1 '\" te
2 .\" To view license terms, attribution, and copyright for IP Filter, the
3 .\" default path is /usr/lib/ipf/IPFILTER.LICENCE. If the Illumos operating
4 .\" environment has been installed anywhere other than the default, modify the
5 .\" given path to access the file at the installed location.
6 .\" Portions Copyright (c) 2015, Joyent, Inc.
7 .TH IPF 4 "Mar 18, 2015"
8 .SH NAME
9 ipf, ipf.conf, ipf6.conf \- IP packet filter rule syntax
10 .SH DESCRIPTION
11 .PP
12 A rule file for \fBipf\fP may have any name or even be stdin. As
13 \fBipfstat\fP produces parsable rules as output when displaying the internal
14 kernel filter lists, it is quite plausible to use its output to feed back
15 into \fBipf\fP. Thus, to remove all filters on input packets, the following
16 could be done:
17 .nf
18
19 \fC# ipfstat \-i | ipf \-rf \-\fP
20 .fi
21 .SH GRAMMAR
22 .PP
23 The format used by \fBipf\fP for construction of filtering rules can be
24 described using the following grammar in BNF:
25 \fC
26 .nf
27 filter-rule = [ insert ] action in-out [ options ] [ tos ] [ ttl ]
28 [ proto ] ip [ group ].
29
30 insert = "@" decnumber .
31 action = block | "pass" | log | "count" | skip | auth | call .
32 in-out = "in" | "out" .
33 options = [ log ] [ tag ] [ "quick" ] [ "on" interface-name [ dup ]
34 [ froute ] [ replyto ] ] .
35 tos = "tos" decnumber | "tos" hexnumber .
36 ttl = "ttl" decnumber .
37 proto = "proto" protocol .
38 ip = srcdst [ flags ] [ with withopt ] [ icmp ] [ keep ] .
39 group = [ "head" decnumber ] [ "group" decnumber ] .
40
41 block = "block" [ return-icmp[return-code] | "return-rst" ] .
42 log = "log" [ "body" ] [ "first" ] [ "or-block" ] [ "level" loglevel ] .
43 tag = "tag" tagid .
44 skip = "skip" decnumber .
45 auth = "auth" | "preauth" .
98 "local3" | "local4" | "local5" | "local6" | "local7" .
99 priority = "emerg" | "alert" | "crit" | "err" | "warn" | "notice" |
100 "info" | "debug" .
101
102 hexnumber = "0" "x" hexstring .
103 hexstring = hexdigit [ hexstring ] .
104 decnumber = digit [ decnumber ] .
105
106 compare = "=" | "!=" | "<" | ">" | "<=" | ">=" | "eq" | "ne" | "lt" |
107 "gt" | "le" | "ge" .
108 range = "<>" | "><" .
109 hexdigit = digit | "a" | "b" | "c" | "d" | "e" | "f" .
110 digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" .
111 flag = "F" | "S" | "R" | "P" | "A" | "U" .
112 .fi
113 .PP
114 This syntax is somewhat simplified for readability, some combinations
115 that match this grammar are disallowed by the software because they do
116 not make sense (such as tcp \fBflags\fP for non-TCP packets).
117 .SH FILTER RULES
118 .PP
119 The "briefest" valid rules are (currently) no-ops and are of the form:
120 .nf
121 block in all
122 pass in all
123 log out all
124 count in all
125 .fi
126 .PP
127 Filter rules are checked in order, with the last matching rule
128 determining the fate of the packet (but see the \fBquick\fP option,
129 below).
130 .PP
131 Filters are installed by default at the end of the kernel's filter
132 lists, prepending the rule with \fB@n\fP will cause it to be inserted
133 as the n'th entry in the current list. This is especially useful when
134 modifying and testing active filter rulesets. See \fBipf\fP(1M) for more
135 information.
136 .SH ACTIONS
137 .PP
138 The action indicates what to do with the packet if it matches the rest
139 of the filter rule. Each rule MUST have an action. The following
140 actions are recognised:
141 .TP
142 .B block
143 indicates that the packet should be flagged to be dropped. In response
144 to blocking a packet, the filter may be instructed to send a reply
145 packet, either an ICMP packet (\fBreturn-icmp\fP), an ICMP packet
146 masquerading as being from the original packet's destination
147 (\fBreturn-icmp-as-dest\fP), or a TCP "reset" (\fBreturn-rst\fP). An
148 ICMP packet may be generated in response to any IP packet, and its
149 type may optionally be specified, but a TCP reset may only be used
150 with a rule which is being applied to TCP packets. When using
151 \fBreturn-icmp\fP or \fBreturn-icmp-as-dest\fP, it is possible to specify
152 the actual unreachable `type'. That is, whether it is a network
153 unreachable, port unreachable or even administratively
154 prohibited. This is done by enclosing the ICMP code associated with
155 it in parenthesis directly following \fBreturn-icmp\fP or
156 \fBreturn-icmp-as-dest\fP as follows:
157 .nf
193 or not. Such a program might look at the source address and request some sort
194 of authentication from the user (such as a password) before allowing the
195 packet through or telling the kernel to drop it if from an unrecognised source.
196 .TP
197 .B preauth
198 tells the filter that for packets of this class, it should look in the
199 pre-authenticated list for further clarification. If no further matching
200 rule is found, the packet will be dropped (the FR_PREAUTH is not the same
201 as FR_PASS). If a further matching rule is found, the result from that is
202 used in its instead. This might be used in a situation where a person
203 \fIlogs in\fP to the firewall and it sets up some temporary rules defining
204 the access for that person.
205 .PP
206 The next word must be either \fBin\fP or \fBout\fP. Each packet
207 moving through the kernel is either inbound (just been received on an
208 interface, and moving towards the kernel's protocol processing) or
209 outbound (transmitted or forwarded by the stack, and on its way to an
210 interface). There is a requirement that each filter rule explicitly
211 state which side of the I/O it is to be used on.
212 .SH OPTIONS
213 .PP
214 The list of options is brief, and all are indeed optional. Where
215 options are used, they must be present in the order shown here. These
216 are the currently supported options:
217 .TP
218 .B log
219 indicates that, should this be the last matching rule, the packet
220 header will be written to the \fBipl\fP log (as described in the
221 LOGGING section below).
222 .TP
223 .B tag tagid
224 indicates that, if this rule causes the packet to be logged or entered
225 in the state table, the tagid will be logged as part of the log entry.
226 This can be used to quickly match "similar" rules in scripts that post
227 process the log files for e.g. generation of security reports or accounting
228 purposes. The tagid is a 32 bit unsigned integer.
229 .TP
230 .B quick
231 allows "short-cut" rules in order to speed up the filter or override
232 later rules. If a packet matches a filter rule which is marked as
233 \fBquick\fP, this rule will be the last rule checked, allowing a
252 This option is especially useful for simple IP-spoofing protection:
253 packets should only be allowed to pass inbound on the interface from
254 which the specified source address would be expected, others may be
255 logged and/or dropped.
256 .TP
257 .B dup-to
258 causes the packet to be copied, and the duplicate packet to be sent
259 outbound on the specified interface, optionally with the destination
260 IP address changed to that specified. This is useful for off-host
261 logging, using a network sniffer.
262 .TP
263 .B to
264 causes the packet to be moved to the outbound queue on the
265 specified interface. This can be used to circumvent kernel routing
266 decisions, and even to bypass the rest of the kernel processing of the
267 packet (if applied to an inbound rule). It is thus possible to
268 construct a firewall that behaves transparently, like a filtering hub
269 or switch, rather than a router. The \fBfastroute\fP keyword is a
270 synonym for this option.
271 .SH MATCHING PARAMETERS
272 .PP
273 The keywords described in this section are used to describe attributes
274 of the packet to be used when determining whether rules match or don't
275 match. The following general-purpose attributes are provided for
276 matching, and must be used in this order:
277 .TP
278 .B tos
279 packets with different Type-Of-Service values can be filtered.
280 Individual service levels or combinations can be filtered upon. The
281 value for the TOS mask can either be represented as a hex number or a
282 decimal integer value.
283 .TP
284 .B ttl
285 packets may also be selected by their Time-To-Live value. The value given in
286 the filter rule must exactly match that in the packet for a match to occur.
287 This value can only be given as a decimal integer value.
288 .TP
289 .B proto
290 allows a specific protocol to be matched against. All protocol names
291 found in \fB/etc/protocols\fP are recognised and may be used.
292 However, the protocol may also be given as a DECIMAL number, allowing
396 # packets with ONLY the SYN flag set.
397
398 ... flags SA
399 # becomes "flags SA/AUPRFS" and will match any
400 # packet with only the SYN and ACK flags set.
401
402 ... flags S/SA
403 # will match any packet with just the SYN flag set
404 # out of the SYN-ACK pair; the common "establish"
405 # keyword action. "S/SA" will NOT match a packet
406 # with BOTH SYN and ACK set, but WILL match "SFP".
407 .fi
408 .TP
409 .B icmp-type
410 is only effective when used with \fBproto icmp\fP and must NOT be used
411 in conjunction with \fBflags\fP. There are a number of types, which can be
412 referred to by an abbreviation recognised by this language, or the numbers
413 with which they are associated can be used. The most important from
414 a security point of view is the ICMP redirect.
415 .SH KEEP HISTORY
416 .PP
417 The second last parameter which can be set for a filter rule is whether or not
418 to record historical information for that packet, and what sort to keep. The
419 following information can be kept:
420 .TP
421 .B state
422 keeps information about the flow of a communication session. State can
423 be kept for TCP, UDP, and ICMP packets.
424 .TP
425 .B frags
426 keeps information on fragmented packets, to be applied to later
427 fragments.
428 .PP
429 allowing packets which match these to flow straight through, rather
430 than going through the access control list.
431 .SH GROUPS
432 The last pair of parameters control filter rule "grouping". By default, all
433 filter rules are placed in group 0 if no other group is specified. To add a
434 rule to a non-default group, the group must first be started by creating a
435 group \fIhead\fP. If a packet matches a rule which is the \fIhead\fP of a
436 group, the filter processing then switches to the group, using that rule as
437 the default for the group. If \fBquick\fP is used with a \fBhead\fP rule, rule
438 processing isn't stopped until it has returned from processing the group.
439 .PP
440 A rule may be both the head for a new group and a member of a non-default
441 group (\fBhead\fP and \fBgroup\fP may be used together in a rule).
442 .TP
443 .B "head <n>"
444 indicates that a new group (number n) should be created.
445 .TP
446 .B "group <n>"
447 indicates that the rule should be put in group (number n) rather than group 0.
448 .SH LOGGING
449 .PP
450 When a packet is logged, with either the \fBlog\fP action or option,
451 the headers of the packet are written to the \fBipl\fP packet logging
452 pseudo-device. Immediately following the \fBlog\fP keyword, the
453 following qualifiers may be used (in order):
454 .TP
455 .B body
456 indicates that the first 128 bytes of the packet contents will be
457 logged after the headers.
458 .TP
459 .B first
460 If log is being used in conjunction with a "keep" option, it is recommended
461 that this option is also applied so that only the triggering packet is logged
462 and not every packet which thereafter matches state information.
463 .TP
464 .B or-block
465 indicates that, if for some reason the filter is unable to log the
466 packet (such as the log reader being too slow) then the rule should be
467 interpreted as if the action was \fBblock\fP for this packet.
468 .TP
469 .B "level <loglevel>"
470 indicates what logging facility and priority, or just priority with
471 the default facility being used, will be used to log information about
472 this packet using ipmon's -s option.
473 .PP
474 See ipl(4) for the format of records written
475 to this device. The ipmon(1M) program can be used to read and format
476 this log.
477 .SH EXAMPLES
478 .PP
479 The \fBquick\fP option is good for rules such as:
480 \fC
481 .nf
482 block in quick from any to any with ipopts
483 .fi
484 .PP
485 which will match any packet with a non-standard header length (IP
486 options present) and abort further processing of later rules,
487 recording a match and also that the packet should be blocked.
488 .PP
489 The "fall-through" rule parsing allows for effects such as this:
490 .LP
491 .nf
492 block in from any to any port < 6000
493 pass in from any to any port >= 6000
494 block in from any to any port > 6003
495 .fi
496 .PP
497 which sets up the range 6000-6003 as being permitted and all others being
498 denied. Note that the effect of the first rule is overridden by subsequent
499 rules. Another (easier) way to do the same is:
500 .LP
506 Note that both the "block" and "pass" are needed here to effect a
507 result as a failed match on the "block" action does not imply a pass,
508 only that the rule hasn't taken effect. To then allow ports < 1024, a
509 rule such as:
510 .LP
511 .nf
512 pass in quick from any to any port < 1024
513 .fi
514 .PP
515 would be needed before the first block. To create a new group for
516 processing all inbound packets on le0/le1/lo0, with the default being to block
517 all inbound packets, we would do something like:
518 .LP
519 .nf
520 block in all
521 block in quick on le0 all head 100
522 block in quick on le1 all head 200
523 block in quick on lo0 all head 300
524 .fi
525 .PP
526
527 and to then allow ICMP packets in on le0, only, we would do:
528 .LP
529 .nf
530 pass in proto icmp all group 100
531 .fi
532 .PP
533 Note that because only inbound packets on le0 are used processed by group 100,
534 there is no need to respecify the interface name. Likewise, we could further
535 breakup processing of TCP, etc, as follows:
536 .LP
537 .nf
538 block in proto tcp all head 110 group 100
539 pass in from any to any port = 23 group 110
540 .fi
541 .PP
542 and so on. The last line, if written without the groups would be:
543 .LP
544 .nf
545 pass in on le0 proto tcp from any to any port = telnet
546 .fi
|
1 '\" te
2 .\" To view license terms, attribution, and copyright for IP Filter, the
3 .\" default path is /usr/lib/ipf/IPFILTER.LICENCE. If the illumos operating
4 .\" environment has been installed anywhere other than the default, modify the
5 .\" given path to access the file at the installed location.
6 .\" Portions Copyright (c) 2015, Joyent, Inc.
7 .TH IPF 4 "Mar 18, 2015"
8 .SH NAME
9 ipf, ipf.conf, ipf6.conf \- IP packet filter rule syntax
10 .SH DESCRIPTION
11 A rule file for \fBipf\fP may have any name or even be stdin. As
12 \fBipfstat\fP produces parsable rules as output when displaying the internal
13 kernel filter lists, it is quite plausible to use its output to feed back
14 into \fBipf\fP. Thus, to remove all filters on input packets, the following
15 could be done:
16 .nf
17
18 # ipfstat \-i | ipf \-rf \-\fP
19 .fi
20 .SH GRAMMAR
21 The format used by \fBipf\fP for construction of filtering rules can be
22 described using the following grammar in BNF:
23 .nf
24 filter-rule = [ insert ] action in-out [ options ] [ tos ] [ ttl ]
25 [ proto ] ip [ group ].
26
27 insert = "@" decnumber .
28 action = block | "pass" | log | "count" | skip | auth | call .
29 in-out = "in" | "out" .
30 options = [ log ] [ tag ] [ "quick" ] [ "on" interface-name [ dup ]
31 [ froute ] [ replyto ] ] .
32 tos = "tos" decnumber | "tos" hexnumber .
33 ttl = "ttl" decnumber .
34 proto = "proto" protocol .
35 ip = srcdst [ flags ] [ with withopt ] [ icmp ] [ keep ] .
36 group = [ "head" decnumber ] [ "group" decnumber ] .
37
38 block = "block" [ return-icmp[return-code] | "return-rst" ] .
39 log = "log" [ "body" ] [ "first" ] [ "or-block" ] [ "level" loglevel ] .
40 tag = "tag" tagid .
41 skip = "skip" decnumber .
42 auth = "auth" | "preauth" .
95 "local3" | "local4" | "local5" | "local6" | "local7" .
96 priority = "emerg" | "alert" | "crit" | "err" | "warn" | "notice" |
97 "info" | "debug" .
98
99 hexnumber = "0" "x" hexstring .
100 hexstring = hexdigit [ hexstring ] .
101 decnumber = digit [ decnumber ] .
102
103 compare = "=" | "!=" | "<" | ">" | "<=" | ">=" | "eq" | "ne" | "lt" |
104 "gt" | "le" | "ge" .
105 range = "<>" | "><" .
106 hexdigit = digit | "a" | "b" | "c" | "d" | "e" | "f" .
107 digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" .
108 flag = "F" | "S" | "R" | "P" | "A" | "U" .
109 .fi
110 .PP
111 This syntax is somewhat simplified for readability, some combinations
112 that match this grammar are disallowed by the software because they do
113 not make sense (such as tcp \fBflags\fP for non-TCP packets).
114 .SH FILTER RULES
115 The "briefest" valid rules are (currently) no-ops and are of the form:
116 .nf
117 block in all
118 pass in all
119 log out all
120 count in all
121 .fi
122 .PP
123 Filter rules are checked in order, with the last matching rule
124 determining the fate of the packet (but see the \fBquick\fP option,
125 below).
126 .PP
127 Filters are installed by default at the end of the kernel's filter
128 lists, prepending the rule with \fB@n\fP will cause it to be inserted
129 as the n'th entry in the current list. This is especially useful when
130 modifying and testing active filter rulesets. See \fBipf\fP(1M) for more
131 information.
132 .SH ACTIONS
133 The action indicates what to do with the packet if it matches the rest
134 of the filter rule. Each rule MUST have an action. The following
135 actions are recognised:
136 .TP
137 .B block
138 indicates that the packet should be flagged to be dropped. In response
139 to blocking a packet, the filter may be instructed to send a reply
140 packet, either an ICMP packet (\fBreturn-icmp\fP), an ICMP packet
141 masquerading as being from the original packet's destination
142 (\fBreturn-icmp-as-dest\fP), or a TCP "reset" (\fBreturn-rst\fP). An
143 ICMP packet may be generated in response to any IP packet, and its
144 type may optionally be specified, but a TCP reset may only be used
145 with a rule which is being applied to TCP packets. When using
146 \fBreturn-icmp\fP or \fBreturn-icmp-as-dest\fP, it is possible to specify
147 the actual unreachable `type'. That is, whether it is a network
148 unreachable, port unreachable or even administratively
149 prohibited. This is done by enclosing the ICMP code associated with
150 it in parenthesis directly following \fBreturn-icmp\fP or
151 \fBreturn-icmp-as-dest\fP as follows:
152 .nf
188 or not. Such a program might look at the source address and request some sort
189 of authentication from the user (such as a password) before allowing the
190 packet through or telling the kernel to drop it if from an unrecognised source.
191 .TP
192 .B preauth
193 tells the filter that for packets of this class, it should look in the
194 pre-authenticated list for further clarification. If no further matching
195 rule is found, the packet will be dropped (the FR_PREAUTH is not the same
196 as FR_PASS). If a further matching rule is found, the result from that is
197 used in its instead. This might be used in a situation where a person
198 \fIlogs in\fP to the firewall and it sets up some temporary rules defining
199 the access for that person.
200 .PP
201 The next word must be either \fBin\fP or \fBout\fP. Each packet
202 moving through the kernel is either inbound (just been received on an
203 interface, and moving towards the kernel's protocol processing) or
204 outbound (transmitted or forwarded by the stack, and on its way to an
205 interface). There is a requirement that each filter rule explicitly
206 state which side of the I/O it is to be used on.
207 .SH OPTIONS
208 The list of options is brief, and all are indeed optional. Where
209 options are used, they must be present in the order shown here. These
210 are the currently supported options:
211 .TP
212 .B log
213 indicates that, should this be the last matching rule, the packet
214 header will be written to the \fBipl\fP log (as described in the
215 LOGGING section below).
216 .TP
217 .B tag tagid
218 indicates that, if this rule causes the packet to be logged or entered
219 in the state table, the tagid will be logged as part of the log entry.
220 This can be used to quickly match "similar" rules in scripts that post
221 process the log files for e.g. generation of security reports or accounting
222 purposes. The tagid is a 32 bit unsigned integer.
223 .TP
224 .B quick
225 allows "short-cut" rules in order to speed up the filter or override
226 later rules. If a packet matches a filter rule which is marked as
227 \fBquick\fP, this rule will be the last rule checked, allowing a
246 This option is especially useful for simple IP-spoofing protection:
247 packets should only be allowed to pass inbound on the interface from
248 which the specified source address would be expected, others may be
249 logged and/or dropped.
250 .TP
251 .B dup-to
252 causes the packet to be copied, and the duplicate packet to be sent
253 outbound on the specified interface, optionally with the destination
254 IP address changed to that specified. This is useful for off-host
255 logging, using a network sniffer.
256 .TP
257 .B to
258 causes the packet to be moved to the outbound queue on the
259 specified interface. This can be used to circumvent kernel routing
260 decisions, and even to bypass the rest of the kernel processing of the
261 packet (if applied to an inbound rule). It is thus possible to
262 construct a firewall that behaves transparently, like a filtering hub
263 or switch, rather than a router. The \fBfastroute\fP keyword is a
264 synonym for this option.
265 .SH MATCHING PARAMETERS
266 The keywords described in this section are used to describe attributes
267 of the packet to be used when determining whether rules match or don't
268 match. The following general-purpose attributes are provided for
269 matching, and must be used in this order:
270 .TP
271 .B tos
272 packets with different Type-Of-Service values can be filtered.
273 Individual service levels or combinations can be filtered upon. The
274 value for the TOS mask can either be represented as a hex number or a
275 decimal integer value.
276 .TP
277 .B ttl
278 packets may also be selected by their Time-To-Live value. The value given in
279 the filter rule must exactly match that in the packet for a match to occur.
280 This value can only be given as a decimal integer value.
281 .TP
282 .B proto
283 allows a specific protocol to be matched against. All protocol names
284 found in \fB/etc/protocols\fP are recognised and may be used.
285 However, the protocol may also be given as a DECIMAL number, allowing
389 # packets with ONLY the SYN flag set.
390
391 ... flags SA
392 # becomes "flags SA/AUPRFS" and will match any
393 # packet with only the SYN and ACK flags set.
394
395 ... flags S/SA
396 # will match any packet with just the SYN flag set
397 # out of the SYN-ACK pair; the common "establish"
398 # keyword action. "S/SA" will NOT match a packet
399 # with BOTH SYN and ACK set, but WILL match "SFP".
400 .fi
401 .TP
402 .B icmp-type
403 is only effective when used with \fBproto icmp\fP and must NOT be used
404 in conjunction with \fBflags\fP. There are a number of types, which can be
405 referred to by an abbreviation recognised by this language, or the numbers
406 with which they are associated can be used. The most important from
407 a security point of view is the ICMP redirect.
408 .SH KEEP HISTORY
409 The second last parameter which can be set for a filter rule is whether or not
410 to record historical information for that packet, and what sort to keep. The
411 following information can be kept:
412 .TP
413 .B state
414 keeps information about the flow of a communication session. State can
415 be kept for TCP, UDP, and ICMP packets.
416 .TP
417 .B frags
418 keeps information on fragmented packets, to be applied to later
419 fragments.
420 .PP
421 allowing packets which match these to flow straight through, rather
422 than going through the access control list.
423 .SH GROUPS
424 The last pair of parameters control filter rule "grouping". By default, all
425 filter rules are placed in group 0 if no other group is specified. To add a
426 rule to a non-default group, the group must first be started by creating a
427 group \fIhead\fP. If a packet matches a rule which is the \fIhead\fP of a
428 group, the filter processing then switches to the group, using that rule as
429 the default for the group. If \fBquick\fP is used with a \fBhead\fP rule, rule
430 processing isn't stopped until it has returned from processing the group.
431 .PP
432 A rule may be both the head for a new group and a member of a non-default
433 group (\fBhead\fP and \fBgroup\fP may be used together in a rule).
434 .TP
435 .B "head <n>"
436 indicates that a new group (number n) should be created.
437 .TP
438 .B "group <n>"
439 indicates that the rule should be put in group (number n) rather than group 0.
440 .SH LOGGING
441 When a packet is logged, with either the \fBlog\fP action or option,
442 the headers of the packet are written to the \fBipl\fP packet logging
443 pseudo-device. Immediately following the \fBlog\fP keyword, the
444 following qualifiers may be used (in order):
445 .TP
446 .B body
447 indicates that the first 128 bytes of the packet contents will be
448 logged after the headers.
449 .TP
450 .B first
451 If log is being used in conjunction with a "keep" option, it is recommended
452 that this option is also applied so that only the triggering packet is logged
453 and not every packet which thereafter matches state information.
454 .TP
455 .B or-block
456 indicates that, if for some reason the filter is unable to log the
457 packet (such as the log reader being too slow) then the rule should be
458 interpreted as if the action was \fBblock\fP for this packet.
459 .TP
460 .B "level <loglevel>"
461 indicates what logging facility and priority, or just priority with
462 the default facility being used, will be used to log information about
463 this packet using ipmon's -s option.
464 .PP
465 See ipl(4) for the format of records written
466 to this device. The ipmon(1M) program can be used to read and format
467 this log.
468 .SH EXAMPLES
469 The \fBquick\fP option is good for rules such as:
470 .nf
471 block in quick from any to any with ipopts
472 .fi
473 .PP
474 which will match any packet with a non-standard header length (IP
475 options present) and abort further processing of later rules,
476 recording a match and also that the packet should be blocked.
477 .PP
478 The "fall-through" rule parsing allows for effects such as this:
479 .LP
480 .nf
481 block in from any to any port < 6000
482 pass in from any to any port >= 6000
483 block in from any to any port > 6003
484 .fi
485 .PP
486 which sets up the range 6000-6003 as being permitted and all others being
487 denied. Note that the effect of the first rule is overridden by subsequent
488 rules. Another (easier) way to do the same is:
489 .LP
495 Note that both the "block" and "pass" are needed here to effect a
496 result as a failed match on the "block" action does not imply a pass,
497 only that the rule hasn't taken effect. To then allow ports < 1024, a
498 rule such as:
499 .LP
500 .nf
501 pass in quick from any to any port < 1024
502 .fi
503 .PP
504 would be needed before the first block. To create a new group for
505 processing all inbound packets on le0/le1/lo0, with the default being to block
506 all inbound packets, we would do something like:
507 .LP
508 .nf
509 block in all
510 block in quick on le0 all head 100
511 block in quick on le1 all head 200
512 block in quick on lo0 all head 300
513 .fi
514 .PP
515 and to then allow ICMP packets in on le0, only, we would do:
516 .LP
517 .nf
518 pass in proto icmp all group 100
519 .fi
520 .PP
521 Note that because only inbound packets on le0 are used processed by group 100,
522 there is no need to respecify the interface name. Likewise, we could further
523 breakup processing of TCP, etc, as follows:
524 .LP
525 .nf
526 block in proto tcp all head 110 group 100
527 pass in from any to any port = 23 group 110
528 .fi
529 .PP
530 and so on. The last line, if written without the groups would be:
531 .LP
532 .nf
533 pass in on le0 proto tcp from any to any port = telnet
534 .fi
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