Reverse ftp-proxy setup

use ftp-proxy -R internal.server.ip -D7 -v can easily setup a reverse FTP proxy on OpenBSD.

Remember to allow packet forwarding in sysctl.conf, and also turn on the ftp-proxy anchor in pf.conf.

Setting up ftpd

1) edit /etc/rc.conf as below then reboot, or:
ftpd_flags="-DllUSA" # for non-inetd use: ftpd_flags="-D"

2) manually fire up your ftpd:
# /usr/libexec/ftpd -DllUSA

3) edit files as below for setting up details of ftpd, such as welcome message, hostname, denied users, and site-wide nologin. Remember that ftp user shell should be set to /sbin/nologin.

/etc/ftpchroot (important!!)
/etc/shells
/etc/ftpwelcome
/etc/myname
/etc/ftpusers
/etc/nologin

REFERENCES:
http://www.tongatapu.net.to/nix/OpenBSD/ftpServer.htm
http://www.twbsd.org/cht/book/ch15.htm