> Further to that, ifindexes of tunnels and PPP sessions can change dynamically as the bearer connection goes up and down, even if the interface has the same name and authenticated identity. That raises the interesting question of whether even the interface name is stable, as on many systems it is pure chance if the same name-identity mapping repeats itself. > > If you want a stable address, you want to use something that actually has the exact stability properties you require, and interface indexes and names are seldom what you actually need. could we simplify the hash to only include the prefix, cookie and DAD counter: RID = F(Prefix, secret_key, DAD_Counter) an implementation that wants a stable address for cases where DAD_Counter > 0, must keep state. e.g. maintain a table of prefix, dad_counter or list of previous addresses. cheers, Ole