Share Internet Connection from computer to new router

Question

On my linux computer I have an external wlan adapter which is connected wirelessly to internet (an access point). Now I want to connect my linux computer via ethernet cable to a new ddwrt router. This ddwrt router should now "get" internet from my linux computer, so that my linux computer is acting like a internet sharing box.

INTERNET <- over wlan (wlan0) -> LINUX COMPUTER <- ethernet eth0 -> DDWRT Router

Anyone should now be able to connect wirelessly to the ddwrt router to get internet. How should I configure my linux computer to make it work? Thanks!

Is the wlan0 a static or dynamic IP? – slm Dec 26 '12 at 20:20 — slm, Dec 26 '12 at 20:20

score 4 · Answer 1 · answered Dec 26 '12 at 20:45

If I understand what you're afer, you want the following:

You <-> Home systems <-> DDWRT Router <-> Linux Box <-> Internet

If so then you'll need to do a couple of things on your Linux laptop. Depending on what distro you're using the steps will be slightly different. My steps are for a Fedora Redhat distro.

% vim /etc/sysconfig/network-scripts/ifcfg-eth0

Contents of ifcfg-eth0:

DEVICE=eth0
BOOTPROTO=none
BROADCAST=xx.xx.xx.255  # Optional Entry
IPADDR=xx.xx.xx.xx
NETMASK=255.255.255.0   # Provided by the ISP
NETWORK=xx.xx.xx.0     # Optional
ONBOOT=yes
TYPE=Ethernet
USERCTL=no
IPV6INIT=no
PEERDNS=yes
GATEWAY=xx.xx.xx.xx # The linux laptop's lan ip

Flush your iptables:

% iptables --flush
% iptables --table nat --flush
% iptables --delete-chain
% iptables --table nat --delete-chain

Now configure masquerading:

% iptables --table nat --append POSTROUTING --out-interface wlan0 -j MASQUERADE
% iptables --append FORWARD --in-interface eth0 -j ACCEPT

Configure NAT forwarding:

% echo 1 > /proc/sys/net/ipv4/ip_forward

Make this permanent, by adding the following line:

% vim /etc/sysctl.conf
net.ipv4.ip_forward = 1

Restart iptables service:

% service iptables restart

These are the steps from my memory so you may run into a issue here or there but they're pretty much all the steps you'll need to setup a Linux box as a router/switch.

NOTE: You'll also need to setup any devices on the LAN side so that their default route is the IP address of the Linux boxes LAN connection (eth0).

Resources

Share Internet Connection from computer to new router

1 Answers1