9 .Nd IP firewall and traffic shaper control program
18 .Op Ar rule | first-last ...
24 .Brq Cm delete | zero | resetlog
29 .Brq Cm firewall | altq | one_pass | debug | verbose | dyn_keepalive
32 .Brq Cm firewall | altq | one_pass | debug | verbose | dyn_keepalive
35 .Cm set Oo Cm disable Ar number ... Oc Op Cm enable Ar number ...
39 .Ar number Cm to Ar number
41 .Cm set swap Ar number number
46 .Cm table Ar number Cm add Ar addr Ns Oo / Ns Ar masklen Oc Op Ar value
48 .Cm table Ar number Cm delete Ar addr Ns Op / Ns Ar masklen
50 .Cm table Ar number Cm flush
52 .Cm table Ar number Cm list
62 .Brq Cm delete | list | show
77 utility is the user interface for controlling the
90 numbered from 1 to 65535.
93 from a number of different places in the protocol stack
94 (depending on the source and destination of the packet,
97 is invoked multiple times on the same packet).
98 The packet passed to the firewall is compared
99 against each of the rules in the firewall
101 When a match is found, the action corresponding to the
102 matching rule is performed.
104 Depending on the action and certain system settings, packets
105 can be reinjected into the firewall at some rule after the
106 matching one for further processing.
110 ruleset always includes a
112 rule (numbered 65535) which cannot be modified or deleted,
113 and matches all packets.
114 The action associated with the
120 depending on how the kernel is configured.
122 If the ruleset includes one or more rules with the
130 behaviour, i.e., upon a match it will create dynamic rules matching
131 the exact parameters (addresses and ports) of the matching packet.
133 These dynamic rules, which have a limited lifetime, are checked
134 at the first occurrence of a
139 rule, and are typically used to open the firewall on-demand to
140 legitimate traffic only.
142 .Sx STATEFUL FIREWALL
145 Sections below for more information on the stateful behaviour of
148 All rules (including dynamic ones) have a few associated counters:
149 a packet count, a byte count, a log count and a timestamp
150 indicating the time of the last match.
151 Counters can be displayed or reset with
155 Rules can be added with the
157 command; deleted individually or in groups with the
159 command, and globally (except those in set 31) with the
161 command; displayed, optionally with the content of the
167 Finally, counters can be reset with the
173 Also, each rule belongs to one of 32 different
177 commands to atomically manipulate sets, such as enable,
178 disable, swap sets, move all rules in a set to another
179 one, delete all rules in a set.
180 These can be useful to
181 install temporary configurations, or to test them.
184 for more information on
187 The following options are available:
188 .Bl -tag -width indent
190 While listing, show counter values.
193 command just implies this option.
195 Only show the action and the comment, not the body of a rule.
199 When entering or showing rules, print them in compact form,
200 i.e., without the optional "ip from any to any" string
201 when this does not carry any additional information.
203 While listing, show dynamic rules in addition to static ones.
205 While listing, if the
207 option was specified, also show expired dynamic rules.
209 Do not ask for confirmation for commands that can cause problems
212 If there is no tty associated with the process, this is implied.
214 Only check syntax of the command strings, without actually passing
217 Try to resolve addresses and service names in output.
225 be quiet about actions
228 This is useful for adjusting rules by executing multiple
232 .Ql sh\ /etc/rc.firewall ) ,
233 or by processing a file of many
235 rules across a remote login session.
238 is performed in normal (verbose) mode (with the default kernel
239 configuration), it prints a message.
240 Because all rules are flushed, the message might not be delivered
241 to the login session, causing the remote login session to be closed
242 and the remainder of the ruleset to not be processed.
243 Access to the console would then be required to recover.
245 While listing rules, show the
247 each rule belongs to.
248 If this flag is not specified, disabled rules will not be
251 While listing pipes, sort according to one of the four
252 counters (total or current packets or bytes).
254 While listing, show last match timestamp (converted with ctime()).
256 While listing, show last match timestamp (as seconds from the epoch).
257 This form can be more convenient for postprocessing by scripts.
260 To ease configuration, rules can be put into a file which is
263 as shown in the last synopsis line.
267 The file will be read line by line and applied as arguments to the
271 Optionally, a preprocessor can be specified using
275 is to be piped through.
276 Useful preprocessors include
282 does not start with a slash
284 as its first character, the usual
286 name search is performed.
287 Care should be taken with this in environments where not all
288 file systems are mounted (yet) by the time
290 is being run (e.g.\& when they are mounted over NFS).
293 has been specified, any additional arguments as passed on to the preprocessor
295 This allows for flexible configuration files (like conditionalizing
296 them on the local hostname) and the use of macros to centralize
297 frequently required arguments like IP addresses.
304 commands are used to configure the traffic shaper, as shown in the
305 .Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION
308 If the world and the kernel get out of sync the
310 ABI may break, preventing you from being able to add any rules.
312 adversely effect the booting process.
317 to temporarily disable the firewall to regain access to the network,
318 allowing you to fix the problem.
320 A packet is checked against the active ruleset in multiple places
321 in the protocol stack, under control of several sysctl variables.
322 These places and variables are shown below, and it is important to
323 have this picture in mind in order to design a correct ruleset.
324 .Bd -literal -offset indent
327 +----------->-----------+
329 [ip(6)_input] [ip(6)_output] net.inet.ip.fw.enable=1
332 [ether_demux] [ether_output_frame] net.link.ether.ipfw=1
334 +-->--[bdg_forward]-->--+ net.link.bridge.ipfw=1
339 As can be noted from the above picture, the number of
340 times the same packet goes through the firewall can
341 vary between 0 and 4 depending on packet source and
342 destination, and system configuration.
344 Note that as packets flow through the stack, headers can be
345 stripped or added to it, and so they may or may not be available
347 E.g., incoming packets will include the MAC header when
351 but the same packets will have the MAC header stripped off when
358 Also note that each packet is always checked against the complete ruleset,
359 irrespective of the place where the check occurs, or the source of the packet.
360 If a rule contains some match patterns or actions which are not valid
361 for the place of invocation (e.g.\& trying to match a MAC header within
365 the match pattern will not match, but a
367 operator in front of such patterns
371 match on those packets.
372 It is thus the responsibility of
373 the programmer, if necessary, to write a suitable ruleset to
374 differentiate among the possible places.
376 rules can be useful here, as an example:
377 .Bd -literal -offset indent
378 # packets from ether_demux or bdg_forward
379 ipfw add 10 skipto 1000 all from any to any layer2 in
380 # packets from ip_input
381 ipfw add 10 skipto 2000 all from any to any not layer2 in
382 # packets from ip_output
383 ipfw add 10 skipto 3000 all from any to any not layer2 out
384 # packets from ether_output_frame
385 ipfw add 10 skipto 4000 all from any to any layer2 out
388 (yes, at the moment there is no way to differentiate between
389 ether_demux and bdg_forward).
391 In general, each keyword or argument must be provided as
392 a separate command line argument, with no leading or trailing
394 Keywords are case-sensitive, whereas arguments may
395 or may not be case-sensitive depending on their nature
396 (e.g.\& uid's are, hostnames are not).
400 you can introduce spaces after commas ',' to make
401 the line more readable.
402 You can also put the entire
403 command (including flags) into a single argument.
404 E.g., the following forms are equivalent:
405 .Bd -literal -offset indent
406 ipfw -q add deny src-ip 10.0.0.0/24,127.0.0.1/8
407 ipfw -q add deny src-ip 10.0.0.0/24, 127.0.0.1/8
408 ipfw "-q add deny src-ip 10.0.0.0/24, 127.0.0.1/8"
413 rules is the following:
414 .Bd -ragged -offset indent
417 .Op Cm set Ar set_number
418 .Op Cm prob Ar match_probability
420 .Op Cm log Op Cm logamount Ar number
426 where the body of the rule specifies which information is used
427 for filtering packets, among the following:
429 .Bl -tag -width "Source and dest. addresses and ports" -offset XXX -compact
430 .It Layer-2 header fields
432 .It IPv4 and IPv6 Protocol
434 .It Source and dest. addresses and ports
438 .It Transmit and receive interface
440 .It Misc. IP header fields
441 Version, type of service, datagram length, identification,
442 fragment flag (non-zero IP offset),
445 .It IPv6 Extension headers
446 Fragmentation, Hop-by-Hop options,
447 source routing, IPSec options.
449 .It Misc. TCP header fields
450 TCP flags (SYN, FIN, ACK, RST, etc.),
451 sequence number, acknowledgment number,
459 When the packet can be associated with a local socket.
461 Whether a packet came from a divert socket (e.g.,
465 Note that some of the above information, e.g.\& source MAC or IP addresses and
466 TCP/UDP ports, could easily be spoofed, so filtering on those fields
467 alone might not guarantee the desired results.
468 .Bl -tag -width indent
470 Each rule is associated with a
472 in the range 1..65535, with the latter reserved for the
475 Rules are checked sequentially by rule number.
476 Multiple rules can have the same number, in which case they are
477 checked (and listed) according to the order in which they have
479 If a rule is entered without specifying a number, the kernel will
480 assign one in such a way that the rule becomes the last one
484 Automatic rule numbers are assigned by incrementing the last
485 non-default rule number by the value of the sysctl variable
486 .Ar net.inet.ip.fw.autoinc_step
487 which defaults to 100.
488 If this is not possible (e.g.\& because we would go beyond the
489 maximum allowed rule number), the number of the last
490 non-default value is used instead.
491 .It Cm set Ar set_number
492 Each rule is associated with a
495 Sets can be individually disabled and enabled, so this parameter
496 is of fundamental importance for atomic ruleset manipulation.
497 It can be also used to simplify deletion of groups of rules.
498 If a rule is entered without specifying a set number,
501 Set 31 is special in that it cannot be disabled,
502 and rules in set 31 are not deleted by the
504 command (but you can delete them with the
505 .Nm ipfw delete set 31
507 Set 31 is also used for the
510 .It Cm prob Ar match_probability
511 A match is only declared with the specified probability
512 (floating point number between 0 and 1).
513 This can be useful for a number of applications such as
514 random packet drop or
517 to simulate the effect of multiple paths leading to out-of-order
520 Note: this condition is checked before any other condition, including
521 ones such as keep-state or check-state which might have side effects.
522 .It Cm log Op Cm logamount Ar number
523 When a packet matches a rule with the
525 keyword, a message will be
531 The logging only occurs if the sysctl variable
532 .Em net.inet.ip.fw.verbose
534 (which is the default when the kernel is compiled with
535 .Dv IPFIREWALL_VERBOSE )
536 and the number of packets logged so far for that
537 particular rule does not exceed the
542 is specified, the limit is taken from the sysctl variable
543 .Em net.inet.ip.fw.verbose_limit .
544 In both cases, a value of 0 removes the logging limit.
546 Once the limit is reached, logging can be re-enabled by
547 clearing the logging counter or the packet counter for that entry, see the
551 Note: logging is done after all other packet matching conditions
552 have been successfully verified, and before performing the final
553 action (accept, deny, etc.) on the packet.
555 When a packet matches a rule with the
557 keyword, the ALTQ identifier for the given
562 Note that this ALTQ tag is only meaningful for packets going "out" of IPFW,
563 and not being rejected or going to divert sockets.
564 Note that if there is insufficient memory at the time the packet is
565 processed, it will not be tagged, so it is wise to make your ALTQ
566 "default" queue policy account for this.
569 rules match a single packet, only the first one adds the ALTQ classification
571 In doing so, traffic may be shaped by using
572 .Cm count Cm altq Ar queue
573 rules for classification early in the ruleset, then later applying
574 the filtering decision.
579 rules may come later and provide the actual filtering decisions in
580 addition to the fallback ALTQ tag.
584 to set up the queues before IPFW will be able to look them up by name,
585 and if the ALTQ disciplines are rearranged, the rules in containing the
586 queue identifiers in the kernel will likely have gone stale and need
588 Stale queue identifiers will probably result in misclassification.
590 All system ALTQ processing can be turned on or off via
595 .Cm disable Ar altq .
597 .Em net.inet.ip.fw.one_pass
598 is irrelevant to ALTQ traffic shaping, as the actual rule action is followed
599 always after adding an ALTQ tag.
602 A rule can be associated with one of the following actions, which
603 will be executed when the packet matches the body of the rule.
604 .Bl -tag -width indent
605 .It Cm allow | accept | pass | permit
606 Allow packets that match rule.
607 The search terminates.
609 Checks the packet against the dynamic ruleset.
610 If a match is found, execute the action associated with
611 the rule which generated this dynamic rule, otherwise
612 move to the next rule.
615 rules do not have a body.
618 rule is found, the dynamic ruleset is checked at the first
624 Update counters for all packets that match rule.
625 The search continues with the next rule.
627 Discard packets that match this rule.
628 The search terminates.
629 .It Cm divert Ar port
630 Divert packets that match this rule to the
634 The search terminates.
635 .It Cm fwd | forward Ar ipaddr Ns Op , Ns Ar port
636 Change the next-hop on matching packets to
638 which can be an IP address or a host name.
639 The search terminates if this rule matches.
643 is a local address, then matching packets will be forwarded to
645 (or the port number in the packet if one is not specified in the rule)
646 on the local machine.
650 is not a local address, then the port number
651 (if specified) is ignored, and the packet will be
652 forwarded to the remote address, using the route as found in
653 the local routing table for that IP.
657 rule will not match layer-2 packets (those received
658 on ether_input, ether_output, or bridged).
662 action does not change the contents of the packet at all.
663 In particular, the destination address remains unmodified, so
664 packets forwarded to another system will usually be rejected by that system
665 unless there is a matching rule on that system to capture them.
666 For packets forwarded locally,
667 the local address of the socket will be
668 set to the original destination address of the packet.
671 entry look rather weird but is intended for
672 use with transparent proxy servers.
676 a custom kernel needs to be compiled with the option
677 .Cd "options IPFIREWALL_FORWARD" .
678 With the additional option
679 .Cd "options IPFIREWALL_FORWARD_EXTENDED"
680 all safeguards are removed and it also makes it possible to redirect
681 packets destined to locally configured IP addresses.
682 Please note that such rules apply to locally generated packets as
683 well and great care is required to ensure proper behaviour for
684 automatically generated packets like ICMP message size exceeded
686 .It Cm pipe Ar pipe_nr
690 (for bandwidth limitation, delay, etc.).
692 .Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION
693 Section for further information.
694 The search terminates; however, on exit from the pipe and if
698 .Em net.inet.ip.fw.one_pass
699 is not set, the packet is passed again to the firewall code
700 starting from the next rule.
701 .It Cm queue Ar queue_nr
705 (for bandwidth limitation using WF2Q+).
711 Discard packets that match this rule, and if the
712 packet is a TCP packet, try to send a TCP reset (RST) notice.
713 The search terminates.
715 Discard packets that match this rule, and if the
716 packet is a TCP packet, try to send a TCP reset (RST) notice.
717 The search terminates.
718 .It Cm skipto Ar number
719 Skip all subsequent rules numbered less than
721 The search continues with the first rule numbered
725 Send a copy of packets matching this rule to the
729 The search continues with the next rule.
730 .It Cm unreach Ar code
731 Discard packets that match this rule, and try to send an ICMP
732 unreachable notice with code
736 is a number from 0 to 255, or one of these aliases:
737 .Cm net , host , protocol , port ,
738 .Cm needfrag , srcfail , net-unknown , host-unknown ,
739 .Cm isolated , net-prohib , host-prohib , tosnet ,
740 .Cm toshost , filter-prohib , host-precedence
742 .Cm precedence-cutoff .
743 The search terminates.
744 .It Cm unreach6 Ar code
745 Discard packets that match this rule, and try to send an ICMPv6
746 unreachable notice with code
750 is a number from 0, 1, 3 or 4, or one of these aliases:
751 .Cm no-route, admin-prohib, address
754 The search terminates.
755 .It Cm netgraph Ar cookie
756 Divert packet into netgraph with given
758 The search terminates.
759 If packet is later returned from netgraph it is either
760 accepted or continues with the next rule, depending on
761 .Em net.inet.ip.fw.one_pass
763 .It Cm ngtee Ar cookie
764 A copy of packet is diverted into netgraph, original
765 packet is either accepted or continues with the next rule, depending on
766 .Em net.inet.ip.fw.one_pass
770 for more information on
777 The body of a rule contains zero or more patterns (such as
778 specific source and destination addresses or ports,
779 protocol options, incoming or outgoing interfaces, etc.)
780 that the packet must match in order to be recognised.
781 In general, the patterns are connected by (implicit)
783 operators -- i.e., all must match in order for the
785 Individual patterns can be prefixed by the
787 operator to reverse the result of the match, as in
789 .Dl "ipfw add 100 allow ip from not 1.2.3.4 to any"
791 Additionally, sets of alternative match patterns
793 can be constructed by putting the patterns in
794 lists enclosed between parentheses ( ) or braces { }, and
799 .Dl "ipfw add 100 allow ip from { x or not y or z } to any"
801 Only one level of parentheses is allowed.
802 Beware that most shells have special meanings for parentheses
803 or braces, so it is advisable to put a backslash \\ in front of them
804 to prevent such interpretations.
806 The body of a rule must in general include a source and destination
810 can be used in various places to specify that the content of
811 a required field is irrelevant.
813 The rule body has the following format:
814 .Bd -ragged -offset indent
815 .Op Ar proto Cm from Ar src Cm to Ar dst
819 The first part (proto from src to dst) is for backward
824 any match pattern (including MAC headers, IP protocols,
825 addresses and ports) can be specified in the
829 Rule fields have the following meaning:
830 .Bl -tag -width indent
831 .It Ar proto : protocol | Cm { Ar protocol Cm or ... }
832 .It Ar protocol : Oo Cm not Oc Ar protocol-name | protocol-number
833 An IP protocol specified by number or name
834 (for a complete list see
835 .Pa /etc/protocols ) ,
836 or one of the following keywords:
837 .Bl -tag -width indent
839 Matches IPv4 packets.
841 Matches IPv6 packets.
852 option will be treated as inner protocol.
860 .Cm { Ar protocol Cm or ... }
863 is provided for convenience only but its use is deprecated.
864 .It Ar src No and Ar dst : Bro Cm addr | Cm { Ar addr Cm or ... } Brc Op Oo Cm not Oc Ar ports
865 An address (or a list, see below)
866 optionally followed by
872 with multiple addresses) is provided for convenience only and
873 its use is discouraged.
874 .It Ar addr : Oo Cm not Oc Bro
876 .Cm table Ns Pq Ar number Ns Op , Ns Ar value
877 .Ar | addr-list | addr-set
880 matches any IP address.
882 matches any IP address configured on an interface in the system.
884 matches any IPv6 address configured on an interface in the system.
885 The address list is evaluated at the time the packet is
887 .It Cm table Ns Pq Ar number Ns Op , Ns Ar value
888 Matches any IPv4 address for which an entry exists in the lookup table
890 If an optional 32-bit unsigned
892 is also specified, an entry will match only if it has this value.
895 section below for more information on lookup tables.
896 .It Ar addr-list : ip-addr Ns Op Ns , Ns Ar addr-list
898 A host or subnet address specified in one of the following ways:
899 .Bl -tag -width indent
900 .It Ar numeric-ip | hostname
901 Matches a single IPv4 address, specified as dotted-quad or a hostname.
902 Hostnames are resolved at the time the rule is added to the firewall list.
903 .It Ar addr Ns / Ns Ar masklen
904 Matches all addresses with base
906 (specified as an IP address or a hostname)
910 As an example, 1.2.3.4/25 will match
911 all IP numbers from 1.2.3.0 to 1.2.3.127 .
912 .It Ar addr Ns : Ns Ar mask
913 Matches all addresses with base
915 (specified as an IP address or a hostname)
918 specified as a dotted quad.
919 As an example, 1.2.3.4:255.0.255.0 will match
921 This form is advised only for non-contiguous
923 It is better to resort to the
924 .Ar addr Ns / Ns Ar masklen
925 format for contiguous masks, which is more compact and less
928 .It Ar addr-set : addr Ns Oo Ns / Ns Ar masklen Oc Ns Cm { Ns Ar list Ns Cm }
929 .It Ar list : Bro Ar num | num-num Brc Ns Op Ns , Ns Ar list
930 Matches all addresses with base address
932 (specified as an IP address or a hostname)
933 and whose last byte is in the list between braces { } .
934 Note that there must be no spaces between braces and
935 numbers (spaces after commas are allowed).
936 Elements of the list can be specified as single entries
940 field is used to limit the size of the set of addresses,
941 and can have any value between 24 and 32.
943 it will be assumed as 24.
945 This format is particularly useful to handle sparse address sets
946 within a single rule.
947 Because the matching occurs using a
948 bitmask, it takes constant time and dramatically reduces
949 the complexity of rulesets.
951 As an example, an address specified as 1.2.3.4/24{128,35-55,89}
952 will match the following IP addresses:
954 1.2.3.128, 1.2.3.35 to 1.2.3.55, 1.2.3.89 .
955 .It Ar addr6-list : ip6-addr Ns Op Ns , Ns Ar addr6-list
957 A host or subnet specified one of the following ways:
959 .Bl -tag -width indent
960 .It Ar numeric-ip | hostname
961 Matches a single IPv6 address as allowed by
964 Hostnames are resolved at the time the rule is added to the firewall
966 .It Ar addr Ns / Ns Ar masklen
967 Matches all IPv6 addresses with base
969 (specified as allowed by
977 No support for sets of IPv6 addresses is provided because IPv6 addresses
978 are typically random past the initial prefix.
979 .It Ar ports : Bro Ar port | port Ns \&- Ns Ar port Ns Brc Ns Op , Ns Ar ports
980 For protocols which support port numbers (such as TCP and UDP), optional
982 may be specified as one or more ports or port ranges, separated
983 by commas but no spaces, and an optional
988 notation specifies a range of ports (including boundaries).
992 may be used instead of numeric port values.
993 The length of the port list is limited to 30 ports or ranges,
994 though one can specify larger ranges by using an
1002 can be used to escape the dash
1004 character in a service name (from a shell, the backslash must be
1005 typed twice to avoid the shell itself interpreting it as an escape
1008 .Dl "ipfw add count tcp from any ftp\e\e-data-ftp to any"
1010 Fragmented packets which have a non-zero offset (i.e., not the first
1011 fragment) will never match a rule which has one or more port
1015 option for details on matching fragmented packets.
1017 .Ss RULE OPTIONS (MATCH PATTERNS)
1018 Additional match patterns can be used within
1020 Zero or more of these so-called
1022 can be present in a rule, optionally prefixed by the
1024 operand, and possibly grouped into
1027 The following match patterns can be used (listed in alphabetical order):
1028 .Bl -tag -width indent
1029 .It Cm // this is a comment.
1030 Inserts the specified text as a comment in the rule.
1031 Everything following // is considered as a comment and stored in the rule.
1032 You can have comment-only rules, which are listed as having a
1034 action followed by the comment.
1039 Matches only packets generated by a divert socket.
1040 .It Cm diverted-loopback
1041 Matches only packets coming from a divert socket back into the IP stack
1043 .It Cm diverted-output
1044 Matches only packets going from a divert socket back outward to the IP
1045 stack output for delivery.
1046 .It Cm dst-ip Ar ip-address
1047 Matches IPv4 packets whose destination IP is one of the address(es)
1048 specified as argument.
1049 .It Bro Cm dst-ip6 | dst-ipv6 Brc Ar ip6-address
1050 Matches IPv6 packets whose destination IP is one of the address(es)
1051 specified as argument.
1052 .It Cm dst-port Ar ports
1053 Matches IP packets whose destination port is one of the port(s)
1054 specified as argument.
1056 Matches TCP packets that have the RST or ACK bits set.
1057 .It Cm ext6hdr Ar header
1058 Matches IPv6 packets containing the extended header given by
1060 Supported headers are:
1070 IPSec authentication headers
1072 and IPSec encapsulated security payload headers
1074 .It Cm flow-id Ar labels
1075 Matches IPv6 packets containing any of the flow labels given in
1078 is a comma seperate list of numeric flow labels.
1080 Matches packets that are fragments and not the first
1081 fragment of an IP datagram.
1082 Note that these packets will not have
1083 the next protocol header (e.g.\& TCP, UDP) so options that look into
1084 these headers cannot match.
1086 Matches all TCP or UDP packets sent by or received for a
1090 may be specified by name or number.
1091 This option should be used only if debug.mpsafenet=0 to avoid possible
1092 deadlocks due to layering violations in its implementation.
1093 .It Cm jail Ar prisonID
1094 Matches all TCP or UDP packets sent by or received for the
1095 jail whos prison ID is
1097 This option should be used only if debug.mpsafenet=0 to avoid possible
1098 deadlocks due to layering violations in its implementation.
1099 .It Cm icmptypes Ar types
1100 Matches ICMP packets whose ICMP type is in the list
1102 The list may be specified as any combination of
1103 individual types (numeric) separated by commas.
1104 .Em Ranges are not allowed.
1105 The supported ICMP types are:
1109 destination unreachable
1117 router advertisement
1121 time-to-live exceeded
1133 address mask request
1135 and address mask reply
1137 .It Cm icmp6types Ar types
1138 Matches ICMP6 packets whose ICMP6 type is in the list of
1140 The list may be specified as any combination of
1141 individual types (numeric) separated by commas.
1142 .Em Ranges are not allowed.
1144 Matches incoming or outgoing packets, respectively.
1148 are mutually exclusive (in fact,
1152 .It Cm ipid Ar id-list
1153 Matches IPv4 packets whose
1155 field has value included in
1157 which is either a single value or a list of values or ranges
1158 specified in the same way as
1160 .It Cm iplen Ar len-list
1161 Matches IP packets whose total length, including header and data, is
1164 which is either a single value or a list of values or ranges
1165 specified in the same way as
1167 .It Cm ipoptions Ar spec
1168 Matches packets whose IPv4 header contains the comma separated list of
1169 options specified in
1171 The supported IP options are:
1174 (strict source route),
1176 (loose source route),
1178 (record packet route) and
1181 The absence of a particular option may be denoted
1184 .It Cm ipprecedence Ar precedence
1185 Matches IPv4 packets whose precedence field is equal to
1188 Matches packets that have IPSEC history associated with them
1189 (i.e., the packet comes encapsulated in IPSEC, the kernel
1190 has IPSEC support and IPSEC_FILTERGIF option, and can correctly
1193 Note that specifying
1195 is different from specifying
1197 as the latter will only look at the specific IP protocol field,
1198 irrespective of IPSEC kernel support and the validity of the IPSEC data.
1200 Further note that this flag is silently ignored in kernels without
1202 It does not affect rule processing when given and the
1203 rules are handled as if with no
1206 .It Cm iptos Ar spec
1207 Matches IPv4 packets whose
1209 field contains the comma separated list of
1210 service types specified in
1212 The supported IP types of service are:
1215 .Pq Dv IPTOS_LOWDELAY ,
1217 .Pq Dv IPTOS_THROUGHPUT ,
1219 .Pq Dv IPTOS_RELIABILITY ,
1221 .Pq Dv IPTOS_MINCOST ,
1224 The absence of a particular type may be denoted
1227 .It Cm ipttl Ar ttl-list
1228 Matches IPv4 packets whose time to live is included in
1230 which is either a single value or a list of values or ranges
1231 specified in the same way as
1233 .It Cm ipversion Ar ver
1234 Matches IP packets whose IP version field is
1237 Upon a match, the firewall will create a dynamic rule, whose
1238 default behaviour is to match bidirectional traffic between
1239 source and destination IP/port using the same protocol.
1240 The rule has a limited lifetime (controlled by a set of
1242 variables), and the lifetime is refreshed every time a matching
1245 Matches only layer2 packets, i.e., those passed to
1247 from ether_demux() and ether_output_frame().
1248 .It Cm limit Bro Cm src-addr | src-port | dst-addr | dst-port Brc Ar N
1249 The firewall will only allow
1251 connections with the same
1252 set of parameters as specified in the rule.
1254 of source and destination addresses and ports can be
1257 only IPv4 flows are supported.
1258 .It Cm { MAC | mac } Ar dst-mac src-mac
1259 Match packets with a given
1263 addresses, specified as the
1265 keyword (matching any MAC address), or six groups of hex digits
1266 separated by colons,
1267 and optionally followed by a mask indicating the significant bits.
1268 The mask may be specified using either of the following methods:
1269 .Bl -enum -width indent
1273 followed by the number of significant bits.
1274 For example, an address with 33 significant bits could be specified as:
1276 .Dl "MAC 10:20:30:40:50:60/33 any"
1281 followed by a bitmask specified as six groups of hex digits separated
1283 For example, an address in which the last 16 bits are significant could
1286 .Dl "MAC 10:20:30:40:50:60&00:00:00:00:ff:ff any"
1288 Note that the ampersand character has a special meaning in many shells
1289 and should generally be escaped.
1292 Note that the order of MAC addresses (destination first,
1294 the same as on the wire, but the opposite of the one used for
1296 .It Cm mac-type Ar mac-type
1297 Matches packets whose Ethernet Type field
1298 corresponds to one of those specified as argument.
1300 is specified in the same way as
1302 (i.e., one or more comma-separated single values or ranges).
1303 You can use symbolic names for known values such as
1304 .Em vlan , ipv4, ipv6 .
1305 Values can be entered as decimal or hexadecimal (if prefixed by 0x),
1306 and they are always printed as hexadecimal (unless the
1308 option is used, in which case symbolic resolution will be attempted).
1309 .It Cm proto Ar protocol
1310 Matches packets with the corresponding IP protocol.
1311 .It Cm recv | xmit | via Brq Ar ifX | Ar if Ns Cm * | Ar ipno | Ar any
1312 Matches packets received, transmitted or going through,
1313 respectively, the interface specified by exact name
1314 .Ns No ( Ar ifX Ns No ),
1316 .Ns No ( Ar if Ns Ar * Ns No ),
1317 by IP address, or through some interface.
1321 keyword causes the interface to always be checked.
1328 then only the receive or transmit interface (respectively)
1330 By specifying both, it is possible to match packets based on
1331 both receive and transmit interface, e.g.:
1333 .Dl "ipfw add deny ip from any to any out recv ed0 xmit ed1"
1337 interface can be tested on either incoming or outgoing packets,
1340 interface can only be tested on outgoing packets.
1345 is invalid) whenever
1349 A packet may not have a receive or transmit interface: packets
1350 originating from the local host have no receive interface,
1351 while packets destined for the local host have no transmit
1354 Matches TCP packets that have the SYN bit set but no ACK bit.
1355 This is the short form of
1356 .Dq Li tcpflags\ syn,!ack .
1357 .It Cm src-ip Ar ip-address
1358 Matches IPv4 packets whose source IP is one of the address(es)
1359 specified as an argument.
1360 .It Cm src-ip6 Ar ip6-address
1361 Matches IPv6 packets whose source IP is one of the address(es)
1362 specified as an argument.
1363 .It Cm src-port Ar ports
1364 Matches IP packets whose source port is one of the port(s)
1365 specified as argument.
1366 .It Cm tcpack Ar ack
1368 Match if the TCP header acknowledgment number field is set to
1370 .It Cm tcpdatalen Ar tcpdatalen-list
1371 Matches TCP packets whose length of TCP data is
1372 .Ar tcpdatalen-list ,
1373 which is either a single value or a list of values or ranges
1374 specified in the same way as
1376 .It Cm tcpflags Ar spec
1378 Match if the TCP header contains the comma separated list of
1381 The supported TCP flags are:
1390 The absence of a particular flag may be denoted
1393 A rule which contains a
1395 specification can never match a fragmented packet which has
1399 option for details on matching fragmented packets.
1400 .It Cm tcpseq Ar seq
1402 Match if the TCP header sequence number field is set to
1404 .It Cm tcpwin Ar win
1406 Match if the TCP header window field is set to
1408 .It Cm tcpoptions Ar spec
1410 Match if the TCP header contains the comma separated list of
1411 options specified in
1413 The supported TCP options are:
1416 (maximum segment size),
1418 (tcp window advertisement),
1422 (rfc1323 timestamp) and
1424 (rfc1644 t/tcp connection count).
1425 The absence of a particular option may be denoted
1429 Match all TCP or UDP packets sent by or received for a
1433 may be matched by name or identification number.
1434 This option should be used only if debug.mpsafenet=0 to avoid possible
1435 deadlocks due to layering violations in its implementation.
1437 For incoming packets,
1438 a routing table lookup is done on the packet's source address.
1439 If the interface on which the packet entered the system matches the
1440 outgoing interface for the route,
1442 If the interfaces do not match up,
1443 the packet does not match.
1444 All outgoing packets or packets with no incoming interface match.
1446 The name and functionality of the option is intentionally similar to
1447 the Cisco IOS command:
1449 .Dl ip verify unicast reverse-path
1451 This option can be used to make anti-spoofing rules to reject all
1452 packets with source addresses not from this interface.
1456 For incoming packets,
1457 a routing table lookup is done on the packet's source address.
1458 If a route to the source address exists, but not the default route
1459 or a blackhole/reject route, the packet matches.
1460 Otherwise, the packet does not match.
1461 All outgoing packets match.
1463 The name and functionality of the option is intentionally similar to
1464 the Cisco IOS command:
1466 .Dl ip verify unicast source reachable-via any
1468 This option can be used to make anti-spoofing rules to reject all
1469 packets whose source address is unreachable.
1471 For incoming packets, the packet's source address is checked if it
1472 belongs to a directly connected network.
1473 If the network is directly connected, then the interface the packet
1474 came on in is compared to the interface the network is connected to.
1475 When incoming interface and directly connected interface are not the
1476 same, the packet does not match.
1477 Otherwise, the packet does match.
1478 All outgoing packets match.
1480 This option can be used to make anti-spoofing rules to reject all
1481 packets that pretend to be from a directly connected network but do
1482 not come in through that interface.
1483 This option is similar to but more restricted than
1485 because it engages only on packets with source addresses of directly
1486 connected networks instead of all source addresses.
1489 Lookup tables are useful to handle large sparse address sets,
1490 typically from a hundred to several thousands of entries.
1491 There may be up to 128 different lookup tables, numbered 0 to 127.
1493 Each entry is represented by an
1494 .Ar addr Ns Op / Ns Ar masklen
1495 and will match all addresses with base
1497 (specified as an IP address or a hostname)
1503 is not specified, it defaults to 32.
1504 When looking up an IP address in a table, the most specific
1506 Associated with each entry is a 32-bit unsigned
1508 which can optionally be checked by a rule matching code.
1509 When adding an entry, if
1511 is not specified, it defaults to 0.
1513 An entry can be added to a table
1515 removed from a table
1517 a table can be examined
1522 Internally, each table is stored in a Radix tree, the same way as
1523 the routing table (see
1526 Lookup tables currently support IPv4 addresses only.
1530 feature provides the ability to use a value, looked up in the table, as
1531 the argument for a rule action.
1532 This can significantly reduce number of rules in some configurations.
1535 argument can be used with the following actions:
1536 .Cm pipe , queue, divert, tee, netgraph, ngtee .
1539 Section for example usage of tables and the tablearg keyword.
1541 Each rule belongs to one of 32 different
1544 Set 31 is reserved for the default rule.
1546 By default, rules are put in set 0, unless you use the
1548 attribute when entering a new rule.
1549 Sets can be individually and atomically enabled or disabled,
1550 so this mechanism permits an easy way to store multiple configurations
1551 of the firewall and quickly (and atomically) switch between them.
1552 The command to enable/disable sets is
1553 .Bd -ragged -offset indent
1555 .Cm set Oo Cm disable Ar number ... Oc Op Cm enable Ar number ...
1562 sections can be specified.
1563 Command execution is atomic on all the sets specified in the command.
1564 By default, all sets are enabled.
1566 When you disable a set, its rules behave as if they do not exist
1567 in the firewall configuration, with only one exception:
1568 .Bd -ragged -offset indent
1569 dynamic rules created from a rule before it had been disabled
1570 will still be active until they expire.
1572 dynamic rules you have to explicitly delete the parent rule
1573 which generated them.
1576 The set number of rules can be changed with the command
1577 .Bd -ragged -offset indent
1580 .Brq Cm rule Ar rule-number | old-set
1584 Also, you can atomically swap two rulesets with the command
1585 .Bd -ragged -offset indent
1587 .Cm set swap Ar first-set second-set
1592 Section on some possible uses of sets of rules.
1593 .Sh STATEFUL FIREWALL
1594 Stateful operation is a way for the firewall to dynamically
1595 create rules for specific flows when packets that
1596 match a given pattern are detected.
1597 Support for stateful
1598 operation comes through the
1599 .Cm check-state , keep-state
1605 Dynamic rules are created when a packet matches a
1609 rule, causing the creation of a
1611 rule which will match all and only packets with
1615 .Em src-ip/src-port dst-ip/dst-port
1620 are used here only to denote the initial match addresses, but they
1621 are completely equivalent afterwards).
1622 Dynamic rules will be checked at the first
1623 .Cm check-state, keep-state
1626 occurrence, and the action performed upon a match will be the same
1627 as in the parent rule.
1629 Note that no additional attributes other than protocol and IP addresses
1630 and ports are checked on dynamic rules.
1632 The typical use of dynamic rules is to keep a closed firewall configuration,
1633 but let the first TCP SYN packet from the inside network install a
1634 dynamic rule for the flow so that packets belonging to that session
1635 will be allowed through the firewall:
1637 .Dl "ipfw add check-state"
1638 .Dl "ipfw add allow tcp from my-subnet to any setup keep-state"
1639 .Dl "ipfw add deny tcp from any to any"
1641 A similar approach can be used for UDP, where an UDP packet coming
1642 from the inside will install a dynamic rule to let the response through
1645 .Dl "ipfw add check-state"
1646 .Dl "ipfw add allow udp from my-subnet to any keep-state"
1647 .Dl "ipfw add deny udp from any to any"
1649 Dynamic rules expire after some time, which depends on the status
1650 of the flow and the setting of some
1654 .Sx SYSCTL VARIABLES
1656 For TCP sessions, dynamic rules can be instructed to periodically
1657 send keepalive packets to refresh the state of the rule when it is
1662 for more examples on how to use dynamic rules.
1663 .Sh TRAFFIC SHAPER (DUMMYNET) CONFIGURATION
1665 is also the user interface for the
1670 operates by first using the firewall to classify packets and divide them into
1672 using any match pattern that can be used in
1675 Depending on local policies, a flow can contain packets for a single
1676 TCP connection, or from/to a given host, or entire subnet, or a
1679 Packets belonging to the same flow are then passed to either of two
1680 different objects, which implement the traffic regulation:
1681 .Bl -hang -offset XXXX
1683 A pipe emulates a link with given bandwidth, propagation delay,
1684 queue size and packet loss rate.
1685 Packets are queued in front of the pipe as they come out from the classifier,
1686 and then transferred to the pipe according to the pipe's parameters.
1690 is an abstraction used to implement the WF2Q+
1691 (Worst-case Fair Weighted Fair Queueing) policy, which is
1692 an efficient variant of the WFQ policy.
1694 The queue associates a
1696 and a reference pipe to each flow, and then all backlogged (i.e.,
1697 with packets queued) flows linked to the same pipe share the pipe's
1698 bandwidth proportionally to their weights.
1699 Note that weights are not priorities; a flow with a lower weight
1700 is still guaranteed to get its fraction of the bandwidth even if a
1701 flow with a higher weight is permanently backlogged.
1706 can be used to set hard limits to the bandwidth that a flow can use, whereas
1708 can be used to determine how different flow share the available bandwidth.
1714 configuration commands are the following:
1715 .Bd -ragged -offset indent
1716 .Cm pipe Ar number Cm config Ar pipe-configuration
1718 .Cm queue Ar number Cm config Ar queue-configuration
1721 The following parameters can be configured for a pipe:
1723 .Bl -tag -width indent -compact
1724 .It Cm bw Ar bandwidth | device
1725 Bandwidth, measured in
1728 .Brq Cm bit/s | Byte/s .
1731 A value of 0 (default) means unlimited bandwidth.
1732 The unit must immediately follow the number, as in
1734 .Dl "ipfw pipe 1 config bw 300Kbit/s"
1736 If a device name is specified instead of a numeric value, as in
1738 .Dl "ipfw pipe 1 config bw tun0"
1740 then the transmit clock is supplied by the specified device.
1741 At the moment only the
1743 device supports this
1744 functionality, for use in conjunction with
1747 .It Cm delay Ar ms-delay
1748 Propagation delay, measured in milliseconds.
1749 The value is rounded to the next multiple of the clock tick
1750 (typically 10ms, but it is a good practice to run kernels
1752 .Dq "options HZ=1000"
1754 the granularity to 1ms or less).
1755 Default value is 0, meaning no delay.
1758 The following parameters can be configured for a queue:
1760 .Bl -tag -width indent -compact
1761 .It Cm pipe Ar pipe_nr
1762 Connects a queue to the specified pipe.
1763 Multiple queues (with the same or different weights) can be connected to
1764 the same pipe, which specifies the aggregate rate for the set of queues.
1766 .It Cm weight Ar weight
1767 Specifies the weight to be used for flows matching this queue.
1768 The weight must be in the range 1..100, and defaults to 1.
1771 Finally, the following parameters can be configured for both
1774 .Bl -tag -width XXXX -compact
1776 .It Cm buckets Ar hash-table-size
1777 Specifies the size of the hash table used for storing the
1779 Default value is 64 controlled by the
1782 .Em net.inet.ip.dummynet.hash_size ,
1783 allowed range is 16 to 65536.
1785 .It Cm mask Ar mask-specifier
1786 Packets sent to a given pipe or queue by an
1788 rule can be further classified into multiple flows, each of which is then
1792 A flow identifier is constructed by masking the IP addresses,
1793 ports and protocol types as specified with the
1795 options in the configuration of the pipe or queue.
1796 For each different flow identifier, a new pipe or queue is created
1797 with the same parameters as the original object, and matching packets
1802 are used, each flow will get the same bandwidth as defined by the pipe,
1805 are used, each flow will share the parent's pipe bandwidth evenly
1806 with other flows generated by the same queue (note that other queues
1807 with different weights might be connected to the same pipe).
1809 Available mask specifiers are a combination of one or more of the following:
1811 .Cm dst-ip Ar mask ,
1812 .Cm dst-ip6 Ar mask ,
1813 .Cm src-ip Ar mask ,
1814 .Cm src-ip6 Ar mask ,
1815 .Cm dst-port Ar mask ,
1816 .Cm src-port Ar mask ,
1817 .Cm flow-id Ar mask ,
1822 where the latter means all bits in all fields are significant.
1825 When a packet is dropped by a dummynet queue or pipe, the error
1826 is normally reported to the caller routine in the kernel, in the
1827 same way as it happens when a device queue fills up.
1829 option reports the packet as successfully delivered, which can be
1830 needed for some experimental setups where you want to simulate
1831 loss or congestion at a remote router.
1833 .It Cm plr Ar packet-loss-rate
1836 .Ar packet-loss-rate
1837 is a floating-point number between 0 and 1, with 0 meaning no
1838 loss, 1 meaning 100% loss.
1839 The loss rate is internally represented on 31 bits.
1841 .It Cm queue Brq Ar slots | size Ns Cm Kbytes
1846 Default value is 50 slots, which
1847 is the typical queue size for Ethernet devices.
1848 Note that for slow speed links you should keep the queue
1849 size short or your traffic might be affected by a significant
1851 E.g., 50 max-sized ethernet packets (1500 bytes) mean 600Kbit
1852 or 20s of queue on a 30Kbit/s pipe.
1853 Even worse effects can result if you get packets from an
1854 interface with a much larger MTU, e.g.\& the loopback interface
1855 with its 16KB packets.
1857 .It Cm red | gred Ar w_q Ns / Ns Ar min_th Ns / Ns Ar max_th Ns / Ns Ar max_p
1858 Make use of the RED (Random Early Detection) queue management algorithm.
1863 point numbers between 0 and 1 (0 not included), while
1867 are integer numbers specifying thresholds for queue management
1868 (thresholds are computed in bytes if the queue has been defined
1869 in bytes, in slots otherwise).
1872 also supports the gentle RED variant (gred).
1875 variables can be used to control the RED behaviour:
1876 .Bl -tag -width indent
1877 .It Em net.inet.ip.dummynet.red_lookup_depth
1878 specifies the accuracy in computing the average queue
1879 when the link is idle (defaults to 256, must be greater than zero)
1880 .It Em net.inet.ip.dummynet.red_avg_pkt_size
1881 specifies the expected average packet size (defaults to 512, must be
1883 .It Em net.inet.ip.dummynet.red_max_pkt_size
1884 specifies the expected maximum packet size, only used when queue
1885 thresholds are in bytes (defaults to 1500, must be greater than zero).
1889 When used with IPv6 data, dummynet currently has several limitations.
1890 First, debug.mpsafenet=0 must be set.
1891 Second, the information necessicary to route link-local packets to an
1892 interface is not avalable after processing by dummynet so those packets
1893 are dropped in the output path.
1894 Care should be taken to insure that link-local packets are not passed to
1897 Here are some important points to consider when designing your
1901 Remember that you filter both packets going
1905 Most connections need packets going in both directions.
1907 Remember to test very carefully.
1908 It is a good idea to be near the console when doing this.
1909 If you cannot be near the console,
1910 use an auto-recovery script such as the one in
1911 .Pa /usr/share/examples/ipfw/change_rules.sh .
1913 Do not forget the loopback interface.
1918 There are circumstances where fragmented datagrams are unconditionally
1920 TCP packets are dropped if they do not contain at least 20 bytes of
1921 TCP header, UDP packets are dropped if they do not contain a full 8
1922 byte UDP header, and ICMP packets are dropped if they do not contain
1923 4 bytes of ICMP header, enough to specify the ICMP type, code, and
1925 These packets are simply logged as
1927 since there may not be enough good data in the packet to produce a
1928 meaningful log entry.
1930 Another type of packet is unconditionally dropped, a TCP packet with a
1931 fragment offset of one.
1932 This is a valid packet, but it only has one use, to try
1933 to circumvent firewalls.
1934 When logging is enabled, these packets are
1935 reported as being dropped by rule -1.
1937 If you are logged in over a network, loading the
1941 is probably not as straightforward as you would think.
1942 I recommend the following command line:
1943 .Bd -literal -offset indent
1945 ipfw add 32000 allow ip from any to any
1948 Along the same lines, doing an
1949 .Bd -literal -offset indent
1953 in similar surroundings is also a bad idea.
1957 filter list may not be modified if the system security level
1958 is set to 3 or higher
1961 for information on system security levels).
1963 .Sh PACKET DIVERSION
1966 socket bound to the specified port will receive all packets
1967 diverted to that port.
1968 If no socket is bound to the destination port, or if the divert module is
1969 not loaded, or if the kernel was not compiled with divert socket support,
1970 the packets are dropped.
1971 .Sh SYSCTL VARIABLES
1974 variables controls the behaviour of the firewall and
1976 .Pq Nm dummynet , bridge .
1977 These are shown below together with their default value
1978 (but always check with the
1980 command what value is actually in use) and meaning:
1981 .Bl -tag -width indent
1982 .It Em net.inet.ip.dummynet.expire : No 1
1983 Lazily delete dynamic pipes/queue once they have no pending traffic.
1984 You can disable this by setting the variable to 0, in which case
1985 the pipes/queues will only be deleted when the threshold is reached.
1986 .It Em net.inet.ip.dummynet.hash_size : No 64
1987 Default size of the hash table used for dynamic pipes/queues.
1988 This value is used when no
1990 option is specified when configuring a pipe/queue.
1991 .It Em net.inet.ip.dummynet.max_chain_len : No 16
1992 Target value for the maximum number of pipes/queues in a hash bucket.
1994 .Cm max_chain_len*hash_size
1995 is used to determine the threshold over which empty pipes/queues
1996 will be expired even when
1997 .Cm net.inet.ip.dummynet.expire=0 .
1998 .It Em net.inet.ip.dummynet.red_lookup_depth : No 256
1999 .It Em net.inet.ip.dummynet.red_avg_pkt_size : No 512
2000 .It Em net.inet.ip.dummynet.red_max_pkt_size : No 1500
2001 Parameters used in the computations of the drop probability
2002 for the RED algorithm.
2003 .It Em net.inet.ip.fw.autoinc_step : No 100
2004 Delta between rule numbers when auto-generating them.
2005 The value must be in the range 1..1000.
2006 This variable is only present in
2008 the delta is hardwired to 100 in
2010 .It Em net.inet.ip.fw.curr_dyn_buckets : Em net.inet.ip.fw.dyn_buckets
2011 The current number of buckets in the hash table for dynamic rules
2013 .It Em net.inet.ip.fw.debug : No 1
2014 Controls debugging messages produced by
2016 .It Em net.inet.ip.fw.dyn_buckets : No 256
2017 The number of buckets in the hash table for dynamic rules.
2018 Must be a power of 2, up to 65536.
2019 It only takes effect when all dynamic rules have expired, so you
2020 are advised to use a
2022 command to make sure that the hash table is resized.
2023 .It Em net.inet.ip.fw.dyn_count : No 3
2024 Current number of dynamic rules
2026 .It Em net.inet.ip.fw.dyn_keepalive : No 1
2027 Enables generation of keepalive packets for
2029 rules on TCP sessions.
2030 A keepalive is generated to both
2031 sides of the connection every 5 seconds for the last 20
2032 seconds of the lifetime of the rule.
2033 .It Em net.inet.ip.fw.dyn_max : No 8192
2034 Maximum number of dynamic rules.
2035 When you hit this limit, no more dynamic rules can be
2036 installed until old ones expire.
2037 .It Em net.inet.ip.fw.dyn_ack_lifetime : No 300
2038 .It Em net.inet.ip.fw.dyn_syn_lifetime : No 20
2039 .It Em net.inet.ip.fw.dyn_fin_lifetime : No 1
2040 .It Em net.inet.ip.fw.dyn_rst_lifetime : No 1
2041 .It Em net.inet.ip.fw.dyn_udp_lifetime : No 5
2042 .It Em net.inet.ip.fw.dyn_short_lifetime : No 30
2043 These variables control the lifetime, in seconds, of dynamic
2045 Upon the initial SYN exchange the lifetime is kept short,
2046 then increased after both SYN have been seen, then decreased
2047 again during the final FIN exchange or when a RST is received.
2049 .Em dyn_fin_lifetime
2051 .Em dyn_rst_lifetime
2052 must be strictly lower than 5 seconds, the period of
2053 repetition of keepalives.
2054 The firewall enforces that.
2055 .It Em net.inet.ip.fw.enable : No 1
2056 Enables the firewall.
2057 Setting this variable to 0 lets you run your machine without
2058 firewall even if compiled in.
2059 .It Em net.inet.ip.fw.one_pass : No 1
2060 When set, the packet exiting from the
2064 node is not passed though the firewall again.
2065 Otherwise, after an action, the packet is
2066 reinjected into the firewall at the next rule.
2067 .It Em net.inet.ip.fw.verbose : No 1
2068 Enables verbose messages.
2069 .It Em net.inet.ip.fw.verbose_limit : No 0
2070 Limits the number of messages produced by a verbose firewall.
2071 .It Em net.inet6.ip6.fw.deny_unknown_exthdrs : No 1
2072 If enabled packets with unknown IPv6 Extension Headers will be denied.
2073 .It Em net.link.ether.ipfw : No 0
2074 Controls whether layer-2 packets are passed to
2077 .It Em net.link.bridge.ipfw : No 0
2078 Controls whether bridged packets are passed to
2083 .Sh IPFW2 ENHANCEMENTS
2084 This Section lists the features that have been introduced in
2086 which were not present in
2088 They are listed in order of the potential impact that they can
2089 have in writing your rulesets.
2090 You might want to consider using these features in order to
2091 write your rulesets in a more efficient way.
2092 .Bl -tag -width indent
2093 .It Syntax and flags
2095 does not support the -n flag (only test syntax),
2096 nor does it allow spaces after commas or support all
2097 rule fields in a single argument.
2099 does not allow the -f flag (force) in conjunction with
2100 the -p flag (preprocessor).
2102 does not support the -c (compact) flag.
2103 .It Handling of non-IPv4 packets
2105 will silently accept all non-IPv4 packets (which
2108 .Em net.link.bridge.ipfw=1 ) .
2110 will filter all packets (including non-IPv4 ones) according to the ruleset.
2111 To achieve the same behaviour as
2113 you can use the following as the very first rule in your ruleset:
2115 .Dl "ipfw add 1 allow layer2 not mac-type ip"
2119 option might seem redundant, but it is necessary -- packets
2120 passed to the firewall from layer3 will not have a MAC header,
2123 pattern will always fail on them, and the
2125 operator will make this rule into a pass-all.
2128 does not support address sets or lists of addresses.
2130 .It Port specifications
2132 only allows one port range when specifying TCP and UDP ports, and
2133 is limited to 10 entries instead of the 30 allowed by
2137 you can only specify ports when the rule is requesting
2144 you can put port specifications in rules matching all packets,
2145 and the match will be attempted only on those packets carrying
2146 protocols which include port identifiers.
2150 allowed the first port entry to be specified as
2154 can be an arbitrary 16-bit mask.
2155 This syntax is of questionable usefulness and it is not
2156 supported anymore in
2160 does not support Or-blocks.
2163 does not generate keepalives for stateful sessions.
2164 As a consequence, it might cause idle sessions to drop because
2165 the lifetime of the dynamic rules expires.
2168 does not implement sets of rules.
2169 .It MAC header filtering and Layer-2 firewalling.
2171 does not implement filtering on MAC header fields, nor is it
2172 invoked on packets from
2175 .Cm ether_output_frame().
2177 .Em net.link.ether.ipfw
2178 has no effect there.
2182 the following options only accept a single value as an argument:
2184 .Cm ipid, iplen, ipttl
2186 The following options are not implemented by
2189 .Cm dst-ip, dst-port, layer2, mac, mac-type, src-ip, src-port.
2191 Additionally, the RELENG_4 version of
2193 does not implement the following options:
2195 .Cm ipid, iplen, ipprecedence, iptos, ipttl,
2196 .Cm ipversion, tcpack, tcpseq, tcpwin .
2197 .It Dummynet options
2198 The following option for
2200 pipes/queues is not supported:
2203 There was no IPv6 support in
2207 There are far too many possible uses of
2209 so this Section will only give a small set of examples.
2211 .Ss BASIC PACKET FILTERING
2212 This command adds an entry which denies all tcp packets from
2213 .Em cracker.evil.org
2214 to the telnet port of
2216 from being forwarded by the host:
2218 .Dl "ipfw add deny tcp from cracker.evil.org to wolf.tambov.su telnet"
2220 This one disallows any connection from the entire cracker's
2223 .Dl "ipfw add deny ip from 123.45.67.0/24 to my.host.org"
2225 A first and efficient way to limit access (not using dynamic rules)
2226 is the use of the following rules:
2228 .Dl "ipfw add allow tcp from any to any established"
2229 .Dl "ipfw add allow tcp from net1 portlist1 to net2 portlist2 setup"
2230 .Dl "ipfw add allow tcp from net3 portlist3 to net3 portlist3 setup"
2232 .Dl "ipfw add deny tcp from any to any"
2234 The first rule will be a quick match for normal TCP packets,
2235 but it will not match the initial SYN packet, which will be
2238 rules only for selected source/destination pairs.
2239 All other SYN packets will be rejected by the final
2243 If you administer one or more subnets, you can take advantage of the
2245 syntax to specify address sets and or-blocks and write extremely
2246 compact rulesets which selectively enable services to blocks
2247 of clients, as below:
2249 .Dl "goodguys=\*q{ 10.1.2.0/24{20,35,66,18} or 10.2.3.0/28{6,3,11} }\*q"
2250 .Dl "badguys=\*q10.1.2.0/24{8,38,60}\*q"
2252 .Dl "ipfw add allow ip from ${goodguys} to any"
2253 .Dl "ipfw add deny ip from ${badguys} to any"
2254 .Dl "... normal policies ..."
2258 syntax would require a separate rule for each IP in the above
2263 option could be used to do automated anti-spoofing by adding the
2264 following to the top of a ruleset:
2266 .Dl "ipfw add deny ip from any to any not verrevpath in"
2268 This rule drops all incoming packets that appear to be coming to the
2269 system on the wrong interface.
2270 For example, a packet with a source
2271 address belonging to a host on a protected internal network would be
2272 dropped if it tried to enter the system from an external interface.
2276 option could be used to do similar but more restricted anti-spoofing
2277 by adding the following to the top of a ruleset:
2279 .Dl "ipfw add deny ip from any to any not antispoof in"
2281 This rule drops all incoming packets that appear to be coming from another
2282 directly connected system but on the wrong interface.
2283 For example, a packet with a source address of
2291 In order to protect a site from flood attacks involving fake
2292 TCP packets, it is safer to use dynamic rules:
2294 .Dl "ipfw add check-state"
2295 .Dl "ipfw add deny tcp from any to any established"
2296 .Dl "ipfw add allow tcp from my-net to any setup keep-state"
2298 This will let the firewall install dynamic rules only for
2299 those connection which start with a regular SYN packet coming
2300 from the inside of our network.
2301 Dynamic rules are checked when encountering the first
2308 rule should usually be placed near the beginning of the
2309 ruleset to minimize the amount of work scanning the ruleset.
2310 Your mileage may vary.
2312 To limit the number of connections a user can open
2313 you can use the following type of rules:
2315 .Dl "ipfw add allow tcp from my-net/24 to any setup limit src-addr 10"
2316 .Dl "ipfw add allow tcp from any to me setup limit src-addr 4"
2318 The former (assuming it runs on a gateway) will allow each host
2319 on a /24 network to open at most 10 TCP connections.
2320 The latter can be placed on a server to make sure that a single
2321 client does not use more than 4 simultaneous connections.
2324 stateful rules can be subject to denial-of-service attacks
2325 by a SYN-flood which opens a huge number of dynamic rules.
2326 The effects of such attacks can be partially limited by
2329 variables which control the operation of the firewall.
2331 Here is a good usage of the
2333 command to see accounting records and timestamp information:
2337 or in short form without timestamps:
2341 which is equivalent to:
2345 Next rule diverts all incoming packets from 192.168.2.0/24
2346 to divert port 5000:
2348 .Dl ipfw divert 5000 ip from 192.168.2.0/24 to any in
2351 The following rules show some of the applications of
2355 for simulations and the like.
2357 This rule drops random incoming packets with a probability
2360 .Dl "ipfw add prob 0.05 deny ip from any to any in"
2362 A similar effect can be achieved making use of dummynet pipes:
2364 .Dl "ipfw add pipe 10 ip from any to any"
2365 .Dl "ipfw pipe 10 config plr 0.05"
2367 We can use pipes to artificially limit bandwidth, e.g.\& on a
2368 machine acting as a router, if we want to limit traffic from
2369 local clients on 192.168.2.0/24 we do:
2371 .Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out"
2372 .Dl "ipfw pipe 1 config bw 300Kbit/s queue 50KBytes"
2374 note that we use the
2376 modifier so that the rule is not used twice.
2377 Remember in fact that
2379 rules are checked both on incoming and outgoing packets.
2381 Should we want to simulate a bidirectional link with bandwidth
2382 limitations, the correct way is the following:
2384 .Dl "ipfw add pipe 1 ip from any to any out"
2385 .Dl "ipfw add pipe 2 ip from any to any in"
2386 .Dl "ipfw pipe 1 config bw 64Kbit/s queue 10Kbytes"
2387 .Dl "ipfw pipe 2 config bw 64Kbit/s queue 10Kbytes"
2389 The above can be very useful, e.g.\& if you want to see how
2390 your fancy Web page will look for a residential user who
2391 is connected only through a slow link.
2392 You should not use only one pipe for both directions, unless
2393 you want to simulate a half-duplex medium (e.g.\& AppleTalk,
2395 It is not necessary that both pipes have the same configuration,
2396 so we can also simulate asymmetric links.
2398 Should we want to verify network performance with the RED queue
2399 management algorithm:
2401 .Dl "ipfw add pipe 1 ip from any to any"
2402 .Dl "ipfw pipe 1 config bw 500Kbit/s queue 100 red 0.002/30/80/0.1"
2404 Another typical application of the traffic shaper is to
2405 introduce some delay in the communication.
2406 This can significantly affect applications which do a lot of Remote
2407 Procedure Calls, and where the round-trip-time of the
2408 connection often becomes a limiting factor much more than
2411 .Dl "ipfw add pipe 1 ip from any to any out"
2412 .Dl "ipfw add pipe 2 ip from any to any in"
2413 .Dl "ipfw pipe 1 config delay 250ms bw 1Mbit/s"
2414 .Dl "ipfw pipe 2 config delay 250ms bw 1Mbit/s"
2416 Per-flow queueing can be useful for a variety of purposes.
2417 A very simple one is counting traffic:
2419 .Dl "ipfw add pipe 1 tcp from any to any"
2420 .Dl "ipfw add pipe 1 udp from any to any"
2421 .Dl "ipfw add pipe 1 ip from any to any"
2422 .Dl "ipfw pipe 1 config mask all"
2424 The above set of rules will create queues (and collect
2425 statistics) for all traffic.
2426 Because the pipes have no limitations, the only effect is
2427 collecting statistics.
2428 Note that we need 3 rules, not just the last one, because
2431 tries to match IP packets it will not consider ports, so we
2432 would not see connections on separate ports as different
2435 A more sophisticated example is limiting the outbound traffic
2436 on a net with per-host limits, rather than per-network limits:
2438 .Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out"
2439 .Dl "ipfw add pipe 2 ip from any to 192.168.2.0/24 in"
2440 .Dl "ipfw pipe 1 config mask src-ip 0x000000ff bw 200Kbit/s queue 20Kbytes"
2441 .Dl "ipfw pipe 2 config mask dst-ip 0x000000ff bw 200Kbit/s queue 20Kbytes"
2443 In the following example, we need to create several traffic bandwidth
2444 classes and we need different hosts/networks to fall into different classes.
2445 We create one pipe for each class and configure them accordingly.
2446 Then we create a single table and fill it with IP subnets and addresses.
2447 For each subnet/host we set the argument equal to the number of the pipe
2449 Then we classify traffic using a single rule:
2451 .Dl "ipfw pipe 1 config bw 1000Kbyte/s"
2452 .Dl "ipfw pipe 4 config bw 4000Kbyte/s"
2454 .Dl "ipfw table 1 add 192.168.2.0/24 1"
2455 .Dl "ipfw table 1 add 192.168.0.0/27 4"
2456 .Dl "ipfw table 1 add 192.168.0.2 1"
2458 .Dl "ipfw pipe tablearg ip from table(1) to any"
2460 To add a set of rules atomically, e.g.\& set 18:
2462 .Dl "ipfw set disable 18"
2463 .Dl "ipfw add NN set 18 ... # repeat as needed"
2464 .Dl "ipfw set enable 18"
2466 To delete a set of rules atomically the command is simply:
2468 .Dl "ipfw delete set 18"
2470 To test a ruleset and disable it and regain control if something goes wrong:
2472 .Dl "ipfw set disable 18"
2473 .Dl "ipfw add NN set 18 ... # repeat as needed"
2474 .Dl "ipfw set enable 18; echo done; sleep 30 && ipfw set disable 18"
2476 Here if everything goes well, you press control-C before the "sleep"
2477 terminates, and your ruleset will be left active.
2478 Otherwise, e.g.\& if
2479 you cannot access your box, the ruleset will be disabled after
2480 the sleep terminates thus restoring the previous situation.
2501 utility first appeared in
2506 Stateful extensions were introduced in
2509 was introduced in Summer 2002.
2511 .An Ugen J. S. Antsilevich ,
2512 .An Poul-Henning Kamp ,
2518 API based upon code written by
2524 traffic shaper supported by Akamba Corp.
2526 Use of dummynet with IPv6 requires that debug.mpsafenet be set to 0.
2528 The syntax has grown over the years and sometimes it might be confusing.
2529 Unfortunately, backward compatibility prevents cleaning up mistakes
2530 made in the definition of the syntax.
2534 Misconfiguring the firewall can put your computer in an unusable state,
2535 possibly shutting down network services and requiring console access to
2536 regain control of it.
2538 Incoming packet fragments diverted by
2540 are reassembled before delivery to the socket.
2541 The action used on those packet is the one from the
2542 rule which matches the first fragment of the packet.
2544 Packets diverted to userland, and then reinserted by a userland process
2545 may lose various packet attributes.
2546 The packet source interface name
2547 will be preserved if it is shorter than 8 bytes and the userland process
2548 saves and reuses the sockaddr_in
2551 otherwise, it may be lost.
2552 If a packet is reinserted in this manner, later rules may be incorrectly
2553 applied, making the order of
2555 rules in the rule sequence very important.
2557 Dummynet drops all packets with IPv6 link-local addresses.
2563 may not behave as expected.
2564 In particular, incoming SYN packets may
2565 have no uid or gid associated with them since they do not yet belong
2566 to a TCP connection, and the uid/gid associated with a packet may not
2567 be as expected if the associated process calls
2569 or similar system calls.
2571 Rules which use uid, gid or jail based matching should be used only
2572 if debug.mpsafenet=0 to avoid possible deadlocks due to layering
2573 violations in its implementation.