Do not use non-replaceable static routes with IPv6 router discovery, when those routes are to destinations that are to be learned through received router advertisements. If these non-replaceable static routes are defined, they cannot be dynamically updated in response to network topology changes.
TCP/IP treats replaceable static routes as last-resort routes. These routes can be replaced by dynamic (router discovery) routes. In addition, if a replaceable static route is replaced with a dynamic route, TCP/IP always retains knowledge of the replaceable static route and can reinstall it if the destination becomes unreachable using dynamic routes. TCP/IP does not need to relearn replaceable static routes that are replaced. For this reason, replaceable static routes can be used with IPv6 router discovery as backup routes, to be used if nothing is learned dynamically.