pdnsd is a proxy dns server with permanent caching (the cache contents are
written to hard disk on exit) that is designed to cope with unreachable or
down dns servers (for example in dial-in networking).
pdnsd can be used with applications that do dns lookups, eg on startup, and
can't be configured to change that behavior, to prevent the often minute-long
hangs (or even crashes) that result from stalled dns queries. Some Netscape
Navigator versions for Unix, for example, expose this behavior.
pdnsd is configurable via a file and supports run-time configuration using the
program pdnsd-ctl that comes with pdnsd. This allows you to set the status
flags of servers that pdnsd knows (to influence which servers pdnsd will
query), and the addition, deletion and invalidation of DNS records in pdnsd's
cache.
Parallel name server queries are supported. This is a technique that allows
querying several servers at the same time so that very slow or unavailable
servers will not block the answer for one timeout interval.
Since version 1.0.0, pdnsd has full IPv6 support.

WWW: http://members.home.nl/p.a.rombouts/pdnsd/