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 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.