9 .Nd User interface for firewall, traffic shaper, packet scheduler,
12 .Ss FIREWALL CONFIGURATION
21 .Op Ar rule | first-last ...
29 .Brq Cm delete | zero | resetlog
33 .Cm set Oo Cm disable Ar number ... Oc Op Cm enable Ar number ...
37 .Ar number Cm to Ar number
39 .Cm set swap Ar number number
46 .Brq Cm firewall | altq | one_pass | debug | verbose | dyn_keepalive
49 .Brq Cm firewall | altq | one_pass | debug | verbose | dyn_keepalive
53 .Cm table Ar number Cm add Ar addr Ns Oo / Ns Ar masklen Oc Op Ar value
55 .Cm table Ar number Cm delete Ar addr Ns Op / Ns Ar masklen
65 .Ss DUMMYNET CONFIGURATION (TRAFFIC SHAPER AND PACKET SCHEDULER)
67 .Brq Cm pipe | queue | sched
73 .Brq Cm pipe | queue | sched
74 .Brq Cm delete | list | show
97 utility is the user interface for controlling the
101 traffic shaper/packet scheduler, and the
102 in-kernel NAT services.
104 A firewall configuration, or
108 numbered from 1 to 65535.
109 Packets are passed to the firewall
110 from a number of different places in the protocol stack
111 (depending on the source and destination of the packet,
112 it is possible for the firewall to be
113 invoked multiple times on the same packet).
114 The packet passed to the firewall is compared
115 against each of the rules in the
118 (multiple rules with the same number are permitted, in which case
119 they are processed in order of insertion).
120 When a match is found, the action corresponding to the
121 matching rule is performed.
123 Depending on the action and certain system settings, packets
124 can be reinjected into the firewall at some rule after the
125 matching one for further processing.
127 A ruleset always includes a
129 rule (numbered 65535) which cannot be modified or deleted,
130 and matches all packets.
131 The action associated with the
137 depending on how the kernel is configured.
139 If the ruleset includes one or more rules with the
144 the firewall will have a
146 behaviour, i.e., upon a match it will create
148 i.e. rules that match packets with the same 5-tuple
149 (protocol, source and destination addresses and ports)
150 as the packet which caused their creation.
151 Dynamic rules, which have a limited lifetime, are checked
152 at the first occurrence of a
157 rule, and are typically used to open the firewall on-demand to
158 legitimate traffic only.
160 .Sx STATEFUL FIREWALL
163 Sections below for more information on the stateful behaviour of
166 All rules (including dynamic ones) have a few associated counters:
167 a packet count, a byte count, a log count and a timestamp
168 indicating the time of the last match.
169 Counters can be displayed or reset with
173 Each rule belongs to one of 32 different
177 commands to atomically manipulate sets, such as enable,
178 disable, swap sets, move all rules in a set to another
179 one, delete all rules in a set.
180 These can be useful to
181 install temporary configurations, or to test them.
184 for more information on
187 Rules can be added with the
189 command; deleted individually or in groups with the
191 command, and globally (except those in set 31) with the
193 command; displayed, optionally with the content of the
199 Finally, counters can be reset with the
206 The following general options are available when invoking
208 .Bl -tag -width indent
210 Show counter values when listing rules.
213 command implies this option.
215 Only show the action and the comment, not the body of a rule.
219 When entering or showing rules, print them in compact form,
220 i.e., omitting the "ip from any to any" string
221 when this does not carry any additional information.
223 When listing, show dynamic rules in addition to static ones.
227 is specified, also show expired dynamic rules.
229 Do not ask for confirmation for commands that can cause problems
232 If there is no tty associated with the process, this is implied.
234 When listing a table (see the
236 section below for more information on lookup tables), format values
237 as IP addresses. By default, values are shown as integers.
239 Only check syntax of the command strings, without actually passing
242 Try to resolve addresses and service names in output.
244 Be quiet when executing the
254 This is useful when updating rulesets by executing multiple
258 .Ql sh\ /etc/rc.firewall ) ,
259 or by processing a file with many
261 rules across a remote login session.
262 It also stops a table add or delete
263 from failing if the entry already exists or is not present.
265 The reason why this option may be important is that
266 for some of these actions,
268 may print a message; if the action results in blocking the
269 traffic to the remote client,
270 the remote login session will be closed
271 and the rest of the ruleset will not be processed.
272 Access to the console would then be required to recover.
274 When listing rules, show the
276 each rule belongs to.
277 If this flag is not specified, disabled rules will not be
280 When listing pipes, sort according to one of the four
281 counters (total or current packets or bytes).
283 When listing, show last match timestamp converted with ctime().
285 When listing, show last match timestamp as seconds from the epoch.
286 This form can be more convenient for postprocessing by scripts.
289 .Ss LIST OF RULES AND PREPROCESSING
290 To ease configuration, rules can be put into a file which is
293 as shown in the last synopsis line.
297 The file will be read line by line and applied as arguments to the
301 Optionally, a preprocessor can be specified using
305 is to be piped through.
306 Useful preprocessors include
312 does not start with a slash
314 as its first character, the usual
316 name search is performed.
317 Care should be taken with this in environments where not all
318 file systems are mounted (yet) by the time
320 is being run (e.g.\& when they are mounted over NFS).
323 has been specified, any additional arguments are passed on to the preprocessor
325 This allows for flexible configuration files (like conditionalizing
326 them on the local hostname) and the use of macros to centralize
327 frequently required arguments like IP addresses.
329 .Ss TRAFFIC SHAPER CONFIGURATION
335 commands are used to configure the traffic shaper and packet scheduler.
337 .Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION
338 Section below for details.
340 If the world and the kernel get out of sync the
342 ABI may break, preventing you from being able to add any rules.
344 adversely effect the booting process.
349 to temporarily disable the firewall to regain access to the network,
350 allowing you to fix the problem.
352 A packet is checked against the active ruleset in multiple places
353 in the protocol stack, under control of several sysctl variables.
354 These places and variables are shown below, and it is important to
355 have this picture in mind in order to design a correct ruleset.
356 .Bd -literal -offset indent
359 +----------->-----------+
361 [ip(6)_input] [ip(6)_output] net.inet(6).ip(6).fw.enable=1
364 [ether_demux] [ether_output_frame] net.link.ether.ipfw=1
366 +-->--[bdg_forward]-->--+ net.link.bridge.ipfw=1
372 times the same packet goes through the firewall can
373 vary between 0 and 4 depending on packet source and
374 destination, and system configuration.
376 Note that as packets flow through the stack, headers can be
377 stripped or added to it, and so they may or may not be available
379 E.g., incoming packets will include the MAC header when
383 but the same packets will have the MAC header stripped off when
390 Also note that each packet is always checked against the complete ruleset,
391 irrespective of the place where the check occurs, or the source of the packet.
392 If a rule contains some match patterns or actions which are not valid
393 for the place of invocation (e.g.\& trying to match a MAC header within
397 the match pattern will not match, but a
399 operator in front of such patterns
403 match on those packets.
404 It is thus the responsibility of
405 the programmer, if necessary, to write a suitable ruleset to
406 differentiate among the possible places.
408 rules can be useful here, as an example:
409 .Bd -literal -offset indent
410 # packets from ether_demux or bdg_forward
411 ipfw add 10 skipto 1000 all from any to any layer2 in
412 # packets from ip_input
413 ipfw add 10 skipto 2000 all from any to any not layer2 in
414 # packets from ip_output
415 ipfw add 10 skipto 3000 all from any to any not layer2 out
416 # packets from ether_output_frame
417 ipfw add 10 skipto 4000 all from any to any layer2 out
420 (yes, at the moment there is no way to differentiate between
421 ether_demux and bdg_forward).
423 In general, each keyword or argument must be provided as
424 a separate command line argument, with no leading or trailing
426 Keywords are case-sensitive, whereas arguments may
427 or may not be case-sensitive depending on their nature
428 (e.g.\& uid's are, hostnames are not).
430 Some arguments (e.g. port or address lists) are comma-separated
432 In this case, spaces after commas ',' are allowed to make
433 the line more readable.
434 You can also put the entire
435 command (including flags) into a single argument.
436 E.g., the following forms are equivalent:
437 .Bd -literal -offset indent
438 ipfw -q add deny src-ip 10.0.0.0/24,127.0.0.1/8
439 ipfw -q add deny src-ip 10.0.0.0/24, 127.0.0.1/8
440 ipfw "-q add deny src-ip 10.0.0.0/24, 127.0.0.1/8"
443 The format of firewall rules is the following:
444 .Bd -ragged -offset indent
447 .Op Cm set Ar set_number
448 .Op Cm prob Ar match_probability
450 .Op Cm log Op Cm logamount Ar number
460 where the body of the rule specifies which information is used
461 for filtering packets, among the following:
463 .Bl -tag -width "Source and dest. addresses and ports" -offset XXX -compact
464 .It Layer-2 header fields
466 .It IPv4 and IPv6 Protocol
468 .It Source and dest. addresses and ports
472 .It Transmit and receive interface
474 .It Misc. IP header fields
475 Version, type of service, datagram length, identification,
476 fragment flag (non-zero IP offset),
479 .It IPv6 Extension headers
480 Fragmentation, Hop-by-Hop options,
481 Routing Headers, Source routing rthdr0, Mobile IPv6 rthdr2, IPSec options.
483 .It Misc. TCP header fields
484 TCP flags (SYN, FIN, ACK, RST, etc.),
485 sequence number, acknowledgment number,
493 When the packet can be associated with a local socket.
495 Whether a packet came from a divert socket (e.g.,
497 .It Fib annotation state
498 Whether a packet has been tagged for using a specific FIB (routing table)
499 in future forwarding decisions.
502 Note that some of the above information, e.g.\& source MAC or IP addresses and
503 TCP/UDP ports, can be easily spoofed, so filtering on those fields
504 alone might not guarantee the desired results.
505 .Bl -tag -width indent
507 Each rule is associated with a
509 in the range 1..65535, with the latter reserved for the
512 Rules are checked sequentially by rule number.
513 Multiple rules can have the same number, in which case they are
514 checked (and listed) according to the order in which they have
516 If a rule is entered without specifying a number, the kernel will
517 assign one in such a way that the rule becomes the last one
521 Automatic rule numbers are assigned by incrementing the last
522 non-default rule number by the value of the sysctl variable
523 .Ar net.inet.ip.fw.autoinc_step
524 which defaults to 100.
525 If this is not possible (e.g.\& because we would go beyond the
526 maximum allowed rule number), the number of the last
527 non-default value is used instead.
528 .It Cm set Ar set_number
529 Each rule is associated with a
532 Sets can be individually disabled and enabled, so this parameter
533 is of fundamental importance for atomic ruleset manipulation.
534 It can be also used to simplify deletion of groups of rules.
535 If a rule is entered without specifying a set number,
538 Set 31 is special in that it cannot be disabled,
539 and rules in set 31 are not deleted by the
541 command (but you can delete them with the
542 .Nm ipfw delete set 31
544 Set 31 is also used for the
547 .It Cm prob Ar match_probability
548 A match is only declared with the specified probability
549 (floating point number between 0 and 1).
550 This can be useful for a number of applications such as
551 random packet drop or
554 to simulate the effect of multiple paths leading to out-of-order
557 Note: this condition is checked before any other condition, including
558 ones such as keep-state or check-state which might have side effects.
559 .It Cm log Op Cm logamount Ar number
560 Packets matching a rule with the
562 keyword will be made available for logging in two ways:
563 if the sysctl variable
564 .Va net.inet.ip.fw.verbose
565 is set to 0 (default), one can use
569 pseudo interface. There is no overhead if no
571 is attached to the pseudo interface.
574 .Va net.inet.ip.fw.verbose
575 is set to 1, packets will be logged to
579 facility up to a maximum of
584 is specified, the limit is taken from the sysctl variable
585 .Va net.inet.ip.fw.verbose_limit .
586 In both cases, a value of 0 means unlimited logging.
588 Once the limit is reached, logging can be re-enabled by
589 clearing the logging counter or the packet counter for that entry, see the
593 Note: logging is done after all other packet matching conditions
594 have been successfully verified, and before performing the final
595 action (accept, deny, etc.) on the packet.
597 When a packet matches a rule with the
599 keyword, the numeric tag for the given
601 in the range 1..65534 will be attached to the packet.
602 The tag acts as an internal marker (it is not sent out over
603 the wire) that can be used to identify these packets later on.
604 This can be used, for example, to provide trust between interfaces
605 and to start doing policy-based filtering.
606 A packet can have multiple tags at the same time.
607 Tags are "sticky", meaning once a tag is applied to a packet by a
608 matching rule it exists until explicit removal.
609 Tags are kept with the packet everywhere within the kernel, but are
610 lost when packet leaves the kernel, for example, on transmitting
611 packet out to the network or sending packet to a
615 To check for previously applied tags, use the
618 To delete previously applied tag, use the
622 Note: since tags are kept with the packet everywhere in kernelspace,
623 they can be set and unset anywhere in the kernel network subsystem
626 facility), not only by means of the
632 For example, there can be a specialized
634 node doing traffic analyzing and tagging for later inspecting
636 .It Cm untag Ar number
637 When a packet matches a rule with the
639 keyword, the tag with the number
641 is searched among the tags attached to this packet and,
642 if found, removed from it.
643 Other tags bound to packet, if present, are left untouched.
645 When a packet matches a rule with the
647 keyword, the ALTQ identifier for the given
652 Note that this ALTQ tag is only meaningful for packets going "out" of IPFW,
653 and not being rejected or going to divert sockets.
654 Note that if there is insufficient memory at the time the packet is
655 processed, it will not be tagged, so it is wise to make your ALTQ
656 "default" queue policy account for this.
659 rules match a single packet, only the first one adds the ALTQ classification
661 In doing so, traffic may be shaped by using
662 .Cm count Cm altq Ar queue
663 rules for classification early in the ruleset, then later applying
664 the filtering decision.
669 rules may come later and provide the actual filtering decisions in
670 addition to the fallback ALTQ tag.
674 to set up the queues before IPFW will be able to look them up by name,
675 and if the ALTQ disciplines are rearranged, the rules in containing the
676 queue identifiers in the kernel will likely have gone stale and need
678 Stale queue identifiers will probably result in misclassification.
680 All system ALTQ processing can be turned on or off via
685 .Cm disable Ar altq .
687 .Va net.inet.ip.fw.one_pass
688 is irrelevant to ALTQ traffic shaping, as the actual rule action is followed
689 always after adding an ALTQ tag.
692 A rule can be associated with one of the following actions, which
693 will be executed when the packet matches the body of the rule.
694 .Bl -tag -width indent
695 .It Cm allow | accept | pass | permit
696 Allow packets that match rule.
697 The search terminates.
699 Checks the packet against the dynamic ruleset.
700 If a match is found, execute the action associated with
701 the rule which generated this dynamic rule, otherwise
702 move to the next rule.
705 rules do not have a body.
708 rule is found, the dynamic ruleset is checked at the first
714 Update counters for all packets that match rule.
715 The search continues with the next rule.
717 Discard packets that match this rule.
718 The search terminates.
719 .It Cm divert Ar port
720 Divert packets that match this rule to the
724 The search terminates.
725 .It Cm fwd | forward Ar ipaddr | tablearg Ns Op , Ns Ar port
726 Change the next-hop on matching packets to
728 which can be an IP address or a host name.
729 For IPv4, the next hop can also be supplied by the last table
730 looked up for the packet by using the
732 keyword instead of an explicit address.
733 The search terminates if this rule matches.
737 is a local address, then matching packets will be forwarded to
739 (or the port number in the packet if one is not specified in the rule)
740 on the local machine.
744 is not a local address, then the port number
745 (if specified) is ignored, and the packet will be
746 forwarded to the remote address, using the route as found in
747 the local routing table for that IP.
751 rule will not match layer-2 packets (those received
752 on ether_input, ether_output, or bridged).
756 action does not change the contents of the packet at all.
757 In particular, the destination address remains unmodified, so
758 packets forwarded to another system will usually be rejected by that system
759 unless there is a matching rule on that system to capture them.
760 For packets forwarded locally,
761 the local address of the socket will be
762 set to the original destination address of the packet.
765 entry look rather weird but is intended for
766 use with transparent proxy servers.
770 a custom kernel needs to be compiled with the option
771 .Cd "options IPFIREWALL_FORWARD" .
775 (for network address translation, address redirect, etc.):
777 .Sx NETWORK ADDRESS TRANSLATION (NAT)
778 Section for further information.
779 .It Cm pipe Ar pipe_nr
783 (for bandwidth limitation, delay, etc.).
785 .Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION
786 Section for further information.
787 The search terminates; however, on exit from the pipe and if
791 .Va net.inet.ip.fw.one_pass
792 is not set, the packet is passed again to the firewall code
793 starting from the next rule.
794 .It Cm queue Ar queue_nr
798 (for bandwidth limitation using WF2Q+).
804 Discard packets that match this rule, and if the
805 packet is a TCP packet, try to send a TCP reset (RST) notice.
806 The search terminates.
808 Discard packets that match this rule, and if the
809 packet is a TCP packet, try to send a TCP reset (RST) notice.
810 The search terminates.
811 .It Cm skipto Ar number | tablearg
812 Skip all subsequent rules numbered less than
814 The search continues with the first rule numbered
817 It is possible to use the
819 keyword with a skipto for a
821 skipto, but care should be used, as no destination caching
822 is possible in this case so the rules are always walked to find it,
825 .It Cm call Ar number | tablearg
826 The current rule number is saved in the internal stack and
827 ruleset processing continues with the first rule numbered
830 If later a rule with the
832 action is encountered, the processing returns to the first rule
835 rule plus one or higher
836 (the same behaviour as with packets returning from
841 This could be used to make somewhat like an assembly language
843 calls to rules with common checks for different interfaces, etc.
845 Rule with any number could be called, not just forward jumps as with
847 So, to prevent endless loops in case of mistakes, both
851 actions don't do any jumps and simply go to the next rule if memory
852 can't be allocated or stack overflowed/undeflowed.
854 Internally stack for rule numbers is implemented using
856 facility and currently has size of 16 entries.
857 As mbuf tags are lost when packet leaves the kernel,
859 should not be used in subroutines to avoid endless loops
860 and other undesired effects.
862 Takes rule number saved to internal stack by the last
864 action and returns ruleset processing to the first rule
865 with number greater than number of corresponding
867 rule. See description of the
869 action for more details.
875 and thus are unconditional, but
877 command-line utility currently requires every action except
880 While it is sometimes useful to return only on some packets,
881 usually you want to print just
884 A workaround for this is to use new syntax and
888 .Bd -literal -offset indent
889 # Add a rule without actual body
890 ipfw add 2999 return via any
892 # List rules without "from any to any" part
896 This cosmetic annoyance may be fixed in future releases.
898 Send a copy of packets matching this rule to the
902 The search continues with the next rule.
903 .It Cm unreach Ar code
904 Discard packets that match this rule, and try to send an ICMP
905 unreachable notice with code
909 is a number from 0 to 255, or one of these aliases:
910 .Cm net , host , protocol , port ,
911 .Cm needfrag , srcfail , net-unknown , host-unknown ,
912 .Cm isolated , net-prohib , host-prohib , tosnet ,
913 .Cm toshost , filter-prohib , host-precedence
915 .Cm precedence-cutoff .
916 The search terminates.
917 .It Cm unreach6 Ar code
918 Discard packets that match this rule, and try to send an ICMPv6
919 unreachable notice with code
923 is a number from 0, 1, 3 or 4, or one of these aliases:
924 .Cm no-route, admin-prohib, address
927 The search terminates.
928 .It Cm netgraph Ar cookie
929 Divert packet into netgraph with given
931 The search terminates.
932 If packet is later returned from netgraph it is either
933 accepted or continues with the next rule, depending on
934 .Va net.inet.ip.fw.one_pass
936 .It Cm ngtee Ar cookie
937 A copy of packet is diverted into netgraph, original
938 packet continues with the next rule.
941 for more information on
946 .It Cm setfib Ar fibnum | tablearg
947 The packet is tagged so as to use the FIB (routing table)
949 in any subsequent forwarding decisions.
950 Initially this is limited to the values 0 through 15, see
952 Processing continues at the next rule.
953 It is possible to use the
955 keyword with a setfib. If tablearg value is not within compiled FIB range packet fib is set to 0.
957 Queue and reassemble ip fragments.
958 If the packet is not fragmented, counters are updated and processing continues with the next rule.
959 If the packet is the last logical fragment, the packet is reassembled and, if
960 .Va net.inet.ip.fw.one_pass
961 is set to 0, processing continues with the next rule, else packet is allowed to pass and search terminates.
962 If the packet is a fragment in the middle, it is consumed and processing stops immediately.
964 Fragments handling can be tuned via
965 .Va net.inet.ip.maxfragpackets
967 .Va net.inet.ip.maxfragsperpacket
968 which limit, respectively, the maximum number of processable fragments (default: 800) and
969 the maximum number of fragments per packet (default: 16).
971 NOTA BENE: since fragments do not contain port numbers, they should be avoided with the
974 Alternatively, direction-based (like
978 ) and source-based (like
980 ) match patterns can be used to select fragments.
982 Usually a simple rule like:
983 .Bd -literal -offset indent
984 # reassemble incoming fragments
985 ipfw add reass all from any to any in
988 is all you need at the beginning of your ruleset.
991 The body of a rule contains zero or more patterns (such as
992 specific source and destination addresses or ports,
993 protocol options, incoming or outgoing interfaces, etc.)
994 that the packet must match in order to be recognised.
995 In general, the patterns are connected by (implicit)
997 operators -- i.e., all must match in order for the
999 Individual patterns can be prefixed by the
1001 operator to reverse the result of the match, as in
1003 .Dl "ipfw add 100 allow ip from not 1.2.3.4 to any"
1005 Additionally, sets of alternative match patterns
1007 can be constructed by putting the patterns in
1008 lists enclosed between parentheses ( ) or braces { }, and
1011 operator as follows:
1013 .Dl "ipfw add 100 allow ip from { x or not y or z } to any"
1015 Only one level of parentheses is allowed.
1016 Beware that most shells have special meanings for parentheses
1017 or braces, so it is advisable to put a backslash \\ in front of them
1018 to prevent such interpretations.
1020 The body of a rule must in general include a source and destination
1024 can be used in various places to specify that the content of
1025 a required field is irrelevant.
1027 The rule body has the following format:
1028 .Bd -ragged -offset indent
1029 .Op Ar proto Cm from Ar src Cm to Ar dst
1033 The first part (proto from src to dst) is for backward
1034 compatibility with earlier versions of
1038 any match pattern (including MAC headers, IP protocols,
1039 addresses and ports) can be specified in the
1043 Rule fields have the following meaning:
1044 .Bl -tag -width indent
1045 .It Ar proto : protocol | Cm { Ar protocol Cm or ... }
1046 .It Ar protocol : Oo Cm not Oc Ar protocol-name | protocol-number
1047 An IP protocol specified by number or name
1048 (for a complete list see
1049 .Pa /etc/protocols ) ,
1050 or one of the following keywords:
1051 .Bl -tag -width indent
1053 Matches IPv4 packets.
1055 Matches IPv6 packets.
1064 option will be treated as inner protocol.
1072 .Cm { Ar protocol Cm or ... }
1075 is provided for convenience only but its use is deprecated.
1076 .It Ar src No and Ar dst : Bro Cm addr | Cm { Ar addr Cm or ... } Brc Op Oo Cm not Oc Ar ports
1077 An address (or a list, see below)
1078 optionally followed by
1084 with multiple addresses) is provided for convenience only and
1085 its use is discouraged.
1086 .It Ar addr : Oo Cm not Oc Bro
1087 .Cm any | me | me6 |
1088 .Cm table Ns Pq Ar number Ns Op , Ns Ar value
1089 .Ar | addr-list | addr-set
1091 .Bl -tag -width indent
1093 matches any IP address.
1095 matches any IP address configured on an interface in the system.
1097 matches any IPv6 address configured on an interface in the system.
1098 The address list is evaluated at the time the packet is
1100 .It Cm table Ns Pq Ar number Ns Op , Ns Ar value
1101 Matches any IPv4 address for which an entry exists in the lookup table
1103 If an optional 32-bit unsigned
1105 is also specified, an entry will match only if it has this value.
1108 section below for more information on lookup tables.
1110 .It Ar addr-list : ip-addr Ns Op Ns , Ns Ar addr-list
1112 A host or subnet address specified in one of the following ways:
1113 .Bl -tag -width indent
1114 .It Ar numeric-ip | hostname
1115 Matches a single IPv4 address, specified as dotted-quad or a hostname.
1116 Hostnames are resolved at the time the rule is added to the firewall list.
1117 .It Ar addr Ns / Ns Ar masklen
1118 Matches all addresses with base
1120 (specified as an IP address, a network number, or a hostname)
1124 As an example, 1.2.3.4/25 or 1.2.3.0/25 will match
1125 all IP numbers from 1.2.3.0 to 1.2.3.127 .
1126 .It Ar addr Ns : Ns Ar mask
1127 Matches all addresses with base
1129 (specified as an IP address, a network number, or a hostname)
1132 specified as a dotted quad.
1133 As an example, 1.2.3.4:255.0.255.0 or 1.0.3.0:255.0.255.0 will match
1135 This form is advised only for non-contiguous
1137 It is better to resort to the
1138 .Ar addr Ns / Ns Ar masklen
1139 format for contiguous masks, which is more compact and less
1142 .It Ar addr-set : addr Ns Oo Ns / Ns Ar masklen Oc Ns Cm { Ns Ar list Ns Cm }
1143 .It Ar list : Bro Ar num | num-num Brc Ns Op Ns , Ns Ar list
1144 Matches all addresses with base address
1146 (specified as an IP address, a network number, or a hostname)
1147 and whose last byte is in the list between braces { } .
1148 Note that there must be no spaces between braces and
1149 numbers (spaces after commas are allowed).
1150 Elements of the list can be specified as single entries
1154 field is used to limit the size of the set of addresses,
1155 and can have any value between 24 and 32.
1157 it will be assumed as 24.
1159 This format is particularly useful to handle sparse address sets
1160 within a single rule.
1161 Because the matching occurs using a
1162 bitmask, it takes constant time and dramatically reduces
1163 the complexity of rulesets.
1165 As an example, an address specified as 1.2.3.4/24{128,35-55,89}
1166 or 1.2.3.0/24{128,35-55,89}
1167 will match the following IP addresses:
1169 1.2.3.128, 1.2.3.35 to 1.2.3.55, 1.2.3.89 .
1170 .It Ar addr6-list : ip6-addr Ns Op Ns , Ns Ar addr6-list
1172 A host or subnet specified one of the following ways:
1173 .Bl -tag -width indent
1174 .It Ar numeric-ip | hostname
1175 Matches a single IPv6 address as allowed by
1178 Hostnames are resolved at the time the rule is added to the firewall
1180 .It Ar addr Ns / Ns Ar masklen
1181 Matches all IPv6 addresses with base
1183 (specified as allowed by
1191 No support for sets of IPv6 addresses is provided because IPv6 addresses
1192 are typically random past the initial prefix.
1193 .It Ar ports : Bro Ar port | port Ns \&- Ns Ar port Ns Brc Ns Op , Ns Ar ports
1194 For protocols which support port numbers (such as TCP and UDP), optional
1196 may be specified as one or more ports or port ranges, separated
1197 by commas but no spaces, and an optional
1202 notation specifies a range of ports (including boundaries).
1206 may be used instead of numeric port values.
1207 The length of the port list is limited to 30 ports or ranges,
1208 though one can specify larger ranges by using an
1212 section of the rule.
1216 can be used to escape the dash
1218 character in a service name (from a shell, the backslash must be
1219 typed twice to avoid the shell itself interpreting it as an escape
1222 .Dl "ipfw add count tcp from any ftp\e\e-data-ftp to any"
1224 Fragmented packets which have a non-zero offset (i.e., not the first
1225 fragment) will never match a rule which has one or more port
1229 option for details on matching fragmented packets.
1231 .Ss RULE OPTIONS (MATCH PATTERNS)
1232 Additional match patterns can be used within
1234 Zero or more of these so-called
1236 can be present in a rule, optionally prefixed by the
1238 operand, and possibly grouped into
1241 The following match patterns can be used (listed in alphabetical order):
1242 .Bl -tag -width indent
1243 .It Cm // this is a comment.
1244 Inserts the specified text as a comment in the rule.
1245 Everything following // is considered as a comment and stored in the rule.
1246 You can have comment-only rules, which are listed as having a
1248 action followed by the comment.
1253 Matches only packets generated by a divert socket.
1254 .It Cm diverted-loopback
1255 Matches only packets coming from a divert socket back into the IP stack
1257 .It Cm diverted-output
1258 Matches only packets going from a divert socket back outward to the IP
1259 stack output for delivery.
1260 .It Cm dst-ip Ar ip-address
1261 Matches IPv4 packets whose destination IP is one of the address(es)
1262 specified as argument.
1263 .It Bro Cm dst-ip6 | dst-ipv6 Brc Ar ip6-address
1264 Matches IPv6 packets whose destination IP is one of the address(es)
1265 specified as argument.
1266 .It Cm dst-port Ar ports
1267 Matches IP packets whose destination port is one of the port(s)
1268 specified as argument.
1270 Matches TCP packets that have the RST or ACK bits set.
1271 .It Cm ext6hdr Ar header
1272 Matches IPv6 packets containing the extended header given by
1274 Supported headers are:
1280 any type of Routing Header
1282 Source routing Routing Header Type 0
1284 Mobile IPv6 Routing Header Type 2
1288 IPSec authentication headers
1290 and IPsec encapsulated security payload headers
1292 .It Cm fib Ar fibnum
1293 Matches a packet that has been tagged to use
1294 the given FIB (routing table) number.
1295 .It Cm flow-id Ar labels
1296 Matches IPv6 packets containing any of the flow labels given in
1299 is a comma separated list of numeric flow labels.
1301 Matches packets that are fragments and not the first
1302 fragment of an IP datagram.
1303 Note that these packets will not have
1304 the next protocol header (e.g.\& TCP, UDP) so options that look into
1305 these headers cannot match.
1307 Matches all TCP or UDP packets sent by or received for a
1311 may be specified by name or number.
1312 .It Cm jail Ar prisonID
1313 Matches all TCP or UDP packets sent by or received for the
1314 jail whos prison ID is
1316 .It Cm icmptypes Ar types
1317 Matches ICMP packets whose ICMP type is in the list
1319 The list may be specified as any combination of
1320 individual types (numeric) separated by commas.
1321 .Em Ranges are not allowed .
1322 The supported ICMP types are:
1326 destination unreachable
1334 router advertisement
1338 time-to-live exceeded
1350 address mask request
1352 and address mask reply
1354 .It Cm icmp6types Ar types
1355 Matches ICMP6 packets whose ICMP6 type is in the list of
1357 The list may be specified as any combination of
1358 individual types (numeric) separated by commas.
1359 .Em Ranges are not allowed .
1361 Matches incoming or outgoing packets, respectively.
1365 are mutually exclusive (in fact,
1369 .It Cm ipid Ar id-list
1370 Matches IPv4 packets whose
1372 field has value included in
1374 which is either a single value or a list of values or ranges
1375 specified in the same way as
1377 .It Cm iplen Ar len-list
1378 Matches IP packets whose total length, including header and data, is
1381 which is either a single value or a list of values or ranges
1382 specified in the same way as
1384 .It Cm ipoptions Ar spec
1385 Matches packets whose IPv4 header contains the comma separated list of
1386 options specified in
1388 The supported IP options are:
1391 (strict source route),
1393 (loose source route),
1395 (record packet route) and
1398 The absence of a particular option may be denoted
1401 .It Cm ipprecedence Ar precedence
1402 Matches IPv4 packets whose precedence field is equal to
1405 Matches packets that have IPSEC history associated with them
1406 (i.e., the packet comes encapsulated in IPSEC, the kernel
1407 has IPSEC support and IPSEC_FILTERTUNNEL option, and can correctly
1410 Note that specifying
1412 is different from specifying
1414 as the latter will only look at the specific IP protocol field,
1415 irrespective of IPSEC kernel support and the validity of the IPSEC data.
1417 Further note that this flag is silently ignored in kernels without
1419 It does not affect rule processing when given and the
1420 rules are handled as if with no
1423 .It Cm iptos Ar spec
1424 Matches IPv4 packets whose
1426 field contains the comma separated list of
1427 service types specified in
1429 The supported IP types of service are:
1432 .Pq Dv IPTOS_LOWDELAY ,
1434 .Pq Dv IPTOS_THROUGHPUT ,
1436 .Pq Dv IPTOS_RELIABILITY ,
1438 .Pq Dv IPTOS_MINCOST ,
1440 .Pq Dv IPTOS_ECN_CE .
1441 The absence of a particular type may be denoted
1444 .It Cm ipttl Ar ttl-list
1445 Matches IPv4 packets whose time to live is included in
1447 which is either a single value or a list of values or ranges
1448 specified in the same way as
1450 .It Cm ipversion Ar ver
1451 Matches IP packets whose IP version field is
1454 Upon a match, the firewall will create a dynamic rule, whose
1455 default behaviour is to match bidirectional traffic between
1456 source and destination IP/port using the same protocol.
1457 The rule has a limited lifetime (controlled by a set of
1459 variables), and the lifetime is refreshed every time a matching
1462 Matches only layer2 packets, i.e., those passed to
1464 from ether_demux() and ether_output_frame().
1465 .It Cm limit Bro Cm src-addr | src-port | dst-addr | dst-port Brc Ar N
1466 The firewall will only allow
1468 connections with the same
1469 set of parameters as specified in the rule.
1471 of source and destination addresses and ports can be
1474 only IPv4 flows are supported.
1475 .It Cm lookup Bro Cm dst-ip | dst-port | src-ip | src-port | uid | jail Brc Ar N
1476 Search an entry in lookup table
1478 that matches the field specified as argument.
1479 If not found, the match fails.
1480 Otherwise, the match succeeds and
1482 is set to the value extracted from the table.
1484 This option can be useful to quickly dispatch traffic based on
1485 certain packet fields.
1488 section below for more information on lookup tables.
1489 .It Cm { MAC | mac } Ar dst-mac src-mac
1490 Match packets with a given
1494 addresses, specified as the
1496 keyword (matching any MAC address), or six groups of hex digits
1497 separated by colons,
1498 and optionally followed by a mask indicating the significant bits.
1499 The mask may be specified using either of the following methods:
1500 .Bl -enum -width indent
1504 followed by the number of significant bits.
1505 For example, an address with 33 significant bits could be specified as:
1507 .Dl "MAC 10:20:30:40:50:60/33 any"
1512 followed by a bitmask specified as six groups of hex digits separated
1514 For example, an address in which the last 16 bits are significant could
1517 .Dl "MAC 10:20:30:40:50:60&00:00:00:00:ff:ff any"
1519 Note that the ampersand character has a special meaning in many shells
1520 and should generally be escaped.
1523 Note that the order of MAC addresses (destination first,
1525 the same as on the wire, but the opposite of the one used for
1527 .It Cm mac-type Ar mac-type
1528 Matches packets whose Ethernet Type field
1529 corresponds to one of those specified as argument.
1531 is specified in the same way as
1533 (i.e., one or more comma-separated single values or ranges).
1534 You can use symbolic names for known values such as
1535 .Em vlan , ipv4, ipv6 .
1536 Values can be entered as decimal or hexadecimal (if prefixed by 0x),
1537 and they are always printed as hexadecimal (unless the
1539 option is used, in which case symbolic resolution will be attempted).
1540 .It Cm proto Ar protocol
1541 Matches packets with the corresponding IP protocol.
1542 .It Cm recv | xmit | via Brq Ar ifX | Ar if Ns Cm * | Ar ipno | Ar any
1543 Matches packets received, transmitted or going through,
1544 respectively, the interface specified by exact name
1545 .Ns No ( Ar ifX Ns No ),
1547 .Ns No ( Ar if Ns Ar * Ns No ),
1548 by IP address, or through some interface.
1552 keyword causes the interface to always be checked.
1559 then only the receive or transmit interface (respectively)
1561 By specifying both, it is possible to match packets based on
1562 both receive and transmit interface, e.g.:
1564 .Dl "ipfw add deny ip from any to any out recv ed0 xmit ed1"
1568 interface can be tested on either incoming or outgoing packets,
1571 interface can only be tested on outgoing packets.
1576 is invalid) whenever
1580 A packet might not have a receive or transmit interface: packets
1581 originating from the local host have no receive interface,
1582 while packets destined for the local host have no transmit
1585 Matches TCP packets that have the SYN bit set but no ACK bit.
1586 This is the short form of
1587 .Dq Li tcpflags\ syn,!ack .
1589 Matches packets that are associated to a local socket and
1590 for which the SO_USER_COOKIE socket option has been set
1591 to a non-zero value. As a side effect, the value of the
1592 option is made available as
1594 value, which in turn can be used as
1599 .It Cm src-ip Ar ip-address
1600 Matches IPv4 packets whose source IP is one of the address(es)
1601 specified as an argument.
1602 .It Cm src-ip6 Ar ip6-address
1603 Matches IPv6 packets whose source IP is one of the address(es)
1604 specified as an argument.
1605 .It Cm src-port Ar ports
1606 Matches IP packets whose source port is one of the port(s)
1607 specified as argument.
1608 .It Cm tagged Ar tag-list
1609 Matches packets whose tags are included in
1611 which is either a single value or a list of values or ranges
1612 specified in the same way as
1614 Tags can be applied to the packet using
1616 rule action parameter (see it's description for details on tags).
1617 .It Cm tcpack Ar ack
1619 Match if the TCP header acknowledgment number field is set to
1621 .It Cm tcpdatalen Ar tcpdatalen-list
1622 Matches TCP packets whose length of TCP data is
1623 .Ar tcpdatalen-list ,
1624 which is either a single value or a list of values or ranges
1625 specified in the same way as
1627 .It Cm tcpflags Ar spec
1629 Match if the TCP header contains the comma separated list of
1632 The supported TCP flags are:
1641 The absence of a particular flag may be denoted
1644 A rule which contains a
1646 specification can never match a fragmented packet which has
1650 option for details on matching fragmented packets.
1651 .It Cm tcpseq Ar seq
1653 Match if the TCP header sequence number field is set to
1655 .It Cm tcpwin Ar win
1657 Match if the TCP header window field is set to
1659 .It Cm tcpoptions Ar spec
1661 Match if the TCP header contains the comma separated list of
1662 options specified in
1664 The supported TCP options are:
1667 (maximum segment size),
1669 (tcp window advertisement),
1673 (rfc1323 timestamp) and
1675 (rfc1644 t/tcp connection count).
1676 The absence of a particular option may be denoted
1680 Match all TCP or UDP packets sent by or received for a
1684 may be matched by name or identification number.
1686 For incoming packets,
1687 a routing table lookup is done on the packet's source address.
1688 If the interface on which the packet entered the system matches the
1689 outgoing interface for the route,
1691 If the interfaces do not match up,
1692 the packet does not match.
1693 All outgoing packets or packets with no incoming interface match.
1695 The name and functionality of the option is intentionally similar to
1696 the Cisco IOS command:
1698 .Dl ip verify unicast reverse-path
1700 This option can be used to make anti-spoofing rules to reject all
1701 packets with source addresses not from this interface.
1705 For incoming packets,
1706 a routing table lookup is done on the packet's source address.
1707 If a route to the source address exists, but not the default route
1708 or a blackhole/reject route, the packet matches.
1709 Otherwise, the packet does not match.
1710 All outgoing packets match.
1712 The name and functionality of the option is intentionally similar to
1713 the Cisco IOS command:
1715 .Dl ip verify unicast source reachable-via any
1717 This option can be used to make anti-spoofing rules to reject all
1718 packets whose source address is unreachable.
1720 For incoming packets, the packet's source address is checked if it
1721 belongs to a directly connected network.
1722 If the network is directly connected, then the interface the packet
1723 came on in is compared to the interface the network is connected to.
1724 When incoming interface and directly connected interface are not the
1725 same, the packet does not match.
1726 Otherwise, the packet does match.
1727 All outgoing packets match.
1729 This option can be used to make anti-spoofing rules to reject all
1730 packets that pretend to be from a directly connected network but do
1731 not come in through that interface.
1732 This option is similar to but more restricted than
1734 because it engages only on packets with source addresses of directly
1735 connected networks instead of all source addresses.
1738 Lookup tables are useful to handle large sparse sets of
1739 addresses or other search keys (e.g. ports, jail IDs).
1740 In the rest of this section we will use the term ``address''
1741 to mean any unsigned value of up to 32-bit.
1742 There may be up to 128 different lookup tables, numbered 0 to 127.
1744 Each entry is represented by an
1745 .Ar addr Ns Op / Ns Ar masklen
1746 and will match all addresses with base
1748 (specified as an IP address, a hostname or an unsigned integer)
1754 is not specified, it defaults to 32.
1755 When looking up an IP address in a table, the most specific
1757 Associated with each entry is a 32-bit unsigned
1759 which can optionally be checked by a rule matching code.
1760 When adding an entry, if
1762 is not specified, it defaults to 0.
1764 An entry can be added to a table
1766 or removed from a table
1768 A table can be examined
1773 Internally, each table is stored in a Radix tree, the same way as
1774 the routing table (see
1777 Lookup tables currently support only ports, jail IDs and IPv4 addresses.
1781 feature provides the ability to use a value, looked up in the table, as
1782 the argument for a rule action, action parameter or rule option.
1783 This can significantly reduce number of rules in some configurations.
1784 If two tables are used in a rule, the result of the second (destination)
1788 argument can be used with the following actions:
1789 .Cm nat, pipe , queue, divert, tee, netgraph, ngtee, fwd, skipto, setfib,
1797 it is possible to supply table entries with values
1798 that are in the form of IP addresses or hostnames.
1801 Section for example usage of tables and the tablearg keyword.
1805 action, the user should be aware that the code will walk the ruleset
1806 up to a rule equal to, or past, the given number, and should therefore try keep the
1807 ruleset compact between the skipto and the target rules.
1809 Each rule belongs to one of 32 different
1812 Set 31 is reserved for the default rule.
1814 By default, rules are put in set 0, unless you use the
1816 attribute when entering a new rule.
1817 Sets can be individually and atomically enabled or disabled,
1818 so this mechanism permits an easy way to store multiple configurations
1819 of the firewall and quickly (and atomically) switch between them.
1820 The command to enable/disable sets is
1821 .Bd -ragged -offset indent
1823 .Cm set Oo Cm disable Ar number ... Oc Op Cm enable Ar number ...
1830 sections can be specified.
1831 Command execution is atomic on all the sets specified in the command.
1832 By default, all sets are enabled.
1834 When you disable a set, its rules behave as if they do not exist
1835 in the firewall configuration, with only one exception:
1836 .Bd -ragged -offset indent
1837 dynamic rules created from a rule before it had been disabled
1838 will still be active until they expire.
1840 dynamic rules you have to explicitly delete the parent rule
1841 which generated them.
1844 The set number of rules can be changed with the command
1845 .Bd -ragged -offset indent
1848 .Brq Cm rule Ar rule-number | old-set
1852 Also, you can atomically swap two rulesets with the command
1853 .Bd -ragged -offset indent
1855 .Cm set swap Ar first-set second-set
1860 Section on some possible uses of sets of rules.
1861 .Sh STATEFUL FIREWALL
1862 Stateful operation is a way for the firewall to dynamically
1863 create rules for specific flows when packets that
1864 match a given pattern are detected.
1865 Support for stateful
1866 operation comes through the
1867 .Cm check-state , keep-state
1873 Dynamic rules are created when a packet matches a
1877 rule, causing the creation of a
1879 rule which will match all and only packets with
1883 .Em src-ip/src-port dst-ip/dst-port
1888 are used here only to denote the initial match addresses, but they
1889 are completely equivalent afterwards).
1890 Dynamic rules will be checked at the first
1891 .Cm check-state, keep-state
1894 occurrence, and the action performed upon a match will be the same
1895 as in the parent rule.
1897 Note that no additional attributes other than protocol and IP addresses
1898 and ports are checked on dynamic rules.
1900 The typical use of dynamic rules is to keep a closed firewall configuration,
1901 but let the first TCP SYN packet from the inside network install a
1902 dynamic rule for the flow so that packets belonging to that session
1903 will be allowed through the firewall:
1905 .Dl "ipfw add check-state"
1906 .Dl "ipfw add allow tcp from my-subnet to any setup keep-state"
1907 .Dl "ipfw add deny tcp from any to any"
1909 A similar approach can be used for UDP, where an UDP packet coming
1910 from the inside will install a dynamic rule to let the response through
1913 .Dl "ipfw add check-state"
1914 .Dl "ipfw add allow udp from my-subnet to any keep-state"
1915 .Dl "ipfw add deny udp from any to any"
1917 Dynamic rules expire after some time, which depends on the status
1918 of the flow and the setting of some
1922 .Sx SYSCTL VARIABLES
1924 For TCP sessions, dynamic rules can be instructed to periodically
1925 send keepalive packets to refresh the state of the rule when it is
1930 for more examples on how to use dynamic rules.
1931 .Sh TRAFFIC SHAPER (DUMMYNET) CONFIGURATION
1933 is also the user interface for the
1935 traffic shaper, packet scheduler and network emulator, a subsystem that
1936 can artificially queue, delay or drop packets
1937 emulating the behaviour of certain network links
1938 or queueing systems.
1941 operates by first using the firewall to select packets
1942 using any match pattern that can be used in
1945 Matching packets are then passed to either of two
1946 different objects, which implement the traffic regulation:
1947 .Bl -hang -offset XXXX
1953 with given bandwidth and propagation delay,
1954 driven by a FIFO scheduler and a single queue with programmable
1955 queue size and packet loss rate.
1956 Packets are appended to the queue as they come out from
1958 and then transferred in FIFO order to the link at the desired rate.
1962 is an abstraction used to implement packet scheduling
1963 using one of several packet scheduling algorithms.
1966 are first grouped into flows according to a mask on the 5-tuple.
1967 Flows are then passed to the scheduler associated to the
1969 and each flow uses scheduling parameters (weight and others)
1970 as configured in the
1973 A scheduler in turn is connected to an emulated link,
1974 and arbitrates the link's bandwidth among backlogged flows according to
1975 weights and to the features of the scheduling algorithm in use.
1980 can be used to set hard limits to the bandwidth that a flow can use, whereas
1982 can be used to determine how different flows share the available bandwidth.
1984 A graphical representation of the binding of queues,
1985 flows, schedulers and links is below.
1986 .Bd -literal -offset indent
1987 (flow_mask|sched_mask) sched_mask
1988 +---------+ weight Wx +-------------+
1989 | |->-[flow]-->--| |-+
1990 -->--| QUEUE x | ... | | |
1991 | |->-[flow]-->--| SCHEDuler N | |
1993 ... | +--[LINK N]-->--
1994 +---------+ weight Wy | | +--[LINK N]-->--
1995 | |->-[flow]-->--| | |
1996 -->--| QUEUE y | ... | | |
1997 | |->-[flow]-->--| | |
1998 +---------+ +-------------+ |
2001 It is important to understand the role of the SCHED_MASK
2002 and FLOW_MASK, which are configured through the commands
2003 .Dl "ipfw sched N config mask SCHED_MASK ..."
2005 .Dl "ipfw queue X config mask FLOW_MASK ..." .
2007 The SCHED_MASK is used to assign flows to one or more
2008 scheduler instances, one for each
2009 value of the packet's 5-tuple after applying SCHED_MASK.
2010 As an example, using ``src-ip 0xffffff00'' creates one instance
2011 for each /24 destination subnet.
2013 The FLOW_MASK, together with the SCHED_MASK, is used to split
2014 packets into flows. As an example, using
2015 ``src-ip 0x000000ff''
2016 together with the previous SCHED_MASK makes a flow for
2017 each individual source address. In turn, flows for each /24
2018 subnet will be sent to the same scheduler instance.
2020 The above diagram holds even for the
2022 case, with the only restriction that a
2024 only supports a SCHED_MASK, and forces the use of a FIFO
2025 scheduler (these are for backward compatibility reasons;
2026 in fact, internally, a
2028 pipe is implemented exactly as above).
2030 There are two modes of
2038 mode tries to emulate a real link: the
2040 scheduler ensures that the packet will not leave the pipe faster than it
2041 would on the real link with a given bandwidth.
2044 mode allows certain packets to bypass the
2046 scheduler (if packet flow does not exceed pipe's bandwidth).
2047 This is the reason why the
2049 mode requires less CPU cycles per packet (on average) and packet latency
2050 can be significantly lower in comparison to a real link with the same
2056 mode can be enabled by setting the
2057 .Va net.inet.ip.dummynet.io_fast
2059 variable to a non-zero value.
2061 .Ss PIPE, QUEUE AND SCHEDULER CONFIGURATION
2067 configuration commands are the following:
2068 .Bd -ragged -offset indent
2069 .Cm pipe Ar number Cm config Ar pipe-configuration
2071 .Cm queue Ar number Cm config Ar queue-configuration
2073 .Cm sched Ar number Cm config Ar sched-configuration
2076 The following parameters can be configured for a pipe:
2078 .Bl -tag -width indent -compact
2079 .It Cm bw Ar bandwidth | device
2080 Bandwidth, measured in
2083 .Brq Cm bit/s | Byte/s .
2086 A value of 0 (default) means unlimited bandwidth.
2087 The unit must immediately follow the number, as in
2089 .Dl "ipfw pipe 1 config bw 300Kbit/s"
2091 If a device name is specified instead of a numeric value, as in
2093 .Dl "ipfw pipe 1 config bw tun0"
2095 then the transmit clock is supplied by the specified device.
2096 At the moment only the
2098 device supports this
2099 functionality, for use in conjunction with
2102 .It Cm delay Ar ms-delay
2103 Propagation delay, measured in milliseconds.
2104 The value is rounded to the next multiple of the clock tick
2105 (typically 10ms, but it is a good practice to run kernels
2107 .Dq "options HZ=1000"
2109 the granularity to 1ms or less).
2110 The default value is 0, meaning no delay.
2112 .It Cm burst Ar size
2113 If the data to be sent exceeds the pipe's bandwidth limit
2114 (and the pipe was previously idle), up to
2116 bytes of data are allowed to bypass the
2118 scheduler, and will be sent as fast as the physical link allows.
2119 Any additional data will be transmitted at the rate specified
2123 The burst size depends on how long the pipe has been idle;
2124 the effective burst size is calculated as follows:
2131 .It Cm profile Ar filename
2132 A file specifying the additional overhead incurred in the transmission
2133 of a packet on the link.
2135 Some link types introduce extra delays in the transmission
2136 of a packet, e.g. because of MAC level framing, contention on
2137 the use of the channel, MAC level retransmissions and so on.
2138 From our point of view, the channel is effectively unavailable
2139 for this extra time, which is constant or variable depending
2140 on the link type. Additionally, packets may be dropped after this
2141 time (e.g. on a wireless link after too many retransmissions).
2142 We can model the additional delay with an empirical curve
2143 that represents its distribution.
2144 .Bd -literal -offset indent
2145 cumulative probability
2155 +-------*------------------->
2158 The empirical curve may have both vertical and horizontal lines.
2159 Vertical lines represent constant delay for a range of
2161 Horizontal lines correspond to a discontinuity in the delay
2162 distribution: the pipe will use the largest delay for a
2165 The file format is the following, with whitespace acting as
2166 a separator and '#' indicating the beginning a comment:
2167 .Bl -tag -width indent
2168 .It Cm name Ar identifier
2169 optional name (listed by "ipfw pipe show")
2170 to identify the delay distribution;
2172 the bandwidth used for the pipe.
2173 If not specified here, it must be present
2174 explicitly as a configuration parameter for the pipe;
2175 .It Cm loss-level Ar L
2176 the probability above which packets are lost.
2177 (0.0 <= L <= 1.0, default 1.0 i.e. no loss);
2179 the number of samples used in the internal
2180 representation of the curve (2..1024; default 100);
2181 .It Cm "delay prob" | "prob delay"
2182 One of these two lines is mandatory and defines
2183 the format of the following lines with data points.
2185 2 or more lines representing points in the curve,
2186 with either delay or probability first, according
2187 to the chosen format.
2188 The unit for delay is milliseconds.
2189 Data points do not need to be sorted.
2190 Also, the number of actual lines can be different
2191 from the value of the "samples" parameter:
2193 utility will sort and interpolate
2194 the curve as needed.
2197 Example of a profile file:
2198 .Bd -literal -offset indent
2203 0 200 # minimum overhead is 200ms
2209 #configuration file end
2213 The following parameters can be configured for a queue:
2215 .Bl -tag -width indent -compact
2216 .It Cm pipe Ar pipe_nr
2217 Connects a queue to the specified pipe.
2218 Multiple queues (with the same or different weights) can be connected to
2219 the same pipe, which specifies the aggregate rate for the set of queues.
2221 .It Cm weight Ar weight
2222 Specifies the weight to be used for flows matching this queue.
2223 The weight must be in the range 1..100, and defaults to 1.
2226 The following parameters can be configured for a scheduler:
2228 .Bl -tag -width indent -compact
2229 .It Cm type Ar {fifo | wf2qp | rr | qfq}
2230 specifies the scheduling algorithm to use.
2231 .Bl -tag -width indent -compact
2233 is just a FIFO scheduler (which means that all packets
2234 are stored in the same queue as they arrive to the scheduler).
2235 FIFO has O(1) per-packet time complexity, with very low
2236 constants (estimate 60-80ns on a 2Ghz desktop machine)
2237 but gives no service guarantees.
2239 implements the WF2Q+ algorithm, which is a Weighted Fair Queueing
2240 algorithm which permits flows to share bandwidth according to
2241 their weights. Note that weights are not priorities; even a flow
2242 with a minuscule weight will never starve.
2243 WF2Q+ has O(log N) per-packet processing cost, where N is the number
2244 of flows, and is the default algorithm used by previous versions
2247 implements the Deficit Round Robin algorithm, which has O(1) processing
2248 costs (roughly, 100-150ns per packet)
2249 and permits bandwidth allocation according to weights, but
2250 with poor service guarantees.
2252 implements the QFQ algorithm, which is a very fast variant of
2253 WF2Q+, with similar service guarantees and O(1) processing
2254 costs (roughly, 200-250ns per packet).
2258 In addition to the type, all parameters allowed for a pipe can also
2259 be specified for a scheduler.
2261 Finally, the following parameters can be configured for both
2264 .Bl -tag -width XXXX -compact
2265 .It Cm buckets Ar hash-table-size
2266 Specifies the size of the hash table used for storing the
2268 Default value is 64 controlled by the
2271 .Va net.inet.ip.dummynet.hash_size ,
2272 allowed range is 16 to 65536.
2274 .It Cm mask Ar mask-specifier
2275 Packets sent to a given pipe or queue by an
2277 rule can be further classified into multiple flows, each of which is then
2281 A flow identifier is constructed by masking the IP addresses,
2282 ports and protocol types as specified with the
2284 options in the configuration of the pipe or queue.
2285 For each different flow identifier, a new pipe or queue is created
2286 with the same parameters as the original object, and matching packets
2291 are used, each flow will get the same bandwidth as defined by the pipe,
2294 are used, each flow will share the parent's pipe bandwidth evenly
2295 with other flows generated by the same queue (note that other queues
2296 with different weights might be connected to the same pipe).
2298 Available mask specifiers are a combination of one or more of the following:
2300 .Cm dst-ip Ar mask ,
2301 .Cm dst-ip6 Ar mask ,
2302 .Cm src-ip Ar mask ,
2303 .Cm src-ip6 Ar mask ,
2304 .Cm dst-port Ar mask ,
2305 .Cm src-port Ar mask ,
2306 .Cm flow-id Ar mask ,
2311 where the latter means all bits in all fields are significant.
2314 When a packet is dropped by a
2316 queue or pipe, the error
2317 is normally reported to the caller routine in the kernel, in the
2318 same way as it happens when a device queue fills up.
2320 option reports the packet as successfully delivered, which can be
2321 needed for some experimental setups where you want to simulate
2322 loss or congestion at a remote router.
2324 .It Cm plr Ar packet-loss-rate
2327 .Ar packet-loss-rate
2328 is a floating-point number between 0 and 1, with 0 meaning no
2329 loss, 1 meaning 100% loss.
2330 The loss rate is internally represented on 31 bits.
2332 .It Cm queue Brq Ar slots | size Ns Cm Kbytes
2337 Default value is 50 slots, which
2338 is the typical queue size for Ethernet devices.
2339 Note that for slow speed links you should keep the queue
2340 size short or your traffic might be affected by a significant
2342 E.g., 50 max-sized ethernet packets (1500 bytes) mean 600Kbit
2343 or 20s of queue on a 30Kbit/s pipe.
2344 Even worse effects can result if you get packets from an
2345 interface with a much larger MTU, e.g.\& the loopback interface
2346 with its 16KB packets.
2350 .Em net.inet.ip.dummynet.pipe_byte_limit
2352 .Em net.inet.ip.dummynet.pipe_slot_limit
2353 control the maximum lengths that can be specified.
2355 .It Cm red | gred Ar w_q Ns / Ns Ar min_th Ns / Ns Ar max_th Ns / Ns Ar max_p
2356 Make use of the RED (Random Early Detection) queue management algorithm.
2361 point numbers between 0 and 1 (0 not included), while
2365 are integer numbers specifying thresholds for queue management
2366 (thresholds are computed in bytes if the queue has been defined
2367 in bytes, in slots otherwise).
2370 also supports the gentle RED variant (gred).
2373 variables can be used to control the RED behaviour:
2374 .Bl -tag -width indent
2375 .It Va net.inet.ip.dummynet.red_lookup_depth
2376 specifies the accuracy in computing the average queue
2377 when the link is idle (defaults to 256, must be greater than zero)
2378 .It Va net.inet.ip.dummynet.red_avg_pkt_size
2379 specifies the expected average packet size (defaults to 512, must be
2381 .It Va net.inet.ip.dummynet.red_max_pkt_size
2382 specifies the expected maximum packet size, only used when queue
2383 thresholds are in bytes (defaults to 1500, must be greater than zero).
2387 When used with IPv6 data,
2389 currently has several limitations.
2390 Information necessary to route link-local packets to an
2391 interface is not available after processing by
2393 so those packets are dropped in the output path.
2394 Care should be taken to ensure that link-local packets are not passed to
2397 Here are some important points to consider when designing your
2401 Remember that you filter both packets going
2405 Most connections need packets going in both directions.
2407 Remember to test very carefully.
2408 It is a good idea to be near the console when doing this.
2409 If you cannot be near the console,
2410 use an auto-recovery script such as the one in
2411 .Pa /usr/share/examples/ipfw/change_rules.sh .
2413 Do not forget the loopback interface.
2418 There are circumstances where fragmented datagrams are unconditionally
2420 TCP packets are dropped if they do not contain at least 20 bytes of
2421 TCP header, UDP packets are dropped if they do not contain a full 8
2422 byte UDP header, and ICMP packets are dropped if they do not contain
2423 4 bytes of ICMP header, enough to specify the ICMP type, code, and
2425 These packets are simply logged as
2427 since there may not be enough good data in the packet to produce a
2428 meaningful log entry.
2430 Another type of packet is unconditionally dropped, a TCP packet with a
2431 fragment offset of one.
2432 This is a valid packet, but it only has one use, to try
2433 to circumvent firewalls.
2434 When logging is enabled, these packets are
2435 reported as being dropped by rule -1.
2437 If you are logged in over a network, loading the
2441 is probably not as straightforward as you would think.
2442 The following command line is recommended:
2443 .Bd -literal -offset indent
2445 ipfw add 32000 allow ip from any to any
2448 Along the same lines, doing an
2449 .Bd -literal -offset indent
2453 in similar surroundings is also a bad idea.
2457 filter list may not be modified if the system security level
2458 is set to 3 or higher
2461 for information on system security levels).
2463 .Sh PACKET DIVERSION
2466 socket bound to the specified port will receive all packets
2467 diverted to that port.
2468 If no socket is bound to the destination port, or if the divert module is
2469 not loaded, or if the kernel was not compiled with divert socket support,
2470 the packets are dropped.
2471 .Sh NETWORK ADDRESS TRANSLATION (NAT)
2474 support in-kernel NAT using the kernel version of
2477 The nat configuration command is the following:
2478 .Bd -ragged -offset indent
2483 .Ar nat-configuration
2487 The following parameters can be configured:
2488 .Bl -tag -width indent
2489 .It Cm ip Ar ip_address
2490 Define an ip address to use for aliasing.
2492 Use ip address of NIC for aliasing, dynamically changing
2493 it if NIC's ip address changes.
2495 Enable logging on this nat instance.
2497 Deny any incoming connection from outside world.
2499 Try to leave the alias port numbers unchanged from
2500 the actual local port numbers.
2502 Traffic on the local network not originating from an
2503 unregistered address spaces will be ignored.
2505 Reset table of the packet aliasing engine on address change.
2507 Reverse the way libalias handles aliasing.
2509 Obey transparent proxy rules only, packet aliasing is not performed.
2511 Skip instance in case of global state lookup (see below).
2514 Some specials value can be supplied instead of
2516 .Bl -tag -width indent
2518 Looks up translation state in all configured nat instances.
2519 If an entry is found, packet is aliased according to that entry.
2520 If no entry was found in any of the instances, packet is passed unchanged,
2521 and no new entry will be created.
2523 .Sx MULTIPLE INSTANCES
2526 for more information.
2528 Uses argument supplied in lookup table. See
2530 section below for more information on lookup tables.
2533 To let the packet continue after being (de)aliased, set the sysctl variable
2534 .Va net.inet.ip.fw.one_pass
2536 For more information about aliasing modes, refer to
2540 for some examples about nat usage.
2541 .Ss REDIRECT AND LSNAT SUPPORT IN IPFW
2542 Redirect and LSNAT support follow closely the syntax used in
2546 for some examples on how to do redirect and lsnat.
2547 .Ss SCTP NAT SUPPORT
2548 SCTP nat can be configured in a similar manner to TCP through the
2551 The main difference is that
2553 does not do port translation.
2554 Since the local and global side ports will be the same,
2555 there is no need to specify both.
2556 Ports are redirected as follows:
2557 .Bd -ragged -offset indent
2563 .Cm redirect_port sctp
2564 .Ar ip_address [,addr_list] {[port | port-port] [,ports]}
2570 configuration can be done in real-time through the
2573 All may be changed dynamically, though the hash_table size will only
2578 .Sx SYSCTL VARIABLES
2580 .Sh SYSCTL VARIABLES
2583 variables controls the behaviour of the firewall and
2585 .Pq Nm dummynet , bridge , sctp nat .
2586 These are shown below together with their default value
2587 (but always check with the
2589 command what value is actually in use) and meaning:
2590 .Bl -tag -width indent
2591 .It Va net.inet.ip.alias.sctp.accept_global_ootb_addip: No 0
2594 responds to receipt of global OOTB ASCONF-AddIP:
2595 .Bl -tag -width indent
2597 No response (unless a partially matching association exists -
2598 ports and vtags match but global address does not)
2601 will accept and process all OOTB global AddIP messages.
2604 Option 1 should never be selected as this forms a security risk.
2606 establish multiple fake associations by sending AddIP messages.
2607 .It Va net.inet.ip.alias.sctp.chunk_proc_limit: No 5
2608 Defines the maximum number of chunks in an SCTP packet that will be parsed for a
2609 packet that matches an existing association.
2610 This value is enforced to be greater or equal than
2611 .Cm net.inet.ip.alias.sctp.initialising_chunk_proc_limit .
2613 a DoS risk yet setting too low a value may result in important control chunks in
2614 the packet not being located and parsed.
2615 .It Va net.inet.ip.alias.sctp.error_on_ootb: No 1
2618 responds to any Out-of-the-Blue (OOTB) packets with ErrorM packets.
2619 An OOTB packet is a packet that arrives with no existing association
2622 and is not an INIT or ASCONF-AddIP packet:
2623 .Bl -tag -width indent
2625 ErrorM is never sent in response to OOTB packets.
2627 ErrorM is only sent to OOTB packets received on the local side.
2629 ErrorM is sent to the local side and on the global side ONLY if there is a
2630 partial match (ports and vtags match but the source global IP does not).
2631 This value is only useful if the
2633 is tracking global IP addresses.
2635 ErrorM is sent in response to all OOTB packets on both the local and global side
2639 At the moment the default is 0, since the ErrorM packet is not yet
2640 supported by most SCTP stacks.
2641 When it is supported, and if not tracking
2642 global addresses, we recommend setting this value to 1 to allow
2643 multi-homed local hosts to function with the
2645 To track global addresses, we recommend setting this value to 2 to
2646 allow global hosts to be informed when they need to (re)send an
2648 Value 3 should never be chosen (except for debugging) as the
2650 will respond to all OOTB global packets (a DoS risk).
2651 .It Va net.inet.ip.alias.sctp.hashtable_size: No 2003
2652 Size of hash tables used for
2654 lookups (100 < prime_number > 1000001).
2657 size for any future created
2659 instance and therefore must be set prior to creating a
2662 The table sizes may be changed to suit specific needs.
2663 If there will be few
2664 concurrent associations, and memory is scarce, you may make these smaller.
2665 If there will be many thousands (or millions) of concurrent associations, you
2666 should make these larger.
2667 A prime number is best for the table size.
2669 update function will adjust your input value to the next highest prime number.
2670 .It Va net.inet.ip.alias.sctp.holddown_time: No 0
2671 Hold association in table for this many seconds after receiving a
2673 This allows endpoints to correct shutdown gracefully if a
2674 shutdown_complete is lost and retransmissions are required.
2675 .It Va net.inet.ip.alias.sctp.init_timer: No 15
2676 Timeout value while waiting for (INIT-ACK|AddIP-ACK).
2677 This value cannot be 0.
2678 .It Va net.inet.ip.alias.sctp.initialising_chunk_proc_limit: No 2
2679 Defines the maximum number of chunks in an SCTP packet that will be parsed when
2680 no existing association exists that matches that packet.
2682 will only be an INIT or ASCONF-AddIP packet.
2683 A higher value may become a DoS
2684 risk as malformed packets can consume processing resources.
2685 .It Va net.inet.ip.alias.sctp.param_proc_limit: No 25
2686 Defines the maximum number of parameters within a chunk that will be parsed in a
2688 As for other similar sysctl variables, larger values pose a DoS risk.
2689 .It Va net.inet.ip.alias.sctp.log_level: No 0
2690 Level of detail in the system log messages (0 \- minimal, 1 \- event,
2691 2 \- info, 3 \- detail, 4 \- debug, 5 \- max debug). May be a good
2692 option in high loss environments.
2693 .It Va net.inet.ip.alias.sctp.shutdown_time: No 15
2694 Timeout value while waiting for SHUTDOWN-COMPLETE.
2695 This value cannot be 0.
2696 .It Va net.inet.ip.alias.sctp.track_global_addresses: No 0
2697 Enables/disables global IP address tracking within the
2700 upper limit on the number of addresses tracked for each association:
2701 .Bl -tag -width indent
2703 Global tracking is disabled
2705 Enables tracking, the maximum number of addresses tracked for each
2706 association is limited to this value
2709 This variable is fully dynamic, the new value will be adopted for all newly
2710 arriving associations, existing associations are treated as they were previously.
2711 Global tracking will decrease the number of collisions within the
2714 of increased processing load, memory usage, complexity, and possible
2717 problems in complex networks with multiple
2719 We recommend not tracking
2720 global IP addresses, this will still result in a fully functional
2722 .It Va net.inet.ip.alias.sctp.up_timer: No 300
2723 Timeout value to keep an association up with no traffic.
2724 This value cannot be 0.
2725 .It Va net.inet.ip.dummynet.expire : No 1
2726 Lazily delete dynamic pipes/queue once they have no pending traffic.
2727 You can disable this by setting the variable to 0, in which case
2728 the pipes/queues will only be deleted when the threshold is reached.
2729 .It Va net.inet.ip.dummynet.hash_size : No 64
2730 Default size of the hash table used for dynamic pipes/queues.
2731 This value is used when no
2733 option is specified when configuring a pipe/queue.
2734 .It Va net.inet.ip.dummynet.io_fast : No 0
2735 If set to a non-zero value,
2740 operation (see above) is enabled.
2741 .It Va net.inet.ip.dummynet.io_pkt
2742 Number of packets passed to
2744 .It Va net.inet.ip.dummynet.io_pkt_drop
2745 Number of packets dropped by
2747 .It Va net.inet.ip.dummynet.io_pkt_fast
2748 Number of packets bypassed by the
2751 .It Va net.inet.ip.dummynet.max_chain_len : No 16
2752 Target value for the maximum number of pipes/queues in a hash bucket.
2754 .Cm max_chain_len*hash_size
2755 is used to determine the threshold over which empty pipes/queues
2756 will be expired even when
2757 .Cm net.inet.ip.dummynet.expire=0 .
2758 .It Va net.inet.ip.dummynet.red_lookup_depth : No 256
2759 .It Va net.inet.ip.dummynet.red_avg_pkt_size : No 512
2760 .It Va net.inet.ip.dummynet.red_max_pkt_size : No 1500
2761 Parameters used in the computations of the drop probability
2762 for the RED algorithm.
2763 .It Va net.inet.ip.dummynet.pipe_byte_limit : No 1048576
2764 .It Va net.inet.ip.dummynet.pipe_slot_limit : No 100
2765 The maximum queue size that can be specified in bytes or packets.
2766 These limits prevent accidental exhaustion of resources such as mbufs.
2767 If you raise these limits,
2768 you should make sure the system is configured so that sufficient resources
2770 .It Va net.inet.ip.fw.autoinc_step : No 100
2771 Delta between rule numbers when auto-generating them.
2772 The value must be in the range 1..1000.
2773 .It Va net.inet.ip.fw.curr_dyn_buckets : Va net.inet.ip.fw.dyn_buckets
2774 The current number of buckets in the hash table for dynamic rules
2776 .It Va net.inet.ip.fw.debug : No 1
2777 Controls debugging messages produced by
2779 .It Va net.inet.ip.fw.default_rule : No 65535
2780 The default rule number (read-only).
2782 .Nm , the default rule is the last one, so its number
2783 can also serve as the highest number allowed for a rule.
2784 .It Va net.inet.ip.fw.dyn_buckets : No 256
2785 The number of buckets in the hash table for dynamic rules.
2786 Must be a power of 2, up to 65536.
2787 It only takes effect when all dynamic rules have expired, so you
2788 are advised to use a
2790 command to make sure that the hash table is resized.
2791 .It Va net.inet.ip.fw.dyn_count : No 3
2792 Current number of dynamic rules
2794 .It Va net.inet.ip.fw.dyn_keepalive : No 1
2795 Enables generation of keepalive packets for
2797 rules on TCP sessions.
2798 A keepalive is generated to both
2799 sides of the connection every 5 seconds for the last 20
2800 seconds of the lifetime of the rule.
2801 .It Va net.inet.ip.fw.dyn_max : No 8192
2802 Maximum number of dynamic rules.
2803 When you hit this limit, no more dynamic rules can be
2804 installed until old ones expire.
2805 .It Va net.inet.ip.fw.dyn_ack_lifetime : No 300
2806 .It Va net.inet.ip.fw.dyn_syn_lifetime : No 20
2807 .It Va net.inet.ip.fw.dyn_fin_lifetime : No 1
2808 .It Va net.inet.ip.fw.dyn_rst_lifetime : No 1
2809 .It Va net.inet.ip.fw.dyn_udp_lifetime : No 5
2810 .It Va net.inet.ip.fw.dyn_short_lifetime : No 30
2811 These variables control the lifetime, in seconds, of dynamic
2813 Upon the initial SYN exchange the lifetime is kept short,
2814 then increased after both SYN have been seen, then decreased
2815 again during the final FIN exchange or when a RST is received.
2817 .Em dyn_fin_lifetime
2819 .Em dyn_rst_lifetime
2820 must be strictly lower than 5 seconds, the period of
2821 repetition of keepalives.
2822 The firewall enforces that.
2823 .It Va net.inet.ip.fw.enable : No 1
2824 Enables the firewall.
2825 Setting this variable to 0 lets you run your machine without
2826 firewall even if compiled in.
2827 .It Va net.inet6.ip6.fw.enable : No 1
2828 provides the same functionality as above for the IPv6 case.
2829 .It Va net.inet.ip.fw.one_pass : No 1
2830 When set, the packet exiting from the
2834 node is not passed though the firewall again.
2835 Otherwise, after an action, the packet is
2836 reinjected into the firewall at the next rule.
2837 .It Va net.inet.ip.fw.tables_max : No 128
2838 Maximum number of tables (read-only).
2839 .It Va net.inet.ip.fw.verbose : No 1
2840 Enables verbose messages.
2841 .It Va net.inet.ip.fw.verbose_limit : No 0
2842 Limits the number of messages produced by a verbose firewall.
2843 .It Va net.inet6.ip6.fw.deny_unknown_exthdrs : No 1
2844 If enabled packets with unknown IPv6 Extension Headers will be denied.
2845 .It Va net.link.ether.ipfw : No 0
2846 Controls whether layer-2 packets are passed to
2849 .It Va net.link.bridge.ipfw : No 0
2850 Controls whether bridged packets are passed to
2856 There are far too many possible uses of
2858 so this Section will only give a small set of examples.
2860 .Ss BASIC PACKET FILTERING
2861 This command adds an entry which denies all tcp packets from
2862 .Em cracker.evil.org
2863 to the telnet port of
2865 from being forwarded by the host:
2867 .Dl "ipfw add deny tcp from cracker.evil.org to wolf.tambov.su telnet"
2869 This one disallows any connection from the entire cracker's
2872 .Dl "ipfw add deny ip from 123.45.67.0/24 to my.host.org"
2874 A first and efficient way to limit access (not using dynamic rules)
2875 is the use of the following rules:
2877 .Dl "ipfw add allow tcp from any to any established"
2878 .Dl "ipfw add allow tcp from net1 portlist1 to net2 portlist2 setup"
2879 .Dl "ipfw add allow tcp from net3 portlist3 to net3 portlist3 setup"
2881 .Dl "ipfw add deny tcp from any to any"
2883 The first rule will be a quick match for normal TCP packets,
2884 but it will not match the initial SYN packet, which will be
2887 rules only for selected source/destination pairs.
2888 All other SYN packets will be rejected by the final
2892 If you administer one or more subnets, you can take advantage
2893 of the address sets and or-blocks and write extremely
2894 compact rulesets which selectively enable services to blocks
2895 of clients, as below:
2897 .Dl "goodguys=\*q{ 10.1.2.0/24{20,35,66,18} or 10.2.3.0/28{6,3,11} }\*q"
2898 .Dl "badguys=\*q10.1.2.0/24{8,38,60}\*q"
2900 .Dl "ipfw add allow ip from ${goodguys} to any"
2901 .Dl "ipfw add deny ip from ${badguys} to any"
2902 .Dl "... normal policies ..."
2906 option could be used to do automated anti-spoofing by adding the
2907 following to the top of a ruleset:
2909 .Dl "ipfw add deny ip from any to any not verrevpath in"
2911 This rule drops all incoming packets that appear to be coming to the
2912 system on the wrong interface.
2913 For example, a packet with a source
2914 address belonging to a host on a protected internal network would be
2915 dropped if it tried to enter the system from an external interface.
2919 option could be used to do similar but more restricted anti-spoofing
2920 by adding the following to the top of a ruleset:
2922 .Dl "ipfw add deny ip from any to any not antispoof in"
2924 This rule drops all incoming packets that appear to be coming from another
2925 directly connected system but on the wrong interface.
2926 For example, a packet with a source address of
2927 .Li 192.168.0.0/24 ,
2934 In order to protect a site from flood attacks involving fake
2935 TCP packets, it is safer to use dynamic rules:
2937 .Dl "ipfw add check-state"
2938 .Dl "ipfw add deny tcp from any to any established"
2939 .Dl "ipfw add allow tcp from my-net to any setup keep-state"
2941 This will let the firewall install dynamic rules only for
2942 those connection which start with a regular SYN packet coming
2943 from the inside of our network.
2944 Dynamic rules are checked when encountering the first
2951 rule should usually be placed near the beginning of the
2952 ruleset to minimize the amount of work scanning the ruleset.
2953 Your mileage may vary.
2955 To limit the number of connections a user can open
2956 you can use the following type of rules:
2958 .Dl "ipfw add allow tcp from my-net/24 to any setup limit src-addr 10"
2959 .Dl "ipfw add allow tcp from any to me setup limit src-addr 4"
2961 The former (assuming it runs on a gateway) will allow each host
2962 on a /24 network to open at most 10 TCP connections.
2963 The latter can be placed on a server to make sure that a single
2964 client does not use more than 4 simultaneous connections.
2967 stateful rules can be subject to denial-of-service attacks
2968 by a SYN-flood which opens a huge number of dynamic rules.
2969 The effects of such attacks can be partially limited by
2972 variables which control the operation of the firewall.
2974 Here is a good usage of the
2976 command to see accounting records and timestamp information:
2980 or in short form without timestamps:
2984 which is equivalent to:
2988 Next rule diverts all incoming packets from 192.168.2.0/24
2989 to divert port 5000:
2991 .Dl ipfw divert 5000 ip from 192.168.2.0/24 to any in
2994 The following rules show some of the applications of
2998 for simulations and the like.
3000 This rule drops random incoming packets with a probability
3003 .Dl "ipfw add prob 0.05 deny ip from any to any in"
3005 A similar effect can be achieved making use of
3009 .Dl "ipfw add pipe 10 ip from any to any"
3010 .Dl "ipfw pipe 10 config plr 0.05"
3012 We can use pipes to artificially limit bandwidth, e.g.\& on a
3013 machine acting as a router, if we want to limit traffic from
3014 local clients on 192.168.2.0/24 we do:
3016 .Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out"
3017 .Dl "ipfw pipe 1 config bw 300Kbit/s queue 50KBytes"
3019 note that we use the
3021 modifier so that the rule is not used twice.
3022 Remember in fact that
3024 rules are checked both on incoming and outgoing packets.
3026 Should we want to simulate a bidirectional link with bandwidth
3027 limitations, the correct way is the following:
3029 .Dl "ipfw add pipe 1 ip from any to any out"
3030 .Dl "ipfw add pipe 2 ip from any to any in"
3031 .Dl "ipfw pipe 1 config bw 64Kbit/s queue 10Kbytes"
3032 .Dl "ipfw pipe 2 config bw 64Kbit/s queue 10Kbytes"
3034 The above can be very useful, e.g.\& if you want to see how
3035 your fancy Web page will look for a residential user who
3036 is connected only through a slow link.
3037 You should not use only one pipe for both directions, unless
3038 you want to simulate a half-duplex medium (e.g.\& AppleTalk,
3040 It is not necessary that both pipes have the same configuration,
3041 so we can also simulate asymmetric links.
3043 Should we want to verify network performance with the RED queue
3044 management algorithm:
3046 .Dl "ipfw add pipe 1 ip from any to any"
3047 .Dl "ipfw pipe 1 config bw 500Kbit/s queue 100 red 0.002/30/80/0.1"
3049 Another typical application of the traffic shaper is to
3050 introduce some delay in the communication.
3051 This can significantly affect applications which do a lot of Remote
3052 Procedure Calls, and where the round-trip-time of the
3053 connection often becomes a limiting factor much more than
3056 .Dl "ipfw add pipe 1 ip from any to any out"
3057 .Dl "ipfw add pipe 2 ip from any to any in"
3058 .Dl "ipfw pipe 1 config delay 250ms bw 1Mbit/s"
3059 .Dl "ipfw pipe 2 config delay 250ms bw 1Mbit/s"
3061 Per-flow queueing can be useful for a variety of purposes.
3062 A very simple one is counting traffic:
3064 .Dl "ipfw add pipe 1 tcp from any to any"
3065 .Dl "ipfw add pipe 1 udp from any to any"
3066 .Dl "ipfw add pipe 1 ip from any to any"
3067 .Dl "ipfw pipe 1 config mask all"
3069 The above set of rules will create queues (and collect
3070 statistics) for all traffic.
3071 Because the pipes have no limitations, the only effect is
3072 collecting statistics.
3073 Note that we need 3 rules, not just the last one, because
3076 tries to match IP packets it will not consider ports, so we
3077 would not see connections on separate ports as different
3080 A more sophisticated example is limiting the outbound traffic
3081 on a net with per-host limits, rather than per-network limits:
3083 .Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out"
3084 .Dl "ipfw add pipe 2 ip from any to 192.168.2.0/24 in"
3085 .Dl "ipfw pipe 1 config mask src-ip 0x000000ff bw 200Kbit/s queue 20Kbytes"
3086 .Dl "ipfw pipe 2 config mask dst-ip 0x000000ff bw 200Kbit/s queue 20Kbytes"
3088 In the following example, we need to create several traffic bandwidth
3089 classes and we need different hosts/networks to fall into different classes.
3090 We create one pipe for each class and configure them accordingly.
3091 Then we create a single table and fill it with IP subnets and addresses.
3092 For each subnet/host we set the argument equal to the number of the pipe
3094 Then we classify traffic using a single rule:
3096 .Dl "ipfw pipe 1 config bw 1000Kbyte/s"
3097 .Dl "ipfw pipe 4 config bw 4000Kbyte/s"
3099 .Dl "ipfw table 1 add 192.168.2.0/24 1"
3100 .Dl "ipfw table 1 add 192.168.0.0/27 4"
3101 .Dl "ipfw table 1 add 192.168.0.2 1"
3103 .Dl "ipfw add pipe tablearg ip from table(1) to any"
3107 action, the table entries may include hostnames and IP addresses.
3109 .Dl "ipfw table 1 add 192.168.2.0/24 10.23.2.1"
3110 .Dl "ipfw table 1 add 192.168.0.0/27 router1.dmz"
3112 .Dl "ipfw add 100 fwd tablearg ip from any to table(1)"
3114 To add a set of rules atomically, e.g.\& set 18:
3116 .Dl "ipfw set disable 18"
3117 .Dl "ipfw add NN set 18 ... # repeat as needed"
3118 .Dl "ipfw set enable 18"
3120 To delete a set of rules atomically the command is simply:
3122 .Dl "ipfw delete set 18"
3124 To test a ruleset and disable it and regain control if something goes wrong:
3126 .Dl "ipfw set disable 18"
3127 .Dl "ipfw add NN set 18 ... # repeat as needed"
3128 .Dl "ipfw set enable 18; echo done; sleep 30 && ipfw set disable 18"
3130 Here if everything goes well, you press control-C before the "sleep"
3131 terminates, and your ruleset will be left active.
3132 Otherwise, e.g.\& if
3133 you cannot access your box, the ruleset will be disabled after
3134 the sleep terminates thus restoring the previous situation.
3136 To show rules of the specific set:
3138 .Dl "ipfw set 18 show"
3140 To show rules of the disabled set:
3142 .Dl "ipfw -S set 18 show"
3144 To clear a specific rule counters of the specific set:
3146 .Dl "ipfw set 18 zero NN"
3148 To delete a specific rule of the specific set:
3150 .Dl "ipfw set 18 delete NN"
3151 .Ss NAT, REDIRECT AND LSNAT
3152 First redirect all the traffic to nat instance 123:
3154 .Dl "ipfw add nat 123 all from any to any"
3156 Then to configure nat instance 123 to alias all the outgoing traffic with ip
3157 192.168.0.123, blocking all incoming connections, trying to keep
3158 same ports on both sides, clearing aliasing table on address change
3159 and keeping a log of traffic/link statistics:
3161 .Dl "ipfw nat 123 config ip 192.168.0.123 log deny_in reset same_ports"
3163 Or to change address of instance 123, aliasing table will be cleared (see
3166 .Dl "ipfw nat 123 config ip 10.0.0.1"
3168 To see configuration of nat instance 123:
3170 .Dl "ipfw nat 123 show config"
3172 To show logs of all the instances in range 111-999:
3174 .Dl "ipfw nat 111-999 show"
3176 To see configurations of all instances:
3178 .Dl "ipfw nat show config"
3180 Or a redirect rule with mixed modes could looks like:
3182 .Dl "ipfw nat 123 config redirect_addr 10.0.0.1 10.0.0.66"
3183 .Dl " redirect_port tcp 192.168.0.1:80 500"
3184 .Dl " redirect_proto udp 192.168.1.43 192.168.1.1"
3185 .Dl " redirect_addr 192.168.0.10,192.168.0.11"
3186 .Dl " 10.0.0.100 # LSNAT"
3187 .Dl " redirect_port tcp 192.168.0.1:80,192.168.0.10:22"
3190 or it could be split in:
3192 .Dl "ipfw nat 1 config redirect_addr 10.0.0.1 10.0.0.66"
3193 .Dl "ipfw nat 2 config redirect_port tcp 192.168.0.1:80 500"
3194 .Dl "ipfw nat 3 config redirect_proto udp 192.168.1.43 192.168.1.1"
3195 .Dl "ipfw nat 4 config redirect_addr 192.168.0.10,192.168.0.11,192.168.0.12"
3197 .Dl "ipfw nat 5 config redirect_port tcp"
3198 .Dl " 192.168.0.1:80,192.168.0.10:22,192.168.0.20:25 500"
3220 utility first appeared in
3225 Stateful extensions were introduced in
3228 was introduced in Summer 2002.
3230 .An Ugen J. S. Antsilevich ,
3231 .An Poul-Henning Kamp ,
3237 API based upon code written by
3241 Dummynet has been introduced by Luigi Rizzo in 1997-1998.
3243 Some early work (1999-2000) on the
3245 traffic shaper supported by Akamba Corp.
3247 The ipfw core (ipfw2) has been completely redesigned and
3248 reimplemented by Luigi Rizzo in summer 2002. Further
3250 options have been added by various developer over the years.
3253 In-kernel NAT support written by
3254 .An Paolo Pisati Aq piso@FreeBSD.org
3255 as part of a Summer of Code 2005 project.
3259 support has been developed by
3260 .An The Centre for Advanced Internet Architectures (CAIA) Aq http://www.caia.swin.edu.au .
3261 The primary developers and maintainers are David Hayes and Jason But.
3262 For further information visit:
3263 .Aq http://www.caia.swin.edu.au/urp/SONATA
3265 Delay profiles have been developed by Alessandro Cerri and
3266 Luigi Rizzo, supported by the
3267 European Commission within Projects Onelab and Onelab2.
3269 The syntax has grown over the years and sometimes it might be confusing.
3270 Unfortunately, backward compatibility prevents cleaning up mistakes
3271 made in the definition of the syntax.
3275 Misconfiguring the firewall can put your computer in an unusable state,
3276 possibly shutting down network services and requiring console access to
3277 regain control of it.
3279 Incoming packet fragments diverted by
3281 are reassembled before delivery to the socket.
3282 The action used on those packet is the one from the
3283 rule which matches the first fragment of the packet.
3285 Packets diverted to userland, and then reinserted by a userland process
3286 may lose various packet attributes.
3287 The packet source interface name
3288 will be preserved if it is shorter than 8 bytes and the userland process
3289 saves and reuses the sockaddr_in
3292 otherwise, it may be lost.
3293 If a packet is reinserted in this manner, later rules may be incorrectly
3294 applied, making the order of
3296 rules in the rule sequence very important.
3298 Dummynet drops all packets with IPv6 link-local addresses.
3304 may not behave as expected.
3305 In particular, incoming SYN packets may
3306 have no uid or gid associated with them since they do not yet belong
3307 to a TCP connection, and the uid/gid associated with a packet may not
3308 be as expected if the associated process calls
3310 or similar system calls.
3312 Rule syntax is subject to the command line environment and some patterns
3313 may need to be escaped with the backslash character
3314 or quoted appropriately.
3316 Due to the architecture of
3318 ipfw nat is not compatible with the TCP segmentation offloading (TSO).
3319 Thus, to reliably nat your network traffic, please disable TSO
3323 ICMP error messages are not implicitly matched by dynamic rules
3324 for the respective conversations.
3325 To avoid failures of network error detection and path MTU discovery,
3326 ICMP error messages may need to be allowed explicitly through static
3333 actions may lead to confusing behaviour if ruleset has mistakes,
3334 and/or interaction with other subsystems (netgraph, dummynet, etc.) is used.
3335 One possible case for this is packet leaving
3337 in subroutine on the input pass, while later on output encountering unpaired
3340 As the call stack is kept intact after input pass, packet will suddenly
3341 return to the rule number used on input pass, not on output one.
3342 Order of processing should be checked carefully to avoid such mistakes.
projects / FreeBSD / releng / 9.0.git / blob