% Expect to see routers being optimized that will only route % the upper 64bits of the address, so you might not want to do % anything smaller than that. This, if it happens, will be exactly opposed to the IPv6 design goal, which was to discourage/prohibit hardware/software designers from making presumptions or assumptions about the size of prefixes and HARDCODING them into products. --bill Opinions expressed may not even be mine by the time you read them, and certainly don't reflect those of any other entity (legal or otherwise).