rdr on $ext_if proto tcp from any to $ext_addr port 80 -> 127.0.0.1 port 3333

pass in all
pass out all

block in all

pass in on lo0
pass out on lo0

# It doesn't work.
# With 'rdr pass inet proto tcp from any to $ext_addr port 80 -> 127.0.0.1 port 3333' it works. But I want to use "flags S/SA keep state" for port 80 (or 3333?). How to do it?