Re:DNS Round-Robin question, redhat-digest Digest V99 #958

[Olmy <olmy thistledown org>]

> >However, there are several issues I wonder about:
> >
> >1)  Does the round-robin feature work well for mail, or is there something I
> >am missing?
> 
> Should work well for outgoing, your DNS might take a beating since your TTL
> has to be short to keep other sites caches flushed for incoming.  Perhaps
> manipulating the MX records would be better.  I'm not expert enough here to
> offer any solid advice.


You can do equal-value MX records to achieve some measure of
load balancing. However, the problem with this is that the actual
calculation of which equal-value MX record to use will vary from
mail server to mail server. In this particular use, it is the
smtp server, NOT the DNS server, that will make that decision.

Newer versions of sendmail support load-balancing based upon
equal-value MX. Other mail servers may not, however -- creating
a heavier load for the first MX that gets returned.

I tried it as an experiment a couple of months ago and it didn't 
work that great. MS Exchange, for example, seemed to ignore the
second equal-value MX entirely unless the first server wasn't
responding to smtp.

On the general subject of load-balancing with DNS, I'd suggest
any interested individuals read the posted discussions at
the following URL:


http://www.isc.org/bind-lb.html



olmy