請問利用natd 使用ftp - BBS

我利用natd&ipfw 想要透過外界來連我nat下的機器 但是連的時候在檢查使用者時
就卡住了 之後就出現invalid username or password
而我的 rc.conf檔
defaultrouter="140.113.91.254"
hostname="sugar.Dorm8.NCTU.edu.tw"
ifconfig_rl0="inet 140.113.X.X netmask 255.255.255.0"
ifconfig_sk0="inet 192.168.0.1 netmask 255.255.255.0"
kern_securelevel_enable="NO"
nfs_reserved_port_only="YES"
sendmail_enable="YES"
sshd_enable="YES"
usbd_enable="YES"
apm_enable="YES"
apmd_enable="YES"
gateway_enable="YES"
firewall_enable="YES"
firewall_script="/usr/local/sbin/firewall.sh"
natd_enable="YES"
firewall_type="OPEN"
natd_interface="rl0"
natd_flags="-redirect_port tcp 192.168.0.53:21 21"
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firewall.sh 檔
#!/bin/sh
fwcmd='/sbin/ipfw -q'
${fwcmd} -f flush
${fwcmd} add allow ip from any to any via rl0
ipfw add allow tcp from 140.113.0.0/16 to me 1-3000
ipfw add 50 divert natd all from any to any via rl0
ipfw add allow all from 192.168.0.53

請問是設定出了什麼問題呢
謝謝

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