1 .\" $OpenBSD: pf.conf.5,v 1.291 2004/02/04 19:38:30 jmc Exp $
2 .\" $DragonFly: src/usr.sbin/pfctl/pf.conf.5,v 1.11 2008/04/06 19:29:23 swildner Exp $
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36 .Nd packet filter configuration file
40 packet filter modifies, drops or passes packets according to rules or
41 definitions specified in
44 There are seven types of statements in
48 User-defined variables may be defined and used later, simplifying
49 the configuration file.
50 Macros must be defined before they are referenced in
53 Tables provide a mechanism for increasing the performance and flexibility of
54 rules with large numbers of source or destination addresses.
56 Options tune the behaviour of the packet filtering engine.
57 .It Cm Traffic Normalization Li (e.g.\& Em scrub )
58 Traffic normalization protects internal machines against inconsistencies
59 in Internet protocols and implementations.
61 Queueing provides rule-based bandwidth control.
62 .It Cm Translation Li (Various forms of NAT)
63 Translation rules specify how addresses are to be mapped or redirected to
65 .It Cm Packet Filtering
66 Stateful and stateless packet filtering provides rule-based blocking or
74 the types of statements should be grouped and appear in
76 in the order shown above, as this matches the operation of the underlying
77 packet filtering engine.
80 enforces this order (see
88 macros can be defined that will later be expanded in context.
89 Macro names must start with a letter, and may contain letters, digits
91 Macro names may not be reserved words (for example
95 Macros are not expanded inside quotes.
98 .Bd -literal -offset indent
100 all_ifs = \&"{\&" $ext_if lo0 \&"}\&"
101 pass out on $ext_if from any to any keep state
102 pass in on $ext_if proto tcp from any to any port 25 keep state
105 Tables are named structures which can hold a collection of addresses and
107 Lookups against tables in
109 are relatively fast, making a single rule with tables much more efficient,
111 processor usage and memory consumption, than a large number of rules which
112 differ only in IP address (either created explicitly or automatically by rule
115 Tables can be used as the source or destination of filter rules,
119 translation rules such as
123 (see below for details on the various rule types).
124 Tables can also be used for the redirect address of
128 rules and in the routing options of filter rules, but only for
132 Tables can be defined with any of the following
135 As with macros, reserved words may not be used as table names.
136 .Bl -tag -width "manually"
138 Persistent tables can be manually created with the
144 before or after the ruleset has been loaded.
146 Table definitions can be placed directly in this file, and loaded at the
147 same time as other rules are loaded, atomically.
148 Table definitions inside
152 statement, and are especially useful to define non-persistent tables.
153 The contents of a pre-existing table defined without a list of addresses
154 to initialize it is not altered when
157 A table initialized with the empty list,
159 will be cleared on load.
162 Tables may be defined with the following two attributes:
163 .Bl -tag -width persist
167 flag forces the kernel to keep the table even when no rules refer to it.
168 If the flag is not set, the kernel will automatically remove the table
169 when the last rule referring to it is flushed.
173 flag prevents the user from altering the contents of the table once it
177 can be used to add or remove addresses from the table at any time, even
184 .Bd -literal -offset indent
185 table <private> const { 10/8, 172.16/12, 192.168/16 }
186 table <badhosts> persist
187 block on fxp0 from { <private>, <badhosts> } to any
190 creates a table called private, to hold RFC 1918 private network
191 blocks, and a table called badhosts, which is initially empty.
192 A filter rule is set up to block all traffic coming from addresses listed in
194 The private table cannot have its contents changed and the badhosts table
195 will exist even when no active filter rules reference it.
196 Addresses may later be added to the badhosts table, so that traffic from
197 these hosts can be blocked by using
198 .Bd -literal -offset indent
199 # pfctl -t badhosts -Tadd 204.92.77.111
202 A table can also be initialized with an address list specified in one or more
203 external files, using the following syntax:
204 .Bd -literal -offset indent
205 table <spam> persist file \&"/etc/spammers\&" file \&"/etc/openrelays\&"
206 block on fxp0 from <spam> to any
213 list IP addresses, one per line.
214 Any lines beginning with a # are treated as comments and ignored.
215 In addition to being specified by IP address, hosts may also be
216 specified by their hostname.
217 When the resolver is called to add a hostname to a table,
219 resulting IPv4 and IPv6 addresses are placed into the table.
220 IP addresses can also be entered in a table by specifying a valid interface
223 keyword, in which case all addresses assigned to the interface(s) will be
227 may be tuned for various situations using the
233 .Bl -tag -width interval -compact
235 Interval between purging expired states and fragments.
237 Seconds before an unassembled fragment is expired.
239 Length of time to retain a source tracking entry after the last state
243 When a packet matches a stateful connection, the seconds to live for the
244 connection will be updated to that of the
246 which corresponds to the connection state.
247 Each packet which matches this state will reset the TTL.
248 Tuning these values may improve the performance of the
249 firewall at the risk of dropping valid idle connections.
251 .Bl -tag -width xxxx -compact
253 The state after the first packet.
255 The state before the destination host ever sends a packet.
256 .It Ar tcp.established
257 The fully established state.
259 The state after the first FIN has been sent.
261 The state after both FINs have been exchanged and the connection is closed.
262 Some hosts (notably web servers on Solaris) send TCP packets even after closing
268 can prevent blocking of such packets.
270 The state after one endpoint sends an RST.
273 ICMP and UDP are handled in a fashion similar to TCP, but with a much more
274 limited set of states:
276 .Bl -tag -width xxxx -compact
278 The state after the first packet.
280 The state if the source host sends more than one packet but the destination
281 host has never sent one back.
283 The state if both hosts have sent packets.
285 The state after the first packet.
287 The state after an ICMP error came back in response to an ICMP packet.
290 Other protocols are handled similarly to UDP:
292 .Bl -tag -width xxxx -compact
295 .It Ar other.multiple
298 Timeout values can be reduced adaptively as the number of state table
301 .Bl -tag -width xxxx -compact
302 .It Ar adaptive.start
303 When the number of state entries exceeds this value, adaptive scaling
305 All timeout values are scaled linearly with factor
306 (adaptive.end - number of states) / (adaptive.end - adaptive.start).
308 When reaching this number of state entries, all timeout values become
309 zero, effectively purging all state entries immediately.
310 This value is used to define the scale factor, it should not actually
311 be reached (set a lower state limit, see below).
314 These values can be defined both globally and for each rule.
315 When used on a per-rule basis, the values relate to the number of
316 states created by the rule, otherwise to the total number of
320 .Bd -literal -offset indent
321 set timeout tcp.first 120
322 set timeout tcp.established 86400
323 set timeout { adaptive.start 6000, adaptive.end 12000 }
324 set limit states 10000
327 With 9000 state table entries, the timeout values are scaled to 50%
328 (tcp.first 60, tcp.established 43200).
330 .It Ar set loginterface
331 Enable collection of packet and byte count statistics for the given interface.
332 These statistics can be viewed using
333 .Bd -literal -offset indent
339 collects statistics on the interface named dc0:
340 .Bd -literal -offset indent
344 One can disable the loginterface using:
345 .Bd -literal -offset indent
346 set loginterface none
350 Sets hard limits on the memory pools used by the packet filter.
353 for an explanation of memory pools.
356 .Bd -literal -offset indent
357 set limit states 20000
360 sets the maximum number of entries in the memory pool used by state table
361 entries (generated by
365 .Bd -literal -offset indent
366 set limit frags 20000
369 sets the maximum number of entries in the memory pool used for fragment
370 reassembly (generated by
374 .Bd -literal -offset indent
375 set limit src-nodes 2000
378 sets the maximum number of entries in the memory pool used for tracking
379 source IP addresses (generated by the
385 These can be combined:
386 .Bd -literal -offset indent
387 set limit { states 20000, frags 20000, src-nodes 2000 }
390 .It Ar set optimization
391 Optimize the engine for one of the following network environments:
393 .Bl -tag -width xxxx -compact
395 A normal network environment.
396 Suitable for almost all networks.
398 A high-latency environment (such as a satellite connection).
403 Aggressively expire connections.
404 This can greatly reduce the memory usage of the firewall at the cost of
405 dropping idle connections early.
407 Extremely conservative settings.
408 Avoid dropping legitimate connections at the
409 expense of greater memory utilization (possibly much greater on a busy
410 network) and slightly increased processor utilization.
414 .Bd -literal -offset indent
415 set optimization aggressive
418 .It Ar set block-policy
421 option sets the default behaviour for the packet
425 .Bl -tag -width xxxxxxxx -compact
427 Packet is silently dropped.
429 A TCP RST is returned for blocked TCP packets,
430 an ICMP UNREACHABLE is returned for blocked UDP packets,
431 and all other packets are silently dropped.
435 .Bd -literal -offset indent
436 set block-policy return
438 .It Ar set state-policy
441 option sets the default behaviour for states:
443 .Bl -tag -width group-bound -compact
445 States are bound to interface.
447 States are bound to interface group (i.e., ppp)
449 States can match packets on any interfaces (the default).
453 .Bd -literal -offset indent
454 set state-policy if-bound
456 .It Ar set require-order
459 enforces an ordering of the statement types in the ruleset to:
465 Setting this option to
467 disables this enforcement.
468 There may be non-trivial and non-obvious implications to an out of
470 Consider carefully before disabling the order enforcement.
471 .It Ar set fingerprints
472 Load fingerprints of known operating systems from the given filename.
473 By default fingerprints of known operating systems are automatically
478 but can be overridden via this option.
479 Setting this option may leave a small period of time where the fingerprints
480 referenced by the currently active ruleset are inconsistent until the new
481 ruleset finishes loading.
485 .Dl set fingerprints \&"/etc/pf.os.devel\&"
490 to one of the following:
492 .Bl -tag -width xxxxxxxxxxxx -compact
494 Don't generate debug messages.
496 Generate debug messages only for serious errors.
498 Generate debug messages for various errors.
500 Generate debug messages for common conditions.
503 .Sh TRAFFIC NORMALIZATION
504 Traffic normalization is used to sanitize packet content in such
505 a way that there are no ambiguities in packet interpretation on
507 The normalizer does IP fragment reassembly to prevent attacks
508 that confuse intrusion detection systems by sending overlapping
510 Packet normalization is invoked with the
515 has the following options:
520 bit from a matching IP packet.
521 Some operating systems are known to generate fragmented packets with the
524 This is particularly true with NFS.
526 will drop such fragmented
532 Unfortunately some operating systems also generate their
534 packets with a zero IP identification field.
537 bit on packets with a zero IP ID may cause deleterious results if an
538 upstream router later fragments the packet.
541 modifier (see below) is recommended in combination with the
543 modifier to ensure unique IP identifiers.
544 .It Ar min-ttl <number>
545 Enforces a minimum TTL for matching IP packets.
546 .It Ar max-mss <number>
547 Enforces a maximum MSS for matching TCP packets.
549 Replaces the IP identification field with random values to compensate
550 for predictable values generated by many hosts.
551 This option only applies to outgoing packets that are not fragmented
552 after the optional fragment reassembly.
553 .It Ar fragment reassemble
556 rules, fragments can be reassembled by normalization.
557 In this case, fragments are buffered until they form a complete
558 packet, and only the completed packet is passed on to the filter.
559 The advantage is that filter rules have to deal only with complete
560 packets, and can ignore fragments.
561 The drawback of caching fragments is the additional memory cost.
562 But the full reassembly method is the only method that currently works
564 This is the default behavior of a
566 rule if no fragmentation modifier is supplied.
568 The default fragment reassembly method is expensive, hence the option
572 will track the fragments and cache a small range descriptor.
573 Duplicate fragments are dropped and overlaps are cropped.
574 Thus data will only occur once on the wire with ambiguities resolving to
575 the first occurrence.
577 .Ar fragment reassemble
578 modifier, fragments are not buffered, they are passed as soon as they
582 reassembly mechanism does not yet work with NAT.
584 .It Ar fragment drop-ovl
585 This option is similar to the
587 modifier except that all overlapping or duplicate fragments will be
588 dropped, and all further corresponding fragments will be
590 .It Ar reassemble tcp
591 Statefully normalizes TCP connections.
592 .Ar scrub reassemble tcp
593 rules may not have the direction (in/out) specified.
595 performs the following normalizations:
597 .Bl -tag -width timeout -compact
599 Neither side of the connection is allowed to reduce their IP TTL.
600 An attacker may send a packet such that it reaches the firewall, affects
601 the firewall state, and expires before reaching the destination host.
603 will raise the TTL of all packets back up to the highest value seen on
605 .It timeout modulation
606 Modern TCP stacks will send a timestamp on every TCP packet and echo
607 the other endpoint's timestamp back to them.
608 Many operating systems will merely start the timestamp at zero when
609 first booted, and increment it several times a second.
610 The uptime of the host can be deduced by reading the timestamp and multiplying
612 Also observing several different timestamps can be used to count hosts
614 And spoofing TCP packets into a connection requires knowing or guessing
616 Timestamps merely need to be monotonically increasing and not derived off a
621 to modulate the TCP timestamps with a random number.
626 .Bd -literal -offset indent
627 scrub in on $ext_if all fragment reassemble
630 Packets can be assigned to queues for the purpose of bandwidth
632 At least two declarations are required to configure queues, and later
633 any packet filtering rule can reference the defined queues by name.
634 During the filtering component of
638 name is where any packets from
640 rules will be queued, while for
642 rules it specifies where any resulting ICMP or TCP RST
643 packets should be queued.
646 defines the algorithm used to decide which packets get delayed, dropped, or
647 sent out immediately.
653 Class Based Queueing.
655 attached to an interface build a tree, thus each
657 can have further child
659 Each queue can have a
665 mainly controls the time packets take to get sent out, while
667 has primarily effects on throughput.
671 are flat attached to the interface, thus,
673 cannot have further child
679 assigned, ranging from 0 to 15.
686 Hierarchical Fair Service Curve.
688 attached to an interface build a tree, thus each
690 can have further child
692 Each queue can have a
698 mainly controls the time packets take to get sent out, while
700 has primarily effects on throughput.
704 are flat attached to the interface, thus,
706 cannot have further child
708 Each queue must be given a unique priority and one must be marked
709 as the default queue.
710 Each queue implements a number of buckets (default 256) which sorts the
711 traffic based on a hash key generated by the
713 facility in your pass rules.
714 Each bucket contains a list of packets controlled by
718 to function properly,
720 must be enabled on most of the rule sets that route packets to the queue.
722 Packet selection operates as follows:
723 The queues are scanned from highest priority to lowest priority.
724 If a queue has pending packets and has not reached its bandwidth limit the
725 scan stops and a packet is selected from that queue.
726 If a queue has reached its bandwidth limit the scan continues searching for
727 other, lower priority queues which have not.
728 If no queue is found to be
729 suitable then the highest priority queue with pending packets is used
730 regardless of whether it has reached its bandwidth limit or not.
734 round robins between its buckets, extracting one packet from each bucket.
735 This essentially prevents large backlogs of packets from high volume
736 connections from destroying the interactive response of other connections.
742 is guaranteed minimum and more will be used if no higher priority traffic is
744 Creating a queue with one bucket as a catch-all for pass rules
748 Such a queue serves as a basic priority queue with a bandwidth
752 The interfaces on which queueing should be activated are declared using
757 has the following keywords:
760 Queueing is enabled on the named interface.
762 Specifies which queueing scheduler to use.
763 Currently supported values
766 for Class Based Queueing,
768 for Priority Queueing,
770 for the Hierarchical Fair Service Curve scheduler, and
772 for the Fair Queueing.
773 .It Ar bandwidth <bw>
774 The maximum bitrate for all queues on an
775 interface may be specified using the
778 The value can be specified as an absolute value or as a
779 percentage of the interface bandwidth.
780 When using an absolute value, the suffixes
786 are used to represent bits, kilobits, megabits, and
787 gigabits per second, respectively.
788 The value must not exceed the interface bandwidth.
791 is not specified, the interface bandwidth is used.
796 specifies a guaranteed minimum but the fairq is allowed to exceed it.
797 .It Ar qlimit <limit>
798 The maximum number of packets held in the queue.
800 .It Ar tbrsize <size>
801 Adjusts the size, in bytes, of the token bucket regulator.
802 If not specified, heuristics based on the
803 interface bandwidth are used to determine the size.
805 Defines a list of subqueues to create on an interface.
808 In the following example, the interface dc0
809 should queue up to 5 Mbit/s in four second-level queues using
810 Class Based Queueing.
811 Those four queues will be shown in a later example.
812 .Bd -literal -offset indent
813 altq on dc0 cbq bandwidth 5Mb queue { std, http, mail, ssh }
816 Once interfaces are activated for queueing using the
818 directive, a sequence of
820 directives may be defined.
821 The name associated with a
823 must match a queue defined in the
825 directive (e.g.\& mail), or, except for the
831 The following keywords can be used:
833 .It Ar on <interface>
834 Specifies the interface the queue operates on.
835 If not given, it operates on all matching interfaces.
836 .It Ar bandwidth <bw>
837 Specifies the maximum bitrate to be processed by the queue.
838 This value must not exceed the value of the parent
840 and can be specified as an absolute value or a percentage of the parent
844 scheduler does not support bandwidth specification.
847 scheduler uses the bandwidth specification as a guaranteed minimum and
849 .It Ar priority <level>
850 Between queues a priority level can be set.
856 the range is 0 to 7 and for
858 the range is 0 to 15.
859 The default for all is 1.
861 queues with a higher priority are always served first.
863 queues with a higher priority are served first unless they exceed their
864 bandwidth specification.
868 queues with a higher priority are preferred in the case of overload.
869 .It Ar qlimit <limit>
870 The maximum number of packets held in the queue.
874 this specified the maximum number of packets held per bucket.
879 can get additional parameters with
880 .Ar <scheduler> Ns Li (\& Ar <parameters> No ) .
881 Parameters are as follows:
884 Packets not matched by another queue are assigned to this one.
885 Exactly one default queue is required.
887 Enable RED (Random Early Detection) on this queue.
888 RED drops packets with a probability proportional to the average
891 Enables RIO on this queue.
892 RIO is RED with IN/OUT, thus running
893 RED two times more than RIO would achieve the same effect.
894 RIO is currently not supported in the GENERIC kernel.
896 Enables ECN (Explicit Congestion Notification) on this queue.
903 supports the following additional options:
905 .It Ar buckets <number>
906 Specify the number of buckets, from 1 to 2048 in powers of 2.
907 A bucket size of 1 causes a
909 to essentially degenerate into a priority queue.
910 .It Ar linkshare <sc>
911 The bandwidth share of a backlogged queue.
912 This option is parsed but not yet supported.
913 .It Ar hogs <bandwidth>
914 This option allows low bandwidth connections to burst up to the specified
915 bandwidth by not advancing the round robin when taking packets out of
917 When using this option a small value no greater then 1/20 available interface
918 bandwidth is recommended.
924 supports an additional option:
927 The queue can borrow bandwidth from the parent.
933 supports some additional options:
936 The minimum required bandwidth for the queue.
937 .It Ar upperlimit <sc>
938 The maximum allowed bandwidth for the queue.
939 .It Ar linkshare <sc>
940 The bandwidth share of a backlogged queue.
943 <sc> is an acronym for
946 The format for service curve specifications is
947 .Ar ( m1 , d , m2 ) .
949 controls the bandwidth assigned to the queue.
953 are optional and can be used to control the initial bandwidth assignment.
956 milliseconds the queue gets the bandwidth given as
958 afterwards the value given in
965 child queues can be specified as in an
967 declaration, thus building a tree of queues using a part of
968 their parent's bandwidth.
970 Packets can be assigned to queues based on filter rules by using the
975 is specified; when a second one is specified it will instead be used for
980 and for TCP ACKs with no data payload.
982 To continue the previous example, the examples below would specify the
984 queues, plus a few child queues.
987 sessions get priority over bulk transfers like
991 The queues may then be referenced by filtering rules (see
995 queue std bandwidth 10% cbq(default)
996 queue http bandwidth 60% priority 2 cbq(borrow red) \e
997 { employees, developers }
998 queue developers bandwidth 75% cbq(borrow)
999 queue employees bandwidth 15%
1000 queue mail bandwidth 10% priority 0 cbq(borrow ecn)
1001 queue ssh bandwidth 20% cbq(borrow) { ssh_interactive, ssh_bulk }
1002 queue ssh_interactive priority 7
1003 queue ssh_bulk priority 0
1005 block return out on dc0 inet all queue std
1006 pass out on dc0 inet proto tcp from $developerhosts to any port 80 \e
1007 keep state queue developers
1008 pass out on dc0 inet proto tcp from $employeehosts to any port 80 \e
1009 keep state queue employees
1010 pass out on dc0 inet proto tcp from any to any port 22 \e
1011 keep state queue(ssh_bulk, ssh_interactive)
1012 pass out on dc0 inet proto tcp from any to any port 25 \e
1013 keep state queue mail
1016 Translation rules modify either the source or destination address of the
1017 packets associated with a stateful connection.
1018 A stateful connection is automatically created to track packets matching
1019 such a rule as long as they are not blocked by the filtering section of
1021 The translation engine modifies the specified address and/or port in the
1022 packet, recalculates IP, TCP and UDP checksums as necessary, and passes it to
1023 the packet filter for evaluation.
1025 Since translation occurs before filtering the filter
1026 engine will see packets as they look after any
1027 addresses and ports have been translated.
1028 Filter rules will therefore have to filter based on the translated
1029 address and port number.
1030 Packets that match a translation rule are only automatically passed if
1033 modifier is given, otherwise they are
1040 The state entry created permits
1042 to keep track of the original address for traffic associated with that state
1043 and correctly direct return traffic for that connection.
1045 Various types of translation are possible with pf:
1046 .Bl -tag -width xxxx
1050 rule specifies a bidirectional mapping between an external IP netblock
1051 and an internal IP netblock.
1055 rule specifies that IP addresses are to be changed as the packet
1056 traverses the given interface.
1057 This technique allows one or more IP addresses
1058 on the translating host to support network traffic for a larger range of
1059 machines on an "inside" network.
1060 Although in theory any IP address can be used on the inside, it is strongly
1061 recommended that one of the address ranges defined by RFC 1918 be used.
1062 These netblocks are:
1064 10.0.0.0 - 10.255.255.255 (all of net 10, i.e., 10/8)
1065 172.16.0.0 - 172.31.255.255 (i.e., 172.16/12)
1066 192.168.0.0 - 192.168.255.255 (i.e., 192.168/16)
1069 The packet is redirected to another destination and possibly a
1072 rules can optionally specify port ranges instead of single ports.
1073 rdr ... port 2000:2999 -> ... port 4000
1074 redirects ports 2000 to 2999 (inclusive) to port 4000.
1075 rdr ... port 2000:2999 -> ... port 4000:*
1076 redirects port 2000 to 4000, 2001 to 4001, ..., 2999 to 4999.
1079 In addition to modifying the address, some translation rules may modify
1080 source or destination ports for
1084 connections; implicitly in the case of
1086 rules and explicitly in the case of
1089 Port numbers are never translated with a
1093 For each packet processed by the translator, the translation rules are
1094 evaluated in sequential order, from first to last.
1095 The first matching rule decides what action is taken.
1099 option prefixed to a translation rule causes packets to remain untranslated,
1100 much in the same way as
1102 works in the packet filter (see below).
1103 If no rule matches the packet it is passed to the filter engine unmodified.
1105 Translation rules apply only to packets that pass through
1106 the specified interface, and if no interface is specified,
1107 translation is applied to packets on all interfaces.
1108 For instance, redirecting port 80 on an external interface to an internal
1109 web server will only work for connections originating from the outside.
1110 Connections to the address of the external interface from local hosts will
1111 not be redirected, since such packets do not actually pass through the
1113 Redirections cannot reflect packets back through the interface they arrive
1114 on, they can only be redirected to hosts connected to different interfaces
1115 or to the firewall itself.
1117 Note that redirecting external incoming connections to the loopback
1119 .Bd -literal -offset indent
1120 rdr on ne3 inet proto tcp to port 8025 -> 127.0.0.1 port 25
1123 will effectively allow an external host to connect to daemons
1124 bound solely to the loopback address, circumventing the traditional
1125 blocking of such connections on a real interface.
1126 Unless this effect is desired, any of the local non-loopback addresses
1127 should be used as redirection target instead, which allows external
1128 connections only to daemons bound to this address or not bound to
1132 .Sx TRANSLATION EXAMPLES
1134 .Sh PACKET FILTERING
1140 packets based on attributes of their layer 3 (see
1150 In addition, packets may also be
1151 assigned to queues for the purpose of bandwidth control.
1153 For each packet processed by the packet filter, the filter rules are
1154 evaluated in sequential order, from first to last.
1155 The last matching rule decides what action is taken.
1157 The following actions can be used in the filter:
1158 .Bl -tag -width xxxx
1160 The packet is blocked.
1161 There are a number of ways in which a
1163 rule can behave when blocking a packet.
1164 The default behaviour is to
1166 packets silently, however this can be overridden or made
1167 explicit either globally, by setting the
1169 option, or on a per-rule basis with one of the following options:
1171 .Bl -tag -width xxxx -compact
1173 The packet is silently dropped.
1175 This applies only to
1177 packets, and issues a TCP RST which closes the
1181 This causes ICMP messages to be returned for packets which match the rule.
1182 By default this is an ICMP UNREACHABLE message, however this
1183 can be overridden by specifying a message as a code or number.
1185 This causes a TCP RST to be returned for
1187 packets and an ICMP UNREACHABLE for UDP and other packets.
1190 Options returning packets have no effect if
1195 The packet is passed.
1198 If no rule matches the packet, the default action is
1201 To block everything by default and only pass packets
1202 that match explicit rules, one uses
1203 .Bd -literal -offset indent
1207 as the first filter rule.
1213 The rule parameters specify the packets to which a rule applies.
1214 A packet always comes in on, or goes out through, one interface.
1215 Most parameters are optional.
1216 If a parameter is specified, the rule only applies to packets with
1217 matching attributes.
1218 Certain parameters can be expressed as lists, in which case
1220 generates all needed rule combinations.
1221 .Bl -tag -width xxxx
1222 .It Ar in No or Ar out
1223 This rule applies to incoming or outgoing packets.
1228 are specified, the rule will match packets in both directions.
1230 In addition to the action specified, a log message is generated.
1231 All packets for that connection are logged, unless the
1236 options are specified, in which case only the
1237 packet that establishes the state is logged.
1244 The logged packets are sent to the
1247 This interface is monitored by the
1249 logging daemon, which dumps the logged packets to the file
1260 rules to force logging of all packets for a connection.
1263 packets are logged to
1266 If a packet matches a rule which has the
1268 option set, this rule
1269 is considered the last matching rule, and evaluation of subsequent rules
1271 .It Ar on <interface>
1272 This rule applies only to packets coming in on, or going out through, this
1273 particular interface.
1274 It is also possible to simply give the interface driver name, like ppp or fxp,
1275 to make the rule match packets flowing through a group of interfaces.
1277 This rule applies only to packets of this address family.
1278 Supported values are
1282 .It Ar proto <protocol>
1283 This rule applies only to packets of this protocol.
1284 Common protocols are
1290 For a list of all the protocol name to number mappings used by
1293 .Pa /etc/protocols .
1295 .Ar from <source> port <source> os <source>
1296 .Ar to <dest> port <dest>
1298 This rule applies only to packets with the specified source and destination
1299 addresses and ports.
1301 Addresses can be specified in CIDR notation (matching netblocks), as
1302 symbolic host names or interface names, or as any of the following keywords:
1304 .Bl -tag -width xxxxxxxxxxxx -compact
1308 Any address which is not currently routable.
1310 Any address that matches the given table.
1313 Interface names can have modifiers appended:
1315 .Bl -tag -width xxxxxxxxxxxx -compact
1317 Translates to the network(s) attached to the interface.
1319 Translates to the interface's broadcast address(es).
1321 Translates to the point to point interface's peer address(es).
1323 Do not include interface aliases.
1326 Host names may also have the
1328 option appended to restrict the name resolution to the first of each
1329 v4 and v6 address found.
1331 Host name resolution and interface to address translation are done at
1333 When the address of an interface (or host name) changes (under DHCP or PPP,
1334 for instance), the ruleset must be reloaded for the change to be reflected
1336 Surrounding the interface name (and optional modifiers) in parentheses
1337 changes this behaviour.
1338 When the interface name is surrounded by parentheses, the rule is
1339 automatically updated whenever the interface changes its address.
1340 The ruleset does not need to be reloaded.
1341 This is especially useful with
1344 Ports can be specified either by number or by name.
1345 For example, port 80 can be specified as
1347 For a list of all port name to number mappings used by
1352 Ports and ranges of ports are specified by using these operators:
1353 .Bd -literal -offset indent
1357 <= (less than or equal)
1359 >= (greater than or equal)
1360 : (range including boundaries)
1361 >< (range excluding boundaries)
1366 are binary operators (they take two arguments).
1369 .It Ar port 2000:2004
1371 .Sq all ports \(>= 2000 and \(<= 2004 ,
1372 hence ports 2000, 2001, 2002, 2003 and 2004.
1373 .It Ar port 2000 >< 2004
1375 .Sq all ports > 2000 and < 2004 ,
1376 hence ports 2001, 2002 and 2003.
1377 .It Ar port 2000 <> 2004
1379 .Sq all ports < 2000 or > 2004 ,
1380 hence ports 1-1999 and 2005-65535.
1383 The operating system of the source host can be specified in the case of TCP
1388 .Sx OPERATING SYSTEM FINGERPRINTING
1389 section for more information.
1391 The host, port and OS specifications are optional, as in the following examples:
1392 .Bd -literal -offset indent
1394 pass in from any to any
1395 pass in proto tcp from any port <= 1024 to any
1396 pass in proto tcp from any to any port 25
1397 pass in proto tcp from 10.0.0.0/8 port > 1024 \e
1398 to ! 10.1.2.3 port != ssh
1399 pass in proto tcp from any os "OpenBSD" flags S/SA
1402 This is equivalent to "from any to any".
1403 .It Ar group <group>
1406 this rule only applies to packets of sockets owned by the specified group.
1408 This rule only applies to packets of sockets owned by the specified user.
1409 For outgoing connections initiated from the firewall, this is the user
1410 that opened the connection.
1411 For incoming connections to the firewall itself, this is the user that
1412 listens on the destination port.
1413 For forwarded connections, where the firewall is not a connection endpoint,
1414 the user and group are
1417 All packets, both outgoing and incoming, of one connection are associated
1418 with the same user and group.
1419 Only TCP and UDP packets can be associated with users; for other protocols
1420 these parameters are ignored.
1422 User and group refer to the effective (as opposed to the real) IDs, in
1423 case the socket is created by a setuid/setgid process.
1424 User and group IDs are stored when a socket is created;
1425 when a process creates a listening socket as root (for instance, by
1426 binding to a privileged port) and subsequently changes to another
1427 user ID (to drop privileges), the credentials will remain root.
1429 User and group IDs can be specified as either numbers or names.
1430 The syntax is similar to the one for ports.
1433 matches packets of forwarded connections.
1435 can only be used with the operators
1439 Other constructs like
1442 Forwarded packets with unknown user and group ID match only rules
1443 that explicitly compare against
1451 does not match forwarded packets.
1452 The following example allows only selected users to open outgoing
1454 .Bd -literal -offset indent
1455 block out proto { tcp, udp } all
1456 pass out proto { tcp, udp } all \e
1457 user { < 1000, dhartmei } keep state
1459 .It Ar flags <a>/<b> | /<b>
1460 This rule only applies to TCP packets that have the flags
1464 Flags not specified in
1467 The flags are: (F)IN, (S)YN, (R)ST, (P)USH, (A)CK, (U)RG, (E)CE, and C(W)R.
1471 The other flags are ignored.
1473 Out of SYN and ACK, exactly SYN may be set.
1474 SYN, SYN+PSH and SYN+RST match, but SYN+ACK, ACK and ACK+RST do not.
1475 This is more restrictive than the previous example.
1477 If the first set is not specified, it defaults to none.
1478 All of SYN, FIN, RST and ACK must be unset.
1480 .It Ar icmp-type <type> code <code>
1481 .It Ar icmp6-type <type> code <code>
1482 This rule only applies to ICMP or ICMPv6 packets with the specified type
1484 This parameter is only valid for rules that cover protocols ICMP or
1486 The protocol and the ICMP type indicator (icmp-type or icmp6-type)
1489 By default, packets which contain IP options are blocked.
1494 rule, packets that pass the filter based on that rule (last matching)
1495 do so even if they contain IP options.
1496 For packets that match state, the rule that initially created the
1500 rule that is used when a packet does not match any rules does not
1502 .It Ar label <string>
1503 Adds a label (name) to the rule, which can be used to identify the rule.
1506 shows per-rule statistics for rules that have labels.
1508 The following macros can be used in labels:
1510 .Bl -tag -width $srcaddr -compact -offset indent
1514 The source IP address.
1516 The destination IP address.
1518 The source port specification.
1520 The destination port specification.
1528 .Bd -literal -offset indent
1529 ips = \&"{ 1.2.3.4, 1.2.3.5 }\&"
1530 pass in proto tcp from any to $ips \e
1531 port > 1023 label \&"$dstaddr:$dstport\&"
1535 .Bd -literal -offset indent
1536 pass in inet proto tcp from any to 1.2.3.4 \e
1537 port > 1023 label \&"1.2.3.4:>1023\&"
1538 pass in inet proto tcp from any to 1.2.3.5 \e
1539 port > 1023 label \&"1.2.3.5:>1023\&"
1542 The macro expansion for the
1544 directive occurs only at configuration file parse time, not during runtime.
1545 .It Ar queue <queue> | ( <queue> , <queue> )
1546 Packets matching this rule will be assigned to the specified queue.
1547 If two queues are given, packets which have a
1551 and TCP ACKs with no data payload will be assigned to the second one.
1557 .Bd -literal -offset indent
1558 pass in proto tcp to port 25 queue mail
1559 pass in proto tcp to port 22 queue(ssh_bulk, ssh_prio)
1562 Packets matching this rule will be tagged with the
1564 The tag acts as an internal marker that can be used to
1565 identify these packets later on.
1566 This can be used, for example, to provide trust between
1567 interfaces and to determine if packets have been
1568 processed by translation rules.
1571 meaning that the packet will be tagged even if the rule
1572 is not the last matching rule.
1573 Further matching rules can replace the tag with a
1574 new one but will not remove a previously applied tag.
1575 A packet is only ever assigned one tag at a time.
1579 keyword must also use
1583 .Ar synproxy state .
1584 Packet tagging can be done during
1589 rules in addition to filter rules.
1590 Tags take the same macros as labels (see above).
1591 .It Ar tagged <string>
1592 Used with filter rules to specify that packets must already
1593 be tagged with the given tag in order to match the rule.
1594 Inverse tag matching can also be done
1602 If a packet matches a rule with a route option set, the packet filter will
1603 route the packet according to the type of route option.
1604 When such a rule creates state, the route option is also applied to all
1605 packets matching the same connection.
1606 .Bl -tag -width xxxx
1610 option does a normal route lookup to find the next hop for the packet.
1614 option routes the packet to the specified interface with an optional address
1618 rule creates state, only packets that pass in the same direction as the
1619 filter rule specifies will be routed in this way.
1620 Packets passing in the opposite direction (replies) are not affected
1621 and are routed normally.
1625 option is similar to
1627 but routes packets that pass in the opposite direction (replies) to the
1628 specified interface.
1629 Opposite direction is only defined in the context of a state entry, and
1631 is useful only in rules that create state.
1632 It can be used on systems with multiple external connections to
1633 route all outgoing packets of a connection through the interface
1634 the incoming connection arrived through (symmetric routing enforcement).
1638 option creates a duplicate of the packet and routes it like
1640 The original packet gets routed as it normally would.
1647 rules, (as well as for the
1652 rule options) for which there is a single redirection address which has a
1653 subnet mask smaller than 32 for IPv4 or 128 for IPv6 (more than one IP
1654 address), a variety of different methods for assigning this address can be
1656 .Bl -tag -width xxxx
1660 option applies the network portion of the redirection address to the address
1661 to be modified (source with
1668 option selects an address at random within the defined block of addresses.
1672 option uses a hash of the source address to determine the redirection address,
1673 ensuring that the redirection address is always the same for a given source.
1674 An optional key can be specified after this keyword either in hex or as a
1677 randomly generates a key for source-hash every time the
1678 ruleset is reloaded.
1682 option loops through the redirection address(es).
1684 When more than one redirection address is specified,
1686 is the only permitted pool type.
1694 from modifying the source port on TCP and UDP packets.
1699 option can be specified to help ensure that multiple connections from the
1700 same source are mapped to the same redirection address.
1701 This option can be used with the
1706 Note that by default these associations are destroyed as soon as there are
1707 no longer states which refer to them; in order to make the mappings last
1708 beyond the lifetime of the states, increase the global options with
1709 .Ar set timeout source-track
1711 .Sx STATEFUL TRACKING OPTIONS
1712 for more ways to control the source tracking.
1713 .Sh STATEFUL INSPECTION
1715 is a stateful packet filter, which means it can track the state of
1717 Instead of passing all traffic to port 25, for instance, it is possible
1718 to pass only the initial packet, and then begin to keep state.
1719 Subsequent traffic will flow because the filter is aware of the connection.
1721 If a packet matches a
1722 .Ar pass ... keep state
1723 rule, the filter creates a state for this connection and automatically
1724 lets pass all subsequent packets of that connection.
1726 Before any rules are evaluated, the filter checks whether the packet
1728 If it does, the packet is passed without evaluation of any rules.
1730 States are removed after the connection is closed or has timed out.
1732 This has several advantages.
1733 Comparing a packet to a state involves checking its sequence numbers.
1734 If the sequence numbers are outside the narrow windows of expected
1735 values, the packet is dropped.
1736 This prevents spoofing attacks, such as when an attacker sends packets with
1737 a fake source address/port but does not know the connection's sequence
1740 Also, looking up states is usually faster than evaluating rules.
1741 If there are 50 rules, all of them are evaluated sequentially in O(n).
1742 Even with 50000 states, only 16 comparisons are needed to match a
1743 state, since states are stored in a binary search tree that allows
1744 searches in O(log2 n).
1747 .Bd -literal -offset indent
1749 pass out proto tcp from any to any flags S/SA keep state
1750 pass in proto tcp from any to any port 25 flags S/SA keep state
1753 This ruleset blocks everything by default.
1754 Only outgoing connections and incoming connections to port 25 are allowed.
1755 The initial packet of each connection has the SYN
1756 flag set, will be passed and creates state.
1757 All further packets of these connections are passed if they match a state.
1759 By default, packets coming in and out of any interface can match a state,
1760 but it is also possible to change that behaviour by assigning states to a
1761 single interface or a group of interfaces.
1763 The default policy is specified by the
1765 global option, but this can be adjusted on a per-rule basis by adding one
1774 For example, if a rule is defined as:
1775 .Bd -literal -offset indent
1776 pass out on ppp from any to 10.12/16 keep state (group-bound)
1779 A state created on ppp0 would match packets an all PPP interfaces,
1780 but not packets flowing through fxp0 or any other interface.
1784 is the more flexible option when the firewall is in a dynamic routing
1786 However, this has some security implications since a state created by one
1787 trusted network could allow potentially hostile packets coming in from other
1792 restricts state creation to the initial SYN
1793 packet of the TCP handshake.
1794 One can also be less restrictive, and allow state creation from
1800 to synchronize to existing connections, for instance
1801 if one flushes the state table.
1803 For UDP, which is stateless by nature,
1805 will create state as well.
1806 UDP packets are matched to states using only host addresses and ports.
1808 ICMP messages fall into two categories: ICMP error messages, which always
1809 refer to a TCP or UDP packet, are matched against the referred to connection.
1810 If one keeps state on a TCP connection, and an ICMP source quench message
1811 referring to this TCP connection arrives, it will be matched to the right
1812 state and get passed.
1816 creates an ICMP state, and
1818 knows how to match ICMP replies to states.
1820 .Bd -literal -offset indent
1821 pass out inet proto icmp all icmp-type echoreq keep state
1824 allows echo requests (such as those created by
1826 out, creates state, and matches incoming echo replies correctly to states.
1829 .Ar nat , binat No and Ar rdr
1830 rules implicitly create state for connections.
1831 .Sh STATE MODULATION
1832 Much of the security derived from TCP is attributable to how well the
1833 initial sequence numbers (ISNs) are chosen.
1834 Some popular stack implementations choose
1836 poor ISNs and thus are normally susceptible to ISN prediction exploits.
1839 rule to a TCP connection,
1841 will create a high quality random sequence number for each connection
1846 directive implicitly keeps state on the rule and is
1847 only applicable to TCP connections.
1850 .Bd -literal -offset indent
1852 pass out proto tcp from any to any modulate state
1853 pass in proto tcp from any to any port 25 flags S/SA modulate state
1856 There are two caveats associated with state modulation:
1859 rule can not be applied to a pre-existing but unmodulated connection.
1860 Such an application would desynchronize TCP's strict
1861 sequencing between the two endpoints.
1868 modifier and the pre-existing connection will be inferred without
1869 the protection conferred by modulation.
1871 The other caveat affects currently modulated states when the state table
1872 is lost (firewall reboot, flushing the state table, etc...).
1874 will not be able to infer a connection again after the state table flushes
1875 the connection's modulator.
1876 When the state is lost, the connection may be left dangling until the
1877 respective endpoints time out the connection.
1878 It is possible on a fast local network for the endpoints to start an ACK
1879 storm while trying to resynchronize after the loss of the modulator.
1884 rules between fast networks is suggested to prevent ACK storms.
1888 passes packets that are part of a
1890 handshake between the endpoints.
1893 option can be used to cause
1895 itself to complete the handshake with the active endpoint, perform a handshake
1896 with the passive endpoint, and then forward packets between the endpoints.
1898 No packets are sent to the passive endpoint before the active endpoint has
1899 completed the handshake, hence so-called SYN floods with spoofed source
1900 addresses will not reach the passive endpoint, as the sender can't complete the
1903 The proxy is transparent to both endpoints, they each see a single
1904 connection from/to the other endpoint.
1906 chooses random initial sequence numbers for both handshakes.
1907 Once the handshakes are completed, the sequence number modulators
1908 (see previous section) are used to translate further packets of the
1925 .Bd -literal -offset indent
1926 pass in proto tcp from any to any port www flags S/SA synproxy state
1928 .Sh STATEFUL TRACKING OPTIONS
1934 support the following options:
1936 .Bl -tag -width xxxx -compact
1938 Limits the number of concurrent states the rule may create.
1939 When this limit is reached, further packets matching the rule that would
1940 create state are dropped, until existing states time out.
1942 Prevent state changes for states created by this rule from appearing on the
1945 .It Ar <timeout> <seconds>
1946 Changes the timeout values used for states created by this rule.
1950 keyword is specified, the number of states per source IP is tracked.
1951 The following limits can be set:
1953 .Bl -tag -width xxxx -compact
1954 .It Ar max-src-nodes
1955 Limits the maximum number of source addresses which can simultaneously
1956 have state table entries.
1957 .It Ar max-src-states
1958 Limits the maximum number of simultaneous state entries that a single
1959 source address can create with this rule.
1961 For a list of all valid timeout names, see
1965 Multiple options can be specified, separated by commas:
1967 pass in proto tcp from any to any \e
1968 port www flags S/SA keep state \e
1969 (max 100, source-track rule, max-src-nodes 75, \e
1970 max-src-states 3, tcp.established 60, tcp.closing 5)
1973 .Sh OPERATING SYSTEM FINGERPRINTING
1974 Passive OS Fingerprinting is a mechanism to inspect nuances of a TCP
1975 connection's initial SYN packet and guess at the host's operating system.
1976 Unfortunately these nuances are easily spoofed by an attacker so the
1977 fingerprint is not useful in making security decisions.
1978 But the fingerprint is typically accurate enough to make policy decisions
1981 The fingerprints may be specified by operating system class, by
1982 version, or by subtype/patchlevel.
1983 The class of an operating system is typically the vendor or genre
1989 The version of the oldest available
1991 release on the main ftp site
1992 would be 2.6 and the fingerprint would be written
1994 .Dl \&"OpenBSD 2.6\&"
1996 The subtype of an operating system is typically used to describe the
1997 patchlevel if that patch led to changes in the TCP stack behavior.
2000 the only subtype is for a fingerprint that was
2003 scrub option and would be specified as
2005 .Dl \&"OpenBSD 3.3 no-df\&"
2007 Fingerprints for most popular operating systems are provided by
2011 is running, a complete list of known operating system fingerprints may
2012 be listed by running:
2016 Filter rules can enforce policy at any level of operating system specification
2017 assuming a fingerprint is present.
2018 Policy could limit traffic to approved operating systems or even ban traffic
2019 from hosts that aren't at the latest service pack.
2023 class can also be used as the fingerprint which will match packets for
2024 which no operating system fingerprint is known.
2027 .Bd -literal -offset indent
2028 pass out proto tcp from any os OpenBSD keep state
2029 block out proto tcp from any os Doors
2030 block out proto tcp from any os "Doors PT"
2031 block out proto tcp from any os "Doors PT SP3"
2032 block out from any os "unknown"
2033 pass on lo0 proto tcp from any os "OpenBSD 3.3 lo0" keep state
2036 Operating system fingerprinting is limited only to the TCP SYN packet.
2037 This means that it will not work on other protocols and will not match
2038 a currently established connection.
2040 Caveat: operating system fingerprints are occasionally wrong.
2041 There are three problems: an attacker can trivially craft his packets to
2042 appear as any operating system he chooses;
2043 an operating system patch could change the stack behavior and no fingerprints
2044 will match it until the database is updated;
2045 and multiple operating systems may have the same fingerprint.
2046 .Sh BLOCKING SPOOFED TRAFFIC
2047 "Spoofing" is the faking of IP addresses, typically for malicious
2051 directive expands to a set of filter rules which will block all
2052 traffic with a source IP from the network(s) directly connected
2053 to the specified interface(s) from entering the system through
2054 any other interface.
2056 For example, the line
2057 .Bd -literal -offset indent
2062 .Bd -literal -offset indent
2063 block drop in on ! lo0 inet from 127.0.0.1/8 to any
2064 block drop in on ! lo0 inet6 from ::1 to any
2067 For non-loopback interfaces, there are additional rules to block incoming
2068 packets with a source IP address identical to the interface's IP(s).
2069 For example, assuming the interface wi0 had an IP address of 10.0.0.1 and a
2070 netmask of 255.255.255.0,
2072 .Bd -literal -offset indent
2073 antispoof for wi0 inet
2077 .Bd -literal -offset indent
2078 block drop in on ! wi0 inet from 10.0.0.0/24 to any
2079 block drop in inet from 10.0.0.1 to any
2082 Caveat: Rules created by the
2084 directive interfere with packets sent over loopback interfaces
2086 One should pass these explicitly.
2087 .Sh FRAGMENT HANDLING
2088 The size of IP datagrams (packets) can be significantly larger than the
2089 maximum transmission unit (MTU) of the network.
2090 In cases when it is necessary or more efficient to send such large packets,
2091 the large packet will be fragmented into many smaller packets that will each
2093 Unfortunately for a firewalling device, only the first logical fragment will
2094 contain the necessary header information for the subprotocol that allows
2096 to filter on things such as TCP ports or to perform NAT.
2100 rules as described in
2101 .Sx TRAFFIC NORMALIZATION
2102 above, there are three options for handling fragments in the packet filter.
2104 One alternative is to filter individual fragments with filter rules.
2107 rule applies to a fragment, it is passed to the filter.
2108 Filter rules with matching IP header parameters decide whether the
2109 fragment is passed or blocked, in the same way as complete packets
2111 Without reassembly, fragments can only be filtered based on IP header
2112 fields (source/destination address, protocol), since subprotocol header
2113 fields are not available (TCP/UDP port numbers, ICMP code/type).
2116 option can be used to restrict filter rules to apply only to
2117 fragments, but not complete packets.
2118 Filter rules without the
2120 option still apply to fragments, if they only specify IP header fields.
2121 For instance, the rule
2122 .Bd -literal -offset indent
2123 pass in proto tcp from any to any port 80
2126 never applies to a fragment, even if the fragment is part of a TCP
2127 packet with destination port 80, because without reassembly this information
2128 is not available for each fragment.
2129 This also means that fragments cannot create new or match existing
2130 state table entries, which makes stateful filtering and address
2131 translation (NAT, redirection) for fragments impossible.
2133 It's also possible to reassemble only certain fragments by specifying
2134 source or destination addresses or protocols as parameters in
2138 In most cases, the benefits of reassembly outweigh the additional
2139 memory cost, and it's recommended to use
2142 all fragments via the
2143 .Ar fragment reassemble
2146 The memory allocated for fragment caching can be limited using
2148 Once this limit is reached, fragments that would have to be cached
2149 are dropped until other entries time out.
2150 The timeout value can also be adjusted.
2152 Currently, only IPv4 fragments are supported and IPv6 fragments
2153 are blocked unconditionally.
2154 .Sh ANCHORS AND NAMED RULESETS
2155 Besides the main ruleset,
2157 can load named rulesets into
2162 contains a list of named rulesets.
2165 has a name which specifies where
2167 can be used to attach sub-rulesets.
2168 A named ruleset contains filter and translation rules, like the
2170 The main ruleset can reference
2173 using the following kinds
2175 .Bl -tag -width xxxx
2176 .It Ar nat-anchor <name>
2179 rules of all named rulesets in the specified
2181 .It Ar rdr-anchor <name>
2184 rules of all named rulesets in the specified
2186 .It Ar binat-anchor <name>
2189 rules of all named rulesets in the specified
2191 .It Ar anchor <name>
2192 Evaluates the filter rules of all named rulesets in the specified
2194 .It Ar load anchor <name>:<ruleset> from <file>
2195 Loads the rules from the specified file into the named
2198 attached to the anchor
2202 When evaluation of the main ruleset reaches an
2206 will proceed to evaluate all rules specified in the
2207 named rulesets attached to that
2210 Matching filter rules in named rulesets with the
2212 option and matching translation rules are final and abort the
2213 evaluation of both the rules in the
2215 and the main ruleset.
2217 Only the main ruleset can contain
2223 contains more than one named ruleset, they are evaluated
2224 in the alphabetical order of their names.
2228 attachment points which do not contain any rules when the main ruleset
2229 is loaded, and later such named rulesets can be manipulated through
2231 without reloading the main ruleset.
2233 .Bd -literal -offset indent
2235 block on $ext_if all
2237 pass out on $ext_if all keep state
2238 pass in on $ext_if proto tcp from any \e
2239 to $ext_if port smtp keep state
2242 blocks all packets on the external interface by default, then evaluates
2245 named "spam", and finally passes all outgoing connections and
2246 incoming connections to port 25.
2247 .Bd -literal -offset indent
2248 # echo \&"block in quick from 1.2.3.4 to any\&" \&| \e
2249 pfctl -a spam:manual -f -
2252 loads a single ruleset containing a single rule into the
2254 which blocks all packets from a specific address.
2256 The named ruleset can also be populated by adding a
2261 .Bd -literal -offset indent
2263 load anchor spam:manual from "/etc/pf-spam.conf"
2270 it will also load all the rules from the file
2271 .Pa /etc/pf-spam.conf
2272 into the named ruleset.
2276 rules can specify the parameter's
2277 direction, interface, address family, protocol and source/destination
2279 using the same syntax as filter rules.
2280 When parameters are used, the
2282 rule is only evaluated for matching packets.
2283 This allows conditional evaluation of named rulesets, like:
2284 .Bd -literal -offset indent
2285 block on $ext_if all
2286 anchor spam proto tcp from any to any port smtp
2287 pass out on $ext_if all keep state
2288 pass in on $ext_if proto tcp from any to $ext_if port smtp keep state
2293 spam are only evaluated for
2295 packets with destination port 25.
2297 .Bd -literal -offset indent
2298 # echo \&"block in quick from 1.2.3.4 to any" \&| \e
2299 pfctl -a spam:manual -f -
2302 will only block connections from 1.2.3.4 to port 25.
2304 .Bl -tag -width "/etc/protocols" -compact
2308 Default location of the ruleset file.
2310 Default location of OS fingerprints.
2311 .It Pa /etc/protocols
2312 Protocol name database.
2313 .It Pa /etc/services
2314 Service name database.
2315 .It Pa /usr/share/examples/pf
2318 .Sh TRANSLATION EXAMPLES
2319 This example maps incoming requests on port 80 to port 8080, on
2320 which a daemon is running (because, for example, it is not run as root,
2321 and therefore lacks permission to bind to port 80).
2323 # use a macro for the interface name, so it can be changed easily
2326 # map daemon on 8080 to appear to be on 80
2327 rdr on $ext_if proto tcp from any to any port 80 -> 127.0.0.1 port 8080
2332 modifier is given, packets matching the translation rule are passed without
2333 inspecting the filter rules:
2335 rdr pass on $ext_if proto tcp from any to any port 80 -> 127.0.0.1 \e
2339 In the example below, vlan12 is configured as 192.168.168.1;
2340 the machine translates all packets coming from 192.168.168.0/24 to 204.92.77.111
2341 when they are going out any interface except vlan12.
2342 This has the net effect of making traffic from the 192.168.168.0/24
2343 network appear as though it is the Internet routable address
2344 204.92.77.111 to nodes behind any interface on the router except
2345 for the nodes on vlan12.
2346 (Thus, 192.168.168.1 can talk to the 192.168.168.0/24 nodes.)
2348 nat on ! vlan12 from 192.168.168.0/24 to any -> 204.92.77.111
2351 In the example below, the machine sits between a fake internal 144.19.74.*
2352 network, and a routable external IP of 204.92.77.100.
2355 rule excludes protocol AH from being translated.
2358 no nat on $ext_if proto ah from 144.19.74.0/24 to any
2359 nat on $ext_if from 144.19.74.0/24 to any -> 204.92.77.100
2362 In the example below, packets bound for one specific server, as well as those
2363 generated by the sysadmins are not proxied; all other connections are.
2366 no rdr on $int_if proto { tcp, udp } from any to $server port 80
2367 no rdr on $int_if proto { tcp, udp } from $sysadmins to any port 80
2368 rdr on $int_if proto { tcp, udp } from any to any port 80 -> 127.0.0.1 \e
2372 This longer example uses both a NAT and a redirection.
2373 The external interface has the address 157.161.48.183.
2374 On the internal interface, we are running
2376 listening for outbound ftp sessions captured to port 8021.
2379 # Translate outgoing packets' source addresses (any protocol).
2380 # In this case, any address but the gateway's external address is mapped.
2381 nat on $ext_if inet from ! ($ext_if) to any -> ($ext_if)
2384 # Map outgoing packets' source port to an assigned proxy port instead of
2385 # an arbitrary port.
2386 # In this case, proxy outgoing isakmp with port 500 on the gateway.
2387 nat on $ext_if inet proto udp from any port = isakmp to any -> ($ext_if) \e
2391 # Translate outgoing packets' source address (any protocol).
2392 # Translate incoming packets' destination address to an internal machine
2394 binat on $ext_if from 10.1.2.150 to any -> ($ext_if)
2397 # Translate incoming packets' destination addresses.
2398 # As an example, redirect a TCP and UDP port to an internal machine.
2399 rdr on $ext_if inet proto tcp from any to ($ext_if) port 8080 \e
2400 -> 10.1.2.151 port 22
2401 rdr on $ext_if inet proto udp from any to ($ext_if) port 8080 \e
2402 -> 10.1.2.151 port 53
2405 # Translate outgoing ftp control connections to send them to localhost
2406 # for proxying with ftp-proxy(8) running on port 8021.
2407 rdr on $int_if proto tcp from any to any port 21 -> 127.0.0.1 port 8021
2410 In this example, a NAT gateway is set up to translate internal addresses
2411 using a pool of public addresses (192.0.2.16/28) and to redirect
2412 incoming web server connections to a group of web servers on the internal
2416 # Translate outgoing packets' source addresses using an address pool.
2417 # A given source address is always translated to the same pool address by
2418 # using the source-hash keyword.
2419 nat on $ext_if inet from any to any -> 192.0.2.16/28 source-hash
2422 # Translate incoming web server connections to a group of web servers on
2423 # the internal network.
2424 rdr on $ext_if proto tcp from any to any port 80 \e
2425 -> { 10.1.2.155, 10.1.2.160, 10.1.2.161 } round-robin
2429 # The external interface is kue0
2430 # (157.161.48.183, the only routable address)
2431 # and the private network is 10.0.0.0/8, for which we are doing NAT.
2433 # use a macro for the interface name, so it can be changed easily
2436 # normalize all incoming traffic
2437 scrub in on $ext_if all fragment reassemble
2439 # block and log everything by default
2440 block return log on $ext_if all
2442 # block anything coming from source we have no back routes for
2443 block in from no-route to any
2445 # block and log outgoing packets that do not have our address as source,
2446 # they are either spoofed or something is misconfigured (NAT disabled,
2447 # for instance), we want to be nice and do not send out garbage.
2448 block out log quick on $ext_if from ! 157.161.48.183 to any
2450 # silently drop broadcasts (cable modem noise)
2451 block in quick on $ext_if from any to 255.255.255.255
2453 # block and log incoming packets from reserved address space and invalid
2454 # addresses, they are either spoofed or misconfigured, we cannot reply to
2455 # them anyway (hence, no return-rst).
2456 block in log quick on $ext_if from { 10.0.0.0/8, 172.16.0.0/12, \e
2457 192.168.0.0/16, 255.255.255.255/32 } to any
2461 # pass out/in certain ICMP queries and keep state (ping)
2462 # state matching is done on host addresses and ICMP id (not type/code),
2463 # so replies (like 0/0 for 8/0) will match queries
2464 # ICMP error messages (which always refer to a TCP/UDP packet) are
2465 # handled by the TCP/UDP states
2466 pass on $ext_if inet proto icmp all icmp-type 8 code 0 keep state
2470 # pass out all UDP connections and keep state
2471 pass out on $ext_if proto udp all keep state
2473 # pass in certain UDP connections and keep state (DNS)
2474 pass in on $ext_if proto udp from any to any port domain keep state
2478 # pass out all TCP connections and modulate state
2479 pass out on $ext_if proto tcp all modulate state
2481 # pass in certain TCP connections and keep state (SSH, SMTP, DNS, IDENT)
2482 pass in on $ext_if proto tcp from any to any port { ssh, smtp, domain, \e
2483 auth } flags S/SA keep state
2485 # pass in data mode connections for ftp-proxy running on this host.
2486 # (see ftp-proxy(8) for details)
2487 pass in on $ext_if proto tcp from any to 157.161.48.183 port >= 49152 \e
2488 flags S/SA keep state
2490 # Do not allow Windows 9x SMTP connections since they are typically
2491 # a viral worm. Alternately we could limit these OSes to 1 connection each.
2492 block in on $ext_if proto tcp from any os {"Windows 95", "Windows 98"} \e
2497 # three interfaces: $int_if, $ext_if, and $wifi_if (wireless). NAT is
2498 # being done on $ext_if for all outgoing packets. tag packets in on
2499 # $int_if and pass those tagged packets out on $ext_if. all other
2500 # outgoing packets (i.e., packets from the wireless network) are only
2501 # permitted to access port 80.
2503 pass in on $int_if from any to any tag INTNET keep state
2504 pass in on $wifi_if from any to any keep state
2506 block out on $ext_if from any to any
2507 pass out quick on $ext_if tagged INTNET keep state
2508 pass out on $ext_if from any to any port 80 keep state
2510 # tag incoming packets as they are redirected to spamd(8). use the tag
2511 # to pass those packets through the packet filter.
2513 rdr on $ext_if inet proto tcp from <spammers> to port smtp \e
2514 tag SPAMD -> 127.0.0.1 port spamd
2517 pass in on $ext_if inet proto tcp tagged SPAMD keep state
2524 line = ( option | pf-rule | nat-rule | binat-rule | rdr-rule |
2525 antispoof-rule | altq-rule | queue-rule | anchor-rule |
2526 trans-anchors | load-anchors | table-rule )
2528 option = "set" ( [ "timeout" ( timeout | "{" timeout-list "}" ) ] |
2529 [ "optimization" [ "default" | "normal" |
2530 "high-latency" | "satellite" |
2531 "aggressive" | "conservative" ] ]
2532 [ "limit" ( limit-item | "{" limit-list "}" ) ] |
2533 [ "loginterface" ( interface-name | "none" ) ] |
2534 [ "block-policy" ( "drop" | "return" ) ] |
2535 [ "state-policy" ( "if-bound" | "group-bound" |
2537 [ "require-order" ( "yes" | "no" ) ]
2538 [ "fingerprints" filename ] |
2539 [ "debug" ( "none" | "urgent" | "misc" | "loud" ) ] )
2541 pf-rule = action [ ( "in" | "out" ) ]
2542 [ "log" | "log-all" ] [ "quick" ]
2543 [ "on" ifspec ] [ route ] [ af ] [ protospec ]
2544 hosts [ filteropt-list ]
2546 filteropt-list = filteropt-list filteropt | filteropt
2547 filteropt = user | group | flags | icmp-type | icmp6-type | tos |
2548 ( "keep" | "modulate" | "synproxy" ) "state"
2549 [ "(" state-opts ")" ] |
2550 "fragment" | "no-df" | "min-ttl" number |
2551 "max-mss" number | "random-id" | "reassemble tcp" |
2552 fragmentation | "allow-opts" |
2553 "label" string | "tag" string | [ ! ] "tagged" string
2554 "queue" ( string | "(" string [ [ "," ] string ] ")" )
2556 nat-rule = [ "no" ] "nat" [ "pass" ] [ "on" ifspec ] [ af ]
2557 [ protospec ] hosts [ "tag" string ]
2558 [ "->" ( redirhost | "{" redirhost-list "}" )
2559 [ portspec ] [ pooltype ] [ "static-port" ] ]
2561 binat-rule = [ "no" ] "binat" [ "pass" ] [ "on" interface-name ]
2562 [ af ] [ "proto" ( proto-name | proto-number ) ]
2563 "from" address [ "/" mask-bits ] "to" ipspec
2565 [ "->" address [ "/" mask-bits ] ]
2567 rdr-rule = [ "no" ] "rdr" [ "pass" ] [ "on" ifspec ] [ af ]
2568 [ protospec ] hosts [ "tag" string ]
2569 [ "->" ( redirhost | "{" redirhost-list "}" )
2570 [ portspec ] [ pooltype ] ]
2572 antispoof-rule = "antispoof" [ "log" ] [ "quick" ]
2573 "for" ( interface-name | "{" interface-list "}" )
2574 [ af ] [ "label" string ]
2576 table-rule = "table" "<" string ">" [ tableopts-list ]
2577 tableopts-list = tableopts-list tableopts | tableopts
2578 tableopts = "persist" | "const" | "file" string |
2579 "{" [ tableaddr-list ] "}"
2580 tableaddr-list = tableaddr-list [ "," ] tableaddr-spec | tableaddr-spec
2581 tableaddr-spec = [ "!" ] tableaddr [ "/" mask-bits ]
2582 tableaddr = hostname | ipv4-dotted-quad | ipv6-coloned-hex |
2583 interface-name | "self"
2585 altq-rule = "altq on" interface-name queueopts-list
2587 queue-rule = "queue" string [ "on" interface-name ] queueopts-list
2590 anchor-rule = "anchor" string [ ( "in" | "out" ) ] [ "on" ifspec ]
2591 [ af ] [ "proto" ] [ protospec ] [ hosts ]
2593 trans-anchors = ( "nat-anchor" | "rdr-anchor" | "binat-anchor" ) string
2594 [ "on" ifspec ] [ af ] [ "proto" ] [ protospec ] [ hosts ]
2596 load-anchor = "load anchor" anchorname:rulesetname "from" filename
2598 queueopts-list = queueopts-list queueopts | queueopts
2599 queueopts = [ "bandwidth" bandwidth-spec ] |
2600 [ "qlimit" number ] | [ "tbrsize" number ] |
2601 [ "priority" number ] | [ schedulers ]
2602 schedulers = ( cbq-def | priq-def | hfsc-def )
2603 bandwidth-spec = "number" ( "b" | "Kb" | "Mb" | "Gb" | "%" )
2605 action = "pass" | "block" [ return ] | "scrub"
2606 return = "drop" | "return" | "return-rst" [ "( ttl" number ")" ] |
2607 "return-icmp" [ "(" icmpcode ["," icmp6code ] ")" ] |
2608 "return-icmp6" [ "(" icmp6code ")" ]
2609 icmpcode = ( icmp-code-name | icmp-code-number )
2610 icmp6code = ( icmp6-code-name | icmp6-code-number )
2612 ifspec = ( [ "!" ] interface-name ) | "{" interface-list "}"
2613 interface-list = [ "!" ] interface-name [ [ "," ] interface-list ]
2614 route = "fastroute" |
2615 ( "route-to" | "reply-to" | "dup-to" )
2616 ( routehost | "{" routehost-list "}" )
2618 af = "inet" | "inet6"
2620 protospec = "proto" ( proto-name | proto-number |
2621 "{" proto-list "}" )
2622 proto-list = ( proto-name | proto-number ) [ [ "," ] proto-list ]
2625 "from" ( "any" | "no-route" | "self" | host |
2626 "{" host-list "}" ) [ port ] [ os ]
2627 "to" ( "any" | "no-route" | "self" | host |
2628 "{" host-list "}" ) [ port ]
2630 ipspec = "any" | host | "{" host-list "}"
2631 host = [ "!" ] ( address [ "/" mask-bits ] | "<" string ">" )
2632 redirhost = address [ "/" mask-bits ]
2633 routehost = ( interface-name [ address [ "/" mask-bits ] ] )
2634 address = ( interface-name | "(" interface-name ")" | hostname |
2635 ipv4-dotted-quad | ipv6-coloned-hex )
2636 host-list = host [ [ "," ] host-list ]
2637 redirhost-list = redirhost [ [ "," ] redirhost-list ]
2638 routehost-list = routehost [ [ "," ] routehost-list ]
2640 port = "port" ( unary-op | binary-op | "{" op-list "}" )
2641 portspec = "port" ( number | name ) [ ":" ( "*" | number | name ) ]
2642 os = "os" ( os-name | "{" os-list "}" )
2643 user = "user" ( unary-op | binary-op | "{" op-list "}" )
2644 group = "group" ( unary-op | binary-op | "{" op-list "}" )
2646 unary-op = [ "=" | "!=" | "<" | "<=" | ">" | ">=" ]
2648 binary-op = number ( "<>" | "><" | ":" ) number
2649 op-list = ( unary-op | binary-op ) [ [ "," ] op-list ]
2651 os-name = operating-system-name
2652 os-list = os-name [ [ "," ] os-list ]
2654 flags = "flags" [ flag-set ] "/" flag-set
2655 flag-set = [ "F" ] [ "S" ] [ "R" ] [ "P" ] [ "A" ] [ "U" ] [ "E" ]
2658 icmp-type = "icmp-type" ( icmp-type-code | "{" icmp-list "}" )
2659 icmp6-type = "icmp6-type" ( icmp-type-code | "{" icmp-list "}" )
2660 icmp-type-code = ( icmp-type-name | icmp-type-number )
2661 [ "code" ( icmp-code-name | icmp-code-number ) ]
2662 icmp-list = icmp-type-code [ [ "," ] icmp-list ]
2664 tos = "tos" ( "lowdelay" | "throughput" | "reliability" |
2667 state-opts = state-opt [ [ "," ] state-opts ]
2668 state-opt = ( "max" number | "no-sync" | timeout |
2669 "source-track" [ ( "rule" | "global" ) ] |
2670 "max-src-nodes" number | "max-src-states" number |
2671 "if-bound" | "group-bound" | "floating" )
2673 fragmentation = [ "fragment reassemble" | "fragment crop" |
2674 "fragment drop-ovl" ]
2676 timeout-list = timeout [ [ "," ] timeout-list ]
2677 timeout = ( "tcp.first" | "tcp.opening" | "tcp.established" |
2678 "tcp.closing" | "tcp.finwait" | "tcp.closed" |
2679 "udp.first" | "udp.single" | "udp.multiple" |
2680 "icmp.first" | "icmp.error" |
2681 "other.first" | "other.single" | "other.multiple" |
2682 "frag" | "interval" | "src.track" |
2683 "adaptive.start" | "adaptive.end" ) number
2685 limit-list = limit-item [ [ "," ] limit-list ]
2686 limit-item = ( "states" | "frags" | "src-nodes" ) number
2688 pooltype = ( "bitmask" | "random" |
2689 "source-hash" [ ( hex-key | string-key ) ] |
2690 "round-robin" ) [ sticky-address ]
2692 subqueue = string | "{" queue-list "}"
2693 queue-list = string [ [ "," ] string ]
2694 cbq-def = "cbq" [ "(" cbq-opt [ [ "," ] cbq-opt ] ")" ]
2695 priq-def = "priq" [ "(" priq-opt [ [ "," ] priq-opt ] ")" ]
2696 hfsc-def = "hfsc" [ "(" hfsc-opt [ [ "," ] hfsc-opt ] ")" ]
2697 cbq-opt = ( "default" | "borrow" | "red" | "ecn" | "rio" )
2698 priq-opt = ( "default" | "red" | "ecn" | "rio" )
2699 hfsc-opt = ( "default" | "red" | "ecn" | "rio" |
2700 linkshare-sc | realtime-sc | upperlimit-sc )
2701 linkshare-sc = "linkshare" sc-spec
2702 realtime-sc = "realtime" sc-spec
2703 upperlimit-sc = "upperlimit" sc-spec
2704 sc-spec = ( bandwidth-spec |
2705 "(" bandwidth-spec number bandwidth-spec ")" )
2726 file format first appeared in