Reverse Delegations for Classless Nets
The fact that emperor.penguin.bv was assigned a classless net complicates reverse lookups. DNS can delegate only zones at the dots (.) in the domain names. But a classless net is specifically not divided at a dot; instead, one or more bits are divided into one of the octets, probably the last one.
As explained in RFC 1466, the use of classless nets is necessary to keep the Internet functioning. However, because this scheme was devised after DNS's reverse lookup method was established, the reverse lookup method was not designed to cope with this situation.
The problem, restated, is that DNS can delegate only whole A, B, or C nets, which are all divided at octet boundaries. After someone is delegated a net ...
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