On Fri, 19 Jul 2002, Ramon Casha wrote: > The Internet Connection Sharing utility in Mandrake Control Centre (8.2) does > not list eth0 or any aliases. Apparently there is an assumption that the > internet connection won't be on the same interface card. However, this can > easily be the case with, for instance, ADSL connections.
My point here is: with most home<->internet connection services, your ISP doesn't want you to share your connection with other machines. IMHO this is a bad policy: technically, sharing your connection doesn't steal bandwidth to anyone. But if the contract with your ISP says that you won't share it and you do, you break the rules. Furthermore, using only one ethernet card on your gateway PC may have some side effects. > I have successfully set up my ADSL connection, using eth0 with the address > 10.0.0.10 making the connection to the modem, and eth0:0 with the address > 192.168.0.1 set up as the connection-sharing interface. I had to twist the > configuration script's arms a little to make it accept eth0:0 but it worked. > Perhaps this limitation can be removed from the script -- unless there was a > good reason for its inclusion that is. I presume you hook all your machines, including the ADSL device, on a common hub. Diagram: local machines including gateway PC <=> hub <->ADSL<->internet Sharing a connection this way works, but is somewhat dirty. Let's assume you do it this way. Technically, there's nothing wrong about having different logical subnets on one physical ethernet link, as long as devices really comply with ethernet rules and RFCs. But are you sure that the ADSL gateway handles properly packets with private IP ? Does it really respect ethernet specifications (e.g. ignore all packets not specifically sent to it) ? Maybe it sends to the other side of the ADSL connection any packets it receives from the ethernet wire ? Why ask ? Well, the ADSL device you have is supposed to handle the case where you link it directly to only one machine. Any other setup may have unexpected results. No one told you that it was configured to be RFCs conformant. It might even be programmed to report any unregular usage to the ISP. What about broadcast packets send from a local machine to the local (private) broadcast destination ? Accorging to ethernet rules, the gateway will receive them (they're broadcast). Perhaps the ADSL gateway doesn't know they're private, and it sends them to the internet, eating your upload bandwidth (usually 128kbps on ADSL). According to RFCs, it shouldn't, but your ISP never claimed anything about that case. Think about what may happen if you have some windows machine on the local net, or some cups server or clients. They like to broadcast information. The clean way: If your home PC has two ethernet cards, and you link it the regular way: local machines <=> hub <->eth1 gateway PC eth0<->ADSL<->internet then as far as the ADSL device and your ISP are concerned, all hypotheses are valid. You can't disturb the ADSL device or let private packets go out. Technically you plug only one PC on the ADSL devices, like your contract says.0 And a bonus: your gateway PC can act as a real, physical firewall (with Bastille for example, for an easy start). A second ethernet card is cheap (less than 15 euros). You can afford it. -- St�phane Gourichon - Labo. d'Informatique de Paris 6 - AnimatLab http://animatlab.lip6.fr/ - philo du dimanche http://amphi-gouri.org/
