vsftpd- other port than 21?

[greengreen]

Hi,
I have Asus-wl500gx and a installed vsftpd server and i have:

Wan --->port 21 Asus:routing to ---->ftp on PC in LAn 192.168.1.2:21 -is now worknig

I would need to have:

Wan ---->port 2121 Asus vsftpd- but isn't runnig :-(

I try add this lines to vsftpd.conf:
listen_port=2121
pasv_min_port=50000
pasv_max_port=50050

and enable in post-firewall now my post-firewall look like:
#!/bin/sh
iptables -D INPUT -j DROP

iptables -A INPUT -p tcp --dport 2121 -j ACCEPT
iptables -A INPUT -p tcp --dport 50000 -j ACCEPT
iptables -A INPUT -p tcp --dport 50050 -j ACCEPT
iptables -A INPUT -p tcp --dport 2122 -j ACCEPT

/tmp/local/sbin/usr/local/sbin/graph.sh diff > /dev/null
iptables -A INPUT -p tcp ! --dport 22 -j DROP

have you anybody idea how to do to by running?
Thanks you very much and sorry for my english ;-)