RewriteEngine On

# ?dev nur intern
RewriteCond %{QUERY_STRING} ^dev$ [NC]
RewriteCond %{REMOTE_ADDR} !^192\.168\.
RewriteRule ^ - [F]

# /dev nur intern
<FilesMatch "^dev$">
    Require all denied
    Require ip 192.168.0.0/16
    Require ip 127.0.0.1
</FilesMatch>