> > >Fortunately the mistake is easily rectified, so long > >as software doesn't get into the habit of expecting the lower 64 bits > >of an address to be a unique interface identifier. > > This is a dangerous prospect. The company I work for makes a networking > stack and our IPv6 implementation expects the lower 64 bits to be the unique > interface identifier. Other implementations do the same. My advice would be for you and your competitors to fix this problem as part of your normal product improvement. Because sooner or later those whose products don't support subnets past /64 will lose business to those that do. It's all well and good to insist that ISPs give out /48s to their customers, but it's not wise to pretend that everyone will comply. There will be customers that can't get better than a /64 and will need to subnet.