mark feature not working as expected

[Sudheer Divakaran <sudheer@svw.com>]

Hi,
    I'm facing a problem with MARK target. 

My Linux box has 3 network cards

    eth0 - LAN1
    eth2 - LAN2
    eth3 - ISP

My problem is that my Lan machines are not able to communicate with each 
other  (i.e. LAN1 <-> LAN2).  Firewall blocks them.  But my lan clients 
have no problem in accessing internet!!.

Here is my configuration.


# eth0 - LAN1
# eth2 - LAN2
# eth3 - ISP
 
iptables -F
iptables -X
iptables -P INPUT   DROP
iptables -P OUTPUT  DROP
iptables -P FORWARD DROP

iptables -t nat -A PREROUTING -i eth0 -o eth2 -j MARK --set-mark 1  
#THIS IS NOT WORKING
iptables -t nat -A PREROUTING -i eth1 -o eth0 -j MARK --set-mark 1  
#THIS IS NOT WORKING

#Other rules follows... Not listed here
 
iptables -A FORWARD -m mark --mark 1 -j ACCEPT   #THIS IS NOT WORKING

#Other rules follows... Not listed here


I know that I can do it directly from the FORWARD chain of filter table, 
but I'm using SQUID for transparent proxying for some machines (Those 
rules are not listed here), so I want to mark some packets. Could 
someone please help me on this?


Thanks
Sudheer