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
45 .Brq Cm firewall | altq | one_pass | debug | verbose | dyn_keepalive
48 .Brq Cm firewall | altq | one_pass | debug | verbose | dyn_keepalive
51 .Oo Cm set Ar N Oc Cm table Ar name Cm create Ar create-options
53 .Oo Cm set Ar N Oc Cm table
57 .Oo Cm set Ar N Oc Cm table Ar name Cm modify Ar modify-options
59 .Oo Cm set Ar N Oc Cm table Ar name Cm swap Ar name
61 .Oo Cm set Ar N Oc Cm table Ar name Cm add Ar table-key Op Ar value
63 .Oo Cm set Ar N Oc Cm table Ar name Cm add Op Ar table-key Ar value ...
65 .Oo Cm set Ar N Oc Cm table Ar name Cm atomic add Op Ar table-key Ar value ...
67 .Oo Cm set Ar N Oc Cm table Ar name Cm delete Op Ar table-key ...
69 .Oo Cm set Ar N Oc Cm table Ar name Cm lookup Ar addr
71 .Oo Cm set Ar N Oc Cm table Ar name Cm lock
73 .Oo Cm set Ar N Oc Cm table Ar name Cm unlock
75 .Oo Cm set Ar N Oc Cm table
79 .Oo Cm set Ar N Oc Cm table
83 .Oo Cm set Ar N Oc Cm table
87 .Oo Cm set Ar N Oc Cm table
90 .Ss DUMMYNET CONFIGURATION (TRAFFIC SHAPER AND PACKET SCHEDULER)
92 .Brq Cm pipe | queue | sched
98 .Brq Cm pipe | queue | sched
99 .Brq Cm delete | list | show
108 .Ss STATEFUL IPv6/IPv4 NETWORK ADDRESS AND PROTOCOL TRANSLATION
110 .Oo Cm set Ar N Oc Cm nat64lsn Ar name Cm create Ar create-options
112 .Oo Cm set Ar N Oc Cm nat64lsn Ar name Cm config Ar config-options
114 .Oo Cm set Ar N Oc Cm nat64lsn
119 .Oo Cm set Ar N Oc Cm nat64lsn
123 .Oo Cm set Ar N Oc Cm nat64lsn Ar name Cm stats Op Cm reset
124 .Ss STATELESS IPv6/IPv4 NETWORK ADDRESS AND PROTOCOL TRANSLATION
126 .Oo Cm set Ar N Oc Cm nat64stl Ar name Cm create Ar create-options
128 .Oo Cm set Ar N Oc Cm nat64stl Ar name Cm config Ar config-options
130 .Oo Cm set Ar N Oc Cm nat64stl
134 .Oo Cm set Ar N Oc Cm nat64stl
138 .Oo Cm set Ar N Oc Cm nat64stl Ar name Cm stats Op Cm reset
139 .Ss IPv6-to-IPv6 NETWORK PREFIX TRANSLATION
141 .Oo Cm set Ar N Oc Cm nptv6 Ar name Cm create Ar create-options
143 .Oo Cm set Ar N Oc Cm nptv6
147 .Oo Cm set Ar N Oc Cm nptv6
151 .Oo Cm set Ar N Oc Cm nptv6 Ar name Cm stats Op Cm reset
152 .Ss INTERNAL DIAGNOSTICS
159 .Ss LIST OF RULES AND PREPROCESSING
172 utility is the user interface for controlling the
176 traffic shaper/packet scheduler, and the
177 in-kernel NAT services.
179 A firewall configuration, or
183 numbered from 1 to 65535.
184 Packets are passed to the firewall
185 from a number of different places in the protocol stack
186 (depending on the source and destination of the packet,
187 it is possible for the firewall to be
188 invoked multiple times on the same packet).
189 The packet passed to the firewall is compared
190 against each of the rules in the
193 (multiple rules with the same number are permitted, in which case
194 they are processed in order of insertion).
195 When a match is found, the action corresponding to the
196 matching rule is performed.
198 Depending on the action and certain system settings, packets
199 can be reinjected into the firewall at some rule after the
200 matching one for further processing.
202 A ruleset always includes a
204 rule (numbered 65535) which cannot be modified or deleted,
205 and matches all packets.
206 The action associated with the
212 depending on how the kernel is configured.
214 If the ruleset includes one or more rules with the
221 the firewall will have a
223 behaviour, i.e., upon a match it will create
225 i.e., rules that match packets with the same 5-tuple
226 (protocol, source and destination addresses and ports)
227 as the packet which caused their creation.
228 Dynamic rules, which have a limited lifetime, are checked
229 at the first occurrence of a
234 rule, and are typically used to open the firewall on-demand to
235 legitimate traffic only.
242 for all packets (not only these matched by the rule) but
249 .Sx STATEFUL FIREWALL
252 Sections below for more information on the stateful behaviour of
255 All rules (including dynamic ones) have a few associated counters:
256 a packet count, a byte count, a log count and a timestamp
257 indicating the time of the last match.
258 Counters can be displayed or reset with
262 Each rule belongs to one of 32 different
266 commands to atomically manipulate sets, such as enable,
267 disable, swap sets, move all rules in a set to another
268 one, delete all rules in a set.
269 These can be useful to
270 install temporary configurations, or to test them.
273 for more information on
276 Rules can be added with the
278 command; deleted individually or in groups with the
280 command, and globally (except those in set 31) with the
282 command; displayed, optionally with the content of the
288 Finally, counters can be reset with the
295 The following general options are available when invoking
297 .Bl -tag -width indent
299 Show counter values when listing rules.
302 command implies this option.
304 Only show the action and the comment, not the body of a rule.
308 When entering or showing rules, print them in compact form,
309 i.e., omitting the "ip from any to any" string
310 when this does not carry any additional information.
312 When listing, show dynamic rules in addition to static ones.
314 When listing, show only dynamic states.
315 When deleting, delete only dynamic states.
317 Run without prompting for confirmation for commands that can cause problems if misused,
320 If there is no tty associated with the process, this is implied.
323 command with this flag ignores possible errors,
324 i.e., nonexistent rule number.
325 And for batched commands execution continues with the next command.
327 When listing a table (see the
329 section below for more information on lookup tables), format values
331 By default, values are shown as integers.
333 Only check syntax of the command strings, without actually passing
336 Try to resolve addresses and service names in output.
338 Be quiet when executing the
348 This is useful when updating rulesets by executing multiple
352 .Ql sh\ /etc/rc.firewall ) ,
353 or by processing a file with many
355 rules across a remote login session.
356 It also stops a table add or delete
357 from failing if the entry already exists or is not present.
359 The reason why this option may be important is that
360 for some of these actions,
362 may print a message; if the action results in blocking the
363 traffic to the remote client,
364 the remote login session will be closed
365 and the rest of the ruleset will not be processed.
366 Access to the console would then be required to recover.
368 When listing rules, show the
370 each rule belongs to.
371 If this flag is not specified, disabled rules will not be
374 When listing pipes, sort according to one of the four
375 counters (total or current packets or bytes).
377 When listing, show last match timestamp converted with ctime().
379 When listing, show last match timestamp as seconds from the epoch.
380 This form can be more convenient for postprocessing by scripts.
382 .Ss LIST OF RULES AND PREPROCESSING
383 To ease configuration, rules can be put into a file which is
386 as shown in the last synopsis line.
390 The file will be read line by line and applied as arguments to the
394 Optionally, a preprocessor can be specified using
398 is to be piped through.
399 Useful preprocessors include
405 does not start with a slash
407 as its first character, the usual
409 name search is performed.
410 Care should be taken with this in environments where not all
411 file systems are mounted (yet) by the time
413 is being run (e.g.\& when they are mounted over NFS).
416 has been specified, any additional arguments are passed on to the preprocessor
418 This allows for flexible configuration files (like conditionalizing
419 them on the local hostname) and the use of macros to centralize
420 frequently required arguments like IP addresses.
421 .Ss TRAFFIC SHAPER CONFIGURATION
427 commands are used to configure the traffic shaper and packet scheduler.
429 .Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION
430 Section below for details.
432 If the world and the kernel get out of sync the
434 ABI may break, preventing you from being able to add any rules.
435 This can adversely affect the booting process.
440 to temporarily disable the firewall to regain access to the network,
441 allowing you to fix the problem.
443 A packet is checked against the active ruleset in multiple places
444 in the protocol stack, under control of several sysctl variables.
445 These places and variables are shown below, and it is important to
446 have this picture in mind in order to design a correct ruleset.
447 .Bd -literal -offset indent
450 +----------->-----------+
452 [ip(6)_input] [ip(6)_output] net.inet(6).ip(6).fw.enable=1
455 [ether_demux] [ether_output_frame] net.link.ether.ipfw=1
457 +-->--[bdg_forward]-->--+ net.link.bridge.ipfw=1
463 times the same packet goes through the firewall can
464 vary between 0 and 4 depending on packet source and
465 destination, and system configuration.
467 Note that as packets flow through the stack, headers can be
468 stripped or added to it, and so they may or may not be available
470 E.g., incoming packets will include the MAC header when
474 but the same packets will have the MAC header stripped off when
481 Also note that each packet is always checked against the complete ruleset,
482 irrespective of the place where the check occurs, or the source of the packet.
483 If a rule contains some match patterns or actions which are not valid
484 for the place of invocation (e.g.\& trying to match a MAC header within
488 the match pattern will not match, but a
490 operator in front of such patterns
494 match on those packets.
495 It is thus the responsibility of
496 the programmer, if necessary, to write a suitable ruleset to
497 differentiate among the possible places.
499 rules can be useful here, as an example:
500 .Bd -literal -offset indent
501 # packets from ether_demux or bdg_forward
502 ipfw add 10 skipto 1000 all from any to any layer2 in
503 # packets from ip_input
504 ipfw add 10 skipto 2000 all from any to any not layer2 in
505 # packets from ip_output
506 ipfw add 10 skipto 3000 all from any to any not layer2 out
507 # packets from ether_output_frame
508 ipfw add 10 skipto 4000 all from any to any layer2 out
511 (yes, at the moment there is no way to differentiate between
512 ether_demux and bdg_forward).
514 Also note that only actions
523 frames and all other actions act as if they were
526 Full set of actions is supported for IP packets without
531 action does not divert
535 In general, each keyword or argument must be provided as
536 a separate command line argument, with no leading or trailing
538 Keywords are case-sensitive, whereas arguments may
539 or may not be case-sensitive depending on their nature
540 (e.g.\& uid's are, hostnames are not).
542 Some arguments (e.g., port or address lists) are comma-separated
544 In this case, spaces after commas ',' are allowed to make
545 the line more readable.
546 You can also put the entire
547 command (including flags) into a single argument.
548 E.g., the following forms are equivalent:
549 .Bd -literal -offset indent
550 ipfw -q add deny src-ip 10.0.0.0/24,127.0.0.1/8
551 ipfw -q add deny src-ip 10.0.0.0/24, 127.0.0.1/8
552 ipfw "-q add deny src-ip 10.0.0.0/24, 127.0.0.1/8"
555 The format of firewall rules is the following:
556 .Bd -ragged -offset indent
559 .Op Cm set Ar set_number
560 .Op Cm prob Ar match_probability
562 .Op Cm log Op Cm logamount Ar number
572 where the body of the rule specifies which information is used
573 for filtering packets, among the following:
575 .Bl -tag -width "Source and dest. addresses and ports" -offset XXX -compact
576 .It Layer-2 header fields
578 .It IPv4 and IPv6 Protocol
579 SCTP, TCP, UDP, ICMP, etc.
580 .It Source and dest. addresses and ports
584 .It Transmit and receive interface
586 .It Misc. IP header fields
587 Version, type of service, datagram length, identification,
588 fragment flag (non-zero IP offset),
591 .It IPv6 Extension headers
592 Fragmentation, Hop-by-Hop options,
593 Routing Headers, Source routing rthdr0, Mobile IPv6 rthdr2, IPSec options.
595 .It Misc. TCP header fields
596 TCP flags (SYN, FIN, ACK, RST, etc.),
597 sequence number, acknowledgment number,
605 When the packet can be associated with a local socket.
607 Whether a packet came from a divert socket (e.g.,
609 .It Fib annotation state
610 Whether a packet has been tagged for using a specific FIB (routing table)
611 in future forwarding decisions.
614 Note that some of the above information, e.g.\& source MAC or IP addresses and
615 TCP/UDP ports, can be easily spoofed, so filtering on those fields
616 alone might not guarantee the desired results.
617 .Bl -tag -width indent
619 Each rule is associated with a
621 in the range 1..65535, with the latter reserved for the
624 Rules are checked sequentially by rule number.
625 Multiple rules can have the same number, in which case they are
626 checked (and listed) according to the order in which they have
628 If a rule is entered without specifying a number, the kernel will
629 assign one in such a way that the rule becomes the last one
633 Automatic rule numbers are assigned by incrementing the last
634 non-default rule number by the value of the sysctl variable
635 .Ar net.inet.ip.fw.autoinc_step
636 which defaults to 100.
637 If this is not possible (e.g.\& because we would go beyond the
638 maximum allowed rule number), the number of the last
639 non-default value is used instead.
640 .It Cm set Ar set_number
641 Each rule is associated with a
644 Sets can be individually disabled and enabled, so this parameter
645 is of fundamental importance for atomic ruleset manipulation.
646 It can be also used to simplify deletion of groups of rules.
647 If a rule is entered without specifying a set number,
650 Set 31 is special in that it cannot be disabled,
651 and rules in set 31 are not deleted by the
653 command (but you can delete them with the
654 .Nm ipfw delete set 31
656 Set 31 is also used for the
659 .It Cm prob Ar match_probability
660 A match is only declared with the specified probability
661 (floating point number between 0 and 1).
662 This can be useful for a number of applications such as
663 random packet drop or
666 to simulate the effect of multiple paths leading to out-of-order
669 Note: this condition is checked before any other condition, including
676 .It Cm log Op Cm logamount Ar number
677 Packets matching a rule with the
679 keyword will be made available for logging in two ways:
680 if the sysctl variable
681 .Va net.inet.ip.fw.verbose
682 is set to 0 (default), one can use
687 This pseudo interface can be created manually after a system
688 boot by using the following command:
689 .Bd -literal -offset indent
690 # ifconfig ipfw0 create
693 Or, automatically at boot time by adding the following
697 .Bd -literal -offset indent
701 There is zero overhead when no
703 is attached to the pseudo interface.
706 .Va net.inet.ip.fw.verbose
707 is set to 1, packets will be logged to
711 facility up to a maximum of
716 is specified, the limit is taken from the sysctl variable
717 .Va net.inet.ip.fw.verbose_limit .
718 In both cases, a value of 0 means unlimited logging.
720 Once the limit is reached, logging can be re-enabled by
721 clearing the logging counter or the packet counter for that entry, see the
725 Note: logging is done after all other packet matching conditions
726 have been successfully verified, and before performing the final
727 action (accept, deny, etc.) on the packet.
729 When a packet matches a rule with the
731 keyword, the numeric tag for the given
733 in the range 1..65534 will be attached to the packet.
734 The tag acts as an internal marker (it is not sent out over
735 the wire) that can be used to identify these packets later on.
736 This can be used, for example, to provide trust between interfaces
737 and to start doing policy-based filtering.
738 A packet can have multiple tags at the same time.
739 Tags are "sticky", meaning once a tag is applied to a packet by a
740 matching rule it exists until explicit removal.
741 Tags are kept with the packet everywhere within the kernel, but are
742 lost when packet leaves the kernel, for example, on transmitting
743 packet out to the network or sending packet to a
747 To check for previously applied tags, use the
750 To delete previously applied tag, use the
754 Note: since tags are kept with the packet everywhere in kernelspace,
755 they can be set and unset anywhere in the kernel network subsystem
758 facility), not only by means of the
764 For example, there can be a specialized
766 node doing traffic analyzing and tagging for later inspecting
768 .It Cm untag Ar number
769 When a packet matches a rule with the
771 keyword, the tag with the number
773 is searched among the tags attached to this packet and,
774 if found, removed from it.
775 Other tags bound to packet, if present, are left untouched.
777 When a packet matches a rule with the
779 keyword, the ALTQ identifier for the given
784 Note that this ALTQ tag is only meaningful for packets going "out" of IPFW,
785 and not being rejected or going to divert sockets.
786 Note that if there is insufficient memory at the time the packet is
787 processed, it will not be tagged, so it is wise to make your ALTQ
788 "default" queue policy account for this.
791 rules match a single packet, only the first one adds the ALTQ classification
793 In doing so, traffic may be shaped by using
794 .Cm count Cm altq Ar queue
795 rules for classification early in the ruleset, then later applying
796 the filtering decision.
801 rules may come later and provide the actual filtering decisions in
802 addition to the fallback ALTQ tag.
806 to set up the queues before IPFW will be able to look them up by name,
807 and if the ALTQ disciplines are rearranged, the rules in containing the
808 queue identifiers in the kernel will likely have gone stale and need
810 Stale queue identifiers will probably result in misclassification.
812 All system ALTQ processing can be turned on or off via
817 .Cm disable Ar altq .
819 .Va net.inet.ip.fw.one_pass
820 is irrelevant to ALTQ traffic shaping, as the actual rule action is followed
821 always after adding an ALTQ tag.
824 A rule can be associated with one of the following actions, which
825 will be executed when the packet matches the body of the rule.
826 .Bl -tag -width indent
827 .It Cm allow | accept | pass | permit
828 Allow packets that match rule.
829 The search terminates.
830 .It Cm check-state Op Ar :flowname | Cm :any
831 Checks the packet against the dynamic ruleset.
832 If a match is found, execute the action associated with
833 the rule which generated this dynamic rule, otherwise
834 move to the next rule.
837 rules do not have a body.
840 rule is found, the dynamic ruleset is checked at the first
847 is symbolic name assigned to dynamic rule by
852 can be used to ignore states flowname when matching.
855 keyword is special name used for compatibility with old rulesets.
857 Update counters for all packets that match rule.
858 The search continues with the next rule.
860 Discard packets that match this rule.
861 The search terminates.
862 .It Cm divert Ar port
863 Divert packets that match this rule to the
867 The search terminates.
868 .It Cm fwd | forward Ar ipaddr | tablearg Ns Op , Ns Ar port
869 Change the next-hop on matching packets to
871 which can be an IP address or a host name.
872 The next hop can also be supplied by the last table
873 looked up for the packet by using the
875 keyword instead of an explicit address.
876 The search terminates if this rule matches.
880 is a local address, then matching packets will be forwarded to
882 (or the port number in the packet if one is not specified in the rule)
883 on the local machine.
887 is not a local address, then the port number
888 (if specified) is ignored, and the packet will be
889 forwarded to the remote address, using the route as found in
890 the local routing table for that IP.
894 rule will not match layer-2 packets (those received
895 on ether_input, ether_output, or bridged).
899 action does not change the contents of the packet at all.
900 In particular, the destination address remains unmodified, so
901 packets forwarded to another system will usually be rejected by that system
902 unless there is a matching rule on that system to capture them.
903 For packets forwarded locally,
904 the local address of the socket will be
905 set to the original destination address of the packet.
908 entry look rather weird but is intended for
909 use with transparent proxy servers.
910 .It Cm nat Ar nat_nr | tablearg
913 (for network address translation, address redirect, etc.):
915 .Sx NETWORK ADDRESS TRANSLATION (NAT)
916 Section for further information.
917 .It Cm nat64lsn Ar name
918 Pass packet to a stateful NAT64 instance (for IPv6/IPv4 network address and
919 protocol translation): see the
920 .Sx IPv6/IPv4 NETWORK ADDRESS AND PROTOCOL TRANSLATION
921 Section for further information.
922 .It Cm nat64stl Ar name
923 Pass packet to a stateless NAT64 instance (for IPv6/IPv4 network address and
924 protocol translation): see the
925 .Sx IPv6/IPv4 NETWORK ADDRESS AND PROTOCOL TRANSLATION
926 Section for further information.
928 Pass packet to a NPTv6 instance (for IPv6-to-IPv6 network prefix translation):
930 .Sx IPv6-to-IPv6 NETWORK PREFIX TRANSLATION (NPTv6)
931 Section for further information.
932 .It Cm pipe Ar pipe_nr
936 (for bandwidth limitation, delay, etc.).
938 .Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION
939 Section for further information.
940 The search terminates; however, on exit from the pipe and if
944 .Va net.inet.ip.fw.one_pass
945 is not set, the packet is passed again to the firewall code
946 starting from the next rule.
947 .It Cm queue Ar queue_nr
951 (for bandwidth limitation using WF2Q+).
957 Discard packets that match this rule, and if the
958 packet is a TCP packet, try to send a TCP reset (RST) notice.
959 The search terminates.
961 Discard packets that match this rule, and if the
962 packet is a TCP packet, try to send a TCP reset (RST) notice.
963 The search terminates.
964 .It Cm skipto Ar number | tablearg
965 Skip all subsequent rules numbered less than
967 The search continues with the first rule numbered
970 It is possible to use the
972 keyword with a skipto for a
974 skipto. Skipto may work either in O(log(N)) or in O(1) depending
975 on amount of memory and/or sysctl variables.
978 section for more details.
979 .It Cm call Ar number | tablearg
980 The current rule number is saved in the internal stack and
981 ruleset processing continues with the first rule numbered
984 If later a rule with the
986 action is encountered, the processing returns to the first rule
989 rule plus one or higher
990 (the same behaviour as with packets returning from
995 This could be used to make somewhat like an assembly language
997 calls to rules with common checks for different interfaces, etc.
999 Rule with any number could be called, not just forward jumps as with
1001 So, to prevent endless loops in case of mistakes, both
1005 actions don't do any jumps and simply go to the next rule if memory
1006 cannot be allocated or stack overflowed/underflowed.
1008 Internally stack for rule numbers is implemented using
1010 facility and currently has size of 16 entries.
1011 As mbuf tags are lost when packet leaves the kernel,
1013 should not be used in subroutines to avoid endless loops
1014 and other undesired effects.
1016 Takes rule number saved to internal stack by the last
1018 action and returns ruleset processing to the first rule
1019 with number greater than number of corresponding
1022 See description of the
1024 action for more details.
1030 and thus are unconditional, but
1032 command-line utility currently requires every action except
1035 While it is sometimes useful to return only on some packets,
1036 usually you want to print just
1039 A workaround for this is to use new syntax and
1042 .Bd -literal -offset indent
1043 # Add a rule without actual body
1044 ipfw add 2999 return via any
1046 # List rules without "from any to any" part
1050 This cosmetic annoyance may be fixed in future releases.
1052 Send a copy of packets matching this rule to the
1054 socket bound to port
1056 The search continues with the next rule.
1057 .It Cm unreach Ar code
1058 Discard packets that match this rule, and try to send an ICMP
1059 unreachable notice with code
1063 is a number from 0 to 255, or one of these aliases:
1064 .Cm net , host , protocol , port ,
1065 .Cm needfrag , srcfail , net-unknown , host-unknown ,
1066 .Cm isolated , net-prohib , host-prohib , tosnet ,
1067 .Cm toshost , filter-prohib , host-precedence
1069 .Cm precedence-cutoff .
1070 The search terminates.
1071 .It Cm unreach6 Ar code
1072 Discard packets that match this rule, and try to send an ICMPv6
1073 unreachable notice with code
1077 is a number from 0, 1, 3 or 4, or one of these aliases:
1078 .Cm no-route, admin-prohib, address
1081 The search terminates.
1082 .It Cm netgraph Ar cookie
1083 Divert packet into netgraph with given
1085 The search terminates.
1086 If packet is later returned from netgraph it is either
1087 accepted or continues with the next rule, depending on
1088 .Va net.inet.ip.fw.one_pass
1090 .It Cm ngtee Ar cookie
1091 A copy of packet is diverted into netgraph, original
1092 packet continues with the next rule.
1095 for more information on
1100 .It Cm setfib Ar fibnum | tablearg
1101 The packet is tagged so as to use the FIB (routing table)
1103 in any subsequent forwarding decisions.
1104 In the current implementation, this is limited to the values 0 through 15, see
1106 Processing continues at the next rule.
1107 It is possible to use the
1109 keyword with setfib.
1110 If the tablearg value is not within the compiled range of fibs,
1111 the packet's fib is set to 0.
1112 .It Cm setdscp Ar DSCP | number | tablearg
1113 Set specified DiffServ codepoint for an IPv4/IPv6 packet.
1114 Processing continues at the next rule.
1115 Supported values are:
1161 Additionally, DSCP value can be specified by number (0..63).
1162 It is also possible to use the
1164 keyword with setdscp.
1165 If the tablearg value is not within the 0..63 range, lower 6 bits of supplied
1167 .It Cm tcp-setmss Ar mss
1168 Set the Maximum Segment Size (MSS) in the TCP segment to value
1172 should be loaded or kernel should have
1173 .Cm options IPFIREWALL_PMOD
1174 to be able use this action.
1175 This command does not change a packet if original MSS value is lower than
1177 Both TCP over IPv4 and over IPv6 are supported.
1178 Regardless of matched a packet or not by the
1180 rule, the search continues with the next rule.
1182 Queue and reassemble IPv4 fragments.
1183 If the packet is not fragmented, counters are updated and
1184 processing continues with the next rule.
1185 If the packet is the last logical fragment, the packet is reassembled and, if
1186 .Va net.inet.ip.fw.one_pass
1187 is set to 0, processing continues with the next rule.
1188 Otherwise, the packet is allowed to pass and the search terminates.
1189 If the packet is a fragment in the middle of a logical group of fragments,
1191 processing stops immediately.
1193 Fragment handling can be tuned via
1194 .Va net.inet.ip.maxfragpackets
1196 .Va net.inet.ip.maxfragsperpacket
1197 which limit, respectively, the maximum number of processable
1198 fragments (default: 800) and
1199 the maximum number of fragments per packet (default: 16).
1201 NOTA BENE: since fragments do not contain port numbers,
1202 they should be avoided with the
1205 Alternatively, direction-based (like
1209 ) and source-based (like
1211 ) match patterns can be used to select fragments.
1213 Usually a simple rule like:
1214 .Bd -literal -offset indent
1215 # reassemble incoming fragments
1216 ipfw add reass all from any to any in
1219 is all you need at the beginning of your ruleset.
1221 Discard packets that match this rule, and if the packet is an SCTP packet,
1222 try to send an SCTP packet containing an ABORT chunk.
1223 The search terminates.
1225 Discard packets that match this rule, and if the packet is an SCTP packet,
1226 try to send an SCTP packet containing an ABORT chunk.
1227 The search terminates.
1230 The body of a rule contains zero or more patterns (such as
1231 specific source and destination addresses or ports,
1232 protocol options, incoming or outgoing interfaces, etc.)
1233 that the packet must match in order to be recognised.
1234 In general, the patterns are connected by (implicit)
1236 operators -- i.e., all must match in order for the
1238 Individual patterns can be prefixed by the
1240 operator to reverse the result of the match, as in
1242 .Dl "ipfw add 100 allow ip from not 1.2.3.4 to any"
1244 Additionally, sets of alternative match patterns
1246 can be constructed by putting the patterns in
1247 lists enclosed between parentheses ( ) or braces { }, and
1250 operator as follows:
1252 .Dl "ipfw add 100 allow ip from { x or not y or z } to any"
1254 Only one level of parentheses is allowed.
1255 Beware that most shells have special meanings for parentheses
1256 or braces, so it is advisable to put a backslash \\ in front of them
1257 to prevent such interpretations.
1259 The body of a rule must in general include a source and destination
1263 can be used in various places to specify that the content of
1264 a required field is irrelevant.
1266 The rule body has the following format:
1267 .Bd -ragged -offset indent
1268 .Op Ar proto Cm from Ar src Cm to Ar dst
1272 The first part (proto from src to dst) is for backward
1273 compatibility with earlier versions of
1277 any match pattern (including MAC headers, IP protocols,
1278 addresses and ports) can be specified in the
1282 Rule fields have the following meaning:
1283 .Bl -tag -width indent
1284 .It Ar proto : protocol | Cm { Ar protocol Cm or ... }
1285 .It Ar protocol : Oo Cm not Oc Ar protocol-name | protocol-number
1286 An IP protocol specified by number or name
1287 (for a complete list see
1288 .Pa /etc/protocols ) ,
1289 or one of the following keywords:
1290 .Bl -tag -width indent
1292 Matches IPv4 packets.
1294 Matches IPv6 packets.
1303 option will be treated as inner protocol.
1311 .Cm { Ar protocol Cm or ... }
1314 is provided for convenience only but its use is deprecated.
1315 .It Ar src No and Ar dst : Bro Cm addr | Cm { Ar addr Cm or ... } Brc Op Oo Cm not Oc Ar ports
1316 An address (or a list, see below)
1317 optionally followed by
1323 with multiple addresses) is provided for convenience only and
1324 its use is discouraged.
1325 .It Ar addr : Oo Cm not Oc Bro
1326 .Cm any | me | me6 |
1327 .Cm table Ns Pq Ar name Ns Op , Ns Ar value
1328 .Ar | addr-list | addr-set
1330 .Bl -tag -width indent
1332 matches any IP address.
1334 matches any IP address configured on an interface in the system.
1336 matches any IPv6 address configured on an interface in the system.
1337 The address list is evaluated at the time the packet is
1339 .It Cm table Ns Pq Ar name Ns Op , Ns Ar value
1340 Matches any IPv4 or IPv6 address for which an entry exists in the lookup table
1342 If an optional 32-bit unsigned
1344 is also specified, an entry will match only if it has this value.
1347 section below for more information on lookup tables.
1349 .It Ar addr-list : ip-addr Ns Op Ns , Ns Ar addr-list
1351 A host or subnet address specified in one of the following ways:
1352 .Bl -tag -width indent
1353 .It Ar numeric-ip | hostname
1354 Matches a single IPv4 address, specified as dotted-quad or a hostname.
1355 Hostnames are resolved at the time the rule is added to the firewall list.
1356 .It Ar addr Ns / Ns Ar masklen
1357 Matches all addresses with base
1359 (specified as an IP address, a network number, or a hostname)
1363 As an example, 1.2.3.4/25 or 1.2.3.0/25 will match
1364 all IP numbers from 1.2.3.0 to 1.2.3.127 .
1365 .It Ar addr Ns : Ns Ar mask
1366 Matches all addresses with base
1368 (specified as an IP address, a network number, or a hostname)
1371 specified as a dotted quad.
1372 As an example, 1.2.3.4:255.0.255.0 or 1.0.3.0:255.0.255.0 will match
1374 This form is advised only for non-contiguous
1376 It is better to resort to the
1377 .Ar addr Ns / Ns Ar masklen
1378 format for contiguous masks, which is more compact and less
1381 .It Ar addr-set : addr Ns Oo Ns / Ns Ar masklen Oc Ns Cm { Ns Ar list Ns Cm }
1382 .It Ar list : Bro Ar num | num-num Brc Ns Op Ns , Ns Ar list
1383 Matches all addresses with base address
1385 (specified as an IP address, a network number, or a hostname)
1386 and whose last byte is in the list between braces { } .
1387 Note that there must be no spaces between braces and
1388 numbers (spaces after commas are allowed).
1389 Elements of the list can be specified as single entries
1393 field is used to limit the size of the set of addresses,
1394 and can have any value between 24 and 32.
1396 it will be assumed as 24.
1398 This format is particularly useful to handle sparse address sets
1399 within a single rule.
1400 Because the matching occurs using a
1401 bitmask, it takes constant time and dramatically reduces
1402 the complexity of rulesets.
1404 As an example, an address specified as 1.2.3.4/24{128,35-55,89}
1405 or 1.2.3.0/24{128,35-55,89}
1406 will match the following IP addresses:
1408 1.2.3.128, 1.2.3.35 to 1.2.3.55, 1.2.3.89 .
1409 .It Ar addr6-list : ip6-addr Ns Op Ns , Ns Ar addr6-list
1411 A host or subnet specified one of the following ways:
1412 .Bl -tag -width indent
1413 .It Ar numeric-ip | hostname
1414 Matches a single IPv6 address as allowed by
1417 Hostnames are resolved at the time the rule is added to the firewall
1419 .It Ar addr Ns / Ns Ar masklen
1420 Matches all IPv6 addresses with base
1422 (specified as allowed by
1428 .It Ar addr Ns / Ns Ar mask
1429 Matches all IPv6 addresses with base
1431 (specified as allowed by
1436 specified as allowed by
1438 As an example, fe::640:0:0/ffff::ffff:ffff:0:0 will match
1440 This form is advised only for non-contiguous
1442 It is better to resort to the
1443 .Ar addr Ns / Ns Ar masklen
1444 format for contiguous masks, which is more compact and less
1448 No support for sets of IPv6 addresses is provided because IPv6 addresses
1449 are typically random past the initial prefix.
1450 .It Ar ports : Bro Ar port | port Ns \&- Ns Ar port Ns Brc Ns Op , Ns Ar ports
1451 For protocols which support port numbers (such as SCTP, TCP and UDP), optional
1453 may be specified as one or more ports or port ranges, separated
1454 by commas but no spaces, and an optional
1459 notation specifies a range of ports (including boundaries).
1463 may be used instead of numeric port values.
1464 The length of the port list is limited to 30 ports or ranges,
1465 though one can specify larger ranges by using an
1469 section of the rule.
1473 can be used to escape the dash
1475 character in a service name (from a shell, the backslash must be
1476 typed twice to avoid the shell itself interpreting it as an escape
1479 .Dl "ipfw add count tcp from any ftp\e\e-data-ftp to any"
1481 Fragmented packets which have a non-zero offset (i.e., not the first
1482 fragment) will never match a rule which has one or more port
1486 option for details on matching fragmented packets.
1488 .Ss RULE OPTIONS (MATCH PATTERNS)
1489 Additional match patterns can be used within
1491 Zero or more of these so-called
1493 can be present in a rule, optionally prefixed by the
1495 operand, and possibly grouped into
1498 The following match patterns can be used (listed in alphabetical order):
1499 .Bl -tag -width indent
1500 .It Cm // this is a comment.
1501 Inserts the specified text as a comment in the rule.
1502 Everything following // is considered as a comment and stored in the rule.
1503 You can have comment-only rules, which are listed as having a
1505 action followed by the comment.
1509 .It Cm defer-immediate-action | defer-action
1510 A rule with this option will not perform normal action
1511 upon a match. This option is intended to be used with
1515 as the dynamic rule, created but ignored on match, will work
1520 .Cm defer-immediate-action
1521 create a dynamic rule and continue with the next rule without actually
1522 performing the action part of this rule. When the rule is later activated
1523 via the state table, the action is performed as usual.
1525 Matches only packets generated by a divert socket.
1526 .It Cm diverted-loopback
1527 Matches only packets coming from a divert socket back into the IP stack
1529 .It Cm diverted-output
1530 Matches only packets going from a divert socket back outward to the IP
1531 stack output for delivery.
1532 .It Cm dst-ip Ar ip-address
1533 Matches IPv4 packets whose destination IP is one of the address(es)
1534 specified as argument.
1535 .It Bro Cm dst-ip6 | dst-ipv6 Brc Ar ip6-address
1536 Matches IPv6 packets whose destination IP is one of the address(es)
1537 specified as argument.
1538 .It Cm dst-port Ar ports
1539 Matches IP packets whose destination port is one of the port(s)
1540 specified as argument.
1542 Matches TCP packets that have the RST or ACK bits set.
1543 .It Cm ext6hdr Ar header
1544 Matches IPv6 packets containing the extended header given by
1546 Supported headers are:
1552 any type of Routing Header
1554 Source routing Routing Header Type 0
1556 Mobile IPv6 Routing Header Type 2
1560 IPSec authentication headers
1562 and IPsec encapsulated security payload headers
1564 .It Cm fib Ar fibnum
1565 Matches a packet that has been tagged to use
1566 the given FIB (routing table) number.
1567 .It Cm flow Ar table Ns Pq Ar name Ns Op , Ns Ar value
1568 Search for the flow entry in lookup table
1570 If not found, the match fails.
1571 Otherwise, the match succeeds and
1573 is set to the value extracted from the table.
1575 This option can be useful to quickly dispatch traffic based on
1576 certain packet fields.
1579 section below for more information on lookup tables.
1580 .It Cm flow-id Ar labels
1581 Matches IPv6 packets containing any of the flow labels given in
1584 is a comma separated list of numeric flow labels.
1586 Matches packets that are fragments and not the first
1587 fragment of an IP datagram.
1588 Note that these packets will not have
1589 the next protocol header (e.g.\& TCP, UDP) so options that look into
1590 these headers cannot match.
1592 Matches all TCP or UDP packets sent by or received for a
1596 may be specified by name or number.
1598 Matches all TCP or UDP packets sent by or received for the
1599 jail whose ID or name is
1601 .It Cm icmptypes Ar types
1602 Matches ICMP packets whose ICMP type is in the list
1604 The list may be specified as any combination of
1605 individual types (numeric) separated by commas.
1606 .Em Ranges are not allowed .
1607 The supported ICMP types are:
1611 destination unreachable
1619 router advertisement
1623 time-to-live exceeded
1635 address mask request
1637 and address mask reply
1639 .It Cm icmp6types Ar types
1640 Matches ICMP6 packets whose ICMP6 type is in the list of
1642 The list may be specified as any combination of
1643 individual types (numeric) separated by commas.
1644 .Em Ranges are not allowed .
1646 Matches incoming or outgoing packets, respectively.
1650 are mutually exclusive (in fact,
1654 .It Cm ipid Ar id-list
1655 Matches IPv4 packets whose
1657 field has value included in
1659 which is either a single value or a list of values or ranges
1660 specified in the same way as
1662 .It Cm iplen Ar len-list
1663 Matches IP packets whose total length, including header and data, is
1666 which is either a single value or a list of values or ranges
1667 specified in the same way as
1669 .It Cm ipoptions Ar spec
1670 Matches packets whose IPv4 header contains the comma separated list of
1671 options specified in
1673 The supported IP options are:
1676 (strict source route),
1678 (loose source route),
1680 (record packet route) and
1683 The absence of a particular option may be denoted
1686 .It Cm ipprecedence Ar precedence
1687 Matches IPv4 packets whose precedence field is equal to
1690 Matches packets that have IPSEC history associated with them
1691 (i.e., the packet comes encapsulated in IPSEC, the kernel
1692 has IPSEC support, and can correctly decapsulate it).
1694 Note that specifying
1696 is different from specifying
1698 as the latter will only look at the specific IP protocol field,
1699 irrespective of IPSEC kernel support and the validity of the IPSEC data.
1701 Further note that this flag is silently ignored in kernels without
1703 It does not affect rule processing when given and the
1704 rules are handled as if with no
1707 .It Cm iptos Ar spec
1708 Matches IPv4 packets whose
1710 field contains the comma separated list of
1711 service types specified in
1713 The supported IP types of service are:
1716 .Pq Dv IPTOS_LOWDELAY ,
1718 .Pq Dv IPTOS_THROUGHPUT ,
1720 .Pq Dv IPTOS_RELIABILITY ,
1722 .Pq Dv IPTOS_MINCOST ,
1724 .Pq Dv IPTOS_ECN_CE .
1725 The absence of a particular type may be denoted
1728 .It Cm dscp spec Ns Op , Ns Ar spec
1729 Matches IPv4/IPv6 packets whose
1731 field value is contained in
1734 Multiple values can be specified via
1735 the comma separated list.
1736 Value can be one of keywords used in
1738 action or exact number.
1739 .It Cm ipttl Ar ttl-list
1740 Matches IPv4 packets whose time to live is included in
1742 which is either a single value or a list of values or ranges
1743 specified in the same way as
1745 .It Cm ipversion Ar ver
1746 Matches IP packets whose IP version field is
1748 .It Cm keep-state Op Ar :flowname
1749 Upon a match, the firewall will create a dynamic rule, whose
1750 default behaviour is to match bidirectional traffic between
1751 source and destination IP/port using the same protocol.
1752 The rule has a limited lifetime (controlled by a set of
1754 variables), and the lifetime is refreshed every time a matching
1758 is used to assign additional to addresses, ports and protocol parameter
1759 to dynamic rule. It can be used for more accurate matching by
1764 keyword is special name used for compatibility with old rulesets.
1766 Matches only layer2 packets, i.e., those passed to
1768 from ether_demux() and ether_output_frame().
1769 .It Cm limit Bro Cm src-addr | src-port | dst-addr | dst-port Brc Ar N Op Ar :flowname
1770 The firewall will only allow
1772 connections with the same
1773 set of parameters as specified in the rule.
1775 of source and destination addresses and ports can be
1777 .It Cm lookup Bro Cm dst-ip | dst-port | src-ip | src-port | uid | jail Brc Ar name
1778 Search an entry in lookup table
1780 that matches the field specified as argument.
1781 If not found, the match fails.
1782 Otherwise, the match succeeds and
1784 is set to the value extracted from the table.
1786 This option can be useful to quickly dispatch traffic based on
1787 certain packet fields.
1790 section below for more information on lookup tables.
1791 .It Cm { MAC | mac } Ar dst-mac src-mac
1792 Match packets with a given
1796 addresses, specified as the
1798 keyword (matching any MAC address), or six groups of hex digits
1799 separated by colons,
1800 and optionally followed by a mask indicating the significant bits.
1801 The mask may be specified using either of the following methods:
1802 .Bl -enum -width indent
1806 followed by the number of significant bits.
1807 For example, an address with 33 significant bits could be specified as:
1809 .Dl "MAC 10:20:30:40:50:60/33 any"
1813 followed by a bitmask specified as six groups of hex digits separated
1815 For example, an address in which the last 16 bits are significant could
1818 .Dl "MAC 10:20:30:40:50:60&00:00:00:00:ff:ff any"
1820 Note that the ampersand character has a special meaning in many shells
1821 and should generally be escaped.
1823 Note that the order of MAC addresses (destination first,
1825 the same as on the wire, but the opposite of the one used for
1827 .It Cm mac-type Ar mac-type
1828 Matches packets whose Ethernet Type field
1829 corresponds to one of those specified as argument.
1831 is specified in the same way as
1833 (i.e., one or more comma-separated single values or ranges).
1834 You can use symbolic names for known values such as
1835 .Em vlan , ipv4, ipv6 .
1836 Values can be entered as decimal or hexadecimal (if prefixed by 0x),
1837 and they are always printed as hexadecimal (unless the
1839 option is used, in which case symbolic resolution will be attempted).
1840 .It Cm proto Ar protocol
1841 Matches packets with the corresponding IP protocol.
1843 Upon a match, the firewall will create a dynamic rule as if
1846 However, this option doesn't imply an implicit
1850 .It Cm recv | xmit | via Brq Ar ifX | Ar if Ns Cm * | Ar table Ns Po Ar name Ns Oo , Ns Ar value Oc Pc | Ar ipno | Ar any
1851 Matches packets received, transmitted or going through,
1852 respectively, the interface specified by exact name
1856 by IP address, or through some interface.
1859 may be used to match interface by its kernel ifindex.
1862 section below for more information on lookup tables.
1866 keyword causes the interface to always be checked.
1873 then only the receive or transmit interface (respectively)
1875 By specifying both, it is possible to match packets based on
1876 both receive and transmit interface, e.g.:
1878 .Dl "ipfw add deny ip from any to any out recv ed0 xmit ed1"
1882 interface can be tested on either incoming or outgoing packets,
1885 interface can only be tested on outgoing packets.
1890 is invalid) whenever
1894 A packet might not have a receive or transmit interface: packets
1895 originating from the local host have no receive interface,
1896 while packets destined for the local host have no transmit
1898 .It Cm set-limit Bro Cm src-addr | src-port | dst-addr | dst-port Brc Ar N
1901 but does not have an implicit
1905 Matches TCP packets that have the SYN bit set but no ACK bit.
1906 This is the short form of
1907 .Dq Li tcpflags\ syn,!ack .
1909 Matches packets that are associated to a local socket and
1910 for which the SO_USER_COOKIE socket option has been set
1911 to a non-zero value.
1912 As a side effect, the value of the
1913 option is made available as
1915 value, which in turn can be used as
1920 .It Cm src-ip Ar ip-address
1921 Matches IPv4 packets whose source IP is one of the address(es)
1922 specified as an argument.
1923 .It Cm src-ip6 Ar ip6-address
1924 Matches IPv6 packets whose source IP is one of the address(es)
1925 specified as an argument.
1926 .It Cm src-port Ar ports
1927 Matches IP packets whose source port is one of the port(s)
1928 specified as argument.
1929 .It Cm tagged Ar tag-list
1930 Matches packets whose tags are included in
1932 which is either a single value or a list of values or ranges
1933 specified in the same way as
1935 Tags can be applied to the packet using
1937 rule action parameter (see it's description for details on tags).
1938 .It Cm tcpack Ar ack
1940 Match if the TCP header acknowledgment number field is set to
1942 .It Cm tcpdatalen Ar tcpdatalen-list
1943 Matches TCP packets whose length of TCP data is
1944 .Ar tcpdatalen-list ,
1945 which is either a single value or a list of values or ranges
1946 specified in the same way as
1948 .It Cm tcpflags Ar spec
1950 Match if the TCP header contains the comma separated list of
1953 The supported TCP flags are:
1962 The absence of a particular flag may be denoted
1965 A rule which contains a
1967 specification can never match a fragmented packet which has
1971 option for details on matching fragmented packets.
1972 .It Cm tcpseq Ar seq
1974 Match if the TCP header sequence number field is set to
1976 .It Cm tcpwin Ar tcpwin-list
1977 Matches TCP packets whose header window field is set to
1979 which is either a single value or a list of values or ranges
1980 specified in the same way as
1982 .It Cm tcpoptions Ar spec
1984 Match if the TCP header contains the comma separated list of
1985 options specified in
1987 The supported TCP options are:
1990 (maximum segment size),
1992 (tcp window advertisement),
1996 (rfc1323 timestamp) and
1998 (rfc1644 t/tcp connection count).
1999 The absence of a particular option may be denoted
2003 Match all TCP or UDP packets sent by or received for a
2007 may be matched by name or identification number.
2009 For incoming packets,
2010 a routing table lookup is done on the packet's source address.
2011 If the interface on which the packet entered the system matches the
2012 outgoing interface for the route,
2014 If the interfaces do not match up,
2015 the packet does not match.
2016 All outgoing packets or packets with no incoming interface match.
2018 The name and functionality of the option is intentionally similar to
2019 the Cisco IOS command:
2021 .Dl ip verify unicast reverse-path
2023 This option can be used to make anti-spoofing rules to reject all
2024 packets with source addresses not from this interface.
2028 For incoming packets,
2029 a routing table lookup is done on the packet's source address.
2030 If a route to the source address exists, but not the default route
2031 or a blackhole/reject route, the packet matches.
2032 Otherwise, the packet does not match.
2033 All outgoing packets match.
2035 The name and functionality of the option is intentionally similar to
2036 the Cisco IOS command:
2038 .Dl ip verify unicast source reachable-via any
2040 This option can be used to make anti-spoofing rules to reject all
2041 packets whose source address is unreachable.
2043 For incoming packets, the packet's source address is checked if it
2044 belongs to a directly connected network.
2045 If the network is directly connected, then the interface the packet
2046 came on in is compared to the interface the network is connected to.
2047 When incoming interface and directly connected interface are not the
2048 same, the packet does not match.
2049 Otherwise, the packet does match.
2050 All outgoing packets match.
2052 This option can be used to make anti-spoofing rules to reject all
2053 packets that pretend to be from a directly connected network but do
2054 not come in through that interface.
2055 This option is similar to but more restricted than
2057 because it engages only on packets with source addresses of directly
2058 connected networks instead of all source addresses.
2061 Lookup tables are useful to handle large sparse sets of
2062 addresses or other search keys (e.g., ports, jail IDs, interface names).
2063 In the rest of this section we will use the term ``key''.
2064 Table name needs to match the following spec:
2066 Tables with the same name can be created in different
2068 However, rule links to the tables in
2071 This behavior can be controlled by
2072 .Va net.inet.ip.fw.tables_sets
2076 section for more information.
2077 There may be up to 65535 different lookup tables.
2079 The following table types are supported:
2080 .Bl -tag -width indent
2081 .It Ar table-type : Ar addr | iface | number | flow
2082 .It Ar table-key : Ar addr Ns Oo / Ns Ar masklen Oc | iface-name | number | flow-spec
2083 .It Ar flow-spec : Ar flow-field Ns Op , Ns Ar flow-spec
2084 .It Ar flow-field : src-ip | proto | src-port | dst-ip | dst-port
2086 matches IPv4 or IPv6 address.
2087 Each entry is represented by an
2088 .Ar addr Ns Op / Ns Ar masklen
2089 and will match all addresses with base
2091 (specified as an IPv4/IPv6 address, or a hostname) and mask width of
2096 is not specified, it defaults to 32 for IPv4 and 128 for IPv6.
2097 When looking up an IP address in a table, the most specific
2100 matches interface names.
2101 Each entry is represented by string treated as interface name.
2102 Wildcards are not supported.
2104 maches protocol ports, uids/gids or jail IDs.
2105 Each entry is represented by 32-bit unsigned integer.
2106 Ranges are not supported.
2108 Matches packet fields specified by
2110 type suboptions with table entries.
2113 Tables require explicit creation via
2117 The following creation options are supported:
2118 .Bl -tag -width indent
2119 .It Ar create-options : Ar create-option | create-options
2120 .It Ar create-option : Cm type Ar table-type | Cm valtype Ar value-mask | Cm algo Ar algo-desc |
2121 .Cm limit Ar number | Cm locked
2127 Table algorithm to use (see below).
2129 Maximum number of items that may be inserted into table.
2131 Restrict any table modifications.
2134 Some of these options may be modified later via
2137 The following options can be changed:
2138 .Bl -tag -width indent
2139 .It Ar modify-options : Ar modify-option | modify-options
2140 .It Ar modify-option : Cm limit Ar number
2142 Alter maximum number of items that may be inserted into table.
2145 Additionally, table can be locked or unlocked using
2153 can be swapped with each other using
2156 Swap may fail if tables limits are set and data exchange
2157 would result in limits hit.
2158 Operation is performed atomically.
2160 One or more entries can be added to a table at once using
2163 Addition of all items are performed atomically.
2164 By default, error in addition of one entry does not influence
2165 addition of other entries. However, non-zero error code is returned
2169 keyword may be specified before
2171 to indicate all-or-none add request.
2173 One or more entries can be removed from a table at once using
2176 By default, error in removal of one entry does not influence
2177 removing of other entries. However, non-zero error code is returned
2180 It may be possible to check what entry will be found on particular
2186 This functionality is optional and may be unsupported in some algorithms.
2188 The following operations can be performed on
2193 .Bl -tag -width indent
2197 Removes all entries.
2199 Shows generic table information.
2201 Shows generic table information and algo-specific data.
2204 The following lookup algorithms are supported:
2205 .Bl -tag -width indent
2206 .It Ar algo-desc : algo-name | "algo-name algo-data"
2207 .It Ar algo-name: Ar addr:radix | addr:hash | iface:array | number:array | flow:hash
2209 Separate Radix trees for IPv4 and IPv6, the same way as the routing table (see
2215 Separate auto-growing hashes for IPv4 and IPv6.
2216 Accepts entries with the same mask length specified initially via
2217 .Cm "addr:hash masks=/v4,/v6"
2218 algorithm creation options.
2219 Assume /32 and /128 masks by default.
2220 Search removes host bits (according to mask) from supplied address and checks
2221 resulting key in appropriate hash.
2222 Mostly optimized for /64 and byte-ranged IPv6 masks.
2224 Array storing sorted indexes for entries which are presented in the system.
2225 Optimized for very fast lookup.
2227 Array storing sorted u32 numbers.
2229 Auto-growing hash storing flow entries.
2230 Search calculates hash on required packet fields and searches for matching
2231 entries in selected bucket.
2236 feature provides the ability to use a value, looked up in the table, as
2237 the argument for a rule action, action parameter or rule option.
2238 This can significantly reduce number of rules in some configurations.
2239 If two tables are used in a rule, the result of the second (destination)
2242 Each record may hold one or more values according to
2244 This mask is set on table creation via
2247 The following value types are supported:
2248 .Bl -tag -width indent
2249 .It Ar value-mask : Ar value-type Ns Op , Ns Ar value-mask
2250 .It Ar value-type : Ar skipto | pipe | fib | nat | dscp | tag | divert |
2251 .Ar netgraph | limit | ipv4
2253 rule number to jump to.
2257 fib number to match/set.
2259 nat number to jump to.
2261 dscp value to match/set.
2263 tag number to match/set.
2265 port number to divert traffic to.
2267 hook number to move packet to.
2269 maximum number of connections.
2271 IPv4 nexthop to fwd packets to.
2273 IPv6 nexthop to fwd packets to.
2278 argument can be used with the following actions:
2279 .Cm nat, pipe , queue, divert, tee, netgraph, ngtee, fwd, skipto, setfib,
2287 action, the user should be aware that the code will walk the ruleset
2288 up to a rule equal to, or past, the given number.
2292 Section for example usage of tables and the tablearg keyword.
2294 Each rule or table belongs to one of 32 different
2297 Set 31 is reserved for the default rule.
2299 By default, rules or tables are put in set 0, unless you use the
2301 attribute when adding a new rule or table.
2302 Sets can be individually and atomically enabled or disabled,
2303 so this mechanism permits an easy way to store multiple configurations
2304 of the firewall and quickly (and atomically) switch between them.
2306 By default, tables from set 0 are referenced when adding rule with
2307 table opcodes regardless of rule set.
2308 This behavior can be changed by setting
2309 .Va net.inet.ip.fw.tables_sets
2311 Rule's set will then be used for table references.
2313 The command to enable/disable sets is
2314 .Bd -ragged -offset indent
2316 .Cm set Oo Cm disable Ar number ... Oc Op Cm enable Ar number ...
2323 sections can be specified.
2324 Command execution is atomic on all the sets specified in the command.
2325 By default, all sets are enabled.
2327 When you disable a set, its rules behave as if they do not exist
2328 in the firewall configuration, with only one exception:
2329 .Bd -ragged -offset indent
2330 dynamic rules created from a rule before it had been disabled
2331 will still be active until they expire.
2333 dynamic rules you have to explicitly delete the parent rule
2334 which generated them.
2337 The set number of rules can be changed with the command
2338 .Bd -ragged -offset indent
2341 .Brq Cm rule Ar rule-number | old-set
2345 Also, you can atomically swap two rulesets with the command
2346 .Bd -ragged -offset indent
2348 .Cm set swap Ar first-set second-set
2353 Section on some possible uses of sets of rules.
2354 .Sh STATEFUL FIREWALL
2355 Stateful operation is a way for the firewall to dynamically
2356 create rules for specific flows when packets that
2357 match a given pattern are detected.
2358 Support for stateful
2359 operation comes through the
2360 .Cm check-state , keep-state , record-state , limit
2366 Dynamic rules are created when a packet matches a
2372 rule, causing the creation of a
2374 rule which will match all and only packets with
2378 .Em src-ip/src-port dst-ip/dst-port
2383 are used here only to denote the initial match addresses, but they
2384 are completely equivalent afterwards).
2390 This name is used in matching together with addresses, ports and protocol.
2391 Dynamic rules will be checked at the first
2392 .Cm check-state, keep-state
2395 occurrence, and the action performed upon a match will be the same
2396 as in the parent rule.
2398 Note that no additional attributes other than protocol and IP addresses
2399 and ports and :flowname are checked on dynamic rules.
2401 The typical use of dynamic rules is to keep a closed firewall configuration,
2402 but let the first TCP SYN packet from the inside network install a
2403 dynamic rule for the flow so that packets belonging to that session
2404 will be allowed through the firewall:
2406 .Dl "ipfw add check-state :OUTBOUND"
2407 .Dl "ipfw add allow tcp from my-subnet to any setup keep-state :OUTBOUND"
2408 .Dl "ipfw add deny tcp from any to any"
2410 A similar approach can be used for UDP, where an UDP packet coming
2411 from the inside will install a dynamic rule to let the response through
2414 .Dl "ipfw add check-state :OUTBOUND"
2415 .Dl "ipfw add allow udp from my-subnet to any keep-state :OUTBOUND"
2416 .Dl "ipfw add deny udp from any to any"
2418 Dynamic rules expire after some time, which depends on the status
2419 of the flow and the setting of some
2423 .Sx SYSCTL VARIABLES
2425 For TCP sessions, dynamic rules can be instructed to periodically
2426 send keepalive packets to refresh the state of the rule when it is
2431 for more examples on how to use dynamic rules.
2432 .Sh TRAFFIC SHAPER (DUMMYNET) CONFIGURATION
2434 is also the user interface for the
2436 traffic shaper, packet scheduler and network emulator, a subsystem that
2437 can artificially queue, delay or drop packets
2438 emulating the behaviour of certain network links
2439 or queueing systems.
2442 operates by first using the firewall to select packets
2443 using any match pattern that can be used in
2446 Matching packets are then passed to either of two
2447 different objects, which implement the traffic regulation:
2448 .Bl -hang -offset XXXX
2454 with given bandwidth and propagation delay,
2455 driven by a FIFO scheduler and a single queue with programmable
2456 queue size and packet loss rate.
2457 Packets are appended to the queue as they come out from
2459 and then transferred in FIFO order to the link at the desired rate.
2463 is an abstraction used to implement packet scheduling
2464 using one of several packet scheduling algorithms.
2467 are first grouped into flows according to a mask on the 5-tuple.
2468 Flows are then passed to the scheduler associated to the
2470 and each flow uses scheduling parameters (weight and others)
2471 as configured in the
2474 A scheduler in turn is connected to an emulated link,
2475 and arbitrates the link's bandwidth among backlogged flows according to
2476 weights and to the features of the scheduling algorithm in use.
2481 can be used to set hard limits to the bandwidth that a flow can use, whereas
2483 can be used to determine how different flows share the available bandwidth.
2485 A graphical representation of the binding of queues,
2486 flows, schedulers and links is below.
2487 .Bd -literal -offset indent
2488 (flow_mask|sched_mask) sched_mask
2489 +---------+ weight Wx +-------------+
2490 | |->-[flow]-->--| |-+
2491 -->--| QUEUE x | ... | | |
2492 | |->-[flow]-->--| SCHEDuler N | |
2494 ... | +--[LINK N]-->--
2495 +---------+ weight Wy | | +--[LINK N]-->--
2496 | |->-[flow]-->--| | |
2497 -->--| QUEUE y | ... | | |
2498 | |->-[flow]-->--| | |
2499 +---------+ +-------------+ |
2502 It is important to understand the role of the SCHED_MASK
2503 and FLOW_MASK, which are configured through the commands
2504 .Dl "ipfw sched N config mask SCHED_MASK ..."
2506 .Dl "ipfw queue X config mask FLOW_MASK ..." .
2508 The SCHED_MASK is used to assign flows to one or more
2509 scheduler instances, one for each
2510 value of the packet's 5-tuple after applying SCHED_MASK.
2511 As an example, using ``src-ip 0xffffff00'' creates one instance
2512 for each /24 destination subnet.
2514 The FLOW_MASK, together with the SCHED_MASK, is used to split
2516 As an example, using
2517 ``src-ip 0x000000ff''
2518 together with the previous SCHED_MASK makes a flow for
2519 each individual source address.
2520 In turn, flows for each /24
2521 subnet will be sent to the same scheduler instance.
2523 The above diagram holds even for the
2525 case, with the only restriction that a
2527 only supports a SCHED_MASK, and forces the use of a FIFO
2528 scheduler (these are for backward compatibility reasons;
2529 in fact, internally, a
2531 pipe is implemented exactly as above).
2533 There are two modes of
2541 mode tries to emulate a real link: the
2543 scheduler ensures that the packet will not leave the pipe faster than it
2544 would on the real link with a given bandwidth.
2547 mode allows certain packets to bypass the
2549 scheduler (if packet flow does not exceed pipe's bandwidth).
2550 This is the reason why the
2552 mode requires less CPU cycles per packet (on average) and packet latency
2553 can be significantly lower in comparison to a real link with the same
2559 mode can be enabled by setting the
2560 .Va net.inet.ip.dummynet.io_fast
2562 variable to a non-zero value.
2564 .Ss PIPE, QUEUE AND SCHEDULER CONFIGURATION
2570 configuration commands are the following:
2571 .Bd -ragged -offset indent
2572 .Cm pipe Ar number Cm config Ar pipe-configuration
2574 .Cm queue Ar number Cm config Ar queue-configuration
2576 .Cm sched Ar number Cm config Ar sched-configuration
2579 The following parameters can be configured for a pipe:
2581 .Bl -tag -width indent -compact
2582 .It Cm bw Ar bandwidth | device
2583 Bandwidth, measured in
2586 .Brq Cm bit/s | Byte/s .
2589 A value of 0 (default) means unlimited bandwidth.
2590 The unit must immediately follow the number, as in
2592 .Dl "ipfw pipe 1 config bw 300Kbit/s"
2594 If a device name is specified instead of a numeric value, as in
2596 .Dl "ipfw pipe 1 config bw tun0"
2598 then the transmit clock is supplied by the specified device.
2599 At the moment only the
2601 device supports this
2602 functionality, for use in conjunction with
2605 .It Cm delay Ar ms-delay
2606 Propagation delay, measured in milliseconds.
2607 The value is rounded to the next multiple of the clock tick
2608 (typically 10ms, but it is a good practice to run kernels
2610 .Dq "options HZ=1000"
2612 the granularity to 1ms or less).
2613 The default value is 0, meaning no delay.
2615 .It Cm burst Ar size
2616 If the data to be sent exceeds the pipe's bandwidth limit
2617 (and the pipe was previously idle), up to
2619 bytes of data are allowed to bypass the
2621 scheduler, and will be sent as fast as the physical link allows.
2622 Any additional data will be transmitted at the rate specified
2626 The burst size depends on how long the pipe has been idle;
2627 the effective burst size is calculated as follows:
2634 .It Cm profile Ar filename
2635 A file specifying the additional overhead incurred in the transmission
2636 of a packet on the link.
2638 Some link types introduce extra delays in the transmission
2639 of a packet, e.g., because of MAC level framing, contention on
2640 the use of the channel, MAC level retransmissions and so on.
2641 From our point of view, the channel is effectively unavailable
2642 for this extra time, which is constant or variable depending
2644 Additionally, packets may be dropped after this
2645 time (e.g., on a wireless link after too many retransmissions).
2646 We can model the additional delay with an empirical curve
2647 that represents its distribution.
2648 .Bd -literal -offset indent
2649 cumulative probability
2659 +-------*------------------->
2662 The empirical curve may have both vertical and horizontal lines.
2663 Vertical lines represent constant delay for a range of
2665 Horizontal lines correspond to a discontinuity in the delay
2666 distribution: the pipe will use the largest delay for a
2669 The file format is the following, with whitespace acting as
2670 a separator and '#' indicating the beginning a comment:
2671 .Bl -tag -width indent
2672 .It Cm name Ar identifier
2673 optional name (listed by "ipfw pipe show")
2674 to identify the delay distribution;
2676 the bandwidth used for the pipe.
2677 If not specified here, it must be present
2678 explicitly as a configuration parameter for the pipe;
2679 .It Cm loss-level Ar L
2680 the probability above which packets are lost.
2681 (0.0 <= L <= 1.0, default 1.0 i.e., no loss);
2683 the number of samples used in the internal
2684 representation of the curve (2..1024; default 100);
2685 .It Cm "delay prob" | "prob delay"
2686 One of these two lines is mandatory and defines
2687 the format of the following lines with data points.
2689 2 or more lines representing points in the curve,
2690 with either delay or probability first, according
2691 to the chosen format.
2692 The unit for delay is milliseconds.
2693 Data points do not need to be sorted.
2694 Also, the number of actual lines can be different
2695 from the value of the "samples" parameter:
2697 utility will sort and interpolate
2698 the curve as needed.
2701 Example of a profile file:
2702 .Bd -literal -offset indent
2707 0 200 # minimum overhead is 200ms
2713 #configuration file end
2717 The following parameters can be configured for a queue:
2719 .Bl -tag -width indent -compact
2720 .It Cm pipe Ar pipe_nr
2721 Connects a queue to the specified pipe.
2722 Multiple queues (with the same or different weights) can be connected to
2723 the same pipe, which specifies the aggregate rate for the set of queues.
2725 .It Cm weight Ar weight
2726 Specifies the weight to be used for flows matching this queue.
2727 The weight must be in the range 1..100, and defaults to 1.
2730 The following case-insensitive parameters can be configured for a
2733 .Bl -tag -width indent -compact
2734 .It Cm type Ar {fifo | wf2q+ | rr | qfq | fq_codel | fq_pie}
2735 specifies the scheduling algorithm to use.
2736 .Bl -tag -width indent -compact
2738 is just a FIFO scheduler (which means that all packets
2739 are stored in the same queue as they arrive to the scheduler).
2740 FIFO has O(1) per-packet time complexity, with very low
2741 constants (estimate 60-80ns on a 2GHz desktop machine)
2742 but gives no service guarantees.
2744 implements the WF2Q+ algorithm, which is a Weighted Fair Queueing
2745 algorithm which permits flows to share bandwidth according to
2747 Note that weights are not priorities; even a flow
2748 with a minuscule weight will never starve.
2749 WF2Q+ has O(log N) per-packet processing cost, where N is the number
2750 of flows, and is the default algorithm used by previous versions
2753 implements the Deficit Round Robin algorithm, which has O(1) processing
2754 costs (roughly, 100-150ns per packet)
2755 and permits bandwidth allocation according to weights, but
2756 with poor service guarantees.
2758 implements the QFQ algorithm, which is a very fast variant of
2759 WF2Q+, with similar service guarantees and O(1) processing
2760 costs (roughly, 200-250ns per packet).
2762 implements the FQ-CoDel (FlowQueue-CoDel) scheduler/AQM algorithm, which
2763 uses a modified Deficit Round Robin scheduler to manage two lists of sub-queues
2764 (old sub-queues and new sub-queues) for providing brief periods of priority to
2765 lightweight or short burst flows.
2766 By default, the total number of sub-queues is 1024.
2767 FQ-CoDel's internal, dynamically
2768 created sub-queues are controlled by separate instances of CoDel AQM.
2770 implements the FQ-PIE (FlowQueue-PIE) scheduler/AQM algorithm, which similar to
2772 but uses per sub-queue PIE AQM instance to control the queue delay.
2776 inherits AQM parameters and options from
2780 inherits AQM parameters and options from
2783 Additionally, both of
2787 have shared scheduler parameters which are:
2788 .Bl -tag -width indent
2791 specifies the quantum (credit) of the scheduler.
2793 is the number of bytes a queue can serve before being moved to the tail
2795 The default is 1514 bytes, and the maximum accepable value
2799 specifies the hard size limit (in unit of packets) of all queues managed by an
2800 instance of the scheduler.
2801 The default value of
2803 is 10240 packets, and the maximum accepable value is 20480 packets.
2806 specifies the total number of flow queues (sub-queues) that fq_*
2807 creates and manages.
2808 By default, 1024 sub-queues are created when an instance
2809 of the fq_{codel/pie} scheduler is created.
2810 The maximum accepable value is
2814 Note that any token after
2818 is considered a parameter for fq_{codel/pie}.
2819 So, ensure all scheduler
2820 configuration options not related to fq_{codel/pie} are written before
2825 In addition to the type, all parameters allowed for a pipe can also
2826 be specified for a scheduler.
2828 Finally, the following parameters can be configured for both
2831 .Bl -tag -width XXXX -compact
2832 .It Cm buckets Ar hash-table-size
2833 Specifies the size of the hash table used for storing the
2835 Default value is 64 controlled by the
2838 .Va net.inet.ip.dummynet.hash_size ,
2839 allowed range is 16 to 65536.
2841 .It Cm mask Ar mask-specifier
2842 Packets sent to a given pipe or queue by an
2844 rule can be further classified into multiple flows, each of which is then
2848 A flow identifier is constructed by masking the IP addresses,
2849 ports and protocol types as specified with the
2851 options in the configuration of the pipe or queue.
2852 For each different flow identifier, a new pipe or queue is created
2853 with the same parameters as the original object, and matching packets
2858 are used, each flow will get the same bandwidth as defined by the pipe,
2861 are used, each flow will share the parent's pipe bandwidth evenly
2862 with other flows generated by the same queue (note that other queues
2863 with different weights might be connected to the same pipe).
2865 Available mask specifiers are a combination of one or more of the following:
2867 .Cm dst-ip Ar mask ,
2868 .Cm dst-ip6 Ar mask ,
2869 .Cm src-ip Ar mask ,
2870 .Cm src-ip6 Ar mask ,
2871 .Cm dst-port Ar mask ,
2872 .Cm src-port Ar mask ,
2873 .Cm flow-id Ar mask ,
2878 where the latter means all bits in all fields are significant.
2881 When a packet is dropped by a
2883 queue or pipe, the error
2884 is normally reported to the caller routine in the kernel, in the
2885 same way as it happens when a device queue fills up.
2887 option reports the packet as successfully delivered, which can be
2888 needed for some experimental setups where you want to simulate
2889 loss or congestion at a remote router.
2891 .It Cm plr Ar packet-loss-rate
2894 .Ar packet-loss-rate
2895 is a floating-point number between 0 and 1, with 0 meaning no
2896 loss, 1 meaning 100% loss.
2897 The loss rate is internally represented on 31 bits.
2899 .It Cm queue Brq Ar slots | size Ns Cm Kbytes
2904 Default value is 50 slots, which
2905 is the typical queue size for Ethernet devices.
2906 Note that for slow speed links you should keep the queue
2907 size short or your traffic might be affected by a significant
2909 E.g., 50 max-sized ethernet packets (1500 bytes) mean 600Kbit
2910 or 20s of queue on a 30Kbit/s pipe.
2911 Even worse effects can result if you get packets from an
2912 interface with a much larger MTU, e.g.\& the loopback interface
2913 with its 16KB packets.
2917 .Em net.inet.ip.dummynet.pipe_byte_limit
2919 .Em net.inet.ip.dummynet.pipe_slot_limit
2920 control the maximum lengths that can be specified.
2922 .It Cm red | gred Ar w_q Ns / Ns Ar min_th Ns / Ns Ar max_th Ns / Ns Ar max_p
2924 Make use of the RED (Random Early Detection) queue management algorithm.
2929 point numbers between 0 and 1 (inclusive), while
2933 are integer numbers specifying thresholds for queue management
2934 (thresholds are computed in bytes if the queue has been defined
2935 in bytes, in slots otherwise).
2936 The two parameters can also be of the same value if needed. The
2938 also supports the gentle RED variant (gred) and ECN (Explicit Congestion
2939 Notification) as optional. Three
2941 variables can be used to control the RED behaviour:
2942 .Bl -tag -width indent
2943 .It Va net.inet.ip.dummynet.red_lookup_depth
2944 specifies the accuracy in computing the average queue
2945 when the link is idle (defaults to 256, must be greater than zero)
2946 .It Va net.inet.ip.dummynet.red_avg_pkt_size
2947 specifies the expected average packet size (defaults to 512, must be
2949 .It Va net.inet.ip.dummynet.red_max_pkt_size
2950 specifies the expected maximum packet size, only used when queue
2951 thresholds are in bytes (defaults to 1500, must be greater than zero).
2954 .It Cm codel Oo Cm target Ar time Oc Oo Cm interval Ar time Oc Oo Cm ecn |
2956 Make use of the CoDel (Controlled-Delay) queue management algorithm.
2958 is interpreted as milliseconds by default but seconds (s), milliseconds (ms) or
2959 microseconds (us) can be specified instead.
2960 CoDel drops or marks (ECN) packets
2961 depending on packet sojourn time in the queue.
2964 (5ms by default) is the minimum acceptable persistent queue delay that CoDel
2966 CoDel does not drop packets directly after packets sojourn time becomes
2973 (100ms default) before dropping.
2976 should be set to maximum RTT for all expected connections.
2978 enables (disabled by default) packet marking (instead of dropping) for
2979 ECN-enabled TCP flows when queue delay becomes high.
2981 Note that any token after
2983 is considered a parameter for CoDel.
2984 So, ensure all pipe/queue
2985 configuration options are written before
2992 .Va net.inet.ip.dummynet.codel.target
2994 .Va net.inet.ip.dummynet.codel.interval
2995 can be used to set CoDel default parameters.
2997 .It Cm pie Oo Cm target Ar time Oc Oo Cm tupdate Ar time Oc Oo
2998 .Cm alpha Ar n Oc Oo Cm beta Ar n Oc Oo Cm max_burst Ar time Oc Oo
2999 .Cm max_ecnth Ar n Oc Oo Cm ecn | Cm noecn Oc Oo Cm capdrop |
3000 .Cm nocapdrop Oc Oo Cm drand | Cm nodrand Oc Oo Cm onoff
3001 .Oc Oo Cm dre | Cm ts Oc
3002 Make use of the PIE (Proportional Integral controller Enhanced) queue management
3004 PIE drops or marks packets depending on a calculated drop probability during
3005 en-queue process, with the aim of achieving high throughput while keeping queue
3007 At regular time intervals of
3010 (15ms by default) a background process (re)calculates the probability based on queue delay
3014 (15ms by default) and queue delay trends.
3015 PIE approximates current queue
3016 delay by using a departure rate estimation method, or (optionally) by using a
3017 packet timestamp method similar to CoDel.
3019 is interpreted as milliseconds by default but seconds (s), milliseconds (ms) or
3020 microseconds (us) can be specified instead.
3021 The other PIE parameters and options are as follows:
3022 .Bl -tag -width indent
3025 is a floating point number between 0 and 7 which specifies the weight of queue
3026 delay deviations that is used in drop probability calculation.
3027 0.125 is the default.
3030 is a floating point number between 0 and 7 which specifies is the weight of queue
3031 delay trend that is used in drop probability calculation.
3032 1.25 is the default.
3033 .It Cm max_burst Ar time
3034 The maximum period of time that PIE does not drop/mark packets.
3036 default and 10s is the maximum value.
3037 .It Cm max_ecnth Ar n
3038 Even when ECN is enabled, PIE drops packets instead of marking them when drop
3039 probability becomes higher than ECN probability threshold
3041 , the default is 0.1 (i.e 10%) and 1 is the maximum value.
3043 enable or disable ECN marking for ECN-enabled TCP flows.
3044 Disabled by default.
3045 .It Cm capdrop | nocapdrop
3046 enable or disable cap drop adjustment.
3047 Cap drop adjustment is enabled by default.
3048 .It Cm drand | nodrand
3049 enable or disable drop probability de-randomisation.
3050 De-randomisation eliminates
3051 the problem of dropping packets too close or too far.
3052 De-randomisation is enabled by default.
3054 enable turning PIE on and off depending on queue load.
3055 If this option is enabled,
3056 PIE turnes on when over 1/3 of queue becomes full.
3057 This option is disabled by
3060 Calculate queue delay using departure rate estimation
3068 Note that any token after
3070 is considered a parameter for PIE.
3071 So ensure all pipe/queue
3072 the configuration options are written before
3076 variables can be used to control the
3080 .Sx SYSCTL VARIABLES
3081 section for more details.
3084 When used with IPv6 data,
3086 currently has several limitations.
3087 Information necessary to route link-local packets to an
3088 interface is not available after processing by
3090 so those packets are dropped in the output path.
3091 Care should be taken to ensure that link-local packets are not passed to
3094 Here are some important points to consider when designing your
3098 Remember that you filter both packets going
3102 Most connections need packets going in both directions.
3104 Remember to test very carefully.
3105 It is a good idea to be near the console when doing this.
3106 If you cannot be near the console,
3107 use an auto-recovery script such as the one in
3108 .Pa /usr/share/examples/ipfw/change_rules.sh .
3110 Do not forget the loopback interface.
3115 There are circumstances where fragmented datagrams are unconditionally
3117 TCP packets are dropped if they do not contain at least 20 bytes of
3118 TCP header, UDP packets are dropped if they do not contain a full 8
3119 byte UDP header, and ICMP packets are dropped if they do not contain
3120 4 bytes of ICMP header, enough to specify the ICMP type, code, and
3122 These packets are simply logged as
3124 since there may not be enough good data in the packet to produce a
3125 meaningful log entry.
3127 Another type of packet is unconditionally dropped, a TCP packet with a
3128 fragment offset of one.
3129 This is a valid packet, but it only has one use, to try
3130 to circumvent firewalls.
3131 When logging is enabled, these packets are
3132 reported as being dropped by rule -1.
3134 If you are logged in over a network, loading the
3138 is probably not as straightforward as you would think.
3139 The following command line is recommended:
3140 .Bd -literal -offset indent
3142 ipfw add 32000 allow ip from any to any
3145 Along the same lines, doing an
3146 .Bd -literal -offset indent
3150 in similar surroundings is also a bad idea.
3154 filter list may not be modified if the system security level
3155 is set to 3 or higher
3158 for information on system security levels).
3160 .Sh PACKET DIVERSION
3163 socket bound to the specified port will receive all packets
3164 diverted to that port.
3165 If no socket is bound to the destination port, or if the divert module is
3166 not loaded, or if the kernel was not compiled with divert socket support,
3167 the packets are dropped.
3168 .Sh NETWORK ADDRESS TRANSLATION (NAT)
3170 support in-kernel NAT using the kernel version of
3173 The nat configuration command is the following:
3174 .Bd -ragged -offset indent
3179 .Ar nat-configuration
3183 The following parameters can be configured:
3184 .Bl -tag -width indent
3185 .It Cm ip Ar ip_address
3186 Define an ip address to use for aliasing.
3188 Use ip address of NIC for aliasing, dynamically changing
3189 it if NIC's ip address changes.
3191 Enable logging on this nat instance.
3193 Deny any incoming connection from outside world.
3195 Try to leave the alias port numbers unchanged from
3196 the actual local port numbers.
3198 Traffic on the local network not originating from an
3199 unregistered address spaces will be ignored.
3201 Reset table of the packet aliasing engine on address change.
3203 Reverse the way libalias handles aliasing.
3205 Obey transparent proxy rules only, packet aliasing is not performed.
3207 Skip instance in case of global state lookup (see below).
3210 Some specials value can be supplied instead of
3212 .Bl -tag -width indent
3214 Looks up translation state in all configured nat instances.
3215 If an entry is found, packet is aliased according to that entry.
3216 If no entry was found in any of the instances, packet is passed unchanged,
3217 and no new entry will be created.
3219 .Sx MULTIPLE INSTANCES
3222 for more information.
3224 Uses argument supplied in lookup table.
3227 section below for more information on lookup tables.
3230 To let the packet continue after being (de)aliased, set the sysctl variable
3231 .Va net.inet.ip.fw.one_pass
3233 For more information about aliasing modes, refer to
3237 for some examples about nat usage.
3238 .Ss REDIRECT AND LSNAT SUPPORT IN IPFW
3239 Redirect and LSNAT support follow closely the syntax used in
3243 for some examples on how to do redirect and lsnat.
3244 .Ss SCTP NAT SUPPORT
3245 SCTP nat can be configured in a similar manner to TCP through the
3248 The main difference is that
3250 does not do port translation.
3251 Since the local and global side ports will be the same,
3252 there is no need to specify both.
3253 Ports are redirected as follows:
3254 .Bd -ragged -offset indent
3260 .Cm redirect_port sctp
3261 .Ar ip_address [,addr_list] {[port | port-port] [,ports]}
3267 configuration can be done in real-time through the
3270 All may be changed dynamically, though the hash_table size will only
3275 .Sx SYSCTL VARIABLES
3277 .Sh IPv6/IPv4 NETWORK ADDRESS AND PROTOCOL TRANSLATION
3279 supports in-kernel IPv6/IPv4 network address and protocol translation.
3280 Stateful NAT64 translation allows IPv6-only clients to contact IPv4 servers
3281 using unicast TCP, UDP or ICMP protocols.
3282 One or more IPv4 addresses assigned to a stateful NAT64 translator are shared
3283 among serveral IPv6-only clients.
3284 When stateful NAT64 is used in conjunction with DNS64, no changes are usually
3285 required in the IPv6 client or the IPv4 server.
3288 should be loaded or kernel should have
3289 .Cm options IPFIREWALL_NAT64
3290 to be able use stateful NAT64 translator.
3292 Stateful NAT64 uses a bunch of memory for several types of objects.
3293 When IPv6 client initiates connection, NAT64 translator creates a host entry
3294 in the states table.
3295 Each host entry has a number of ports group entries allocated on demand.
3296 Ports group entries contains connection state entries.
3297 There are several options to control limits and lifetime for these objects.
3299 NAT64 translator follows RFC7915 when does ICMPv6/ICMP translation,
3300 unsupported message types will be silently dropped.
3301 IPv6 needs several ICMPv6 message types to be explicitly allowed for correct
3303 Make sure that ND6 neighbor solicitation (ICMPv6 type 135) and neighbor
3304 advertisement (ICMPv6 type 136) messages will not be handled by translation
3307 After translation NAT64 translator sends packets through corresponding netisr
3309 Thus translator host should be configured as IPv4 and IPv6 router.
3311 The stateful NAT64 configuration command is the following:
3312 .Bd -ragged -offset indent
3321 The following parameters can be configured:
3322 .Bl -tag -width indent
3323 .It Cm prefix4 Ar ipv4_prefix/plen
3324 The IPv4 prefix with mask defines the pool of IPv4 addresses used as
3325 source address after translation.
3326 Stateful NAT64 module translates IPv6 source address of client to one
3327 IPv4 address from this pool.
3328 Note that incoming IPv4 packets that don't have corresponding state entry
3329 in the states table will be dropped by translator.
3330 Make sure that translation rules handle packets, destined to configured prefix.
3331 .It Cm prefix6 Ar ipv6_prefix/length
3332 The IPv6 prefix defines IPv4-embedded IPv6 addresses used by translator
3333 to represent IPv4 addresses. This IPv6 prefix should be configured in DNS64.
3334 The translator implementation follows RFC6052, that restricts the length of
3335 prefixes to one of following: 32, 40, 48, 56, 64, or 96.
3336 The Well-Known IPv6 Prefix 64:ff9b:: must be 96 bits long.
3337 .It Cm max_ports Ar number
3338 Maximum number of ports reserved for upper level protocols to one IPv6 client.
3339 All reserved ports are divided into chunks between supported protocols.
3340 The number of connections from one IPv6 client is limited by this option.
3341 Note that closed TCP connections still remain in the list of connections until
3343 interval will not expire.
3346 .It Cm host_del_age Ar seconds
3347 The number of seconds until the host entry for a IPv6 client will be deleted
3348 and all its resources will be released due to inactivity.
3351 .It Cm pg_del_age Ar seconds
3352 The number of seconds until a ports group with unused state entries will
3356 .It Cm tcp_syn_age Ar seconds
3357 The number of seconds while a state entry for TCP connection with only SYN
3359 If TCP connection establishing will not be finished,
3360 state entry will be deleted.
3363 .It Cm tcp_est_age Ar seconds
3364 The number of seconds while a state entry for established TCP connection
3368 .It Cm tcp_close_age Ar seconds
3369 The number of seconds while a state entry for closed TCP connection
3371 Keeping state entries for closed connections is needed, because IPv4 servers
3372 typically keep closed connections in a TIME_WAIT state for a several minutes.
3373 Since translator's IPv4 addresses are shared among all IPv6 clients,
3374 new connections from the same addresses and ports may be rejected by server,
3375 because these connections are still in a TIME_WAIT state.
3376 Keeping them in translator's state table protects from such rejects.
3379 .It Cm udp_age Ar seconds
3380 The number of seconds while translator keeps state entry in a waiting for
3381 reply to the sent UDP datagram.
3384 .It Cm icmp_age Ar seconds
3385 The number of seconds while translator keeps state entry in a waiting for
3386 reply to the sent ICMP message.
3390 Turn on logging of all handled packets via BPF through
3394 is a pseudo interface and can be created after a boot manually with
3397 Note that it has different purpose than
3400 Translators sends to BPF an additional information with each packet.
3403 you are able to see each handled packet before and after translation.
3405 Turn off logging of all handled packets via BPF.
3408 To inspect a states table of stateful NAT64 the following command can be used:
3409 .Bd -ragged -offset indent
3418 Stateless NAT64 translator doesn't use a states table for translation
3419 and converts IPv4 addresses to IPv6 and vice versa solely based on the
3420 mappings taken from configured lookup tables.
3421 Since a states table doesn't used by stateless translator,
3422 it can be configured to pass IPv4 clients to IPv6-only servers.
3424 The stateless NAT64 configuration command is the following:
3425 .Bd -ragged -offset indent
3434 The following parameters can be configured:
3435 .Bl -tag -width indent
3436 .It Cm prefix6 Ar ipv6_prefix/length
3437 The IPv6 prefix defines IPv4-embedded IPv6 addresses used by translator
3438 to represent IPv4 addresses. This IPv6 prefix should be configured in DNS64.
3439 .It Cm table4 Ar table46
3442 contains mapping how IPv4 addresses should be translated to IPv6 addresses.
3443 .It Cm table6 Ar table64
3446 contains mapping how IPv6 addresses should be translated to IPv4 addresses.
3448 Turn on logging of all handled packets via BPF through
3452 Turn off logging of all handled packets via BPF.
3455 Note that the behavior of stateless translator with respect to not matched
3456 packets differs from stateful translator.
3457 If corresponding addresses was not found in the lookup tables, the packet
3458 will not be dropped and the search continues.
3459 .Sh IPv6-to-IPv6 NETWORK PREFIX TRANSLATION (NPTv6)
3461 supports in-kernel IPv6-to-IPv6 network prefix translation as described
3465 should be loaded or kernel should has
3466 .Cm options IPFIREWALL_NPTV6
3467 to be able use NPTv6 translator.
3469 The NPTv6 configuration command is the following:
3470 .Bd -ragged -offset indent
3479 The following parameters can be configured:
3480 .Bl -tag -width indent
3481 .It Cm int_prefix Ar ipv6_prefix
3482 IPv6 prefix used in internal network.
3483 NPTv6 module translates source address when it matches this prefix.
3484 .It Cm ext_prefix Ar ipv6_prefix
3485 IPv6 prefix used in external network.
3486 NPTv6 module translates destination address when it matches this prefix.
3487 .It Cm prefixlen Ar length
3488 The length of specified IPv6 prefixes. It must be in range from 8 to 64.
3491 Note that the prefix translation rules are silently ignored when IPv6 packet
3492 forwarding is disabled.
3493 To enable the packet forwarding, set the sysctl variable
3494 .Va net.inet6.ip6.forwarding
3497 To let the packet continue after being translated, set the sysctl variable
3498 .Va net.inet.ip.fw.one_pass
3501 Tunables can be set in
3507 before ipfw module gets loaded.
3508 .Bl -tag -width indent
3509 .It Va net.inet.ip.fw.default_to_accept: No 0
3510 Defines ipfw last rule behavior.
3511 This value overrides
3512 .Cd "options IPFW_DEFAULT_TO_(ACCEPT|DENY)"
3513 from kernel configuration file.
3514 .It Va net.inet.ip.fw.tables_max: No 128
3515 Defines number of tables available in ipfw.
3516 Number cannot exceed 65534.
3518 .Sh SYSCTL VARIABLES
3521 variables controls the behaviour of the firewall and
3523 .Pq Nm dummynet , bridge , sctp nat .
3524 These are shown below together with their default value
3525 (but always check with the
3527 command what value is actually in use) and meaning:
3528 .Bl -tag -width indent
3529 .It Va net.inet.ip.alias.sctp.accept_global_ootb_addip: No 0
3532 responds to receipt of global OOTB ASCONF-AddIP:
3533 .Bl -tag -width indent
3535 No response (unless a partially matching association exists -
3536 ports and vtags match but global address does not)
3539 will accept and process all OOTB global AddIP messages.
3542 Option 1 should never be selected as this forms a security risk.
3544 establish multiple fake associations by sending AddIP messages.
3545 .It Va net.inet.ip.alias.sctp.chunk_proc_limit: No 5
3546 Defines the maximum number of chunks in an SCTP packet that will be
3548 packet that matches an existing association.
3549 This value is enforced to be greater or equal than
3550 .Cm net.inet.ip.alias.sctp.initialising_chunk_proc_limit .
3552 a DoS risk yet setting too low a value may result in
3553 important control chunks in
3554 the packet not being located and parsed.
3555 .It Va net.inet.ip.alias.sctp.error_on_ootb: No 1
3558 responds to any Out-of-the-Blue (OOTB) packets with ErrorM packets.
3559 An OOTB packet is a packet that arrives with no existing association
3562 and is not an INIT or ASCONF-AddIP packet:
3563 .Bl -tag -width indent
3565 ErrorM is never sent in response to OOTB packets.
3567 ErrorM is only sent to OOTB packets received on the local side.
3569 ErrorM is sent to the local side and on the global side ONLY if there is a
3570 partial match (ports and vtags match but the source global IP does not).
3571 This value is only useful if the
3573 is tracking global IP addresses.
3575 ErrorM is sent in response to all OOTB packets on both
3576 the local and global side
3580 At the moment the default is 0, since the ErrorM packet is not yet
3581 supported by most SCTP stacks.
3582 When it is supported, and if not tracking
3583 global addresses, we recommend setting this value to 1 to allow
3584 multi-homed local hosts to function with the
3586 To track global addresses, we recommend setting this value to 2 to
3587 allow global hosts to be informed when they need to (re)send an
3589 Value 3 should never be chosen (except for debugging) as the
3591 will respond to all OOTB global packets (a DoS risk).
3592 .It Va net.inet.ip.alias.sctp.hashtable_size: No 2003
3593 Size of hash tables used for
3595 lookups (100 < prime_number > 1000001).
3598 size for any future created
3600 instance and therefore must be set prior to creating a
3603 The table sizes may be changed to suit specific needs.
3604 If there will be few
3605 concurrent associations, and memory is scarce, you may make these smaller.
3606 If there will be many thousands (or millions) of concurrent associations, you
3607 should make these larger.
3608 A prime number is best for the table size.
3610 update function will adjust your input value to the next highest prime number.
3611 .It Va net.inet.ip.alias.sctp.holddown_time: No 0
3612 Hold association in table for this many seconds after receiving a
3614 This allows endpoints to correct shutdown gracefully if a
3615 shutdown_complete is lost and retransmissions are required.
3616 .It Va net.inet.ip.alias.sctp.init_timer: No 15
3617 Timeout value while waiting for (INIT-ACK|AddIP-ACK).
3618 This value cannot be 0.
3619 .It Va net.inet.ip.alias.sctp.initialising_chunk_proc_limit: No 2
3620 Defines the maximum number of chunks in an SCTP packet that will be parsed when
3621 no existing association exists that matches that packet.
3623 will only be an INIT or ASCONF-AddIP packet.
3624 A higher value may become a DoS
3625 risk as malformed packets can consume processing resources.
3626 .It Va net.inet.ip.alias.sctp.param_proc_limit: No 25
3627 Defines the maximum number of parameters within a chunk that will be
3630 As for other similar sysctl variables, larger values pose a DoS risk.
3631 .It Va net.inet.ip.alias.sctp.log_level: No 0
3632 Level of detail in the system log messages (0 \- minimal, 1 \- event,
3633 2 \- info, 3 \- detail, 4 \- debug, 5 \- max debug).
3635 option in high loss environments.
3636 .It Va net.inet.ip.alias.sctp.shutdown_time: No 15
3637 Timeout value while waiting for SHUTDOWN-COMPLETE.
3638 This value cannot be 0.
3639 .It Va net.inet.ip.alias.sctp.track_global_addresses: No 0
3640 Enables/disables global IP address tracking within the
3643 upper limit on the number of addresses tracked for each association:
3644 .Bl -tag -width indent
3646 Global tracking is disabled
3648 Enables tracking, the maximum number of addresses tracked for each
3649 association is limited to this value
3652 This variable is fully dynamic, the new value will be adopted for all newly
3653 arriving associations, existing associations are treated
3654 as they were previously.
3655 Global tracking will decrease the number of collisions within the
3658 of increased processing load, memory usage, complexity, and possible
3661 problems in complex networks with multiple
3663 We recommend not tracking
3664 global IP addresses, this will still result in a fully functional
3666 .It Va net.inet.ip.alias.sctp.up_timer: No 300
3667 Timeout value to keep an association up with no traffic.
3668 This value cannot be 0.
3669 .It Va net.inet.ip.dummynet.codel.interval : No 100000
3672 AQM interval in microseconds.
3673 The value must be in the range 1..5000000.
3674 .It Va net.inet.ip.dummynet.codel.target : No 5000
3677 AQM target delay time in microseconds (the minimum acceptable persistent queue
3679 The value must be in the range 1..5000000.
3680 .It Va net.inet.ip.dummynet.expire : No 1
3681 Lazily delete dynamic pipes/queue once they have no pending traffic.
3682 You can disable this by setting the variable to 0, in which case
3683 the pipes/queues will only be deleted when the threshold is reached.
3684 .It Va net.inet.ip.dummynet.fqcodel.flows : No 1024
3685 Defines the default total number of flow queues (sub-queues) that
3687 creates and manages.
3688 The value must be in the range 1..65536.
3689 .It Va net.inet.ip.dummynet.fqcodel.interval : No 100000
3692 scheduler/AQM interval in microseconds.
3693 The value must be in the range 1..5000000.
3694 .It Va net.inet.ip.dummynet.fqcodel.limit : No 10240
3695 The default hard size limit (in unit of packet) of all queues managed by an
3699 The value must be in the range 1..20480.
3700 .It Va net.inet.ip.dummynet.fqcodel.quantum : No 1514
3701 The default quantum (credit) of the
3704 The value must be in the range 1..9000.
3705 .It Va net.inet.ip.dummynet.fqcodel.target : No 5000
3708 scheduler/AQM target delay time in microseconds (the minimum acceptable
3709 persistent queue delay).
3710 The value must be in the range 1..5000000.
3711 .It Va net.inet.ip.dummynet.fqpie.alpha : No 125
3714 parameter (scaled by 1000) for
3717 The value must be in the range 1..7000.
3718 .It Va net.inet.ip.dummynet.fqpie.beta : No 1250
3721 parameter (scaled by 1000) for
3724 The value must be in the range 1..7000.
3725 .It Va net.inet.ip.dummynet.fqpie.flows : No 1024
3726 Defines the default total number of flow queues (sub-queues) that
3728 creates and manages.
3729 The value must be in the range 1..65536.
3730 .It Va net.inet.ip.dummynet.fqpie.limit : No 10240
3731 The default hard size limit (in unit of packet) of all queues managed by an
3735 The value must be in the range 1..20480.
3736 .It Va net.inet.ip.dummynet.fqpie.max_burst : No 150000
3737 The default maximum period of microseconds that
3739 scheduler/AQM does not drop/mark packets.
3740 The value must be in the range 1..10000000.
3741 .It Va net.inet.ip.dummynet.fqpie.max_ecnth : No 99
3742 The default maximum ECN probability threshold (scaled by 1000) for
3745 The value must be in the range 1..7000.
3746 .It Va net.inet.ip.dummynet.fqpie.quantum : No 1514
3747 The default quantum (credit) of the
3750 The value must be in the range 1..9000.
3751 .It Va net.inet.ip.dummynet.fqpie.target : No 15000
3756 in unit of microsecond.
3757 The value must be in the range 1..5000000.
3758 .It Va net.inet.ip.dummynet.fqpie.tupdate : No 15000
3763 in unit of microsecond.
3764 The value must be in the range 1..5000000.
3765 .It Va net.inet.ip.dummynet.hash_size : No 64
3766 Default size of the hash table used for dynamic pipes/queues.
3767 This value is used when no
3769 option is specified when configuring a pipe/queue.
3770 .It Va net.inet.ip.dummynet.io_fast : No 0
3771 If set to a non-zero value,
3776 operation (see above) is enabled.
3777 .It Va net.inet.ip.dummynet.io_pkt
3778 Number of packets passed to
3780 .It Va net.inet.ip.dummynet.io_pkt_drop
3781 Number of packets dropped by
3783 .It Va net.inet.ip.dummynet.io_pkt_fast
3784 Number of packets bypassed by the
3787 .It Va net.inet.ip.dummynet.max_chain_len : No 16
3788 Target value for the maximum number of pipes/queues in a hash bucket.
3790 .Cm max_chain_len*hash_size
3791 is used to determine the threshold over which empty pipes/queues
3792 will be expired even when
3793 .Cm net.inet.ip.dummynet.expire=0 .
3794 .It Va net.inet.ip.dummynet.red_lookup_depth : No 256
3795 .It Va net.inet.ip.dummynet.red_avg_pkt_size : No 512
3796 .It Va net.inet.ip.dummynet.red_max_pkt_size : No 1500
3797 Parameters used in the computations of the drop probability
3798 for the RED algorithm.
3799 .It Va net.inet.ip.dummynet.pie.alpha : No 125
3802 parameter (scaled by 1000) for
3805 The value must be in the range 1..7000.
3806 .It Va net.inet.ip.dummynet.pie.beta : No 1250
3809 parameter (scaled by 1000) for
3812 The value must be in the range 1..7000.
3813 .It Va net.inet.ip.dummynet.pie.max_burst : No 150000
3814 The default maximum period of microseconds that
3816 AQM does not drop/mark packets.
3817 The value must be in the range 1..10000000.
3818 .It Va net.inet.ip.dummynet.pie.max_ecnth : No 99
3819 The default maximum ECN probability threshold (scaled by 1000) for
3822 The value must be in the range 1..7000.
3823 .It Va net.inet.ip.dummynet.pie.target : No 15000
3828 AQM in unit of microsecond.
3829 The value must be in the range 1..5000000.
3830 .It Va net.inet.ip.dummynet.pie.tupdate : No 15000
3835 AQM in unit of microsecond.
3836 The value must be in the range 1..5000000.
3837 .It Va net.inet.ip.dummynet.pipe_byte_limit : No 1048576
3838 .It Va net.inet.ip.dummynet.pipe_slot_limit : No 100
3839 The maximum queue size that can be specified in bytes or packets.
3840 These limits prevent accidental exhaustion of resources such as mbufs.
3841 If you raise these limits,
3842 you should make sure the system is configured so that sufficient resources
3844 .It Va net.inet.ip.fw.autoinc_step : No 100
3845 Delta between rule numbers when auto-generating them.
3846 The value must be in the range 1..1000.
3847 .It Va net.inet.ip.fw.curr_dyn_buckets : Va net.inet.ip.fw.dyn_buckets
3848 The current number of buckets in the hash table for dynamic rules
3850 .It Va net.inet.ip.fw.debug : No 1
3851 Controls debugging messages produced by
3853 .It Va net.inet.ip.fw.default_rule : No 65535
3854 The default rule number (read-only).
3856 .Nm , the default rule is the last one, so its number
3857 can also serve as the highest number allowed for a rule.
3858 .It Va net.inet.ip.fw.dyn_buckets : No 256
3859 The number of buckets in the hash table for dynamic rules.
3860 Must be a power of 2, up to 65536.
3861 It only takes effect when all dynamic rules have expired, so you
3862 are advised to use a
3864 command to make sure that the hash table is resized.
3865 .It Va net.inet.ip.fw.dyn_count : No 3
3866 Current number of dynamic rules
3868 .It Va net.inet.ip.fw.dyn_keepalive : No 1
3869 Enables generation of keepalive packets for
3871 rules on TCP sessions.
3872 A keepalive is generated to both
3873 sides of the connection every 5 seconds for the last 20
3874 seconds of the lifetime of the rule.
3875 .It Va net.inet.ip.fw.dyn_max : No 8192
3876 Maximum number of dynamic rules.
3877 When you hit this limit, no more dynamic rules can be
3878 installed until old ones expire.
3879 .It Va net.inet.ip.fw.dyn_ack_lifetime : No 300
3880 .It Va net.inet.ip.fw.dyn_syn_lifetime : No 20
3881 .It Va net.inet.ip.fw.dyn_fin_lifetime : No 1
3882 .It Va net.inet.ip.fw.dyn_rst_lifetime : No 1
3883 .It Va net.inet.ip.fw.dyn_udp_lifetime : No 5
3884 .It Va net.inet.ip.fw.dyn_short_lifetime : No 30
3885 These variables control the lifetime, in seconds, of dynamic
3887 Upon the initial SYN exchange the lifetime is kept short,
3888 then increased after both SYN have been seen, then decreased
3889 again during the final FIN exchange or when a RST is received.
3891 .Em dyn_fin_lifetime
3893 .Em dyn_rst_lifetime
3894 must be strictly lower than 5 seconds, the period of
3895 repetition of keepalives.
3896 The firewall enforces that.
3897 .It Va net.inet.ip.fw.dyn_keep_states: No 0
3898 Keep dynamic states on rule/set deletion.
3899 States are relinked to default rule (65535).
3900 This can be handly for ruleset reload.
3901 Turned off by default.
3902 .It Va net.inet.ip.fw.enable : No 1
3903 Enables the firewall.
3904 Setting this variable to 0 lets you run your machine without
3905 firewall even if compiled in.
3906 .It Va net.inet6.ip6.fw.enable : No 1
3907 provides the same functionality as above for the IPv6 case.
3908 .It Va net.inet.ip.fw.one_pass : No 1
3909 When set, the packet exiting from the
3913 node is not passed though the firewall again.
3914 Otherwise, after an action, the packet is
3915 reinjected into the firewall at the next rule.
3916 .It Va net.inet.ip.fw.tables_max : No 128
3917 Maximum number of tables.
3918 .It Va net.inet.ip.fw.verbose : No 1
3919 Enables verbose messages.
3920 .It Va net.inet.ip.fw.verbose_limit : No 0
3921 Limits the number of messages produced by a verbose firewall.
3922 .It Va net.inet6.ip6.fw.deny_unknown_exthdrs : No 1
3923 If enabled packets with unknown IPv6 Extension Headers will be denied.
3924 .It Va net.link.ether.ipfw : No 0
3925 Controls whether layer-2 packets are passed to
3928 .It Va net.link.bridge.ipfw : No 0
3929 Controls whether bridged packets are passed to
3933 .Sh INTERNAL DIAGNOSTICS
3934 There are some commands that may be useful to understand current state
3935 of certain subsystems inside kernel module.
3936 These commands provide debugging output which may change without notice.
3938 Currently the following commands are available as
3941 .Bl -tag -width indent
3943 Lists all interface which are currently tracked by
3945 with their in-kernel status.
3947 List all table lookup algorithms currently available.
3950 There are far too many possible uses of
3952 so this Section will only give a small set of examples.
3954 .Ss BASIC PACKET FILTERING
3955 This command adds an entry which denies all tcp packets from
3956 .Em cracker.evil.org
3957 to the telnet port of
3959 from being forwarded by the host:
3961 .Dl "ipfw add deny tcp from cracker.evil.org to wolf.tambov.su telnet"
3963 This one disallows any connection from the entire cracker's
3966 .Dl "ipfw add deny ip from 123.45.67.0/24 to my.host.org"
3968 A first and efficient way to limit access (not using dynamic rules)
3969 is the use of the following rules:
3971 .Dl "ipfw add allow tcp from any to any established"
3972 .Dl "ipfw add allow tcp from net1 portlist1 to net2 portlist2 setup"
3973 .Dl "ipfw add allow tcp from net3 portlist3 to net3 portlist3 setup"
3975 .Dl "ipfw add deny tcp from any to any"
3977 The first rule will be a quick match for normal TCP packets,
3978 but it will not match the initial SYN packet, which will be
3981 rules only for selected source/destination pairs.
3982 All other SYN packets will be rejected by the final
3986 If you administer one or more subnets, you can take advantage
3987 of the address sets and or-blocks and write extremely
3988 compact rulesets which selectively enable services to blocks
3989 of clients, as below:
3991 .Dl "goodguys=\*q{ 10.1.2.0/24{20,35,66,18} or 10.2.3.0/28{6,3,11} }\*q"
3992 .Dl "badguys=\*q10.1.2.0/24{8,38,60}\*q"
3994 .Dl "ipfw add allow ip from ${goodguys} to any"
3995 .Dl "ipfw add deny ip from ${badguys} to any"
3996 .Dl "... normal policies ..."
4000 option could be used to do automated anti-spoofing by adding the
4001 following to the top of a ruleset:
4003 .Dl "ipfw add deny ip from any to any not verrevpath in"
4005 This rule drops all incoming packets that appear to be coming to the
4006 system on the wrong interface.
4007 For example, a packet with a source
4008 address belonging to a host on a protected internal network would be
4009 dropped if it tried to enter the system from an external interface.
4013 option could be used to do similar but more restricted anti-spoofing
4014 by adding the following to the top of a ruleset:
4016 .Dl "ipfw add deny ip from any to any not antispoof in"
4018 This rule drops all incoming packets that appear to be coming from another
4019 directly connected system but on the wrong interface.
4020 For example, a packet with a source address of
4021 .Li 192.168.0.0/24 ,
4030 option could be used to (re)mark user traffic,
4031 by adding the following to the appropriate place in ruleset:
4033 .Dl "ipfw add setdscp be ip from any to any dscp af11,af21"
4034 .Ss SELECTIVE MIRRORING
4035 If your network has network traffic analyzer
4036 connected to your host directly via dedicated interface
4037 or remotely via RSPAN vlan, you can selectively mirror
4038 some ethernet layer2 frames to the analyzer.
4040 First, make sure your firewall is already configured and runs.
4041 Then, enable layer2 processing if not already enabled:
4043 .Dl "sysctl net.link.ether.ipfw=1"
4045 Next, load needed additional kernel modules:
4047 .Dl "kldload ng_ether ng_ipfw"
4049 Optionally, make system load these modules automatically
4052 .Dl sysrc kld_list+="ng_ether ng_ipfw"
4056 kernel module to transmit mirrored copies of layer2 frames
4057 out via vlan900 interface:
4059 .Dl "ngctl connect ipfw: vlan900: 1 lower"
4061 Think of "1" here as of "mirroring instance index" and vlan900 is its
4063 You can have arbitrary number of instances.
4068 At last, actually start mirroring of selected frames using "instance 1".
4069 For frames incoming from em0 interface:
4071 .Dl "ipfw add ngtee 1 ip from any to 192.168.0.1 layer2 in recv em0"
4073 For frames outgoing to em0 interface:
4075 .Dl "ipfw add ngtee 1 ip from any to 192.168.0.1 layer2 out xmit em0"
4077 For both incoming and outgoing frames while flowing through em0:
4079 .Dl "ipfw add ngtee 1 ip from any to 192.168.0.1 layer2 via em0"
4081 Make sure you do not perform mirroring for already duplicated frames
4082 or kernel may hang as there is no safety net.
4084 In order to protect a site from flood attacks involving fake
4085 TCP packets, it is safer to use dynamic rules:
4087 .Dl "ipfw add check-state"
4088 .Dl "ipfw add deny tcp from any to any established"
4089 .Dl "ipfw add allow tcp from my-net to any setup keep-state"
4091 This will let the firewall install dynamic rules only for
4092 those connection which start with a regular SYN packet coming
4093 from the inside of our network.
4094 Dynamic rules are checked when encountering the first
4103 rule should usually be placed near the beginning of the
4104 ruleset to minimize the amount of work scanning the ruleset.
4105 Your mileage may vary.
4107 For more complex scenarios with dynamic rules
4111 can be used to precisely control creation and checking of dynamic rules.
4112 Example of usage of these options are provided in
4113 .Sx NETWORK ADDRESS TRANSLATION (NAT)
4116 To limit the number of connections a user can open
4117 you can use the following type of rules:
4119 .Dl "ipfw add allow tcp from my-net/24 to any setup limit src-addr 10"
4120 .Dl "ipfw add allow tcp from any to me setup limit src-addr 4"
4122 The former (assuming it runs on a gateway) will allow each host
4123 on a /24 network to open at most 10 TCP connections.
4124 The latter can be placed on a server to make sure that a single
4125 client does not use more than 4 simultaneous connections.
4128 stateful rules can be subject to denial-of-service attacks
4129 by a SYN-flood which opens a huge number of dynamic rules.
4130 The effects of such attacks can be partially limited by
4133 variables which control the operation of the firewall.
4135 Here is a good usage of the
4137 command to see accounting records and timestamp information:
4141 or in short form without timestamps:
4145 which is equivalent to:
4149 Next rule diverts all incoming packets from 192.168.2.0/24
4150 to divert port 5000:
4152 .Dl ipfw divert 5000 ip from 192.168.2.0/24 to any in
4154 The following rules show some of the applications of
4158 for simulations and the like.
4160 This rule drops random incoming packets with a probability
4163 .Dl "ipfw add prob 0.05 deny ip from any to any in"
4165 A similar effect can be achieved making use of
4169 .Dl "ipfw add pipe 10 ip from any to any"
4170 .Dl "ipfw pipe 10 config plr 0.05"
4172 We can use pipes to artificially limit bandwidth, e.g.\& on a
4173 machine acting as a router, if we want to limit traffic from
4174 local clients on 192.168.2.0/24 we do:
4176 .Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out"
4177 .Dl "ipfw pipe 1 config bw 300Kbit/s queue 50KBytes"
4179 note that we use the
4181 modifier so that the rule is not used twice.
4182 Remember in fact that
4184 rules are checked both on incoming and outgoing packets.
4186 Should we want to simulate a bidirectional link with bandwidth
4187 limitations, the correct way is the following:
4189 .Dl "ipfw add pipe 1 ip from any to any out"
4190 .Dl "ipfw add pipe 2 ip from any to any in"
4191 .Dl "ipfw pipe 1 config bw 64Kbit/s queue 10Kbytes"
4192 .Dl "ipfw pipe 2 config bw 64Kbit/s queue 10Kbytes"
4194 The above can be very useful, e.g.\& if you want to see how
4195 your fancy Web page will look for a residential user who
4196 is connected only through a slow link.
4197 You should not use only one pipe for both directions, unless
4198 you want to simulate a half-duplex medium (e.g.\& AppleTalk,
4200 It is not necessary that both pipes have the same configuration,
4201 so we can also simulate asymmetric links.
4203 Should we want to verify network performance with the RED queue
4204 management algorithm:
4206 .Dl "ipfw add pipe 1 ip from any to any"
4207 .Dl "ipfw pipe 1 config bw 500Kbit/s queue 100 red 0.002/30/80/0.1"
4209 Another typical application of the traffic shaper is to
4210 introduce some delay in the communication.
4211 This can significantly affect applications which do a lot of Remote
4212 Procedure Calls, and where the round-trip-time of the
4213 connection often becomes a limiting factor much more than
4216 .Dl "ipfw add pipe 1 ip from any to any out"
4217 .Dl "ipfw add pipe 2 ip from any to any in"
4218 .Dl "ipfw pipe 1 config delay 250ms bw 1Mbit/s"
4219 .Dl "ipfw pipe 2 config delay 250ms bw 1Mbit/s"
4221 Per-flow queueing can be useful for a variety of purposes.
4222 A very simple one is counting traffic:
4224 .Dl "ipfw add pipe 1 tcp from any to any"
4225 .Dl "ipfw add pipe 1 udp from any to any"
4226 .Dl "ipfw add pipe 1 ip from any to any"
4227 .Dl "ipfw pipe 1 config mask all"
4229 The above set of rules will create queues (and collect
4230 statistics) for all traffic.
4231 Because the pipes have no limitations, the only effect is
4232 collecting statistics.
4233 Note that we need 3 rules, not just the last one, because
4236 tries to match IP packets it will not consider ports, so we
4237 would not see connections on separate ports as different
4240 A more sophisticated example is limiting the outbound traffic
4241 on a net with per-host limits, rather than per-network limits:
4243 .Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out"
4244 .Dl "ipfw add pipe 2 ip from any to 192.168.2.0/24 in"
4245 .Dl "ipfw pipe 1 config mask src-ip 0x000000ff bw 200Kbit/s queue 20Kbytes"
4246 .Dl "ipfw pipe 2 config mask dst-ip 0x000000ff bw 200Kbit/s queue 20Kbytes"
4248 In the following example, we need to create several traffic bandwidth
4249 classes and we need different hosts/networks to fall into different classes.
4250 We create one pipe for each class and configure them accordingly.
4251 Then we create a single table and fill it with IP subnets and addresses.
4252 For each subnet/host we set the argument equal to the number of the pipe
4254 Then we classify traffic using a single rule:
4256 .Dl "ipfw pipe 1 config bw 1000Kbyte/s"
4257 .Dl "ipfw pipe 4 config bw 4000Kbyte/s"
4259 .Dl "ipfw table T1 create type addr"
4260 .Dl "ipfw table T1 add 192.168.2.0/24 1"
4261 .Dl "ipfw table T1 add 192.168.0.0/27 4"
4262 .Dl "ipfw table T1 add 192.168.0.2 1"
4264 .Dl "ipfw add pipe tablearg ip from 'table(T1)' to any"
4268 action, the table entries may include hostnames and IP addresses.
4270 .Dl "ipfw table T2 create type addr ftype ip"
4271 .Dl "ipfw table T2 add 192.168.2.0/24 10.23.2.1"
4272 .Dl "ipfw table T21 add 192.168.0.0/27 router1.dmz"
4274 .Dl "ipfw add 100 fwd tablearg ip from any to table(1)"
4276 In the following example per-interface firewall is created:
4278 .Dl "ipfw table IN create type iface valtype skipto,fib"
4279 .Dl "ipfw table IN add vlan20 12000,12"
4280 .Dl "ipfw table IN add vlan30 13000,13"
4281 .Dl "ipfw table OUT create type iface valtype skipto"
4282 .Dl "ipfw table OUT add vlan20 22000"
4283 .Dl "ipfw table OUT add vlan30 23000"
4285 .Dl "ipfw add 100 setfib tablearg ip from any to any recv 'table(IN)' in"
4286 .Dl "ipfw add 200 skipto tablearg ip from any to any recv 'table(IN)' in"
4287 .Dl "ipfw add 300 skipto tablearg ip from any to any xmit 'table(OUT)' out"
4289 The following example illustrate usage of flow tables:
4291 .Dl "ipfw table fl create type flow:src-ip,proto,dst-ip,dst-port"
4292 .Dl "ipfw table fl add 2a02:6b8:77::88,tcp,2a02:6b8:77::99,80 11"
4293 .Dl "ipfw table fl add 10.0.0.1,udp,10.0.0.2,53 12"
4295 .Dl "ipfw add 100 allow ip from any to any flow 'table(fl,11)' recv ix0"
4297 To add a set of rules atomically, e.g.\& set 18:
4299 .Dl "ipfw set disable 18"
4300 .Dl "ipfw add NN set 18 ... # repeat as needed"
4301 .Dl "ipfw set enable 18"
4303 To delete a set of rules atomically the command is simply:
4305 .Dl "ipfw delete set 18"
4307 To test a ruleset and disable it and regain control if something goes wrong:
4309 .Dl "ipfw set disable 18"
4310 .Dl "ipfw add NN set 18 ... # repeat as needed"
4311 .Dl "ipfw set enable 18; echo done; sleep 30 && ipfw set disable 18"
4313 Here if everything goes well, you press control-C before the "sleep"
4314 terminates, and your ruleset will be left active.
4315 Otherwise, e.g.\& if
4316 you cannot access your box, the ruleset will be disabled after
4317 the sleep terminates thus restoring the previous situation.
4319 To show rules of the specific set:
4321 .Dl "ipfw set 18 show"
4323 To show rules of the disabled set:
4325 .Dl "ipfw -S set 18 show"
4327 To clear a specific rule counters of the specific set:
4329 .Dl "ipfw set 18 zero NN"
4331 To delete a specific rule of the specific set:
4333 .Dl "ipfw set 18 delete NN"
4334 .Ss NAT, REDIRECT AND LSNAT
4335 First redirect all the traffic to nat instance 123:
4337 .Dl "ipfw add nat 123 all from any to any"
4339 Then to configure nat instance 123 to alias all the outgoing traffic with ip
4340 192.168.0.123, blocking all incoming connections, trying to keep
4341 same ports on both sides, clearing aliasing table on address change
4342 and keeping a log of traffic/link statistics:
4344 .Dl "ipfw nat 123 config ip 192.168.0.123 log deny_in reset same_ports"
4346 Or to change address of instance 123, aliasing table will be cleared (see
4349 .Dl "ipfw nat 123 config ip 10.0.0.1"
4351 To see configuration of nat instance 123:
4353 .Dl "ipfw nat 123 show config"
4355 To show logs of all the instances in range 111-999:
4357 .Dl "ipfw nat 111-999 show"
4359 To see configurations of all instances:
4361 .Dl "ipfw nat show config"
4363 Or a redirect rule with mixed modes could looks like:
4365 .Dl "ipfw nat 123 config redirect_addr 10.0.0.1 10.0.0.66"
4366 .Dl " redirect_port tcp 192.168.0.1:80 500"
4367 .Dl " redirect_proto udp 192.168.1.43 192.168.1.1"
4368 .Dl " redirect_addr 192.168.0.10,192.168.0.11"
4369 .Dl " 10.0.0.100 # LSNAT"
4370 .Dl " redirect_port tcp 192.168.0.1:80,192.168.0.10:22"
4373 or it could be split in:
4375 .Dl "ipfw nat 1 config redirect_addr 10.0.0.1 10.0.0.66"
4376 .Dl "ipfw nat 2 config redirect_port tcp 192.168.0.1:80 500"
4377 .Dl "ipfw nat 3 config redirect_proto udp 192.168.1.43 192.168.1.1"
4378 .Dl "ipfw nat 4 config redirect_addr 192.168.0.10,192.168.0.11,192.168.0.12"
4380 .Dl "ipfw nat 5 config redirect_port tcp"
4381 .Dl " 192.168.0.1:80,192.168.0.10:22,192.168.0.20:25 500"
4383 Sometimes you may want to mix NAT and dynamic rules. It could be achived with
4387 options. Problem is, you need to create dynamic rule before NAT and check it
4388 after NAT actions (or vice versa) to have consistent addresses and ports.
4391 option will trigger activation of existing dynamic state, and action of such
4392 rule will be performed as soon as rule is matched. In case of NAT and
4394 rule packet need to be passed to NAT, not allowed as soon is possible.
4396 There is example of set of rules to achive this. Bear in mind that this
4397 is exmaple only and it is not very usefult by itself.
4399 On way out, after all checks place this rules:
4401 .Dl "ipfw add allow record-state skip-action"
4402 .Dl "ipfw add nat 1"
4404 And on way in there should be something like this:
4406 .Dl "ipfw add nat 1"
4407 .Dl "ipfw add check-state"
4409 Please note, that first rule on way out doesn't allow packet and doesn't
4410 execute existing dynamic rules. All it does, create new dynamic rule with
4412 action, if it is not created yet. Later, this dynamic rule is used on way
4416 .Ss CONFIGURING CODEL, PIE, FQ-CODEL and FQ-PIE AQM
4420 AQM can be configured for
4430 AQM using default configuration for traffic from 192.168.0.0/24 and 1Mbits/s
4433 .Dl "ipfw pipe 1 config bw 1mbits/s codel"
4434 .Dl "ipfw add 100 pipe 1 ip from 192.168.0.0/24 to any"
4440 AQM using different configurations parameters for traffic from
4441 192.168.0.0/24 and 1Mbits/s rate limit, we do:
4443 .Dl "ipfw pipe 1 config bw 1mbits/s"
4444 .Dl "ipfw queue 1 config pipe 1 codel target 8ms interval 160ms ecn"
4445 .Dl "ipfw add 100 queue 1 ip from 192.168.0.0/24 to any"
4451 AQM using default configuration for traffic from 192.168.0.0/24 and 1Mbits/s
4454 .Dl "ipfw pipe 1 config bw 1mbits/s pie"
4455 .Dl "ipfw add 100 pipe 1 ip from 192.168.0.0/24 to any"
4461 AQM using different configuration parameters for traffic from
4462 192.168.0.0/24 and 1Mbits/s rate limit, we do:
4464 .Dl "ipfw pipe 1 config bw 1mbits/s"
4465 .Dl "ipfw queue 1 config pipe 1 pie target 20ms tupdate 30ms ecn"
4466 .Dl "ipfw add 100 queue 1 ip from 192.168.0.0/24 to any"
4471 AQM can be configured for
4477 scheduler using different configurations parameters for traffic from
4478 192.168.0.0/24 and 1Mbits/s rate limit, we do:
4480 .Dl "ipfw pipe 1 config bw 1mbits/s"
4481 .Dl "ipfw sched 1 config pipe 1 type fq_codel"
4482 .Dl "ipfw queue 1 config sched 1"
4483 .Dl "ipfw add 100 queue 1 ip from 192.168.0.0/24 to any"
4487 default configuration for a
4489 such as disable ECN and change the
4493 .Dl "ipfw sched 1 config pipe 1 type fq_codel target 10ms noecn"
4499 scheduler using different configurations parameters for traffic from
4500 192.168.0.0/24 and 1Mbits/s rate limit, we do:
4502 .Dl "ipfw pipe 1 config bw 1mbits/s"
4503 .Dl "ipfw sched 1 config pipe 1 type fq_pie"
4504 .Dl "ipfw queue 1 config sched 1"
4505 .Dl "ipfw add 100 queue 1 ip from 192.168.0.0/24 to any"
4507 The configurations of
4510 can be changed in a similar way as for
4534 utility first appeared in
4539 Stateful extensions were introduced in
4542 was introduced in Summer 2002.
4544 .An Ugen J. S. Antsilevich ,
4545 .An Poul-Henning Kamp ,
4549 .An Rasool Al-Saadi .
4552 API based upon code written by
4556 Dummynet has been introduced by Luigi Rizzo in 1997-1998.
4558 Some early work (1999-2000) on the
4560 traffic shaper supported by Akamba Corp.
4562 The ipfw core (ipfw2) has been completely redesigned and
4563 reimplemented by Luigi Rizzo in summer 2002.
4566 options have been added by various developers over the years.
4569 In-kernel NAT support written by
4570 .An Paolo Pisati Aq Mt piso@FreeBSD.org
4571 as part of a Summer of Code 2005 project.
4575 support has been developed by
4576 .An The Centre for Advanced Internet Architectures (CAIA) Aq http://www.caia.swin.edu.au .
4577 The primary developers and maintainers are David Hayes and Jason But.
4578 For further information visit:
4579 .Aq http://www.caia.swin.edu.au/urp/SONATA
4581 Delay profiles have been developed by Alessandro Cerri and
4582 Luigi Rizzo, supported by the
4583 European Commission within Projects Onelab and Onelab2.
4585 CoDel, PIE, FQ-CoDel and FQ-PIE AQM for Dummynet have been implemented by
4586 .An The Centre for Advanced Internet Architectures (CAIA)
4587 in 2016, supported by The Comcast Innovation Fund.
4588 The primary developer is
4591 The syntax has grown over the years and sometimes it might be confusing.
4592 Unfortunately, backward compatibility prevents cleaning up mistakes
4593 made in the definition of the syntax.
4597 Misconfiguring the firewall can put your computer in an unusable state,
4598 possibly shutting down network services and requiring console access to
4599 regain control of it.
4601 Incoming packet fragments diverted by
4603 are reassembled before delivery to the socket.
4604 The action used on those packet is the one from the
4605 rule which matches the first fragment of the packet.
4607 Packets diverted to userland, and then reinserted by a userland process
4608 may lose various packet attributes.
4609 The packet source interface name
4610 will be preserved if it is shorter than 8 bytes and the userland process
4611 saves and reuses the sockaddr_in
4614 otherwise, it may be lost.
4615 If a packet is reinserted in this manner, later rules may be incorrectly
4616 applied, making the order of
4618 rules in the rule sequence very important.
4620 Dummynet drops all packets with IPv6 link-local addresses.
4626 may not behave as expected.
4627 In particular, incoming SYN packets may
4628 have no uid or gid associated with them since they do not yet belong
4629 to a TCP connection, and the uid/gid associated with a packet may not
4630 be as expected if the associated process calls
4632 or similar system calls.
4634 Rule syntax is subject to the command line environment and some patterns
4635 may need to be escaped with the backslash character
4636 or quoted appropriately.
4638 Due to the architecture of
4640 ipfw nat is not compatible with the TCP segmentation offloading (TSO).
4641 Thus, to reliably nat your network traffic, please disable TSO
4645 ICMP error messages are not implicitly matched by dynamic rules
4646 for the respective conversations.
4647 To avoid failures of network error detection and path MTU discovery,
4648 ICMP error messages may need to be allowed explicitly through static
4655 actions may lead to confusing behaviour if ruleset has mistakes,
4656 and/or interaction with other subsystems (netgraph, dummynet, etc.) is used.
4657 One possible case for this is packet leaving
4659 in subroutine on the input pass, while later on output encountering unpaired
4662 As the call stack is kept intact after input pass, packet will suddenly
4663 return to the rule number used on input pass, not on output one.
4664 Order of processing should be checked carefully to avoid such mistakes.
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