pf の基本文法

action direction [log] [quick] on interface [af] [proto protocol]
from src_addr [port src_port] to dst_addr [port dst_port] [tcp_flags] [state]

action	direction	[log]	[quick]	on	interface	[af]	[proto	protocol]
pass block block drop block return	in out	[log] [log-all]	[quick]	on	interface	inet inet6	proto	tcp udp icmp icmp6 0〜255

from	src_addr	[port	src_port]	to	dst_addr	[port	dst_port]	[tcp_flags]	[state]
from	src_addr	port	src_port	to	dst_addr	port	dst_port	[flags S/SA] [flags FUP/FUP] ...	[keep state] [modulate state] [synproxy state]

参考サイト

http://blog.pdns.jp/pf%EF%BC%88%E3%83%91%E3%82%B1%E3%83%83%E3%83%88%E3%83%95%E3%82%A3%E3%83%AB%E3%82%BF%EF%BC%89-on-freebsd/