1IP6TABLES(8) IP6TABLES(8)
2
6 ip6tables - IPv6 packet filter administration
7
9 ip6tables [-t table] -[AD] chain rule-specification [options]
10 ip6tables [-t table] -I chain [rulenum] rule-specification [options]
11 ip6tables [-t table] -R chain rulenum rule-specification [options]
12 ip6tables [-t table] -D chain rulenum [options]
13 ip6tables [-t table] -[LFZ] [chain] [options]
14 ip6tables [-t table] -N chain
15 ip6tables [-t table] -X [chain]
16 ip6tables [-t table] -P chain target [options]
17 ip6tables [-t table] -E old-chain-name new-chain-name
18
20 Ip6tables is used to set up, maintain, and inspect the tables of IPv6
21 packet filter rules in the Linux kernel. Several different tables may
22 be defined. Each table contains a number of built-in chains and may
23 also contain user-defined chains.
24 Each chain is a list of rules which can match a set of packets. Each
26 rule specifies what to do with a packet that matches. This is called a
27 `target', which may be a jump to a user-defined chain in the same ta‐
28 ble.
29
32 A firewall rule specifies criteria for a packet, and a target. If the
33 packet does not match, the next rule in the chain is the examined; if
34 it does match, then the next rule is specified by the value of the tar‐
35 get, which can be the name of a user-defined chain or one of the spe‐
36 cial values ACCEPT, DROP, QUEUE, or RETURN.
37 ACCEPT means to let the packet through. DROP means to drop the packet
39 on the floor. QUEUE means to pass the packet to userspace. (How the
40 packet can be received by a userspace process differs by the particular
41 queue handler. 2.4.x and 2.6.x kernels up to 2.6.13 include the
42 ip_queue queue handler. Kernels 2.6.14 and later additionally include
43 the nfnetlink_queue queue handler. Packets with a target of QUEUE will
44 be sent to queue number '0' in this case. Please also see the NFQUEUE
45 target as described later in this man page.) RETURN means stop
46 traversing this chain and resume at the next rule in the previous
47 (calling) chain. If the end of a built-in chain is reached or a rule
48 in a built-in chain with target RETURN is matched, the target specified
49 by the chain policy determines the fate of the packet.
50
52 There are currently two independent tables (which tables are present at
53 any time depends on the kernel configuration options and which modules
54 are present), as nat table has not been implemented yet.
55 -t, --table table
57 This option specifies the packet matching table which the com‐
58 mand should operate on. If the kernel is configured with auto‐
59 matic module loading, an attempt will be made to load the appro‐
60 priate module for that table if it is not already there.
61 The tables are as follows:
63 filter:
65 This is the default table (if no -t option is passed). It
66 contains the built-in chains INPUT (for packets coming into
67 the box itself), FORWARD (for packets being routed through
68 the box), and OUTPUT (for locally-generated packets).
69 mangle:
71 This table is used for specialized packet alteration. Until
72 kernel 2.4.17 it had two built-in chains: PREROUTING (for
73 altering incoming packets before routing) and OUTPUT (for
74 altering locally-generated packets before routing). Since
75 kernel 2.4.18, three other built-in chains are also sup‐
76 ported: INPUT (for packets coming into the box itself), FOR‐
77 WARD (for altering packets being routed through the box),
78 and POSTROUTING (for altering packets as they are about to
79 go out).
80 raw:
82 This table is used mainly for configuring exemptions from
83 connection tracking in combination with the NOTRACK target.
84 It registers at the netfilter hooks with higher priority and
85 is thus called before nf_conntrack, or any other IP6 tables.
86 It provides the following built-in chains: PREROUTING (for
87 packets arriving via any network interface) OUTPUT (for
88 packets generated by local processes)
89
91 The options that are recognized by ip6tables can be divided into sev‐
92 eral different groups.
93 COMMANDS
95 These options specify the specific action to perform. Only one of them
96 can be specified on the command line unless otherwise specified below.
97 For all the long versions of the command and option names, you need to
98 use only enough letters to ensure that ip6tables can differentiate it
99 from all other options.
100 -A, --append chain rule-specification
102 Append one or more rules to the end of the selected chain. When
103 the source and/or destination names resolve to more than one
104 address, a rule will be added for each possible address combina‐
105 tion.
106 -D, --delete chain rule-specification
108 -D, --delete chain rulenum
109 Delete one or more rules from the selected chain. There are two
110 versions of this command: the rule can be specified as a number
111 in the chain (starting at 1 for the first rule) or a rule to
112 match.
113 -I, --insert
115 Insert one or more rules in the selected chain as the given rule
116 number. So, if the rule number is 1, the rule or rules are
117 inserted at the head of the chain. This is also the default if
118 no rule number is specified.
119 -R, --replace chain rulenum rule-specification
121 Replace a rule in the selected chain. If the source and/or des‐
122 tination names resolve to multiple addresses, the command will
123 fail. Rules are numbered starting at 1.
124 -L, --list [chain]
126 List all rules in the selected chain. If no chain is selected,
127 all chains are listed. As every other iptables command, it
128 applies to the specified table (filter is the default), so man‐
129 gle rules get listed by
130 ip6tables -t mangle -n -L
131 Please note that it is often used with the -n option, in order
132 to avoid long reverse DNS lookups. It is legal to specify the
133 -Z (zero) option as well, in which case the chain(s) will be
134 atomically listed and zeroed. The exact output is affected by
135 the other arguments given. The exact rules are suppressed until
136 you use
137 ip6tables -L -v
138 -F, --flush [chain]
140 Flush the selected chain (all the chains in the table if none is
141 given). This is equivalent to deleting all the rules one by
142 one.
143 -Z, --zero [chain]
145 Zero the packet and byte counters in all chains. It is legal to
146 specify the -L, --list (list) option as well, to see the coun‐
147 ters immediately before they are cleared. (See above.)
148 -N, --new-chain chain
150 Create a new user-defined chain by the given name. There must
151 be no target of that name already.
152 -X, --delete-chain [chain]
154 Delete the optional user-defined chain specified. There must be
155 no references to the chain. If there are, you must delete or
156 replace the referring rules before the chain can be deleted. If
157 no argument is given, it will attempt to delete every non-
158 builtin chain in the table.
159 -P, --policy chain target
161 Set the policy for the chain to the given target. See the sec‐
162 tion TARGETS for the legal targets. Only built-in (non-user-
163 defined) chains can have policies, and neither built-in nor
164 user-defined chains can be policy targets.
165 -E, --rename-chain old-chain new-chain
167 Rename the user specified chain to the user supplied name. This
168 is cosmetic, and has no effect on the structure of the table.
169 -h Help. Give a (currently very brief) description of the command
171 syntax.
172 PARAMETERS
174 The following parameters make up a rule specification (as used in the
175 add, delete, insert, replace and append commands).
176 -p, --protocol [!] protocol
178 The protocol of the rule or of the packet to check. The speci‐
179 fied protocol can be one of tcp, udp, icmpv6, esp, all, or it
180 can be a numeric value, representing one of these protocols or a
181 different one. A protocol name from /etc/protocols is also
182 allowed. But IPv6 extension headers except esp are not allowed.
183 esp, and ipv6-nonext can be used with Kernel version 2.6.11 or
184 later. A "!" argument before the protocol inverts the test.
185 The number zero is equivalent to all. Protocol all will match
186 with all protocols and is taken as default when this option is
187 omitted.
188 -s, --source [!] address[/mask]
190 Source specification. Address can be either a hostname (please
191 note that specifying any name to be resolved with a remote query
192 such as DNS is a really bad idea), a network IPv6 address (with
193 /mask), or a plain IPv6 address. (the network name isn't sup‐
194 ported now). The mask can be either a network mask or a plain
195 number, specifying the number of 1's at the left side of the
196 network mask. Thus, a mask of 64 is equivalent to
197 ffff:ffff:ffff:ffff:0000:0000:0000:0000. A "!" argument before
198 the address specification inverts the sense of the address. The
199 flag --src is an alias for this option.
200 -d, --destination [!] address[/mask]
202 Destination specification. See the description of the -s
203 (source) flag for a detailed description of the syntax. The
204 flag --dst is an alias for this option.
205 -j, --jump target
207 This specifies the target of the rule; i.e., what to do if the
208 packet matches it. The target can be a user-defined chain
209 (other than the one this rule is in), one of the special builtin
210 targets which decide the fate of the packet immediately, or an
211 extension (see EXTENSIONS below). If this option is omitted in
212 a rule, then matching the rule will have no effect on the
213 packet's fate, but the counters on the rule will be incremented.
214 -i, --in-interface [!] name
216 Name of an interface via which a packet is going to be received
217 (only for packets entering the INPUT, FORWARD and PREROUTING
218 chains). When the "!" argument is used before the interface
219 name, the sense is inverted. If the interface name ends in a
220 "+", then any interface which begins with this name will match.
221 If this option is omitted, any interface name will match.
222 -o, --out-interface [!] name
224 Name of an interface via which a packet is going to be sent (for
225 packets entering the FORWARD and OUTPUT chains). When the "!"
226 argument is used before the interface name, the sense is
227 inverted. If the interface name ends in a "+", then any inter‐
228 face which begins with this name will match. If this option is
229 omitted, any interface name will match.
230 -c, --set-counters PKTS BYTES
232 This enables the administrator to initialize the packet and byte
233 counters of a rule (during INSERT, APPEND, REPLACE operations).
234 OTHER OPTIONS
236 The following additional options can be specified:
237 -v, --verbose
239 Verbose output. This option makes the list command show the
240 interface name, the rule options (if any), and the TOS masks.
241 The packet and byte counters are also listed, with the suffix
242 'K', 'M' or 'G' for 1000, 1,000,000 and 1,000,000,000 multipli‐
243 ers respectively (but see the -x flag to change this). For
244 appending, insertion, deletion and replacement, this causes
245 detailed information on the rule or rules to be printed.
246 -n, --numeric
248 Numeric output. IP addresses and port numbers will be printed
249 in numeric format. By default, the program will try to display
250 them as host names, network names, or services (whenever appli‐
251 cable).
252 -x, --exact
254 Expand numbers. Display the exact value of the packet and byte
255 counters, instead of only the rounded number in K's (multiples
256 of 1000) M's (multiples of 1000K) or G's (multiples of 1000M).
257 This option is only relevant for the -L command.
258 --line-numbers
260 When listing rules, add line numbers to the beginning of each
261 rule, corresponding to that rule's position in the chain.
262 --modprobe=command
264 When adding or inserting rules into a chain, use command to load
265 any necessary modules (targets, match extensions, etc).
266
268 ip6tables can use extended packet matching modules. These are loaded
269 in two ways: implicitly, when -p or --protocol is specified, or with
270 the -m or --match options, followed by the matching module name; after
271 these, various extra command line options become available, depending
272 on the specific module. You can specify multiple extended match mod‐
273 ules in one line, and you can use the -h or --help options after the
274 module has been specified to receive help specific to that module.
275 The following are included in the base package, and most of these can
277 be preceded by a ! to invert the sense of the match.
278 ah
280 This module matches the parameters in Authentication header of IPsec
281 packets.
282 --ahspi [!] spi[:spi]
284 Matches SPI.
285 --ahlen [!] length
287 Total length of this header in octets.
288 --ahres
290 Matches if the reserved field is filled with zero.
291 condition
293 This matches if a specific /proc filename is '0' or '1'.
294 --condition [!] filename
296 Match on boolean value stored in /proc/net/ip6t_condition/file‐
297 name file
298 dst
300 This module matches the parameters in Destination Options header
301 --dst-len [!] length
303 Total length of this header in octets.
304 --dst-opts type[:length][,type[:length]...]
306 numeric type of option and the length of the option data in
307 octets.
308 esp
310 This module matches the SPIs in ESP header of IPsec packets.
311 --espspi [!] spi[:spi]
313 eui64
315 This module matches the EUI-64 part of a stateless autoconfigured IPv6
316 address. It compares the EUI-64 derived from the source MAC address in
317 Ethernet frame with the lower 64 bits of the IPv6 source address. But
318 "Universal/Local" bit is not compared. This module doesn't match other
319 link layer frame, and is only valid in the PREROUTING, INPUT and FOR‐
320 WARD chains.
321 frag
323 This module matches the parameters in Fragment header.
324 --fragid [!] id[:id]
326 Matches the given Identification or range of it.
327 --fraglen [!] length
329 This option cannot be used with kernel version 2.6.10 or later.
330 The length of Fragment header is static and this option doesn't
331 make sense.
332 --fragres
334 Matches if the reserved fields are filled with zero.
335 --fragfirst
337 Matches on the first fragment.
338 [--fragmore]
340 Matches if there are more fragments.
341 [--fraglast]
343 Matches if this is the last fragement.
344 hbh
346 This module matches the parameters in Hop-by-Hop Options header
347 --hbh-len [!] length
349 Total length of this header in octets.
350 --hbh-opts type[:length][,type[:length]...]
352 numeric type of option and the length of the option data in
353 octets.
354 hl
356 This module matches the Hop Limit field in the IPv6 header.
357 --hl-eq [!] value
359 Matches if Hop Limit equals value.
360 --hl-lt value
362 Matches if Hop Limit is less than value.
363 --hl-gt value
365 Matches if Hop Limit is greater than value.
366 icmp6
368 This extension can be used if `--protocol ipv6-icmp' or `--protocol
369 icmpv6' is specified. It provides the following option:
370 --icmpv6-type [!] type[/code]|typename
372 This allows specification of the ICMPv6 type, which can be a
373 numeric ICMPv6 type, type and code, or one of the ICMPv6 type
374 names shown by the command
375 ip6tables -p ipv6-icmp -h
376 ipv6header
378 This module matches IPv6 extension headers and/or upper layer header.
379 --header [!] header[,header...]
381 Matches the packet which EXACTLY includes all specified headers.
382 The headers encapsulated with ESP header are out of scope.
383 header can be hop|hop-by-hop (Hop-by-Hop Options header), dst
384 (Destination Options header), route (Routing header), frag
385 (Fragment header), auth (Authentication header), esp (Encapsu‐
386 lating Security Payload header), none (No Next header) which
387 matches 59 in the 'Next Header field' of IPv6 header or any IPv6
388 extension headers, or proto which matches any upper layer proto‐
389 col header. A protocol name from /etc/protocols and numeric
390 value also allowed. The number 255 is equivalent to proto.
391 [--soft]
393 Matches if the packet includes all specified headers with
394 --header, AT LEAST.
395 length
397 This module matches the length of the IPv6 payload in octets, or range
398 of it. IPv6 header itself isn't counted.
399 --length [!] length[:length]
401 limit
403 This module matches at a limited rate using a token bucket filter. A
404 rule using this extension will match until this limit is reached.
405 It can be used in combination with the LOG target to give limited
406 logging, for example.
407 --limit rate
409 Maximum average matching rate: specified as a number, with an
410 optional `/second', `/minute', `/hour', or `/day' suffix; the
411 default is 3/hour.
412 --limit-burst number
414 Maximum initial number of packets to match: this number gets
415 recharged by one every time the limit specified above is not
416 reached, up to this number; the default is 5.
417 mac
419 --mac-source [!] address
420 Match source MAC address. It must be of the form
421 XX:XX:XX:XX:XX:XX. Note that this only makes sense for packets
422 coming from an Ethernet device and entering the PREROUTING, FOR‐
423 WARD or INPUT chains.
424 mark
426 This module matches the netfilter mark field associated with a packet
427 (which can be set using the MARK target below).
428 --mark value[/mask]
430 Matches packets with the given unsigned mark value (if a mask is
431 specified, this is logically ANDed with the mask before the com‐
432 parison).
433 mh
435 This extension is loaded if `--protocol ipv6-mh' or `--protocol mh' is
436 specified. It provides the following option:
437 --mh-type [!] type[:type]
439 This allows specification of the Mobility Header(MH) type, which
440 can be a numeric MH type, type or one of the MH type names shown
441 by the command
442 ip6tables -p ipv6-mh -h
443 multiport
445 This module matches a set of source or destination ports. Up to 15
446 ports can be specified. It can only be used in conjunction with -p tcp
447 or -p udp.
448 --source-ports [!] port[,port[,port...]]
450 Match if the source port is one of the given ports. The flag
451 --sports is a convenient alias for this option.
452 --destination-ports [!] port[,port[,port...]]
454 Match if the destination port is one of the given ports. The
455 flag --dports is a convenient alias for this option.
456 --ports [!] port[,port[,port...]]
458 Match if the both the source and destination ports are equal to
459 each other and to one of the given ports.
460 owner
462 This module attempts to match various characteristics of the packet
463 creator, for locally-generated packets. It is only valid in the OUTPUT
464 chain, and even this some packets (such as ICMPv6 ping responses) may
465 have no owner, and hence never match. This is regarded as experimen‐
466 tal.
467 --uid-owner userid
469 Matches if the packet was created by a process with the given
470 effective user id.
471 --gid-owner groupid
473 Matches if the packet was created by a process with the given
474 effective group id.
475 --pid-owner processid
477 Matches if the packet was created by a process with the given
478 process id.
479 --sid-owner sessionid
481 Matches if the packet was created by a process in the given ses‐
482 sion group.
483 NOTE: pid, sid and command matching are broken on SMP
485 physdev
487 This module matches on the bridge port input and output devices
488 enslaved to a bridge device. This module is a part of the infrastruc‐
489 ture that enables a transparent bridging IP firewall and is only useful
490 for kernel versions above version 2.5.44.
491 --physdev-in [!] name
493 Name of a bridge port via which a packet is received (only for
494 packets entering the INPUT, FORWARD and PREROUTING chains). If
495 the interface name ends in a "+", then any interface which
496 begins with this name will match. If the packet didn't arrive
497 through a bridge device, this packet won't match this option,
498 unless '!' is used.
499 --physdev-out [!] name
501 Name of a bridge port via which a packet is going to be sent
502 (for packets entering the FORWARD, OUTPUT and POSTROUTING
503 chains). If the interface name ends in a "+", then any inter‐
504 face which begins with this name will match. Note that in the
505 nat and mangle OUTPUT chains one cannot match on the bridge out‐
506 put port, however one can in the filter OUTPUT chain. If the
507 packet won't leave by a bridge device or it is yet unknown what
508 the output device will be, then the packet won't match this
509 option, unless
510 [!] --physdev-is-in
512 Matches if the packet has entered through a bridge interface.
513 [!] --physdev-is-out
515 Matches if the packet will leave through a bridge interface.
516 [!] --physdev-is-bridged
518 Matches if the packet is being bridged and therefore is not
519 being routed. This is only useful in the FORWARD and POSTROUT‐
520 ING chains.
521 policy
523 This modules matches the policy used by IPsec for handling a packet.
524 --dir in|out
526 Used to select whether to match the policy used for decapsula‐
527 tion or the policy that will be used for encapsulation. in is
528 valid in the PREROUTING, INPUT and FORWARD chains, out is valid
529 in the POSTROUTING, OUTPUT and FORWARD chains.
530 --pol none|ipsec
532 Matches if the packet is subject to IPsec processing.
533 --strict
535 Selects whether to match the exact policy or match if any rule
536 of the policy matches the given policy.
537 --reqid id
539 Matches the reqid of the policy rule. The reqid can be specified
540 with setkey(8) using unique:id as level.
541 --spi spi
543 Matches the SPI of the SA.
544 --proto ah|esp|ipcomp
546 Matches the encapsulation protocol.
547 --mode tunnel|transport
549 Matches the encapsulation mode.
550 --tunnel-src addr[/mask]
552 Matches the source end-point address of a tunnel mode SA. Only
553 valid with --mode tunnel.
554 --tunnel-dst addr[/mask]
556 Matches the destination end-point address of a tunnel mode SA.
557 Only valid with --mode tunnel.
558 --next Start the next element in the policy specification. Can only be
560 used with --strict
561 rt
563 Match on IPv6 routing header
564 --rt-type [!] type
566 Match the type (numeric).
567 --rt-segsleft [!] num[:num]
569 Match the `segments left' field (range).
570 --rt-len [!] length
572 Match the length of this header.
573 --rt-0-res
575 Match the reserved field, too (type=0)
576 --rt-0-addrs ADDR[,ADDR...]
578 Match type=0 addresses (list).
579 --rt-0-not-strict
581 List of type=0 addresses is not a strict list.
582 tcp
584 These extensions can be used if `--protocol tcp' is specified. It pro‐
585 vides the following options:
586 --source-port [!] port[:port]
588 Source port or port range specification. This can either be a
589 service name or a port number. An inclusive range can also be
590 specified, using the format port:port. If the first port is
591 omitted, "0" is assumed; if the last is omitted, "65535" is
592 assumed. If the second port greater then the first they will be
593 swapped. The flag --sport is a convenient alias for this
594 option.
595 --destination-port [!] port[:port]
597 Destination port or port range specification. The flag --dport
598 is a convenient alias for this option.
599 --tcp-flags [!] mask comp
601 Match when the TCP flags are as specified. The first argument
602 is the flags which we should examine, written as a comma-sepa‐
603 rated list, and the second argument is a comma-separated list of
604 flags which must be set. Flags are: SYN ACK FIN RST URG PSH ALL
605 NONE. Hence the command
606 ip6tables -A FORWARD -p tcp --tcp-flags SYN,ACK,FIN,RST SYN
607 will only match packets with the SYN flag set, and the ACK, FIN
608 and RST flags unset.
609 [!] --syn
611 Only match TCP packets with the SYN bit set and the ACK and RST
612 bits cleared. Such packets are used to request TCP connection
613 initiation; for example, blocking such packets coming in an
614 interface will prevent incoming TCP connections, but outgoing
615 TCP connections will be unaffected. It is equivalent to --tcp-
616 flags SYN,RST,ACK SYN. If the "!" flag precedes the "--syn",
617 the sense of the option is inverted.
618 --tcp-option [!] number
620 Match if TCP option set.
621 udp
623 These extensions can be used if `--protocol udp' is specified. It pro‐
624 vides the following options:
625 --source-port [!] port[:port]
627 Source port or port range specification. See the description of
628 the --source-port option of the TCP extension for details.
629 --destination-port [!] port[:port]
631 Destination port or port range specification. See the descrip‐
632 tion of the --destination-port option of the TCP extension for
633 details.
634
636 ip6tables can use extended target modules: the following are included
637 in the standard distribution.
638 CONNSECMARK
640 This module copies security markings from packets to connections (if
641 unlabeled), and from connections back to packets (also only if unla‐
642 beled). Typically used in conjunction with SECMARK, it is only valid
643 in the mangle table.
644 --save If the packet has a security marking, copy it to the connection
646 if the connection is not marked.
647 --restore
649 If the packet does not have a security marking, and the connec‐
650 tion does, copy the security marking from the connection to the
651 packet.
652 HL
655 This is used to modify the Hop Limit field in IPv6 header. The Hop
656 Limit field is similar to what is known as TTL value in IPv4. Setting
657 or incrementing the Hop Limit field can potentially be very dangerous,
658 so it should be avoided at any cost. This target is only valid in man‐
659 gle table.
660 Don't ever set or increment the value on packets that leave your local
662 network!
663 --hl-set value
665 Set the Hop Limit to `value'.
666 --hl-dec value
668 Decrement the Hop Limit `value' times.
669 --hl-inc value
671 Increment the Hop Limit `value' times.
672 LOG
674 Turn on kernel logging of matching packets. When this option is set
675 for a rule, the Linux kernel will print some information on all match‐
676 ing packets (like most IPv6 IPv6-header fields) via the kernel log
677 (where it can be read with dmesg or syslogd(8)). This is a "non-termi‐
678 nating target", i.e. rule traversal continues at the next rule. So if
679 you want to LOG the packets you refuse, use two separate rules with the
680 same matching criteria, first using target LOG then DROP (or REJECT).
681 --log-level level
683 Level of logging (numeric or see syslog.conf(5)).
684 --log-prefix prefix
686 Prefix log messages with the specified prefix; up to 29 letters
687 long, and useful for distinguishing messages in the logs.
688 --log-tcp-sequence
690 Log TCP sequence numbers. This is a security risk if the log is
691 readable by users.
692 --log-tcp-options
694 Log options from the TCP packet header.
695 --log-ip-options
697 Log options from the IPv6 packet header.
698 --log-uid
700 Log the userid of the process which generated the packet.
701 MARK
703 This is used to set the netfilter mark value associated with the
704 packet. It is only valid in the mangle table.
705 --set-mark mark
707 NFQUEUE
709 This target is an extension of the QUEUE target. As opposed to QUEUE,
710 it allows you to put a packet into any specific queue, identified by
711 its 16-bit queue number.
712 --queue-num value
714 This specifies the QUEUE number to use. Valud queue numbers are
715 0 to 65535. The default value is 0.
716 It can only be used with Kernel versions 2.6.14 or later, since it
718 requires
719 the nfnetlink_queue kernel support.
720 REJECT
722 This is used to send back an error packet in response to the matched
723 packet: otherwise it is equivalent to DROP so it is a terminating TAR‐
724 GET, ending rule traversal. This target is only valid in the INPUT,
725 FORWARD and OUTPUT chains, and user-defined chains which are only
726 called from those chains. The following option controls the nature of
727 the error packet returned:
728 --reject-with type
730 The type given can be
731 icmp6-no-route
732 no-route
733 icmp6-adm-prohibited
734 adm-prohibited
735 icmp6-addr-unreachable
736 addr-unreach
737 icmp6-port-unreachable
738 port-unreach
739 which return the appropriate ICMPv6 error message (port-unreach
740 is the default). Finally, the option tcp-reset can be used on
741 rules which only match the TCP protocol: this causes a TCP RST
742 packet to be sent back. This is mainly useful for blocking
743 ident (113/tcp) probes which frequently occur when sending mail
744 to broken mail hosts (which won't accept your mail otherwise).
745 tcp-reset can only be used with kernel versions 2.6.14 or later.
746 SECMARK
749 This is used to set the security mark value associated with the packet
750 for use by security subsystems such as SELinux. It is only valid in
751 the mangle table.
752 --selctx security_context
754 TCPMSS
756 This target allows to alter the MSS value of TCP SYN packets, to con‐
757 trol the maximum size for that connection (usually limiting it to your
758 outgoing interface's MTU minus 60). Of course, it can only be used in
759 conjunction with -p tcp. It is only valid in the mangle table.
760 This target is used to overcome criminally braindead ISPs or servers
761 which block ICMPv6 Packet Too Big packets or are unable to send them.
762 The symptoms of this problem are that everything works fine from your
763 Linux firewall/router, but machines behind it can never exchange large
764 packets:
765 1) Web browsers connect, then hang with no data received.
766 2) Small mail works fine, but large emails hang.
767 3) ssh works fine, but scp hangs after initial handshaking.
768 Workaround: activate this option and add a rule to your firewall con‐
769 figuration like:
770 ip6tables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN \
771 -j TCPMSS --clamp-mss-to-pmtu
772 --set-mss value
774 Explicitly set MSS option to specified value.
775 --clamp-mss-to-pmtu
777 Automatically clamp MSS value to (path_MTU - 60).
778 These options are mutually exclusive.
780
783 Various error messages are printed to standard error. The exit code is
784 0 for correct functioning. Errors which appear to be caused by invalid
785 or abused command line parameters cause an exit code of 2, and other
786 errors cause an exit code of 1.
787
789 Bugs? What's this? ;-) Well... the counters are not reliable on
790 sparc64.
791
793 This ip6tables is very similar to ipchains by Rusty Russell. The main
794 difference is that the chains INPUT and OUTPUT are only traversed for
795 packets coming into the local host and originating from the local host
796 respectively. Hence every packet only passes through one of the three
797 chains (except loopback traffic, which involves both INPUT and OUTPUT
798 chains); previously a forwarded packet would pass through all three.
799 The other main difference is that -i refers to the input interface; -o
801 refers to the output interface, and both are available for packets
802 entering the FORWARD chain. There are several other changes in
803 ip6tables.
804
806 ip6tables-save(8), ip6tables-restore(8), iptables(8), iptables-save(8),
807 iptables-restore(8), libipq(3).
808 The packet-filtering-HOWTO details iptables usage for packet filtering,
810 the NAT-HOWTO details NAT, the netfilter-extensions-HOWTO details the
811 extensions that are not in the standard distribution, and the netfil‐
812 ter-hacking-HOWTO details the netfilter internals.
813 See http://www.netfilter.org/.
814
816 Rusty Russell wrote iptables, in early consultation with Michael Neul‐
817 ing.
818 Marc Boucher made Rusty abandon ipnatctl by lobbying for a generic
820 packet selection framework in iptables, then wrote the mangle table,
821 the owner match, the mark stuff, and ran around doing cool stuff every‐
822 where.
823 James Morris wrote the TOS target, and tos match.
825 Jozsef Kadlecsik wrote the REJECT target.
827 Harald Welte wrote the ULOG and NFQUEUE target, the new libiptc, aswell
829 as TTL match+target and libipulog.
830 The Netfilter Core Team is: Marc Boucher, Martin Josefsson, Yasuyuki
832 Kozakai, Jozsef Kadlecsik, Patrick McHardy, James Morris, Pablo Neira
833 Ayuso, Harald Welte and Rusty Russell.
834 ip6tables man page created by Andras Kis-Szabo, based on iptables man
836 page written by Herve Eychenne <rv@wallfire.org>.
837 Jan 22, 2006 IP6TABLES(8)