Same-Preference MX Records

[Brad Knowles]

At 9:01 PM -0700 7/3/01, Matt Prigge wrote:

>  I have two incoming mail servers that Id like to evenly balance load across
>  and still maintain redundancy. Someone suggested offlist that I use two
>  same-preference MX records pointing to my servers, but I am not sure that
>  using same-preference MX records is an accepted practice (thus the reason
>  for my question).

	Nope, this is the suggested way of doing things.

>                     I can see quite clearly that AOL does this, but that
>  doesnt always mean its right. *grin* Are there any downsides to doing this?

	Yeah.  If one of the machines goes down and you put up a 
replacement, it may take a while for the IP address of the new 
machine to get distributed.  If you have the new machine steal the IP 
address of the old one, then you've got problems when the old machine 
tries to come back up.  As you add more machines, you will tend to 
get an imbalance of traffic across them, as some large sites cache 
DNS queries regarding your MXes, and will always prefer them in the 
order they cached them, until such time as they refresh their cache.

	The best solution to avoid all these problems is to implement a 
proper L4 load-balancing switch, behind which you hide all your mail 
servers.  See <http://www.vegan.net/lb/> for more information.

-- 
Brad Knowles, <brad.knowles at skynet.be>

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