Do many ISP's cache A records with TTL of 0 ?

[Marc.Thach at radianz.com]

IIRC an old colleague of mine was looking at this and that BIND 4.9 was
immune, only really early BIND versions did this.  We had a device with a
modified BIND 4.8.3 which cached correctly (however I know that it would
tinker with TTLs when required so maybe vanilla 4.8.3 would have failed).
We used to use TTL of zero as standard and since I was involved we never
had any issues with this sort of failover.
We did and still do have problems with web browsers that cache for constant
periods regardless of returned TTL  e.g. Communicator 4.5 900 seconds, IE
5.5 1800 seconds TTL by default (IE 3.x did 24 hours).  IIRC Sun Java SDK
was also a problem some years ago.

Marc TXK
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                    Simon Waters                                                                                       
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                    Sent by:                  Subject:     Re: Do many ISP's cache A records with TTL of 0 ?           
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Mark van Kerkwyk wrote:
>
>          I was looking for some information on whether many ISP's out
there
> ran name server caches which are very unfriendly to A records/zones with
a
> TTL of 0 (or very low anyway) for global server load balancing purposes.

TTL's of zero are known to cause problems and should be avoided.

BIND 4 is the culprit according to Cricket.

> I was told that a while back AOL used to cache all records for a number
of
> days, irrespective of whether it had a TTL of 0 or anything (eg over 1
> day).

We have a resident expert who would never have let them do that
when he worked there.

It is definitely against the standards, and I'm not aware of
anyone doing it.

Some people reduce very large TTL values by setting a maximum, I
guess it is okay to forget things early, but not to remember
stuff which is out of date.

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