Help sharing a dial-up modem with two Ubuntu 6.10 computers

So close and yet so far...
I have two computers running Ubuntu 6.10 (Edgy Eft) at home. One has
an external dial-up modem to connect to the internet, which works
great (but obviously slow). We'll call this Computer A. The other one
has only a networking card, and we'll call it Computer B. Last night I
got the two computers to recognize each other over the network and
share files using (I think) a Samba share. I'm trying to get Computer
B to be able to access the internet when Computer A is dialed in.

I followed the instructions on the Firestarter website
http://www.fs-security.com/docs/connection-sharing.php but took the
path of static IPs instead of mucking around with a DHCP server.
_Almost_ everything works. I'm using IPs of 192.168.0.1 for Computer A
and 192.168.0.2 for Computer B. I can ping each one from the other and
get a response. As mentioned above, Computer B was able to copy files
from a shared folder on Computer A. So for the most part, networking
works. In the Firestarter preferences panel I have the "Internet
connected network device" set to the modem (PPP0) and the "Local
network connected device" set to the networking card (ETH0). Internet
connection sharing is checked, and the DHCP is diabled (not checked).

Now, here's the question: what do I need to do on Computer B to let
programs such as Firefox, Synaptic, etc. see the big bad intarweb-
hicky? They just sort of sit there twiddling their thumbs and saying
no connection found. The more detailed the instructions, the better.
Screenshots are good. I spent all night hunting the web for answers
and they were all hand-wavy and vague.

-Will

(E-Mail Removed) wrote:
> So close and yet so far...
> I have two computers running Ubuntu 6.10 (Edgy Eft) at home. One has
> an external dial-up modem to connect to the internet, which works
> great (but obviously slow). We'll call this Computer A. The other one
> has only a networking card, and we'll call it Computer B. Last night I
> got the two computers to recognize each other over the network and
> share files using (I think) a Samba share. I'm trying to get Computer
> B to be able to access the internet when Computer A is dialed in.
>
> I followed the instructions on the Firestarter website
> http://www.fs-security.com/docs/connection-sharing.php but took the
> path of static IPs instead of mucking around with a DHCP server.
> _Almost_ everything works. I'm using IPs of 192.168.0.1 for Computer A
> and 192.168.0.2 for Computer B. I can ping each one from the other and
> get a response. As mentioned above, Computer B was able to copy files
> from a shared folder on Computer A. So for the most part, networking
> works. In the Firestarter preferences panel I have the "Internet
> connected network device" set to the modem (PPP0) and the "Local
> network connected device" set to the networking card (ETH0). Internet
> connection sharing is checked, and the DHCP is diabled (not checked).
>
> Now, here's the question: what do I need to do on Computer B to let
> programs such as Firefox, Synaptic, etc. see the big bad intarweb-
> hicky? They just sort of sit there twiddling their thumbs and saying
> no connection found. The more detailed the instructions, the better.
> Screenshots are good. I spent all night hunting the web for answers
> and they were all hand-wavy and vague.
>
> -Will
>
Computer B needs to be set up to use Computer A as a gateway (to the
rest of the world). I don't know about firestarter, but Computer B's
/etc/network/interfaces file should look like:

auto eth0
iface eth0
address 192.168.0.2
netmask 255.255.255.0
gateway 192.168.0.1

and its /etc/resolv.conf file should contain the same as Computer A's.

Computer A should have a similar description of eth0 (with different
address and without the gateway line. It should also be configured to do
network address translation for Computer B. (the package ipmasq does it
well for be but I'm sure that there must be better ways by now).

Robert

> (E-Mail Removed) wrote:
>> [Using Computer A as gateway for Computer B]
>> Now, here's the question: what do I need to do on Computer B to let
>> programs such as Firefox, Synaptic, etc. see the big bad intarweb-
>> hicky?

Robert Harris covered most of the things you need to do.

In addition, Computer A needs to have IP forwarding turned on. If

$ cat /proc/sys/net/ipv4/ip_forward

returns 0, arrange for /etc/sysctl.conf to contain the line

net.ipv4.ip_forward = 1

Disclaimer: If Ubuntu puts this configuration information in some other
place, I'm sure someone will post a correction...