Re: [Gen-art] Gen-ART Review of draft-ietf-trill-pseudonode-nickname-05

[Mingui Zhang <[e-mail]>]

Hi Donald,

Thanks for the suggestion. That change will be incorporated in the new version.

Thanks,
Mingui

> -----Original Message-----
> From: Donald Eastlake [mailto:[e-mail]]
> Sent: Monday, September 21, 2015 4:39 AM
> To: Jari Arkko
> Cc: IETF Gen-ART; IETF; [e-mail]
> Subject: Re: Gen-ART Review of draft-ietf-trill-pseudonode-nickname-05
> 
> On Fri, Sep 18, 2015 at 9:49 AM, Jari Arkko <[e-mail]> 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   [phone] (cell)
>  155 Beaver Street, Milford, MA 01757 USA  [e-mail]