Redirect DHCP requests to DMZ?

Carsten Maass <cm@xxxxxxxxxxxxxxxxx> · Wed, 23 Apr 2003 12:08:52 +0200

Hello List!

My network layout looks like this:

Local LAN (192.168.20.*)
    |
    |
  Switch
    |
    |
Router/Firewall ---- DMZ (192.168.21.*)
    |
    |
    |
 Internet

Everything runs smoothly, except for one thing: I am unable to redirect 
DHCP request from the clients on the local LAN to the DHCP server inside 
the DMZ.

So my question is: How can I accomplish this task? Is it at all possible 
to redirect broadcasts from one subnet to another with the help of iptables?

I tried the following rules, but they didn't work out:

$IPTABLES -A FORWARD -p UDP -i $LAN_IFACE --dport 67 --sport 68 -j ACCEPT

$IPTABLES -t nat -A PREROUTING -p UDP -i $LAN_IFACE -d 255.255.255.255 
--dport 67 -j DNAT --to-destination $DMZ_DHCP_IP

I am running iptables v1.2.6a with kernel 2.4.20 on Debian GNU/Linux 3.0.

Any hint would be highly appreciated.

Thanks in advance,
Carsten.