2 computer network from Wi-Fi

[Kevin J. Cummings]

THUFIR HAWAT wrote:
> I don't have physical access to the router which provides the internet
> access.  an asus wl-330g,
> <http://usa.asus.com/products/communication/wireless/wl-330g/overview.htm>,
> provides
> the connection to the router.  the wl-330g has been tested, and works,
> in both eth0 and eth1 for the arrakis computer.
> 
> there are two computers, named arrakis and caladan.  the setup is:
> 
> internet        -->  router
> router          -->  wireless signal
> wireless signal -->  wl-330g network adapter
> wl-330g         -->  arrakis eth0
> arrakis eth1    -->  hub
> hub             -->  caladan eth1
> hub             -->  PAP2
> PAP2            -->  telephone
> 
> the PAP2 <http://www.linksys.com/products/product.asp?prid=651&scid=38>
> is for VOIP and is from <http://www.telnetphone.ca/>.
> 
> does arrakis need to be configured as a gateway?

If you want arrakis to forward packets from eth1 to eth0, you need to 
enable IP forwarding.  Its a kernel parameter, and can be specified in 
your /etc/sysctl.conf by adding the following lines:

> # Controls IP packet forwarding
> net.ipv4.ip_forward = 1

(without the "> " parts)

Make sure to reboot your kernel after adding those lines, *or*

/sbin/sysctl net.ipv4.ip_forward=1

to make it happen immediately.  This will allow packets from caladan to 
be forwarded through arrakis to the internet.  Caution:  routers beyond 
arrakis *must* know how to route back to caladan!  If they don't 
recognize the IP address, you won't get a packets back!  If this is the 
case, you might be able to get around that by enabling masquarading 
(NAT) on arrakis.  Then caladan's packets will be sent out with arrakis' 
IP address as the return point, and arrakis will forward any return 
packets to caladan.  NAT must be enabled in arrakis' iptables 
configuration.  I used the following rules:

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

and my computer forwards and NATs the computers on my home and USB 
networks.....

-- 
Kevin J. Cummings
kjchome at rcn.com
cummings at kjchome.homeip.net
cummings at kjc386.framingham.ma.us