[rbldnsd] TTLs and negative caching

[Jon Lewis]

On Tue, 3 Aug 2004, Jeff Chan wrote:

> 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.

I'm not so sure about that.  A typical server sees more rejected
deliveries than accepted ones at this point, but I've never looked at
stats on the actual number of accepted vs rejected unique sources.

The idea is a small negative TTL makes additions recognized faster.

> 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.

It might be interesting if there were a way to have negative TTLs for
certain specific unlisted IPs.  i.e. give the AOL outgoing mail servers a
big negative TTL...since they're unlikely to ever get listed.

Without such an ability, negative TTL is just a compromise between how
much query load you can handle and how fast you want additions to be
recognized by servers that have already cached negative answers.

----------------------------------------------------------------------
 Jon Lewis                   |  I route
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