How do ISP know???

[beavereater]

I am not a computer genius, so maybe someone can tell me how it is exactly that ISP servers tell when we are using p2p...and if we they can tell, how do they know that what we are using it for is or isn't legal???

[sacajaweeda]

Some ISPs actually monitor traffic on known suspected ports, some are simply notified by others that users with IP addresses originating from their domain are sharing/downloading copyrighted material. They only know what they find out for themselves through monitoring their own network or what is reported to them by others. They have no way of actually monitoring the P2P networks other than using a client and logging on as a user themselves.

[Zal42]

P2P software (or any software) uses specific ports the internet connections. ISPs can easily tell what ports you're using, without even looking at what the traffic actually is.

And there are many legitimate reasons to be using a P2P system, so they shouldn't infer guilt just because you're using the software. On the other hand, I seem to remember a clause in my service contract specifically prohibiting P2P software (as well as any type of server), regardless of why you're using it.

My guess is that your average ISP simply doesn't care whether you're running P2P software, or why, unless they recieve some kind of complaint or you are using up an unusual amount of bandwidth.