[rbldnsd] Custom TTL for NXDOMAIN replies for certain queries

[Lorenzo Martignoni]

Hello,

I am interested in extending rbldnsd to support a custom TTL for certain
negative replies.  The intent is to reduce the number of queries that
target well known benign network blocks.

For example, imagine 192.168.0.0/16 is a well known network block, that
is not listed in your blacklist and never will be, and that your rbldnsd
server receives a lot of queries about addresses in this block. In the
current implementation the server replies to each query about addresses
in this block with NXDOMAIN and the TLL of the responses is set to the
minimum (as defined in the command line or in the SOA record).  Thus,
clients keep querying, very frequently, your server.  I am interested in
the ability to specify in the blacklist file that 192.168.0.0/16 is not
blacklisted (like for exclusion entries) and that a custom TTL should be
used when replying to queries involving addresses in this block. A
custom and higher TTL allows to significantly reduce the number of queries.

I don't think that such a feature would be difficult to implement.
However, I'm concerned about a clean way to do that. In particular my
main concern is about the syntax to use to declare a custom TTL in the
blacklist file.

Do you have any suggestions?

Thank you very much,
Lorenzo