How to detect ADSL user share its network to more pepole
 

hello,everyone

To prevent more than one user share one ADSL line to conect internet, I want to know whether there is such a software can be used.

I want to run it on lnux box and be free .

also, the principle is provided is very useful

Thanks
Yufei

mail to me : yufeixiaoyu@hotmail.com

English is probably not your home langauge and I am presuming you need to know how to share an adsl internet connection. Can you confirm this.

my poor english
 

thanks for your reply

ADSL user can use NAT technology to share his line to others,

Now, I have heard a few method

1,check the MAC address in every IP pakage,if there are many diffrent MAC address,so he share his ineternet connection.

2, scan port 161 with snmp to check the LIB

3, check sessions

etc......

I only to get such a software with GPL

Help me and excue my poor english

thanks

yufei

yufeixiaoyu@hotmail.com

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.

I don't have the solution, though.

Yves.

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.