I have tried use what you just suggest:
RewriteCond %{REMOTE_ADDR} ^192\.168\.1\.*$
RewriteCond %{REMOTE_ADDR} !^192\.168\.1\.4$
RewriteCond %{REMOTE_ADDR} !^192\.168\.1\.5$
RewriteCond %{REMOTE_ADDR} !^192\.168\.1\.6$
But it didn't work.
