[CentOS] Firewall frustration

Thu Jan 3 04:34:32 UTC 2008
Robert Moskowitz <rgm at htt-consult.com>

Christopher Chan wrote:
>
>> I spent much of the past 24 hours trying to find out how to set up 
>> iptables for firewall routing WITHOUT NATing. Could not find anything.
>>
>
> Eh? You just need to enable ip forwarding to enable routing. After 
> that, it is put up the firewall rules as is necessary, build the 
> appropriate routing tables on the firewall box and the boxes on the 
> intranet(s).
>
> iptables does not handle routing. 
No, but iptables controls what is allowed to route, or it seems when you 
read the tutorials on iptables. I know about routing, Comer taught me, 
and I reviewed Stevens book. I know about firewalls; Belovin and I go 
back quite a ways. But configuring software to do what **I** want, well 
that is were the car hits the brick wall. As Belovin would say, "Here be 
Dragons."

Those little words, "put up the firewall rules as necessary" are 
equivalent to "and magic happens here."

I tried it. I had everything open. Then I blocked everything. Then I set 
up a rule to allow SSH in to eth0 and out eth1 (and the other way). At 
least I thought that was what the rules said, but no SSH connectivity 
through the firewall. That was when I realized that I had not found the 
necessary incantation, and I had already shot most of tuesday.

Up and running. I can understand what shorewall rules are saying. And I 
can see the results.