dns and software, was Re: Reliable Cloud host ?

Mark Andrews marka at isc.org
Wed Feb 29 01:46:56 UTC 2012

In message <CAP-guGXK3WQGPLpmnVsnM0xnnU8==4zONK=UWTLkYWuduA6T9Q at mail.gmail.com>,
 William Herrin writes:
> On Tue, Feb 28, 2012 at 4:06 PM, Mark Andrews <marka at isc.org> wrote:
> > DNS TTL works. =A0Applications that don't honour it arn't a indication th=
> at
> > it doesn't work.
> Mark,
> If three people died and the building burned down then the sprinkler
> system didn't work. It may have sprayed water, but it didn't *work*.

Not enough evidence to say if it worked or not.  Sprinkler systems
are designed to handle particular classes of fire, not every fire.

A 0 TTL means use this information for this transaction.  We don't
tear down TCP sessions on DNS TTL going to zero.

If one really want to deprecate addresses we need something a lot
more complicated than A and AAAA records in the DNS.  We need stuff
like "use this address for new transactions", "this address is going
away soon, don't use it unless no other works".  One also has to use
multiple addresses at the same time.

Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org

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