Re: [Nmh-workers] [OT] Strange DNS for cyrus.andrew.cmu.edu was: IMAP/nmh, again

[valdis . kletnieks]

On Thu, 26 Oct 2017 22:42:12 -0400, Ken Hornstein said:
> >Thus said Ken Hornstein on Thu, 26 Oct 2017 14:22:37 -0400:
> >But the A record for that name is only 1 second... strange:
> >
> >$ dnsqr a cyrus.andrew.cmu.edu
> >1 cyrus.andrew.cmu.edu:
> >86 bytes, 1+3+0+0 records, response, noerror
> >query: 1 cyrus.andrew.cmu.edu
> >answer: cyrus.andrew.cmu.edu 1 A 128.2.158.26
> >answer: cyrus.andrew.cmu.edu 1 A 128.2.105.45
> >answer: cyrus.andrew.cmu.edu 1 A 128.2.158.29
> >
> >I wonder  what the  purpose of  such a  configuration might  be.
>
> I suspect they wanted to provide high reliability and have clients fall
> over to one of the other servers quickly.  But even Google has a TTL
> of 300 seconds for imap.gmail.com.

This can also happen if you've been slowly ramping down the TTL before an
address change - you may have 3 days as the TTL.  A week before, set TTL to one
day, 2 days before, set to an hour, etc and then for the last hour finally down
to some tiny like a few seconds.  After the new DNS entry is out, you push out
a new one with a more sane TTL.

And if you forget that last step, this is what you get.

pgpNnY3eNFeMu.pgp
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