If we used squid, and each one of the computers client's was restricted for access was based on the configuration in squid. However had a person who was naughty that is by replacing MAC Address or IP Address in order to be able to access the internet through it. There was a method in the style of the tukang nggame , that possibly could become the solution. Despite still had the gap at least could be useful moreover if the client was still lay about the security of the network. Get found it easy.

Make a file exp fixip.sh
It's contents (exp)

#!/bin/bash
/usr/sbin/arp -s 192.168.1.67     00:14:76:1D:F1:11
/usr/sbin/arp -s 192.168.1.68     00:15:F5:74:B1:51
/usr/sbin/arp -s 192.168.1.69     00:16:46:F2:B1:F1

#cmod +x fixip.sh

#./fixip.sh

acl     foo67           src             192.168.1.67/255.255.255.255
acl     foo67_mac	arp		00:14:76:1D:F1:11

acl     foo68           src             192.168.1.68/255.255.255.255
acl     foo68_mac       arp             00:15:F5:74:B1:51

acl     foo69           src             192.168.1.69/255.255.255.255
acl     foo69_mac       arp             00:16:46:F2:B1:F1

http_access    allow   foo67   foo67_mac
http_access    allow   foo68   foo68_mac
http_access    allow   foo69   foo69_mac

http_reply_access    allow   foo67   foo67_mac
http_reply_access    allow   foo68   foo68_mac
http_reply_access    allow   foo69   foo69_mac

#/etc/init.d/squid  force-reload