You probably want the following:
$rdr_ip = "pcn0" # or $rdr_ip = inet4(pcn0) on the latest netbsd-6 kernel
map pcn0 dynamic 127.0.0.1 port 3890 <- $rdr_ip port 389
That would redirect all traffic coming into the machine on port 389, to port 3890. I only want to redirect traffic from one machine (10.0.0.53) to the service on port 3890, leaving all other machines to access the service on port 389.
Which NetBSD version are you using? You need 6.0.1 or newer kernel which
contains a bug fix affecting redirection to loopback.
I'm using 6.0.1 on i386
Many thanks for replying,