diff --git a/config.json b/config.json
index 988100f..55f12b5 100644
--- a/config.json
+++ b/config.json
@@ -15,6 +15,7 @@
     "speed_limit_per_user": 0,
 
     "additional_ports" : {}, // only works under multi-user mode
+    "additional_ports_only" : false, // only works under multi-user mode
     "timeout": 120,
     "udp_timeout": 60,
     "dns_ipv6": false,
diff --git a/db_transfer.py b/db_transfer.py
index a5fb862..17a28fc 100644
--- a/db_transfer.py
+++ b/db_transfer.py
@@ -152,8 +152,9 @@ class TransferBase(object):
 				else:
 					self.new_server(port, passwd, cfg)
 			else:
+				config = shell.get_config(False)
 				if ServerPool.get_instance().server_is_run(port) > 0:
-					if not allow:
+					if config['additional_ports_only'] or not allow:
 						logging.info('db stop server at port [%s]' % (port,))
 						ServerPool.get_instance().cb_del_server(port)
 						self.force_update_transfer.add(port)
@@ -164,7 +165,7 @@ class TransferBase(object):
 							self.force_update_transfer.add(port)
 							new_servers[port] = (passwd, cfg)
 
-				elif allow and port > 0 and port < 65536 and ServerPool.get_instance().server_run_status(port) is False:
+				elif not config['additional_ports_only'] and allow and port > 0 and port < 65536 and ServerPool.get_instance().server_run_status(port) is False:
 					self.new_server(port, passwd, cfg)
 
 		for row in last_rows:
diff --git a/shadowsocks/shell.py b/shadowsocks/shell.py
index 1540412..f0e0cb0 100755
--- a/shadowsocks/shell.py
+++ b/shadowsocks/shell.py
@@ -245,6 +245,7 @@ def get_config(is_local):
     config['obfs_param'] = to_str(config.get('obfs_param', ''))
     config['port_password'] = config.get('port_password', None)
     config['additional_ports'] = config.get('additional_ports', {})
+    config['additional_ports_only'] = config.get('additional_ports_only', False)
     config['timeout'] = int(config.get('timeout', 300))
     config['udp_timeout'] = int(config.get('udp_timeout', 120))
     config['udp_cache'] = int(config.get('udp_cache', 64))