rbldns runs chrooted in the directory specified by the $ROOT environment variable, under the uid and gid specified by the $UID and $GID environment variables.
rbldns listens for incoming UDP packets addressed to port 53 of $IP. It discards packets from low ports other than 53. It does not listen for TCP queries.
rbldns handles domains of the form d.c.b.a.base where a.b.c.d is the IP address in question and base is given by the $BASE environment variable.
rbldns rejects inverse queries, non-Internet-class queries, truncated packets, packets that contain anything other than a single query, query types other than A, TXT, or *, and queries for domains outside $BASE. It looks up other queries inside data.cdb, a binary file created by rbldns-data.