xref: /freebsd/sbin/ipfw/ipfw.8 (revision 721351876cd4d3a8a700f62d2061331fa951a488)
1.\"
2.\" $FreeBSD$
3.\"
4.Dd November 26, 2007
5.Dt IPFW 8
6.Os
7.Sh NAME
8.Nm ipfw
9.Nd IP firewall and traffic shaper control program
10.Sh SYNOPSIS
11.Nm
12.Op Fl cq
13.Cm add
14.Ar rule
15.Nm
16.Op Fl acdefnNStT
17.Op Cm set Ar N
18.Brq Cm list | show
19.Op Ar rule | first-last ...
20.Nm
21.Op Fl f | q
22.Op Cm set Ar N
23.Cm flush
24.Nm
25.Op Fl q
26.Op Cm set Ar N
27.Brq Cm delete | zero | resetlog
28.Op Ar number ...
29.Nm
30.Cm enable
31.Brq Cm firewall | altq | one_pass | debug | verbose | dyn_keepalive
32.Nm
33.Cm disable
34.Brq Cm firewall | altq | one_pass | debug | verbose | dyn_keepalive
35.Pp
36.Nm
37.Cm set Oo Cm disable Ar number ... Oc Op Cm enable Ar number ...
38.Nm
39.Cm set move
40.Op Cm rule
41.Ar number Cm to Ar number
42.Nm
43.Cm set swap Ar number number
44.Nm
45.Cm set show
46.Pp
47.Nm
48.Cm table Ar number Cm add Ar addr Ns Oo / Ns Ar masklen Oc Op Ar value
49.Nm
50.Cm table Ar number Cm delete Ar addr Ns Op / Ns Ar masklen
51.Nm
52.Cm table Ar number Cm flush
53.Nm
54.Cm table Ar number Cm list
55.Pp
56.Nm
57.Brq Cm pipe | queue
58.Ar number
59.Cm config
60.Ar config-options
61.Nm
62.Op Fl s Op Ar field
63.Brq Cm pipe | queue
64.Brq Cm delete | list | show
65.Op Ar number ...
66.Pp
67.Nm
68.Cm nat
69.Ar number
70.Cm config
71.Ar config-options
72.Pp
73.Nm
74.Op Fl cfnNqS
75.Oo
76.Fl p Ar preproc
77.Oo
78.Ar preproc-flags
79.Oc
80.Oc
81.Ar pathname
82.Sh DESCRIPTION
83The
84.Nm
85utility is the user interface for controlling the
86.Xr ipfw 4
87firewall and the
88.Xr dummynet 4
89traffic shaper in
90.Fx .
91.Pp
92An
93.Nm
94configuration, or
95.Em ruleset ,
96is made of a list of
97.Em rules
98numbered from 1 to 65535.
99Packets are passed to
100.Nm
101from a number of different places in the protocol stack
102(depending on the source and destination of the packet,
103it is possible that
104.Nm
105is invoked multiple times on the same packet).
106The packet passed to the firewall is compared
107against each of the rules in the firewall
108.Em ruleset .
109When a match is found, the action corresponding to the
110matching rule is performed.
111.Pp
112Depending on the action and certain system settings, packets
113can be reinjected into the firewall at some rule after the
114matching one for further processing.
115.Pp
116An
117.Nm
118ruleset always includes a
119.Em default
120rule (numbered 65535) which cannot be modified or deleted,
121and matches all packets.
122The action associated with the
123.Em default
124rule can be either
125.Cm deny
126or
127.Cm allow
128depending on how the kernel is configured.
129.Pp
130If the ruleset includes one or more rules with the
131.Cm keep-state
132or
133.Cm limit
134option, then
135.Nm
136assumes a
137.Em stateful
138behaviour, i.e., upon a match it will create dynamic rules matching
139the exact parameters (addresses and ports) of the matching packet.
140.Pp
141These dynamic rules, which have a limited lifetime, are checked
142at the first occurrence of a
143.Cm check-state ,
144.Cm keep-state
145or
146.Cm limit
147rule, and are typically used to open the firewall on-demand to
148legitimate traffic only.
149See the
150.Sx STATEFUL FIREWALL
151and
152.Sx EXAMPLES
153Sections below for more information on the stateful behaviour of
154.Nm .
155.Pp
156All rules (including dynamic ones) have a few associated counters:
157a packet count, a byte count, a log count and a timestamp
158indicating the time of the last match.
159Counters can be displayed or reset with
160.Nm
161commands.
162.Pp
163Rules can be added with the
164.Cm add
165command; deleted individually or in groups with the
166.Cm delete
167command, and globally (except those in set 31) with the
168.Cm flush
169command; displayed, optionally with the content of the
170counters, using the
171.Cm show
172and
173.Cm list
174commands.
175Finally, counters can be reset with the
176.Cm zero
177and
178.Cm resetlog
179commands.
180.Pp
181Also, each rule belongs to one of 32 different
182.Em sets
183, and there are
184.Nm
185commands to atomically manipulate sets, such as enable,
186disable, swap sets, move all rules in a set to another
187one, delete all rules in a set.
188These can be useful to
189install temporary configurations, or to test them.
190See Section
191.Sx SETS OF RULES
192for more information on
193.Em sets .
194.Pp
195The following options are available:
196.Bl -tag -width indent
197.It Fl a
198While listing, show counter values.
199The
200.Cm show
201command just implies this option.
202.It Fl b
203Only show the action and the comment, not the body of a rule.
204Implies
205.Fl c .
206.It Fl c
207When entering or showing rules, print them in compact form,
208i.e., without the optional "ip from any to any" string
209when this does not carry any additional information.
210.It Fl d
211While listing, show dynamic rules in addition to static ones.
212.It Fl e
213While listing, if the
214.Fl d
215option was specified, also show expired dynamic rules.
216.It Fl f
217Do not ask for confirmation for commands that can cause problems
218if misused,
219.No i.e. Cm flush .
220If there is no tty associated with the process, this is implied.
221.It Fl i
222While listing a table (see the
223.Sx LOOKUP TABLES
224section below for more information on lookup tables), format values
225as IP addresses. By default, values are shown as integers.
226.It Fl n
227Only check syntax of the command strings, without actually passing
228them to the kernel.
229.It Fl N
230Try to resolve addresses and service names in output.
231.It Fl q
232While
233.Cm add Ns ing ,
234.Cm zero Ns ing ,
235.Cm resetlog Ns ging
236or
237.Cm flush Ns ing ,
238be quiet about actions
239(implies
240.Fl f ) .
241This is useful for adjusting rules by executing multiple
242.Nm
243commands in a script
244(e.g.,
245.Ql sh\ /etc/rc.firewall ) ,
246or by processing a file of many
247.Nm
248rules across a remote login session.
249It also stops a table add or delete
250from failing if the entry already exists or is not present.
251If a
252.Cm flush
253is performed in normal (verbose) mode (with the default kernel
254configuration), it prints a message.
255Because all rules are flushed, the message might not be delivered
256to the login session, causing the remote login session to be closed
257and the remainder of the ruleset to not be processed.
258Access to the console would then be required to recover.
259.It Fl S
260While listing rules, show the
261.Em set
262each rule belongs to.
263If this flag is not specified, disabled rules will not be
264listed.
265.It Fl s Op Ar field
266While listing pipes, sort according to one of the four
267counters (total or current packets or bytes).
268.It Fl t
269While listing, show last match timestamp (converted with ctime()).
270.It Fl T
271While listing, show last match timestamp (as seconds from the epoch).
272This form can be more convenient for postprocessing by scripts.
273.El
274.Pp
275To ease configuration, rules can be put into a file which is
276processed using
277.Nm
278as shown in the last synopsis line.
279An absolute
280.Ar pathname
281must be used.
282The file will be read line by line and applied as arguments to the
283.Nm
284utility.
285.Pp
286Optionally, a preprocessor can be specified using
287.Fl p Ar preproc
288where
289.Ar pathname
290is to be piped through.
291Useful preprocessors include
292.Xr cpp 1
293and
294.Xr m4 1 .
295If
296.Ar preproc
297does not start with a slash
298.Pq Ql /
299as its first character, the usual
300.Ev PATH
301name search is performed.
302Care should be taken with this in environments where not all
303file systems are mounted (yet) by the time
304.Nm
305is being run (e.g.\& when they are mounted over NFS).
306Once
307.Fl p
308has been specified, any additional arguments as passed on to the preprocessor
309for interpretation.
310This allows for flexible configuration files (like conditionalizing
311them on the local hostname) and the use of macros to centralize
312frequently required arguments like IP addresses.
313.Pp
314The
315.Nm
316.Cm pipe
317and
318.Cm queue
319commands are used to configure the traffic shaper, as shown in the
320.Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION
321Section below.
322.Pp
323If the world and the kernel get out of sync the
324.Nm
325ABI may break, preventing you from being able to add any rules.
326This can
327adversely effect the booting process.
328You can use
329.Nm
330.Cm disable
331.Cm firewall
332to temporarily disable the firewall to regain access to the network,
333allowing you to fix the problem.
334.Sh PACKET FLOW
335A packet is checked against the active ruleset in multiple places
336in the protocol stack, under control of several sysctl variables.
337These places and variables are shown below, and it is important to
338have this picture in mind in order to design a correct ruleset.
339.Bd -literal -offset indent
340       ^    to upper layers    V
341       |                       |
342       +----------->-----------+
343       ^                       V
344 [ip(6)_input]           [ip(6)_output]     net.inet(6).ip(6).fw.enable=1
345       |                       |
346       ^                       V
347 [ether_demux]        [ether_output_frame]  net.link.ether.ipfw=1
348       |                       |
349       +-->--[bdg_forward]-->--+            net.link.bridge.ipfw=1
350       ^                       V
351       |      to devices       |
352.Ed
353.Pp
354As can be noted from the above picture, the number of
355times the same packet goes through the firewall can
356vary between 0 and 4 depending on packet source and
357destination, and system configuration.
358.Pp
359Note that as packets flow through the stack, headers can be
360stripped or added to it, and so they may or may not be available
361for inspection.
362E.g., incoming packets will include the MAC header when
363.Nm
364is invoked from
365.Cm ether_demux() ,
366but the same packets will have the MAC header stripped off when
367.Nm
368is invoked from
369.Cm ip_input()
370or
371.Cm ip6_input() .
372.Pp
373Also note that each packet is always checked against the complete ruleset,
374irrespective of the place where the check occurs, or the source of the packet.
375If a rule contains some match patterns or actions which are not valid
376for the place of invocation (e.g.\& trying to match a MAC header within
377.Cm ip_input
378or
379.Cm ip6_input ),
380the match pattern will not match, but a
381.Cm not
382operator in front of such patterns
383.Em will
384cause the pattern to
385.Em always
386match on those packets.
387It is thus the responsibility of
388the programmer, if necessary, to write a suitable ruleset to
389differentiate among the possible places.
390.Cm skipto
391rules can be useful here, as an example:
392.Bd -literal -offset indent
393# packets from ether_demux or bdg_forward
394ipfw add 10 skipto 1000 all from any to any layer2 in
395# packets from ip_input
396ipfw add 10 skipto 2000 all from any to any not layer2 in
397# packets from ip_output
398ipfw add 10 skipto 3000 all from any to any not layer2 out
399# packets from ether_output_frame
400ipfw add 10 skipto 4000 all from any to any layer2 out
401.Ed
402.Pp
403(yes, at the moment there is no way to differentiate between
404ether_demux and bdg_forward).
405.Sh SYNTAX
406In general, each keyword or argument must be provided as
407a separate command line argument, with no leading or trailing
408spaces.
409Keywords are case-sensitive, whereas arguments may
410or may not be case-sensitive depending on their nature
411(e.g.\& uid's are, hostnames are not).
412.Pp
413In
414.Nm ipfw2
415you can introduce spaces after commas ',' to make
416the line more readable.
417You can also put the entire
418command (including flags) into a single argument.
419E.g., the following forms are equivalent:
420.Bd -literal -offset indent
421ipfw -q add deny src-ip 10.0.0.0/24,127.0.0.1/8
422ipfw -q add deny src-ip 10.0.0.0/24, 127.0.0.1/8
423ipfw "-q add deny src-ip 10.0.0.0/24, 127.0.0.1/8"
424.Ed
425.Sh RULE FORMAT
426The format of
427.Nm
428rules is the following:
429.Bd -ragged -offset indent
430.Bk -words
431.Op Ar rule_number
432.Op Cm set Ar set_number
433.Op Cm prob Ar match_probability
434.Ar action
435.Op Cm log Op Cm logamount Ar number
436.Op Cm altq Ar queue
437.Oo
438.Bro Cm tag | untag
439.Brc Ar number
440.Oc
441.Ar body
442.Ek
443.Ed
444.Pp
445where the body of the rule specifies which information is used
446for filtering packets, among the following:
447.Pp
448.Bl -tag -width "Source and dest. addresses and ports" -offset XXX -compact
449.It Layer-2 header fields
450When available
451.It IPv4 and IPv6 Protocol
452TCP, UDP, ICMP, etc.
453.It Source and dest. addresses and ports
454.It Direction
455See Section
456.Sx PACKET FLOW
457.It Transmit and receive interface
458By name or address
459.It Misc. IP header fields
460Version, type of service, datagram length, identification,
461fragment flag (non-zero IP offset),
462Time To Live
463.It IP options
464.It IPv6 Extension headers
465Fragmentation, Hop-by-Hop options,
466Routing Headers, Source routing rthdr0, Mobile IPv6 rthdr2, IPSec options.
467.It IPv6 Flow-ID
468.It Misc. TCP header fields
469TCP flags (SYN, FIN, ACK, RST, etc.),
470sequence number, acknowledgment number,
471window
472.It TCP options
473.It ICMP types
474for ICMP packets
475.It ICMP6 types
476for ICMP6 packets
477.It User/group ID
478When the packet can be associated with a local socket.
479.It Divert status
480Whether a packet came from a divert socket (e.g.,
481.Xr natd 8 ) .
482.It Fib annotation state
483Whether a packet has been tagged for using a specific FIB (routing table)
484in future forwarding decisions.
485.El
486.Pp
487Note that some of the above information, e.g.\& source MAC or IP addresses and
488TCP/UDP ports, could easily be spoofed, so filtering on those fields
489alone might not guarantee the desired results.
490.Bl -tag -width indent
491.It Ar rule_number
492Each rule is associated with a
493.Ar rule_number
494in the range 1..65535, with the latter reserved for the
495.Em default
496rule.
497Rules are checked sequentially by rule number.
498Multiple rules can have the same number, in which case they are
499checked (and listed) according to the order in which they have
500been added.
501If a rule is entered without specifying a number, the kernel will
502assign one in such a way that the rule becomes the last one
503before the
504.Em default
505rule.
506Automatic rule numbers are assigned by incrementing the last
507non-default rule number by the value of the sysctl variable
508.Ar net.inet.ip.fw.autoinc_step
509which defaults to 100.
510If this is not possible (e.g.\& because we would go beyond the
511maximum allowed rule number), the number of the last
512non-default value is used instead.
513.It Cm set Ar set_number
514Each rule is associated with a
515.Ar set_number
516in the range 0..31.
517Sets can be individually disabled and enabled, so this parameter
518is of fundamental importance for atomic ruleset manipulation.
519It can be also used to simplify deletion of groups of rules.
520If a rule is entered without specifying a set number,
521set 0 will be used.
522.br
523Set 31 is special in that it cannot be disabled,
524and rules in set 31 are not deleted by the
525.Nm ipfw flush
526command (but you can delete them with the
527.Nm ipfw delete set 31
528command).
529Set 31 is also used for the
530.Em default
531rule.
532.It Cm prob Ar match_probability
533A match is only declared with the specified probability
534(floating point number between 0 and 1).
535This can be useful for a number of applications such as
536random packet drop or
537(in conjunction with
538.Nm dummynet )
539to simulate the effect of multiple paths leading to out-of-order
540packet delivery.
541.Pp
542Note: this condition is checked before any other condition, including
543ones such as keep-state or check-state which might have side effects.
544.It Cm log Op Cm logamount Ar number
545When a packet matches a rule with the
546.Cm log
547keyword, a message will be
548logged to
549.Xr syslogd 8
550with a
551.Dv LOG_SECURITY
552facility.
553The logging only occurs if the sysctl variable
554.Va net.inet.ip.fw.verbose
555is set to 1
556(which is the default when the kernel is compiled with
557.Dv IPFIREWALL_VERBOSE )
558and the number of packets logged so far for that
559particular rule does not exceed the
560.Cm logamount
561parameter.
562If no
563.Cm logamount
564is specified, the limit is taken from the sysctl variable
565.Va net.inet.ip.fw.verbose_limit .
566In both cases, a value of 0 removes the logging limit.
567.Pp
568Once the limit is reached, logging can be re-enabled by
569clearing the logging counter or the packet counter for that entry, see the
570.Cm resetlog
571command.
572.Pp
573Note: logging is done after all other packet matching conditions
574have been successfully verified, and before performing the final
575action (accept, deny, etc.) on the packet.
576.It Cm tag Ar number
577When a packet matches a rule with the
578.Cm tag
579keyword, the numeric tag for the given
580.Ar number
581in the range 1..65534 will be attached to the packet.
582The tag acts as an internal marker (it is not sent out over
583the wire) that can be used to identify these packets later on.
584This can be used, for example, to provide trust between interfaces
585and to start doing policy-based filtering.
586A packet can have mutiple tags at the same time.
587Tags are "sticky", meaning once a tag is applied to a packet by a
588matching rule it exists until explicit removal.
589Tags are kept with the packet everywhere within the kernel, but are
590lost when packet leaves the kernel, for example, on transmitting
591packet out to the network or sending packet to a
592.Xr divert 4
593socket.
594.Pp
595To check for previously applied tags, use the
596.Cm tagged
597rule option.
598To delete previously applied tag, use the
599.Cm untag
600keyword.
601.Pp
602Note: since tags are kept with the packet everywhere in kernelspace,
603they can be set and unset anywhere in kernel network subsystem
604(using
605.Xr mbuf_tags 9
606facility), not only by means of
607.Xr ipfw 4
608.Cm tag
609and
610.Cm untag
611keywords.
612For example, there can be a specialized
613.Xr netgraph 4
614node doing traffic analyzing and tagging for later inspecting
615in firewall.
616.It Cm untag Ar number
617When a packet matches a rule with the
618.Cm untag
619keyword, the tag with the number
620.Ar number
621is searched among the tags attached to this packet and,
622if found, removed from it.
623Other tags bound to packet, if present, are left untouched.
624.It Cm altq Ar queue
625When a packet matches a rule with the
626.Cm altq
627keyword, the ALTQ identifier for the given
628.Ar queue
629(see
630.Xr altq 4 )
631will be attached.
632Note that this ALTQ tag is only meaningful for packets going "out" of IPFW,
633and not being rejected or going to divert sockets.
634Note that if there is insufficient memory at the time the packet is
635processed, it will not be tagged, so it is wise to make your ALTQ
636"default" queue policy account for this.
637If multiple
638.Cm altq
639rules match a single packet, only the first one adds the ALTQ classification
640tag.
641In doing so, traffic may be shaped by using
642.Cm count Cm altq Ar queue
643rules for classification early in the ruleset, then later applying
644the filtering decision.
645For example,
646.Cm check-state
647and
648.Cm keep-state
649rules may come later and provide the actual filtering decisions in
650addition to the fallback ALTQ tag.
651.Pp
652You must run
653.Xr pfctl 8
654to set up the queues before IPFW will be able to look them up by name,
655and if the ALTQ disciplines are rearranged, the rules in containing the
656queue identifiers in the kernel will likely have gone stale and need
657to be reloaded.
658Stale queue identifiers will probably result in misclassification.
659.Pp
660All system ALTQ processing can be turned on or off via
661.Nm
662.Cm enable Ar altq
663and
664.Nm
665.Cm disable Ar altq .
666The usage of
667.Va net.inet.ip.fw.one_pass
668is irrelevant to ALTQ traffic shaping, as the actual rule action is followed
669always after adding an ALTQ tag.
670.El
671.Ss RULE ACTIONS
672A rule can be associated with one of the following actions, which
673will be executed when the packet matches the body of the rule.
674.Bl -tag -width indent
675.It Cm allow | accept | pass | permit
676Allow packets that match rule.
677The search terminates.
678.It Cm check-state
679Checks the packet against the dynamic ruleset.
680If a match is found, execute the action associated with
681the rule which generated this dynamic rule, otherwise
682move to the next rule.
683.br
684.Cm Check-state
685rules do not have a body.
686If no
687.Cm check-state
688rule is found, the dynamic ruleset is checked at the first
689.Cm keep-state
690or
691.Cm limit
692rule.
693.It Cm count
694Update counters for all packets that match rule.
695The search continues with the next rule.
696.It Cm deny | drop
697Discard packets that match this rule.
698The search terminates.
699.It Cm divert Ar port
700Divert packets that match this rule to the
701.Xr divert 4
702socket bound to port
703.Ar port .
704The search terminates.
705.It Cm fwd | forward Ar ipaddr | tablearg Ns Op , Ns Ar port
706Change the next-hop on matching packets to
707.Ar ipaddr ,
708which can be an IP address or a host name.
709The next hop can also be supplied by the last table
710looked up for the packet by using the
711.Cm tablearg
712keyword instead of an explicit address.
713The search terminates if this rule matches.
714.Pp
715If
716.Ar ipaddr
717is a local address, then matching packets will be forwarded to
718.Ar port
719(or the port number in the packet if one is not specified in the rule)
720on the local machine.
721.br
722If
723.Ar ipaddr
724is not a local address, then the port number
725(if specified) is ignored, and the packet will be
726forwarded to the remote address, using the route as found in
727the local routing table for that IP.
728.br
729A
730.Ar fwd
731rule will not match layer-2 packets (those received
732on ether_input, ether_output, or bridged).
733.br
734The
735.Cm fwd
736action does not change the contents of the packet at all.
737In particular, the destination address remains unmodified, so
738packets forwarded to another system will usually be rejected by that system
739unless there is a matching rule on that system to capture them.
740For packets forwarded locally,
741the local address of the socket will be
742set to the original destination address of the packet.
743This makes the
744.Xr netstat 1
745entry look rather weird but is intended for
746use with transparent proxy servers.
747.Pp
748To enable
749.Cm fwd
750a custom kernel needs to be compiled with the option
751.Cd "options IPFIREWALL_FORWARD" .
752.It Cm nat Ar nat_nr
753Pass packet to a
754nat instance
755(for network address translation, address redirect, etc.):
756see the
757.Sx NETWORK ADDRESS TRANSLATION (NAT)
758Section for further information.
759.It Cm pipe Ar pipe_nr
760Pass packet to a
761.Nm dummynet
762.Dq pipe
763(for bandwidth limitation, delay, etc.).
764See the
765.Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION
766Section for further information.
767The search terminates; however, on exit from the pipe and if
768the
769.Xr sysctl 8
770variable
771.Va net.inet.ip.fw.one_pass
772is not set, the packet is passed again to the firewall code
773starting from the next rule.
774.It Cm queue Ar queue_nr
775Pass packet to a
776.Nm dummynet
777.Dq queue
778(for bandwidth limitation using WF2Q+).
779.It Cm reject
780(Deprecated).
781Synonym for
782.Cm unreach host .
783.It Cm reset
784Discard packets that match this rule, and if the
785packet is a TCP packet, try to send a TCP reset (RST) notice.
786The search terminates.
787.It Cm reset6
788Discard packets that match this rule, and if the
789packet is a TCP packet, try to send a TCP reset (RST) notice.
790The search terminates.
791.It Cm skipto Ar number
792Skip all subsequent rules numbered less than
793.Ar number .
794The search continues with the first rule numbered
795.Ar number
796or higher.
797.It Cm tee Ar port
798Send a copy of packets matching this rule to the
799.Xr divert 4
800socket bound to port
801.Ar port .
802The search continues with the next rule.
803.It Cm unreach Ar code
804Discard packets that match this rule, and try to send an ICMP
805unreachable notice with code
806.Ar code ,
807where
808.Ar code
809is a number from 0 to 255, or one of these aliases:
810.Cm net , host , protocol , port ,
811.Cm needfrag , srcfail , net-unknown , host-unknown ,
812.Cm isolated , net-prohib , host-prohib , tosnet ,
813.Cm toshost , filter-prohib , host-precedence
814or
815.Cm precedence-cutoff .
816The search terminates.
817.It Cm unreach6 Ar code
818Discard packets that match this rule, and try to send an ICMPv6
819unreachable notice with code
820.Ar code ,
821where
822.Ar code
823is a number from 0, 1, 3 or 4, or one of these aliases:
824.Cm no-route, admin-prohib, address
825or
826.Cm port .
827The search terminates.
828.It Cm netgraph Ar cookie
829Divert packet into netgraph with given
830.Ar cookie .
831The search terminates.
832If packet is later returned from netgraph it is either
833accepted or continues with the next rule, depending on
834.Va net.inet.ip.fw.one_pass
835sysctl variable.
836.It Cm ngtee Ar cookie
837A copy of packet is diverted into netgraph, original
838packet is either accepted or continues with the next rule, depending on
839.Va net.inet.ip.fw.one_pass
840sysctl variable.
841See
842.Xr ng_ipfw 4
843for more information on
844.Cm netgraph
845and
846.Cm ngtee
847actions.
848.It Cm setfib Ar fibnum
849The packet is tagged so as to use the FIB (routing table)
850.Ar fibnum
851in any subsequent forwarding decisions. Initially this is
852limited to the values  0 through 15. See
853.Xr setfib 8
854.El
855.Ss RULE BODY
856The body of a rule contains zero or more patterns (such as
857specific source and destination addresses or ports,
858protocol options, incoming or outgoing interfaces, etc.)
859that the packet must match in order to be recognised.
860In general, the patterns are connected by (implicit)
861.Cm and
862operators -- i.e., all must match in order for the
863rule to match.
864Individual patterns can be prefixed by the
865.Cm not
866operator to reverse the result of the match, as in
867.Pp
868.Dl "ipfw add 100 allow ip from not 1.2.3.4 to any"
869.Pp
870Additionally, sets of alternative match patterns
871.Pq Em or-blocks
872can be constructed by putting the patterns in
873lists enclosed between parentheses ( ) or braces { }, and
874using the
875.Cm or
876operator as follows:
877.Pp
878.Dl "ipfw add 100 allow ip from { x or not y or z } to any"
879.Pp
880Only one level of parentheses is allowed.
881Beware that most shells have special meanings for parentheses
882or braces, so it is advisable to put a backslash \\ in front of them
883to prevent such interpretations.
884.Pp
885The body of a rule must in general include a source and destination
886address specifier.
887The keyword
888.Ar any
889can be used in various places to specify that the content of
890a required field is irrelevant.
891.Pp
892The rule body has the following format:
893.Bd -ragged -offset indent
894.Op Ar proto Cm from Ar src Cm to Ar dst
895.Op Ar options
896.Ed
897.Pp
898The first part (proto from src to dst) is for backward
899compatibility with earlier versions of
900.Fx .
901In modern
902.Fx
903any match pattern (including MAC headers, IP protocols,
904addresses and ports) can be specified in the
905.Ar options
906section.
907.Pp
908Rule fields have the following meaning:
909.Bl -tag -width indent
910.It Ar proto : protocol | Cm { Ar protocol Cm or ... }
911.It Ar protocol : Oo Cm not Oc Ar protocol-name | protocol-number
912An IP protocol specified by number or name
913(for a complete list see
914.Pa /etc/protocols ) ,
915or one of the following keywords:
916.Bl -tag -width indent
917.It Cm ip4 | ipv4
918Matches IPv4 packets.
919.It Cm ip6 | ipv6
920Matches IPv6 packets.
921.It Cm ip | all
922Matches any packet.
923.El
924.Pp
925The
926.Cm ipv6
927in
928.Cm proto
929option will be treated as inner protocol.
930And, the
931.Cm ipv4
932is not available in
933.Cm proto
934option.
935.Pp
936The
937.Cm { Ar protocol Cm or ... }
938format (an
939.Em or-block )
940is provided for convenience only but its use is deprecated.
941.It Ar src No and Ar dst : Bro Cm addr | Cm { Ar addr Cm or ... } Brc Op Oo Cm not Oc Ar ports
942An address (or a list, see below)
943optionally followed by
944.Ar ports
945specifiers.
946.Pp
947The second format
948.Em ( or-block
949with multiple addresses) is provided for convenience only and
950its use is discouraged.
951.It Ar addr : Oo Cm not Oc Bro
952.Cm any | me | me6 |
953.Cm table Ns Pq Ar number Ns Op , Ns Ar value
954.Ar | addr-list | addr-set
955.Brc
956.It Cm any
957matches any IP address.
958.It Cm me
959matches any IP address configured on an interface in the system.
960.It Cm me6
961matches any IPv6 address configured on an interface in the system.
962The address list is evaluated at the time the packet is
963analysed.
964.It Cm table Ns Pq Ar number Ns Op , Ns Ar value
965Matches any IPv4 address for which an entry exists in the lookup table
966.Ar number .
967If an optional 32-bit unsigned
968.Ar value
969is also specified, an entry will match only if it has this value.
970See the
971.Sx LOOKUP TABLES
972section below for more information on lookup tables.
973.It Ar addr-list : ip-addr Ns Op Ns , Ns Ar addr-list
974.It Ar ip-addr :
975A host or subnet address specified in one of the following ways:
976.Bl -tag -width indent
977.It Ar numeric-ip | hostname
978Matches a single IPv4 address, specified as dotted-quad or a hostname.
979Hostnames are resolved at the time the rule is added to the firewall list.
980.It Ar addr Ns / Ns Ar masklen
981Matches all addresses with base
982.Ar addr
983(specified as an IP address, a network number, or a hostname)
984and mask width of
985.Cm masklen
986bits.
987As an example, 1.2.3.4/25 or 1.2.3.0/25 will match
988all IP numbers from 1.2.3.0 to 1.2.3.127 .
989.It Ar addr Ns : Ns Ar mask
990Matches all addresses with base
991.Ar addr
992(specified as an IP address, a network number, or a hostname)
993and the mask of
994.Ar mask ,
995specified as a dotted quad.
996As an example, 1.2.3.4:255.0.255.0 or 1.0.3.0:255.0.255.0 will match
9971.*.3.*.
998This form is advised only for non-contiguous
999masks.
1000It is better to resort to the
1001.Ar addr Ns / Ns Ar masklen
1002format for contiguous masks, which is more compact and less
1003error-prone.
1004.El
1005.It Ar addr-set : addr Ns Oo Ns / Ns Ar masklen Oc Ns Cm { Ns Ar list Ns Cm }
1006.It Ar list : Bro Ar num | num-num Brc Ns Op Ns , Ns Ar list
1007Matches all addresses with base address
1008.Ar addr
1009(specified as an IP address, a network number, or a hostname)
1010and whose last byte is in the list between braces { } .
1011Note that there must be no spaces between braces and
1012numbers (spaces after commas are allowed).
1013Elements of the list can be specified as single entries
1014or ranges.
1015The
1016.Ar masklen
1017field is used to limit the size of the set of addresses,
1018and can have any value between 24 and 32.
1019If not specified,
1020it will be assumed as 24.
1021.br
1022This format is particularly useful to handle sparse address sets
1023within a single rule.
1024Because the matching occurs using a
1025bitmask, it takes constant time and dramatically reduces
1026the complexity of rulesets.
1027.br
1028As an example, an address specified as 1.2.3.4/24{128,35-55,89}
1029or 1.2.3.0/24{128,35-55,89}
1030will match the following IP addresses:
1031.br
10321.2.3.128, 1.2.3.35 to 1.2.3.55, 1.2.3.89 .
1033.It Ar addr6-list : ip6-addr Ns Op Ns , Ns Ar addr6-list
1034.It Ar ip6-addr :
1035A host or subnet specified one of the following ways:
1036.Pp
1037.Bl -tag -width indent
1038.It Ar numeric-ip | hostname
1039Matches a single IPv6 address as allowed by
1040.Xr inet_pton 3
1041or a hostname.
1042Hostnames are resolved at the time the rule is added to the firewall
1043list.
1044.It Ar addr Ns / Ns Ar masklen
1045Matches all IPv6 addresses with base
1046.Ar addr
1047(specified as allowed by
1048.Xr inet_pton
1049or a hostname)
1050and mask width of
1051.Cm masklen
1052bits.
1053.El
1054.Pp
1055No support for sets of IPv6 addresses is provided because IPv6 addresses
1056are typically random past the initial prefix.
1057.It Ar ports : Bro Ar port | port Ns \&- Ns Ar port Ns Brc Ns Op , Ns Ar ports
1058For protocols which support port numbers (such as TCP and UDP), optional
1059.Cm ports
1060may be specified as one or more ports or port ranges, separated
1061by commas but no spaces, and an optional
1062.Cm not
1063operator.
1064The
1065.Ql \&-
1066notation specifies a range of ports (including boundaries).
1067.Pp
1068Service names (from
1069.Pa /etc/services )
1070may be used instead of numeric port values.
1071The length of the port list is limited to 30 ports or ranges,
1072though one can specify larger ranges by using an
1073.Em or-block
1074in the
1075.Cm options
1076section of the rule.
1077.Pp
1078A backslash
1079.Pq Ql \e
1080can be used to escape the dash
1081.Pq Ql -
1082character in a service name (from a shell, the backslash must be
1083typed twice to avoid the shell itself interpreting it as an escape
1084character).
1085.Pp
1086.Dl "ipfw add count tcp from any ftp\e\e-data-ftp to any"
1087.Pp
1088Fragmented packets which have a non-zero offset (i.e., not the first
1089fragment) will never match a rule which has one or more port
1090specifications.
1091See the
1092.Cm frag
1093option for details on matching fragmented packets.
1094.El
1095.Ss RULE OPTIONS (MATCH PATTERNS)
1096Additional match patterns can be used within
1097rules.
1098Zero or more of these so-called
1099.Em options
1100can be present in a rule, optionally prefixed by the
1101.Cm not
1102operand, and possibly grouped into
1103.Em or-blocks .
1104.Pp
1105The following match patterns can be used (listed in alphabetical order):
1106.Bl -tag -width indent
1107.It Cm // this is a comment.
1108Inserts the specified text as a comment in the rule.
1109Everything following // is considered as a comment and stored in the rule.
1110You can have comment-only rules, which are listed as having a
1111.Cm count
1112action followed by the comment.
1113.It Cm bridged
1114Alias for
1115.Cm layer2 .
1116.It Cm diverted
1117Matches only packets generated by a divert socket.
1118.It Cm diverted-loopback
1119Matches only packets coming from a divert socket back into the IP stack
1120input for delivery.
1121.It Cm diverted-output
1122Matches only packets going from a divert socket back outward to the IP
1123stack output for delivery.
1124.It Cm dst-ip Ar ip-address
1125Matches IPv4 packets whose destination IP is one of the address(es)
1126specified as argument.
1127.It Bro Cm dst-ip6 | dst-ipv6 Brc Ar ip6-address
1128Matches IPv6 packets whose destination IP is one of the address(es)
1129specified as argument.
1130.It Cm dst-port Ar ports
1131Matches IP packets whose destination port is one of the port(s)
1132specified as argument.
1133.It Cm established
1134Matches TCP packets that have the RST or ACK bits set.
1135.It Cm ext6hdr Ar header
1136Matches IPv6 packets containing the extended header given by
1137.Ar header .
1138Supported headers are:
1139.Pp
1140Fragment,
1141.Pq Cm frag ,
1142Hop-to-hop options
1143.Pq Cm hopopt ,
1144any type of Routing Header
1145.Pq Cm route ,
1146Source routing Routing Header Type 0
1147.Pq Cm rthdr0 ,
1148Mobile IPv6 Routing Header Type 2
1149.Pq Cm rthdr2 ,
1150Destination options
1151.Pq Cm dstopt ,
1152IPSec authentication headers
1153.Pq Cm ah ,
1154and IPSec encapsulated security payload headers
1155.Pq Cm esp .
1156.It Cm fib Ar fibnum
1157Matches a packet that has been tagged to use
1158the given FIB (routing table) number.
1159.It Cm flow-id Ar labels
1160Matches IPv6 packets containing any of the flow labels given in
1161.Ar labels .
1162.Ar labels
1163is a comma seperate list of numeric flow labels.
1164.It Cm frag
1165Matches packets that are fragments and not the first
1166fragment of an IP datagram.
1167Note that these packets will not have
1168the next protocol header (e.g.\& TCP, UDP) so options that look into
1169these headers cannot match.
1170.It Cm gid Ar group
1171Matches all TCP or UDP packets sent by or received for a
1172.Ar group .
1173A
1174.Ar group
1175may be specified by name or number.
1176.It Cm jail Ar prisonID
1177Matches all TCP or UDP packets sent by or received for the
1178jail whos prison ID is
1179.Ar prisonID .
1180.It Cm icmptypes Ar types
1181Matches ICMP packets whose ICMP type is in the list
1182.Ar types .
1183The list may be specified as any combination of
1184individual types (numeric) separated by commas.
1185.Em Ranges are not allowed .
1186The supported ICMP types are:
1187.Pp
1188echo reply
1189.Pq Cm 0 ,
1190destination unreachable
1191.Pq Cm 3 ,
1192source quench
1193.Pq Cm 4 ,
1194redirect
1195.Pq Cm 5 ,
1196echo request
1197.Pq Cm 8 ,
1198router advertisement
1199.Pq Cm 9 ,
1200router solicitation
1201.Pq Cm 10 ,
1202time-to-live exceeded
1203.Pq Cm 11 ,
1204IP header bad
1205.Pq Cm 12 ,
1206timestamp request
1207.Pq Cm 13 ,
1208timestamp reply
1209.Pq Cm 14 ,
1210information request
1211.Pq Cm 15 ,
1212information reply
1213.Pq Cm 16 ,
1214address mask request
1215.Pq Cm 17
1216and address mask reply
1217.Pq Cm 18 .
1218.It Cm icmp6types Ar types
1219Matches ICMP6 packets whose ICMP6 type is in the list of
1220.Ar types .
1221The list may be specified as any combination of
1222individual types (numeric) separated by commas.
1223.Em Ranges are not allowed .
1224.It Cm in | out
1225Matches incoming or outgoing packets, respectively.
1226.Cm in
1227and
1228.Cm out
1229are mutually exclusive (in fact,
1230.Cm out
1231is implemented as
1232.Cm not in Ns No ).
1233.It Cm ipid Ar id-list
1234Matches IPv4 packets whose
1235.Cm ip_id
1236field has value included in
1237.Ar id-list ,
1238which is either a single value or a list of values or ranges
1239specified in the same way as
1240.Ar ports .
1241.It Cm iplen Ar len-list
1242Matches IP packets whose total length, including header and data, is
1243in the set
1244.Ar len-list ,
1245which is either a single value or a list of values or ranges
1246specified in the same way as
1247.Ar ports .
1248.It Cm ipoptions Ar spec
1249Matches packets whose IPv4 header contains the comma separated list of
1250options specified in
1251.Ar spec .
1252The supported IP options are:
1253.Pp
1254.Cm ssrr
1255(strict source route),
1256.Cm lsrr
1257(loose source route),
1258.Cm rr
1259(record packet route) and
1260.Cm ts
1261(timestamp).
1262The absence of a particular option may be denoted
1263with a
1264.Ql \&! .
1265.It Cm ipprecedence Ar precedence
1266Matches IPv4 packets whose precedence field is equal to
1267.Ar precedence .
1268.It Cm ipsec
1269Matches packets that have IPSEC history associated with them
1270(i.e., the packet comes encapsulated in IPSEC, the kernel
1271has IPSEC support and IPSEC_FILTERTUNNEL option, and can correctly
1272decapsulate it).
1273.Pp
1274Note that specifying
1275.Cm ipsec
1276is different from specifying
1277.Cm proto Ar ipsec
1278as the latter will only look at the specific IP protocol field,
1279irrespective of IPSEC kernel support and the validity of the IPSEC data.
1280.Pp
1281Further note that this flag is silently ignored in kernels without
1282IPSEC support.
1283It does not affect rule processing when given and the
1284rules are handled as if with no
1285.Cm ipsec
1286flag.
1287.It Cm iptos Ar spec
1288Matches IPv4 packets whose
1289.Cm tos
1290field contains the comma separated list of
1291service types specified in
1292.Ar spec .
1293The supported IP types of service are:
1294.Pp
1295.Cm lowdelay
1296.Pq Dv IPTOS_LOWDELAY ,
1297.Cm throughput
1298.Pq Dv IPTOS_THROUGHPUT ,
1299.Cm reliability
1300.Pq Dv IPTOS_RELIABILITY ,
1301.Cm mincost
1302.Pq Dv IPTOS_MINCOST ,
1303.Cm congestion
1304.Pq Dv IPTOS_ECN_CE .
1305The absence of a particular type may be denoted
1306with a
1307.Ql \&! .
1308.It Cm ipttl Ar ttl-list
1309Matches IPv4 packets whose time to live is included in
1310.Ar ttl-list ,
1311which is either a single value or a list of values or ranges
1312specified in the same way as
1313.Ar ports .
1314.It Cm ipversion Ar ver
1315Matches IP packets whose IP version field is
1316.Ar ver .
1317.It Cm keep-state
1318Upon a match, the firewall will create a dynamic rule, whose
1319default behaviour is to match bidirectional traffic between
1320source and destination IP/port using the same protocol.
1321The rule has a limited lifetime (controlled by a set of
1322.Xr sysctl 8
1323variables), and the lifetime is refreshed every time a matching
1324packet is found.
1325.It Cm layer2
1326Matches only layer2 packets, i.e., those passed to
1327.Nm
1328from ether_demux() and ether_output_frame().
1329.It Cm limit Bro Cm src-addr | src-port | dst-addr | dst-port Brc Ar N
1330The firewall will only allow
1331.Ar N
1332connections with the same
1333set of parameters as specified in the rule.
1334One or more
1335of source and destination addresses and ports can be
1336specified.
1337Currently,
1338only IPv4 flows are supported.
1339.It Cm { MAC | mac } Ar dst-mac src-mac
1340Match packets with a given
1341.Ar dst-mac
1342and
1343.Ar src-mac
1344addresses, specified as the
1345.Cm any
1346keyword (matching any MAC address), or six groups of hex digits
1347separated by colons,
1348and optionally followed by a mask indicating the significant bits.
1349The mask may be specified using either of the following methods:
1350.Bl -enum -width indent
1351.It
1352A slash
1353.Pq /
1354followed by the number of significant bits.
1355For example, an address with 33 significant bits could be specified as:
1356.Pp
1357.Dl "MAC 10:20:30:40:50:60/33 any"
1358.Pp
1359.It
1360An ampersand
1361.Pq &
1362followed by a bitmask specified as six groups of hex digits separated
1363by colons.
1364For example, an address in which the last 16 bits are significant could
1365be specified as:
1366.Pp
1367.Dl "MAC 10:20:30:40:50:60&00:00:00:00:ff:ff any"
1368.Pp
1369Note that the ampersand character has a special meaning in many shells
1370and should generally be escaped.
1371.Pp
1372.El
1373Note that the order of MAC addresses (destination first,
1374source second) is
1375the same as on the wire, but the opposite of the one used for
1376IP addresses.
1377.It Cm mac-type Ar mac-type
1378Matches packets whose Ethernet Type field
1379corresponds to one of those specified as argument.
1380.Ar mac-type
1381is specified in the same way as
1382.Cm port numbers
1383(i.e., one or more comma-separated single values or ranges).
1384You can use symbolic names for known values such as
1385.Em vlan , ipv4, ipv6 .
1386Values can be entered as decimal or hexadecimal (if prefixed by 0x),
1387and they are always printed as hexadecimal (unless the
1388.Cm -N
1389option is used, in which case symbolic resolution will be attempted).
1390.It Cm proto Ar protocol
1391Matches packets with the corresponding IP protocol.
1392.It Cm recv | xmit | via Brq Ar ifX | Ar if Ns Cm * | Ar ipno | Ar any
1393Matches packets received, transmitted or going through,
1394respectively, the interface specified by exact name
1395.Ns No ( Ar ifX Ns No ),
1396by device name
1397.Ns No ( Ar if Ns Ar * Ns No ),
1398by IP address, or through some interface.
1399.Pp
1400The
1401.Cm via
1402keyword causes the interface to always be checked.
1403If
1404.Cm recv
1405or
1406.Cm xmit
1407is used instead of
1408.Cm via ,
1409then only the receive or transmit interface (respectively)
1410is checked.
1411By specifying both, it is possible to match packets based on
1412both receive and transmit interface, e.g.:
1413.Pp
1414.Dl "ipfw add deny ip from any to any out recv ed0 xmit ed1"
1415.Pp
1416The
1417.Cm recv
1418interface can be tested on either incoming or outgoing packets,
1419while the
1420.Cm xmit
1421interface can only be tested on outgoing packets.
1422So
1423.Cm out
1424is required (and
1425.Cm in
1426is invalid) whenever
1427.Cm xmit
1428is used.
1429.Pp
1430A packet may not have a receive or transmit interface: packets
1431originating from the local host have no receive interface,
1432while packets destined for the local host have no transmit
1433interface.
1434.It Cm setup
1435Matches TCP packets that have the SYN bit set but no ACK bit.
1436This is the short form of
1437.Dq Li tcpflags\ syn,!ack .
1438.It Cm src-ip Ar ip-address
1439Matches IPv4 packets whose source IP is one of the address(es)
1440specified as an argument.
1441.It Cm src-ip6 Ar ip6-address
1442Matches IPv6 packets whose source IP is one of the address(es)
1443specified as an argument.
1444.It Cm src-port Ar ports
1445Matches IP packets whose source port is one of the port(s)
1446specified as argument.
1447.It Cm tagged Ar tag-list
1448Matches packets whose tags are included in
1449.Ar tag-list ,
1450which is either a single value or a list of values or ranges
1451specified in the same way as
1452.Ar ports .
1453Tags can be applied to the packet using
1454.Cm tag
1455rule action parameter (see it's description for details on tags).
1456.It Cm tcpack Ar ack
1457TCP packets only.
1458Match if the TCP header acknowledgment number field is set to
1459.Ar ack .
1460.It Cm tcpdatalen Ar tcpdatalen-list
1461Matches TCP packets whose length of TCP data is
1462.Ar tcpdatalen-list ,
1463which is either a single value or a list of values or ranges
1464specified in the same way as
1465.Ar ports .
1466.It Cm tcpflags Ar spec
1467TCP packets only.
1468Match if the TCP header contains the comma separated list of
1469flags specified in
1470.Ar spec .
1471The supported TCP flags are:
1472.Pp
1473.Cm fin ,
1474.Cm syn ,
1475.Cm rst ,
1476.Cm psh ,
1477.Cm ack
1478and
1479.Cm urg .
1480The absence of a particular flag may be denoted
1481with a
1482.Ql \&! .
1483A rule which contains a
1484.Cm tcpflags
1485specification can never match a fragmented packet which has
1486a non-zero offset.
1487See the
1488.Cm frag
1489option for details on matching fragmented packets.
1490.It Cm tcpseq Ar seq
1491TCP packets only.
1492Match if the TCP header sequence number field is set to
1493.Ar seq .
1494.It Cm tcpwin Ar win
1495TCP packets only.
1496Match if the TCP header window field is set to
1497.Ar win .
1498.It Cm tcpoptions Ar spec
1499TCP packets only.
1500Match if the TCP header contains the comma separated list of
1501options specified in
1502.Ar spec .
1503The supported TCP options are:
1504.Pp
1505.Cm mss
1506(maximum segment size),
1507.Cm window
1508(tcp window advertisement),
1509.Cm sack
1510(selective ack),
1511.Cm ts
1512(rfc1323 timestamp) and
1513.Cm cc
1514(rfc1644 t/tcp connection count).
1515The absence of a particular option may be denoted
1516with a
1517.Ql \&! .
1518.It Cm uid Ar user
1519Match all TCP or UDP packets sent by or received for a
1520.Ar user .
1521A
1522.Ar user
1523may be matched by name or identification number.
1524.It Cm verrevpath
1525For incoming packets,
1526a routing table lookup is done on the packet's source address.
1527If the interface on which the packet entered the system matches the
1528outgoing interface for the route,
1529the packet matches.
1530If the interfaces do not match up,
1531the packet does not match.
1532All outgoing packets or packets with no incoming interface match.
1533.Pp
1534The name and functionality of the option is intentionally similar to
1535the Cisco IOS command:
1536.Pp
1537.Dl ip verify unicast reverse-path
1538.Pp
1539This option can be used to make anti-spoofing rules to reject all
1540packets with source addresses not from this interface.
1541See also the option
1542.Cm antispoof .
1543.It Cm versrcreach
1544For incoming packets,
1545a routing table lookup is done on the packet's source address.
1546If a route to the source address exists, but not the default route
1547or a blackhole/reject route, the packet matches.
1548Otherwise, the packet does not match.
1549All outgoing packets match.
1550.Pp
1551The name and functionality of the option is intentionally similar to
1552the Cisco IOS command:
1553.Pp
1554.Dl ip verify unicast source reachable-via any
1555.Pp
1556This option can be used to make anti-spoofing rules to reject all
1557packets whose source address is unreachable.
1558.It Cm antispoof
1559For incoming packets, the packet's source address is checked if it
1560belongs to a directly connected network.
1561If the network is directly connected, then the interface the packet
1562came on in is compared to the interface the network is connected to.
1563When incoming interface and directly connected interface are not the
1564same, the packet does not match.
1565Otherwise, the packet does match.
1566All outgoing packets match.
1567.Pp
1568This option can be used to make anti-spoofing rules to reject all
1569packets that pretend to be from a directly connected network but do
1570not come in through that interface.
1571This option is similar to but more restricted than
1572.Cm verrevpath
1573because it engages only on packets with source addresses of directly
1574connected networks instead of all source addresses.
1575.El
1576.Sh LOOKUP TABLES
1577Lookup tables are useful to handle large sparse address sets,
1578typically from a hundred to several thousands of entries.
1579There may be up to 128 different lookup tables, numbered 0 to 127.
1580.Pp
1581Each entry is represented by an
1582.Ar addr Ns Op / Ns Ar masklen
1583and will match all addresses with base
1584.Ar addr
1585(specified as an IP address or a hostname)
1586and mask width of
1587.Ar masklen
1588bits.
1589If
1590.Ar masklen
1591is not specified, it defaults to 32.
1592When looking up an IP address in a table, the most specific
1593entry will match.
1594Associated with each entry is a 32-bit unsigned
1595.Ar value ,
1596which can optionally be checked by a rule matching code.
1597When adding an entry, if
1598.Ar value
1599is not specified, it defaults to 0.
1600.Pp
1601An entry can be added to a table
1602.Pq Cm add ,
1603removed from a table
1604.Pq Cm delete ,
1605a table can be examined
1606.Pq Cm list
1607or flushed
1608.Pq Cm flush .
1609.Pp
1610Internally, each table is stored in a Radix tree, the same way as
1611the routing table (see
1612.Xr route 4 ) .
1613.Pp
1614Lookup tables currently support IPv4 addresses only.
1615.Pp
1616The
1617.Cm tablearg
1618feature provides the ability to use a value, looked up in the table, as
1619the argument for a rule action, action parameter or rule option.
1620This can significantly reduce number of rules in some configurations.
1621The
1622.Cm tablearg
1623argument can be used with the following actions:
1624.Cm nat, pipe , queue, divert, tee, netgraph, ngtee, fwd
1625action parameters:
1626.Cm tag, untag,
1627rule options:
1628.Cm limit, tagged.
1629.Pp
1630When used with
1631.Cm fwd
1632it is possible to supply table entries with values
1633that are in the form of IP addresses or hostnames.
1634See the
1635.Sx EXAMPLES
1636Section for example usage of tables and the tablearg keyword.
1637.Sh SETS OF RULES
1638Each rule belongs to one of 32 different
1639.Em sets
1640, numbered 0 to 31.
1641Set 31 is reserved for the default rule.
1642.Pp
1643By default, rules are put in set 0, unless you use the
1644.Cm set N
1645attribute when entering a new rule.
1646Sets can be individually and atomically enabled or disabled,
1647so this mechanism permits an easy way to store multiple configurations
1648of the firewall and quickly (and atomically) switch between them.
1649The command to enable/disable sets is
1650.Bd -ragged -offset indent
1651.Nm
1652.Cm set Oo Cm disable Ar number ... Oc Op Cm enable Ar number ...
1653.Ed
1654.Pp
1655where multiple
1656.Cm enable
1657or
1658.Cm disable
1659sections can be specified.
1660Command execution is atomic on all the sets specified in the command.
1661By default, all sets are enabled.
1662.Pp
1663When you disable a set, its rules behave as if they do not exist
1664in the firewall configuration, with only one exception:
1665.Bd -ragged -offset indent
1666dynamic rules created from a rule before it had been disabled
1667will still be active until they expire.
1668In order to delete
1669dynamic rules you have to explicitly delete the parent rule
1670which generated them.
1671.Ed
1672.Pp
1673The set number of rules can be changed with the command
1674.Bd -ragged -offset indent
1675.Nm
1676.Cm set move
1677.Brq Cm rule Ar rule-number | old-set
1678.Cm to Ar new-set
1679.Ed
1680.Pp
1681Also, you can atomically swap two rulesets with the command
1682.Bd -ragged -offset indent
1683.Nm
1684.Cm set swap Ar first-set second-set
1685.Ed
1686.Pp
1687See the
1688.Sx EXAMPLES
1689Section on some possible uses of sets of rules.
1690.Sh STATEFUL FIREWALL
1691Stateful operation is a way for the firewall to dynamically
1692create rules for specific flows when packets that
1693match a given pattern are detected.
1694Support for stateful
1695operation comes through the
1696.Cm check-state , keep-state
1697and
1698.Cm limit
1699options of
1700.Nm rules .
1701.Pp
1702Dynamic rules are created when a packet matches a
1703.Cm keep-state
1704or
1705.Cm limit
1706rule, causing the creation of a
1707.Em dynamic
1708rule which will match all and only packets with
1709a given
1710.Em protocol
1711between a
1712.Em src-ip/src-port dst-ip/dst-port
1713pair of addresses
1714.Em ( src
1715and
1716.Em dst
1717are used here only to denote the initial match addresses, but they
1718are completely equivalent afterwards).
1719Dynamic rules will be checked at the first
1720.Cm check-state, keep-state
1721or
1722.Cm limit
1723occurrence, and the action performed upon a match will be the same
1724as in the parent rule.
1725.Pp
1726Note that no additional attributes other than protocol and IP addresses
1727and ports are checked on dynamic rules.
1728.Pp
1729The typical use of dynamic rules is to keep a closed firewall configuration,
1730but let the first TCP SYN packet from the inside network install a
1731dynamic rule for the flow so that packets belonging to that session
1732will be allowed through the firewall:
1733.Pp
1734.Dl "ipfw add check-state"
1735.Dl "ipfw add allow tcp from my-subnet to any setup keep-state"
1736.Dl "ipfw add deny tcp from any to any"
1737.Pp
1738A similar approach can be used for UDP, where an UDP packet coming
1739from the inside will install a dynamic rule to let the response through
1740the firewall:
1741.Pp
1742.Dl "ipfw add check-state"
1743.Dl "ipfw add allow udp from my-subnet to any keep-state"
1744.Dl "ipfw add deny udp from any to any"
1745.Pp
1746Dynamic rules expire after some time, which depends on the status
1747of the flow and the setting of some
1748.Cm sysctl
1749variables.
1750See Section
1751.Sx SYSCTL VARIABLES
1752for more details.
1753For TCP sessions, dynamic rules can be instructed to periodically
1754send keepalive packets to refresh the state of the rule when it is
1755about to expire.
1756.Pp
1757See Section
1758.Sx EXAMPLES
1759for more examples on how to use dynamic rules.
1760.Sh TRAFFIC SHAPER (DUMMYNET) CONFIGURATION
1761.Nm
1762is also the user interface for the
1763.Nm dummynet
1764traffic shaper.
1765.Pp
1766.Nm dummynet
1767operates by first using the firewall to classify packets and divide them into
1768.Em flows ,
1769using any match pattern that can be used in
1770.Nm
1771rules.
1772Depending on local policies, a flow can contain packets for a single
1773TCP connection, or from/to a given host, or entire subnet, or a
1774protocol type, etc.
1775.Pp
1776There are two modes of
1777.Nm dummynet
1778operation:
1779.Dq normal
1780and
1781.Dq fast .
1782The
1783.Dq normal
1784mode tries to emulate a real link: the
1785.Nm dummynet
1786scheduler ensures that the packet will not leave the pipe faster than it
1787would on the real link with a given bandwidth.
1788The
1789.Dq fast
1790mode allows certain packets to bypass the
1791.Nm dummynet
1792scheduler (if packet flow does not exceed pipe's bandwidth).
1793This is the reason why the
1794.Dq fast
1795mode requires less CPU cycles per packet (on average) and packet latency
1796can be significantly lower in comparison to a real link with the same
1797bandwidth.
1798The default mode is
1799.Dq normal .
1800The
1801.Dq fast
1802mode can be enabled by setting the
1803.Va net.inet.ip.dummynet.io_fast
1804.Xr sysctl 8
1805variable to a non-zero value.
1806.Pp
1807Packets belonging to the same flow are then passed to either of two
1808different objects, which implement the traffic regulation:
1809.Bl -hang -offset XXXX
1810.It Em pipe
1811A pipe emulates a link with given bandwidth, propagation delay,
1812queue size and packet loss rate.
1813Packets are queued in front of the pipe as they come out from the classifier,
1814and then transferred to the pipe according to the pipe's parameters.
1815.Pp
1816.It Em queue
1817A queue
1818is an abstraction used to implement the WF2Q+
1819(Worst-case Fair Weighted Fair Queueing) policy, which is
1820an efficient variant of the WFQ policy.
1821.br
1822The queue associates a
1823.Em weight
1824and a reference pipe to each flow, and then all backlogged (i.e.,
1825with packets queued) flows linked to the same pipe share the pipe's
1826bandwidth proportionally to their weights.
1827Note that weights are not priorities; a flow with a lower weight
1828is still guaranteed to get its fraction of the bandwidth even if a
1829flow with a higher weight is permanently backlogged.
1830.Pp
1831.El
1832In practice,
1833.Em pipes
1834can be used to set hard limits to the bandwidth that a flow can use, whereas
1835.Em queues
1836can be used to determine how different flow share the available bandwidth.
1837.Pp
1838The
1839.Em pipe
1840and
1841.Em queue
1842configuration commands are the following:
1843.Bd -ragged -offset indent
1844.Cm pipe Ar number Cm config Ar pipe-configuration
1845.Pp
1846.Cm queue Ar number Cm config Ar queue-configuration
1847.Ed
1848.Pp
1849The following parameters can be configured for a pipe:
1850.Pp
1851.Bl -tag -width indent -compact
1852.It Cm bw Ar bandwidth | device
1853Bandwidth, measured in
1854.Sm off
1855.Op Cm K | M
1856.Brq Cm bit/s | Byte/s .
1857.Sm on
1858.Pp
1859A value of 0 (default) means unlimited bandwidth.
1860The unit must immediately follow the number, as in
1861.Pp
1862.Dl "ipfw pipe 1 config bw 300Kbit/s"
1863.Pp
1864If a device name is specified instead of a numeric value, as in
1865.Pp
1866.Dl "ipfw pipe 1 config bw tun0"
1867.Pp
1868then the transmit clock is supplied by the specified device.
1869At the moment only the
1870.Xr tun 4
1871device supports this
1872functionality, for use in conjunction with
1873.Xr ppp 8 .
1874.Pp
1875.It Cm delay Ar ms-delay
1876Propagation delay, measured in milliseconds.
1877The value is rounded to the next multiple of the clock tick
1878(typically 10ms, but it is a good practice to run kernels
1879with
1880.Dq "options HZ=1000"
1881to reduce
1882the granularity to 1ms or less).
1883Default value is 0, meaning no delay.
1884.El
1885.Pp
1886The following parameters can be configured for a queue:
1887.Pp
1888.Bl -tag -width indent -compact
1889.It Cm pipe Ar pipe_nr
1890Connects a queue to the specified pipe.
1891Multiple queues (with the same or different weights) can be connected to
1892the same pipe, which specifies the aggregate rate for the set of queues.
1893.Pp
1894.It Cm weight Ar weight
1895Specifies the weight to be used for flows matching this queue.
1896The weight must be in the range 1..100, and defaults to 1.
1897.El
1898.Pp
1899Finally, the following parameters can be configured for both
1900pipes and queues:
1901.Pp
1902.Bl -tag -width XXXX -compact
1903.Pp
1904.It Cm buckets Ar hash-table-size
1905Specifies the size of the hash table used for storing the
1906various queues.
1907Default value is 64 controlled by the
1908.Xr sysctl 8
1909variable
1910.Va net.inet.ip.dummynet.hash_size ,
1911allowed range is 16 to 65536.
1912.Pp
1913.It Cm mask Ar mask-specifier
1914Packets sent to a given pipe or queue by an
1915.Nm
1916rule can be further classified into multiple flows, each of which is then
1917sent to a different
1918.Em dynamic
1919pipe or queue.
1920A flow identifier is constructed by masking the IP addresses,
1921ports and protocol types as specified with the
1922.Cm mask
1923options in the configuration of the pipe or queue.
1924For each different flow identifier, a new pipe or queue is created
1925with the same parameters as the original object, and matching packets
1926are sent to it.
1927.Pp
1928Thus, when
1929.Em dynamic pipes
1930are used, each flow will get the same bandwidth as defined by the pipe,
1931whereas when
1932.Em dynamic queues
1933are used, each flow will share the parent's pipe bandwidth evenly
1934with other flows generated by the same queue (note that other queues
1935with different weights might be connected to the same pipe).
1936.br
1937Available mask specifiers are a combination of one or more of the following:
1938.Pp
1939.Cm dst-ip Ar mask ,
1940.Cm dst-ip6 Ar mask ,
1941.Cm src-ip Ar mask ,
1942.Cm src-ip6 Ar mask ,
1943.Cm dst-port Ar mask ,
1944.Cm src-port Ar mask ,
1945.Cm flow-id Ar mask ,
1946.Cm proto Ar mask
1947or
1948.Cm all ,
1949.Pp
1950where the latter means all bits in all fields are significant.
1951.Pp
1952.It Cm noerror
1953When a packet is dropped by a
1954.Nm dummynet
1955queue or pipe, the error
1956is normally reported to the caller routine in the kernel, in the
1957same way as it happens when a device queue fills up.
1958Setting this
1959option reports the packet as successfully delivered, which can be
1960needed for some experimental setups where you want to simulate
1961loss or congestion at a remote router.
1962.Pp
1963.It Cm plr Ar packet-loss-rate
1964Packet loss rate.
1965Argument
1966.Ar packet-loss-rate
1967is a floating-point number between 0 and 1, with 0 meaning no
1968loss, 1 meaning 100% loss.
1969The loss rate is internally represented on 31 bits.
1970.Pp
1971.It Cm queue Brq Ar slots | size Ns Cm Kbytes
1972Queue size, in
1973.Ar slots
1974or
1975.Cm KBytes .
1976Default value is 50 slots, which
1977is the typical queue size for Ethernet devices.
1978Note that for slow speed links you should keep the queue
1979size short or your traffic might be affected by a significant
1980queueing delay.
1981E.g., 50 max-sized ethernet packets (1500 bytes) mean 600Kbit
1982or 20s of queue on a 30Kbit/s pipe.
1983Even worse effects can result if you get packets from an
1984interface with a much larger MTU, e.g.\& the loopback interface
1985with its 16KB packets.
1986The
1987.Xr sysctl 8
1988variables
1989.Em net.inet.ip.dummynet.pipe_byte_limit
1990and
1991.Em net.inet.ip.dummynet.pipe_slot_limit
1992control the maximum lengths that can be specified.
1993.Pp
1994.It Cm red | gred Ar w_q Ns / Ns Ar min_th Ns / Ns Ar max_th Ns / Ns Ar max_p
1995Make use of the RED (Random Early Detection) queue management algorithm.
1996.Ar w_q
1997and
1998.Ar max_p
1999are floating
2000point numbers between 0 and 1 (0 not included), while
2001.Ar min_th
2002and
2003.Ar max_th
2004are integer numbers specifying thresholds for queue management
2005(thresholds are computed in bytes if the queue has been defined
2006in bytes, in slots otherwise).
2007The
2008.Nm dummynet
2009also supports the gentle RED variant (gred).
2010Three
2011.Xr sysctl 8
2012variables can be used to control the RED behaviour:
2013.Bl -tag -width indent
2014.It Va net.inet.ip.dummynet.red_lookup_depth
2015specifies the accuracy in computing the average queue
2016when the link is idle (defaults to 256, must be greater than zero)
2017.It Va net.inet.ip.dummynet.red_avg_pkt_size
2018specifies the expected average packet size (defaults to 512, must be
2019greater than zero)
2020.It Va net.inet.ip.dummynet.red_max_pkt_size
2021specifies the expected maximum packet size, only used when queue
2022thresholds are in bytes (defaults to 1500, must be greater than zero).
2023.El
2024.El
2025.Pp
2026When used with IPv6 data,
2027.Nm dummynet
2028currently has several limitations.
2029Information necessary to route link-local packets to an
2030interface is not available after processing by
2031.Nm dummynet
2032so those packets are dropped in the output path.
2033Care should be taken to insure that link-local packets are not passed to
2034.Nm dummynet .
2035.Sh CHECKLIST
2036Here are some important points to consider when designing your
2037rules:
2038.Bl -bullet
2039.It
2040Remember that you filter both packets going
2041.Cm in
2042and
2043.Cm out .
2044Most connections need packets going in both directions.
2045.It
2046Remember to test very carefully.
2047It is a good idea to be near the console when doing this.
2048If you cannot be near the console,
2049use an auto-recovery script such as the one in
2050.Pa /usr/share/examples/ipfw/change_rules.sh .
2051.It
2052Do not forget the loopback interface.
2053.El
2054.Sh FINE POINTS
2055.Bl -bullet
2056.It
2057There are circumstances where fragmented datagrams are unconditionally
2058dropped.
2059TCP packets are dropped if they do not contain at least 20 bytes of
2060TCP header, UDP packets are dropped if they do not contain a full 8
2061byte UDP header, and ICMP packets are dropped if they do not contain
20624 bytes of ICMP header, enough to specify the ICMP type, code, and
2063checksum.
2064These packets are simply logged as
2065.Dq pullup failed
2066since there may not be enough good data in the packet to produce a
2067meaningful log entry.
2068.It
2069Another type of packet is unconditionally dropped, a TCP packet with a
2070fragment offset of one.
2071This is a valid packet, but it only has one use, to try
2072to circumvent firewalls.
2073When logging is enabled, these packets are
2074reported as being dropped by rule -1.
2075.It
2076If you are logged in over a network, loading the
2077.Xr kld 4
2078version of
2079.Nm
2080is probably not as straightforward as you would think.
2081I recommend the following command line:
2082.Bd -literal -offset indent
2083kldload ipfw && \e
2084ipfw add 32000 allow ip from any to any
2085.Ed
2086.Pp
2087Along the same lines, doing an
2088.Bd -literal -offset indent
2089ipfw flush
2090.Ed
2091.Pp
2092in similar surroundings is also a bad idea.
2093.It
2094The
2095.Nm
2096filter list may not be modified if the system security level
2097is set to 3 or higher
2098(see
2099.Xr init 8
2100for information on system security levels).
2101.El
2102.Sh PACKET DIVERSION
2103A
2104.Xr divert 4
2105socket bound to the specified port will receive all packets
2106diverted to that port.
2107If no socket is bound to the destination port, or if the divert module is
2108not loaded, or if the kernel was not compiled with divert socket support,
2109the packets are dropped.
2110.Sh NETWORK ADDRESS TRANSLATION (NAT)
2111The nat configuration command is the following:
2112.Bd -ragged -offset indent
2113.Bk -words
2114.Cm nat
2115.Ar nat_number
2116.Cm config
2117.Ar nat-configuration
2118.Ek
2119.Ed
2120.Pp
2121.
2122The following parameters can be configured:
2123.Bl -tag -width indent
2124.It Cm ip Ar ip_address
2125Define an ip address to use for aliasing.
2126.It Cm if Ar nic
2127Use ip addres of NIC for aliasing, dynamically changing
2128it if NIC's ip address change.
2129.It Cm log
2130Enable logging on this nat instance.
2131.It Cm deny_in
2132Deny any incoming connection from outside world.
2133.It Cm same_ports
2134Try to leave the alias port numbers unchanged from
2135the actual local port numbers.
2136.It Cm unreg_only
2137Traffic on the local network not originating from an
2138unregistered address spaces will be ignored.
2139.It Cm reset
2140Reset table of the packet aliasing engine on address change.
2141.It Cm reverse
2142Reverse the way libalias handles aliasing.
2143.It Cm proxy_only
2144Obey transparent proxy rules only, packet aliasing is not performed.
2145.El
2146.Pp
2147To let the packet continue after being (de)aliased, set the sysctl variable
2148.Va net.inet.ip.fw.one_pass
2149to 0.
2150For more information about aliasing modes, refer to
2151.Xr libalias 3
2152.
2153See Section
2154.Sx EXAMPLES
2155for some examples about nat usage.
2156.Sh REDIRECT AND LSNAT SUPPORT IN IPFW
2157Redirect and LSNAT support follow closely the syntax used in
2158.Xr natd 8
2159.
2160See Section
2161.Sx EXAMPLES
2162for some examples on how to do redirect and lsnat.
2163.Sh SYSCTL VARIABLES
2164A set of
2165.Xr sysctl 8
2166variables controls the behaviour of the firewall and
2167associated modules
2168.Pq Nm dummynet , bridge .
2169These are shown below together with their default value
2170(but always check with the
2171.Xr sysctl 8
2172command what value is actually in use) and meaning:
2173.Bl -tag -width indent
2174.It Va net.inet.ip.dummynet.expire : No 1
2175Lazily delete dynamic pipes/queue once they have no pending traffic.
2176You can disable this by setting the variable to 0, in which case
2177the pipes/queues will only be deleted when the threshold is reached.
2178.It Va net.inet.ip.dummynet.hash_size : No 64
2179Default size of the hash table used for dynamic pipes/queues.
2180This value is used when no
2181.Cm buckets
2182option is specified when configuring a pipe/queue.
2183.It Va net.inet.ip.dummynet.io_fast : No 0
2184If set to a non-zero value,
2185the
2186.Dq fast
2187mode of
2188.Nm dummynet
2189operation (see above) is enabled.
2190.It Va net.inet.ip.dummynet.io_pkt
2191Number of packets passed to
2192.Nm dummynet .
2193.It Va net.inet.ip.dummynet.io_pkt_drop
2194Number of packets dropped by
2195.Nm dummynet .
2196.It Va net.inet.ip.dummynet.io_pkt_fast
2197Number of packets bypassed by the
2198.Nm dummynet
2199scheduler.
2200.It Va net.inet.ip.dummynet.max_chain_len : No 16
2201Target value for the maximum number of pipes/queues in a hash bucket.
2202The product
2203.Cm max_chain_len*hash_size
2204is used to determine the threshold over which empty pipes/queues
2205will be expired even when
2206.Cm net.inet.ip.dummynet.expire=0 .
2207.It Va net.inet.ip.dummynet.red_lookup_depth : No 256
2208.It Va net.inet.ip.dummynet.red_avg_pkt_size : No 512
2209.It Va net.inet.ip.dummynet.red_max_pkt_size : No 1500
2210Parameters used in the computations of the drop probability
2211for the RED algorithm.
2212.It Va net.inet.ip.dummynet.pipe_byte_limit : No 1048576
2213.It Va net.inet.ip.dummynet.pipe_slot_limit : No 100
2214The maximum queue size that can be specified in bytes or packets.
2215These limits prevent accidental exhaustion of resources such as mbufs.
2216If you raise these limits,
2217you should make sure the system is configured so that sufficient resources
2218are available.
2219.It Va net.inet.ip.fw.autoinc_step : No 100
2220Delta between rule numbers when auto-generating them.
2221The value must be in the range 1..1000.
2222.It Va net.inet.ip.fw.curr_dyn_buckets : Va net.inet.ip.fw.dyn_buckets
2223The current number of buckets in the hash table for dynamic rules
2224(readonly).
2225.It Va net.inet.ip.fw.debug : No 1
2226Controls debugging messages produced by
2227.Nm .
2228.It Va net.inet.ip.fw.dyn_buckets : No 256
2229The number of buckets in the hash table for dynamic rules.
2230Must be a power of 2, up to 65536.
2231It only takes effect when all dynamic rules have expired, so you
2232are advised to use a
2233.Cm flush
2234command to make sure that the hash table is resized.
2235.It Va net.inet.ip.fw.dyn_count : No 3
2236Current number of dynamic rules
2237(read-only).
2238.It Va net.inet.ip.fw.dyn_keepalive : No 1
2239Enables generation of keepalive packets for
2240.Cm keep-state
2241rules on TCP sessions.
2242A keepalive is generated to both
2243sides of the connection every 5 seconds for the last 20
2244seconds of the lifetime of the rule.
2245.It Va net.inet.ip.fw.dyn_max : No 8192
2246Maximum number of dynamic rules.
2247When you hit this limit, no more dynamic rules can be
2248installed until old ones expire.
2249.It Va net.inet.ip.fw.dyn_ack_lifetime : No 300
2250.It Va net.inet.ip.fw.dyn_syn_lifetime : No 20
2251.It Va net.inet.ip.fw.dyn_fin_lifetime : No 1
2252.It Va net.inet.ip.fw.dyn_rst_lifetime : No 1
2253.It Va net.inet.ip.fw.dyn_udp_lifetime : No 5
2254.It Va net.inet.ip.fw.dyn_short_lifetime : No 30
2255These variables control the lifetime, in seconds, of dynamic
2256rules.
2257Upon the initial SYN exchange the lifetime is kept short,
2258then increased after both SYN have been seen, then decreased
2259again during the final FIN exchange or when a RST is received.
2260Both
2261.Em dyn_fin_lifetime
2262and
2263.Em dyn_rst_lifetime
2264must be strictly lower than 5 seconds, the period of
2265repetition of keepalives.
2266The firewall enforces that.
2267.It Va net.inet.ip.fw.enable : No 1
2268Enables the firewall.
2269Setting this variable to 0 lets you run your machine without
2270firewall even if compiled in.
2271.It Va net.inet6.ip6.fw.enable : No 1
2272provides the same functionality as above for the IPv6 case.
2273.It Va net.inet.ip.fw.one_pass : No 1
2274When set, the packet exiting from the
2275.Nm dummynet
2276pipe or from
2277.Xr ng_ipfw 4
2278node is not passed though the firewall again.
2279Otherwise, after an action, the packet is
2280reinjected into the firewall at the next rule.
2281.It Va net.inet.ip.fw.verbose : No 1
2282Enables verbose messages.
2283.It Va net.inet.ip.fw.verbose_limit : No 0
2284Limits the number of messages produced by a verbose firewall.
2285.It Va net.inet6.ip6.fw.deny_unknown_exthdrs : No 1
2286If enabled packets with unknown IPv6 Extension Headers will be denied.
2287.It Va net.link.ether.ipfw : No 0
2288Controls whether layer-2 packets are passed to
2289.Nm .
2290Default is no.
2291.It Va net.link.bridge.ipfw : No 0
2292Controls whether bridged packets are passed to
2293.Nm .
2294Default is no.
2295.El
2296.Pp
2297.Sh EXAMPLES
2298There are far too many possible uses of
2299.Nm
2300so this Section will only give a small set of examples.
2301.Pp
2302.Ss BASIC PACKET FILTERING
2303This command adds an entry which denies all tcp packets from
2304.Em cracker.evil.org
2305to the telnet port of
2306.Em wolf.tambov.su
2307from being forwarded by the host:
2308.Pp
2309.Dl "ipfw add deny tcp from cracker.evil.org to wolf.tambov.su telnet"
2310.Pp
2311This one disallows any connection from the entire cracker's
2312network to my host:
2313.Pp
2314.Dl "ipfw add deny ip from 123.45.67.0/24 to my.host.org"
2315.Pp
2316A first and efficient way to limit access (not using dynamic rules)
2317is the use of the following rules:
2318.Pp
2319.Dl "ipfw add allow tcp from any to any established"
2320.Dl "ipfw add allow tcp from net1 portlist1 to net2 portlist2 setup"
2321.Dl "ipfw add allow tcp from net3 portlist3 to net3 portlist3 setup"
2322.Dl "..."
2323.Dl "ipfw add deny tcp from any to any"
2324.Pp
2325The first rule will be a quick match for normal TCP packets,
2326but it will not match the initial SYN packet, which will be
2327matched by the
2328.Cm setup
2329rules only for selected source/destination pairs.
2330All other SYN packets will be rejected by the final
2331.Cm deny
2332rule.
2333.Pp
2334If you administer one or more subnets, you can take advantage
2335of the address sets and or-blocks and write extremely
2336compact rulesets which selectively enable services to blocks
2337of clients, as below:
2338.Pp
2339.Dl "goodguys=\*q{ 10.1.2.0/24{20,35,66,18} or 10.2.3.0/28{6,3,11} }\*q"
2340.Dl "badguys=\*q10.1.2.0/24{8,38,60}\*q"
2341.Dl ""
2342.Dl "ipfw add allow ip from ${goodguys} to any"
2343.Dl "ipfw add deny ip from ${badguys} to any"
2344.Dl "... normal policies ..."
2345.Pp
2346The
2347.Cm verrevpath
2348option could be used to do automated anti-spoofing by adding the
2349following to the top of a ruleset:
2350.Pp
2351.Dl "ipfw add deny ip from any to any not verrevpath in"
2352.Pp
2353This rule drops all incoming packets that appear to be coming to the
2354system on the wrong interface.
2355For example, a packet with a source
2356address belonging to a host on a protected internal network would be
2357dropped if it tried to enter the system from an external interface.
2358.Pp
2359The
2360.Cm antispoof
2361option could be used to do similar but more restricted anti-spoofing
2362by adding the following to the top of a ruleset:
2363.Pp
2364.Dl "ipfw add deny ip from any to any not antispoof in"
2365.Pp
2366This rule drops all incoming packets that appear to be coming from another
2367directly connected system but on the wrong interface.
2368For example, a packet with a source address of
2369.Li 192.168.0.0/24
2370, configured on
2371.Li fxp0
2372, but coming in on
2373.Li fxp1
2374would be dropped.
2375.Ss DYNAMIC RULES
2376In order to protect a site from flood attacks involving fake
2377TCP packets, it is safer to use dynamic rules:
2378.Pp
2379.Dl "ipfw add check-state"
2380.Dl "ipfw add deny tcp from any to any established"
2381.Dl "ipfw add allow tcp from my-net to any setup keep-state"
2382.Pp
2383This will let the firewall install dynamic rules only for
2384those connection which start with a regular SYN packet coming
2385from the inside of our network.
2386Dynamic rules are checked when encountering the first
2387.Cm check-state
2388or
2389.Cm keep-state
2390rule.
2391A
2392.Cm check-state
2393rule should usually be placed near the beginning of the
2394ruleset to minimize the amount of work scanning the ruleset.
2395Your mileage may vary.
2396.Pp
2397To limit the number of connections a user can open
2398you can use the following type of rules:
2399.Pp
2400.Dl "ipfw add allow tcp from my-net/24 to any setup limit src-addr 10"
2401.Dl "ipfw add allow tcp from any to me setup limit src-addr 4"
2402.Pp
2403The former (assuming it runs on a gateway) will allow each host
2404on a /24 network to open at most 10 TCP connections.
2405The latter can be placed on a server to make sure that a single
2406client does not use more than 4 simultaneous connections.
2407.Pp
2408.Em BEWARE :
2409stateful rules can be subject to denial-of-service attacks
2410by a SYN-flood which opens a huge number of dynamic rules.
2411The effects of such attacks can be partially limited by
2412acting on a set of
2413.Xr sysctl 8
2414variables which control the operation of the firewall.
2415.Pp
2416Here is a good usage of the
2417.Cm list
2418command to see accounting records and timestamp information:
2419.Pp
2420.Dl ipfw -at list
2421.Pp
2422or in short form without timestamps:
2423.Pp
2424.Dl ipfw -a list
2425.Pp
2426which is equivalent to:
2427.Pp
2428.Dl ipfw show
2429.Pp
2430Next rule diverts all incoming packets from 192.168.2.0/24
2431to divert port 5000:
2432.Pp
2433.Dl ipfw divert 5000 ip from 192.168.2.0/24 to any in
2434.Pp
2435.Ss TRAFFIC SHAPING
2436The following rules show some of the applications of
2437.Nm
2438and
2439.Nm dummynet
2440for simulations and the like.
2441.Pp
2442This rule drops random incoming packets with a probability
2443of 5%:
2444.Pp
2445.Dl "ipfw add prob 0.05 deny ip from any to any in"
2446.Pp
2447A similar effect can be achieved making use of
2448.Nm dummynet
2449pipes:
2450.Pp
2451.Dl "ipfw add pipe 10 ip from any to any"
2452.Dl "ipfw pipe 10 config plr 0.05"
2453.Pp
2454We can use pipes to artificially limit bandwidth, e.g.\& on a
2455machine acting as a router, if we want to limit traffic from
2456local clients on 192.168.2.0/24 we do:
2457.Pp
2458.Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out"
2459.Dl "ipfw pipe 1 config bw 300Kbit/s queue 50KBytes"
2460.Pp
2461note that we use the
2462.Cm out
2463modifier so that the rule is not used twice.
2464Remember in fact that
2465.Nm
2466rules are checked both on incoming and outgoing packets.
2467.Pp
2468Should we want to simulate a bidirectional link with bandwidth
2469limitations, the correct way is the following:
2470.Pp
2471.Dl "ipfw add pipe 1 ip from any to any out"
2472.Dl "ipfw add pipe 2 ip from any to any in"
2473.Dl "ipfw pipe 1 config bw 64Kbit/s queue 10Kbytes"
2474.Dl "ipfw pipe 2 config bw 64Kbit/s queue 10Kbytes"
2475.Pp
2476The above can be very useful, e.g.\& if you want to see how
2477your fancy Web page will look for a residential user who
2478is connected only through a slow link.
2479You should not use only one pipe for both directions, unless
2480you want to simulate a half-duplex medium (e.g.\& AppleTalk,
2481Ethernet, IRDA).
2482It is not necessary that both pipes have the same configuration,
2483so we can also simulate asymmetric links.
2484.Pp
2485Should we want to verify network performance with the RED queue
2486management algorithm:
2487.Pp
2488.Dl "ipfw add pipe 1 ip from any to any"
2489.Dl "ipfw pipe 1 config bw 500Kbit/s queue 100 red 0.002/30/80/0.1"
2490.Pp
2491Another typical application of the traffic shaper is to
2492introduce some delay in the communication.
2493This can significantly affect applications which do a lot of Remote
2494Procedure Calls, and where the round-trip-time of the
2495connection often becomes a limiting factor much more than
2496bandwidth:
2497.Pp
2498.Dl "ipfw add pipe 1 ip from any to any out"
2499.Dl "ipfw add pipe 2 ip from any to any in"
2500.Dl "ipfw pipe 1 config delay 250ms bw 1Mbit/s"
2501.Dl "ipfw pipe 2 config delay 250ms bw 1Mbit/s"
2502.Pp
2503Per-flow queueing can be useful for a variety of purposes.
2504A very simple one is counting traffic:
2505.Pp
2506.Dl "ipfw add pipe 1 tcp from any to any"
2507.Dl "ipfw add pipe 1 udp from any to any"
2508.Dl "ipfw add pipe 1 ip from any to any"
2509.Dl "ipfw pipe 1 config mask all"
2510.Pp
2511The above set of rules will create queues (and collect
2512statistics) for all traffic.
2513Because the pipes have no limitations, the only effect is
2514collecting statistics.
2515Note that we need 3 rules, not just the last one, because
2516when
2517.Nm
2518tries to match IP packets it will not consider ports, so we
2519would not see connections on separate ports as different
2520ones.
2521.Pp
2522A more sophisticated example is limiting the outbound traffic
2523on a net with per-host limits, rather than per-network limits:
2524.Pp
2525.Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out"
2526.Dl "ipfw add pipe 2 ip from any to 192.168.2.0/24 in"
2527.Dl "ipfw pipe 1 config mask src-ip 0x000000ff bw 200Kbit/s queue 20Kbytes"
2528.Dl "ipfw pipe 2 config mask dst-ip 0x000000ff bw 200Kbit/s queue 20Kbytes"
2529.Ss LOOKUP TABLES
2530In the following example, we need to create several traffic bandwidth
2531classes and we need different hosts/networks to fall into different classes.
2532We create one pipe for each class and configure them accordingly.
2533Then we create a single table and fill it with IP subnets and addresses.
2534For each subnet/host we set the argument equal to the number of the pipe
2535that it should use.
2536Then we classify traffic using a single rule:
2537.Pp
2538.Dl "ipfw pipe 1 config bw 1000Kbyte/s"
2539.Dl "ipfw pipe 4 config bw 4000Kbyte/s"
2540.Dl "..."
2541.Dl "ipfw table 1 add 192.168.2.0/24 1"
2542.Dl "ipfw table 1 add 192.168.0.0/27 4"
2543.Dl "ipfw table 1 add 192.168.0.2 1"
2544.Dl "..."
2545.Dl "ipfw add pipe tablearg ip from table(1) to any"
2546.Pp
2547Using the
2548.Cm fwd
2549action, the table entries may include hostnames and IP addresses.
2550.Pp
2551.Dl "ipfw table 1 add 192.168.2.0/24 10.23.2.1"
2552.Dl "ipfw table 1 add 192.168.0.0/27 router1.dmz"
2553.Dl "..."
2554.Dl "ipfw add 100 fwd tablearg ip from any to table(1)"
2555.Ss SETS OF RULES
2556To add a set of rules atomically, e.g.\& set 18:
2557.Pp
2558.Dl "ipfw set disable 18"
2559.Dl "ipfw add NN set 18 ...         # repeat as needed"
2560.Dl "ipfw set enable 18"
2561.Pp
2562To delete a set of rules atomically the command is simply:
2563.Pp
2564.Dl "ipfw delete set 18"
2565.Pp
2566To test a ruleset and disable it and regain control if something goes wrong:
2567.Pp
2568.Dl "ipfw set disable 18"
2569.Dl "ipfw add NN set 18 ...         # repeat as needed"
2570.Dl "ipfw set enable 18; echo done; sleep 30 && ipfw set disable 18"
2571.Pp
2572Here if everything goes well, you press control-C before the "sleep"
2573terminates, and your ruleset will be left active.
2574Otherwise, e.g.\& if
2575you cannot access your box, the ruleset will be disabled after
2576the sleep terminates thus restoring the previous situation.
2577.Pp
2578To show rules of the specific set:
2579.Pp
2580.Dl "ipfw set 18 show"
2581.Pp
2582To show rules of the disabled set:
2583.Pp
2584.Dl "ipfw -S set 18 show"
2585.Pp
2586To clear a specific rule counters of the specific set:
2587.Pp
2588.Dl "ipfw set 18 zero NN"
2589.Pp
2590To delete a specific rule of the specific set:
2591.Pp
2592.Dl "ipfw set 18 delete NN"
2593.Ss NAT, REDIRECT AND LSNAT
2594First redirect all the traffic to nat instance 123:
2595.Pp
2596.Dl "ipfw add nat 123 all from any to any"
2597.Pp
2598Then to configure nat instance 123 to alias all the outgoing traffic with ip
2599192.168.0.123, blocking all incoming connections, trying to keep
2600same ports on both sides, clearing aliasing table on address change
2601and keeping a log of traffic/link statistics:
2602.Pp
2603.Dl "ipfw nat 123 config ip 192.168.0.123 log deny_in reset same_ports"
2604.Pp
2605Or to change address of instance 123, aliasing table will be cleared (see
2606reset option):
2607.Pp
2608.Dl "ipfw nat 123 config ip 10.0.0.1"
2609.Pp
2610To see configuration of nat instance 123:
2611.Pp
2612.Dl "ipfw nat 123 show config"
2613.Pp
2614To show logs of all the instances in range 111-999:
2615.Pp
2616.Dl "ipfw nat 111-999 show"
2617.Pp
2618To see configurations of all instances:
2619.Pp
2620.Dl "ipfw nat show config"
2621.Pp
2622Or a redirect rule with mixed modes could looks like:
2623.Pp
2624.Dl "ipfw nat 123 config redirect_addr 10.0.0.1 10.0.0.66"
2625.Dl "			 redirect_port tcp 192.168.0.1:80 500"
2626.Dl "			 redirect_proto udp 192.168.1.43 192.168.1.1"
2627.Dl "			 redirect_addr 192.168.0.10,192.168.0.11"
2628.Dl "			 	    10.0.0.100	# LSNAT"
2629.Dl "			 redirect_port tcp 192.168.0.1:80,192.168.0.10:22"
2630.Dl "			 	    500		# LSNAT"
2631.Pp
2632or it could be splitted in:
2633.Pp
2634.Dl "ipfw nat 1 config redirect_addr 10.0.0.1 10.0.0.66"
2635.Dl "ipfw nat 2 config redirect_port tcp 192.168.0.1:80 500"
2636.Dl "ipfw nat 3 config redirect_proto udp 192.168.1.43 192.168.1.1"
2637.Dl "ipfw nat 4 config redirect_addr 192.168.0.10,192.168.0.11,192.168.0.12"
2638.Dl "				         10.0.0.100"
2639.Dl "ipfw nat 5 config redirect_port tcp"
2640.Dl "			192.168.0.1:80,192.168.0.10:22,192.168.0.20:25 500"
2641.Pp
2642.Sh SEE ALSO
2643.Xr cpp 1 ,
2644.Xr m4 1 ,
2645.Xr altq 4 ,
2646.Xr divert 4 ,
2647.Xr dummynet 4 ,
2648.Xr if_bridge 4 ,
2649.Xr ip 4 ,
2650.Xr ipfirewall 4 ,
2651.Xr ng_ipfw 4 ,
2652.Xr protocols 5 ,
2653.Xr services 5 ,
2654.Xr init 8 ,
2655.Xr kldload 8 ,
2656.Xr reboot 8 ,
2657.Xr sysctl 8 ,
2658.Xr syslogd 8
2659.Sh HISTORY
2660The
2661.Nm
2662utility first appeared in
2663.Fx 2.0 .
2664.Nm dummynet
2665was introduced in
2666.Fx 2.2.8 .
2667Stateful extensions were introduced in
2668.Fx 4.0 .
2669.Nm ipfw2
2670was introduced in Summer 2002.
2671.Sh AUTHORS
2672.An Ugen J. S. Antsilevich ,
2673.An Poul-Henning Kamp ,
2674.An Alex Nash ,
2675.An Archie Cobbs ,
2676.An Luigi Rizzo .
2677.Pp
2678.An -nosplit
2679API based upon code written by
2680.An Daniel Boulet
2681for BSDI.
2682.Pp
2683.An -nosplit
2684In-kernel NAT support written by
2685.An Paolo Pisati Aq piso@FreeBSD.org
2686as part of a Summer of Code 2005 project.
2687.Pp
2688Work on
2689.Nm dummynet
2690traffic shaper supported by Akamba Corp.
2691.Sh BUGS
2692The syntax has grown over the years and sometimes it might be confusing.
2693Unfortunately, backward compatibility prevents cleaning up mistakes
2694made in the definition of the syntax.
2695.Pp
2696.Em !!! WARNING !!!
2697.Pp
2698Misconfiguring the firewall can put your computer in an unusable state,
2699possibly shutting down network services and requiring console access to
2700regain control of it.
2701.Pp
2702Incoming packet fragments diverted by
2703.Cm divert
2704are reassembled before delivery to the socket.
2705The action used on those packet is the one from the
2706rule which matches the first fragment of the packet.
2707.Pp
2708Packets diverted to userland, and then reinserted by a userland process
2709may lose various packet attributes.
2710The packet source interface name
2711will be preserved if it is shorter than 8 bytes and the userland process
2712saves and reuses the sockaddr_in
2713(as does
2714.Xr natd 8 ) ;
2715otherwise, it may be lost.
2716If a packet is reinserted in this manner, later rules may be incorrectly
2717applied, making the order of
2718.Cm divert
2719rules in the rule sequence very important.
2720.Pp
2721Dummynet drops all packets with IPv6 link-local addresses.
2722.Pp
2723Rules using
2724.Cm uid
2725or
2726.Cm gid
2727may not behave as expected.
2728In particular, incoming SYN packets may
2729have no uid or gid associated with them since they do not yet belong
2730to a TCP connection, and the uid/gid associated with a packet may not
2731be as expected if the associated process calls
2732.Xr setuid 2
2733or similar system calls.
2734.Pp
2735Rule syntax is subject to the command line environment and some patterns
2736may need to be escaped with the backslash character
2737or quoted appropriately.
2738.Pp
2739Due to the architecture of
2740.Xr libalias 3 ,
2741ipfw nat is not compatible with the tcp segmentation offloading
2742(TSO). Thus, to reliably nat your network traffic, please disable TSO
2743on your NICs using
2744.Xr ifconfig 8 .
2745.Pp
2746ICMP error messages are not implicitly matched by dynamic rules
2747for the respective conversations.
2748To avoid failures of network error detection and path MTU discovery,
2749ICMP error messages may need to be allowed explicitly through static
2750rules.
2751