rbldns-data updates data.cdb atomically, so you can use it safely while rbldns is running. If anything goes wrong with the creation of data.cdb, rbldns-data stops and leaves the old data.cdb in place.
ip4/n : All IPv4 addresses that share the first n bits of the IP address ip4 are on the list. For example, 1.2.3./24 means all 1.2.3.* addresses.
ip6 : The IPv6 address ip6 provided in compactified format is on the list.
ip6/n : All IPv6 addresses sharing the first n bits of ip6 are considered. A rule 2002:/16 would block all 6to4 addresses. For practical reasons, n needs to smaller/equal than 64, since the lower bits of an IPv6 address denominates the link token and is not relevant for routing.
=a:txt : DNS queries for addresses on the list will receive an A record of a and a TXT record of txt. Typically a is 127.0.0.2 and txt is a pointer to a web page about the list.
If txt ends with $, rbldns replaces the $ with the IP address.
#comment : Comment line. The line is ignored.
Note: The generated data.cdb is not binary compatible with older versions of rbldns. In addition, IP addresses are evaluated at bit level to comply with the CIDR requirements.