OK, Darren, I give up :-)  How does IPFilter's FTP Proxy actually
work?  My specific requirement is to have host 172.24.16.4 act as
both FTP server and FTP client, I can get FTP service to work by
providing NAT as

	map ne0 196.30.44.140/32 port 21 -> 172.24.16.4/32 port 21 ...

plus some, but I can't quite get a handle, from the examples in
/usr/share/examples/ipf, on how to make FTP Proxy work.  NAT
makes FTP passive mode impractical, while active mode seems to
require some serious gymnastics I can't quite bend my mind around.

Any help welcome.  The machine I'm trying all this on runs NetBSD
1.3.2 on i386.

++L