1filter-rule = [ insert ] action in-out [ options ] [ tos ] [ ttl ]
2	      [ proto ] [ ip ] [ group ] [ tag ] [ pps ] .
3
4insert	= "@" decnumber .
5action	= block | "pass" | log | "count" | auth | call .
6in-out	= "in" | "out" .
7options	= [ log ] [ "quick" ] [ onif [ dup ] [ froute ] ] .
8tos	= "tos" decnumber | "tos" hexnumber .
9ttl	= "ttl" decnumber .
10proto	= "proto" protocol .
11ip	= srcdst [ flags ] [ with withopt ] [ icmp ] [ keep ] .
12group	= [ "head" decnumber ] [ "group" decnumber ] .
13pps	= "pps" decnumber .
14
15onif	= "on" interface-name [ "out-via" interface-name ] .
16block	= "block" [ return-icmp[return-code] | "return-rst" ] .
17auth	= "auth" | "preauth" .
18log	= "log" [ "body" ] [ "first" ] [ "or-block" ] [ "level" loglevel ] .
19tag	= "tag" tagid .
20call	= "call" [ "now" ] function-name "/" decnumber.
21dup	= "dup-to" interface-name[":"ipaddr] .
22froute	= "fastroute" | "to" interface-name .
23replyto = "reply-to" interface-name [ ":" ipaddr ] .
24protocol = "tcp/udp" | "udp" | "tcp" | "icmp" | decnumber .
25srcdst	= "all" | fromto .
26fromto	= "from" object "to" object .
27
28return-icmp = "return-icmp" | "return-icmp-as-dest" .
29loglevel = facility"."priority | priority .
30object	= addr [ port-comp | port-range ] .
31addr	= "any" | nummask | host-name [ "mask" ipaddr | "mask" hexnumber ] .
32port-comp = "port" compare port-num .
33port-range = "port" port-num range port-num .
34flags	= "flags" flag { flag } [ "/" flag { flag } ] .
35with	= "with" | "and" .
36icmp	= "icmp-type" icmp-type [ "code" decnumber ] .
37return-code = "("icmp-code")" .
38keep	= "keep" "state" [ "limit" number ] | "keep" "frags" .
39
40nummask	= host-name [ "/" decnumber ] .
41host-name = ipaddr | hostname | "any" .
42ipaddr	= host-num "." host-num "." host-num "." host-num .
43host-num = digit [ digit [ digit ] ] .
44port-num = service-name | decnumber .
45
46withopt = [ "not" | "no" ] opttype [ [ "," ] withopt ] .
47opttype = "ipopts" | "short" | "nat" | "bad-src" | "lowttl" | "frag" |
48          "mbcast" | "opt" ipopts  .
49optname	= ipopts [ "," optname ] .
50ipopts  = optlist | "sec-class" [ secname ] .
51secname	= seclvl [ "," secname ] .
52seclvl  = "unclass" | "confid" | "reserv-1" | "reserv-2" | "reserv-3" |
53	  "reserv-4" | "secret" | "topsecret" .
54icmp-type = "unreach" | "echo" | "echorep" | "squench" | "redir" |
55	    "timex" | "paramprob" | "timest" | "timestrep" | "inforeq" |
56	    "inforep" | "maskreq" | "maskrep"  | "routerad" |
57	    "routersol" | decnumber .
58icmp-code = decumber | "net-unr" | "host-unr" | "proto-unr" | "port-unr" |
59	    "needfrag" | "srcfail" | "net-unk" | "host-unk" | "isolate" |
60	    "net-prohib" | "host-prohib" | "net-tos" | "host-tos" |
61	    "filter-prohib" | "host-preced" | "cutoff-preced" .
62optlist	= "nop" | "rr" | "zsu" | "mtup" | "mtur" | "encode" | "ts" | "tr" |
63	  "sec" | "lsrr" | "e-sec" | "cipso" | "satid" | "ssrr" | "addext" |
64	  "visa" | "imitd" | "eip" | "finn" .
65facility = "kern" | "user" | "mail" | "daemon" | "auth" | "syslog" |
66	   "lpr" | "news" | "uucp" | "cron" | "ftp" | "authpriv" |
67	   "audit" | "logalert" | "local0" | "local1" | "local2" |
68	   "local3" | "local4" | "local5" | "local6" | "local7" .
69priority = "emerg" | "alert" | "crit" | "err" | "warn" | "notice" |
70	   "info" | "debug" .
71
72hexnumber = "0" "x" hexstring .
73hexstring = hexdigit [ hexstring ] .
74decnumber = digit [ decnumber ] .
75
76compare = "=" | "!=" | "<" | ">" | "<=" | ">=" | "eq" | "ne" | "lt" | "gt" |
77	  "le" | "ge" .
78range	= "<>" | "><" .
79hexdigit = digit | "a" | "b" | "c" | "d" | "e" | "f" .
80digit	= "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" .
81flag	= "F" | "S" | "R" | "P" | "A" | "U" | "C" | "W" .
82