Port mapping & NAT with pf

1) edit /etc/sysctl.conf to enable packet forwarding first. Then reboot.

net.inet.ip.forwarding=1        # 1=Permit forwarding (routing) of IPv4 packets

2) edit /etc/pf.conf, and run #pfctl -f /etc/pf.conf.

# Port mapping

pass in on $ext_if proto tcp from any to $ext_ip port 80 rdr-to $inside_server_ip port 80

# NAT rules

# This is not necessary because the stateful pf will add it automatically with rdr-to rules.

# pass out on $ext_if from $inside_server_ip port 80 to any nat-to $ext_if