dns A RR as failover

[feenberg at gmail.com]

Aleksander wrote:
> Hi,
>
> This question does not concern bind directly, but DNS generally.
>
> MX records are setup with priorities to create failover servers. That's
> nice. But could something like that be done with A records?
>
> Say, if I specify two A records for domain.com, which one will the
> clients use and what if the first one they tried, fails? I can't specify
> priorities for them like with MX.
>
> For example google.com has several A records. How does failover work for
> A records work in DNS?
>
> Thanks in advance,
>        Alex

Several years ago I studied this and produced

http://www.nber.org/redundant.html
 .
In short, of Outlook, Eudora and Pine, only Pine would try the second A
record after the first had failed.  As far as I know, no mail client
supports SRV records - too bad. My boss generally thinks redundant
servers should cost double, and I find it hard to explain that the
difference is more like a factor of ten, because most software is very
uncooperative with any simple redundancy setup.

Daniel Feenberg
feenberg isat nber dotte org

Daniel Feenberg