After much ado, I got my local LAN working. I can see files on the other computer, etc.
But I can't connect to the net from newcomp (192.168.3.10) via oldcomp (192.168.3.9), although that is the address set as gateway.
Can anyone help? A tip about what conf files may need altering? I set things up by hand in exports, host.allow and host.deny, as I found the wizards couldn't do it right.

If you have iptables:


#enable forwarding
echo 1 > /proc/sys/net/ipv4/ip_forward

iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

(assuming eth0 is your external nic)

I think this is enough to have internet on both computers...

You should search a bit more the forum and the internet. There are lots of how-to about this. You should also read the iptables documentation at iptables website (netfilter) and undestand how it works and set up a firewall.

I started by using some iptables rules I found on this forum. After understanding how iptables works, I changed them to fit my needs.

/proc/sys//net/ipv4/ipforward contains only
0

The last time I messed with iptables via LinWiz, an automatic configurer, nothing worked and the network was blocked.
If I enter the above iptables command, where does it write to? The conf file? So that I can erase it if needed!

ip_forward should contain 1 or you wont be able to share internet. Type this to put 1 into that file

echo 1 > /proc/sys/net/ipv4/ip_forward



That iptables rule wont block anything and will be lost when rebooting. If you want to keep it you'll have to had it to an initialization script.

You can also delete it without rebooting by entering iptables -F (flush rules)

iptables is an executable, right? Does it read a .conf file when executed? Which file contains all the ACCEPT and REJECT and CHAINS and so on? I didn't see that in the man page, but then it is very long!
Thanks
Peter

AFAIK, iptables doesn't read any conf file by default. You can save iptables rules to a file and then restore them with iptables-save and iptables-restore.

I did exactly as you said, I have a 1 in ip_forward, and entered the command
/sbin/iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
but, no access from the computer without a modem!
I just get "could not be found".
Got any more tips??

Have you set the dns servers on the new computer?

No, I don't know if I have a DNS service running, but I'll look into it. Now, as the wife and boys aren't here, it's quiet!
But I know that on the new computer I did set the gateway to 192.168.3.9, somewhere in a wizard.

Your ISP should have a DNS server running. The computers using the gateway must know the DNS server address or they wont be able to query it about hostnames. DNS servers translate hostnames into IP addresses.

I have a DHCP server running on my gateway that automaticaly configures all computers' network interfaces with this info. You can learn how to configure something like this or you can add a fixed address to each computer.

But I'm not sure this is your only problem. To test this you can try pinging an IP address from your new computer. Try

ping 64.179.4.149

This is linuxquestions.org ip address. If you get an answer, you can connect to the internet. Now try

ping www.linuxquestions.org

If this time you don't get any answer, you're problem is the name resolution, ie, you have to configure your new computer with the DNS server IP address.

My comps have fixed addresses
oldcomp is 192.168.3.9
newcomp is 192.168.3.10

I told the newcomp to use oldcomp as a gateway, using the number, not the name.
ping 64.179.4.149 is stalled at this moment, so I guess it can't reach outside. I'll have to kill it.
With just two comps, I don't think I need dhcp, although I have set it up, once.
Ping is still stalled, I'll get back to you,
Thanks Peter

Don't forget that iptables loses it's rules when you reboot.

If you can't ping, I may not be able to help you anymore Maybe someone else has more ideas