> But is it the ISP's business to "stop" the user to start using > native v6 instead (if it doesn't work automatically)? At most, > the mechanism should provide a means to show the user a message > that ISP is also providing native v6 service (possible e.g. if the > user switched to new service class, or replaced the NAT box) even > though the user is not obtaining it at the moment.
Yes. This is the concern I have, ISP now offer native, but the box is still configured to use the tunnel.
Right. But is it a good idea to "cancel" service like that? I mean, in most cases, it's fine if the user is able to (automatically!) get v6 using other means -- but if it's not automatic, the user would be left without service altogether!
In other words, the ISP can cease tunneling service by taking down the tunnel server or making sure it provides no further allocations if the ISP wants to be "draconian". The most we should probably do is have a means for the client software to state that native v6 is available (whether mentioned by the server or not)..