Help with routing problem?

A friend is having problems setting up a small network. He has a PC server
with three NICs in configured as below:
____
| |-----192.168.10.1
192.168.0.2----| PC |
|____|-----192.168.20.1

The 192.168.0.2 goes via a smoothwall server (192.168.0.50) and asdl modem
to the internet. The 192.168.10 and 20 have hubs connected to them.

The problem is anything connected to either hub cannot connect to the
internet even though the PC can. We are assuming this is some kind of
routing problem but cannot figure it out. Can somebody help us out here.

Output of route -n is:

Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Ifac
192.168.20.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1
192.168.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth2
192.168.10.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
127.0.0.0 0.0.0.0 255.0.0.0 U 0 0 0 lo
0.0.0.0 192.168.0.50 0.0.0.0 UG 0 0 0 eth2

On Thu, 4 Sep 2003, A Ymous wrote:

> A friend is having problems setting up a small network. He has a PC server
> with three NICs in configured as below:
> ____
> | |-----192.168.10.1
> 192.168.0.2----| PC |
> |____|-----192.168.20.1
>
> The 192.168.0.2 goes via a smoothwall server (192.168.0.50) and asdl modem
> to the internet. The 192.168.10 and 20 have hubs connected to them.
>
> The problem is anything connected to either hub cannot connect to the
> internet even though the PC can. We are assuming this is some kind of
> routing problem but cannot figure it out. Can somebody help us out here.

Have you turned on forwarding?
% echo "1" > /proc/sys/net/ipv4/ip_forward

On Thu, 4 Sep 2003 23:17:21 +0000 (UTC), A Ymous <(E-Mail Removed)> wrote:
> A friend is having problems setting up a small network. He has a PC server
> with three NICs in configured as below:
> ____
> | |-----192.168.10.1
> 192.168.0.2----| PC |
> |____|-----192.168.20.1
>
> The 192.168.0.2 goes via a smoothwall server (192.168.0.50) and asdl modem
> to the internet. The 192.168.10 and 20 have hubs connected to them.
>
> The problem is anything connected to either hub cannot connect to the
> internet even though the PC can. We are assuming this is some kind of
> routing problem but cannot figure it out. Can somebody help us out here.

Assuming the 3 nic PC has ip_forward enabled, does the smoothwall server
know to route 192.168.10.0 and 192.168.20.0 networks to 192.168.0.2
(and to masquerade them to internet)? For example, on smoothwall:

route add -net 192.168.10.0 gw 192.168.0.2
route add -net 192.168.20.0 gw 192.168.0.2

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On Thu, 4 Sep 2003 23:17:21 +0000 (UTC), A Ymous <(E-Mail Removed)>
wrote:

>A friend is having problems setting up a small network. He has a PC server
>with three NICs in configured as below:
> ____
> | |-----192.168.10.1
>192.168.0.2----| PC |
> |____|-----192.168.20.1
>
>The 192.168.0.2 goes via a smoothwall server (192.168.0.50) and asdl modem
>to the internet. The 192.168.10 and 20 have hubs connected to them.
>
>The problem is anything connected to either hub cannot connect to the
>internet even though the PC can. We are assuming this is some kind of
>routing problem but cannot figure it out. Can somebody help us out here.
>
>Output of route -n is:
>
>Kernel IP routing table
>Destination Gateway Genmask Flags Metric Ref Use Ifac
>192.168.20.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1
>192.168.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth2
>192.168.10.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
>127.0.0.0 0.0.0.0 255.0.0.0 U 0 0 0 lo
>0.0.0.0 192.168.0.50 0.0.0.0 UG 0 0 0 eth2

The solution was to set up IP masquerading in iptables with the following
command:

iptables -t nat -A POSTROUTING -o eth2 -j MASQUERADE

Is this the right solution?

If it worked, it is a fine solution. Normally, you should not need to NAT
from one 192.168.x.x address to another, because the packets must be NATed
again anyway to be routable on the Internet. It may be that the DSL router
will only accept traffic from a single IP address as a way of trying to get
you to pay extra to the ISP to hook up multiple machines.

--

wcardwell at nc dot rr dot com