On Fri, Sep 18, 2015 at 9:49 AM, Jari Arkko <[email protected]> wrote: > Donald, > >>> (Maybe this helps: I’m not actually sure why in a k-element set you order >>> them based <something> mod k because that would seem to produce likely >>> duplicates. Since your backup option in the case of duplicates is proper >>> numeric sort, why just not do that and only that? E.g. "RBridges are sorted >>> in byte string ascending order by their LAALP IDs, or if they are equal, by >>> their System IDs considered as unsigned integers.” But it could also be >>> that it is too early and I have not yet had enough Diet Coke…) >> >> I believe the idea is to quasi-randomize the order. The DF election is >> per VLAN and a goal is to spread the multicast traffic across the >> RBridges in the active-active edge group. > > It is a fine goal to randomise the order. > > My only observation of the current setup is that if you randomise a > k-element group through "mod k” operation, you will likely have > some number of collisions in the result. I don’t know enough > about math to calculate the percentage. But for the sake of > argument, if k=2 it seems that the likelihood of collision is 50%. > > And for every collision, your order becomes no longer random > but simply numerical order of the identifiers. In our degenerate > k=2 example it seems that in 50% of the cases you have a random > order and 50% of the cases you have numerical order. I’m sure > there would be other ways to randomise the order with less > collisions, if avoiding numerical order is important.
Well, the way to randomize the order with quite low probability of collisions is to sort by the hash of (System IDj | LAALP IDi), for example SHA-1(System IDj | LAALP IDi). Ties could still be broken by System ID which is guaranteed to be unique but ties would be quite rare. This seems like a minor localized change. > Jari Thanks, Donald ============================= Donald E. Eastlake 3rd +1-508-333-2270 (cell) 155 Beaver Street, Milford, MA 01757 USA [email protected] _______________________________________________ Gen-art mailing list [email protected] https://www.ietf.org/mailman/listinfo/gen-art
