tor and hornet can isp stop it?

As far as I understood, everyone on "the line" knows you use Tor if he/she wants to to: lists of Tor routers are public. The ISP knows who you are (you signed a contract with it) and it know you use Tor, unless you use a Tor bridge, i.e., an entry node that is not in the public lists (a solution if your ISP censors Tor and you know of a Tor bridge). But the ISP does not know what site you communicate with. The site knows that you use Tor but does not know who you are.

If your connection goes like this: VPN -> Tor -> Internet
then your ISP can only see encrypted data and assume you use a VPN but it can not know whether you are using Tor or not. The main advantage of connecting to Tor behind a VPN is precisely to hide its usage to the ISP. Now, Tor is not illegal but it certainly attracts a lot more of attention than a VPN. Another good point of connecting first to the VPN and then to Tor would be in case a global adversary manages to control both the exit and the entry node of a given Tor circuit, in which case the entry node would see the IP address of your VPN provider and not your ISP's one. The downside though is that the vast majority of VPN providers do declare not to keep logs but you can not know if that is the actual case and you should assume that they do indeed keep logs (metadata - ip addresses, time of connection, webpages you connected to) so .. choose well if you are going the VPN way..
cheers

You likely know tor.
http://www.netsec.ethz.ch/research/anonymity.php hornet wants to provide
anonymity on the home router. At close to full speed.

When you use tor, does the isp know, if he wants to? Can an isp find tor and
selectively close those tor routers? Can an isp find and close hornet
routers? Can isp config a setup that if a hornet router is running, internet
stops and starts again if common router is reconnected?

As far as I understood, everybody knows you use Tor (if they want to to). The
ISP know who you are and, unless you use a Tor bridge, it know you use Tor.
But it does not know what site you communicate with. The site knows that you
use Tor but does not know who you are.

If your connection goes like this: VPN -> Tor -> Internet
then your ISP can only see encrypted data and assume you use a VPN but it can
not know whether you are using Tor or not. The main advantage of connecting
to Tor behind a VPN is precisely to hide its usage to the ISP. Now, Tor is
not illegal but it certainly attracts a lot more of attention than a VPN.
Another good point of connecting first to the VPN and then to Tor would be in
case a global adversary manages to control both the exit and the entry node
of a given Tor circuit, in which case the entry node would see the IP address
of your VPN provider and not your ISP's one. The downside though is that the
vast majority of VPN providers do declare not to keep logs but you can not
know if that is the actual case and you should assume that they do indeed
keep logs (metadata - ip addresses, time of connection, webpages you
connected to) so .. choose well if you are going the VPN way..
cheers