Scripting a firewall in front of a SMTP server

Seferovic Edvin edvin.seferovic at kolp.at
Sun Nov 27 17:36:43 CET 2005


Hi,

why do you need this line?

iptables -A INPUT -i eth0 -m state --state ESTABLISHED -p tcp --sport 80 -j
ACCEPT

Regards,

Edvin



-----Original Message-----
From: netfilter-bounces at lists.netfilter.org
[mailto:netfilter-bounces at lists.netfilter.org] On Behalf Of Fernando Martins
Sent: Sonntag, 27. November 2005 17:29
To: netfilter at lists.netfilter.org
Subject: Scripting a firewall in front of a SMTP server

Hello,

I have a  firewall in front of an Exchange serveur. I can't receive
any mail from outside. It seems I have a problem with my script. When
I do a telnet on my server on port 25, from the outside, there is a
connection but this one is closed before I reach the HELO messages.
Moreover, when I try to connect friom the firewall to the SMTP server(
telnet 25)
I have more or less the message:
"
escape caracter is :^]
Connection closed by foreign host
"

My network is :

Internet
|
|
|
Firewall
|
|
SMTP

Internet-Firewall interface: eth0 ip adress xxx.yyy.zzz.ttt
corresponding to the MX

Firewall-SMTP= eth1

SMTP: 192.168.0.2


Any idea?
Here is the script:

#!/bin/sh
# script /etc/firewall.sh
echo 1 > /proc/sys/net/ipv4/ip_forward
echo "Activation du forwarding :[OK]\n"
if [ -e /proc/sys/net/ipv4/conf/all/rp_filter ]
then
for filtre in /proc/sys/net/ipv4/conf/*/rp_filter
do
echo 1 > $filtre
done
fi

echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_all
echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts

modprobe ip_tables
modprobe iptable_filter
modprobe iptable_nat

iptables -F
iptables -X

iptables -N LOG_DROP


iptables -A LOG_DROP -j LOG --log-prefix '[IPTABLES DROP] : '
iptables -A LOG_DROP -j DROP


iptables -N LOG_ACCEPT
iptables -A LOG_ACCEPT -j LOG --log-prefix '[IPTABLES ACCEPT] : '
iptables -A LOG_ACCEPT -j ACCEPT

iptables -P INPUT DROP
iptables -P OUTPUT DROP
iptables -P FORWARD DROP

iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT

iptables -A OUTPUT -o eth0 -m state --state NEW,ESTABLISHED -p tcp
--dport 80 -j ACCEPT

iptables -A INPUT -i eth0 -m state --state ESTABLISHED -p tcp --sport
80 -j ACCEPT

iptables -A OUTPUT -o eth0 -m state --state NEW,ESTABLISHED -p tcp
--dport 80 -j ACCEPT

iptables -A INPUT -i eth0 -m state --state ESTABLISHED -p tcp --sport
80 -j ACCEPT

iptables -t nat -A PREROUTING -d xxx.yyy.zzz.ttt -p tcp --dport 80 -j
DNAT --to-destination 192.168.0.2:80

iptables -t nat -A PREROUTING -d xxx.yyy.zzz.ttt -p tcp --dport 25 -j
DNAT --to-destination 192.168.0.2:25

iptables -A FORWARD -i eth1 -o eth0 -j ACCEPT
iptables -A FORWARD -o eth1 -i eth0 -j ACCEPT

iptables -A FORWARD -i eth0 -o eth1 -p tcp --destination-port 80 -m
state --state NEW,ESTABLISHED -j ACCEPT

iptables -A FORWARD -o eth0 -i eth1 -p tcp --source-port 80 -m state
--state NEW,ESTABLISHED -j ACCEPT

iptables -A FORWARD -i eth0 -o eth1 -p tcp --destination-port 25 -m
state --state NEW,ESTABLISHED -j ACCEPT
iptables -A FORWARD -o eth0 -i eth1 -p tcp --source-port 25 -m state
--state ESTABLISHED -j ACCEPT

iptables -A FORWARD -j LOG_DROP
iptables -A INPUT -j LOG_DROP
iptables -A OUTPUT -j LOG_DROP





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