[rbldnsd] TTLs and negative caching

[Jeff Chan]

On Tuesday, August 3, 2004, 4:51:56 AM, Jon Lewis wrote:
> set a small TTL via the SOA record (this
> will be used as the negative cache TTL).  You can set the positive answer
> TTL separately via a -t commandline arg or $TTL special in datasets.

> If you look at the NJABL servers, positive answers have a TTL of 21600,
> but negatives have 900.

That makes some sense, as if to say "remember the positive
entries longer than the negative ones."  But it seems to
differ from Michael's intuition that there is a lot more
negative caching than positive, so a short TTL on negative
would have a much larger effect on increasing traffic.

The thing to keep in mind is that most of the queries to
an RBL result in negative responses, as in "this domain
or ip is not on the list" since the lists are much smaller
than the superset of everything else on the Internet, which
might be checked against an RBL.

Jeff C.
-- 
Jeff Chan
mailto:jeffc at surbl.org
http://www.surbl.org/