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To make use of the proxy, pf.conf(5) needs the following rules. All
anchors are mandatory.  Adjust the rules as needed.

In the NAT section:

  nat-anchor "ftp-proxy/*"
  rdr-anchor "ftp-proxy/*"
  rdr pass on $int_if proto tcp from $lan to any port 21 -> \
      127.0.0.1 port 8021

In the rule section:

  anchor "ftp-proxy/*"
  pass out proto tcp from $proxy to any port 21 keep state

Add the following line to your /etc/rc.conf to enable the proxy on
startup:

  ftpproxy_enable="YES"

Please consult the man page ftp-proxy(8) for more information.
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