Round Robin and BIND
kcd at daimlerchrysler.com
Tue Feb 21 21:24:19 UTC 2006
The default ordering is "cyclic", which picks the first record at random
from the set, and arranges the remaining records in "rotational" order,
relative to that first record. So, yes, sometimes you will see exactly
the same records in the same order on consecutive queries. The fewer
records in the set, the more likely this is to happen.
This, of course, is *bad* for address failover. It combines the worst
aspect of random ordering, i.e. unpredictable "spikiness", with the
skewing effect of "pure" round-robin, i.e. when one server is down, the
next server in the rotational sequence gets a disproportionate share of
traffic because of failover. The only saving grace, perhaps, is that by
not storing any dynamic state, "cyclic" ordering might save a few bytes
of memory here and there.
Vahric MUHTARYAN wrote:
>Thanks For your answers
>No I'm not talking about reqursive query :) also thanks for explanation but
>I know How it work but my question is sometimes bind did not make right
>rotation ! sometimes it's giving same response
>From: bind-users-bounce at isc.org [mailto:bind-users-bounce at isc.org] On Behalf
>Of Barry Margolin
>Sent: Monday, February 20, 2006 9:38 PM
>To: comp-protocols-dns-bind at isc.org
>Subject: Re: Round Robin and BIND
>In article <dtd4q2$2tiq$1 at sf1.isc.org>,
> "Vahric MUHTARYAN" <vahric at doruk.net.tr> wrote:
>>I tested to run round robin on BIND ( old version 9.2.3 I guess ) but I
>>that bind is sending request to nodes not equal . Anybody have a knowledge
>>about this ? Maybe in new version it starts to work much better ? or any
>Round-robin refers to the order of the answers in a response. To see
>this, do "dig yahoo.com a" several times and you'll see that the A
>records are in a different order each time.
>It sounds like you're talking about the order in which it selects
>nameservers to send recursive queries to. That is *not* round-robin.
>It remembers the response time of previous queries, and prefers servers
>that respond quicker.
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