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Re: iptables filtering ports under nat


You'd be use FORWARD chain in the table filter.

POSTROUTING and PREROUTING is in the nat table.

# The first rule allow traffic in port tcp/80
/sbin/iptables -A FORWARD -s -p tcp --dport 80 -j ACCEPT

# The second rule allow the trafic inbound to source from port tcp/80.
/sbin/iptables -A FORWARD -d -p tcp --sport 80 -j ACCEPT

# The third rule drop all trafics in all ports and protocols.
/sbin/iptables -A FORWARD -s  -j DROP

Best Regards,
Diego Lilioso

2008/10/16 James Shupe <shupej@hermetek.com>

You'd be better off with a DROP policy where you could just use:

/sbin/iptables .... -d $EXTERNAL_HOST -p 80 -j ACCEPT

With your ACCEPT policy, just use inverse:

/sbin/iptables .... -d ! $EXTERNAL_HOST -p 80 -j DROP

"-p 80" needs to be "-p tcp --dport 80". Not sure how I overlooked it.

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On Thu, 2008-10-16 at 15:27 -0400, Luis Rondon Paz wrote:
> hello everyone i have a question
> i have this in my iptables
> EXT_IF=eth1
> #############
> /sbin/iptables -t nat -A POSTROUTING -s -o $EXT_IF -j MASQUERADE
> now
> how can i DROP ALL TRAFIC FROM IP ??? exept port 80 to one
> external ip ?
> example
> i neeed to drop all traffic
> and  i need to allow the traffic to one address only
> how can i do that Ç????
> /sbin/iptables -t nat -A POSTROUTING -s -d EXTERNALONEHOSTONLY
> -o $EXT_IF -j  ACCEPT
> /sbin/iptables -t nat -A POSTROUTING -s -d -o $EXT_IF
> -j  DROP ???
> thanks for reading me .

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