The following in an .htaccess file, will redirect all web-browser clients except the one using IP 111.111.111.111
<IfModule mod_rewrite.c> RewriteEngine on RewriteCond %{REMOTE_ADDR} !^111\.111\.111\.111 RewriteCond %{REQUEST_URI} !/maint.html$ [NC] RewriteCond %{REQUEST_URI} !\.(jpe?g?|png|gif) [NC] RewriteRule .* /maint.html [R=302,L] </IfModule>