To setup internet connection sharing in Linux system using IPTables

Enable IP forwarding

Run as root

sysctl -w net.ipv4.ip_forward=1

To enable it in system startup, edit the file /etc/sysctl.conf and set

net.ipv4.ip_forward = 1

iptables

Run command as root

iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
service iptables save

Configuration

The configuration should be like this

Router

Connected to the internet provider
IP : 192.168.1.1

Internet Connected System

eth0 (LAN Card 1)

Connected to router

• IP : 192.168.1.10
• Netmask : 255.255.255.0
• Gateway : 192.168.1.1 (IP of the router)

eth1 (LAN Card 2)

Connected to the other system

• IP : 192.168.0.20 (Not the same network as the first card)
• Netmask : 255.255.255.0
• Gateway : 192.168.1.1 (IP of the router)

Second System

LAN Card connected to the first system

• IP : 192.168.0.30
• Netmask : 255.255.255.0
• Gateway : 192.168.0.20 (IP of the second Card in the first system)

Disclaimer

Linux networks is not a subject I am an expert on. So take my advice with a pinch of salt. The above procedure worked for me - so I am documenting it here so that I can reproduce it if I need it someday. YMMV.

This method can be used to share an internet connection from a Linux system(I used Fedora Core 6, but it should work on other distibutions that support iptables) to a Windows system. I used Windows XP.

Status

Some results of various commands are shown here. Check to see if it matches the result on your system.

# iptables -t nat -L POSTROUTING
Chain POSTROUTING (policy ACCEPT)
target     prot opt source               destination
MASQUERADE  all  --  anywhere             anywhere

# cat /proc/sys/net/ipv4/ip_forward
1

# iptables -L
Chain INPUT (policy ACCEPT)
target     prot opt source               destination

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

[tags]linux,network,internet,connection,sharing,iptables,cli,command,fedora[/tags]

Download the MS Core Fonts Smart Package File
wget http://corefonts.sourceforge.net/msttcorefonts-2.0-1.spec
Make sure that the rpm-build and cabextract packages are installed:
yum install rpm-build cabextract
Build the Core Fonts package:
rpmbuild -ba msttcorefonts-2.0-1.spec
Install the Core Fonts package:
rpm -Uvh /usr/src/redhat/RPMS/noarch/msttcorefonts-2.0-1.noarch.rpm

[tags]fonts,linux,design,install,reinstall[/tags]

Using yum command

usage: yum [options] < upgrade, install, update, info, search >

Use the -y option to bypass the confirmation.

Stuff I had to install after doing a Fedora Core 6 Install from DVD

Libraries

qca-tls

Multimedia

mplayer vlc xine gstreamer mplayer-fonts videolan-client
xine xine-lib xine-skins xine-lib-extras-nonfree libdvdcss
banshee
xmms xmms-mp3 gstreamer-plugins-ugly audacious-plugins-nonfree-mp3 kdemultimedia-extras-nonfree

Internet

ktorrent konversation

Coding

rapidsvn php-mysql

Tk

tclx tkinter gtkdevel ruby-tcltk pygtk2-devel tk-devel tcl-devel pygtk2 stardict tk pygtk2-libglade tkdnd perl-Gtk2 perl-Tk scite tkcon itcl itk iwidgets wxGTK wxGTK-devel compat-wxGTK compat-wxGTK2 compat-wxGTK-devel kgtk gtk-qt-engine

Others

fish
katapult
wine cabextract
comix d4x gtk-recordmydesktop