Make sure that you have a kernel with iptables compiled into it or a module-based kernel with the iptables modules installed. This is NOT possible when ipchains is still installed. If ipchains is installed (default for RedHat 7.1) you need to do "rmmod ipchains" first before running this script.
- It requires /bin/sh (should live on any Unix system by default)
- My scripts needs the following binaries in your path: ifconfig, modprobe, logger, grep, uname, sed, date, cut & awk.
- If you want to enable resolving of IPs ($RESOLV_IPS) then the command 'dig' should also be available.
Now we need to determine whether you have a single- or dual-homed machine.
Single means you ONLY have one network-interface, which is the one connected to the outside "evil" world (internet). Dual-homed also have a local subnet connected to an additional network interface.
Put arno-iptables-firewall in either /etc/init.d or /etc/rc.d (depending on your distribution and put the contents of the tarball's /etc/ to your system's /etc/. You probably also want to automatically start the firewall-script at system boot. There are various ways to accomplish this (depending on your distribution), here are some examples:
- RedHat / Fedora:
  Drop a line like "/etc/rc.d/arno-iptables-firewall start" in the file "/etc/rc.d/rc.local" (probably at or near the end). Note that the script has a chkconfig-compatible header, so if you're familar with it you can use this to stop/start the script in the different runlevels. In this case don't start it from "/etc/rc.d/rc.local" but instead put the script itself in /etc/init.d/ (instead of /etc/rc.d/) and run "chkconfig arno-iptables-firewall on".
- Debian:
  Put arno-iptables-firewall in "/etc/init.d/" and create a symlink to it in "/etc/rcS.d/" (eg. "ln -s /etc/init.d/arno-iptables-firewall /etc/rcS.d/S99-arno-iptables-firewall").
  On Debian (but also possibly with other distributions) you probably want to modify your klogd daemon to get rid of firewall logs being spit to the console. Just peform the following actions (the order is very important!):
  - Change "/etc/init.d/klogd" and make KLOGD="-c 4" (when having problems with logging you may also want to try KLOGD="-c 4 -s")
  - /etc/init.d/sysklogd stop
  - /etc/init.d/klogd stop
  - /etc/init.d/sysklogd start
  - /etc/init.d/klogd start

This should circumvent a lot of irritation :-D

Now we will change the required settings in "firewall.conf" :

4) Configure your external network interfaces, EXT_IF. In case of a

dual(multi)-homed it's the interface which is connected to the internet, in case of a LAN it's the one connected to your network. When you have an (dynamically) IP assigned to you (by your ISP) via DHCP, you should set "EXT_IF_DHCP_IP=1" else leave it off (0, default).

5a) For dual-homed machines you should also configure INT_IF, the interface

used for the local network and you should set your local subnet range in "INTERNAL_NET=". If you want your internal network to be able to access the internet (aka. internet-sharing), you should also enable NAT (masquerading) by setting "NAT=1").

5b) For single-homed machines (part of a LAN), you shouldn't touch INT_IF

(leave it disabled) and just stick to using EXT_IF (as you did in step 4). In this case you can make your local subnet trusted by adding your local subnet range to "FULL_ACCESS_HOSTS".

6) If you don't have an (A)DSL modem (which works with a PPtP connection to

your machine) or you have a bridging (transparent) modem, you can continue with step 7 (You can verify this with 'ifconfig', if a ppp device with your public IP exists you should (most likely) configure the (A)DSL MODEM settings).

Now we must configure the network interface(ethX) to which your modem is physically(!) connected (=MODEM_IF, which is commented(#) out by default), and this is NOT ppp+, ppp0 etc.! Here are some examples on how to do it for some providers (it's assumed that the modem is connected to eth0):

PPPoE connection with a static public IP (eg. MxStream in the Netherlands) (setup with the ADSL4Linux package from http://www.adsl4linux.nl):

MODEM_IF="eth0"
MODEM_IF_IP="10.0.0.150"
MODEM_IP="10.0.0.138" # Make sure this IP corresponds to the
one used by your modem!
EXT_IF_DHCP_IP=0

T-DSL (Germany) with a dynamic public IP:

MODEM_IF="eth0"
MODEM_IF_IP="192.168.99.1"
MODEM_IP=""
EXT_IF_DHCP_IP=1

PPPoA connection with a dynamic public IP:

MODEM_IF="eth0"
MODEM_IF_IP="" # This MUST be unset("") (default)
MODEM_IP="10.0.0.138" # Make sure this IP corresponds to the
one used by your modem!
EXT_IF_DHCP_IP=1

NOTE 1: For extra security you can set the IP of your modem (MODEM_IP),

           but it's not neccessary (anymore). If you don't know its IP or
           believe it doesn't have an IP, you can leave MODEM_IP="" (default).
           The same applies for the IP of the modem network interface
           (MODEM_IF_IP).

NOTE 2: If both your modem AND your network interface don't have an IP

you probably don't have to configure your modem settings (at all).

NOTE 3: In case of a PPPoA (PPP-over-ATM) you MUST leave MODEM_IF_IP

unset(="")!

7) When your public IP is assigned to you by your ISP (through DHCP) then you

should enable support for an DHCP external assigned IP by setting "EXT_IF_DHCP_IP=1".

8) Now we configure what ports should be open for the outside world. If you, for

example, are running an HTTP-server(port 80), an SSH-server(port 22), and/or an FTP-server (port 21) which should be accessible from the internet you should configure the OPEN_TCP / OPEN_UDP variables like this: OPEN_TCP="21 22 80"
OPEN_UDP=""

Some people mentioned that protocols like IRC or some (older) FTP/POP3/SMTP servers don't work (properly) if port 113(Identd) is filtered (firewalled). I really hate the fact that these type of protocols still depend on the "not-so-secure" IDENT-protocol. But if you really need it, you can do 2 things to make them work properly:

If you don't want to run an IDENT-daemon, simply add port 113 to the REJECT_TCP-variable (Recommended).
Or if you really want to run an IDENT-daemon, you should add port 113 to the OPEN_TCP-variable. (Not recommended)
You're now ready to start the firewall by issueing
"/etc/init.d/arno-iptables-firewall start" (or whatever place you've put in). Everything should now work OK, if it doesn't, carefully review all steps and your configuration. For troubleshouting you can consult my webpage (FAQ).

NOTE 1: Make sure that when you use NAT, you should properly configure the

           client's "default gateway" and the (public) DNS server(s) it should
           use! Note that you don't have to setup any proxy settings in eg.
           your client's browser.

NOTE 2: Additional (more advanced) options are (also) explained in the

           configuration-file comments and in the QA's on my webpage (eg.
           Freeswan/VPN support).

What if it doesn't work?:

Check your settings (.conf) at least 10 times. It's quite common for a human being to make mistakes. TIPS / Common errors:
- Make sure that EXT_IF, MODEM_IF and/or INT_IF are not the same. If they are, YOU made a mistake, as they can never EVER be the same!
- Another error I once saw was someone that used something like "127.0.0.0/24" for his local subnet. "127.0.0.0" is the address of the local loopback and therefor should never ever appear in the configuration file!
Obtain the latest version of your (distribution) kernel & iptables.
Make sure your (self-built) kernel supports all required options.
Carefully inspect the output generated by arno-iptables-firewall when the "start" command is invoked.
Read the README file at least 3 times
Download the latest (beta) version of my script and check whether this fixes your problem.
Read the README file one more time and review your .conf-file also one more time, just in case ;-)
Post your question on the firewall mailing list. Provide us with:
- your (firewall) *.conf files
- any screen output (including the output generated by arno-iptables-firewall when the "start" command is invoked! )
- the output of 'ifconfig'
- (firewall) logs
- the version of my script you're using (or date if you use the development script)
- detailed explanation of your setup
- and anything else that might help Remember that people that don't obey these rules, get a low, very low priority, or won't get any reaction at all!

Plugin support

As of version 1.8.7-RC2 my firewall also supports plugins -> little scripts that implement specific stuff which doesn't exist in the main script (yet). They latest versions of all supported plugins can be found here:

http://rocky.eld.leidenuniv.nl/iptables-firewall/plugins/

Notes on plugins:

Plugins should be put in /etc/arno-iptables-firewall/plugins/
The priority/loading order of the plugins can be adjusted by the changing the number in front of the plugin-name (50=default). Increasing the number gives lower priority, decreasing the number gives higher priority.
All plugins have an option called "ENABLED" (in their config file) which is set to 0 by default, meaning it is disabled. So if you actually want to use a plugin, you have to make ENABLED=1
Plugins can have their own additional set of configuration variables, don't forget to set/review those too.

Currently plugins exist that implement Racoon/IPSEC(VPN) support, Freeswan/IPSEC support, multirouting support and SSH-Brute Force Protection. Everyone is invited to write their own plugins to implement other things, and to submit them.

Notes on writing your own plugins:

When you write your own plugins, make sure you know what you're doing. You can severely compromise security or break things with buggy plugins.
The plugin should have/use these variables:
- PLUGIN_NAME (Plugin name/description)
- PLUGIN_VERSION (Plugin version)
- CONF_FILE (Location of the plugin config file)

Furthermore it should honour the ENABLED variable from the config-file to enable/disable the plugin.

Use one of my plugins as a template(skeleton) for writing your own plugins (I recommend to have a look at the "SSH Brute-Force protection"-plugin), in this way it's easier to understand for me and for others. 3) Plugins should have a seperate config file (.conf) with all user-configurable

variables. It should at least contain the "ENABLED="-variable to enable/disable the plugin.
4) Plugins should also have a seperate file with their CHANGELOG (.CHANGELOG) 5) Plugins can use all variables/functions from the main-script and main

configuration file. Plugin specific configuration variables should be put inside the plugin's configuration file (.conf). 6) Make sure that when you create new iptables-chains, that they don't conflict

with the main script or other plugins. The same goes for the iptables MARK-module, make sure that you use an unique MARK-number that doesn't conflict with other plugins.
7) Submit plugins to me, if you think they can be of use to others, but note

that I always reserve the right to decline the plugin (because it was ie. poorly written). Submitted plugins must be (at least) compatible with the GPLv2 license.

Loadbalancing/multirouting (with multiroute masquerade/SNAT)

My firewall also supports multirouting (loadbalancing), optionally in conjunction with NAT. Although this works with both conventional masquerading and SNAT, it's strongly recommended to use SNAT. This is because the latter is known to have a much lower chance of causing problems. Also note that I haven't found a way (yet) to make this work with dynamic external(internet) IP's, meaning you need static IP's from your ISP.

First of all, if you want to use multirouting, make sure that your (vanilla)-kernel has the following network features enabled (ie. when building from source):
- CONFIG_IP_ADVANCED_ROUTER=y
- CONFIG_IP_MULTIPLE_TABLES=y
- CONFIG_IP_ROUTE_MULTIPATH=y

Second, you should configure/enable the multiroute-plugin. And last but not least, you should setup the firewall: adding (all) the used external interfaces to EXT_IF. And when SNAT is used, add the corresponding external IP's to NAT_STATIC_IP. That's it!

NOTE: Redundant connections are (currently) not supported! This is limitation of the (current) Linux kernel (not of my firewall).

Info when building your own kernel (2.4 & 2.6) through "make menuconfig":

For the firewall to work properly you need the following options enabled (as modules or compiled in your kernel):
- "Loadable module support"

"Enable loadable module support" (If you want to build iptables as modules)
"Automatic kernel module loading" (Strongly recommended if you build iptables as modules) (Only available in newer 2.6 kernels) - "Networking", "Networking Support", "Networking Options" :
"Packet socket" (If you want to use dhcp client and/or server)
"TCP/IP networking"
- "IP: Multicasting"
- "IP: advanced router"
  - "IP: policy routing" (If you want to use load balancing, ie. multiroute masquerading)
  - "IP: equal cost multipath" (If you want to use load balancing, ie. multiroute masquerading)
- "IP: TCP syncookie support"
("Network packet filtering")
- "Core Netfilter Configuration" (For kernel =>2.6.16)
  - "Netfilter Xtables support (Required for ip_tables)"
    - "MARK" target support (Only required for special purposes like eg. traffic shaping & kernel 2.6 VPN support)
    - "conntrack" connection tracking match support
    - "limit" match support
    - "mac" address match support (If you want to use MAC filtering)
    - "state" match support
    - "tcpmss" match support (If you want to use tcpmss clamping)
- "IP: Netfilter Configuration":
  - "Connection tracking"
    - "Connection tracking flow accounting" (If you want to do accounting on your network traffic. (kernel 2.6 only)
    - "FTP protocol support"
  - "IP tables support" (NOTE: The order of sub-options can
    differ between kernel versions):
    - "IP range match support"
    - "Multiple port match support"
    - "TOS match support" (If you want to use TOS mangling)
    - "recent match support" (required for IDS & SSH brute-force protection)
    - "TTL match support" (If you want to use TTL manipulation)
    - "limit match support" (kernel <2.6.16)
    - "MAC address match support" (If you want to use MAC filtering) (kernel <2.6.16)
    - "Multiple port match support" (kernel <2.6.16)
    - "tcpmss match support" (If you use tcpmss clamping) (kernel <2.6.16)
    - "Connection state match support" (Kernel <2.6.16)
    - "Packet filtering" (kernel <2.6.16)
      - "REJECT target support"
    - "LOG target support"
    - "TCPMSS target support (If you want to use tcpmss-clamping)
    - "Full NAT" (If you use NAT/masquerading aka internet-sharing or transparent proxies)
      - "MASQUERADE target" (If you want to use masquerading)
      - "REDIRECT target support" (If you want to use port- forwarding, -redirection or transparent proxies)
    - "Packet mangling"
      - "TOS target support" (If you want to use TOS mangling)
      - "MARK target support" (Only required for special purposes like eg. traffic shaping & kernel 2.6 VPN support) (kernel <2.6.16)
      - "TTL target support" (if you want to use TTL manipulation