ristrtciting a machine from lan's Proxy server

i have RHL5.2 as a proxy server for my lan. i have the rc.fw as follows
echo "Enabling Internet Gatewaying : "
/sbin/ipfwadm -F -f
/sbin/ipfwadm -F -p deny
/sbin/ipfwadm -F -a m -S -D
/sbin/ipfwadm -F -l -n      "

But it is that i want to restrit some of the machines on the lan from being given the TCP/IP packets so that they have no web access .
i tried to read the man pages for the "ipfwadm" but was unable to remove the machine from the proxy.
Help !!!!!!!!!!!!!!        

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There are ways to base rules on the source of the request, but it's easier to restrict those machines at those machines than it is to come up with elaborate FW rules.

Set those machines up to have a default gateway
Just make sure they have a route to the local net.

route -f
route add -net netmask eth0
route add default gw lo

Since only root can add routes, it should be secure.

Adjust the numbers and device names in the second line to reflect your network. Any packet not destined to the local net gets dropped on the loopback device.

Sorry, I should have read more carefully.  The proxy server is on the local net.  But you can still do it this way.  Define a route based on the proxyserver's IP to 'lo'.
tiwariAuthor Commented:
Sorry ,
but  what i wanted is that the server is a Linuc 5.2 RedHat. Other m/c's on the lan r Windows.
Now if i do something at those m/c's then it can be changed by the user on that m/c i want that, that m/c should not be given any tcp/ip packets.
Since they r windows i have to have a FW way of stopping them
Ahhh. . .  Windows does have a route command, but no user security, so that won't work.

You need to add a deny rule for each of those machines prior to your "ipfwadm -F -a m -S" line.  I use ipchains (which is the newer version), not ipfwadmn, so I can't look up the syntax. That line give everyone on the local net access to the proxy.

The list of rules is a top-down filter.  As soon as a rule fits, it's applied.  So if there's a deny rule for before then it will get rejected prior
to the "allow all local" rule.

IF you just add a rule it goes to the end of the chain, and the "allow all local" catches the packet first and causes it to be forwarded.

I think you want

ipfwadmn -F -a m -S 192.168.42.xx deny

for each machine (replace the xx) you want to block, and it has to be before the "ipfwadm -F -a m -S . ." line.  But doublecheck the rule syntax against the man page.

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