Hello everyone ,
this is my network scenerio:

CABLE MODEM ==> HUB == > {( eth1) Linux ROUTER (eth0) } ==> FW/SQUID ==> LAN Clients

I am very new to Linux Networking Operating System. I have setup my network as above, I configured my router machine to forward and allow incoming packet on ports (20,21,22,80 and 443).but my problem lies on the firewall/squid machine configuration. All I intend to have on the machine is to allow incoming and outgoing packets from the client machines on ports (20,21,22,80 and 443) using iptables. But I wondered how this could be done since I have One Ethernet card on it.
Please can anyone assist me in writing iptables and or to give me an assistance on how I could achieve this goal.

Thanks in advanced
Jamal

I'm not completely clear what you diagram shows; is it processes or computers? Maybe its flow of data. Assuming that your diagram does show computers/boxes/hardware, then, while the set up that you chosen may not be the most desirable (hey, but you didn't ask about that, right?) it looks as if it is relatively simple to get something that 'sort-of' works. If, on the other hand, you have serious concerns about the users of the lan clients as hackers or you want to ensure that your system is set up to minimise the pain of maintaining it in future, maybe you want to reconsider this, rather than presenting as a fait accompli.

It seems to me that you could achieve what you want by using iptables on the router box to only allow connections on eth0 from the FW/SQUID box. You could limit connections by mac address or IP address. I don't generally like this solution because it builds in a maintenance problem, but then its your mainteneance problem, not mine.

You should also note that you don't seem to be protecting your router box from the internet. Maybe this is something that you have just omitted from the diagram because it wasn't really relevant to this particular question.

thanks for your reply. Yes my point is that I needed to protect my router from the internet but I dont know how.

CABLE MODEM ==> {( eth1) Linux ROUTER (eth0) } [ (eth0 )FW/SQUID (eth1)] ==> LAN Clients

I cannot do much on the router because it is a floppy firewalling. I run my firewall on a separate machine as drawn above.

My question is , what is the best practises to protect my router machine from the internet.