9 .Nd User interface for firewall, traffic shaper, packet scheduler,
12 .Ss FIREWALL CONFIGURATION
21 .Op Ar rule | first-last ...
29 .Brq Cm delete | zero | resetlog
33 .Cm set Oo Cm disable Ar number ... Oc Op Cm enable Ar number ...
37 .Ar number Cm to Ar number
39 .Cm set swap Ar number number
46 .Brq Cm firewall | altq | one_pass | debug | verbose | dyn_keepalive
49 .Brq Cm firewall | altq | one_pass | debug | verbose | dyn_keepalive
53 .Cm table Ar number Cm add Ar addr Ns Oo / Ns Ar masklen Oc Op Ar value
55 .Cm table Ar number Cm delete Ar addr Ns Op / Ns Ar masklen
65 .Ss DUMMYNET CONFIGURATION (TRAFFIC SHAPER AND PACKET SCHEDULER)
67 .Brq Cm pipe | queue | sched
73 .Brq Cm pipe | queue | sched
74 .Brq Cm delete | list | show
97 utility is the user interface for controlling the
101 traffic shaper/packet scheduler, and the
102 in-kernel NAT services.
104 A firewall configuration, or
108 numbered from 1 to 65535.
109 Packets are passed to the firewall
110 from a number of different places in the protocol stack
111 (depending on the source and destination of the packet,
112 it is possible for the firewall to be
113 invoked multiple times on the same packet).
114 The packet passed to the firewall is compared
115 against each of the rules in the
118 (multiple rules with the same number are permitted, in which case
119 they are processed in order of insertion).
120 When a match is found, the action corresponding to the
121 matching rule is performed.
123 Depending on the action and certain system settings, packets
124 can be reinjected into the firewall at some rule after the
125 matching one for further processing.
127 A ruleset always includes a
129 rule (numbered 65535) which cannot be modified or deleted,
130 and matches all packets.
131 The action associated with the
137 depending on how the kernel is configured.
139 If the ruleset includes one or more rules with the
144 the firewall will have a
146 behaviour, i.e., upon a match it will create
148 i.e. rules that match packets with the same 5-tuple
149 (protocol, source and destination addresses and ports)
150 as the packet which caused their creation.
151 Dynamic rules, which have a limited lifetime, are checked
152 at the first occurrence of a
157 rule, and are typically used to open the firewall on-demand to
158 legitimate traffic only.
160 .Sx STATEFUL FIREWALL
163 Sections below for more information on the stateful behaviour of
166 All rules (including dynamic ones) have a few associated counters:
167 a packet count, a byte count, a log count and a timestamp
168 indicating the time of the last match.
169 Counters can be displayed or reset with
173 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 Rules can be added with the
189 command; deleted individually or in groups with the
191 command, and globally (except those in set 31) with the
193 command; displayed, optionally with the content of the
199 Finally, counters can be reset with the
206 The following general options are available when invoking
208 .Bl -tag -width indent
210 Show counter values when listing rules.
213 command implies this option.
215 Only show the action and the comment, not the body of a rule.
219 When entering or showing rules, print them in compact form,
220 i.e., omitting the "ip from any to any" string
221 when this does not carry any additional information.
223 When listing, show dynamic rules in addition to static ones.
227 is specified, also show expired dynamic rules.
229 Do not ask for confirmation for commands that can cause problems
232 If there is no tty associated with the process, this is implied.
234 When listing a table (see the
236 section below for more information on lookup tables), format values
237 as IP addresses. By default, values are shown as integers.
239 Only check syntax of the command strings, without actually passing
242 Try to resolve addresses and service names in output.
244 Be quiet when executing the
254 This is useful when updating rulesets by executing multiple
258 .Ql sh\ /etc/rc.firewall ) ,
259 or by processing a file with many
261 rules across a remote login session.
262 It also stops a table add or delete
263 from failing if the entry already exists or is not present.
265 The reason why this option may be important is that
266 for some of these actions,
268 may print a message; if the action results in blocking the
269 traffic to the remote client,
270 the remote login session will be closed
271 and the rest of the ruleset will not be processed.
272 Access to the console would then be required to recover.
274 When listing rules, show the
276 each rule belongs to.
277 If this flag is not specified, disabled rules will not be
280 When listing pipes, sort according to one of the four
281 counters (total or current packets or bytes).
283 When listing, show last match timestamp converted with ctime().
285 When listing, show last match timestamp as seconds from the epoch.
286 This form can be more convenient for postprocessing by scripts.
289 .Ss LIST OF RULES AND PREPROCESSING
290 To ease configuration, rules can be put into a file which is
293 as shown in the last synopsis line.
297 The file will be read line by line and applied as arguments to the
301 Optionally, a preprocessor can be specified using
305 is to be piped through.
306 Useful preprocessors include
312 does not start with a slash
314 as its first character, the usual
316 name search is performed.
317 Care should be taken with this in environments where not all
318 file systems are mounted (yet) by the time
320 is being run (e.g.\& when they are mounted over NFS).
323 has been specified, any additional arguments are passed on to the preprocessor
325 This allows for flexible configuration files (like conditionalizing
326 them on the local hostname) and the use of macros to centralize
327 frequently required arguments like IP addresses.
329 .Ss TRAFFIC SHAPER CONFIGURATION
335 commands are used to configure the traffic shaper and packet scheduler.
337 .Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION
338 Section below for details.
340 If the world and the kernel get out of sync the
342 ABI may break, preventing you from being able to add any rules.
344 adversely effect the booting process.
349 to temporarily disable the firewall to regain access to the network,
350 allowing you to fix the problem.
352 A packet is checked against the active ruleset in multiple places
353 in the protocol stack, under control of several sysctl variables.
354 These places and variables are shown below, and it is important to
355 have this picture in mind in order to design a correct ruleset.
356 .Bd -literal -offset indent
359 +----------->-----------+
361 [ip(6)_input] [ip(6)_output] net.inet(6).ip(6).fw.enable=1
364 [ether_demux] [ether_output_frame] net.link.ether.ipfw=1
366 +-->--[bdg_forward]-->--+ net.link.bridge.ipfw=1
372 times the same packet goes through the firewall can
373 vary between 0 and 4 depending on packet source and
374 destination, and system configuration.
376 Note that as packets flow through the stack, headers can be
377 stripped or added to it, and so they may or may not be available
379 E.g., incoming packets will include the MAC header when
383 but the same packets will have the MAC header stripped off when
390 Also note that each packet is always checked against the complete ruleset,
391 irrespective of the place where the check occurs, or the source of the packet.
392 If a rule contains some match patterns or actions which are not valid
393 for the place of invocation (e.g.\& trying to match a MAC header within
397 the match pattern will not match, but a
399 operator in front of such patterns
403 match on those packets.
404 It is thus the responsibility of
405 the programmer, if necessary, to write a suitable ruleset to
406 differentiate among the possible places.
408 rules can be useful here, as an example:
409 .Bd -literal -offset indent
410 # packets from ether_demux or bdg_forward
411 ipfw add 10 skipto 1000 all from any to any layer2 in
412 # packets from ip_input
413 ipfw add 10 skipto 2000 all from any to any not layer2 in
414 # packets from ip_output
415 ipfw add 10 skipto 3000 all from any to any not layer2 out
416 # packets from ether_output_frame
417 ipfw add 10 skipto 4000 all from any to any layer2 out
420 (yes, at the moment there is no way to differentiate between
421 ether_demux and bdg_forward).
423 In general, each keyword or argument must be provided as
424 a separate command line argument, with no leading or trailing
426 Keywords are case-sensitive, whereas arguments may
427 or may not be case-sensitive depending on their nature
428 (e.g.\& uid's are, hostnames are not).
430 Some arguments (e.g. port or address lists) are comma-separated
432 In this case, spaces after commas ',' are allowed to make
433 the line more readable.
434 You can also put the entire
435 command (including flags) into a single argument.
436 E.g., the following forms are equivalent:
437 .Bd -literal -offset indent
438 ipfw -q add deny src-ip 10.0.0.0/24,127.0.0.1/8
439 ipfw -q add deny src-ip 10.0.0.0/24, 127.0.0.1/8
440 ipfw "-q add deny src-ip 10.0.0.0/24, 127.0.0.1/8"
443 The format of firewall rules is the following:
444 .Bd -ragged -offset indent
447 .Op Cm set Ar set_number
448 .Op Cm prob Ar match_probability
450 .Op Cm log Op Cm logamount Ar number
460 where the body of the rule specifies which information is used
461 for filtering packets, among the following:
463 .Bl -tag -width "Source and dest. addresses and ports" -offset XXX -compact
464 .It Layer-2 header fields
466 .It IPv4 and IPv6 Protocol
468 .It Source and dest. addresses and ports
472 .It Transmit and receive interface
474 .It Misc. IP header fields
475 Version, type of service, datagram length, identification,
476 fragment flag (non-zero IP offset),
479 .It IPv6 Extension headers
480 Fragmentation, Hop-by-Hop options,
481 Routing Headers, Source routing rthdr0, Mobile IPv6 rthdr2, IPSec options.
483 .It Misc. TCP header fields
484 TCP flags (SYN, FIN, ACK, RST, etc.),
485 sequence number, acknowledgment number,
493 When the packet can be associated with a local socket.
495 Whether a packet came from a divert socket (e.g.,
497 .It Fib annotation state
498 Whether a packet has been tagged for using a specific FIB (routing table)
499 in future forwarding decisions.
502 Note that some of the above information, e.g.\& source MAC or IP addresses and
503 TCP/UDP ports, can be easily spoofed, so filtering on those fields
504 alone might not guarantee the desired results.
505 .Bl -tag -width indent
507 Each rule is associated with a
509 in the range 1..65535, with the latter reserved for the
512 Rules are checked sequentially by rule number.
513 Multiple rules can have the same number, in which case they are
514 checked (and listed) according to the order in which they have
516 If a rule is entered without specifying a number, the kernel will
517 assign one in such a way that the rule becomes the last one
521 Automatic rule numbers are assigned by incrementing the last
522 non-default rule number by the value of the sysctl variable
523 .Ar net.inet.ip.fw.autoinc_step
524 which defaults to 100.
525 If this is not possible (e.g.\& because we would go beyond the
526 maximum allowed rule number), the number of the last
527 non-default value is used instead.
528 .It Cm set Ar set_number
529 Each rule is associated with a
532 Sets can be individually disabled and enabled, so this parameter
533 is of fundamental importance for atomic ruleset manipulation.
534 It can be also used to simplify deletion of groups of rules.
535 If a rule is entered without specifying a set number,
538 Set 31 is special in that it cannot be disabled,
539 and rules in set 31 are not deleted by the
541 command (but you can delete them with the
542 .Nm ipfw delete set 31
544 Set 31 is also used for the
547 .It Cm prob Ar match_probability
548 A match is only declared with the specified probability
549 (floating point number between 0 and 1).
550 This can be useful for a number of applications such as
551 random packet drop or
554 to simulate the effect of multiple paths leading to out-of-order
557 Note: this condition is checked before any other condition, including
558 ones such as keep-state or check-state which might have side effects.
559 .It Cm log Op Cm logamount Ar number
560 Packets matching a rule with the
562 keyword will be made available for logging in two ways:
563 if the sysctl variable
564 .Va net.inet.ip.fw.verbose
565 is set to 0 (default), one can use
569 pseudo interface. There is no overhead if no
571 is attached to the pseudo interface.
574 .Va net.inet.ip.fw.verbose
575 is set to 1, packets will be logged to
579 facility up to a maximum of
584 is specified, the limit is taken from the sysctl variable
585 .Va net.inet.ip.fw.verbose_limit .
586 In both cases, a value of 0 means unlimited logging.
588 Once the limit is reached, logging can be re-enabled by
589 clearing the logging counter or the packet counter for that entry, see the
593 Note: logging is done after all other packet matching conditions
594 have been successfully verified, and before performing the final
595 action (accept, deny, etc.) on the packet.
597 When a packet matches a rule with the
599 keyword, the numeric tag for the given
601 in the range 1..65534 will be attached to the packet.
602 The tag acts as an internal marker (it is not sent out over
603 the wire) that can be used to identify these packets later on.
604 This can be used, for example, to provide trust between interfaces
605 and to start doing policy-based filtering.
606 A packet can have multiple tags at the same time.
607 Tags are "sticky", meaning once a tag is applied to a packet by a
608 matching rule it exists until explicit removal.
609 Tags are kept with the packet everywhere within the kernel, but are
610 lost when packet leaves the kernel, for example, on transmitting
611 packet out to the network or sending packet to a
615 To check for previously applied tags, use the
618 To delete previously applied tag, use the
622 Note: since tags are kept with the packet everywhere in kernelspace,
623 they can be set and unset anywhere in the kernel network subsystem
626 facility), not only by means of the
632 For example, there can be a specialized
634 node doing traffic analyzing and tagging for later inspecting
636 .It Cm untag Ar number
637 When a packet matches a rule with the
639 keyword, the tag with the number
641 is searched among the tags attached to this packet and,
642 if found, removed from it.
643 Other tags bound to packet, if present, are left untouched.
645 When a packet matches a rule with the
647 keyword, the ALTQ identifier for the given
652 Note that this ALTQ tag is only meaningful for packets going "out" of IPFW,
653 and not being rejected or going to divert sockets.
654 Note that if there is insufficient memory at the time the packet is
655 processed, it will not be tagged, so it is wise to make your ALTQ
656 "default" queue policy account for this.
659 rules match a single packet, only the first one adds the ALTQ classification
661 In doing so, traffic may be shaped by using
662 .Cm count Cm altq Ar queue
663 rules for classification early in the ruleset, then later applying
664 the filtering decision.
669 rules may come later and provide the actual filtering decisions in
670 addition to the fallback ALTQ tag.
674 to set up the queues before IPFW will be able to look them up by name,
675 and if the ALTQ disciplines are rearranged, the rules in containing the
676 queue identifiers in the kernel will likely have gone stale and need
678 Stale queue identifiers will probably result in misclassification.
680 All system ALTQ processing can be turned on or off via
685 .Cm disable Ar altq .
687 .Va net.inet.ip.fw.one_pass
688 is irrelevant to ALTQ traffic shaping, as the actual rule action is followed
689 always after adding an ALTQ tag.
692 A rule can be associated with one of the following actions, which
693 will be executed when the packet matches the body of the rule.
694 .Bl -tag -width indent
695 .It Cm allow | accept | pass | permit
696 Allow packets that match rule.
697 The search terminates.
699 Checks the packet against the dynamic ruleset.
700 If a match is found, execute the action associated with
701 the rule which generated this dynamic rule, otherwise
702 move to the next rule.
705 rules do not have a body.
708 rule is found, the dynamic ruleset is checked at the first
714 Update counters for all packets that match rule.
715 The search continues with the next rule.
717 Discard packets that match this rule.
718 The search terminates.
719 .It Cm divert Ar port
720 Divert packets that match this rule to the
724 The search terminates.
725 .It Cm fwd | forward Ar ipaddr | tablearg Ns Op , Ns Ar port
726 Change the next-hop on matching packets to
728 which can be an IP address or a host name.
729 For IPv4, the next hop can also be supplied by the last table
730 looked up for the packet by using the
732 keyword instead of an explicit address.
733 The search terminates if this rule matches.
737 is a local address, then matching packets will be forwarded to
739 (or the port number in the packet if one is not specified in the rule)
740 on the local machine.
744 is not a local address, then the port number
745 (if specified) is ignored, and the packet will be
746 forwarded to the remote address, using the route as found in
747 the local routing table for that IP.
751 rule will not match layer-2 packets (those received
752 on ether_input, ether_output, or bridged).
756 action does not change the contents of the packet at all.
757 In particular, the destination address remains unmodified, so
758 packets forwarded to another system will usually be rejected by that system
759 unless there is a matching rule on that system to capture them.
760 For packets forwarded locally,
761 the local address of the socket will be
762 set to the original destination address of the packet.
765 entry look rather weird but is intended for
766 use with transparent proxy servers.
767 .It Cm nat Ar nat_nr | tablearg
770 (for network address translation, address redirect, etc.):
772 .Sx NETWORK ADDRESS TRANSLATION (NAT)
773 Section for further information.
774 .It Cm pipe Ar pipe_nr
778 (for bandwidth limitation, delay, etc.).
780 .Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION
781 Section for further information.
782 The search terminates; however, on exit from the pipe and if
786 .Va net.inet.ip.fw.one_pass
787 is not set, the packet is passed again to the firewall code
788 starting from the next rule.
789 .It Cm queue Ar queue_nr
793 (for bandwidth limitation using WF2Q+).
799 Discard packets that match this rule, and if the
800 packet is a TCP packet, try to send a TCP reset (RST) notice.
801 The search terminates.
803 Discard packets that match this rule, and if the
804 packet is a TCP packet, try to send a TCP reset (RST) notice.
805 The search terminates.
806 .It Cm skipto Ar number | tablearg
807 Skip all subsequent rules numbered less than
809 The search continues with the first rule numbered
812 It is possible to use the
814 keyword with a skipto for a
816 skipto, but care should be used, as no destination caching
817 is possible in this case so the rules are always walked to find it,
820 .It Cm call Ar number | tablearg
821 The current rule number is saved in the internal stack and
822 ruleset processing continues with the first rule numbered
825 If later a rule with the
827 action is encountered, the processing returns to the first rule
830 rule plus one or higher
831 (the same behaviour as with packets returning from
836 This could be used to make somewhat like an assembly language
838 calls to rules with common checks for different interfaces, etc.
840 Rule with any number could be called, not just forward jumps as with
842 So, to prevent endless loops in case of mistakes, both
846 actions don't do any jumps and simply go to the next rule if memory
847 can't be allocated or stack overflowed/undeflowed.
849 Internally stack for rule numbers is implemented using
851 facility and currently has size of 16 entries.
852 As mbuf tags are lost when packet leaves the kernel,
854 should not be used in subroutines to avoid endless loops
855 and other undesired effects.
857 Takes rule number saved to internal stack by the last
859 action and returns ruleset processing to the first rule
860 with number greater than number of corresponding
862 rule. See description of the
864 action for more details.
870 and thus are unconditional, but
872 command-line utility currently requires every action except
875 While it is sometimes useful to return only on some packets,
876 usually you want to print just
879 A workaround for this is to use new syntax and
883 .Bd -literal -offset indent
884 # Add a rule without actual body
885 ipfw add 2999 return via any
887 # List rules without "from any to any" part
891 This cosmetic annoyance may be fixed in future releases.
893 Send a copy of packets matching this rule to the
897 The search continues with the next rule.
898 .It Cm unreach Ar code
899 Discard packets that match this rule, and try to send an ICMP
900 unreachable notice with code
904 is a number from 0 to 255, or one of these aliases:
905 .Cm net , host , protocol , port ,
906 .Cm needfrag , srcfail , net-unknown , host-unknown ,
907 .Cm isolated , net-prohib , host-prohib , tosnet ,
908 .Cm toshost , filter-prohib , host-precedence
910 .Cm precedence-cutoff .
911 The search terminates.
912 .It Cm unreach6 Ar code
913 Discard packets that match this rule, and try to send an ICMPv6
914 unreachable notice with code
918 is a number from 0, 1, 3 or 4, or one of these aliases:
919 .Cm no-route, admin-prohib, address
922 The search terminates.
923 .It Cm netgraph Ar cookie
924 Divert packet into netgraph with given
926 The search terminates.
927 If packet is later returned from netgraph it is either
928 accepted or continues with the next rule, depending on
929 .Va net.inet.ip.fw.one_pass
931 .It Cm ngtee Ar cookie
932 A copy of packet is diverted into netgraph, original
933 packet continues with the next rule.
936 for more information on
941 .It Cm setfib Ar fibnum | tablearg
942 The packet is tagged so as to use the FIB (routing table)
944 in any subsequent forwarding decisions.
945 Initially this is limited to the values 0 through 15, see
947 Processing continues at the next rule.
948 It is possible to use the
950 keyword with a setfib. If tablearg value is not within compiled FIB range packet fib is set to 0.
952 Queue and reassemble ip fragments.
953 If the packet is not fragmented, counters are updated and processing continues with the next rule.
954 If the packet is the last logical fragment, the packet is reassembled and, if
955 .Va net.inet.ip.fw.one_pass
956 is set to 0, processing continues with the next rule, else packet is allowed to pass and search terminates.
957 If the packet is a fragment in the middle, it is consumed and processing stops immediately.
959 Fragments handling can be tuned via
960 .Va net.inet.ip.maxfragpackets
962 .Va net.inet.ip.maxfragsperpacket
963 which limit, respectively, the maximum number of processable fragments (default: 800) and
964 the maximum number of fragments per packet (default: 16).
966 NOTA BENE: since fragments do not contain port numbers, they should be avoided with the
969 Alternatively, direction-based (like
973 ) and source-based (like
975 ) match patterns can be used to select fragments.
977 Usually a simple rule like:
978 .Bd -literal -offset indent
979 # reassemble incoming fragments
980 ipfw add reass all from any to any in
983 is all you need at the beginning of your ruleset.
986 The body of a rule contains zero or more patterns (such as
987 specific source and destination addresses or ports,
988 protocol options, incoming or outgoing interfaces, etc.)
989 that the packet must match in order to be recognised.
990 In general, the patterns are connected by (implicit)
992 operators -- i.e., all must match in order for the
994 Individual patterns can be prefixed by the
996 operator to reverse the result of the match, as in
998 .Dl "ipfw add 100 allow ip from not 1.2.3.4 to any"
1000 Additionally, sets of alternative match patterns
1002 can be constructed by putting the patterns in
1003 lists enclosed between parentheses ( ) or braces { }, and
1006 operator as follows:
1008 .Dl "ipfw add 100 allow ip from { x or not y or z } to any"
1010 Only one level of parentheses is allowed.
1011 Beware that most shells have special meanings for parentheses
1012 or braces, so it is advisable to put a backslash \\ in front of them
1013 to prevent such interpretations.
1015 The body of a rule must in general include a source and destination
1019 can be used in various places to specify that the content of
1020 a required field is irrelevant.
1022 The rule body has the following format:
1023 .Bd -ragged -offset indent
1024 .Op Ar proto Cm from Ar src Cm to Ar dst
1028 The first part (proto from src to dst) is for backward
1029 compatibility with earlier versions of
1033 any match pattern (including MAC headers, IP protocols,
1034 addresses and ports) can be specified in the
1038 Rule fields have the following meaning:
1039 .Bl -tag -width indent
1040 .It Ar proto : protocol | Cm { Ar protocol Cm or ... }
1041 .It Ar protocol : Oo Cm not Oc Ar protocol-name | protocol-number
1042 An IP protocol specified by number or name
1043 (for a complete list see
1044 .Pa /etc/protocols ) ,
1045 or one of the following keywords:
1046 .Bl -tag -width indent
1048 Matches IPv4 packets.
1050 Matches IPv6 packets.
1059 option will be treated as inner protocol.
1067 .Cm { Ar protocol Cm or ... }
1070 is provided for convenience only but its use is deprecated.
1071 .It Ar src No and Ar dst : Bro Cm addr | Cm { Ar addr Cm or ... } Brc Op Oo Cm not Oc Ar ports
1072 An address (or a list, see below)
1073 optionally followed by
1079 with multiple addresses) is provided for convenience only and
1080 its use is discouraged.
1081 .It Ar addr : Oo Cm not Oc Bro
1082 .Cm any | me | me6 |
1083 .Cm table Ns Pq Ar number Ns Op , Ns Ar value
1084 .Ar | addr-list | addr-set
1086 .Bl -tag -width indent
1088 matches any IP address.
1090 matches any IP address configured on an interface in the system.
1092 matches any IPv6 address configured on an interface in the system.
1093 The address list is evaluated at the time the packet is
1095 .It Cm table Ns Pq Ar number Ns Op , Ns Ar value
1096 Matches any IPv4 address for which an entry exists in the lookup table
1098 If an optional 32-bit unsigned
1100 is also specified, an entry will match only if it has this value.
1103 section below for more information on lookup tables.
1105 .It Ar addr-list : ip-addr Ns Op Ns , Ns Ar addr-list
1107 A host or subnet address specified in one of the following ways:
1108 .Bl -tag -width indent
1109 .It Ar numeric-ip | hostname
1110 Matches a single IPv4 address, specified as dotted-quad or a hostname.
1111 Hostnames are resolved at the time the rule is added to the firewall list.
1112 .It Ar addr Ns / Ns Ar masklen
1113 Matches all addresses with base
1115 (specified as an IP address, a network number, or a hostname)
1119 As an example, 1.2.3.4/25 or 1.2.3.0/25 will match
1120 all IP numbers from 1.2.3.0 to 1.2.3.127 .
1121 .It Ar addr Ns : Ns Ar mask
1122 Matches all addresses with base
1124 (specified as an IP address, a network number, or a hostname)
1127 specified as a dotted quad.
1128 As an example, 1.2.3.4:255.0.255.0 or 1.0.3.0:255.0.255.0 will match
1130 This form is advised only for non-contiguous
1132 It is better to resort to the
1133 .Ar addr Ns / Ns Ar masklen
1134 format for contiguous masks, which is more compact and less
1137 .It Ar addr-set : addr Ns Oo Ns / Ns Ar masklen Oc Ns Cm { Ns Ar list Ns Cm }
1138 .It Ar list : Bro Ar num | num-num Brc Ns Op Ns , Ns Ar list
1139 Matches all addresses with base address
1141 (specified as an IP address, a network number, or a hostname)
1142 and whose last byte is in the list between braces { } .
1143 Note that there must be no spaces between braces and
1144 numbers (spaces after commas are allowed).
1145 Elements of the list can be specified as single entries
1149 field is used to limit the size of the set of addresses,
1150 and can have any value between 24 and 32.
1152 it will be assumed as 24.
1154 This format is particularly useful to handle sparse address sets
1155 within a single rule.
1156 Because the matching occurs using a
1157 bitmask, it takes constant time and dramatically reduces
1158 the complexity of rulesets.
1160 As an example, an address specified as 1.2.3.4/24{128,35-55,89}
1161 or 1.2.3.0/24{128,35-55,89}
1162 will match the following IP addresses:
1164 1.2.3.128, 1.2.3.35 to 1.2.3.55, 1.2.3.89 .
1165 .It Ar addr6-list : ip6-addr Ns Op Ns , Ns Ar addr6-list
1167 A host or subnet specified one of the following ways:
1168 .Bl -tag -width indent
1169 .It Ar numeric-ip | hostname
1170 Matches a single IPv6 address as allowed by
1173 Hostnames are resolved at the time the rule is added to the firewall
1175 .It Ar addr Ns / Ns Ar masklen
1176 Matches all IPv6 addresses with base
1178 (specified as allowed by
1186 No support for sets of IPv6 addresses is provided because IPv6 addresses
1187 are typically random past the initial prefix.
1188 .It Ar ports : Bro Ar port | port Ns \&- Ns Ar port Ns Brc Ns Op , Ns Ar ports
1189 For protocols which support port numbers (such as TCP and UDP), optional
1191 may be specified as one or more ports or port ranges, separated
1192 by commas but no spaces, and an optional
1197 notation specifies a range of ports (including boundaries).
1201 may be used instead of numeric port values.
1202 The length of the port list is limited to 30 ports or ranges,
1203 though one can specify larger ranges by using an
1207 section of the rule.
1211 can be used to escape the dash
1213 character in a service name (from a shell, the backslash must be
1214 typed twice to avoid the shell itself interpreting it as an escape
1217 .Dl "ipfw add count tcp from any ftp\e\e-data-ftp to any"
1219 Fragmented packets which have a non-zero offset (i.e., not the first
1220 fragment) will never match a rule which has one or more port
1224 option for details on matching fragmented packets.
1226 .Ss RULE OPTIONS (MATCH PATTERNS)
1227 Additional match patterns can be used within
1229 Zero or more of these so-called
1231 can be present in a rule, optionally prefixed by the
1233 operand, and possibly grouped into
1236 The following match patterns can be used (listed in alphabetical order):
1237 .Bl -tag -width indent
1238 .It Cm // this is a comment.
1239 Inserts the specified text as a comment in the rule.
1240 Everything following // is considered as a comment and stored in the rule.
1241 You can have comment-only rules, which are listed as having a
1243 action followed by the comment.
1248 Matches only packets generated by a divert socket.
1249 .It Cm diverted-loopback
1250 Matches only packets coming from a divert socket back into the IP stack
1252 .It Cm diverted-output
1253 Matches only packets going from a divert socket back outward to the IP
1254 stack output for delivery.
1255 .It Cm dst-ip Ar ip-address
1256 Matches IPv4 packets whose destination IP is one of the address(es)
1257 specified as argument.
1258 .It Bro Cm dst-ip6 | dst-ipv6 Brc Ar ip6-address
1259 Matches IPv6 packets whose destination IP is one of the address(es)
1260 specified as argument.
1261 .It Cm dst-port Ar ports
1262 Matches IP packets whose destination port is one of the port(s)
1263 specified as argument.
1265 Matches TCP packets that have the RST or ACK bits set.
1266 .It Cm ext6hdr Ar header
1267 Matches IPv6 packets containing the extended header given by
1269 Supported headers are:
1275 any type of Routing Header
1277 Source routing Routing Header Type 0
1279 Mobile IPv6 Routing Header Type 2
1283 IPSec authentication headers
1285 and IPsec encapsulated security payload headers
1287 .It Cm fib Ar fibnum
1288 Matches a packet that has been tagged to use
1289 the given FIB (routing table) number.
1290 .It Cm flow-id Ar labels
1291 Matches IPv6 packets containing any of the flow labels given in
1294 is a comma separated list of numeric flow labels.
1296 Matches packets that are fragments and not the first
1297 fragment of an IP datagram.
1298 Note that these packets will not have
1299 the next protocol header (e.g.\& TCP, UDP) so options that look into
1300 these headers cannot match.
1302 Matches all TCP or UDP packets sent by or received for a
1306 may be specified by name or number.
1307 .It Cm jail Ar prisonID
1308 Matches all TCP or UDP packets sent by or received for the
1309 jail whos prison ID is
1311 .It Cm icmptypes Ar types
1312 Matches ICMP packets whose ICMP type is in the list
1314 The list may be specified as any combination of
1315 individual types (numeric) separated by commas.
1316 .Em Ranges are not allowed .
1317 The supported ICMP types are:
1321 destination unreachable
1329 router advertisement
1333 time-to-live exceeded
1345 address mask request
1347 and address mask reply
1349 .It Cm icmp6types Ar types
1350 Matches ICMP6 packets whose ICMP6 type is in the list of
1352 The list may be specified as any combination of
1353 individual types (numeric) separated by commas.
1354 .Em Ranges are not allowed .
1356 Matches incoming or outgoing packets, respectively.
1360 are mutually exclusive (in fact,
1364 .It Cm ipid Ar id-list
1365 Matches IPv4 packets whose
1367 field has value included in
1369 which is either a single value or a list of values or ranges
1370 specified in the same way as
1372 .It Cm iplen Ar len-list
1373 Matches IP packets whose total length, including header and data, is
1376 which is either a single value or a list of values or ranges
1377 specified in the same way as
1379 .It Cm ipoptions Ar spec
1380 Matches packets whose IPv4 header contains the comma separated list of
1381 options specified in
1383 The supported IP options are:
1386 (strict source route),
1388 (loose source route),
1390 (record packet route) and
1393 The absence of a particular option may be denoted
1396 .It Cm ipprecedence Ar precedence
1397 Matches IPv4 packets whose precedence field is equal to
1400 Matches packets that have IPSEC history associated with them
1401 (i.e., the packet comes encapsulated in IPSEC, the kernel
1402 has IPSEC support and IPSEC_FILTERTUNNEL option, and can correctly
1405 Note that specifying
1407 is different from specifying
1409 as the latter will only look at the specific IP protocol field,
1410 irrespective of IPSEC kernel support and the validity of the IPSEC data.
1412 Further note that this flag is silently ignored in kernels without
1414 It does not affect rule processing when given and the
1415 rules are handled as if with no
1418 .It Cm iptos Ar spec
1419 Matches IPv4 packets whose
1421 field contains the comma separated list of
1422 service types specified in
1424 The supported IP types of service are:
1427 .Pq Dv IPTOS_LOWDELAY ,
1429 .Pq Dv IPTOS_THROUGHPUT ,
1431 .Pq Dv IPTOS_RELIABILITY ,
1433 .Pq Dv IPTOS_MINCOST ,
1435 .Pq Dv IPTOS_ECN_CE .
1436 The absence of a particular type may be denoted
1439 .It Cm ipttl Ar ttl-list
1440 Matches IPv4 packets whose time to live is included in
1442 which is either a single value or a list of values or ranges
1443 specified in the same way as
1445 .It Cm ipversion Ar ver
1446 Matches IP packets whose IP version field is
1449 Upon a match, the firewall will create a dynamic rule, whose
1450 default behaviour is to match bidirectional traffic between
1451 source and destination IP/port using the same protocol.
1452 The rule has a limited lifetime (controlled by a set of
1454 variables), and the lifetime is refreshed every time a matching
1457 Matches only layer2 packets, i.e., those passed to
1459 from ether_demux() and ether_output_frame().
1460 .It Cm limit Bro Cm src-addr | src-port | dst-addr | dst-port Brc Ar N
1461 The firewall will only allow
1463 connections with the same
1464 set of parameters as specified in the rule.
1466 of source and destination addresses and ports can be
1469 only IPv4 flows are supported.
1470 .It Cm lookup Bro Cm dst-ip | dst-port | src-ip | src-port | uid | jail Brc Ar N
1471 Search an entry in lookup table
1473 that matches the field specified as argument.
1474 If not found, the match fails.
1475 Otherwise, the match succeeds and
1477 is set to the value extracted from the table.
1479 This option can be useful to quickly dispatch traffic based on
1480 certain packet fields.
1483 section below for more information on lookup tables.
1484 .It Cm { MAC | mac } Ar dst-mac src-mac
1485 Match packets with a given
1489 addresses, specified as the
1491 keyword (matching any MAC address), or six groups of hex digits
1492 separated by colons,
1493 and optionally followed by a mask indicating the significant bits.
1494 The mask may be specified using either of the following methods:
1495 .Bl -enum -width indent
1499 followed by the number of significant bits.
1500 For example, an address with 33 significant bits could be specified as:
1502 .Dl "MAC 10:20:30:40:50:60/33 any"
1507 followed by a bitmask specified as six groups of hex digits separated
1509 For example, an address in which the last 16 bits are significant could
1512 .Dl "MAC 10:20:30:40:50:60&00:00:00:00:ff:ff any"
1514 Note that the ampersand character has a special meaning in many shells
1515 and should generally be escaped.
1518 Note that the order of MAC addresses (destination first,
1520 the same as on the wire, but the opposite of the one used for
1522 .It Cm mac-type Ar mac-type
1523 Matches packets whose Ethernet Type field
1524 corresponds to one of those specified as argument.
1526 is specified in the same way as
1528 (i.e., one or more comma-separated single values or ranges).
1529 You can use symbolic names for known values such as
1530 .Em vlan , ipv4, ipv6 .
1531 Values can be entered as decimal or hexadecimal (if prefixed by 0x),
1532 and they are always printed as hexadecimal (unless the
1534 option is used, in which case symbolic resolution will be attempted).
1535 .It Cm proto Ar protocol
1536 Matches packets with the corresponding IP protocol.
1537 .It Cm recv | xmit | via Brq Ar ifX | Ar if Ns Cm * | Ar table Ns Pq Ar number Ns Op , Ns Ar value | Ar ipno | Ar any
1538 Matches packets received, transmitted or going through,
1539 respectively, the interface specified by exact name
1540 .Ns No ( Ar ifX Ns No ),
1542 .Ns No ( Ar if Ns Ar * Ns No ),
1543 by IP address, or through some interface.
1547 keyword causes the interface to always be checked.
1554 then only the receive or transmit interface (respectively)
1556 By specifying both, it is possible to match packets based on
1557 both receive and transmit interface, e.g.:
1559 .Dl "ipfw add deny ip from any to any out recv ed0 xmit ed1"
1563 interface can be tested on either incoming or outgoing packets,
1566 interface can only be tested on outgoing packets.
1571 is invalid) whenever
1575 A packet might not have a receive or transmit interface: packets
1576 originating from the local host have no receive interface,
1577 while packets destined for the local host have no transmit
1580 Matches TCP packets that have the SYN bit set but no ACK bit.
1581 This is the short form of
1582 .Dq Li tcpflags\ syn,!ack .
1584 Matches packets that are associated to a local socket and
1585 for which the SO_USER_COOKIE socket option has been set
1586 to a non-zero value. As a side effect, the value of the
1587 option is made available as
1589 value, which in turn can be used as
1594 .It Cm src-ip Ar ip-address
1595 Matches IPv4 packets whose source IP is one of the address(es)
1596 specified as an argument.
1597 .It Cm src-ip6 Ar ip6-address
1598 Matches IPv6 packets whose source IP is one of the address(es)
1599 specified as an argument.
1600 .It Cm src-port Ar ports
1601 Matches IP packets whose source port is one of the port(s)
1602 specified as argument.
1603 .It Cm tagged Ar tag-list
1604 Matches packets whose tags are included in
1606 which is either a single value or a list of values or ranges
1607 specified in the same way as
1609 Tags can be applied to the packet using
1611 rule action parameter (see it's description for details on tags).
1612 .It Cm tcpack Ar ack
1614 Match if the TCP header acknowledgment number field is set to
1616 .It Cm tcpdatalen Ar tcpdatalen-list
1617 Matches TCP packets whose length of TCP data is
1618 .Ar tcpdatalen-list ,
1619 which is either a single value or a list of values or ranges
1620 specified in the same way as
1622 .It Cm tcpflags Ar spec
1624 Match if the TCP header contains the comma separated list of
1627 The supported TCP flags are:
1636 The absence of a particular flag may be denoted
1639 A rule which contains a
1641 specification can never match a fragmented packet which has
1645 option for details on matching fragmented packets.
1646 .It Cm tcpseq Ar seq
1648 Match if the TCP header sequence number field is set to
1650 .It Cm tcpwin Ar tcpwin-list
1651 Matches TCP packets whose header window field is set to
1653 which is either a single value or a list of values or ranges
1654 specified in the same way as
1656 .It Cm tcpoptions Ar spec
1658 Match if the TCP header contains the comma separated list of
1659 options specified in
1661 The supported TCP options are:
1664 (maximum segment size),
1666 (tcp window advertisement),
1670 (rfc1323 timestamp) and
1672 (rfc1644 t/tcp connection count).
1673 The absence of a particular option may be denoted
1677 Match all TCP or UDP packets sent by or received for a
1681 may be matched by name or identification number.
1683 For incoming packets,
1684 a routing table lookup is done on the packet's source address.
1685 If the interface on which the packet entered the system matches the
1686 outgoing interface for the route,
1688 If the interfaces do not match up,
1689 the packet does not match.
1690 All outgoing packets or packets with no incoming interface match.
1692 The name and functionality of the option is intentionally similar to
1693 the Cisco IOS command:
1695 .Dl ip verify unicast reverse-path
1697 This option can be used to make anti-spoofing rules to reject all
1698 packets with source addresses not from this interface.
1702 For incoming packets,
1703 a routing table lookup is done on the packet's source address.
1704 If a route to the source address exists, but not the default route
1705 or a blackhole/reject route, the packet matches.
1706 Otherwise, the packet does not match.
1707 All outgoing packets match.
1709 The name and functionality of the option is intentionally similar to
1710 the Cisco IOS command:
1712 .Dl ip verify unicast source reachable-via any
1714 This option can be used to make anti-spoofing rules to reject all
1715 packets whose source address is unreachable.
1717 For incoming packets, the packet's source address is checked if it
1718 belongs to a directly connected network.
1719 If the network is directly connected, then the interface the packet
1720 came on in is compared to the interface the network is connected to.
1721 When incoming interface and directly connected interface are not the
1722 same, the packet does not match.
1723 Otherwise, the packet does match.
1724 All outgoing packets match.
1726 This option can be used to make anti-spoofing rules to reject all
1727 packets that pretend to be from a directly connected network but do
1728 not come in through that interface.
1729 This option is similar to but more restricted than
1731 because it engages only on packets with source addresses of directly
1732 connected networks instead of all source addresses.
1735 Lookup tables are useful to handle large sparse sets of
1736 addresses or other search keys (e.g. ports, jail IDs, interface names).
1737 In the rest of this section we will use the term ``address''.
1738 There may be up to 4096 different lookup tables, numbered 0 to 4095.
1740 Each entry is represented by an
1741 .Ar addr Ns Op / Ns Ar masklen
1742 and will match all addresses with base
1744 (specified as an IPv4/IPv6 address, a hostname or an unsigned integer)
1750 is not specified, it defaults to 32 for IPv4 and 128 for IPv6.
1751 When looking up an IP address in a table, the most specific
1753 Associated with each entry is a 32-bit unsigned
1755 which can optionally be checked by a rule matching code.
1756 When adding an entry, if
1758 is not specified, it defaults to 0.
1760 An entry can be added to a table
1762 or removed from a table
1764 A table can be examined
1769 Internally, each table is stored in a Radix tree, the same way as
1770 the routing table (see
1773 Lookup tables currently support only ports, jail IDs, IPv4/IPv6 addresses
1774 and interface names. Wildcards is not supported for interface names.
1778 feature provides the ability to use a value, looked up in the table, as
1779 the argument for a rule action, action parameter or rule option.
1780 This can significantly reduce number of rules in some configurations.
1781 If two tables are used in a rule, the result of the second (destination)
1785 argument can be used with the following actions:
1786 .Cm nat, pipe , queue, divert, tee, netgraph, ngtee, fwd, skipto, setfib,
1794 it is possible to supply table entries with values
1795 that are in the form of IP addresses or hostnames.
1798 Section for example usage of tables and the tablearg keyword.
1802 action, the user should be aware that the code will walk the ruleset
1803 up to a rule equal to, or past, the given number, and should therefore try keep the
1804 ruleset compact between the skipto and the target rules.
1806 Each rule belongs to one of 32 different
1809 Set 31 is reserved for the default rule.
1811 By default, rules are put in set 0, unless you use the
1813 attribute when entering a new rule.
1814 Sets can be individually and atomically enabled or disabled,
1815 so this mechanism permits an easy way to store multiple configurations
1816 of the firewall and quickly (and atomically) switch between them.
1817 The command to enable/disable sets is
1818 .Bd -ragged -offset indent
1820 .Cm set Oo Cm disable Ar number ... Oc Op Cm enable Ar number ...
1827 sections can be specified.
1828 Command execution is atomic on all the sets specified in the command.
1829 By default, all sets are enabled.
1831 When you disable a set, its rules behave as if they do not exist
1832 in the firewall configuration, with only one exception:
1833 .Bd -ragged -offset indent
1834 dynamic rules created from a rule before it had been disabled
1835 will still be active until they expire.
1837 dynamic rules you have to explicitly delete the parent rule
1838 which generated them.
1841 The set number of rules can be changed with the command
1842 .Bd -ragged -offset indent
1845 .Brq Cm rule Ar rule-number | old-set
1849 Also, you can atomically swap two rulesets with the command
1850 .Bd -ragged -offset indent
1852 .Cm set swap Ar first-set second-set
1857 Section on some possible uses of sets of rules.
1858 .Sh STATEFUL FIREWALL
1859 Stateful operation is a way for the firewall to dynamically
1860 create rules for specific flows when packets that
1861 match a given pattern are detected.
1862 Support for stateful
1863 operation comes through the
1864 .Cm check-state , keep-state
1870 Dynamic rules are created when a packet matches a
1874 rule, causing the creation of a
1876 rule which will match all and only packets with
1880 .Em src-ip/src-port dst-ip/dst-port
1885 are used here only to denote the initial match addresses, but they
1886 are completely equivalent afterwards).
1887 Dynamic rules will be checked at the first
1888 .Cm check-state, keep-state
1891 occurrence, and the action performed upon a match will be the same
1892 as in the parent rule.
1894 Note that no additional attributes other than protocol and IP addresses
1895 and ports are checked on dynamic rules.
1897 The typical use of dynamic rules is to keep a closed firewall configuration,
1898 but let the first TCP SYN packet from the inside network install a
1899 dynamic rule for the flow so that packets belonging to that session
1900 will be allowed through the firewall:
1902 .Dl "ipfw add check-state"
1903 .Dl "ipfw add allow tcp from my-subnet to any setup keep-state"
1904 .Dl "ipfw add deny tcp from any to any"
1906 A similar approach can be used for UDP, where an UDP packet coming
1907 from the inside will install a dynamic rule to let the response through
1910 .Dl "ipfw add check-state"
1911 .Dl "ipfw add allow udp from my-subnet to any keep-state"
1912 .Dl "ipfw add deny udp from any to any"
1914 Dynamic rules expire after some time, which depends on the status
1915 of the flow and the setting of some
1919 .Sx SYSCTL VARIABLES
1921 For TCP sessions, dynamic rules can be instructed to periodically
1922 send keepalive packets to refresh the state of the rule when it is
1927 for more examples on how to use dynamic rules.
1928 .Sh TRAFFIC SHAPER (DUMMYNET) CONFIGURATION
1930 is also the user interface for the
1932 traffic shaper, packet scheduler and network emulator, a subsystem that
1933 can artificially queue, delay or drop packets
1934 emulating the behaviour of certain network links
1935 or queueing systems.
1938 operates by first using the firewall to select packets
1939 using any match pattern that can be used in
1942 Matching packets are then passed to either of two
1943 different objects, which implement the traffic regulation:
1944 .Bl -hang -offset XXXX
1950 with given bandwidth and propagation delay,
1951 driven by a FIFO scheduler and a single queue with programmable
1952 queue size and packet loss rate.
1953 Packets are appended to the queue as they come out from
1955 and then transferred in FIFO order to the link at the desired rate.
1959 is an abstraction used to implement packet scheduling
1960 using one of several packet scheduling algorithms.
1963 are first grouped into flows according to a mask on the 5-tuple.
1964 Flows are then passed to the scheduler associated to the
1966 and each flow uses scheduling parameters (weight and others)
1967 as configured in the
1970 A scheduler in turn is connected to an emulated link,
1971 and arbitrates the link's bandwidth among backlogged flows according to
1972 weights and to the features of the scheduling algorithm in use.
1977 can be used to set hard limits to the bandwidth that a flow can use, whereas
1979 can be used to determine how different flows share the available bandwidth.
1981 A graphical representation of the binding of queues,
1982 flows, schedulers and links is below.
1983 .Bd -literal -offset indent
1984 (flow_mask|sched_mask) sched_mask
1985 +---------+ weight Wx +-------------+
1986 | |->-[flow]-->--| |-+
1987 -->--| QUEUE x | ... | | |
1988 | |->-[flow]-->--| SCHEDuler N | |
1990 ... | +--[LINK N]-->--
1991 +---------+ weight Wy | | +--[LINK N]-->--
1992 | |->-[flow]-->--| | |
1993 -->--| QUEUE y | ... | | |
1994 | |->-[flow]-->--| | |
1995 +---------+ +-------------+ |
1998 It is important to understand the role of the SCHED_MASK
1999 and FLOW_MASK, which are configured through the commands
2000 .Dl "ipfw sched N config mask SCHED_MASK ..."
2002 .Dl "ipfw queue X config mask FLOW_MASK ..." .
2004 The SCHED_MASK is used to assign flows to one or more
2005 scheduler instances, one for each
2006 value of the packet's 5-tuple after applying SCHED_MASK.
2007 As an example, using ``src-ip 0xffffff00'' creates one instance
2008 for each /24 destination subnet.
2010 The FLOW_MASK, together with the SCHED_MASK, is used to split
2011 packets into flows. As an example, using
2012 ``src-ip 0x000000ff''
2013 together with the previous SCHED_MASK makes a flow for
2014 each individual source address. In turn, flows for each /24
2015 subnet will be sent to the same scheduler instance.
2017 The above diagram holds even for the
2019 case, with the only restriction that a
2021 only supports a SCHED_MASK, and forces the use of a FIFO
2022 scheduler (these are for backward compatibility reasons;
2023 in fact, internally, a
2025 pipe is implemented exactly as above).
2027 There are two modes of
2035 mode tries to emulate a real link: the
2037 scheduler ensures that the packet will not leave the pipe faster than it
2038 would on the real link with a given bandwidth.
2041 mode allows certain packets to bypass the
2043 scheduler (if packet flow does not exceed pipe's bandwidth).
2044 This is the reason why the
2046 mode requires less CPU cycles per packet (on average) and packet latency
2047 can be significantly lower in comparison to a real link with the same
2053 mode can be enabled by setting the
2054 .Va net.inet.ip.dummynet.io_fast
2056 variable to a non-zero value.
2058 .Ss PIPE, QUEUE AND SCHEDULER CONFIGURATION
2064 configuration commands are the following:
2065 .Bd -ragged -offset indent
2066 .Cm pipe Ar number Cm config Ar pipe-configuration
2068 .Cm queue Ar number Cm config Ar queue-configuration
2070 .Cm sched Ar number Cm config Ar sched-configuration
2073 The following parameters can be configured for a pipe:
2075 .Bl -tag -width indent -compact
2076 .It Cm bw Ar bandwidth | device
2077 Bandwidth, measured in
2080 .Brq Cm bit/s | Byte/s .
2083 A value of 0 (default) means unlimited bandwidth.
2084 The unit must immediately follow the number, as in
2086 .Dl "ipfw pipe 1 config bw 300Kbit/s"
2088 If a device name is specified instead of a numeric value, as in
2090 .Dl "ipfw pipe 1 config bw tun0"
2092 then the transmit clock is supplied by the specified device.
2093 At the moment only the
2095 device supports this
2096 functionality, for use in conjunction with
2099 .It Cm delay Ar ms-delay
2100 Propagation delay, measured in milliseconds.
2101 The value is rounded to the next multiple of the clock tick
2102 (typically 10ms, but it is a good practice to run kernels
2104 .Dq "options HZ=1000"
2106 the granularity to 1ms or less).
2107 The default value is 0, meaning no delay.
2109 .It Cm burst Ar size
2110 If the data to be sent exceeds the pipe's bandwidth limit
2111 (and the pipe was previously idle), up to
2113 bytes of data are allowed to bypass the
2115 scheduler, and will be sent as fast as the physical link allows.
2116 Any additional data will be transmitted at the rate specified
2120 The burst size depends on how long the pipe has been idle;
2121 the effective burst size is calculated as follows:
2128 .It Cm profile Ar filename
2129 A file specifying the additional overhead incurred in the transmission
2130 of a packet on the link.
2132 Some link types introduce extra delays in the transmission
2133 of a packet, e.g. because of MAC level framing, contention on
2134 the use of the channel, MAC level retransmissions and so on.
2135 From our point of view, the channel is effectively unavailable
2136 for this extra time, which is constant or variable depending
2137 on the link type. Additionally, packets may be dropped after this
2138 time (e.g. on a wireless link after too many retransmissions).
2139 We can model the additional delay with an empirical curve
2140 that represents its distribution.
2141 .Bd -literal -offset indent
2142 cumulative probability
2152 +-------*------------------->
2155 The empirical curve may have both vertical and horizontal lines.
2156 Vertical lines represent constant delay for a range of
2158 Horizontal lines correspond to a discontinuity in the delay
2159 distribution: the pipe will use the largest delay for a
2162 The file format is the following, with whitespace acting as
2163 a separator and '#' indicating the beginning a comment:
2164 .Bl -tag -width indent
2165 .It Cm name Ar identifier
2166 optional name (listed by "ipfw pipe show")
2167 to identify the delay distribution;
2169 the bandwidth used for the pipe.
2170 If not specified here, it must be present
2171 explicitly as a configuration parameter for the pipe;
2172 .It Cm loss-level Ar L
2173 the probability above which packets are lost.
2174 (0.0 <= L <= 1.0, default 1.0 i.e. no loss);
2176 the number of samples used in the internal
2177 representation of the curve (2..1024; default 100);
2178 .It Cm "delay prob" | "prob delay"
2179 One of these two lines is mandatory and defines
2180 the format of the following lines with data points.
2182 2 or more lines representing points in the curve,
2183 with either delay or probability first, according
2184 to the chosen format.
2185 The unit for delay is milliseconds.
2186 Data points do not need to be sorted.
2187 Also, the number of actual lines can be different
2188 from the value of the "samples" parameter:
2190 utility will sort and interpolate
2191 the curve as needed.
2194 Example of a profile file:
2195 .Bd -literal -offset indent
2200 0 200 # minimum overhead is 200ms
2206 #configuration file end
2210 The following parameters can be configured for a queue:
2212 .Bl -tag -width indent -compact
2213 .It Cm pipe Ar pipe_nr
2214 Connects a queue to the specified pipe.
2215 Multiple queues (with the same or different weights) can be connected to
2216 the same pipe, which specifies the aggregate rate for the set of queues.
2218 .It Cm weight Ar weight
2219 Specifies the weight to be used for flows matching this queue.
2220 The weight must be in the range 1..100, and defaults to 1.
2223 The following case-insensitive parameters can be configured for a
2226 .Bl -tag -width indent -compact
2227 .It Cm type Ar {fifo | wf2q+ | rr | qfq}
2228 specifies the scheduling algorithm to use.
2229 .Bl -tag -width indent -compact
2231 is just a FIFO scheduler (which means that all packets
2232 are stored in the same queue as they arrive to the scheduler).
2233 FIFO has O(1) per-packet time complexity, with very low
2234 constants (estimate 60-80ns on a 2GHz desktop machine)
2235 but gives no service guarantees.
2237 implements the WF2Q+ algorithm, which is a Weighted Fair Queueing
2238 algorithm which permits flows to share bandwidth according to
2239 their weights. Note that weights are not priorities; even a flow
2240 with a minuscule weight will never starve.
2241 WF2Q+ has O(log N) per-packet processing cost, where N is the number
2242 of flows, and is the default algorithm used by previous versions
2245 implements the Deficit Round Robin algorithm, which has O(1) processing
2246 costs (roughly, 100-150ns per packet)
2247 and permits bandwidth allocation according to weights, but
2248 with poor service guarantees.
2250 implements the QFQ algorithm, which is a very fast variant of
2251 WF2Q+, with similar service guarantees and O(1) processing
2252 costs (roughly, 200-250ns per packet).
2256 In addition to the type, all parameters allowed for a pipe can also
2257 be specified for a scheduler.
2259 Finally, the following parameters can be configured for both
2262 .Bl -tag -width XXXX -compact
2263 .It Cm buckets Ar hash-table-size
2264 Specifies the size of the hash table used for storing the
2266 Default value is 64 controlled by the
2269 .Va net.inet.ip.dummynet.hash_size ,
2270 allowed range is 16 to 65536.
2272 .It Cm mask Ar mask-specifier
2273 Packets sent to a given pipe or queue by an
2275 rule can be further classified into multiple flows, each of which is then
2279 A flow identifier is constructed by masking the IP addresses,
2280 ports and protocol types as specified with the
2282 options in the configuration of the pipe or queue.
2283 For each different flow identifier, a new pipe or queue is created
2284 with the same parameters as the original object, and matching packets
2289 are used, each flow will get the same bandwidth as defined by the pipe,
2292 are used, each flow will share the parent's pipe bandwidth evenly
2293 with other flows generated by the same queue (note that other queues
2294 with different weights might be connected to the same pipe).
2296 Available mask specifiers are a combination of one or more of the following:
2298 .Cm dst-ip Ar mask ,
2299 .Cm dst-ip6 Ar mask ,
2300 .Cm src-ip Ar mask ,
2301 .Cm src-ip6 Ar mask ,
2302 .Cm dst-port Ar mask ,
2303 .Cm src-port Ar mask ,
2304 .Cm flow-id Ar mask ,
2309 where the latter means all bits in all fields are significant.
2312 When a packet is dropped by a
2314 queue or pipe, the error
2315 is normally reported to the caller routine in the kernel, in the
2316 same way as it happens when a device queue fills up.
2318 option reports the packet as successfully delivered, which can be
2319 needed for some experimental setups where you want to simulate
2320 loss or congestion at a remote router.
2322 .It Cm plr Ar packet-loss-rate
2325 .Ar packet-loss-rate
2326 is a floating-point number between 0 and 1, with 0 meaning no
2327 loss, 1 meaning 100% loss.
2328 The loss rate is internally represented on 31 bits.
2330 .It Cm queue Brq Ar slots | size Ns Cm Kbytes
2335 Default value is 50 slots, which
2336 is the typical queue size for Ethernet devices.
2337 Note that for slow speed links you should keep the queue
2338 size short or your traffic might be affected by a significant
2340 E.g., 50 max-sized ethernet packets (1500 bytes) mean 600Kbit
2341 or 20s of queue on a 30Kbit/s pipe.
2342 Even worse effects can result if you get packets from an
2343 interface with a much larger MTU, e.g.\& the loopback interface
2344 with its 16KB packets.
2348 .Em net.inet.ip.dummynet.pipe_byte_limit
2350 .Em net.inet.ip.dummynet.pipe_slot_limit
2351 control the maximum lengths that can be specified.
2353 .It Cm red | gred Ar w_q Ns / Ns Ar min_th Ns / Ns Ar max_th Ns / Ns Ar max_p
2354 Make use of the RED (Random Early Detection) queue management algorithm.
2359 point numbers between 0 and 1 (0 not included), while
2363 are integer numbers specifying thresholds for queue management
2364 (thresholds are computed in bytes if the queue has been defined
2365 in bytes, in slots otherwise).
2368 also supports the gentle RED variant (gred).
2371 variables can be used to control the RED behaviour:
2372 .Bl -tag -width indent
2373 .It Va net.inet.ip.dummynet.red_lookup_depth
2374 specifies the accuracy in computing the average queue
2375 when the link is idle (defaults to 256, must be greater than zero)
2376 .It Va net.inet.ip.dummynet.red_avg_pkt_size
2377 specifies the expected average packet size (defaults to 512, must be
2379 .It Va net.inet.ip.dummynet.red_max_pkt_size
2380 specifies the expected maximum packet size, only used when queue
2381 thresholds are in bytes (defaults to 1500, must be greater than zero).
2385 When used with IPv6 data,
2387 currently has several limitations.
2388 Information necessary to route link-local packets to an
2389 interface is not available after processing by
2391 so those packets are dropped in the output path.
2392 Care should be taken to ensure that link-local packets are not passed to
2395 Here are some important points to consider when designing your
2399 Remember that you filter both packets going
2403 Most connections need packets going in both directions.
2405 Remember to test very carefully.
2406 It is a good idea to be near the console when doing this.
2407 If you cannot be near the console,
2408 use an auto-recovery script such as the one in
2409 .Pa /usr/share/examples/ipfw/change_rules.sh .
2411 Do not forget the loopback interface.
2416 There are circumstances where fragmented datagrams are unconditionally
2418 TCP packets are dropped if they do not contain at least 20 bytes of
2419 TCP header, UDP packets are dropped if they do not contain a full 8
2420 byte UDP header, and ICMP packets are dropped if they do not contain
2421 4 bytes of ICMP header, enough to specify the ICMP type, code, and
2423 These packets are simply logged as
2425 since there may not be enough good data in the packet to produce a
2426 meaningful log entry.
2428 Another type of packet is unconditionally dropped, a TCP packet with a
2429 fragment offset of one.
2430 This is a valid packet, but it only has one use, to try
2431 to circumvent firewalls.
2432 When logging is enabled, these packets are
2433 reported as being dropped by rule -1.
2435 If you are logged in over a network, loading the
2439 is probably not as straightforward as you would think.
2440 The following command line is recommended:
2441 .Bd -literal -offset indent
2443 ipfw add 32000 allow ip from any to any
2446 Along the same lines, doing an
2447 .Bd -literal -offset indent
2451 in similar surroundings is also a bad idea.
2455 filter list may not be modified if the system security level
2456 is set to 3 or higher
2459 for information on system security levels).
2461 .Sh PACKET DIVERSION
2464 socket bound to the specified port will receive all packets
2465 diverted to that port.
2466 If no socket is bound to the destination port, or if the divert module is
2467 not loaded, or if the kernel was not compiled with divert socket support,
2468 the packets are dropped.
2469 .Sh NETWORK ADDRESS TRANSLATION (NAT)
2472 support in-kernel NAT using the kernel version of
2475 The nat configuration command is the following:
2476 .Bd -ragged -offset indent
2481 .Ar nat-configuration
2485 The following parameters can be configured:
2486 .Bl -tag -width indent
2487 .It Cm ip Ar ip_address
2488 Define an ip address to use for aliasing.
2490 Use ip address of NIC for aliasing, dynamically changing
2491 it if NIC's ip address changes.
2493 Enable logging on this nat instance.
2495 Deny any incoming connection from outside world.
2497 Try to leave the alias port numbers unchanged from
2498 the actual local port numbers.
2500 Traffic on the local network not originating from an
2501 unregistered address spaces will be ignored.
2503 Reset table of the packet aliasing engine on address change.
2505 Reverse the way libalias handles aliasing.
2507 Obey transparent proxy rules only, packet aliasing is not performed.
2509 Skip instance in case of global state lookup (see below).
2512 Some specials value can be supplied instead of
2514 .Bl -tag -width indent
2516 Looks up translation state in all configured nat instances.
2517 If an entry is found, packet is aliased according to that entry.
2518 If no entry was found in any of the instances, packet is passed unchanged,
2519 and no new entry will be created.
2521 .Sx MULTIPLE INSTANCES
2524 for more information.
2526 Uses argument supplied in lookup table. See
2528 section below for more information on lookup tables.
2531 To let the packet continue after being (de)aliased, set the sysctl variable
2532 .Va net.inet.ip.fw.one_pass
2534 For more information about aliasing modes, refer to
2538 for some examples about nat usage.
2539 .Ss REDIRECT AND LSNAT SUPPORT IN IPFW
2540 Redirect and LSNAT support follow closely the syntax used in
2544 for some examples on how to do redirect and lsnat.
2545 .Ss SCTP NAT SUPPORT
2546 SCTP nat can be configured in a similar manner to TCP through the
2549 The main difference is that
2551 does not do port translation.
2552 Since the local and global side ports will be the same,
2553 there is no need to specify both.
2554 Ports are redirected as follows:
2555 .Bd -ragged -offset indent
2561 .Cm redirect_port sctp
2562 .Ar ip_address [,addr_list] {[port | port-port] [,ports]}
2568 configuration can be done in real-time through the
2571 All may be changed dynamically, though the hash_table size will only
2576 .Sx SYSCTL VARIABLES
2579 Tunables can be set in
2585 before ipfw module gets loaded.
2586 .Bl -tag -width indent
2587 .It Va net.inet.ip.fw.default_to_accept: No 0
2588 Defines ipfw last rule behavior. This value overrides
2589 .Cd "options IPFW_DEFAULT_TO_(ACCEPT|DENY)"
2590 from kernel configuration file.
2591 .It Va net.inet.ip.fw.tables_max: No 128
2592 Defines number of tables available in ipfw. Number cannot exceed 65534.
2594 .Sh SYSCTL VARIABLES
2597 variables controls the behaviour of the firewall and
2599 .Pq Nm dummynet , bridge , sctp nat .
2600 These are shown below together with their default value
2601 (but always check with the
2603 command what value is actually in use) and meaning:
2604 .Bl -tag -width indent
2605 .It Va net.inet.ip.alias.sctp.accept_global_ootb_addip: No 0
2608 responds to receipt of global OOTB ASCONF-AddIP:
2609 .Bl -tag -width indent
2611 No response (unless a partially matching association exists -
2612 ports and vtags match but global address does not)
2615 will accept and process all OOTB global AddIP messages.
2618 Option 1 should never be selected as this forms a security risk.
2620 establish multiple fake associations by sending AddIP messages.
2621 .It Va net.inet.ip.alias.sctp.chunk_proc_limit: No 5
2622 Defines the maximum number of chunks in an SCTP packet that will be parsed for a
2623 packet that matches an existing association.
2624 This value is enforced to be greater or equal than
2625 .Cm net.inet.ip.alias.sctp.initialising_chunk_proc_limit .
2627 a DoS risk yet setting too low a value may result in important control chunks in
2628 the packet not being located and parsed.
2629 .It Va net.inet.ip.alias.sctp.error_on_ootb: No 1
2632 responds to any Out-of-the-Blue (OOTB) packets with ErrorM packets.
2633 An OOTB packet is a packet that arrives with no existing association
2636 and is not an INIT or ASCONF-AddIP packet:
2637 .Bl -tag -width indent
2639 ErrorM is never sent in response to OOTB packets.
2641 ErrorM is only sent to OOTB packets received on the local side.
2643 ErrorM is sent to the local side and on the global side ONLY if there is a
2644 partial match (ports and vtags match but the source global IP does not).
2645 This value is only useful if the
2647 is tracking global IP addresses.
2649 ErrorM is sent in response to all OOTB packets on both the local and global side
2653 At the moment the default is 0, since the ErrorM packet is not yet
2654 supported by most SCTP stacks.
2655 When it is supported, and if not tracking
2656 global addresses, we recommend setting this value to 1 to allow
2657 multi-homed local hosts to function with the
2659 To track global addresses, we recommend setting this value to 2 to
2660 allow global hosts to be informed when they need to (re)send an
2662 Value 3 should never be chosen (except for debugging) as the
2664 will respond to all OOTB global packets (a DoS risk).
2665 .It Va net.inet.ip.alias.sctp.hashtable_size: No 2003
2666 Size of hash tables used for
2668 lookups (100 < prime_number > 1000001).
2671 size for any future created
2673 instance and therefore must be set prior to creating a
2676 The table sizes may be changed to suit specific needs.
2677 If there will be few
2678 concurrent associations, and memory is scarce, you may make these smaller.
2679 If there will be many thousands (or millions) of concurrent associations, you
2680 should make these larger.
2681 A prime number is best for the table size.
2683 update function will adjust your input value to the next highest prime number.
2684 .It Va net.inet.ip.alias.sctp.holddown_time: No 0
2685 Hold association in table for this many seconds after receiving a
2687 This allows endpoints to correct shutdown gracefully if a
2688 shutdown_complete is lost and retransmissions are required.
2689 .It Va net.inet.ip.alias.sctp.init_timer: No 15
2690 Timeout value while waiting for (INIT-ACK|AddIP-ACK).
2691 This value cannot be 0.
2692 .It Va net.inet.ip.alias.sctp.initialising_chunk_proc_limit: No 2
2693 Defines the maximum number of chunks in an SCTP packet that will be parsed when
2694 no existing association exists that matches that packet.
2696 will only be an INIT or ASCONF-AddIP packet.
2697 A higher value may become a DoS
2698 risk as malformed packets can consume processing resources.
2699 .It Va net.inet.ip.alias.sctp.param_proc_limit: No 25
2700 Defines the maximum number of parameters within a chunk that will be parsed in a
2702 As for other similar sysctl variables, larger values pose a DoS risk.
2703 .It Va net.inet.ip.alias.sctp.log_level: No 0
2704 Level of detail in the system log messages (0 \- minimal, 1 \- event,
2705 2 \- info, 3 \- detail, 4 \- debug, 5 \- max debug). May be a good
2706 option in high loss environments.
2707 .It Va net.inet.ip.alias.sctp.shutdown_time: No 15
2708 Timeout value while waiting for SHUTDOWN-COMPLETE.
2709 This value cannot be 0.
2710 .It Va net.inet.ip.alias.sctp.track_global_addresses: No 0
2711 Enables/disables global IP address tracking within the
2714 upper limit on the number of addresses tracked for each association:
2715 .Bl -tag -width indent
2717 Global tracking is disabled
2719 Enables tracking, the maximum number of addresses tracked for each
2720 association is limited to this value
2723 This variable is fully dynamic, the new value will be adopted for all newly
2724 arriving associations, existing associations are treated as they were previously.
2725 Global tracking will decrease the number of collisions within the
2728 of increased processing load, memory usage, complexity, and possible
2731 problems in complex networks with multiple
2733 We recommend not tracking
2734 global IP addresses, this will still result in a fully functional
2736 .It Va net.inet.ip.alias.sctp.up_timer: No 300
2737 Timeout value to keep an association up with no traffic.
2738 This value cannot be 0.
2739 .It Va net.inet.ip.dummynet.expire : No 1
2740 Lazily delete dynamic pipes/queue once they have no pending traffic.
2741 You can disable this by setting the variable to 0, in which case
2742 the pipes/queues will only be deleted when the threshold is reached.
2743 .It Va net.inet.ip.dummynet.hash_size : No 64
2744 Default size of the hash table used for dynamic pipes/queues.
2745 This value is used when no
2747 option is specified when configuring a pipe/queue.
2748 .It Va net.inet.ip.dummynet.io_fast : No 0
2749 If set to a non-zero value,
2754 operation (see above) is enabled.
2755 .It Va net.inet.ip.dummynet.io_pkt
2756 Number of packets passed to
2758 .It Va net.inet.ip.dummynet.io_pkt_drop
2759 Number of packets dropped by
2761 .It Va net.inet.ip.dummynet.io_pkt_fast
2762 Number of packets bypassed by the
2765 .It Va net.inet.ip.dummynet.max_chain_len : No 16
2766 Target value for the maximum number of pipes/queues in a hash bucket.
2768 .Cm max_chain_len*hash_size
2769 is used to determine the threshold over which empty pipes/queues
2770 will be expired even when
2771 .Cm net.inet.ip.dummynet.expire=0 .
2772 .It Va net.inet.ip.dummynet.red_lookup_depth : No 256
2773 .It Va net.inet.ip.dummynet.red_avg_pkt_size : No 512
2774 .It Va net.inet.ip.dummynet.red_max_pkt_size : No 1500
2775 Parameters used in the computations of the drop probability
2776 for the RED algorithm.
2777 .It Va net.inet.ip.dummynet.pipe_byte_limit : No 1048576
2778 .It Va net.inet.ip.dummynet.pipe_slot_limit : No 100
2779 The maximum queue size that can be specified in bytes or packets.
2780 These limits prevent accidental exhaustion of resources such as mbufs.
2781 If you raise these limits,
2782 you should make sure the system is configured so that sufficient resources
2784 .It Va net.inet.ip.fw.autoinc_step : No 100
2785 Delta between rule numbers when auto-generating them.
2786 The value must be in the range 1..1000.
2787 .It Va net.inet.ip.fw.curr_dyn_buckets : Va net.inet.ip.fw.dyn_buckets
2788 The current number of buckets in the hash table for dynamic rules
2790 .It Va net.inet.ip.fw.debug : No 1
2791 Controls debugging messages produced by
2793 .It Va net.inet.ip.fw.default_rule : No 65535
2794 The default rule number (read-only).
2796 .Nm , the default rule is the last one, so its number
2797 can also serve as the highest number allowed for a rule.
2798 .It Va net.inet.ip.fw.dyn_buckets : No 256
2799 The number of buckets in the hash table for dynamic rules.
2800 Must be a power of 2, up to 65536.
2801 It only takes effect when all dynamic rules have expired, so you
2802 are advised to use a
2804 command to make sure that the hash table is resized.
2805 .It Va net.inet.ip.fw.dyn_count : No 3
2806 Current number of dynamic rules
2808 .It Va net.inet.ip.fw.dyn_keepalive : No 1
2809 Enables generation of keepalive packets for
2811 rules on TCP sessions.
2812 A keepalive is generated to both
2813 sides of the connection every 5 seconds for the last 20
2814 seconds of the lifetime of the rule.
2815 .It Va net.inet.ip.fw.dyn_max : No 8192
2816 Maximum number of dynamic rules.
2817 When you hit this limit, no more dynamic rules can be
2818 installed until old ones expire.
2819 .It Va net.inet.ip.fw.dyn_ack_lifetime : No 300
2820 .It Va net.inet.ip.fw.dyn_syn_lifetime : No 20
2821 .It Va net.inet.ip.fw.dyn_fin_lifetime : No 1
2822 .It Va net.inet.ip.fw.dyn_rst_lifetime : No 1
2823 .It Va net.inet.ip.fw.dyn_udp_lifetime : No 5
2824 .It Va net.inet.ip.fw.dyn_short_lifetime : No 30
2825 These variables control the lifetime, in seconds, of dynamic
2827 Upon the initial SYN exchange the lifetime is kept short,
2828 then increased after both SYN have been seen, then decreased
2829 again during the final FIN exchange or when a RST is received.
2831 .Em dyn_fin_lifetime
2833 .Em dyn_rst_lifetime
2834 must be strictly lower than 5 seconds, the period of
2835 repetition of keepalives.
2836 The firewall enforces that.
2837 .It Va net.inet.ip.fw.enable : No 1
2838 Enables the firewall.
2839 Setting this variable to 0 lets you run your machine without
2840 firewall even if compiled in.
2841 .It Va net.inet6.ip6.fw.enable : No 1
2842 provides the same functionality as above for the IPv6 case.
2843 .It Va net.inet.ip.fw.one_pass : No 1
2844 When set, the packet exiting from the
2848 node is not passed though the firewall again.
2849 Otherwise, after an action, the packet is
2850 reinjected into the firewall at the next rule.
2851 .It Va net.inet.ip.fw.tables_max : No 128
2852 Maximum number of tables.
2853 .It Va net.inet.ip.fw.verbose : No 1
2854 Enables verbose messages.
2855 .It Va net.inet.ip.fw.verbose_limit : No 0
2856 Limits the number of messages produced by a verbose firewall.
2857 .It Va net.inet6.ip6.fw.deny_unknown_exthdrs : No 1
2858 If enabled packets with unknown IPv6 Extension Headers will be denied.
2859 .It Va net.link.ether.ipfw : No 0
2860 Controls whether layer-2 packets are passed to
2863 .It Va net.link.bridge.ipfw : No 0
2864 Controls whether bridged packets are passed to
2870 There are far too many possible uses of
2872 so this Section will only give a small set of examples.
2874 .Ss BASIC PACKET FILTERING
2875 This command adds an entry which denies all tcp packets from
2876 .Em cracker.evil.org
2877 to the telnet port of
2879 from being forwarded by the host:
2881 .Dl "ipfw add deny tcp from cracker.evil.org to wolf.tambov.su telnet"
2883 This one disallows any connection from the entire cracker's
2886 .Dl "ipfw add deny ip from 123.45.67.0/24 to my.host.org"
2888 A first and efficient way to limit access (not using dynamic rules)
2889 is the use of the following rules:
2891 .Dl "ipfw add allow tcp from any to any established"
2892 .Dl "ipfw add allow tcp from net1 portlist1 to net2 portlist2 setup"
2893 .Dl "ipfw add allow tcp from net3 portlist3 to net3 portlist3 setup"
2895 .Dl "ipfw add deny tcp from any to any"
2897 The first rule will be a quick match for normal TCP packets,
2898 but it will not match the initial SYN packet, which will be
2901 rules only for selected source/destination pairs.
2902 All other SYN packets will be rejected by the final
2906 If you administer one or more subnets, you can take advantage
2907 of the address sets and or-blocks and write extremely
2908 compact rulesets which selectively enable services to blocks
2909 of clients, as below:
2911 .Dl "goodguys=\*q{ 10.1.2.0/24{20,35,66,18} or 10.2.3.0/28{6,3,11} }\*q"
2912 .Dl "badguys=\*q10.1.2.0/24{8,38,60}\*q"
2914 .Dl "ipfw add allow ip from ${goodguys} to any"
2915 .Dl "ipfw add deny ip from ${badguys} to any"
2916 .Dl "... normal policies ..."
2920 option could be used to do automated anti-spoofing by adding the
2921 following to the top of a ruleset:
2923 .Dl "ipfw add deny ip from any to any not verrevpath in"
2925 This rule drops all incoming packets that appear to be coming to the
2926 system on the wrong interface.
2927 For example, a packet with a source
2928 address belonging to a host on a protected internal network would be
2929 dropped if it tried to enter the system from an external interface.
2933 option could be used to do similar but more restricted anti-spoofing
2934 by adding the following to the top of a ruleset:
2936 .Dl "ipfw add deny ip from any to any not antispoof in"
2938 This rule drops all incoming packets that appear to be coming from another
2939 directly connected system but on the wrong interface.
2940 For example, a packet with a source address of
2941 .Li 192.168.0.0/24 ,
2948 In order to protect a site from flood attacks involving fake
2949 TCP packets, it is safer to use dynamic rules:
2951 .Dl "ipfw add check-state"
2952 .Dl "ipfw add deny tcp from any to any established"
2953 .Dl "ipfw add allow tcp from my-net to any setup keep-state"
2955 This will let the firewall install dynamic rules only for
2956 those connection which start with a regular SYN packet coming
2957 from the inside of our network.
2958 Dynamic rules are checked when encountering the first
2965 rule should usually be placed near the beginning of the
2966 ruleset to minimize the amount of work scanning the ruleset.
2967 Your mileage may vary.
2969 To limit the number of connections a user can open
2970 you can use the following type of rules:
2972 .Dl "ipfw add allow tcp from my-net/24 to any setup limit src-addr 10"
2973 .Dl "ipfw add allow tcp from any to me setup limit src-addr 4"
2975 The former (assuming it runs on a gateway) will allow each host
2976 on a /24 network to open at most 10 TCP connections.
2977 The latter can be placed on a server to make sure that a single
2978 client does not use more than 4 simultaneous connections.
2981 stateful rules can be subject to denial-of-service attacks
2982 by a SYN-flood which opens a huge number of dynamic rules.
2983 The effects of such attacks can be partially limited by
2986 variables which control the operation of the firewall.
2988 Here is a good usage of the
2990 command to see accounting records and timestamp information:
2994 or in short form without timestamps:
2998 which is equivalent to:
3002 Next rule diverts all incoming packets from 192.168.2.0/24
3003 to divert port 5000:
3005 .Dl ipfw divert 5000 ip from 192.168.2.0/24 to any in
3008 The following rules show some of the applications of
3012 for simulations and the like.
3014 This rule drops random incoming packets with a probability
3017 .Dl "ipfw add prob 0.05 deny ip from any to any in"
3019 A similar effect can be achieved making use of
3023 .Dl "ipfw add pipe 10 ip from any to any"
3024 .Dl "ipfw pipe 10 config plr 0.05"
3026 We can use pipes to artificially limit bandwidth, e.g.\& on a
3027 machine acting as a router, if we want to limit traffic from
3028 local clients on 192.168.2.0/24 we do:
3030 .Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out"
3031 .Dl "ipfw pipe 1 config bw 300Kbit/s queue 50KBytes"
3033 note that we use the
3035 modifier so that the rule is not used twice.
3036 Remember in fact that
3038 rules are checked both on incoming and outgoing packets.
3040 Should we want to simulate a bidirectional link with bandwidth
3041 limitations, the correct way is the following:
3043 .Dl "ipfw add pipe 1 ip from any to any out"
3044 .Dl "ipfw add pipe 2 ip from any to any in"
3045 .Dl "ipfw pipe 1 config bw 64Kbit/s queue 10Kbytes"
3046 .Dl "ipfw pipe 2 config bw 64Kbit/s queue 10Kbytes"
3048 The above can be very useful, e.g.\& if you want to see how
3049 your fancy Web page will look for a residential user who
3050 is connected only through a slow link.
3051 You should not use only one pipe for both directions, unless
3052 you want to simulate a half-duplex medium (e.g.\& AppleTalk,
3054 It is not necessary that both pipes have the same configuration,
3055 so we can also simulate asymmetric links.
3057 Should we want to verify network performance with the RED queue
3058 management algorithm:
3060 .Dl "ipfw add pipe 1 ip from any to any"
3061 .Dl "ipfw pipe 1 config bw 500Kbit/s queue 100 red 0.002/30/80/0.1"
3063 Another typical application of the traffic shaper is to
3064 introduce some delay in the communication.
3065 This can significantly affect applications which do a lot of Remote
3066 Procedure Calls, and where the round-trip-time of the
3067 connection often becomes a limiting factor much more than
3070 .Dl "ipfw add pipe 1 ip from any to any out"
3071 .Dl "ipfw add pipe 2 ip from any to any in"
3072 .Dl "ipfw pipe 1 config delay 250ms bw 1Mbit/s"
3073 .Dl "ipfw pipe 2 config delay 250ms bw 1Mbit/s"
3075 Per-flow queueing can be useful for a variety of purposes.
3076 A very simple one is counting traffic:
3078 .Dl "ipfw add pipe 1 tcp from any to any"
3079 .Dl "ipfw add pipe 1 udp from any to any"
3080 .Dl "ipfw add pipe 1 ip from any to any"
3081 .Dl "ipfw pipe 1 config mask all"
3083 The above set of rules will create queues (and collect
3084 statistics) for all traffic.
3085 Because the pipes have no limitations, the only effect is
3086 collecting statistics.
3087 Note that we need 3 rules, not just the last one, because
3090 tries to match IP packets it will not consider ports, so we
3091 would not see connections on separate ports as different
3094 A more sophisticated example is limiting the outbound traffic
3095 on a net with per-host limits, rather than per-network limits:
3097 .Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out"
3098 .Dl "ipfw add pipe 2 ip from any to 192.168.2.0/24 in"
3099 .Dl "ipfw pipe 1 config mask src-ip 0x000000ff bw 200Kbit/s queue 20Kbytes"
3100 .Dl "ipfw pipe 2 config mask dst-ip 0x000000ff bw 200Kbit/s queue 20Kbytes"
3102 In the following example, we need to create several traffic bandwidth
3103 classes and we need different hosts/networks to fall into different classes.
3104 We create one pipe for each class and configure them accordingly.
3105 Then we create a single table and fill it with IP subnets and addresses.
3106 For each subnet/host we set the argument equal to the number of the pipe
3108 Then we classify traffic using a single rule:
3110 .Dl "ipfw pipe 1 config bw 1000Kbyte/s"
3111 .Dl "ipfw pipe 4 config bw 4000Kbyte/s"
3113 .Dl "ipfw table 1 add 192.168.2.0/24 1"
3114 .Dl "ipfw table 1 add 192.168.0.0/27 4"
3115 .Dl "ipfw table 1 add 192.168.0.2 1"
3117 .Dl "ipfw add pipe tablearg ip from table(1) to any"
3121 action, the table entries may include hostnames and IP addresses.
3123 .Dl "ipfw table 1 add 192.168.2.0/24 10.23.2.1"
3124 .Dl "ipfw table 1 add 192.168.0.0/27 router1.dmz"
3126 .Dl "ipfw add 100 fwd tablearg ip from any to table(1)"
3128 In the following example per-interface firewall is created:
3130 .Dl "ipfw table 10 add vlan20 12000"
3131 .Dl "ipfw table 10 add vlan30 13000"
3132 .Dl "ipfw table 20 add vlan20 22000"
3133 .Dl "ipfw table 20 add vlan30 23000"
3135 .Dl "ipfw add 100 ipfw skipto tablearg ip from any to any recv 'table(10)' in"
3136 .Dl "ipfw add 200 ipfw skipto tablearg ip from any to any xmit 'table(10)' out"
3138 To add a set of rules atomically, e.g.\& set 18:
3140 .Dl "ipfw set disable 18"
3141 .Dl "ipfw add NN set 18 ... # repeat as needed"
3142 .Dl "ipfw set enable 18"
3144 To delete a set of rules atomically the command is simply:
3146 .Dl "ipfw delete set 18"
3148 To test a ruleset and disable it and regain control if something goes wrong:
3150 .Dl "ipfw set disable 18"
3151 .Dl "ipfw add NN set 18 ... # repeat as needed"
3152 .Dl "ipfw set enable 18; echo done; sleep 30 && ipfw set disable 18"
3154 Here if everything goes well, you press control-C before the "sleep"
3155 terminates, and your ruleset will be left active.
3156 Otherwise, e.g.\& if
3157 you cannot access your box, the ruleset will be disabled after
3158 the sleep terminates thus restoring the previous situation.
3160 To show rules of the specific set:
3162 .Dl "ipfw set 18 show"
3164 To show rules of the disabled set:
3166 .Dl "ipfw -S set 18 show"
3168 To clear a specific rule counters of the specific set:
3170 .Dl "ipfw set 18 zero NN"
3172 To delete a specific rule of the specific set:
3174 .Dl "ipfw set 18 delete NN"
3175 .Ss NAT, REDIRECT AND LSNAT
3176 First redirect all the traffic to nat instance 123:
3178 .Dl "ipfw add nat 123 all from any to any"
3180 Then to configure nat instance 123 to alias all the outgoing traffic with ip
3181 192.168.0.123, blocking all incoming connections, trying to keep
3182 same ports on both sides, clearing aliasing table on address change
3183 and keeping a log of traffic/link statistics:
3185 .Dl "ipfw nat 123 config ip 192.168.0.123 log deny_in reset same_ports"
3187 Or to change address of instance 123, aliasing table will be cleared (see
3190 .Dl "ipfw nat 123 config ip 10.0.0.1"
3192 To see configuration of nat instance 123:
3194 .Dl "ipfw nat 123 show config"
3196 To show logs of all the instances in range 111-999:
3198 .Dl "ipfw nat 111-999 show"
3200 To see configurations of all instances:
3202 .Dl "ipfw nat show config"
3204 Or a redirect rule with mixed modes could looks like:
3206 .Dl "ipfw nat 123 config redirect_addr 10.0.0.1 10.0.0.66"
3207 .Dl " redirect_port tcp 192.168.0.1:80 500"
3208 .Dl " redirect_proto udp 192.168.1.43 192.168.1.1"
3209 .Dl " redirect_addr 192.168.0.10,192.168.0.11"
3210 .Dl " 10.0.0.100 # LSNAT"
3211 .Dl " redirect_port tcp 192.168.0.1:80,192.168.0.10:22"
3214 or it could be split in:
3216 .Dl "ipfw nat 1 config redirect_addr 10.0.0.1 10.0.0.66"
3217 .Dl "ipfw nat 2 config redirect_port tcp 192.168.0.1:80 500"
3218 .Dl "ipfw nat 3 config redirect_proto udp 192.168.1.43 192.168.1.1"
3219 .Dl "ipfw nat 4 config redirect_addr 192.168.0.10,192.168.0.11,192.168.0.12"
3221 .Dl "ipfw nat 5 config redirect_port tcp"
3222 .Dl " 192.168.0.1:80,192.168.0.10:22,192.168.0.20:25 500"
3244 utility first appeared in
3249 Stateful extensions were introduced in
3252 was introduced in Summer 2002.
3254 .An Ugen J. S. Antsilevich ,
3255 .An Poul-Henning Kamp ,
3261 API based upon code written by
3265 Dummynet has been introduced by Luigi Rizzo in 1997-1998.
3267 Some early work (1999-2000) on the
3269 traffic shaper supported by Akamba Corp.
3271 The ipfw core (ipfw2) has been completely redesigned and
3272 reimplemented by Luigi Rizzo in summer 2002. Further
3274 options have been added by various developer over the years.
3277 In-kernel NAT support written by
3278 .An Paolo Pisati Aq piso@FreeBSD.org
3279 as part of a Summer of Code 2005 project.
3283 support has been developed by
3284 .An The Centre for Advanced Internet Architectures (CAIA) Aq http://www.caia.swin.edu.au .
3285 The primary developers and maintainers are David Hayes and Jason But.
3286 For further information visit:
3287 .Aq http://www.caia.swin.edu.au/urp/SONATA
3289 Delay profiles have been developed by Alessandro Cerri and
3290 Luigi Rizzo, supported by the
3291 European Commission within Projects Onelab and Onelab2.
3293 The syntax has grown over the years and sometimes it might be confusing.
3294 Unfortunately, backward compatibility prevents cleaning up mistakes
3295 made in the definition of the syntax.
3299 Misconfiguring the firewall can put your computer in an unusable state,
3300 possibly shutting down network services and requiring console access to
3301 regain control of it.
3303 Incoming packet fragments diverted by
3305 are reassembled before delivery to the socket.
3306 The action used on those packet is the one from the
3307 rule which matches the first fragment of the packet.
3309 Packets diverted to userland, and then reinserted by a userland process
3310 may lose various packet attributes.
3311 The packet source interface name
3312 will be preserved if it is shorter than 8 bytes and the userland process
3313 saves and reuses the sockaddr_in
3316 otherwise, it may be lost.
3317 If a packet is reinserted in this manner, later rules may be incorrectly
3318 applied, making the order of
3320 rules in the rule sequence very important.
3322 Dummynet drops all packets with IPv6 link-local addresses.
3328 may not behave as expected.
3329 In particular, incoming SYN packets may
3330 have no uid or gid associated with them since they do not yet belong
3331 to a TCP connection, and the uid/gid associated with a packet may not
3332 be as expected if the associated process calls
3334 or similar system calls.
3336 Rule syntax is subject to the command line environment and some patterns
3337 may need to be escaped with the backslash character
3338 or quoted appropriately.
3340 Due to the architecture of
3342 ipfw nat is not compatible with the TCP segmentation offloading (TSO).
3343 Thus, to reliably nat your network traffic, please disable TSO
3347 ICMP error messages are not implicitly matched by dynamic rules
3348 for the respective conversations.
3349 To avoid failures of network error detection and path MTU discovery,
3350 ICMP error messages may need to be allowed explicitly through static
3357 actions may lead to confusing behaviour if ruleset has mistakes,
3358 and/or interaction with other subsystems (netgraph, dummynet, etc.) is used.
3359 One possible case for this is packet leaving
3361 in subroutine on the input pass, while later on output encountering unpaired
3364 As the call stack is kept intact after input pass, packet will suddenly
3365 return to the rule number used on input pass, not on output one.
3366 Order of processing should be checked carefully to avoid such mistakes.