Forward to DMZ addresses

jonathan at innovativesource.net jonathan at innovativesource.net
Tue Aug 16 18:15:42 CEST 2005


Kind of... I'm trying to redirect _any_ traffic destined for my DMZ
address to be forwarded to the machines themselves.  I tried the rule you
suggested, and I also realized that I had already tried that.

Basically, I want to forward any traffic destined for DMZ address pass the
firewall and onto the DMZ machines themselves, well once they gone through
some bad packet checks...

FYI, the rule didn't work as expected.  The following is my script thus far:

#************************************
/sbin/modprobe ip_tables
/sbin/modprobe ip_conntrack
/sbin/modprobe ip_conntrack_ftp
/sbin/modprobe iptable_filter
/sbin/modprobe ipt_LOG
/sbin/modprobe ipt_limit
/sbin/modprobe iptable_nat
/sbin/modprobe ipt_REJECT
/sbin/modprobe ipt_state

#
# Enable IP forwarding
#

echo "1" > /proc/sys/net/ipv4/ip_forward

$ipt -F
$ipt -X
$ipt -Z


$ipt -P INPUT DROP
$ipt -P OUTPUT ACCEPT
$ipt -P FORWARD DROP

###########################################
#
# Rules
#

#
# Accept EST. and REL. packets
#
$ipt -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT
$ipt -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

#
# Forward all from LAN through WAN
#
$ipt -A FORWARD -i $LAN_INTERFACE -o $WAN_INTERFACE -j ACCEPT

#
# NAT all outgoing packets
#
$ipt -t nat -A POSTROUTING -o $WAN_INTERFACE  -j SNAT --to-source $WAN_IP

#
# temp - this does the actual allowing of outgoing packets
# from the dmz server... but it still nat's them... I don't want to nat
# them, I want them to appear as they are
#
$ipt -A FORWARD -i $DMZ_INTERFACE -o $WAN_INTERFACE -j ACCEPT
############################################################
#
# Firewall specific rules
#

#
# Allow access from LAN to firewall
#
$ipt -A INPUT -i $LAN_INTERFACE -j ACCEPT

#
# Save rules
#
/etc/init.d/iptables save

#************************************

this is basic, as I'm trying to take it one step at a time.  I'm currently
dealing with 2 issues.  the one mentioned above...and the other is not
NATing the outgoing DMZ packets...  I would like them to go out with their
IP addresses...


> Jonathan, are you needing to add a rule to your nat table PREROUTING chain
> to cause any (ssh) traffic that is destined to your firewall's WAN
> interface to be redirected over to your DMZ server?  If so you just need
> to add a rule like this:
>
> iptables -t nat -A PREROUTING -i eth1 -d xx.xx.xx.xx -p tcp --dport 22 -j
> DNAT --to-destination yy.yy.yy.yy
>
> Where xx.xx.xx.xx is your globally routable WAN IP and yy.yy.yy.yy is the
> IP of your DMZ server.
>
>
>
> Grant. . . .
>
> jonathan at innovativesource.net wrote:
>> I have a machine that I using as a firewall, separting WAN / LAN / DMZ
>>
>> Rules thus far are to NAT all outgoing packets that come in from the LAN
>> interface.
>>
>>>From the machine itself, I can ping machines on my DMZ interface (eth2)
>> and my LAN interface (eth0)
>>
>> I'm having trouble getting through the firewall to my DMZ machines, but
>> I
>> can access the NIC that routes to the DMZ machine via SSH...  I've tried
>> various forwarding rules, and even changed the default FORWARD policy to
>> ACCEPT anything.  Here is a basic rule I'm trying:
>>
>> #eth1 = WAN NIC
>> #eth2 = DMZ NIC
>> iptables -A FORWARD -i eth1 -o eth2 -d xx.xx.xx.xx  -p tcp --dport 22 -j
>> ACCEPT
>>
>> now, if I do a netstat on the firewall nothing... if I do a netstat on
>> the
>> machine I'm attempting to connect from... all I see is SYN_SENT
>>
>> **I'm trying from external machines...i.e. machines not on my network.
>>
>> physical network is
>>
>> router -> vlan -> firewall -> DMZ
>> router -> vlan -> firewall -> LAN
>>
>> I can also access the DMZ machine via the firewall itself and vice
>> versa,
>> but once logged into the DMZ machine, I can't get to anything past the
>> firewall.  I have the following rules for that
>>
>> iptables -A FORWARD -i eth2 -o eth1 -j ACCEPT
>>
>> Kinda confused here...
>>
>> the LAN stuff works... at least for now... to simply forward the packets
>> out through the WAN NIC and NAT them...
>>
>> *shrug*
>
>





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