[LARTC] iptables marks

[Alejandro Ramos Encinosa]

Hi all!!

I was trying to figure out how iptables marks work. I thought that a packet 
could just be marked once into a chain (if the packet matchs the criteria, 
then it the action is applied, and that's all for the packet into this 
chain), but I was wrong: I did

iptables -t mangle -A INPUT -i eth0 -j MARK --set-mark 7
iptables -t mangle -A INPUT -i eth0 -j MARK --set-mark 8

and then I did `iptables -t mangle -L -x -v' and I got

Chain INPUT (policy ACCEPT 9565560 packets, 4954706655 bytes)
 pkts bytes target prot opt in   out source   destination
   45 31630  MARK     0 --  eth0 any anywhere anywhere    MARK set 0x7
   45 31630  MARK     0 --  eth0 any anywhere anywhere    MARK set 0x8

Can someone tell me how can I be sure one packet will just be marked once into 
the chain?