2 Ubuntu PCs, 1 WIFI, 1 Ethernet cable. How do I get them to share the WIFI?

Question

How do I get both my PCs connected to the modem on the other end of the house. The 2 PCs are next to each other and the Ethernet cable is just enough to connect the PCs together. Only one of the PCs has working wireless connection.

Answer 1

as root
echo 1 > /proc/sys/net/ipv4/ip_forward
set up dhcp
as root edit /etc/dhcp3/dhcpd.conf and make your network declaration look kind of like one that is commented out, substituting appropriate variables where necessary.

subnet 192.168.254.0 netmask 255.255.255.0 {  
  range 192.168.254.2 192.168.254.128;  
  option domain-name-servers 4.4.4.4;  
  option routers 192.168.254.1;  
  option broadcast-address 192.168.254.255;  
  default-lease-time 600;  
  max-lease-time 7200;  
}  

you could copy and paste that into the end of the file, but i think it's better to understand it

and the eth0 interface with a static ip of 192.168.254.1 would be a pretty reasonable setup

sudo service dhcp3-server restart

change any pertinent firewall rules - adding the following lines to the end of rc.local should do it to enable nat on next boot

/sbin/iptables -P FORWARD ACCEPT
/sbin/iptables --table nat -A POSTROUTING -o wlan0 -j MASQUERADE

I have a shell script that does this for me on startup

depending on the cards, the cable might need to be a crossover cable

one additional note, for ip_forward to be set at boot time edit /etc/sysctl.conf
and uncomment
net.ipv4.ip_forward=1

a more in depth tutorial is here: http://ubuntuforums.org/showthread.php?t=713874