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 .Cm table Ar number Cm add Ar addr Ns Oo / Ns Ar masklen Oc Op Ar value
53 .Cm table Ar number Cm delete Ar addr Ns Op / Ns Ar masklen
62 .Ss DUMMYNET CONFIGURATION (TRAFFIC SHAPER AND PACKET SCHEDULER)
64 .Brq Cm pipe | queue | sched
70 .Brq Cm pipe | queue | sched
71 .Brq Cm delete | list | show
93 utility is the user interface for controlling the
97 traffic shaper/packet scheduler, and the
98 in-kernel NAT services.
100 A firewall configuration, or
104 numbered from 1 to 65535.
105 Packets are passed to the firewall
106 from a number of different places in the protocol stack
107 (depending on the source and destination of the packet,
108 it is possible for the firewall to be
109 invoked multiple times on the same packet).
110 The packet passed to the firewall is compared
111 against each of the rules in the
114 (multiple rules with the same number are permitted, in which case
115 they are processed in order of insertion).
116 When a match is found, the action corresponding to the
117 matching rule is performed.
119 Depending on the action and certain system settings, packets
120 can be reinjected into the firewall at some rule after the
121 matching one for further processing.
123 A ruleset always includes a
125 rule (numbered 65535) which cannot be modified or deleted,
126 and matches all packets.
127 The action associated with the
133 depending on how the kernel is configured.
135 If the ruleset includes one or more rules with the
140 the firewall will have a
142 behaviour, i.e., upon a match it will create
144 i.e., rules that match packets with the same 5-tuple
145 (protocol, source and destination addresses and ports)
146 as the packet which caused their creation.
147 Dynamic rules, which have a limited lifetime, are checked
148 at the first occurrence of a
153 rule, and are typically used to open the firewall on-demand to
154 legitimate traffic only.
156 .Sx STATEFUL FIREWALL
159 Sections below for more information on the stateful behaviour of
162 All rules (including dynamic ones) have a few associated counters:
163 a packet count, a byte count, a log count and a timestamp
164 indicating the time of the last match.
165 Counters can be displayed or reset with
169 Each rule belongs to one of 32 different
173 commands to atomically manipulate sets, such as enable,
174 disable, swap sets, move all rules in a set to another
175 one, delete all rules in a set.
176 These can be useful to
177 install temporary configurations, or to test them.
180 for more information on
183 Rules can be added with the
185 command; deleted individually or in groups with the
187 command, and globally (except those in set 31) with the
189 command; displayed, optionally with the content of the
195 Finally, counters can be reset with the
202 The following general options are available when invoking
204 .Bl -tag -width indent
206 Show counter values when listing rules.
209 command implies this option.
211 Only show the action and the comment, not the body of a rule.
215 When entering or showing rules, print them in compact form,
216 i.e., omitting the "ip from any to any" string
217 when this does not carry any additional information.
219 When listing, show dynamic rules in addition to static ones.
223 is specified, also show expired dynamic rules.
225 Do not ask for confirmation for commands that can cause problems
228 If there is no tty associated with the process, this is implied.
230 When listing a table (see the
232 section below for more information on lookup tables), format values
234 By default, values are shown as integers.
236 Only check syntax of the command strings, without actually passing
239 Try to resolve addresses and service names in output.
241 Be quiet when executing the
251 This is useful when updating rulesets by executing multiple
255 .Ql sh\ /etc/rc.firewall ) ,
256 or by processing a file with many
258 rules across a remote login session.
259 It also stops a table add or delete
260 from failing if the entry already exists or is not present.
262 The reason why this option may be important is that
263 for some of these actions,
265 may print a message; if the action results in blocking the
266 traffic to the remote client,
267 the remote login session will be closed
268 and the rest of the ruleset will not be processed.
269 Access to the console would then be required to recover.
271 When listing rules, show the
273 each rule belongs to.
274 If this flag is not specified, disabled rules will not be
277 When listing pipes, sort according to one of the four
278 counters (total or current packets or bytes).
280 When listing, show last match timestamp converted with ctime().
282 When listing, show last match timestamp as seconds from the epoch.
283 This form can be more convenient for postprocessing by scripts.
285 .Ss LIST OF RULES AND PREPROCESSING
286 To ease configuration, rules can be put into a file which is
289 as shown in the last synopsis line.
293 The file will be read line by line and applied as arguments to the
297 Optionally, a preprocessor can be specified using
301 is to be piped through.
302 Useful preprocessors include
308 does not start with a slash
310 as its first character, the usual
312 name search is performed.
313 Care should be taken with this in environments where not all
314 file systems are mounted (yet) by the time
316 is being run (e.g.\& when they are mounted over NFS).
319 has been specified, any additional arguments are passed on to the preprocessor
321 This allows for flexible configuration files (like conditionalizing
322 them on the local hostname) and the use of macros to centralize
323 frequently required arguments like IP addresses.
324 .Ss TRAFFIC SHAPER CONFIGURATION
330 commands are used to configure the traffic shaper and packet scheduler.
332 .Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION
333 Section below for details.
335 If the world and the kernel get out of sync the
337 ABI may break, preventing you from being able to add any rules.
339 adversely effect the booting process.
344 to temporarily disable the firewall to regain access to the network,
345 allowing you to fix the problem.
347 A packet is checked against the active ruleset in multiple places
348 in the protocol stack, under control of several sysctl variables.
349 These places and variables are shown below, and it is important to
350 have this picture in mind in order to design a correct ruleset.
351 .Bd -literal -offset indent
354 +----------->-----------+
356 [ip(6)_input] [ip(6)_output] net.inet(6).ip(6).fw.enable=1
359 [ether_demux] [ether_output_frame] net.link.ether.ipfw=1
361 +-->--[bdg_forward]-->--+ net.link.bridge.ipfw=1
367 times the same packet goes through the firewall can
368 vary between 0 and 4 depending on packet source and
369 destination, and system configuration.
371 Note that as packets flow through the stack, headers can be
372 stripped or added to it, and so they may or may not be available
374 E.g., incoming packets will include the MAC header when
378 but the same packets will have the MAC header stripped off when
385 Also note that each packet is always checked against the complete ruleset,
386 irrespective of the place where the check occurs, or the source of the packet.
387 If a rule contains some match patterns or actions which are not valid
388 for the place of invocation (e.g.\& trying to match a MAC header within
392 the match pattern will not match, but a
394 operator in front of such patterns
398 match on those packets.
399 It is thus the responsibility of
400 the programmer, if necessary, to write a suitable ruleset to
401 differentiate among the possible places.
403 rules can be useful here, as an example:
404 .Bd -literal -offset indent
405 # packets from ether_demux or bdg_forward
406 ipfw add 10 skipto 1000 all from any to any layer2 in
407 # packets from ip_input
408 ipfw add 10 skipto 2000 all from any to any not layer2 in
409 # packets from ip_output
410 ipfw add 10 skipto 3000 all from any to any not layer2 out
411 # packets from ether_output_frame
412 ipfw add 10 skipto 4000 all from any to any layer2 out
415 (yes, at the moment there is no way to differentiate between
416 ether_demux and bdg_forward).
418 In general, each keyword or argument must be provided as
419 a separate command line argument, with no leading or trailing
421 Keywords are case-sensitive, whereas arguments may
422 or may not be case-sensitive depending on their nature
423 (e.g.\& uid's are, hostnames are not).
425 Some arguments (e.g., port or address lists) are comma-separated
427 In this case, spaces after commas ',' are allowed to make
428 the line more readable.
429 You can also put the entire
430 command (including flags) into a single argument.
431 E.g., the following forms are equivalent:
432 .Bd -literal -offset indent
433 ipfw -q add deny src-ip 10.0.0.0/24,127.0.0.1/8
434 ipfw -q add deny src-ip 10.0.0.0/24, 127.0.0.1/8
435 ipfw "-q add deny src-ip 10.0.0.0/24, 127.0.0.1/8"
438 The format of firewall rules is the following:
439 .Bd -ragged -offset indent
442 .Op Cm set Ar set_number
443 .Op Cm prob Ar match_probability
445 .Op Cm log Op Cm logamount Ar number
455 where the body of the rule specifies which information is used
456 for filtering packets, among the following:
458 .Bl -tag -width "Source and dest. addresses and ports" -offset XXX -compact
459 .It Layer-2 header fields
461 .It IPv4 and IPv6 Protocol
463 .It Source and dest. addresses and ports
467 .It Transmit and receive interface
469 .It Misc. IP header fields
470 Version, type of service, datagram length, identification,
471 fragment flag (non-zero IP offset),
474 .It IPv6 Extension headers
475 Fragmentation, Hop-by-Hop options,
476 Routing Headers, Source routing rthdr0, Mobile IPv6 rthdr2, IPSec options.
478 .It Misc. TCP header fields
479 TCP flags (SYN, FIN, ACK, RST, etc.),
480 sequence number, acknowledgment number,
488 When the packet can be associated with a local socket.
490 Whether a packet came from a divert socket (e.g.,
492 .It Fib annotation state
493 Whether a packet has been tagged for using a specific FIB (routing table)
494 in future forwarding decisions.
497 Note that some of the above information, e.g.\& source MAC or IP addresses and
498 TCP/UDP ports, can be easily spoofed, so filtering on those fields
499 alone might not guarantee the desired results.
500 .Bl -tag -width indent
502 Each rule is associated with a
504 in the range 1..65535, with the latter reserved for the
507 Rules are checked sequentially by rule number.
508 Multiple rules can have the same number, in which case they are
509 checked (and listed) according to the order in which they have
511 If a rule is entered without specifying a number, the kernel will
512 assign one in such a way that the rule becomes the last one
516 Automatic rule numbers are assigned by incrementing the last
517 non-default rule number by the value of the sysctl variable
518 .Ar net.inet.ip.fw.autoinc_step
519 which defaults to 100.
520 If this is not possible (e.g.\& because we would go beyond the
521 maximum allowed rule number), the number of the last
522 non-default value is used instead.
523 .It Cm set Ar set_number
524 Each rule is associated with a
527 Sets can be individually disabled and enabled, so this parameter
528 is of fundamental importance for atomic ruleset manipulation.
529 It can be also used to simplify deletion of groups of rules.
530 If a rule is entered without specifying a set number,
533 Set 31 is special in that it cannot be disabled,
534 and rules in set 31 are not deleted by the
536 command (but you can delete them with the
537 .Nm ipfw delete set 31
539 Set 31 is also used for the
542 .It Cm prob Ar match_probability
543 A match is only declared with the specified probability
544 (floating point number between 0 and 1).
545 This can be useful for a number of applications such as
546 random packet drop or
549 to simulate the effect of multiple paths leading to out-of-order
552 Note: this condition is checked before any other condition, including
553 ones such as keep-state or check-state which might have side effects.
554 .It Cm log Op Cm logamount Ar number
555 Packets matching a rule with the
557 keyword will be made available for logging in two ways:
558 if the sysctl variable
559 .Va net.inet.ip.fw.verbose
560 is set to 0 (default), one can use
565 This pseudo interface can be created after a boot
566 manually by using the following command:
567 .Bd -literal -offset indent
568 # ifconfig ipfw0 create
571 Or, automatically at boot time by adding the following
575 .Bd -literal -offset indent
579 There is no overhead if no
581 is attached to the pseudo interface.
584 .Va net.inet.ip.fw.verbose
585 is set to 1, packets will be logged to
589 facility up to a maximum of
594 is specified, the limit is taken from the sysctl variable
595 .Va net.inet.ip.fw.verbose_limit .
596 In both cases, a value of 0 means unlimited logging.
598 Once the limit is reached, logging can be re-enabled by
599 clearing the logging counter or the packet counter for that entry, see the
603 Note: logging is done after all other packet matching conditions
604 have been successfully verified, and before performing the final
605 action (accept, deny, etc.) on the packet.
607 When a packet matches a rule with the
609 keyword, the numeric tag for the given
611 in the range 1..65534 will be attached to the packet.
612 The tag acts as an internal marker (it is not sent out over
613 the wire) that can be used to identify these packets later on.
614 This can be used, for example, to provide trust between interfaces
615 and to start doing policy-based filtering.
616 A packet can have multiple tags at the same time.
617 Tags are "sticky", meaning once a tag is applied to a packet by a
618 matching rule it exists until explicit removal.
619 Tags are kept with the packet everywhere within the kernel, but are
620 lost when packet leaves the kernel, for example, on transmitting
621 packet out to the network or sending packet to a
625 To check for previously applied tags, use the
628 To delete previously applied tag, use the
632 Note: since tags are kept with the packet everywhere in kernelspace,
633 they can be set and unset anywhere in the kernel network subsystem
636 facility), not only by means of the
642 For example, there can be a specialized
644 node doing traffic analyzing and tagging for later inspecting
646 .It Cm untag Ar number
647 When a packet matches a rule with the
649 keyword, the tag with the number
651 is searched among the tags attached to this packet and,
652 if found, removed from it.
653 Other tags bound to packet, if present, are left untouched.
655 When a packet matches a rule with the
657 keyword, the ALTQ identifier for the given
662 Note that this ALTQ tag is only meaningful for packets going "out" of IPFW,
663 and not being rejected or going to divert sockets.
664 Note that if there is insufficient memory at the time the packet is
665 processed, it will not be tagged, so it is wise to make your ALTQ
666 "default" queue policy account for this.
669 rules match a single packet, only the first one adds the ALTQ classification
671 In doing so, traffic may be shaped by using
672 .Cm count Cm altq Ar queue
673 rules for classification early in the ruleset, then later applying
674 the filtering decision.
679 rules may come later and provide the actual filtering decisions in
680 addition to the fallback ALTQ tag.
684 to set up the queues before IPFW will be able to look them up by name,
685 and if the ALTQ disciplines are rearranged, the rules in containing the
686 queue identifiers in the kernel will likely have gone stale and need
688 Stale queue identifiers will probably result in misclassification.
690 All system ALTQ processing can be turned on or off via
695 .Cm disable Ar altq .
697 .Va net.inet.ip.fw.one_pass
698 is irrelevant to ALTQ traffic shaping, as the actual rule action is followed
699 always after adding an ALTQ tag.
702 A rule can be associated with one of the following actions, which
703 will be executed when the packet matches the body of the rule.
704 .Bl -tag -width indent
705 .It Cm allow | accept | pass | permit
706 Allow packets that match rule.
707 The search terminates.
709 Checks the packet against the dynamic ruleset.
710 If a match is found, execute the action associated with
711 the rule which generated this dynamic rule, otherwise
712 move to the next rule.
715 rules do not have a body.
718 rule is found, the dynamic ruleset is checked at the first
724 Update counters for all packets that match rule.
725 The search continues with the next rule.
727 Discard packets that match this rule.
728 The search terminates.
729 .It Cm divert Ar port
730 Divert packets that match this rule to the
734 The search terminates.
735 .It Cm fwd | forward Ar ipaddr | tablearg Ns Op , Ns Ar port
736 Change the next-hop on matching packets to
738 which can be an IP address or a host name.
739 For IPv4, the next hop can also be supplied by the last table
740 looked up for the packet by using the
742 keyword instead of an explicit address.
743 The search terminates if this rule matches.
747 is a local address, then matching packets will be forwarded to
749 (or the port number in the packet if one is not specified in the rule)
750 on the local machine.
754 is not a local address, then the port number
755 (if specified) is ignored, and the packet will be
756 forwarded to the remote address, using the route as found in
757 the local routing table for that IP.
761 rule will not match layer-2 packets (those received
762 on ether_input, ether_output, or bridged).
766 action does not change the contents of the packet at all.
767 In particular, the destination address remains unmodified, so
768 packets forwarded to another system will usually be rejected by that system
769 unless there is a matching rule on that system to capture them.
770 For packets forwarded locally,
771 the local address of the socket will be
772 set to the original destination address of the packet.
775 entry look rather weird but is intended for
776 use with transparent proxy servers.
777 .It Cm nat Ar nat_nr | tablearg
780 (for network address translation, address redirect, etc.):
782 .Sx NETWORK ADDRESS TRANSLATION (NAT)
783 Section for further information.
784 .It Cm pipe Ar pipe_nr
788 (for bandwidth limitation, delay, etc.).
790 .Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION
791 Section for further information.
792 The search terminates; however, on exit from the pipe and if
796 .Va net.inet.ip.fw.one_pass
797 is not set, the packet is passed again to the firewall code
798 starting from the next rule.
799 .It Cm queue Ar queue_nr
803 (for bandwidth limitation using WF2Q+).
809 Discard packets that match this rule, and if the
810 packet is a TCP packet, try to send a TCP reset (RST) notice.
811 The search terminates.
813 Discard packets that match this rule, and if the
814 packet is a TCP packet, try to send a TCP reset (RST) notice.
815 The search terminates.
816 .It Cm skipto Ar number | tablearg
817 Skip all subsequent rules numbered less than
819 The search continues with the first rule numbered
822 It is possible to use the
824 keyword with a skipto for a
826 skipto, but care should be used, as no destination caching
827 is possible in this case so the rules are always walked to find it,
830 .It Cm call Ar number | tablearg
831 The current rule number is saved in the internal stack and
832 ruleset processing continues with the first rule numbered
835 If later a rule with the
837 action is encountered, the processing returns to the first rule
840 rule plus one or higher
841 (the same behaviour as with packets returning from
846 This could be used to make somewhat like an assembly language
848 calls to rules with common checks for different interfaces, etc.
850 Rule with any number could be called, not just forward jumps as with
852 So, to prevent endless loops in case of mistakes, both
856 actions don't do any jumps and simply go to the next rule if memory
857 cannot be allocated or stack overflowed/underflowed.
859 Internally stack for rule numbers is implemented using
861 facility and currently has size of 16 entries.
862 As mbuf tags are lost when packet leaves the kernel,
864 should not be used in subroutines to avoid endless loops
865 and other undesired effects.
867 Takes rule number saved to internal stack by the last
869 action and returns ruleset processing to the first rule
870 with number greater than number of corresponding
873 See description of the
875 action for more details.
881 and thus are unconditional, but
883 command-line utility currently requires every action except
886 While it is sometimes useful to return only on some packets,
887 usually you want to print just
890 A workaround for this is to use new syntax and
893 .Bd -literal -offset indent
894 # Add a rule without actual body
895 ipfw add 2999 return via any
897 # List rules without "from any to any" part
901 This cosmetic annoyance may be fixed in future releases.
903 Send a copy of packets matching this rule to the
907 The search continues with the next rule.
908 .It Cm unreach Ar code
909 Discard packets that match this rule, and try to send an ICMP
910 unreachable notice with code
914 is a number from 0 to 255, or one of these aliases:
915 .Cm net , host , protocol , port ,
916 .Cm needfrag , srcfail , net-unknown , host-unknown ,
917 .Cm isolated , net-prohib , host-prohib , tosnet ,
918 .Cm toshost , filter-prohib , host-precedence
920 .Cm precedence-cutoff .
921 The search terminates.
922 .It Cm unreach6 Ar code
923 Discard packets that match this rule, and try to send an ICMPv6
924 unreachable notice with code
928 is a number from 0, 1, 3 or 4, or one of these aliases:
929 .Cm no-route, admin-prohib, address
932 The search terminates.
933 .It Cm netgraph Ar cookie
934 Divert packet into netgraph with given
936 The search terminates.
937 If packet is later returned from netgraph it is either
938 accepted or continues with the next rule, depending on
939 .Va net.inet.ip.fw.one_pass
941 .It Cm ngtee Ar cookie
942 A copy of packet is diverted into netgraph, original
943 packet continues with the next rule.
946 for more information on
951 .It Cm setfib Ar fibnum | tablearg
952 The packet is tagged so as to use the FIB (routing table)
954 in any subsequent forwarding decisions.
955 In the current implementation, this is limited to the values 0 through 15, see
957 Processing continues at the next rule.
958 It is possible to use the
961 If the tablearg value is not within the compiled range of fibs,
962 the packet's fib is set to 0.
963 .It Cm setdscp Ar DSCP | number | tablearg
964 Set specified DiffServ codepoint for an IPv4/IPv6 packet.
965 Processing continues at the next rule.
966 Supported values are:
1012 Additionally, DSCP value can be specified by number (0..64).
1013 It is also possible to use the
1015 keyword with setdscp.
1016 If the tablearg value is not within the 0..64 range, lower 6 bits of supplied
1019 Queue and reassemble IP fragments.
1020 If the packet is not fragmented, counters are updated and
1021 processing continues with the next rule.
1022 If the packet is the last logical fragment, the packet is reassembled and, if
1023 .Va net.inet.ip.fw.one_pass
1024 is set to 0, processing continues with the next rule.
1025 Otherwise, the packet is allowed to pass and the search terminates.
1026 If the packet is a fragment in the middle of a logical group of fragments,
1028 processing stops immediately.
1030 Fragment handling can be tuned via
1031 .Va net.inet.ip.maxfragpackets
1033 .Va net.inet.ip.maxfragsperpacket
1034 which limit, respectively, the maximum number of processable
1035 fragments (default: 800) and
1036 the maximum number of fragments per packet (default: 16).
1038 NOTA BENE: since fragments do not contain port numbers,
1039 they should be avoided with the
1042 Alternatively, direction-based (like
1046 ) and source-based (like
1048 ) match patterns can be used to select fragments.
1050 Usually a simple rule like:
1051 .Bd -literal -offset indent
1052 # reassemble incoming fragments
1053 ipfw add reass all from any to any in
1056 is all you need at the beginning of your ruleset.
1059 The body of a rule contains zero or more patterns (such as
1060 specific source and destination addresses or ports,
1061 protocol options, incoming or outgoing interfaces, etc.)
1062 that the packet must match in order to be recognised.
1063 In general, the patterns are connected by (implicit)
1065 operators -- i.e., all must match in order for the
1067 Individual patterns can be prefixed by the
1069 operator to reverse the result of the match, as in
1071 .Dl "ipfw add 100 allow ip from not 1.2.3.4 to any"
1073 Additionally, sets of alternative match patterns
1075 can be constructed by putting the patterns in
1076 lists enclosed between parentheses ( ) or braces { }, and
1079 operator as follows:
1081 .Dl "ipfw add 100 allow ip from { x or not y or z } to any"
1083 Only one level of parentheses is allowed.
1084 Beware that most shells have special meanings for parentheses
1085 or braces, so it is advisable to put a backslash \\ in front of them
1086 to prevent such interpretations.
1088 The body of a rule must in general include a source and destination
1092 can be used in various places to specify that the content of
1093 a required field is irrelevant.
1095 The rule body has the following format:
1096 .Bd -ragged -offset indent
1097 .Op Ar proto Cm from Ar src Cm to Ar dst
1101 The first part (proto from src to dst) is for backward
1102 compatibility with earlier versions of
1106 any match pattern (including MAC headers, IP protocols,
1107 addresses and ports) can be specified in the
1111 Rule fields have the following meaning:
1112 .Bl -tag -width indent
1113 .It Ar proto : protocol | Cm { Ar protocol Cm or ... }
1114 .It Ar protocol : Oo Cm not Oc Ar protocol-name | protocol-number
1115 An IP protocol specified by number or name
1116 (for a complete list see
1117 .Pa /etc/protocols ) ,
1118 or one of the following keywords:
1119 .Bl -tag -width indent
1121 Matches IPv4 packets.
1123 Matches IPv6 packets.
1132 option will be treated as inner protocol.
1140 .Cm { Ar protocol Cm or ... }
1143 is provided for convenience only but its use is deprecated.
1144 .It Ar src No and Ar dst : Bro Cm addr | Cm { Ar addr Cm or ... } Brc Op Oo Cm not Oc Ar ports
1145 An address (or a list, see below)
1146 optionally followed by
1152 with multiple addresses) is provided for convenience only and
1153 its use is discouraged.
1154 .It Ar addr : Oo Cm not Oc Bro
1155 .Cm any | me | me6 |
1156 .Cm table Ns Pq Ar number Ns Op , Ns Ar value
1157 .Ar | addr-list | addr-set
1159 .Bl -tag -width indent
1161 matches any IP address.
1163 matches any IP address configured on an interface in the system.
1165 matches any IPv6 address configured on an interface in the system.
1166 The address list is evaluated at the time the packet is
1168 .It Cm table Ns Pq Ar number Ns Op , Ns Ar value
1169 Matches any IPv4 address for which an entry exists in the lookup table
1171 If an optional 32-bit unsigned
1173 is also specified, an entry will match only if it has this value.
1176 section below for more information on lookup tables.
1178 .It Ar addr-list : ip-addr Ns Op Ns , Ns Ar addr-list
1180 A host or subnet address specified in one of the following ways:
1181 .Bl -tag -width indent
1182 .It Ar numeric-ip | hostname
1183 Matches a single IPv4 address, specified as dotted-quad or a hostname.
1184 Hostnames are resolved at the time the rule is added to the firewall list.
1185 .It Ar addr Ns / Ns Ar masklen
1186 Matches all addresses with base
1188 (specified as an IP address, a network number, or a hostname)
1192 As an example, 1.2.3.4/25 or 1.2.3.0/25 will match
1193 all IP numbers from 1.2.3.0 to 1.2.3.127 .
1194 .It Ar addr Ns : Ns Ar mask
1195 Matches all addresses with base
1197 (specified as an IP address, a network number, or a hostname)
1200 specified as a dotted quad.
1201 As an example, 1.2.3.4:255.0.255.0 or 1.0.3.0:255.0.255.0 will match
1203 This form is advised only for non-contiguous
1205 It is better to resort to the
1206 .Ar addr Ns / Ns Ar masklen
1207 format for contiguous masks, which is more compact and less
1210 .It Ar addr-set : addr Ns Oo Ns / Ns Ar masklen Oc Ns Cm { Ns Ar list Ns Cm }
1211 .It Ar list : Bro Ar num | num-num Brc Ns Op Ns , Ns Ar list
1212 Matches all addresses with base address
1214 (specified as an IP address, a network number, or a hostname)
1215 and whose last byte is in the list between braces { } .
1216 Note that there must be no spaces between braces and
1217 numbers (spaces after commas are allowed).
1218 Elements of the list can be specified as single entries
1222 field is used to limit the size of the set of addresses,
1223 and can have any value between 24 and 32.
1225 it will be assumed as 24.
1227 This format is particularly useful to handle sparse address sets
1228 within a single rule.
1229 Because the matching occurs using a
1230 bitmask, it takes constant time and dramatically reduces
1231 the complexity of rulesets.
1233 As an example, an address specified as 1.2.3.4/24{128,35-55,89}
1234 or 1.2.3.0/24{128,35-55,89}
1235 will match the following IP addresses:
1237 1.2.3.128, 1.2.3.35 to 1.2.3.55, 1.2.3.89 .
1238 .It Ar addr6-list : ip6-addr Ns Op Ns , Ns Ar addr6-list
1240 A host or subnet specified one of the following ways:
1241 .Bl -tag -width indent
1242 .It Ar numeric-ip | hostname
1243 Matches a single IPv6 address as allowed by
1246 Hostnames are resolved at the time the rule is added to the firewall
1248 .It Ar addr Ns / Ns Ar masklen
1249 Matches all IPv6 addresses with base
1251 (specified as allowed by
1259 No support for sets of IPv6 addresses is provided because IPv6 addresses
1260 are typically random past the initial prefix.
1261 .It Ar ports : Bro Ar port | port Ns \&- Ns Ar port Ns Brc Ns Op , Ns Ar ports
1262 For protocols which support port numbers (such as TCP and UDP), optional
1264 may be specified as one or more ports or port ranges, separated
1265 by commas but no spaces, and an optional
1270 notation specifies a range of ports (including boundaries).
1274 may be used instead of numeric port values.
1275 The length of the port list is limited to 30 ports or ranges,
1276 though one can specify larger ranges by using an
1280 section of the rule.
1284 can be used to escape the dash
1286 character in a service name (from a shell, the backslash must be
1287 typed twice to avoid the shell itself interpreting it as an escape
1290 .Dl "ipfw add count tcp from any ftp\e\e-data-ftp to any"
1292 Fragmented packets which have a non-zero offset (i.e., not the first
1293 fragment) will never match a rule which has one or more port
1297 option for details on matching fragmented packets.
1299 .Ss RULE OPTIONS (MATCH PATTERNS)
1300 Additional match patterns can be used within
1302 Zero or more of these so-called
1304 can be present in a rule, optionally prefixed by the
1306 operand, and possibly grouped into
1309 The following match patterns can be used (listed in alphabetical order):
1310 .Bl -tag -width indent
1311 .It Cm // this is a comment.
1312 Inserts the specified text as a comment in the rule.
1313 Everything following // is considered as a comment and stored in the rule.
1314 You can have comment-only rules, which are listed as having a
1316 action followed by the comment.
1321 Matches only packets generated by a divert socket.
1322 .It Cm diverted-loopback
1323 Matches only packets coming from a divert socket back into the IP stack
1325 .It Cm diverted-output
1326 Matches only packets going from a divert socket back outward to the IP
1327 stack output for delivery.
1328 .It Cm dst-ip Ar ip-address
1329 Matches IPv4 packets whose destination IP is one of the address(es)
1330 specified as argument.
1331 .It Bro Cm dst-ip6 | dst-ipv6 Brc Ar ip6-address
1332 Matches IPv6 packets whose destination IP is one of the address(es)
1333 specified as argument.
1334 .It Cm dst-port Ar ports
1335 Matches IP packets whose destination port is one of the port(s)
1336 specified as argument.
1338 Matches TCP packets that have the RST or ACK bits set.
1339 .It Cm ext6hdr Ar header
1340 Matches IPv6 packets containing the extended header given by
1342 Supported headers are:
1348 any type of Routing Header
1350 Source routing Routing Header Type 0
1352 Mobile IPv6 Routing Header Type 2
1356 IPSec authentication headers
1358 and IPsec encapsulated security payload headers
1360 .It Cm fib Ar fibnum
1361 Matches a packet that has been tagged to use
1362 the given FIB (routing table) number.
1363 .It Cm flow-id Ar labels
1364 Matches IPv6 packets containing any of the flow labels given in
1367 is a comma separated list of numeric flow labels.
1369 Matches packets that are fragments and not the first
1370 fragment of an IP datagram.
1371 Note that these packets will not have
1372 the next protocol header (e.g.\& TCP, UDP) so options that look into
1373 these headers cannot match.
1375 Matches all TCP or UDP packets sent by or received for a
1379 may be specified by name or number.
1380 .It Cm jail Ar prisonID
1381 Matches all TCP or UDP packets sent by or received for the
1382 jail whos prison ID is
1384 .It Cm icmptypes Ar types
1385 Matches ICMP packets whose ICMP type is in the list
1387 The list may be specified as any combination of
1388 individual types (numeric) separated by commas.
1389 .Em Ranges are not allowed .
1390 The supported ICMP types are:
1394 destination unreachable
1402 router advertisement
1406 time-to-live exceeded
1418 address mask request
1420 and address mask reply
1422 .It Cm icmp6types Ar types
1423 Matches ICMP6 packets whose ICMP6 type is in the list of
1425 The list may be specified as any combination of
1426 individual types (numeric) separated by commas.
1427 .Em Ranges are not allowed .
1429 Matches incoming or outgoing packets, respectively.
1433 are mutually exclusive (in fact,
1437 .It Cm ipid Ar id-list
1438 Matches IPv4 packets whose
1440 field has value included in
1442 which is either a single value or a list of values or ranges
1443 specified in the same way as
1445 .It Cm iplen Ar len-list
1446 Matches IP packets whose total length, including header and data, is
1449 which is either a single value or a list of values or ranges
1450 specified in the same way as
1452 .It Cm ipoptions Ar spec
1453 Matches packets whose IPv4 header contains the comma separated list of
1454 options specified in
1456 The supported IP options are:
1459 (strict source route),
1461 (loose source route),
1463 (record packet route) and
1466 The absence of a particular option may be denoted
1469 .It Cm ipprecedence Ar precedence
1470 Matches IPv4 packets whose precedence field is equal to
1473 Matches packets that have IPSEC history associated with them
1474 (i.e., the packet comes encapsulated in IPSEC, the kernel
1475 has IPSEC support and IPSEC_FILTERTUNNEL option, and can correctly
1478 Note that specifying
1480 is different from specifying
1482 as the latter will only look at the specific IP protocol field,
1483 irrespective of IPSEC kernel support and the validity of the IPSEC data.
1485 Further note that this flag is silently ignored in kernels without
1487 It does not affect rule processing when given and the
1488 rules are handled as if with no
1491 .It Cm iptos Ar spec
1492 Matches IPv4 packets whose
1494 field contains the comma separated list of
1495 service types specified in
1497 The supported IP types of service are:
1500 .Pq Dv IPTOS_LOWDELAY ,
1502 .Pq Dv IPTOS_THROUGHPUT ,
1504 .Pq Dv IPTOS_RELIABILITY ,
1506 .Pq Dv IPTOS_MINCOST ,
1508 .Pq Dv IPTOS_ECN_CE .
1509 The absence of a particular type may be denoted
1512 .It Cm dscp spec Ns Op , Ns Ar spec
1513 Matches IPv4/IPv6 packets whose
1515 field value is contained in
1518 Multiple values can be specified via
1519 the comma separated list.
1520 Value can be one of keywords used in
1522 action or exact number.
1523 .It Cm ipttl Ar ttl-list
1524 Matches IPv4 packets whose time to live is included in
1526 which is either a single value or a list of values or ranges
1527 specified in the same way as
1529 .It Cm ipversion Ar ver
1530 Matches IP packets whose IP version field is
1533 Upon a match, the firewall will create a dynamic rule, whose
1534 default behaviour is to match bidirectional traffic between
1535 source and destination IP/port using the same protocol.
1536 The rule has a limited lifetime (controlled by a set of
1538 variables), and the lifetime is refreshed every time a matching
1541 Matches only layer2 packets, i.e., those passed to
1543 from ether_demux() and ether_output_frame().
1544 .It Cm limit Bro Cm src-addr | src-port | dst-addr | dst-port Brc Ar N
1545 The firewall will only allow
1547 connections with the same
1548 set of parameters as specified in the rule.
1550 of source and destination addresses and ports can be
1553 only IPv4 flows are supported.
1554 .It Cm lookup Bro Cm dst-ip | dst-port | src-ip | src-port | uid | jail Brc Ar N
1555 Search an entry in lookup table
1557 that matches the field specified as argument.
1558 If not found, the match fails.
1559 Otherwise, the match succeeds and
1561 is set to the value extracted from the table.
1563 This option can be useful to quickly dispatch traffic based on
1564 certain packet fields.
1567 section below for more information on lookup tables.
1568 .It Cm { MAC | mac } Ar dst-mac src-mac
1569 Match packets with a given
1573 addresses, specified as the
1575 keyword (matching any MAC address), or six groups of hex digits
1576 separated by colons,
1577 and optionally followed by a mask indicating the significant bits.
1578 The mask may be specified using either of the following methods:
1579 .Bl -enum -width indent
1583 followed by the number of significant bits.
1584 For example, an address with 33 significant bits could be specified as:
1586 .Dl "MAC 10:20:30:40:50:60/33 any"
1591 followed by a bitmask specified as six groups of hex digits separated
1593 For example, an address in which the last 16 bits are significant could
1596 .Dl "MAC 10:20:30:40:50:60&00:00:00:00:ff:ff any"
1598 Note that the ampersand character has a special meaning in many shells
1599 and should generally be escaped.
1602 Note that the order of MAC addresses (destination first,
1604 the same as on the wire, but the opposite of the one used for
1606 .It Cm mac-type Ar mac-type
1607 Matches packets whose Ethernet Type field
1608 corresponds to one of those specified as argument.
1610 is specified in the same way as
1612 (i.e., one or more comma-separated single values or ranges).
1613 You can use symbolic names for known values such as
1614 .Em vlan , ipv4, ipv6 .
1615 Values can be entered as decimal or hexadecimal (if prefixed by 0x),
1616 and they are always printed as hexadecimal (unless the
1618 option is used, in which case symbolic resolution will be attempted).
1619 .It Cm proto Ar protocol
1620 Matches packets with the corresponding IP protocol.
1621 .It Cm recv | xmit | via Brq Ar ifX | Ar if Ns Cm * | Ar table Ns Pq Ar number Ns Op , Ns Ar value | Ar ipno | Ar any
1622 Matches packets received, transmitted or going through,
1623 respectively, the interface specified by exact name
1627 by IP address, or through some interface.
1631 keyword causes the interface to always be checked.
1638 then only the receive or transmit interface (respectively)
1640 By specifying both, it is possible to match packets based on
1641 both receive and transmit interface, e.g.:
1643 .Dl "ipfw add deny ip from any to any out recv ed0 xmit ed1"
1647 interface can be tested on either incoming or outgoing packets,
1650 interface can only be tested on outgoing packets.
1655 is invalid) whenever
1659 A packet might not have a receive or transmit interface: packets
1660 originating from the local host have no receive interface,
1661 while packets destined for the local host have no transmit
1664 Matches TCP packets that have the SYN bit set but no ACK bit.
1665 This is the short form of
1666 .Dq Li tcpflags\ syn,!ack .
1668 Matches packets that are associated to a local socket and
1669 for which the SO_USER_COOKIE socket option has been set
1670 to a non-zero value.
1671 As a side effect, the value of the
1672 option is made available as
1674 value, which in turn can be used as
1679 .It Cm src-ip Ar ip-address
1680 Matches IPv4 packets whose source IP is one of the address(es)
1681 specified as an argument.
1682 .It Cm src-ip6 Ar ip6-address
1683 Matches IPv6 packets whose source IP is one of the address(es)
1684 specified as an argument.
1685 .It Cm src-port Ar ports
1686 Matches IP packets whose source port is one of the port(s)
1687 specified as argument.
1688 .It Cm tagged Ar tag-list
1689 Matches packets whose tags are included in
1691 which is either a single value or a list of values or ranges
1692 specified in the same way as
1694 Tags can be applied to the packet using
1696 rule action parameter (see it's description for details on tags).
1697 .It Cm tcpack Ar ack
1699 Match if the TCP header acknowledgment number field is set to
1701 .It Cm tcpdatalen Ar tcpdatalen-list
1702 Matches TCP packets whose length of TCP data is
1703 .Ar tcpdatalen-list ,
1704 which is either a single value or a list of values or ranges
1705 specified in the same way as
1707 .It Cm tcpflags Ar spec
1709 Match if the TCP header contains the comma separated list of
1712 The supported TCP flags are:
1721 The absence of a particular flag may be denoted
1724 A rule which contains a
1726 specification can never match a fragmented packet which has
1730 option for details on matching fragmented packets.
1731 .It Cm tcpseq Ar seq
1733 Match if the TCP header sequence number field is set to
1735 .It Cm tcpwin Ar tcpwin-list
1736 Matches TCP packets whose header window field is set to
1738 which is either a single value or a list of values or ranges
1739 specified in the same way as
1741 .It Cm tcpoptions Ar spec
1743 Match if the TCP header contains the comma separated list of
1744 options specified in
1746 The supported TCP options are:
1749 (maximum segment size),
1751 (tcp window advertisement),
1755 (rfc1323 timestamp) and
1757 (rfc1644 t/tcp connection count).
1758 The absence of a particular option may be denoted
1762 Match all TCP or UDP packets sent by or received for a
1766 may be matched by name or identification number.
1768 For incoming packets,
1769 a routing table lookup is done on the packet's source address.
1770 If the interface on which the packet entered the system matches the
1771 outgoing interface for the route,
1773 If the interfaces do not match up,
1774 the packet does not match.
1775 All outgoing packets or packets with no incoming interface match.
1777 The name and functionality of the option is intentionally similar to
1778 the Cisco IOS command:
1780 .Dl ip verify unicast reverse-path
1782 This option can be used to make anti-spoofing rules to reject all
1783 packets with source addresses not from this interface.
1787 For incoming packets,
1788 a routing table lookup is done on the packet's source address.
1789 If a route to the source address exists, but not the default route
1790 or a blackhole/reject route, the packet matches.
1791 Otherwise, the packet does not match.
1792 All outgoing packets match.
1794 The name and functionality of the option is intentionally similar to
1795 the Cisco IOS command:
1797 .Dl ip verify unicast source reachable-via any
1799 This option can be used to make anti-spoofing rules to reject all
1800 packets whose source address is unreachable.
1802 For incoming packets, the packet's source address is checked if it
1803 belongs to a directly connected network.
1804 If the network is directly connected, then the interface the packet
1805 came on in is compared to the interface the network is connected to.
1806 When incoming interface and directly connected interface are not the
1807 same, the packet does not match.
1808 Otherwise, the packet does match.
1809 All outgoing packets match.
1811 This option can be used to make anti-spoofing rules to reject all
1812 packets that pretend to be from a directly connected network but do
1813 not come in through that interface.
1814 This option is similar to but more restricted than
1816 because it engages only on packets with source addresses of directly
1817 connected networks instead of all source addresses.
1820 Lookup tables are useful to handle large sparse sets of
1821 addresses or other search keys (e.g., ports, jail IDs, interface names).
1822 In the rest of this section we will use the term ``address''.
1823 There may be up to 65535 different lookup tables, numbered 0 to 65534.
1825 Each entry is represented by an
1826 .Ar addr Ns Op / Ns Ar masklen
1827 and will match all addresses with base
1829 (specified as an IPv4/IPv6 address, a hostname or an unsigned integer)
1835 is not specified, it defaults to 32 for IPv4 and 128 for IPv6.
1836 When looking up an IP address in a table, the most specific
1838 Associated with each entry is a 32-bit unsigned
1840 which can optionally be checked by a rule matching code.
1841 When adding an entry, if
1843 is not specified, it defaults to 0.
1845 An entry can be added to a table
1847 or removed from a table
1849 A table can be examined
1854 Internally, each table is stored in a Radix tree, the same way as
1855 the routing table (see
1858 Lookup tables currently support only ports, jail IDs, IPv4/IPv6 addresses
1859 and interface names.
1860 Wildcards is not supported for interface names.
1864 feature provides the ability to use a value, looked up in the table, as
1865 the argument for a rule action, action parameter or rule option.
1866 This can significantly reduce number of rules in some configurations.
1867 If two tables are used in a rule, the result of the second (destination)
1871 argument can be used with the following actions:
1872 .Cm nat, pipe , queue, divert, tee, netgraph, ngtee, fwd, skipto, setfib,
1880 it is possible to supply table entries with values
1881 that are in the form of IP addresses or hostnames.
1884 Section for example usage of tables and the tablearg keyword.
1888 action, the user should be aware that the code will walk the ruleset
1889 up to a rule equal to, or past, the given number,
1890 and should therefore try keep the
1891 ruleset compact between the skipto and the target rules.
1893 Each rule belongs to one of 32 different
1896 Set 31 is reserved for the default rule.
1898 By default, rules are put in set 0, unless you use the
1900 attribute when entering a new rule.
1901 Sets can be individually and atomically enabled or disabled,
1902 so this mechanism permits an easy way to store multiple configurations
1903 of the firewall and quickly (and atomically) switch between them.
1904 The command to enable/disable sets is
1905 .Bd -ragged -offset indent
1907 .Cm set Oo Cm disable Ar number ... Oc Op Cm enable Ar number ...
1914 sections can be specified.
1915 Command execution is atomic on all the sets specified in the command.
1916 By default, all sets are enabled.
1918 When you disable a set, its rules behave as if they do not exist
1919 in the firewall configuration, with only one exception:
1920 .Bd -ragged -offset indent
1921 dynamic rules created from a rule before it had been disabled
1922 will still be active until they expire.
1924 dynamic rules you have to explicitly delete the parent rule
1925 which generated them.
1928 The set number of rules can be changed with the command
1929 .Bd -ragged -offset indent
1932 .Brq Cm rule Ar rule-number | old-set
1936 Also, you can atomically swap two rulesets with the command
1937 .Bd -ragged -offset indent
1939 .Cm set swap Ar first-set second-set
1944 Section on some possible uses of sets of rules.
1945 .Sh STATEFUL FIREWALL
1946 Stateful operation is a way for the firewall to dynamically
1947 create rules for specific flows when packets that
1948 match a given pattern are detected.
1949 Support for stateful
1950 operation comes through the
1951 .Cm check-state , keep-state
1957 Dynamic rules are created when a packet matches a
1961 rule, causing the creation of a
1963 rule which will match all and only packets with
1967 .Em src-ip/src-port dst-ip/dst-port
1972 are used here only to denote the initial match addresses, but they
1973 are completely equivalent afterwards).
1974 Dynamic rules will be checked at the first
1975 .Cm check-state, keep-state
1978 occurrence, and the action performed upon a match will be the same
1979 as in the parent rule.
1981 Note that no additional attributes other than protocol and IP addresses
1982 and ports are checked on dynamic rules.
1984 The typical use of dynamic rules is to keep a closed firewall configuration,
1985 but let the first TCP SYN packet from the inside network install a
1986 dynamic rule for the flow so that packets belonging to that session
1987 will be allowed through the firewall:
1989 .Dl "ipfw add check-state"
1990 .Dl "ipfw add allow tcp from my-subnet to any setup keep-state"
1991 .Dl "ipfw add deny tcp from any to any"
1993 A similar approach can be used for UDP, where an UDP packet coming
1994 from the inside will install a dynamic rule to let the response through
1997 .Dl "ipfw add check-state"
1998 .Dl "ipfw add allow udp from my-subnet to any keep-state"
1999 .Dl "ipfw add deny udp from any to any"
2001 Dynamic rules expire after some time, which depends on the status
2002 of the flow and the setting of some
2006 .Sx SYSCTL VARIABLES
2008 For TCP sessions, dynamic rules can be instructed to periodically
2009 send keepalive packets to refresh the state of the rule when it is
2014 for more examples on how to use dynamic rules.
2015 .Sh TRAFFIC SHAPER (DUMMYNET) CONFIGURATION
2017 is also the user interface for the
2019 traffic shaper, packet scheduler and network emulator, a subsystem that
2020 can artificially queue, delay or drop packets
2021 emulating the behaviour of certain network links
2022 or queueing systems.
2025 operates by first using the firewall to select packets
2026 using any match pattern that can be used in
2029 Matching packets are then passed to either of two
2030 different objects, which implement the traffic regulation:
2031 .Bl -hang -offset XXXX
2037 with given bandwidth and propagation delay,
2038 driven by a FIFO scheduler and a single queue with programmable
2039 queue size and packet loss rate.
2040 Packets are appended to the queue as they come out from
2042 and then transferred in FIFO order to the link at the desired rate.
2046 is an abstraction used to implement packet scheduling
2047 using one of several packet scheduling algorithms.
2050 are first grouped into flows according to a mask on the 5-tuple.
2051 Flows are then passed to the scheduler associated to the
2053 and each flow uses scheduling parameters (weight and others)
2054 as configured in the
2057 A scheduler in turn is connected to an emulated link,
2058 and arbitrates the link's bandwidth among backlogged flows according to
2059 weights and to the features of the scheduling algorithm in use.
2064 can be used to set hard limits to the bandwidth that a flow can use, whereas
2066 can be used to determine how different flows share the available bandwidth.
2068 A graphical representation of the binding of queues,
2069 flows, schedulers and links is below.
2070 .Bd -literal -offset indent
2071 (flow_mask|sched_mask) sched_mask
2072 +---------+ weight Wx +-------------+
2073 | |->-[flow]-->--| |-+
2074 -->--| QUEUE x | ... | | |
2075 | |->-[flow]-->--| SCHEDuler N | |
2077 ... | +--[LINK N]-->--
2078 +---------+ weight Wy | | +--[LINK N]-->--
2079 | |->-[flow]-->--| | |
2080 -->--| QUEUE y | ... | | |
2081 | |->-[flow]-->--| | |
2082 +---------+ +-------------+ |
2085 It is important to understand the role of the SCHED_MASK
2086 and FLOW_MASK, which are configured through the commands
2087 .Dl "ipfw sched N config mask SCHED_MASK ..."
2089 .Dl "ipfw queue X config mask FLOW_MASK ..." .
2091 The SCHED_MASK is used to assign flows to one or more
2092 scheduler instances, one for each
2093 value of the packet's 5-tuple after applying SCHED_MASK.
2094 As an example, using ``src-ip 0xffffff00'' creates one instance
2095 for each /24 destination subnet.
2097 The FLOW_MASK, together with the SCHED_MASK, is used to split
2099 As an example, using
2100 ``src-ip 0x000000ff''
2101 together with the previous SCHED_MASK makes a flow for
2102 each individual source address.
2103 In turn, flows for each /24
2104 subnet will be sent to the same scheduler instance.
2106 The above diagram holds even for the
2108 case, with the only restriction that a
2110 only supports a SCHED_MASK, and forces the use of a FIFO
2111 scheduler (these are for backward compatibility reasons;
2112 in fact, internally, a
2114 pipe is implemented exactly as above).
2116 There are two modes of
2124 mode tries to emulate a real link: the
2126 scheduler ensures that the packet will not leave the pipe faster than it
2127 would on the real link with a given bandwidth.
2130 mode allows certain packets to bypass the
2132 scheduler (if packet flow does not exceed pipe's bandwidth).
2133 This is the reason why the
2135 mode requires less CPU cycles per packet (on average) and packet latency
2136 can be significantly lower in comparison to a real link with the same
2142 mode can be enabled by setting the
2143 .Va net.inet.ip.dummynet.io_fast
2145 variable to a non-zero value.
2147 .Ss PIPE, QUEUE AND SCHEDULER CONFIGURATION
2153 configuration commands are the following:
2154 .Bd -ragged -offset indent
2155 .Cm pipe Ar number Cm config Ar pipe-configuration
2157 .Cm queue Ar number Cm config Ar queue-configuration
2159 .Cm sched Ar number Cm config Ar sched-configuration
2162 The following parameters can be configured for a pipe:
2164 .Bl -tag -width indent -compact
2165 .It Cm bw Ar bandwidth | device
2166 Bandwidth, measured in
2169 .Brq Cm bit/s | Byte/s .
2172 A value of 0 (default) means unlimited bandwidth.
2173 The unit must immediately follow the number, as in
2175 .Dl "ipfw pipe 1 config bw 300Kbit/s"
2177 If a device name is specified instead of a numeric value, as in
2179 .Dl "ipfw pipe 1 config bw tun0"
2181 then the transmit clock is supplied by the specified device.
2182 At the moment only the
2184 device supports this
2185 functionality, for use in conjunction with
2188 .It Cm delay Ar ms-delay
2189 Propagation delay, measured in milliseconds.
2190 The value is rounded to the next multiple of the clock tick
2191 (typically 10ms, but it is a good practice to run kernels
2193 .Dq "options HZ=1000"
2195 the granularity to 1ms or less).
2196 The default value is 0, meaning no delay.
2198 .It Cm burst Ar size
2199 If the data to be sent exceeds the pipe's bandwidth limit
2200 (and the pipe was previously idle), up to
2202 bytes of data are allowed to bypass the
2204 scheduler, and will be sent as fast as the physical link allows.
2205 Any additional data will be transmitted at the rate specified
2209 The burst size depends on how long the pipe has been idle;
2210 the effective burst size is calculated as follows:
2217 .It Cm profile Ar filename
2218 A file specifying the additional overhead incurred in the transmission
2219 of a packet on the link.
2221 Some link types introduce extra delays in the transmission
2222 of a packet, e.g., because of MAC level framing, contention on
2223 the use of the channel, MAC level retransmissions and so on.
2224 From our point of view, the channel is effectively unavailable
2225 for this extra time, which is constant or variable depending
2227 Additionally, packets may be dropped after this
2228 time (e.g., on a wireless link after too many retransmissions).
2229 We can model the additional delay with an empirical curve
2230 that represents its distribution.
2231 .Bd -literal -offset indent
2232 cumulative probability
2242 +-------*------------------->
2245 The empirical curve may have both vertical and horizontal lines.
2246 Vertical lines represent constant delay for a range of
2248 Horizontal lines correspond to a discontinuity in the delay
2249 distribution: the pipe will use the largest delay for a
2252 The file format is the following, with whitespace acting as
2253 a separator and '#' indicating the beginning a comment:
2254 .Bl -tag -width indent
2255 .It Cm name Ar identifier
2256 optional name (listed by "ipfw pipe show")
2257 to identify the delay distribution;
2259 the bandwidth used for the pipe.
2260 If not specified here, it must be present
2261 explicitly as a configuration parameter for the pipe;
2262 .It Cm loss-level Ar L
2263 the probability above which packets are lost.
2264 (0.0 <= L <= 1.0, default 1.0 i.e., no loss);
2266 the number of samples used in the internal
2267 representation of the curve (2..1024; default 100);
2268 .It Cm "delay prob" | "prob delay"
2269 One of these two lines is mandatory and defines
2270 the format of the following lines with data points.
2272 2 or more lines representing points in the curve,
2273 with either delay or probability first, according
2274 to the chosen format.
2275 The unit for delay is milliseconds.
2276 Data points do not need to be sorted.
2277 Also, the number of actual lines can be different
2278 from the value of the "samples" parameter:
2280 utility will sort and interpolate
2281 the curve as needed.
2284 Example of a profile file:
2285 .Bd -literal -offset indent
2290 0 200 # minimum overhead is 200ms
2296 #configuration file end
2300 The following parameters can be configured for a queue:
2302 .Bl -tag -width indent -compact
2303 .It Cm pipe Ar pipe_nr
2304 Connects a queue to the specified pipe.
2305 Multiple queues (with the same or different weights) can be connected to
2306 the same pipe, which specifies the aggregate rate for the set of queues.
2308 .It Cm weight Ar weight
2309 Specifies the weight to be used for flows matching this queue.
2310 The weight must be in the range 1..100, and defaults to 1.
2313 The following case-insensitive parameters can be configured for a
2316 .Bl -tag -width indent -compact
2317 .It Cm type Ar {fifo | wf2q+ | rr | qfq}
2318 specifies the scheduling algorithm to use.
2319 .Bl -tag -width indent -compact
2321 is just a FIFO scheduler (which means that all packets
2322 are stored in the same queue as they arrive to the scheduler).
2323 FIFO has O(1) per-packet time complexity, with very low
2324 constants (estimate 60-80ns on a 2GHz desktop machine)
2325 but gives no service guarantees.
2327 implements the WF2Q+ algorithm, which is a Weighted Fair Queueing
2328 algorithm which permits flows to share bandwidth according to
2330 Note that weights are not priorities; even a flow
2331 with a minuscule weight will never starve.
2332 WF2Q+ has O(log N) per-packet processing cost, where N is the number
2333 of flows, and is the default algorithm used by previous versions
2336 implements the Deficit Round Robin algorithm, which has O(1) processing
2337 costs (roughly, 100-150ns per packet)
2338 and permits bandwidth allocation according to weights, but
2339 with poor service guarantees.
2341 implements the QFQ algorithm, which is a very fast variant of
2342 WF2Q+, with similar service guarantees and O(1) processing
2343 costs (roughly, 200-250ns per packet).
2347 In addition to the type, all parameters allowed for a pipe can also
2348 be specified for a scheduler.
2350 Finally, the following parameters can be configured for both
2353 .Bl -tag -width XXXX -compact
2354 .It Cm buckets Ar hash-table-size
2355 Specifies the size of the hash table used for storing the
2357 Default value is 64 controlled by the
2360 .Va net.inet.ip.dummynet.hash_size ,
2361 allowed range is 16 to 65536.
2363 .It Cm mask Ar mask-specifier
2364 Packets sent to a given pipe or queue by an
2366 rule can be further classified into multiple flows, each of which is then
2370 A flow identifier is constructed by masking the IP addresses,
2371 ports and protocol types as specified with the
2373 options in the configuration of the pipe or queue.
2374 For each different flow identifier, a new pipe or queue is created
2375 with the same parameters as the original object, and matching packets
2380 are used, each flow will get the same bandwidth as defined by the pipe,
2383 are used, each flow will share the parent's pipe bandwidth evenly
2384 with other flows generated by the same queue (note that other queues
2385 with different weights might be connected to the same pipe).
2387 Available mask specifiers are a combination of one or more of the following:
2389 .Cm dst-ip Ar mask ,
2390 .Cm dst-ip6 Ar mask ,
2391 .Cm src-ip Ar mask ,
2392 .Cm src-ip6 Ar mask ,
2393 .Cm dst-port Ar mask ,
2394 .Cm src-port Ar mask ,
2395 .Cm flow-id Ar mask ,
2400 where the latter means all bits in all fields are significant.
2403 When a packet is dropped by a
2405 queue or pipe, the error
2406 is normally reported to the caller routine in the kernel, in the
2407 same way as it happens when a device queue fills up.
2409 option reports the packet as successfully delivered, which can be
2410 needed for some experimental setups where you want to simulate
2411 loss or congestion at a remote router.
2413 .It Cm plr Ar packet-loss-rate
2416 .Ar packet-loss-rate
2417 is a floating-point number between 0 and 1, with 0 meaning no
2418 loss, 1 meaning 100% loss.
2419 The loss rate is internally represented on 31 bits.
2421 .It Cm queue Brq Ar slots | size Ns Cm Kbytes
2426 Default value is 50 slots, which
2427 is the typical queue size for Ethernet devices.
2428 Note that for slow speed links you should keep the queue
2429 size short or your traffic might be affected by a significant
2431 E.g., 50 max-sized ethernet packets (1500 bytes) mean 600Kbit
2432 or 20s of queue on a 30Kbit/s pipe.
2433 Even worse effects can result if you get packets from an
2434 interface with a much larger MTU, e.g.\& the loopback interface
2435 with its 16KB packets.
2439 .Em net.inet.ip.dummynet.pipe_byte_limit
2441 .Em net.inet.ip.dummynet.pipe_slot_limit
2442 control the maximum lengths that can be specified.
2444 .It Cm red | gred Ar w_q Ns / Ns Ar min_th Ns / Ns Ar max_th Ns / Ns Ar max_p
2446 Make use of the RED (Random Early Detection) queue management algorithm.
2451 point numbers between 0 and 1 (inclusive), while
2455 are integer numbers specifying thresholds for queue management
2456 (thresholds are computed in bytes if the queue has been defined
2457 in bytes, in slots otherwise).
2458 The two parameters can also be of the same value if needed. The
2460 also supports the gentle RED variant (gred) and ECN (Explicit Congestion
2461 Notification) as optional. Three
2463 variables can be used to control the RED behaviour:
2464 .Bl -tag -width indent
2465 .It Va net.inet.ip.dummynet.red_lookup_depth
2466 specifies the accuracy in computing the average queue
2467 when the link is idle (defaults to 256, must be greater than zero)
2468 .It Va net.inet.ip.dummynet.red_avg_pkt_size
2469 specifies the expected average packet size (defaults to 512, must be
2471 .It Va net.inet.ip.dummynet.red_max_pkt_size
2472 specifies the expected maximum packet size, only used when queue
2473 thresholds are in bytes (defaults to 1500, must be greater than zero).
2477 When used with IPv6 data,
2479 currently has several limitations.
2480 Information necessary to route link-local packets to an
2481 interface is not available after processing by
2483 so those packets are dropped in the output path.
2484 Care should be taken to ensure that link-local packets are not passed to
2487 Here are some important points to consider when designing your
2491 Remember that you filter both packets going
2495 Most connections need packets going in both directions.
2497 Remember to test very carefully.
2498 It is a good idea to be near the console when doing this.
2499 If you cannot be near the console,
2500 use an auto-recovery script such as the one in
2501 .Pa /usr/share/examples/ipfw/change_rules.sh .
2503 Do not forget the loopback interface.
2508 There are circumstances where fragmented datagrams are unconditionally
2510 TCP packets are dropped if they do not contain at least 20 bytes of
2511 TCP header, UDP packets are dropped if they do not contain a full 8
2512 byte UDP header, and ICMP packets are dropped if they do not contain
2513 4 bytes of ICMP header, enough to specify the ICMP type, code, and
2515 These packets are simply logged as
2517 since there may not be enough good data in the packet to produce a
2518 meaningful log entry.
2520 Another type of packet is unconditionally dropped, a TCP packet with a
2521 fragment offset of one.
2522 This is a valid packet, but it only has one use, to try
2523 to circumvent firewalls.
2524 When logging is enabled, these packets are
2525 reported as being dropped by rule -1.
2527 If you are logged in over a network, loading the
2531 is probably not as straightforward as you would think.
2532 The following command line is recommended:
2533 .Bd -literal -offset indent
2535 ipfw add 32000 allow ip from any to any
2538 Along the same lines, doing an
2539 .Bd -literal -offset indent
2543 in similar surroundings is also a bad idea.
2547 filter list may not be modified if the system security level
2548 is set to 3 or higher
2551 for information on system security levels).
2553 .Sh PACKET DIVERSION
2556 socket bound to the specified port will receive all packets
2557 diverted to that port.
2558 If no socket is bound to the destination port, or if the divert module is
2559 not loaded, or if the kernel was not compiled with divert socket support,
2560 the packets are dropped.
2561 .Sh NETWORK ADDRESS TRANSLATION (NAT)
2563 support in-kernel NAT using the kernel version of
2566 The nat configuration command is the following:
2567 .Bd -ragged -offset indent
2572 .Ar nat-configuration
2576 The following parameters can be configured:
2577 .Bl -tag -width indent
2578 .It Cm ip Ar ip_address
2579 Define an ip address to use for aliasing.
2581 Use ip address of NIC for aliasing, dynamically changing
2582 it if NIC's ip address changes.
2584 Enable logging on this nat instance.
2586 Deny any incoming connection from outside world.
2588 Try to leave the alias port numbers unchanged from
2589 the actual local port numbers.
2591 Traffic on the local network not originating from an
2592 unregistered address spaces will be ignored.
2594 Reset table of the packet aliasing engine on address change.
2596 Reverse the way libalias handles aliasing.
2598 Obey transparent proxy rules only, packet aliasing is not performed.
2600 Skip instance in case of global state lookup (see below).
2603 Some specials value can be supplied instead of
2605 .Bl -tag -width indent
2607 Looks up translation state in all configured nat instances.
2608 If an entry is found, packet is aliased according to that entry.
2609 If no entry was found in any of the instances, packet is passed unchanged,
2610 and no new entry will be created.
2612 .Sx MULTIPLE INSTANCES
2615 for more information.
2617 Uses argument supplied in lookup table.
2620 section below for more information on lookup tables.
2623 To let the packet continue after being (de)aliased, set the sysctl variable
2624 .Va net.inet.ip.fw.one_pass
2626 For more information about aliasing modes, refer to
2630 for some examples about nat usage.
2631 .Ss REDIRECT AND LSNAT SUPPORT IN IPFW
2632 Redirect and LSNAT support follow closely the syntax used in
2636 for some examples on how to do redirect and lsnat.
2637 .Ss SCTP NAT SUPPORT
2638 SCTP nat can be configured in a similar manner to TCP through the
2641 The main difference is that
2643 does not do port translation.
2644 Since the local and global side ports will be the same,
2645 there is no need to specify both.
2646 Ports are redirected as follows:
2647 .Bd -ragged -offset indent
2653 .Cm redirect_port sctp
2654 .Ar ip_address [,addr_list] {[port | port-port] [,ports]}
2660 configuration can be done in real-time through the
2663 All may be changed dynamically, though the hash_table size will only
2668 .Sx SYSCTL VARIABLES
2671 Tunables can be set in
2677 before ipfw module gets loaded.
2678 .Bl -tag -width indent
2679 .It Va net.inet.ip.fw.default_to_accept: No 0
2680 Defines ipfw last rule behavior.
2681 This value overrides
2682 .Cd "options IPFW_DEFAULT_TO_(ACCEPT|DENY)"
2683 from kernel configuration file.
2684 .It Va net.inet.ip.fw.tables_max: No 128
2685 Defines number of tables available in ipfw.
2686 Number cannot exceed 65534.
2688 .Sh SYSCTL VARIABLES
2691 variables controls the behaviour of the firewall and
2693 .Pq Nm dummynet , bridge , sctp nat .
2694 These are shown below together with their default value
2695 (but always check with the
2697 command what value is actually in use) and meaning:
2698 .Bl -tag -width indent
2699 .It Va net.inet.ip.alias.sctp.accept_global_ootb_addip: No 0
2702 responds to receipt of global OOTB ASCONF-AddIP:
2703 .Bl -tag -width indent
2705 No response (unless a partially matching association exists -
2706 ports and vtags match but global address does not)
2709 will accept and process all OOTB global AddIP messages.
2712 Option 1 should never be selected as this forms a security risk.
2714 establish multiple fake associations by sending AddIP messages.
2715 .It Va net.inet.ip.alias.sctp.chunk_proc_limit: No 5
2716 Defines the maximum number of chunks in an SCTP packet that will be
2718 packet that matches an existing association.
2719 This value is enforced to be greater or equal than
2720 .Cm net.inet.ip.alias.sctp.initialising_chunk_proc_limit .
2722 a DoS risk yet setting too low a value may result in
2723 important control chunks in
2724 the packet not being located and parsed.
2725 .It Va net.inet.ip.alias.sctp.error_on_ootb: No 1
2728 responds to any Out-of-the-Blue (OOTB) packets with ErrorM packets.
2729 An OOTB packet is a packet that arrives with no existing association
2732 and is not an INIT or ASCONF-AddIP packet:
2733 .Bl -tag -width indent
2735 ErrorM is never sent in response to OOTB packets.
2737 ErrorM is only sent to OOTB packets received on the local side.
2739 ErrorM is sent to the local side and on the global side ONLY if there is a
2740 partial match (ports and vtags match but the source global IP does not).
2741 This value is only useful if the
2743 is tracking global IP addresses.
2745 ErrorM is sent in response to all OOTB packets on both
2746 the local and global side
2750 At the moment the default is 0, since the ErrorM packet is not yet
2751 supported by most SCTP stacks.
2752 When it is supported, and if not tracking
2753 global addresses, we recommend setting this value to 1 to allow
2754 multi-homed local hosts to function with the
2756 To track global addresses, we recommend setting this value to 2 to
2757 allow global hosts to be informed when they need to (re)send an
2759 Value 3 should never be chosen (except for debugging) as the
2761 will respond to all OOTB global packets (a DoS risk).
2762 .It Va net.inet.ip.alias.sctp.hashtable_size: No 2003
2763 Size of hash tables used for
2765 lookups (100 < prime_number > 1000001).
2768 size for any future created
2770 instance and therefore must be set prior to creating a
2773 The table sizes may be changed to suit specific needs.
2774 If there will be few
2775 concurrent associations, and memory is scarce, you may make these smaller.
2776 If there will be many thousands (or millions) of concurrent associations, you
2777 should make these larger.
2778 A prime number is best for the table size.
2780 update function will adjust your input value to the next highest prime number.
2781 .It Va net.inet.ip.alias.sctp.holddown_time: No 0
2782 Hold association in table for this many seconds after receiving a
2784 This allows endpoints to correct shutdown gracefully if a
2785 shutdown_complete is lost and retransmissions are required.
2786 .It Va net.inet.ip.alias.sctp.init_timer: No 15
2787 Timeout value while waiting for (INIT-ACK|AddIP-ACK).
2788 This value cannot be 0.
2789 .It Va net.inet.ip.alias.sctp.initialising_chunk_proc_limit: No 2
2790 Defines the maximum number of chunks in an SCTP packet that will be parsed when
2791 no existing association exists that matches that packet.
2793 will only be an INIT or ASCONF-AddIP packet.
2794 A higher value may become a DoS
2795 risk as malformed packets can consume processing resources.
2796 .It Va net.inet.ip.alias.sctp.param_proc_limit: No 25
2797 Defines the maximum number of parameters within a chunk that will be
2800 As for other similar sysctl variables, larger values pose a DoS risk.
2801 .It Va net.inet.ip.alias.sctp.log_level: No 0
2802 Level of detail in the system log messages (0 \- minimal, 1 \- event,
2803 2 \- info, 3 \- detail, 4 \- debug, 5 \- max debug).
2805 option in high loss environments.
2806 .It Va net.inet.ip.alias.sctp.shutdown_time: No 15
2807 Timeout value while waiting for SHUTDOWN-COMPLETE.
2808 This value cannot be 0.
2809 .It Va net.inet.ip.alias.sctp.track_global_addresses: No 0
2810 Enables/disables global IP address tracking within the
2813 upper limit on the number of addresses tracked for each association:
2814 .Bl -tag -width indent
2816 Global tracking is disabled
2818 Enables tracking, the maximum number of addresses tracked for each
2819 association is limited to this value
2822 This variable is fully dynamic, the new value will be adopted for all newly
2823 arriving associations, existing associations are treated
2824 as they were previously.
2825 Global tracking will decrease the number of collisions within the
2828 of increased processing load, memory usage, complexity, and possible
2831 problems in complex networks with multiple
2833 We recommend not tracking
2834 global IP addresses, this will still result in a fully functional
2836 .It Va net.inet.ip.alias.sctp.up_timer: No 300
2837 Timeout value to keep an association up with no traffic.
2838 This value cannot be 0.
2839 .It Va net.inet.ip.dummynet.expire : No 1
2840 Lazily delete dynamic pipes/queue once they have no pending traffic.
2841 You can disable this by setting the variable to 0, in which case
2842 the pipes/queues will only be deleted when the threshold is reached.
2843 .It Va net.inet.ip.dummynet.hash_size : No 64
2844 Default size of the hash table used for dynamic pipes/queues.
2845 This value is used when no
2847 option is specified when configuring a pipe/queue.
2848 .It Va net.inet.ip.dummynet.io_fast : No 0
2849 If set to a non-zero value,
2854 operation (see above) is enabled.
2855 .It Va net.inet.ip.dummynet.io_pkt
2856 Number of packets passed to
2858 .It Va net.inet.ip.dummynet.io_pkt_drop
2859 Number of packets dropped by
2861 .It Va net.inet.ip.dummynet.io_pkt_fast
2862 Number of packets bypassed by the
2865 .It Va net.inet.ip.dummynet.max_chain_len : No 16
2866 Target value for the maximum number of pipes/queues in a hash bucket.
2868 .Cm max_chain_len*hash_size
2869 is used to determine the threshold over which empty pipes/queues
2870 will be expired even when
2871 .Cm net.inet.ip.dummynet.expire=0 .
2872 .It Va net.inet.ip.dummynet.red_lookup_depth : No 256
2873 .It Va net.inet.ip.dummynet.red_avg_pkt_size : No 512
2874 .It Va net.inet.ip.dummynet.red_max_pkt_size : No 1500
2875 Parameters used in the computations of the drop probability
2876 for the RED algorithm.
2877 .It Va net.inet.ip.dummynet.pipe_byte_limit : No 1048576
2878 .It Va net.inet.ip.dummynet.pipe_slot_limit : No 100
2879 The maximum queue size that can be specified in bytes or packets.
2880 These limits prevent accidental exhaustion of resources such as mbufs.
2881 If you raise these limits,
2882 you should make sure the system is configured so that sufficient resources
2884 .It Va net.inet.ip.fw.autoinc_step : No 100
2885 Delta between rule numbers when auto-generating them.
2886 The value must be in the range 1..1000.
2887 .It Va net.inet.ip.fw.curr_dyn_buckets : Va net.inet.ip.fw.dyn_buckets
2888 The current number of buckets in the hash table for dynamic rules
2890 .It Va net.inet.ip.fw.debug : No 1
2891 Controls debugging messages produced by
2893 .It Va net.inet.ip.fw.default_rule : No 65535
2894 The default rule number (read-only).
2896 .Nm , the default rule is the last one, so its number
2897 can also serve as the highest number allowed for a rule.
2898 .It Va net.inet.ip.fw.dyn_buckets : No 256
2899 The number of buckets in the hash table for dynamic rules.
2900 Must be a power of 2, up to 65536.
2901 It only takes effect when all dynamic rules have expired, so you
2902 are advised to use a
2904 command to make sure that the hash table is resized.
2905 .It Va net.inet.ip.fw.dyn_count : No 3
2906 Current number of dynamic rules
2908 .It Va net.inet.ip.fw.dyn_keepalive : No 1
2909 Enables generation of keepalive packets for
2911 rules on TCP sessions.
2912 A keepalive is generated to both
2913 sides of the connection every 5 seconds for the last 20
2914 seconds of the lifetime of the rule.
2915 .It Va net.inet.ip.fw.dyn_max : No 8192
2916 Maximum number of dynamic rules.
2917 When you hit this limit, no more dynamic rules can be
2918 installed until old ones expire.
2919 .It Va net.inet.ip.fw.dyn_ack_lifetime : No 300
2920 .It Va net.inet.ip.fw.dyn_syn_lifetime : No 20
2921 .It Va net.inet.ip.fw.dyn_fin_lifetime : No 1
2922 .It Va net.inet.ip.fw.dyn_rst_lifetime : No 1
2923 .It Va net.inet.ip.fw.dyn_udp_lifetime : No 5
2924 .It Va net.inet.ip.fw.dyn_short_lifetime : No 30
2925 These variables control the lifetime, in seconds, of dynamic
2927 Upon the initial SYN exchange the lifetime is kept short,
2928 then increased after both SYN have been seen, then decreased
2929 again during the final FIN exchange or when a RST is received.
2931 .Em dyn_fin_lifetime
2933 .Em dyn_rst_lifetime
2934 must be strictly lower than 5 seconds, the period of
2935 repetition of keepalives.
2936 The firewall enforces that.
2937 .It Va net.inet.ip.fw.enable : No 1
2938 Enables the firewall.
2939 Setting this variable to 0 lets you run your machine without
2940 firewall even if compiled in.
2941 .It Va net.inet6.ip6.fw.enable : No 1
2942 provides the same functionality as above for the IPv6 case.
2943 .It Va net.inet.ip.fw.one_pass : No 1
2944 When set, the packet exiting from the
2948 node is not passed though the firewall again.
2949 Otherwise, after an action, the packet is
2950 reinjected into the firewall at the next rule.
2951 .It Va net.inet.ip.fw.tables_max : No 128
2952 Maximum number of tables.
2953 .It Va net.inet.ip.fw.verbose : No 1
2954 Enables verbose messages.
2955 .It Va net.inet.ip.fw.verbose_limit : No 0
2956 Limits the number of messages produced by a verbose firewall.
2957 .It Va net.inet6.ip6.fw.deny_unknown_exthdrs : No 1
2958 If enabled packets with unknown IPv6 Extension Headers will be denied.
2959 .It Va net.link.ether.ipfw : No 0
2960 Controls whether layer-2 packets are passed to
2963 .It Va net.link.bridge.ipfw : No 0
2964 Controls whether bridged packets are passed to
2969 There are far too many possible uses of
2971 so this Section will only give a small set of examples.
2973 .Ss BASIC PACKET FILTERING
2974 This command adds an entry which denies all tcp packets from
2975 .Em cracker.evil.org
2976 to the telnet port of
2978 from being forwarded by the host:
2980 .Dl "ipfw add deny tcp from cracker.evil.org to wolf.tambov.su telnet"
2982 This one disallows any connection from the entire cracker's
2985 .Dl "ipfw add deny ip from 123.45.67.0/24 to my.host.org"
2987 A first and efficient way to limit access (not using dynamic rules)
2988 is the use of the following rules:
2990 .Dl "ipfw add allow tcp from any to any established"
2991 .Dl "ipfw add allow tcp from net1 portlist1 to net2 portlist2 setup"
2992 .Dl "ipfw add allow tcp from net3 portlist3 to net3 portlist3 setup"
2994 .Dl "ipfw add deny tcp from any to any"
2996 The first rule will be a quick match for normal TCP packets,
2997 but it will not match the initial SYN packet, which will be
3000 rules only for selected source/destination pairs.
3001 All other SYN packets will be rejected by the final
3005 If you administer one or more subnets, you can take advantage
3006 of the address sets and or-blocks and write extremely
3007 compact rulesets which selectively enable services to blocks
3008 of clients, as below:
3010 .Dl "goodguys=\*q{ 10.1.2.0/24{20,35,66,18} or 10.2.3.0/28{6,3,11} }\*q"
3011 .Dl "badguys=\*q10.1.2.0/24{8,38,60}\*q"
3013 .Dl "ipfw add allow ip from ${goodguys} to any"
3014 .Dl "ipfw add deny ip from ${badguys} to any"
3015 .Dl "... normal policies ..."
3019 option could be used to do automated anti-spoofing by adding the
3020 following to the top of a ruleset:
3022 .Dl "ipfw add deny ip from any to any not verrevpath in"
3024 This rule drops all incoming packets that appear to be coming to the
3025 system on the wrong interface.
3026 For example, a packet with a source
3027 address belonging to a host on a protected internal network would be
3028 dropped if it tried to enter the system from an external interface.
3032 option could be used to do similar but more restricted anti-spoofing
3033 by adding the following to the top of a ruleset:
3035 .Dl "ipfw add deny ip from any to any not antispoof in"
3037 This rule drops all incoming packets that appear to be coming from another
3038 directly connected system but on the wrong interface.
3039 For example, a packet with a source address of
3040 .Li 192.168.0.0/24 ,
3049 option could be used to (re)mark user traffic,
3050 by adding the following to the appropriate place in ruleset:
3052 .Dl "ipfw add setdscp be ip from any to any dscp af11,af21"
3054 In order to protect a site from flood attacks involving fake
3055 TCP packets, it is safer to use dynamic rules:
3057 .Dl "ipfw add check-state"
3058 .Dl "ipfw add deny tcp from any to any established"
3059 .Dl "ipfw add allow tcp from my-net to any setup keep-state"
3061 This will let the firewall install dynamic rules only for
3062 those connection which start with a regular SYN packet coming
3063 from the inside of our network.
3064 Dynamic rules are checked when encountering the first
3073 rule should usually be placed near the beginning of the
3074 ruleset to minimize the amount of work scanning the ruleset.
3075 Your mileage may vary.
3077 To limit the number of connections a user can open
3078 you can use the following type of rules:
3080 .Dl "ipfw add allow tcp from my-net/24 to any setup limit src-addr 10"
3081 .Dl "ipfw add allow tcp from any to me setup limit src-addr 4"
3083 The former (assuming it runs on a gateway) will allow each host
3084 on a /24 network to open at most 10 TCP connections.
3085 The latter can be placed on a server to make sure that a single
3086 client does not use more than 4 simultaneous connections.
3089 stateful rules can be subject to denial-of-service attacks
3090 by a SYN-flood which opens a huge number of dynamic rules.
3091 The effects of such attacks can be partially limited by
3094 variables which control the operation of the firewall.
3096 Here is a good usage of the
3098 command to see accounting records and timestamp information:
3102 or in short form without timestamps:
3106 which is equivalent to:
3110 Next rule diverts all incoming packets from 192.168.2.0/24
3111 to divert port 5000:
3113 .Dl ipfw divert 5000 ip from 192.168.2.0/24 to any in
3115 The following rules show some of the applications of
3119 for simulations and the like.
3121 This rule drops random incoming packets with a probability
3124 .Dl "ipfw add prob 0.05 deny ip from any to any in"
3126 A similar effect can be achieved making use of
3130 .Dl "ipfw add pipe 10 ip from any to any"
3131 .Dl "ipfw pipe 10 config plr 0.05"
3133 We can use pipes to artificially limit bandwidth, e.g.\& on a
3134 machine acting as a router, if we want to limit traffic from
3135 local clients on 192.168.2.0/24 we do:
3137 .Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out"
3138 .Dl "ipfw pipe 1 config bw 300Kbit/s queue 50KBytes"
3140 note that we use the
3142 modifier so that the rule is not used twice.
3143 Remember in fact that
3145 rules are checked both on incoming and outgoing packets.
3147 Should we want to simulate a bidirectional link with bandwidth
3148 limitations, the correct way is the following:
3150 .Dl "ipfw add pipe 1 ip from any to any out"
3151 .Dl "ipfw add pipe 2 ip from any to any in"
3152 .Dl "ipfw pipe 1 config bw 64Kbit/s queue 10Kbytes"
3153 .Dl "ipfw pipe 2 config bw 64Kbit/s queue 10Kbytes"
3155 The above can be very useful, e.g.\& if you want to see how
3156 your fancy Web page will look for a residential user who
3157 is connected only through a slow link.
3158 You should not use only one pipe for both directions, unless
3159 you want to simulate a half-duplex medium (e.g.\& AppleTalk,
3161 It is not necessary that both pipes have the same configuration,
3162 so we can also simulate asymmetric links.
3164 Should we want to verify network performance with the RED queue
3165 management algorithm:
3167 .Dl "ipfw add pipe 1 ip from any to any"
3168 .Dl "ipfw pipe 1 config bw 500Kbit/s queue 100 red 0.002/30/80/0.1"
3170 Another typical application of the traffic shaper is to
3171 introduce some delay in the communication.
3172 This can significantly affect applications which do a lot of Remote
3173 Procedure Calls, and where the round-trip-time of the
3174 connection often becomes a limiting factor much more than
3177 .Dl "ipfw add pipe 1 ip from any to any out"
3178 .Dl "ipfw add pipe 2 ip from any to any in"
3179 .Dl "ipfw pipe 1 config delay 250ms bw 1Mbit/s"
3180 .Dl "ipfw pipe 2 config delay 250ms bw 1Mbit/s"
3182 Per-flow queueing can be useful for a variety of purposes.
3183 A very simple one is counting traffic:
3185 .Dl "ipfw add pipe 1 tcp from any to any"
3186 .Dl "ipfw add pipe 1 udp from any to any"
3187 .Dl "ipfw add pipe 1 ip from any to any"
3188 .Dl "ipfw pipe 1 config mask all"
3190 The above set of rules will create queues (and collect
3191 statistics) for all traffic.
3192 Because the pipes have no limitations, the only effect is
3193 collecting statistics.
3194 Note that we need 3 rules, not just the last one, because
3197 tries to match IP packets it will not consider ports, so we
3198 would not see connections on separate ports as different
3201 A more sophisticated example is limiting the outbound traffic
3202 on a net with per-host limits, rather than per-network limits:
3204 .Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out"
3205 .Dl "ipfw add pipe 2 ip from any to 192.168.2.0/24 in"
3206 .Dl "ipfw pipe 1 config mask src-ip 0x000000ff bw 200Kbit/s queue 20Kbytes"
3207 .Dl "ipfw pipe 2 config mask dst-ip 0x000000ff bw 200Kbit/s queue 20Kbytes"
3209 In the following example, we need to create several traffic bandwidth
3210 classes and we need different hosts/networks to fall into different classes.
3211 We create one pipe for each class and configure them accordingly.
3212 Then we create a single table and fill it with IP subnets and addresses.
3213 For each subnet/host we set the argument equal to the number of the pipe
3215 Then we classify traffic using a single rule:
3217 .Dl "ipfw pipe 1 config bw 1000Kbyte/s"
3218 .Dl "ipfw pipe 4 config bw 4000Kbyte/s"
3220 .Dl "ipfw table 1 add 192.168.2.0/24 1"
3221 .Dl "ipfw table 1 add 192.168.0.0/27 4"
3222 .Dl "ipfw table 1 add 192.168.0.2 1"
3224 .Dl "ipfw add pipe tablearg ip from table(1) to any"
3228 action, the table entries may include hostnames and IP addresses.
3230 .Dl "ipfw table 1 add 192.168.2.0/24 10.23.2.1"
3231 .Dl "ipfw table 1 add 192.168.0.0/27 router1.dmz"
3233 .Dl "ipfw add 100 fwd tablearg ip from any to table(1)"
3235 In the following example per-interface firewall is created:
3237 .Dl "ipfw table 10 add vlan20 12000"
3238 .Dl "ipfw table 10 add vlan30 13000"
3239 .Dl "ipfw table 20 add vlan20 22000"
3240 .Dl "ipfw table 20 add vlan30 23000"
3242 .Dl "ipfw add 100 ipfw skipto tablearg ip from any to any recv 'table(10)' in"
3243 .Dl "ipfw add 200 ipfw skipto tablearg ip from any to any xmit 'table(10)' out"
3245 To add a set of rules atomically, e.g.\& set 18:
3247 .Dl "ipfw set disable 18"
3248 .Dl "ipfw add NN set 18 ... # repeat as needed"
3249 .Dl "ipfw set enable 18"
3251 To delete a set of rules atomically the command is simply:
3253 .Dl "ipfw delete set 18"
3255 To test a ruleset and disable it and regain control if something goes wrong:
3257 .Dl "ipfw set disable 18"
3258 .Dl "ipfw add NN set 18 ... # repeat as needed"
3259 .Dl "ipfw set enable 18; echo done; sleep 30 && ipfw set disable 18"
3261 Here if everything goes well, you press control-C before the "sleep"
3262 terminates, and your ruleset will be left active.
3263 Otherwise, e.g.\& if
3264 you cannot access your box, the ruleset will be disabled after
3265 the sleep terminates thus restoring the previous situation.
3267 To show rules of the specific set:
3269 .Dl "ipfw set 18 show"
3271 To show rules of the disabled set:
3273 .Dl "ipfw -S set 18 show"
3275 To clear a specific rule counters of the specific set:
3277 .Dl "ipfw set 18 zero NN"
3279 To delete a specific rule of the specific set:
3281 .Dl "ipfw set 18 delete NN"
3282 .Ss NAT, REDIRECT AND LSNAT
3283 First redirect all the traffic to nat instance 123:
3285 .Dl "ipfw add nat 123 all from any to any"
3287 Then to configure nat instance 123 to alias all the outgoing traffic with ip
3288 192.168.0.123, blocking all incoming connections, trying to keep
3289 same ports on both sides, clearing aliasing table on address change
3290 and keeping a log of traffic/link statistics:
3292 .Dl "ipfw nat 123 config ip 192.168.0.123 log deny_in reset same_ports"
3294 Or to change address of instance 123, aliasing table will be cleared (see
3297 .Dl "ipfw nat 123 config ip 10.0.0.1"
3299 To see configuration of nat instance 123:
3301 .Dl "ipfw nat 123 show config"
3303 To show logs of all the instances in range 111-999:
3305 .Dl "ipfw nat 111-999 show"
3307 To see configurations of all instances:
3309 .Dl "ipfw nat show config"
3311 Or a redirect rule with mixed modes could looks like:
3313 .Dl "ipfw nat 123 config redirect_addr 10.0.0.1 10.0.0.66"
3314 .Dl " redirect_port tcp 192.168.0.1:80 500"
3315 .Dl " redirect_proto udp 192.168.1.43 192.168.1.1"
3316 .Dl " redirect_addr 192.168.0.10,192.168.0.11"
3317 .Dl " 10.0.0.100 # LSNAT"
3318 .Dl " redirect_port tcp 192.168.0.1:80,192.168.0.10:22"
3321 or it could be split in:
3323 .Dl "ipfw nat 1 config redirect_addr 10.0.0.1 10.0.0.66"
3324 .Dl "ipfw nat 2 config redirect_port tcp 192.168.0.1:80 500"
3325 .Dl "ipfw nat 3 config redirect_proto udp 192.168.1.43 192.168.1.1"
3326 .Dl "ipfw nat 4 config redirect_addr 192.168.0.10,192.168.0.11,192.168.0.12"
3328 .Dl "ipfw nat 5 config redirect_port tcp"
3329 .Dl " 192.168.0.1:80,192.168.0.10:22,192.168.0.20:25 500"
3350 utility first appeared in
3355 Stateful extensions were introduced in
3358 was introduced in Summer 2002.
3360 .An Ugen J. S. Antsilevich ,
3361 .An Poul-Henning Kamp ,
3367 API based upon code written by
3371 Dummynet has been introduced by Luigi Rizzo in 1997-1998.
3373 Some early work (1999-2000) on the
3375 traffic shaper supported by Akamba Corp.
3377 The ipfw core (ipfw2) has been completely redesigned and
3378 reimplemented by Luigi Rizzo in summer 2002.
3381 options have been added by various developer over the years.
3384 In-kernel NAT support written by
3385 .An Paolo Pisati Aq piso@FreeBSD.org
3386 as part of a Summer of Code 2005 project.
3390 support has been developed by
3391 .An The Centre for Advanced Internet Architectures (CAIA) Aq http://www.caia.swin.edu.au .
3392 The primary developers and maintainers are David Hayes and Jason But.
3393 For further information visit:
3394 .Aq http://www.caia.swin.edu.au/urp/SONATA
3396 Delay profiles have been developed by Alessandro Cerri and
3397 Luigi Rizzo, supported by the
3398 European Commission within Projects Onelab and Onelab2.
3400 The syntax has grown over the years and sometimes it might be confusing.
3401 Unfortunately, backward compatibility prevents cleaning up mistakes
3402 made in the definition of the syntax.
3406 Misconfiguring the firewall can put your computer in an unusable state,
3407 possibly shutting down network services and requiring console access to
3408 regain control of it.
3410 Incoming packet fragments diverted by
3412 are reassembled before delivery to the socket.
3413 The action used on those packet is the one from the
3414 rule which matches the first fragment of the packet.
3416 Packets diverted to userland, and then reinserted by a userland process
3417 may lose various packet attributes.
3418 The packet source interface name
3419 will be preserved if it is shorter than 8 bytes and the userland process
3420 saves and reuses the sockaddr_in
3423 otherwise, it may be lost.
3424 If a packet is reinserted in this manner, later rules may be incorrectly
3425 applied, making the order of
3427 rules in the rule sequence very important.
3429 Dummynet drops all packets with IPv6 link-local addresses.
3435 may not behave as expected.
3436 In particular, incoming SYN packets may
3437 have no uid or gid associated with them since they do not yet belong
3438 to a TCP connection, and the uid/gid associated with a packet may not
3439 be as expected if the associated process calls
3441 or similar system calls.
3443 Rule syntax is subject to the command line environment and some patterns
3444 may need to be escaped with the backslash character
3445 or quoted appropriately.
3447 Due to the architecture of
3449 ipfw nat is not compatible with the TCP segmentation offloading (TSO).
3450 Thus, to reliably nat your network traffic, please disable TSO
3454 ICMP error messages are not implicitly matched by dynamic rules
3455 for the respective conversations.
3456 To avoid failures of network error detection and path MTU discovery,
3457 ICMP error messages may need to be allowed explicitly through static
3464 actions may lead to confusing behaviour if ruleset has mistakes,
3465 and/or interaction with other subsystems (netgraph, dummynet, etc.) is used.
3466 One possible case for this is packet leaving
3468 in subroutine on the input pass, while later on output encountering unpaired
3471 As the call stack is kept intact after input pass, packet will suddenly
3472 return to the rule number used on input pass, not on output one.
3473 Order of processing should be checked carefully to avoid such mistakes.
projects / FreeBSD / stable / 10.git / blob