... Apache HTTP Server Version 2.4 . ... This page could be summarized with the statement: don't configure Apache HTTP Server in such a way that it relies on DNS resolution for parsing of the configuration files. If httpd requires DNS resolution to parse the configuration files then your server may be subject to reliability problems (ie. it might not start up), or denial and theft of service attacks (including virtual hosts able to steal hits from other virtual hosts). ... The "main server" Address . ...

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This page could be summarized with the statement: don't require Apache to use DNS for any parsing of the configuration files . ... In order for Apache to function properly it absolutely needs to have two pieces of information about each virtual host: the ServerName and at least one IP address that the server responds to. ... use IP addresses in Listen . ... In any event it doesn't seem possible to reliably boot a virtual-hosted web server when DNS has failed unless IP addresses are used. ...