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

Simon Waters Simon at wretched.demon.co.uk
Fri Aug 31 20:05:17 UTC 2001


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stuff which is out of date.
 
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