simple routing rules
 

hello every 1
here is my lan :

[[ISP]]______serial0[Cisco router]Ethernet0______eth0[LINUX]eth1___||LAN||

{internet}..................................{LAN}

the provider from where i got the LINK E1 brings me 1 class C of public address (254 machines) ; my lan is set as this :
router defaul gw : the ISP serial
ip route $mylan gw Ethernet0

then the LINUX BOX do a masquerading for the clients with provate address
the other clients who want to have a public address just put a public one and set the router as default gw

what i want to do is to oblige everybody to use the linux as default gw even those who have a public one , in other words , make a real router with my linux box i thought about adding a new interface (eth2) and set a public address for it and then add a line such :
route add net $public class C gw $Ip_of_ETH2
then set some acls in the router to prevent ppl tp use is as default gw
i need some advices about how to set the linux box !
any help would be welcome :)
thnx