Brent Clark wrote:
Hi all
Just something I would like to pick someones brain with.
If I use the default policy of drop, BUT at the end of the chain use
the following
$IPT -t filter -A FORWARD -j REJECT --reject-with icmp-host-unreachable
Would that be ok, or does is another ICMP message I can reply back with.
Reason I ask this is because I find that by using the default policy
(DROP), some applications keep retrying to make a
connection etc.
Where as this approach, seems to slow things down (I stand to
correction on this).
If someone could maybe help me understand this or assit I would be
most grateful.
I recommend using --reject-with icmp-host-unreachable and here are the
reasons:
1) What is the only reason you would receive nothing? When a firewall
is in place. That's it. Everything else you either get a host
unreachable, network unreachable, port unreachable, reset, etc. 2) What
do DDoS attacks rely on? Slow/no connection resets. If your address
space is spoofed and you do not send a reject or reset message, the
victim still has the connection open. You are aiding the cracker with
their DDoS by DROPing the connection and not rejecting/reseting it.
3) If I remember right, it is against RFC to DROP a connection without
rejecting/reseting it. If anybody could point me to the correct RFC,
that would be great.
--
Nathaniel Hall, GSEC GCFW GCIA
