Re: [Fwd: Server machines behind Firewall]

[Jason Opperisano <opie@817west.com>]

On Fri, Jan 07, 2005 at 11:07:10PM +0800, edwardspl@ita.org.mo wrote:
> > EXT_IF="eth0"
> > INT_IF="eth1"
> > SRV1="10.1.1.10"
> >
> > iptables -t nat -A PREROUTING -i $EXT_IF -p tcp --dport 80 \
> > ? -j DNAT --to-destination $SRV1
> 
> I want to know why needn't to define the original IP ( Public IP ) ?
> eg :
> 
> iptables -t nat -A PREROUTING -i $EXT_IF -p tcp -s 202.175.xxx.xxx --dport
> 80 \
> ? -j DNAT --to-destination 192.168.xxx.xxx

you can; if the original, public IP is different from the firewall's
external IP.  if you want specify the original DESTINATION of the
packet, you would use "-d" not "-s" like so:

  iptables -t nat -A PREROUTING -i $EXT_IF -p tcp -d $PUB_IP \
    --dport 80 -j DNAT --to-destination $SRV1

> Sorry, what useful about the following function ( command line ) ?
> 
> > iptables -A FORWARD -i $EXT_IF -o $INT_IF -p tcp --syn -d $SRV1 \
> > ? --dport 80 -j ACCEPT

um--it allows the packet through the FORWARD chain of the filter table.
remember--you're trying to build a firewall here.

> In additional, if I want to setup a NAT ( 192.168.101.0/24 ) with a Server
> machines ( 192.168.100.1 ) behind Firewall...
> So, is there more than one sample ( nat scripts ) for reference ?

go read everything linked from the netfilter home page in the docs
section:

  http://netfilter.org/documentation/index.html

-j

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