linuxbox as router

I think I've got most of this put together quite nicely but there is
one critical part I don't know what to do about, the networks can't
communicate with each other.

I have one normal pc with linux on (kubuntu 6.10, fresh install) and it
has one ethernet port on the motherboard (eth2) which is connected to a
cable modem that does not require any authentication. in this box I
have 2 pci ethernet cards, one is connected to a wireless access point
(eth0) that does not require any authentication and the other is
connected to a wired switch (eth1).

on eth2 I get a global ip (83.249.178.41/19), on eth0 I've set
192.168.1.1/24 and on eth1 I've set 192.168.2.1/24. I've installed
dhcp3-server and set it to listen on eth0 and eth1. I've created the
two subnets and all wireless gets 192.168.1.11-100/24 and all wired
gets 192.168.2.11-100/24 and the default gateways 192.168.1.1 and
192.168.2.1 respectively. everybody also gets the broadcast address
192.168.255.255 and the 2 dns servers from my isp as well as the 2 dns
servers of opendns.
all connected computers run windows xp home or pro.

the linuxbox can ping the internet, 192.168.1.* and 192.168.2.* and all
connected computers can ping all of the 3 linuxbox ip addresses and
everybody in their network but no one in the other network and no one
on the internet.

so now I need some help on what to do so that both networks can
communicate with each other and the internet.

xix xeaon wrote:
> I think I've got most of this put together quite nicely but there is
> one critical part I don't know what to do about, the networks can't
> communicate with each other.
>
> I have one normal pc with linux on (kubuntu 6.10, fresh install) and it
> has one ethernet port on the motherboard (eth2) which is connected to a
> cable modem that does not require any authentication. in this box I
> have 2 pci ethernet cards, one is connected to a wireless access point
> (eth0) that does not require any authentication and the other is
> connected to a wired switch (eth1).
>
> on eth2 I get a global ip (83.249.178.41/19), on eth0 I've set
> 192.168.1.1/24 and on eth1 I've set 192.168.2.1/24. I've installed
> dhcp3-server and set it to listen on eth0 and eth1. I've created the
> two subnets and all wireless gets 192.168.1.11-100/24 and all wired
> gets 192.168.2.11-100/24 and the default gateways 192.168.1.1 and
> 192.168.2.1 respectively. everybody also gets the broadcast address
> 192.168.255.255 and the 2 dns servers from my isp as well as the 2 dns
> servers of opendns.
> all connected computers run windows xp home or pro.
>
> the linuxbox can ping the internet, 192.168.1.* and 192.168.2.* and all
> connected computers can ping all of the 3 linuxbox ip addresses and
> everybody in their network but no one in the other network and no one
> on the internet.
>
> so now I need some help on what to do so that both networks can
> communicate with each other and the internet.

Short answer:

ip_forward and iptables. If you only wanted to go from 192.168 OUT to
the Internet, then you could also do this with a squid-proxy (if you're
only looking to get out with HTTP).

ip_forward (use /etc/sysctl.conf and set to "1) makes the Linux box
route. Ubuntu doesn't offer anything via Search so I can't verify a
command for ya.

iptables will do the NAT, start here:
http://www.netfilter.org/documentati...NAT-HOWTO.html,
specifically, look into masquerading.

This site looks like a good intro:
http://www.gophernet.org/articles/iptables/

-Gary

On Fri, 05 Jan 2007 10:57:12 -0800, xix xeaon wrote:

> the linuxbox can ping the internet, 192.168.1.* and 192.168.2.* and all
> connected computers can ping all of the 3 linuxbox ip addresses and
> everybody in their network but no one in the other network and no one on
> the internet.
>
> so now I need some help on what to do so that both networks can
> communicate with each other and the internet.

Running the following commands should achieve what you need, namely
load the iptable_nat module, masquerade your eth2 interface via NAT, and
enable IP forwarding.

sudo modprobe iptable_nat
sudo iptables -t nat -A POSTROUTING -o eth2 -j MASQUERADE
sudo sh -c "echo 1 > /proc/sys/net/ipv4/ip_forward

More details at
https://help.ubuntu.com/community/In...nectionSharing


> everybody also gets the broadcast address 192.168.255.255

They shouldn't. There should be a broadcast address for each subnet:
192.168.1.0/24 broadcast address 192.168.1.255
192.168.2.0/24 broadcast address 192.168.2.255



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