tib at tigerknight.org
Sat Jun 11 19:16:43 CEST 2005
Thought I'd chip in since this used to be identical to how I had my system
setup. I had a block of 5 useable from my isp.
Whichever you are going to use as your actual firewall box IP (as opposed
to the machines you want to run behind it), you set as eth0 ip config.
After that you setup the other ip's as virtual interfaces on the same card
(eth0:1, eth0:2, etc). Set your internal IP nic to be eth1 and make sure
the routing table is set to go through it out to eth0 and the world. Have
your other internal IP boxes use eth1 as their gateway.
After that, you setup destniation nat'ing using something like this:
iptables -t nat -A PREROUTING -d $REAL-IP$ \
-j DNAT --to-destination $INTERNAL-IP$
iptables -t nat -A POSTROUTING -s $INTERNAL-IP$ \
-j SNAT --to-source $REAL-IP$
for each internal/ip pair you want to have mapped.
After you've done this - you're likely going to want to protect them from
certain types of traffic, since the basic INPUT rules won't cover it - put
anything you DON'T want to reach those hosts under the FORWARD ruleset as
That's it - you're set.
One item of note - be sure to put those snat/dnat rules into the table
BEFORE the catchall masquerading rule (if you use one) otherwise they will
hit the masquerade rule first and your traffic will not match in/out ip's
and things will bork up.
This is a setup I've used for a number of years, it's nice and clean and
gives good protection through the forward ruleset. If you cover your bases
right and practice safe net, things like zone alarm become unnecessary.
I blocked the following on forward and have done very well by it:
These will vary depending on your particular software usage and such - but
are a good start.
On Sat, 11 Jun 2005, Billie Joe wrote:
> I have 3 IPs on Internet, and I want to put them behind my firewall
> machine. So I have the question: Put all 3 IPs in the same network
> card (with alias) or a card for each IP ?? What you suggest and why ??
> pS.: Consider that I have another NIC for my LAN.
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