> > IPv6 requires renumbering when an address that has been used is no longer > > appropriate (which will generally be because of changed topology, which > > may be local topology changes - moving a host to a different LAN, or > > global ones - connecting to a different provider). That is the only > > reason. As long as prefixes remain usable, they can keep on being used, > > with other prefixes added as required. > > Well.. all you need to do to fix this is to make a rule that if a > global prefix becomes available, the site-local prefix is no longer > appropriate and must be withdrawn. this only solves one of several problems with site-locals, and it removes one of the few supposed benefits of site-locals - that such addresses will be stable across prefix changes.