RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{HTTP_HOST} ^([a-z0-9-]+).dominio.com.br [NC]
RewriteRule (.*) index.php?insubdominio=%1&inrouter=$1 [NC,L,QSA]
ErrorDocument 404 /404.php