# guest:
$ cc -O2 -o trigger_div0 trigger_div0.c      -> exit 0 (warnings only)
$ pfctl -nvf rdr_div0.conf
rdr pass on lo0 inet proto tcp from any to 127.0.0.1 port = 9998 -> 127.0.0.1 port 5001:5000
pass all flags any keep state (pickups, sloppy)
(pfctl ACCEPTS the reversed range - parseport() keeps a>b)