What is HostnameLookups and what's the target?

Question

i'm trying to get the meaning of HostnameLookups in apache configuration file (httpd.conf). I'm also interested about the target of this directive.

Thanks Alessandro

Answer 1

http://httpd.apache.org/docs/2.2/mod/core.html#hostnamelookups

Quoth the Manual:

This directive enables DNS lookups so that host names can be logged
(and passed to CGIs/SSIs in REMOTE_HOST). The value Double refers to
doing double-reverse DNS lookup. That is, after a reverse lookup is
performed, a forward lookup is then performed on that result. At
least one of the IP addresses in the forward lookup must match the
original address. (In "tcpwrappers" terminology this is called PARANOID.)