I have turned off DNS lookups for one of my virtual servers, but the web server continues to log hostnames in the access log. Why is this?

For performance reasons, the web server initiates the asynchronous DNS reverse lookup of the client's IP address before it has parsed the HTTP Host: header to determine which virtual server the request belongs to. Therefore, turning on DNS lookups for any of your virtual servers effectively enables DNS lookups for all of them.

If you wish to disable DNS lookups, you should ensure that they are turned off for all virtual servers.

The tunable 'dnslookup' in the virtual server configuration files determines whether or not reverse lookups will occur. Set it to 'no' to disable lookups.