cache-size

(Optional) Specifies how many entries are contained in the cache. Acceptable values are 32 to 32768. The default value is 1024.

expire

(Optional) Specifies how long in seconds before a cache entry should expire. Acceptable values are 1 to 31536000 (1 year). The default value is 1200 seconds (20 minutes).

negative-dns-cache

Enables or disables the caching of invalid host names. The default value is yes.