/etc/ipnat.rules
  Hardware Dependent
# Uncomment if you need to run non-passive FTP
#map ep0 <--------
192.168.0.0/24 -> 0/32 proxy port ftp ftp/tcp <--------
User Choice
# THESE are the only two lines that actually are needed
map ep0 192.168.0.0/24 -> ep0/32 portmap tcp/udp 10000:20000
map ep0 192.168.0.0/24 -> ep0/32  
LEGEND
Red hardware dependent
Purple variable (user choice)
Black same for everyone
Green dependent on outside circumstances (e.g. ISP)