Two questions about the name server address sorting functionality

Mark_Andrews at Mark_Andrews at
Mon Oct 14 23:59:14 UTC 2002

> "Johan Larsson (EAB)" wrote:
> > Hi Mark!
> >
> > Do you know when BIND 9.3 will be available?
> >
> > I also would like to know if the following features are going to be support
> ed in BIND 9.3:
> >
> > True Round Robin (not only random-cyclic as in BIND 9.1.3)?
> Do you *really* want *true* round-robin? With *true* round-robin, whenever yo
> u have one
> address fail, the address which is rotationally "after" that address, gets ha
> mmered by all of
> the clients which fail over, e.g. in a ABC/BCA/CAB sequence, "B" gets hammere
> d with as much
> as 2x normal traffic if "A" fails.
> AFAIK, the optimal sort order is "permuted", i.e. all possible permutations p
> resented with
> equal frequency (e.g. ABC/BCA/CAB/ACB/BAC/CBA, for a 3-valued RRset), so that
>  the traffic is
> as equally spread as possible, even in the face of failures (in the same fail
> ure scenario,
> "B" only gets max 1.5x traffic, and, unlike "true" round-robin, this ratio de
> creases the
> larger the RRset gets). Unfortunately, "permuted" sort order requires storing
>  a significant
> amount of state about each multi-valued RRset (the number of permutations goe
> s up factorially
> with the number of records in the RRset), so it tends to be rather resource-i
> ntensive.
> Still, if someone is coding "true" round-robin anyway, perhaps they might giv
> e some
> consideration to adding "permuted" order as well...

	Well "permuted" is a lot of work and really does not provide any
	benefit over "random" which is available in BIND 8 and BIND 9.3.

> - Kevin
Mark Andrews, Internet Software Consortium
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark.Andrews at

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