I am running a network on LAN which has 700 systems and i am in deep trouble as my clients are telling me their ip's are beign used i also have their mac addresses but i cant trace them out cause they dont match with the mac addresses of any of my 700 clients i am facing a biig time problem even after blocking all the free ips' and also i assigned ip's tht is binding of mac addresses i need ..to know wht can be done .i am totally a newbie and my network admin left a few weeks back ..my new admin does nt have any through knowledge on LINUX

DID you bind IP with MAC and again MAC with IP. I mean VICE VERSA.Then let's say you will be dropping everything on your iptables chains. then applying the rule.The above idea will do the following.

the mac address defined should have the defined IPaddress
the ipaddress defined should have the defined mac address.

any other scenerao will be droped.

Tell me what actually are you doing Forwarding ,routing.Natting etc..