rbldnsd is a small and fast DNS daemon which is especially made to
serve DNSBL zones. This daemon was inspired by Dan J. Bernstein's
rbldns program found in the djbdns package.
rbldnsd is extremely fast - it outperforms both bind and djbdns
greatly. It has very small memory footprint.
The daemon can serve both IP-based (ordb.org, dsbl.org etc) and
name-based (rfc-ignorant.org) blocklists. Unlike DJB's rbldns, it
has ability to specify individual values for every entry, can
serve as many zones on a single IP address as you wish, and,
finally, it is a real nameserver: it can reply to DNS metadata
requests. The daemon keeps all zones in memory for faster
operations, but its memory usage is very efficient, especially for
repeated TXT values which are stored only once.