  * Local Cache
  
    dnrd can work as a local DNS cache if caching is not turned off with
    the "--cache=off" command line switch.  This is done by storing the
    complete DNS server responses from the master servers in a local cache.
  
    Normal responses are held for at least 60 minutes but not longer than
    6 hours. Negative responses from master servers are stored for five
    minutes.  These settings are defined in cache.h

    The cache knows also a high- and a low-water mark.  If the number of
    stored items is above the high-water mark (default 1000),
    cache items are removed until the low-water mark (default 750) is
    reached.  The values can be set with `--cache=[<low>:]high' on the
    command line.

