Round-Robin for mail/smtp hosts

[Brad Knowles]

At 7:31 PM -0700 7/3/01, Matt Prigge wrote:

>  What I am most curious about is how the clients (OE/Netscape/etc) implement
>  failover using multi-A RRsets.

	They don't.  They latch onto the first IP address they are told, 
and they will never, ever try a different one (no matter how many 
times you have them re-query for correct information) until they are 
rebooted.

>                                  Is it handled by the underlying OS?

	In my experience, it's not handled at all.  It should be handled 
by the OS, but it simply isn't.

>                                                                       Or is it
>  the client really responsible for trying the first RR and then, if that
>  fails, trying subsequent RRs out of the same set?

	There may be clients out there that have been written to by-pass 
this problem within Microsoft OSes, but I have never personally 
experienced any.

>                                                     Do some clients not do
>  this?

	I have not yet encountered a client on a Microsoft OS that goes 
to this length.

>         This scheme seems like it will work well as a low-grade form of load
>  balancing, but how well will it work as far as redundancy is concerned?

	In my experience, it won't.

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

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