On Jul 20 2009, Tech W. wrote:
I have Bind-9.6.1 running on our university environment, have been
using dynamic update.
My question is, when other DNS query my named for a record, for example
test.example.com, but this record doesn't exist. How long time will the
remote DNS cache this nonexist record?
Read RFC 2308 "Negative Caching of DNS Queries". Roughly, the answer is
"(at most) the (now misnamed) MINIMUM field of the SOA record for the zone".
I found the problem that if this nonexist record was cached by remote
DNS, even if I added the corresponding record to named zone soon, the
remote DNS can't find it quickly.
This is not good for dynamic update IMO, for example, I need to change
a record, then I have to do:
nsupdate delete ....
nsupdate add ....
If the remote DNS query for this record just after 'nsupdate delete',
then it will get nothing and cache this nonexist record for some time,
even though the correct record has been added. How to deal with this case?
Do the delete and the add in the same update transaction:
nsupdate <<EOF
update delete ...
update add ...
send
EOF
--
Chris Thompson
Email: c...@cam.ac.uk
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