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On Sun, 2001-11-11 at 01:43, David Ranch wrote:
>  >every think work fine  my internal computer goes to the Internet   but   i
>  >having a problem configure the iptables
>  >so it will PORT forward   port 80  /   21    to local machine on my local
>  >lan.
> 
> A new HOWTO will be released shortly that fixes a bug (missing
> "NEW" option) in its PORTFW FTP example.
> 
> Anyway, to do PORTFW under IPTABLES, add the following in addition
> to your existing ruleset.  (make sure you put these before any
> DROP/REJECT rules)
> 
> --
> #note: I cannot use -d $EXTIP as the rule never seems to match
> #
> $IPTABLES -A FORWARD -i $EXTIF -o $INTIF -p tcp --dport 21 -m state \
> --state NEW,ESTABLISHED,RELATED -j ACCEPT
> 
> $IPTABLES -A PREROUTING -t nat -p tcp -d $EXTIP --dport 21 \
> -j DNAT --to $PORTFWIP:21
> --

This will work for loose rulesets.  However it only works with the NAT
and FILTER tables.  It is highly advisable to work toward a strong
ruleset for your firewall.  The first step in doing this is to change
all policies to DROP and then get only what you need working.

I have what I believe to be a fairly strong ruleset (at least stronger
than anything else I've found).  My script can be found at
http://www.asgardsrealm.net.  Here some of the port forwarding code from
the script:

<code>
echo -n "Forwarding $EXT_F to $INT_F:"
$IPTABLES -t filter -I FORWARD -p tcp -d $INT_IP \
        --dport $INT_PORT -j ACCEPT && \
$IPTABLES -t filter -I FORWARD -p udp -d $INT_IP \
        --dport $INT_PORT -j ACCEPT && \
$IPTABLES -t nat -I POSTROUTING -p tcp -d $INT_IP \
        --dport $INT_PORT -j ACCEPT && \
$IPTABLES -t nat -I POSTROUTING -p udp -d $INT_IP \
        --dport $INT_PORT -j ACCEPT && \
$IPTABLES -t mangle -I PREROUTING -p tcp -d $EXT_IP \
        --dport $EXT_PORT -j ACCEPT && \
$IPTABLES -t mangle -I PREROUTING -p udp -d $EXT_IP \
        --dport $EXT_PORT -j ACCEPT && \
$IPTABLES -t nat -I PREROUTING -p tcp -d $EXT_IP --dport $EXT_PORT \
        -j DNAT --to-destination "$INT_IP:$INT_PORT" && \
$IPTABLES -t nat -I PREROUTING -p udp -d $EXT_IP --dport $EXT_PORT \
        -j DNAT --to-destination "$INT_IP:$INT_PORT" && \
success $"Forwarding $EXT_F to $INT_F:" || \
failure $"Forwarding $EXT_F to $INT_F:"
echo ""
</code>

Jamin W. Collins
-- 
"Life is the art of drawing without an eraser." - John Gardner

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