Re: iptables dnat to loopback

["Klemen Kecman" <klemen@sting.si>]

----- Original Message -----
From: "Damian Gatabria" <damian_g@speedy.com.ar>
To: "Lista Netfilter" <netfilter@lists.netfilter.org>
Sent: Friday, August 06, 2004 1:38 PM
Subject: iptables dnat to loopback


> Hello listers.
>
> I know this is probably not the proper place to ask
> a support question, but after a long googling
> session and asking in my regular lists i was unable to
> get an answer for what i think is a rather tough situation..
>
> So, flame me if you must, but here it is =oP
>
> I have a rather busy server box hosting several web
> sites in separate independent installation directories,
> which means several apache, mysql and tomcat installations
> running simultaneously, with each mysql instance binding
> a port in the loopback interface.
>
> Now, for a very specific reason, i need to provide someone
> with remote access to one of these mysql instances.
>
> It would be a real hassle to change mysql's config
> (and the webapps' working with it) so i just decided
> to use DNAT to redirect incoming tcp connections
> to the loopback interface.... but for some reason you
> hopefully already know about, it doesn't seem to work.
>
> So, while this iptables rule does work for port forwarding
> to another host:
>
> iptables -t nat -A PREROUTING -p tcp -i eth0 -m multiport \
>         --dports mysql -j DNAT --to some.other.host
>
> changing "some.other.host" to 127.0.0.1 doesn't work
> as expected, and packets seem to be dropped altogether.
> Using tcpdump i can see packets reaching eth0, but
> never reaching loopback.
>
> Is there any way to make iptables do what i'm looking
> for? Any help will be greatly appreciated.
>
> Thanks much.
>
> --
> Damian Gatabria <damian_g@speedy.com.ar>
>
>

Is your FORWARD chain set to DROP? Is so, do you have the rule in the
FORWARD chain that allows traffic from eth0 to localhost?

Example:
iptables -t nat -A PREROUTING -p tcp -i eth0 -m multiport \
        --dports mysql -j DNAT --to some.other.host
iptables -A FORWARD -p tcp -d some.other.host --dport some.port -j ACCEPT

Correct me if I'm wrong.

Greets,
Klemen Kecman