Visit Jeremy's Blog.
Go Back > Forums > Linux Forums > Linux - Newbie
User Name
Linux - Newbie This Linux forum is for members that are new to Linux.
Just starting out and have a question? If it is not in the man pages or the how-to's this is the place!


  Search this Thread
Old 05-10-2003, 09:44 PM   #1
LQ Newbie
Registered: May 2003
Posts: 2

Rep: Reputation: 0
Linux box as a router

I would like to use my old comp (PII400, 128 MB, 6.4 GB) as a router.
I have SuSE 8.1 installed and don't know what software do I need.

Please reply in simple English because I am a 100% newbie.

Step by step instructions would be great.

I have 2 more computers and cable connection (Windows 2000).

Old 05-10-2003, 10:29 PM   #2
LQ Guru
Registered: Mar 2002
Location: Salt Lake City, UT - USA
Distribution: Gentoo ; LFS ; Kubuntu ; CentOS ; Raspbian
Posts: 12,613

Rep: Reputation: 69
I wish it were that simple...

You might need to brush up a bit on Networking first, but here's my go at it:

Slap a few Ethernet Cards (fast ones, 10/100/1000 are preferable) into your box. Configure each one as eth0 eth1 eth2 and so on (depending on how many boxes will be connecting, remember you'll need a line in from your DSL/Cable modem so include an extra Card)

Configuring the cards will be the easy part. You'll need to install certain applications such as dhcp(both client and server) BIND and DNS (If you are going be running your own internal network). From there it's just following step by step tutorials/README's associated with each application. You can also find How-To's over at on these things.

IPMasquerading, IPTables, and DHCP are going to be the things to get setup first though.


Old 05-10-2003, 11:00 PM   #3
Registered: Apr 2003
Location: North Hollywood Ca
Distribution: RedHat FreeBSD
Posts: 130

Rep: Reputation: 16
if your pc's are already pinging by hostname through the servers internal interface simply place this script in /etc/init.d

# rc.firewall-2.4
# Initial SIMPLE IP Masquerade test for 2.4.x kernels
# using IPTABLES.
# Once IP Masquerading has been tested, with this simple
# ruleset, it is highly recommended to use a stronger
# IPTABLES ruleset either given later in this HOWTO or
# from another reputable resource.
# Log:
# 0.73 - REJECT is not a legal policy yet; back to DROP
# 0.72 - Changed the default block behavior to REJECT not DROP
# 0.71 - Added clarification that PPPoE users need to use
# "ppp0" instead of "eth0" for their external interface
# 0.70 - Added commented option for IRC nat module
# - Added additional use of environment variables
# - Added additional formatting
# 0.63 - Added support for the IRC IPTABLES module
# 0.62 - Fixed a typo on the MASQ enable line that used eth0
# instead of $EXTIF
# 0.61 - Changed the firewall to use variables for the internal
# and external interfaces.
# 0.60 - 0.50 had a mistake where the ruleset had a rule to DROP
# all forwarded packets but it didn't have a rule to ACCEPT
# any packets to be forwarded either
# - Load the ip_nat_ftp and ip_conntrack_ftp modules by default
# 0.50 - Initial draft

echo -e "\n\nLoading simple rc.firewall version $FWVER..\n"

# The location of the iptables and kernel module programs
# If your Linux distribution came with a copy of iptables,
# most likely all the programs will be located in /sbin. If
# you manually compiled iptables, the default location will
# be in /usr/local/sbin
# ** Please use the "whereis iptables" command to figure out
# ** where your copy is and change the path below to reflect
# ** your setup

#Setting the EXTERNAL and INTERNAL interfaces for the network
# Each IP Masquerade network needs to have at least one
# external and one internal network. The external network
# is where the natting will occur and the internal network
# should preferably be addressed with a RFC1918 private address
# scheme.
# For this example, "eth0" is external and "eth1" is internal"
# NOTE: If this doesnt EXACTLY fit your configuration, you must
# change the EXTIF or INTIF variables above. For example:
# If you are a PPPoE or analog modem user:
# EXTIF="ppp0"
echo " External Interface: $EXTIF"
echo " Internal Interface: $INTIF"

#== No editing beyond this line is required for initial MASQ testing ==

echo -en " loading modules: "

# Need to verify that all modules have all required dependencies
echo " - Verifying that all kernel modules are ok"

# With the new IPTABLES code, the core MASQ functionality is now either
# modular or compiled into the kernel. This HOWTO shows ALL IPTABLES
# options as MODULES. If your kernel is compiled correctly, there is
# NO need to load the kernel modules manually.
# NOTE: The following items are listed ONLY for informational reasons.
# There is no reason to manual load these modules unless your
# kernel is either mis-configured or you intentionally disabled
# the kernel module autoloader.

# Upon the commands of starting up IP Masq on the server, the
# following kernel modules will be automatically loaded:
# NOTE: Only load the IP MASQ modules you need. All current IP MASQ
# modules are shown below but are commented out from loading.
# ===============================================================

echo "----------------------------------------------------------------------"

#Load the main body of the IPTABLES module - "iptable"
# - Loaded automatically when the "iptables" command is invoked
# - Loaded manually to clean up kernel auto-loading timing issues
echo -en "ip_tables, "
$INSMOD ip_tables

#Load the IPTABLES filtering module - "iptable_filter"
# - Loaded automatically when filter policies are activated

#Load the stateful connection tracking framework - "ip_conntrack"
# The conntrack module in itself does nothing without other specific
# conntrack modules being loaded afterwards such as the "ip_conntrack_ftp"
# module
# - This module is loaded automatically when MASQ functionality is
# enabled
# - Loaded manually to clean up kernel auto-loading timing issues
echo -en "ip_conntrack, "
$INSMOD ip_conntrack

#Load the FTP tracking mechanism for full FTP tracking
# Enabled by default -- insert a "#" on the next line to deactivate
echo -en "ip_conntrack_ftp, "
$INSMOD ip_conntrack_ftp

#Load the IRC tracking mechanism for full IRC tracking
# Enabled by default -- insert a "#" on the next line to deactivate
echo -en "ip_conntrack_irc, "
$INSMOD ip_conntrack_irc

#Load the general IPTABLES NAT code - "iptable_nat"
# - Loaded automatically when MASQ functionality is turned on
# - Loaded manually to clean up kernel auto-loading timing issues
echo -en "iptable_nat, "
$INSMOD iptable_nat

#Loads the FTP NAT functionality into the core IPTABLES code
# Required to support non-PASV FTP.
# Enabled by default -- insert a "#" on the next line to deactivate
echo -en "ip_nat_ftp, "
$INSMOD ip_nat_ftp

#Loads the IRC NAT functionality into the core IPTABLES code
# Require to support NAT of IRC DCC requests
# Disabled by default -- remove the "#" on the next line to activate
#echo -e "ip_nat_irc"
#$INSMOD ip_nat_irc

echo "----------------------------------------------------------------------"

# Just to be complete, here is a list of the remaining kernel modules
# and their function. Please note that several modules should be only
# loaded by the correct master kernel module for proper operation.
# --------------------------------------------------------------------
# ipt_mark - this target marks a given packet for future action.
# This automatically loads the ipt_MARK module
# ipt_tcpmss - this target allows to manipulate the TCP MSS
# option for braindead remote firewalls.
# This automatically loads the ipt_TCPMSS module
# ipt_limit - this target allows for packets to be limited to
# to many hits per sec/min/hr
# ipt_multiport - this match allows for targets within a range
# of port numbers vs. listing each port individually
# ipt_state - this match allows to catch packets with various
# IP and TCP flags set/unset
# ipt_unclean - this match allows to catch packets that have invalid
# IP/TCP flags set
# iptable_filter - this module allows for packets to be DROPped,
# REJECTed, or LOGged. This module automatically
# loads the following modules:
# ipt_LOG - this target allows for packets to be
# logged
# ipt_REJECT - this target DROPs the packet and returns
# a configurable ICMP packet back to the
# sender.
# iptable_mangle - this target allows for packets to be manipulated
# for things like the TCPMSS option, etc.

echo -e " Done loading modules.\n"

#CRITICAL: Enable IP forwarding since it is disabled by default since
# Redhat Users: you may try changing the options in
# /etc/sysconfig/network from:
# FORWARD_IPV4=false
# to
echo " Enabling forwarding.."
echo "1" > /proc/sys/net/ipv4/ip_forward

# Dynamic IP users:
# If you get your IP address dynamically from SLIP, PPP, or DHCP,
# enable this following option. This enables dynamic-address hacking
# which makes the life with Diald and similar programs much easier.
echo " Enabling DynamicAddr.."
echo "1" > /proc/sys/net/ipv4/ip_dynaddr

# Enable simple IP forwarding and Masquerading
# NOTE: In IPTABLES speak, IP Masquerading is a form of SourceNAT or SNAT.
# NOTE #2: The following is an example for an internal LAN address in the
# 192.168.0.x network with a or a "24" bit subnet mask
# connecting to the Internet on external interface "eth0". This
# example will MASQ internal traffic out to the Internet but not
# allow non-initiated traffic into your internal network.
# ** Please change the above network numbers, subnet mask, and your
# *** Internet connection interface name to match your setup

#Clearing any previous configuration
# Unless specified, the defaults for INPUT and OUTPUT is ACCEPT
# The default for FORWARD is DROP (REJECT is not a valid policy)
echo " Clearing any existing rules and setting default policy.."
$IPTABLES -t nat -F

echo " FWD: Allow all connections OUT and only existing and related ones IN"

echo " Enabling SNAT (MASQUERADE) functionality on $EXTIF"

echo -e "\nDone.\n"

read at top what to change for your configuration. only a couple of things ie location of iptables and inetface config ie ppp0, eth1, eth0

then to load at start up paste this at the end of /etc/rc.d/rc.local.
be shure to chmod 700 /etc/rc.d/rc.firewall to make it executable
then /etc/rc.d/rc.firewall will load ruleset and your golden.

# This script will be executed *after* all the other init scripts.
# You can put your own initialization stuff in here if you don't
# want to do the full Sys V style init stuff.

touch /var/lock/subsys/local

echo "Loading the rc.firewall ruleset.."

Old 05-11-2003, 12:37 AM   #4
LQ Newbie
Registered: May 2003
Posts: 2

Original Poster
Rep: Reputation: 0
Thanks for your help I'll try this in the morning.
Old 05-11-2003, 03:18 PM   #5
Registered: May 2003
Location: Israel
Distribution: Ubuntu 5.10
Posts: 32

Rep: Reputation: 15
Look at

They have a free mini linux distro which, i think may do exactly what you want - you just need any old pc with two network cards.

I'm told it has never been breached as a firewall and is a very fast router (although i guess you will need a hub/switch behind it to get all your computers on).

Best of luck

Let us know how u get on as i'm interested in trying it (when i get my hands on another pc!!)

Old 05-11-2003, 03:20 PM   #6
Registered: May 2003
Location: Israel
Distribution: Ubuntu 5.10
Posts: 32

Rep: Reputation: 15

I should add that you wont be able to do anything else with your box once you have smoothwall installed. maybe not suitable for you.

Old 05-12-2003, 10:16 AM   #7
LQ Newbie
Registered: May 2003
Location: Canada, BC, White Rock
Distribution: slackware
Posts: 4

Rep: Reputation: 0
I think that routerlinux (RLP) would be best bet for you, but get a crappyer comp for sumthin like a router, u want sumthin like a p1
133mhz with 8mb ram and like a floppy drive/cdrom drive oh and a 200mb harddrive should be all u need.
Old 05-18-2003, 01:56 PM   #8
Registered: Mar 2003
Location: a little west of Birmingham, AL, USA.
Distribution: Porteus 3.1
Posts: 934

Rep: Reputation: 32
I prefer a Pentium MMX with about 32MB Ram since they're so available to me. Also, I'd like to hold on to this!
Old 08-08-2003, 04:05 PM   #9
Registered: Jun 2001
Location: Recycle Bin
Distribution: Linux & Everything else on VirtualBox
Posts: 144

Rep: Reputation: 15
That script is from the Linux Masquerading HOWTO and it states that it is for "TESTING ONLY". Basically it opens your computer wide open so you can see if everything will work. If you are using that script as a firewall/router then you are at great risk. The other script in the HOWTO i.e. the "STRONGER" one is much better to use as a firewall/router.


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
linux box as a router cambie Linux - Networking 4 11-21-2004 10:01 AM
linux box as router cambie Linux - Networking 10 11-16-2004 12:20 AM
Using Linux Box as a Router wasabi Linux - Networking 5 09-04-2003 05:08 PM
Linux box as router AkumaLoka Linux - Networking 3 10-14-2002 04:57 PM
Linux box as router Kapone Linux - Networking 5 07-04-2001 06:50 AM > Forums > Linux Forums > Linux - Newbie

All times are GMT -5. The time now is 12:29 PM.

Main Menu
Write for LQ is looking for people interested in writing Editorials, Articles, Reviews, and more. If you'd like to contribute content, let us know.
Main Menu
RSS1  Latest Threads
RSS1  LQ News
Twitter: @linuxquestions
Open Source Consulting | Domain Registration