How to detect ADSL user share its network to more pepole
Linux - NetworkingThis forum is for any issue related to networks or networking.
Routing, network cards, OSI, etc. Anything is fair game.
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The most commonly used method is ip-masquerading. This page provides most of the background on achieving this. I personally use ip-masquerading in conjunction with MonMotha's firewall script .
Basic rules are that the ethernet card (eth0)connected to the adsl modem/router must be on a different subnet address to the ethernet card (eth1) attached to the lan. The box connected to the modem/router via eth0 uses the ip-address of the router as the gateway and all boxes attached to eth1 use the ip-address of eth1 as the gateway.
As I understand his posts, he actually wants to detect that someone is using NAT/masquerading/whatever else to share the DSL connection. He needs something that will inspect the network traffic from some IP, and gives an alert whenever it appears that multiple PCs are behind this IP address.
If you want to determine whether users are behind a NAT system then good luck. You'll find a technical discussion on this here and from what is said this is extremely complex and none too accurate.
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