关于配置wu-ftpd的问题！

Question

我用ckconfig检查，输出以下结果：
Checking _PATH_FTPUSERS :: /etc/ftpusers
ok.

Checking _PATH_FTPSERVERS :: /etc/ftpservers
I can't find it... look in doc/examples for an example.

Checking _PATH_FTPACCESS :: /etc/ftpaccess
ok.

Checking _PATH_PIDNAMES :: /var/run/ftp.pids-%s
ok.

Checking _PATH_CVT :: /etc/ftpconversions
ok.

Checking _PATH_XFERLOG :: /var/log/xferlog
ok.

Checking _PATH_PRIVATE :: /etc/ftpgroups
ok.

Checking _PATH_FTPHOSTS :: /etc/ftphosts
ok.
经查看，/etc/ftpservers不存在，这台服务器需要提供ftp服务，但是现在连接ftp总是拒绝，不知道什么问题？如果是iptables的限制，该如何限制？