$ vlc rtsp://192.168.1.123:554//mpeg4cif
Username: admin
Password: 123456
I found the suggestion for this RTSP path at http://www.ispyconnect.com/man.aspx?n=china
Update: You can call it directly without enter user/pass all the time:
$ vlc rtsp://admin:123456@192.168.1.123:554/mpeg4cif