UNIX for Dummies Questions & Answers

Ok, I'm kind of in between newbie and experienced somewhere. I'm an advanced computer user but only have a little experience with linux and a lot of problems with it. Currently I'm using Linux-Mandrake 8.0 (I know, I know, but let's not go into the many reasons why it's not even close to the best distro.) I tried using the little ICS setup wizard or whatever you would call it and it didn't work. The client would get an IP that was correctly assigned, but it couldn't get DNS resolutions or connect to any addresses.

Basically what I want to do is get help aimed more at a newbie on how to properly set up the normal way of ICS in linux using IP tables and whatever. I don't need the linux box to act as a firewall really because, for reasons that are too complicated to explain all out right now, the linux box is actually going through another proxy, so I have two network cards set up in it. I set up the one going to the LAN and the proxy to use 192.168.0.2 and the one that this computer would be connecting to is 192.168.1.1 so that the os would know which one to use for what.

I know this all sounds a little crazy, but, please, bear with me.

Basically, I have a computer sharing the internet connection on the LAN using the IP address 192.168.0.1 and there are two other computers on that LAN which connect through it. I would like to set up this linux box on 192.168.0.2 or any other IP address in that general range and connect my computer through it via that two network card method. This way I have a linux server on the lan among other things. (Don't worry, there's more than one reason I'm trying to do this, just too many.)

Also, I would really like to be able to set it up as a DNS server as well and to be able to manually refresh the DNS tables. I have problems every now and then with DNS and using the hosts file on my windows computer just isn't working for a few sites. Besides, presumably internet based things will go a little faster when they don't have to wait for a reply from my ISP to get the IP address.

In anutshell you want to do:

# In the NAT table (-t nat), Append a rule (-A) after routing
# (POSTROUTING) for all packets going out eth0 (-o eth0) which says to
# MASQUERADE the connection (-j MASQUERADE).
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

# Turn on IP forwarding
echo 1 > /proc/sys/net/ipv4/ip_forward


Lets call the box running iptables "router". You would set the default gateway on your other machines to point at router. Their DNS could point to an external box, or your internal machine.
(Above examples assumes eth0 is your internet interface).
See http://netfilter.samba.org for lots of docs on how to use iptables.

Setup BIND (ugh...lots of security problems) or djbdns (http://cr.yp.to) on your internal box to do DNS (most likely a caching server which points at the external world).

Thanks. I'll look into that as soon as I get the chance. As for security issues, well, I'm not really too concerned. The pc isn't exactly vital for anything and, besides, it's behind that first PC anyway, but even if someone did attack it it wouldn't do much damage. Even if I have to reinstall, once I get ICS working once, I should be able to remember well enough how to do it again.