我用ＳＥＲＶ－Ｕ建立了一个ＦＴＰ服务器，显示无法登陆，详细消息是无法与服务器建立连接，我是照书上做的，不知是什么原因，有那位能告诉我，谢谢.请问我要怎么做才知道是那方面的问题

这是会话日志的内容：
Fri 01Dec06 08:52:14 - Serv-U FTP Server v6.3 (6.3.0.0) - Copyright (c) 1995-2006 Rhino Software, Inc., All Rights Reserved
Fri 01Dec06 08:52:14 - Build Date: 2006年6月12日 9:09
Fri 01Dec06 08:52:15 - Using WinSock 2.0 - max. 32767 sockets
Fri 01Dec06 08:52:21 - Loaded SSL/TLS libraries
Fri 01Dec06 08:52:21 - FTP Server listening on port number 18915, IP 127.0.0.1
Fri 01Dec06 08:52:22 - FTP Server listening on port number 21, IP 172.25.144.218
Fri 01Dec06 08:52:22 - Valid registration key found

这是域日志：
[1] Fri 01Dec06 08:52:15 - Starting FTP Server...
[1] Fri 01Dec06 08:52:22 - FTP Server listening on port number 21, IP 172.25.144.218
[5] Fri 01Dec06 15:16:13 - (000001) Connected to 172.25.144.218 (Local address 172.25.144.218)
[5] Fri 01Dec06 15:16:13 - Connection denied to IP-number 172.25.144.218
[5] Fri 01Dec06 15:16:13 - (000001) Closing connection
[5] Fri 01Dec06 15:16:13 - (000002) Connected to 172.25.144.218 (Local address 172.25.144.218)
[5] Fri 01Dec06 15:16:13 - Connection denied to IP-number 172.25.144.218
[5] Fri 01Dec06 15:16:13 - (000002) Closing connection
[5] Fri 01Dec06 15:20:40 - (000004) Connected to 172.25.144.218 (Local address 172.25.144.218)
[5] Fri 01Dec06 15:20:40 - Connection denied to IP-number 172.25.144.218
[5] Fri 01Dec06 15:20:40 - (000004) Closing connection
[5] Fri 01Dec06 15:20:40 - (000005) Connected to 172.25.144.218 (Local address 172.25.144.218)
[5] Fri 01Dec06 15:20:40 - Connection denied to IP-number 172.25.144.218
[5] Fri 01Dec06 15:20:40 - (000005) Closing connection


请问是否必须建立域