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Re: [vox-tech] Firewall question...
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Re: [vox-tech] Firewall question...

On Tue, Jul 03, 2001 at 10:09:10PM -0700, Doug Barbieri wrote:
[dns firewalling snipped]
> This cleared up the connection problem. My question, however, is this--why
> should I care from which port a DNS client on a remote machine may connect
> *from*? As long as I only allow connections *to* port 53, shouldn't that
> be good enough? So why do I have the sneaking suspicion that my solution
> isn't very secure? :)

Here's how I do it:

# begin
ME='romana.hajhouse.org' # Machine's Internet address
IFACE_INET='eth0' # External interface
NS_SERVERS=`perl -ne '/^nameserver ([0-9.]+)/ && print "$1 "' /etc/resolv.conf` # a regex, how apropos ;-)

# ...

for server in $NS_SERVERS; do
	ipchains -A output -i $IFACE_INET -p tcp  \
		-s $ME 1024:65535 \
		-d $server domain -j ACCEPT 
	ipchains -A input  -i $IFACE_INET -p tcp  \
		-s $server domain \
		-d $ME 1024:65535 -j ACCEPT 
	ipchains -A output -i $IFACE_INET -p udp  \
		-s $ME 1024:65535 \
		-d $server domain -j ACCEPT 
	ipchains -A input  -i $IFACE_INET -p udp  \
		-s $server domain \
		-d $ME 1024:65535 -j ACCEPT 
# end

The only significant difference is that I only allow traffic to the
nameservers listed in /etc/resolv.conf. That's about as secure as you can
get without resorting to extreme measures.

Henry House
OpenPGP key available from http://romana.hajhouse.org/hajhouse.asc

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