[clug] How to prevent port forwarding

[Christopher Zhang]

Hi,

I am interested to find out if it is possible, if so, how, that some  
ISPs prevent 1 registered Internet user to distribute their Internet  
connection by running their computer as a gateway for other users to  
route through. The closest thing I can think of is TTL, since if  
other hosts are routed through the legitimate host, then their TTL  
will be at least be 1 less than if it were coming from the legitimate  
host, without any artificial changes. Is this a plausible way for  
ISPs ? Can anyone show me some iptables commands that the ISPs would  
do? and also how can I change my TTLs and so on.

Thanks

Chris