I have a squid proxy server 192.168.1.1, internet is on eth0 and eth1 is local LAN, and several other boxes getting their IP's via DHCP, all fine no problem. Squid uses port 3128 and I had to point all the browsers of the other boxes to this port using the rules added to my firewall:-

iptables -t nat -A PREROUTING -i eth1 -p tcp --dport 80 \

-j REDIRECT --to-ports 3128

iptables -A OUTPUT -j ACCEPT -m state --state NEW -o eth0 \

-p tcp --dport 80

Is it possible to configure the iptables rules so that all the browsers point to the standard port 80 and it gets redirected to 3128. I have httpd running, but only for the LAN, I do not require it to be accessible from 'outside'.

Thanx in advance.

My knowledge of iptbales is limited to say the least....

What your asking for is called transparent proxy.
As far I can see from your setup this is exactly what you have accomplished.
First rule syas: "Before determining the interface to send the packet, check to see if it is comming in on eth1 and if it is a port 80 packet. If so then redirect it to localhost:3128, which is your squid proxy."

Isn't it working?

Its working but not exactly how I'd like. I was wanting to leave all the browsers on the network using port 80 but have my firewall redirect all traffic to squid on port 3128 on the same interface?

Your squid server isn't on the same machine as your firewall?

Then you will have to use another destination. This is accomplished using DNAT (Destination Network Address Translation)
That should do it. Exchange the ipaddress to your squid server.
This rule says: "Before determine the destination interface (routing), cheeck to see if the packet came in on eth1 and was a port 80 packet. If that's the case then change destination to ipaddressort."
Also make sure the rule gets in the right place in the chain so that no other rules stop your packets before they reach this rule.

My main box is has 2 eth cards, eth0 is internet and gets its ip via dhcp from cable modem, and eth1 is my internal network range 192.168.1.1 staic. This nic give out ip's in the range 192.168.1.100-200 to the boxes on the network. This main box is my dhcp, www, ftp, apache, squid and name server for the small network, i was wanting to use squid as the proxy for the network but without having to reconfigure every browser, and still have internal acess only to my apache sever, a kind of local intranet? Does that help in anyway!?

Then we're back to the first situation, rule with REDIRECT target.
Instead of running iptables rules with -A option, try to enter the rules using -I instead.
This would ensure that your rules get inserted as first rule instead of being appended at the end.
There might be some rule high in the chain blocking your squid packets before they reach this transproxy rule.