dns server and client load blancing behavior
Brad Knowles
brad.knowles at skynet.be
Fri Sep 14 22:54:39 UTC 2001
At 10:45 AM +0800 9/14/01, Æ}Æ©[ wrote:
> if I has following RR
> ms1 IN MX 0 ms1_1
> IN MX 0 ms1_2
First off, don't use underscores. They are illegal in hostnames.
> ms1_1 IN A 10.10.10.1
> IN A 10.10.10.2
> IN A 10.10.10.3
> ms1_2 IN A 10.10.10.4
> IN A 10.10.10.5
> IN A 10.10.10.6
>
> then query mx Record for ms1,will name server response all the above RRs for
> client,and the what the RR order?
The order will be non-determinate, in accordance with the RFCs.
Some servers will do a round-robin (listing one first on one query
and then the other first on the next query), and other servers will
use other randomization mechanisms.
> How long do Mircrosoft client or any other client will cache the RR?
Unfortunately, Microsoft OSes will only ever attempt to contact
the first IP address listed for any machine that they look up (they
simply never see the second or other IP addresses), and they will
cache this one IP address forever -- well, until they get rebooted.
So, the generally accepted solution is to have an
application-layer proxy, or a layer 4 load-balancing switch sitting
in front of however many back-end machines you have, and then you
list only the one IP address of the application proxy or L4
load-balancing switch, and it hides the rest of that complexity from
the Microsoft client.
--
Brad Knowles, <brad.knowles at skynet.be>
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