lucy24 - 6:19 am on Feb 14, 2012 (gmt 0)
This is an interesting coincidence. Only a day or two back, I discovered that adding even a single Regular Expression to my IP block list has the same effect. Something as rock-bottom simple as changing
(I experimented to confirm it.)
Regardless of the setting, when mod_authz_host is used for controlling access by hostname, a double reverse lookup will be performed. This is necessary for security. Note that the result of this double-reverse isn't generally available unless you set HostnameLookups Double. For example, if only HostnameLookups On and a request is made to an object that is protected by hostname restrictions, regardless of whether the double-reverse fails or not, CGIs will still be passed the single-reverse result in REMOTE_HOST.
This configuration will cause Apache to perform a double reverse DNS lookup on the client IP address, regardless of the setting of the HostnameLookups directive.
None of this leaves me any the wiser :( I can't think where else to look.