[rbldnsd] TTLs and negative caching

[Jon Lewis]

On Tue, 3 Aug 2004, Jeff Chan wrote:

> We run SURBL which has RBLs containing spam URI domains.
> They are used to block spam based on URI domains contained
> in message bodies.
>
> Currently some of our zone files have fairly long TTLs
> of several hours.  This appears to be causing new entries
> to take several hours to become active.
>
> 1.  Does that sound right?  In other words does TTL apply
> to negative caching or only to positive caching (or to both).
> By observing the behavior of an rbldnsd installation, TTL
> does seem to affect negative caching.
>
> 2.  Can we expect a lot more DNS traffic if we lower our
> TTLs to say 10 minutes?

Yes.  Don't do that.  Instead, 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.

----------------------------------------------------------------------
 Jon Lewis                   |  I route
 Senior Network Engineer     |  therefore you are
 Atlantic Net                |
_________ http://www.lewis.org/~jlewis/pgp for PGP public key_________