1iptables-extensions(8) iptables 1.8.7 iptables-extensions(8)
2
6 iptables-extensions — list of extensions in the standard iptables dis‐
7 tribution
8
10 ip6tables [-m name [module-options...]] [-j target-name [target-op‐
11 tions...]
12 iptables [-m name [module-options...]] [-j target-name [target-op‐
14 tions...]
15
17 iptables can use extended packet matching modules with the -m or
18 --match options, followed by the matching module name; after these,
19 various extra command line options become available, depending on the
20 specific module. You can specify multiple extended match modules in
21 one line, and you can use the -h or --help options after the module has
22 been specified to receive help specific to that module. The extended
23 match modules are evaluated in the order they are specified in the
24 rule.
25 If the -p or --protocol was specified and if and only if an unknown op‐
27 tion is encountered, iptables will try load a match module of the same
28 name as the protocol, to try making the option available.
29 addrtype
31 This module matches packets based on their address type. Address types
32 are used within the kernel networking stack and categorize addresses
33 into various groups. The exact definition of that group depends on the
34 specific layer three protocol.
35 The following address types are possible:
37 UNSPEC an unspecified address (i.e. 0.0.0.0)
39 UNICAST
41 an unicast address
42 LOCAL a local address
44 BROADCAST
46 a broadcast address
47 ANYCAST
49 an anycast packet
50 MULTICAST
52 a multicast address
53 BLACKHOLE
55 a blackhole address
56 UNREACHABLE
58 an unreachable address
59 PROHIBIT
61 a prohibited address
62 THROW FIXME
64 NAT FIXME
66 XRESOLVE
68 [!] --src-type type
70 Matches if the source address is of given type
71 [!] --dst-type type
73 Matches if the destination address is of given type
74 --limit-iface-in
76 The address type checking can be limited to the interface the
77 packet is coming in. This option is only valid in the PREROUT‐
78 ING, INPUT and FORWARD chains. It cannot be specified with the
79 --limit-iface-out option.
80 --limit-iface-out
82 The address type checking can be limited to the interface the
83 packet is going out. This option is only valid in the POSTROUT‐
84 ING, OUTPUT and FORWARD chains. It cannot be specified with the
85 --limit-iface-in option.
86 ah (IPv6-specific)
88 This module matches the parameters in Authentication header of IPsec
89 packets.
90 [!] --ahspi spi[:spi]
92 Matches SPI.
93 [!] --ahlen length
95 Total length of this header in octets.
96 --ahres
98 Matches if the reserved field is filled with zero.
99 ah (IPv4-specific)
101 This module matches the SPIs in Authentication header of IPsec packets.
102 [!] --ahspi spi[:spi]
104 bpf
106 Match using Linux Socket Filter. Expects a path to an eBPF object or a
107 cBPF program in decimal format.
108 --object-pinned path
110 Pass a path to a pinned eBPF object.
111 Applications load eBPF programs into the kernel with the bpf() system
113 call and BPF_PROG_LOAD command and can pin them in a virtual filesystem
114 with BPF_OBJ_PIN. To use a pinned object in iptables, mount the bpf
115 filesystem using
116 mount -t bpf bpf ${BPF_MOUNT}
118 then insert the filter in iptables by path:
120 iptables -A OUTPUT -m bpf --object-pinned
122 ${BPF_MOUNT}/{PINNED_PATH} -j ACCEPT
123 --bytecode code
125 Pass the BPF byte code format as generated by the nfbpf_compile
126 utility.
127 The code format is similar to the output of the tcpdump -ddd command:
129 one line that stores the number of instructions, followed by one line
130 for each instruction. Instruction lines follow the pattern 'u16 u8 u8
131 u32' in decimal notation. Fields encode the operation, jump offset if
132 true, jump offset if false and generic multiuse field 'K'. Comments are
133 not supported.
134 For example, to read only packets matching 'ip proto 6', insert the
136 following, without the comments or trailing whitespace:
137 4 # number of instructions
139 48 0 0 9 # load byte ip->proto
140 21 0 1 6 # jump equal IPPROTO_TCP
141 6 0 0 1 # return pass (non-zero)
142 6 0 0 0 # return fail (zero)
143 You can pass this filter to the bpf match with the following command:
145 iptables -A OUTPUT -m bpf --bytecode '4,48 0 0 9,21 0 1 6,6 0 0
147 1,6 0 0 0' -j ACCEPT
148 Or instead, you can invoke the nfbpf_compile utility.
150 iptables -A OUTPUT -m bpf --bytecode "`nfbpf_compile RAW 'ip
152 proto 6'`" -j ACCEPT
153 Or use tcpdump -ddd. In that case, generate BPF targeting a device with
155 the same data link type as the xtables match. Iptables passes packets
156 from the network layer up, without mac layer. Select a device with data
157 link type RAW, such as a tun device:
158 ip tuntap add tun0 mode tun
160 ip link set tun0 up
161 tcpdump -ddd -i tun0 ip proto 6
162 See tcpdump -L -i $dev for a list of known data link types for a given
164 device.
165 You may want to learn more about BPF from FreeBSD's bpf(4) manpage.
167 cgroup
169 [!] --path path
170 Match cgroup2 membership.
171 Each socket is associated with the v2 cgroup of the creating
173 process. This matches packets coming from or going to all sock‐
174 ets in the sub-hierarchy of the specified path. The path should
175 be relative to the root of the cgroup2 hierarchy.
176 [!] --cgroup classid
178 Match cgroup net_cls classid.
179 classid is the marker set through the cgroup net_cls controller.
181 This option and --path can't be used together.
182 Example:
184 iptables -A OUTPUT -p tcp --sport 80 -m cgroup ! --path ser‐
186 vice/http-server -j DROP
187 iptables -A OUTPUT -p tcp --sport 80 -m cgroup ! --cgroup 1 -j
189 DROP
190 IMPORTANT: when being used in the INPUT chain, the cgroup matcher is
192 currently only of limited functionality, meaning it will only match on
193 packets that are processed for local sockets through early socket de‐
194 muxing. Therefore, general usage on the INPUT chain is not advised un‐
195 less the implications are well understood.
196 Available since Linux 3.14.
198 cluster
200 Allows you to deploy gateway and back-end load-sharing clusters without
201 the need of load-balancers.
202 This match requires that all the nodes see the same packets. Thus, the
204 cluster match decides if this node has to handle a packet given the
205 following options:
206 --cluster-total-nodes num
208 Set number of total nodes in cluster.
209 [!] --cluster-local-node num
211 Set the local node number ID.
212 [!] --cluster-local-nodemask mask
214 Set the local node number ID mask. You can use this option in‐
215 stead of --cluster-local-node.
216 --cluster-hash-seed value
218 Set seed value of the Jenkins hash.
219 Example:
221 iptables -A PREROUTING -t mangle -i eth1 -m cluster --clus‐
223 ter-total-nodes 2 --cluster-local-node 1 --cluster-hash-seed
224 0xdeadbeef -j MARK --set-mark 0xffff
225 iptables -A PREROUTING -t mangle -i eth2 -m cluster --clus‐
227 ter-total-nodes 2 --cluster-local-node 1 --cluster-hash-seed
228 0xdeadbeef -j MARK --set-mark 0xffff
229 iptables -A PREROUTING -t mangle -i eth1 -m mark ! --mark 0xffff
231 -j DROP
232 iptables -A PREROUTING -t mangle -i eth2 -m mark ! --mark 0xffff
234 -j DROP
235 And the following commands to make all nodes see the same packets:
237 ip maddr add 01:00:5e:00:01:01 dev eth1
239 ip maddr add 01:00:5e:00:01:02 dev eth2
241 arptables -A OUTPUT -o eth1 --h-length 6 -j mangle --mangle-mac-
243 s 01:00:5e:00:01:01
244 arptables -A INPUT -i eth1 --h-length 6 --destination-mac
246 01:00:5e:00:01:01 -j mangle --mangle-mac-d 00:zz:yy:xx:5a:27
247 arptables -A OUTPUT -o eth2 --h-length 6 -j mangle --man‐
249 gle-mac-s 01:00:5e:00:01:02
250 arptables -A INPUT -i eth2 --h-length 6 --destination-mac
252 01:00:5e:00:01:02 -j mangle --mangle-mac-d 00:zz:yy:xx:5a:27
253 NOTE: the arptables commands above use mainstream syntax. If you are
255 using arptables-jf included in some RedHat, CentOS and Fedora versions,
256 you will hit syntax errors. Therefore, you'll have to adapt these to
257 the arptables-jf syntax to get them working.
258 In the case of TCP connections, pickup facility has to be disabled to
260 avoid marking TCP ACK packets coming in the reply direction as valid.
261 echo 0 > /proc/sys/net/netfilter/nf_conntrack_tcp_loose
263 comment
265 Allows you to add comments (up to 256 characters) to any rule.
266 --comment comment
268 Example:
270 iptables -A INPUT -i eth1 -m comment --comment "my local LAN"
271 connbytes
273 Match by how many bytes or packets a connection (or one of the two
274 flows constituting the connection) has transferred so far, or by aver‐
275 age bytes per packet.
276 The counters are 64-bit and are thus not expected to overflow ;)
278 The primary use is to detect long-lived downloads and mark them to be
280 scheduled using a lower priority band in traffic control.
281 The transferred bytes per connection can also be viewed through `con‐
283 ntrack -L` and accessed via ctnetlink.
284 NOTE that for connections which have no accounting information, the
286 match will always return false. The "net.netfilter.nf_conntrack_acct"
287 sysctl flag controls whether new connections will be byte/packet
288 counted. Existing connection flows will not be gaining/losing a/the ac‐
289 counting structure when be sysctl flag is flipped.
290 [!] --connbytes from[:to]
292 match packets from a connection whose packets/bytes/average
293 packet size is more than FROM and less than TO bytes/packets. if
294 TO is omitted only FROM check is done. "!" is used to match
295 packets not falling in the range.
296 --connbytes-dir {original|reply|both}
298 which packets to consider
299 --connbytes-mode {packets|bytes|avgpkt}
301 whether to check the amount of packets, number of bytes trans‐
302 ferred or the average size (in bytes) of all packets received so
303 far. Note that when "both" is used together with "avgpkt", and
304 data is going (mainly) only in one direction (for example HTTP),
305 the average packet size will be about half of the actual data
306 packets.
307 Example:
309 iptables .. -m connbytes --connbytes 10000:100000
310 --connbytes-dir both --connbytes-mode bytes ...
311 connlabel
313 Module matches or adds connlabels to a connection. connlabels are sim‐
314 ilar to connmarks, except labels are bit-based; i.e. all labels may be
315 attached to a flow at the same time. Up to 128 unique labels are cur‐
316 rently supported.
317 [!] --label name
319 matches if label name has been set on a connection. Instead of
320 a name (which will be translated to a number, see EXAMPLE be‐
321 low), a number may be used instead. Using a number always over‐
322 rides connlabel.conf.
323 --set if the label has not been set on the connection, set it. Note
325 that setting a label can fail. This is because the kernel allo‐
326 cates the conntrack label storage area when the connection is
327 created, and it only reserves the amount of memory required by
328 the ruleset that exists at the time the connection is created.
329 In this case, the match will fail (or succeed, in case --label
330 option was negated).
331 This match depends on libnetfilter_conntrack 1.0.4 or later. Label
333 translation is done via the /etc/xtables/connlabel.conf configuration
334 file.
335 Example:
337 0 eth0-in
339 1 eth0-out
340 2 ppp-in
341 3 ppp-out
342 4 bulk-traffic
343 5 interactive
344 connlimit
346 Allows you to restrict the number of parallel connections to a server
347 per client IP address (or client address block).
348 --connlimit-upto n
350 Match if the number of existing connections is below or equal n.
351 --connlimit-above n
353 Match if the number of existing connections is above n.
354 --connlimit-mask prefix_length
356 Group hosts using the prefix length. For IPv4, this must be a
357 number between (including) 0 and 32. For IPv6, between 0 and
358 128. If not specified, the maximum prefix length for the appli‐
359 cable protocol is used.
360 --connlimit-saddr
362 Apply the limit onto the source group. This is the default if
363 --connlimit-daddr is not specified.
364 --connlimit-daddr
366 Apply the limit onto the destination group.
367 Examples:
369 # allow 2 telnet connections per client host
371 iptables -A INPUT -p tcp --syn --dport 23 -m connlimit
372 --connlimit-above 2 -j REJECT
373 # you can also match the other way around:
375 iptables -A INPUT -p tcp --syn --dport 23 -m connlimit
376 --connlimit-upto 2 -j ACCEPT
377 # limit the number of parallel HTTP requests to 16 per class C sized
379 source network (24 bit netmask)
380 iptables -p tcp --syn --dport 80 -m connlimit --connlimit-above
381 16 --connlimit-mask 24 -j REJECT
382 # limit the number of parallel HTTP requests to 16 for the link local
384 network
385 (ipv6) ip6tables -p tcp --syn --dport 80 -s fe80::/64 -m
386 connlimit --connlimit-above 16 --connlimit-mask 64 -j REJECT
387 # Limit the number of connections to a particular host:
389 ip6tables -p tcp --syn --dport 49152:65535 -d 2001:db8::1 -m
390 connlimit --connlimit-above 100 -j REJECT
391 connmark
393 This module matches the netfilter mark field associated with a connec‐
394 tion (which can be set using the CONNMARK target below).
395 [!] --mark value[/mask]
397 Matches packets in connections with the given mark value (if a
398 mask is specified, this is logically ANDed with the mark before
399 the comparison).
400 conntrack
402 This module, when combined with connection tracking, allows access to
403 the connection tracking state for this packet/connection.
404 [!] --ctstate statelist
406 statelist is a comma separated list of the connection states to
407 match. Possible states are listed below.
408 [!] --ctproto l4proto
410 Layer-4 protocol to match (by number or name)
411 [!] --ctorigsrc address[/mask]
413 [!] --ctorigdst address[/mask]
415 [!] --ctreplsrc address[/mask]
417 [!] --ctrepldst address[/mask]
419 Match against original/reply source/destination address
420 [!] --ctorigsrcport port[:port]
422 [!] --ctorigdstport port[:port]
424 [!] --ctreplsrcport port[:port]
426 [!] --ctrepldstport port[:port]
428 Match against original/reply source/destination port
429 (TCP/UDP/etc.) or GRE key. Matching against port ranges is only
430 supported in kernel versions above 2.6.38.
431 [!] --ctstatus statelist
433 statuslist is a comma separated list of the connection statuses
434 to match. Possible statuses are listed below.
435 [!] --ctexpire time[:time]
437 Match remaining lifetime in seconds against given value or range
438 of values (inclusive)
439 --ctdir {ORIGINAL|REPLY}
441 Match packets that are flowing in the specified direction. If
442 this flag is not specified at all, matches packets in both di‐
443 rections.
444 States for --ctstate:
446 INVALID
448 The packet is associated with no known connection.
449 NEW The packet has started a new connection or otherwise associated
451 with a connection which has not seen packets in both directions.
452 ESTABLISHED
454 The packet is associated with a connection which has seen pack‐
455 ets in both directions.
456 RELATED
458 The packet is starting a new connection, but is associated with
459 an existing connection, such as an FTP data transfer or an ICMP
460 error.
461 UNTRACKED
463 The packet is not tracked at all, which happens if you explic‐
464 itly untrack it by using -j CT --notrack in the raw table.
465 SNAT A virtual state, matching if the original source address differs
467 from the reply destination.
468 DNAT A virtual state, matching if the original destination differs
470 from the reply source.
471 Statuses for --ctstatus:
473 NONE None of the below.
475 EXPECTED
477 This is an expected connection (i.e. a conntrack helper set it
478 up).
479 SEEN_REPLY
481 Conntrack has seen packets in both directions.
482 ASSURED
484 Conntrack entry should never be early-expired.
485 CONFIRMED
487 Connection is confirmed: originating packet has left box.
488 cpu
490 [!] --cpu number
491 Match cpu handling this packet. cpus are numbered from 0 to
492 NR_CPUS-1 Can be used in combination with RPS (Remote Packet
493 Steering) or multiqueue NICs to spread network traffic on dif‐
494 ferent queues.
495 Example:
497 iptables -t nat -A PREROUTING -p tcp --dport 80 -m cpu --cpu 0 -j REDI‐
499 RECT --to-port 8080
500 iptables -t nat -A PREROUTING -p tcp --dport 80 -m cpu --cpu 1 -j REDI‐
502 RECT --to-port 8081
503 Available since Linux 2.6.36.
505 dccp
507 [!] --source-port,--sport port[:port]
508 [!] --destination-port,--dport port[:port]
510 [!] --dccp-types mask
512 Match when the DCCP packet type is one of 'mask'. 'mask' is a
513 comma-separated list of packet types. Packet types are: REQUEST
514 RESPONSE DATA ACK DATAACK CLOSEREQ CLOSE RESET SYNC SYNCACK IN‐
515 VALID.
516 [!] --dccp-option number
518 Match if DCCP option set.
519 devgroup
521 Match device group of a packets incoming/outgoing interface.
522 [!] --src-group name
524 Match device group of incoming device
525 [!] --dst-group name
527 Match device group of outgoing device
528 dscp
530 This module matches the 6 bit DSCP field within the TOS field in the IP
531 header. DSCP has superseded TOS within the IETF.
532 [!] --dscp value
534 Match against a numeric (decimal or hex) value [0-63].
535 [!] --dscp-class class
537 Match the DiffServ class. This value may be any of the BE, EF,
538 AFxx or CSx classes. It will then be converted into its accord‐
539 ing numeric value.
540 dst (IPv6-specific)
542 This module matches the parameters in Destination Options header
543 [!] --dst-len length
545 Total length of this header in octets.
546 --dst-opts type[:length][,type[:length]...]
548 numeric type of option and the length of the option data in
549 octets.
550 ecn
552 This allows you to match the ECN bits of the IPv4/IPv6 and TCP header.
553 ECN is the Explicit Congestion Notification mechanism as specified in
554 RFC3168
555 [!] --ecn-tcp-cwr
557 This matches if the TCP ECN CWR (Congestion Window Received) bit
558 is set.
559 [!] --ecn-tcp-ece
561 This matches if the TCP ECN ECE (ECN Echo) bit is set.
562 [!] --ecn-ip-ect num
564 This matches a particular IPv4/IPv6 ECT (ECN-Capable Transport).
565 You have to specify a number between `0' and `3'.
566 esp
568 This module matches the SPIs in ESP header of IPsec packets.
569 [!] --espspi spi[:spi]
571 eui64 (IPv6-specific)
573 This module matches the EUI-64 part of a stateless autoconfigured IPv6
574 address. It compares the EUI-64 derived from the source MAC address in
575 Ethernet frame with the lower 64 bits of the IPv6 source address. But
576 "Universal/Local" bit is not compared. This module doesn't match other
577 link layer frame, and is only valid in the PREROUTING, INPUT and FOR‐
578 WARD chains.
579 frag (IPv6-specific)
581 This module matches the parameters in Fragment header.
582 [!] --fragid id[:id]
584 Matches the given Identification or range of it.
585 [!] --fraglen length
587 This option cannot be used with kernel version 2.6.10 or later.
588 The length of Fragment header is static and this option doesn't
589 make sense.
590 --fragres
592 Matches if the reserved fields are filled with zero.
593 --fragfirst
595 Matches on the first fragment.
596 --fragmore
598 Matches if there are more fragments.
599 --fraglast
601 Matches if this is the last fragment.
602 hashlimit
604 hashlimit uses hash buckets to express a rate limiting match (like the
605 limit match) for a group of connections using a single iptables rule.
606 Grouping can be done per-hostgroup (source and/or destination address)
607 and/or per-port. It gives you the ability to express "N packets per
608 time quantum per group" or "N bytes per seconds" (see below for some
609 examples).
610 A hash limit option (--hashlimit-upto, --hashlimit-above) and --hash‐
612 limit-name are required.
613 --hashlimit-upto amount[/second|/minute|/hour|/day]
615 Match if the rate is below or equal to amount/quantum. It is
616 specified either as a number, with an optional time quantum suf‐
617 fix (the default is 3/hour), or as amountb/second (number of
618 bytes per second).
619 --hashlimit-above amount[/second|/minute|/hour|/day]
621 Match if the rate is above amount/quantum.
622 --hashlimit-burst amount
624 Maximum initial number of packets to match: this number gets
625 recharged by one every time the limit specified above is not
626 reached, up to this number; the default is 5. When byte-based
627 rate matching is requested, this option specifies the amount of
628 bytes that can exceed the given rate. This option should be
629 used with caution -- if the entry expires, the burst value is
630 reset too.
631 --hashlimit-mode {srcip|srcport|dstip|dstport},...
633 A comma-separated list of objects to take into consideration. If
634 no --hashlimit-mode option is given, hashlimit acts like limit,
635 but at the expensive of doing the hash housekeeping.
636 --hashlimit-srcmask prefix
638 When --hashlimit-mode srcip is used, all source addresses en‐
639 countered will be grouped according to the given prefix length
640 and the so-created subnet will be subject to hashlimit. prefix
641 must be between (inclusive) 0 and 32. Note that --hashlimit-src‐
642 mask 0 is basically doing the same thing as not specifying srcip
643 for --hashlimit-mode, but is technically more expensive.
644 --hashlimit-dstmask prefix
646 Like --hashlimit-srcmask, but for destination addresses.
647 --hashlimit-name foo
649 The name for the /proc/net/ipt_hashlimit/foo entry.
650 --hashlimit-htable-size buckets
652 The number of buckets of the hash table
653 --hashlimit-htable-max entries
655 Maximum entries in the hash.
656 --hashlimit-htable-expire msec
658 After how many milliseconds do hash entries expire.
659 --hashlimit-htable-gcinterval msec
661 How many milliseconds between garbage collection intervals.
662 --hashlimit-rate-match
664 Classify the flow instead of rate-limiting it. This acts like a
665 true/false match on whether the rate is above/below a certain
666 number
667 --hashlimit-rate-interval sec
669 Can be used with --hashlimit-rate-match to specify the interval
670 at which the rate should be sampled
671 Examples:
673 matching on source host
675 "1000 packets per second for every host in 192.168.0.0/16" => -s
676 192.168.0.0/16 --hashlimit-mode srcip --hashlimit-upto 1000/sec
677 matching on source port
679 "100 packets per second for every service of 192.168.1.1" => -s
680 192.168.1.1 --hashlimit-mode srcport --hashlimit-upto 100/sec
681 matching on subnet
683 "10000 packets per minute for every /28 subnet (groups of 8 ad‐
684 dresses) in 10.0.0.0/8" => -s 10.0.0.0/8 --hashlimit-mask 28
685 --hashlimit-upto 10000/min
686 matching bytes per second
688 "flows exceeding 512kbyte/s" => --hashlimit-mode srcip,dstip,sr‐
689 cport,dstport --hashlimit-above 512kb/s
690 matching bytes per second
692 "hosts that exceed 512kbyte/s, but permit up to 1Megabytes with‐
693 out matching" --hashlimit-mode dstip --hashlimit-above 512kb/s
694 --hashlimit-burst 1mb
695 hbh (IPv6-specific)
697 This module matches the parameters in Hop-by-Hop Options header
698 [!] --hbh-len length
700 Total length of this header in octets.
701 --hbh-opts type[:length][,type[:length]...]
703 numeric type of option and the length of the option data in
704 octets.
705 helper
707 This module matches packets related to a specific conntrack-helper.
708 [!] --helper string
710 Matches packets related to the specified conntrack-helper.
711 string can be "ftp" for packets related to a ftp-session on de‐
713 fault port. For other ports append -portnr to the value, ie.
714 "ftp-2121".
715 Same rules apply for other conntrack-helpers.
717 hl (IPv6-specific)
719 This module matches the Hop Limit field in the IPv6 header.
720 [!] --hl-eq value
722 Matches if Hop Limit equals value.
723 --hl-lt value
725 Matches if Hop Limit is less than value.
726 --hl-gt value
728 Matches if Hop Limit is greater than value.
729 icmp (IPv4-specific)
731 This extension can be used if `--protocol icmp' is specified. It pro‐
732 vides the following option:
733 [!] --icmp-type {type[/code]|typename}
735 This allows specification of the ICMP type, which can be a nu‐
736 meric ICMP type, type/code pair, or one of the ICMP type names
737 shown by the command
738 iptables -p icmp -h
739 icmp6 (IPv6-specific)
741 This extension can be used if `--protocol ipv6-icmp' or `--protocol
742 icmpv6' is specified. It provides the following option:
743 [!] --icmpv6-type type[/code]|typename
745 This allows specification of the ICMPv6 type, which can be a nu‐
746 meric ICMPv6 type, type and code, or one of the ICMPv6 type
747 names shown by the command
748 ip6tables -p ipv6-icmp -h
749 iprange
751 This matches on a given arbitrary range of IP addresses.
752 [!] --src-range from[-to]
754 Match source IP in the specified range.
755 [!] --dst-range from[-to]
757 Match destination IP in the specified range.
758 ipv6header (IPv6-specific)
760 This module matches IPv6 extension headers and/or upper layer header.
761 --soft Matches if the packet includes any of the headers specified with
763 --header.
764 [!] --header header[,header...]
766 Matches the packet which EXACTLY includes all specified headers.
767 The headers encapsulated with ESP header are out of scope. Pos‐
768 sible header types can be:
769 hop|hop-by-hop
771 Hop-by-Hop Options header
772 dst Destination Options header
774 route Routing header
776 frag Fragment header
778 auth Authentication header
780 esp Encapsulating Security Payload header
782 none No Next header which matches 59 in the 'Next Header field' of
784 IPv6 header or any IPv6 extension headers
785 prot which matches any upper layer protocol header. A protocol name
787 from /etc/protocols and numeric value also allowed. The number
788 255 is equivalent to prot.
789 ipvs
791 Match IPVS connection properties.
792 [!] --ipvs
794 packet belongs to an IPVS connection
795 Any of the following options implies --ipvs (even negated)
797 [!] --vproto protocol
799 VIP protocol to match; by number or name, e.g. "tcp"
800 [!] --vaddr address[/mask]
802 VIP address to match
803 [!] --vport port
805 VIP port to match; by number or name, e.g. "http"
806 --vdir {ORIGINAL|REPLY}
808 flow direction of packet
809 [!] --vmethod {GATE|IPIP|MASQ}
811 IPVS forwarding method used
812 [!] --vportctl port
814 VIP port of the controlling connection to match, e.g. 21 for FTP
815 length
817 This module matches the length of the layer-3 payload (e.g. layer-4
818 packet) of a packet against a specific value or range of values.
819 [!] --length length[:length]
821 limit
823 This module matches at a limited rate using a token bucket filter. A
824 rule using this extension will match until this limit is reached. It
825 can be used in combination with the LOG target to give limited logging,
826 for example.
827 xt_limit has no negation support - you will have to use -m hashlimit !
829 --hashlimit rate in this case whilst omitting --hashlimit-mode.
830 --limit rate[/second|/minute|/hour|/day]
832 Maximum average matching rate: specified as a number, with an
833 optional `/second', `/minute', `/hour', or `/day' suffix; the
834 default is 3/hour.
835 --limit-burst number
837 Maximum initial number of packets to match: this number gets
838 recharged by one every time the limit specified above is not
839 reached, up to this number; the default is 5.
840 mac
842 [!] --mac-source address
843 Match source MAC address. It must be of the form
844 XX:XX:XX:XX:XX:XX. Note that this only makes sense for packets
845 coming from an Ethernet device and entering the PREROUTING, FOR‐
846 WARD or INPUT chains.
847 mark
849 This module matches the netfilter mark field associated with a packet
850 (which can be set using the MARK target below).
851 [!] --mark value[/mask]
853 Matches packets with the given unsigned mark value (if a mask is
854 specified, this is logically ANDed with the mask before the com‐
855 parison).
856 mh (IPv6-specific)
858 This extension is loaded if `--protocol ipv6-mh' or `--protocol mh' is
859 specified. It provides the following option:
860 [!] --mh-type type[:type]
862 This allows specification of the Mobility Header(MH) type, which
863 can be a numeric MH type, type or one of the MH type names shown
864 by the command
865 ip6tables -p mh -h
866 multiport
868 This module matches a set of source or destination ports. Up to 15
869 ports can be specified. A port range (port:port) counts as two ports.
870 It can only be used in conjunction with one of the following protocols:
871 tcp, udp, udplite, dccp and sctp.
872 [!] --source-ports,--sports port[,port|,port:port]...
874 Match if the source port is one of the given ports. The flag
875 --sports is a convenient alias for this option. Multiple ports
876 or port ranges are separated using a comma, and a port range is
877 specified using a colon. 53,1024:65535 would therefore match
878 ports 53 and all from 1024 through 65535.
879 [!] --destination-ports,--dports port[,port|,port:port]...
881 Match if the destination port is one of the given ports. The
882 flag --dports is a convenient alias for this option.
883 [!] --ports port[,port|,port:port]...
885 Match if either the source or destination ports are equal to one
886 of the given ports.
887 nfacct
889 The nfacct match provides the extended accounting infrastructure for
890 iptables. You have to use this match together with the standalone
891 user-space utility nfacct(8)
892 The only option available for this match is the following:
894 --nfacct-name name
896 This allows you to specify the existing object name that will be
897 use for accounting the traffic that this rule-set is matching.
898 To use this extension, you have to create an accounting object:
900 nfacct add http-traffic
902 Then, you have to attach it to the accounting object via iptables:
904 iptables -I INPUT -p tcp --sport 80 -m nfacct --nfacct-name
906 http-traffic
907 iptables -I OUTPUT -p tcp --dport 80 -m nfacct --nfacct-name
909 http-traffic
910 Then, you can check for the amount of traffic that the rules match:
912 nfacct get http-traffic
914 { pkts = 00000000000000000156, bytes = 00000000000000151786 } =
916 http-traffic;
917 You can obtain nfacct(8) from http://www.netfilter.org or, alterna‐
919 tively, from the git.netfilter.org repository.
920 osf
922 The osf module does passive operating system fingerprinting. This mod‐
923 ule compares some data (Window Size, MSS, options and their order, TTL,
924 DF, and others) from packets with the SYN bit set.
925 [!] --genre string
927 Match an operating system genre by using a passive fingerprint‐
928 ing.
929 --ttl level
931 Do additional TTL checks on the packet to determine the operat‐
932 ing system. level can be one of the following values:
933 • 0 - True IP address and fingerprint TTL comparison. This generally
935 works for LANs.
936 • 1 - Check if the IP header's TTL is less than the fingerprint one.
938 Works for globally-routable addresses.
939 • 2 - Do not compare the TTL at all.
941 --log level
943 Log determined genres into dmesg even if they do not match the de‐
944 sired one. level can be one of the following values:
945 • 0 - Log all matched or unknown signatures
947 • 1 - Log only the first one
949 • 2 - Log all known matched signatures
951 You may find something like this in syslog:
953 Windows [2000:SP3:Windows XP Pro SP1, 2000 SP3]: 11.22.33.55:4024 ->
955 11.22.33.44:139 hops=3 Linux [2.5-2.6:] : 1.2.3.4:42624 -> 1.2.3.5:22
956 hops=4
957 OS fingerprints are loadable using the nfnl_osf program. To load fin‐
959 gerprints from a file, use:
960 nfnl_osf -f /usr/share/xtables/pf.os
962 To remove them again,
964 nfnl_osf -f /usr/share/xtables/pf.os -d
966 The fingerprint database can be downloaded from http://www.open‐
968 bsd.org/cgi-bin/cvsweb/src/etc/pf.os .
969 owner
971 This module attempts to match various characteristics of the packet
972 creator, for locally generated packets. This match is only valid in the
973 OUTPUT and POSTROUTING chains. Forwarded packets do not have any socket
974 associated with them. Packets from kernel threads do have a socket, but
975 usually no owner.
976 [!] --uid-owner username
978 [!] --uid-owner userid[-userid]
980 Matches if the packet socket's file structure (if it has one) is
981 owned by the given user. You may also specify a numerical UID,
982 or an UID range.
983 [!] --gid-owner groupname
985 [!] --gid-owner groupid[-groupid]
987 Matches if the packet socket's file structure is owned by the
988 given group. You may also specify a numerical GID, or a GID
989 range.
990 --suppl-groups
992 Causes group(s) specified with --gid-owner to be also checked in
993 the supplementary groups of a process.
994 [!] --socket-exists
996 Matches if the packet is associated with a socket.
997 physdev
999 This module matches on the bridge port input and output devices en‐
1000 slaved to a bridge device. This module is a part of the infrastructure
1001 that enables a transparent bridging IP firewall and is only useful for
1002 kernel versions above version 2.5.44.
1003 [!] --physdev-in name
1005 Name of a bridge port via which a packet is received (only for
1006 packets entering the INPUT, FORWARD and PREROUTING chains). If
1007 the interface name ends in a "+", then any interface which be‐
1008 gins with this name will match. If the packet didn't arrive
1009 through a bridge device, this packet won't match this option,
1010 unless '!' is used.
1011 [!] --physdev-out name
1013 Name of a bridge port via which a packet is going to be sent
1014 (for bridged packets entering the FORWARD and POSTROUTING
1015 chains). If the interface name ends in a "+", then any inter‐
1016 face which begins with this name will match.
1017 [!] --physdev-is-in
1019 Matches if the packet has entered through a bridge interface.
1020 [!] --physdev-is-out
1022 Matches if the packet will leave through a bridge interface.
1023 [!] --physdev-is-bridged
1025 Matches if the packet is being bridged and therefore is not be‐
1026 ing routed. This is only useful in the FORWARD and POSTROUTING
1027 chains.
1028 pkttype
1030 This module matches the link-layer packet type.
1031 [!] --pkt-type {unicast|broadcast|multicast}
1033 policy
1035 This module matches the policy used by IPsec for handling a packet.
1036 --dir {in|out}
1038 Used to select whether to match the policy used for decapsula‐
1039 tion or the policy that will be used for encapsulation. in is
1040 valid in the PREROUTING, INPUT and FORWARD chains, out is valid
1041 in the POSTROUTING, OUTPUT and FORWARD chains.
1042 --pol {none|ipsec}
1044 Matches if the packet is subject to IPsec processing. --pol none
1045 cannot be combined with --strict.
1046 --strict
1048 Selects whether to match the exact policy or match if any rule
1049 of the policy matches the given policy.
1050 For each policy element that is to be described, one can use one or
1052 more of the following options. When --strict is in effect, at least one
1053 must be used per element.
1054 [!] --reqid id
1056 Matches the reqid of the policy rule. The reqid can be specified
1057 with setkey(8) using unique:id as level.
1058 [!] --spi spi
1060 Matches the SPI of the SA.
1061 [!] --proto {ah|esp|ipcomp}
1063 Matches the encapsulation protocol.
1064 [!] --mode {tunnel|transport}
1066 Matches the encapsulation mode.
1067 [!] --tunnel-src addr[/mask]
1069 Matches the source end-point address of a tunnel mode SA. Only
1070 valid with --mode tunnel.
1071 [!] --tunnel-dst addr[/mask]
1073 Matches the destination end-point address of a tunnel mode SA.
1074 Only valid with --mode tunnel.
1075 --next Start the next element in the policy specification. Can only be
1077 used with --strict.
1078 quota
1080 Implements network quotas by decrementing a byte counter with each
1081 packet. The condition matches until the byte counter reaches zero. Be‐
1082 havior is reversed with negation (i.e. the condition does not match un‐
1083 til the byte counter reaches zero).
1084 [!] --quota bytes
1086 The quota in bytes.
1087 rateest
1089 The rate estimator can match on estimated rates as collected by the RA‐
1090 TEEST target. It supports matching on absolute bps/pps values, compar‐
1091 ing two rate estimators and matching on the difference between two rate
1092 estimators.
1093 For a better understanding of the available options, these are all pos‐
1095 sible combinations:
1096 • rateest operator rateest-bps
1098 • rateest operator rateest-pps
1100 • (rateest minus rateest-bps1) operator rateest-bps2
1102 • (rateest minus rateest-pps1) operator rateest-pps2
1104 • rateest1 operator rateest2 rateest-bps(without rate!)
1106 • rateest1 operator rateest2 rateest-pps(without rate!)
1108 • (rateest1 minus rateest-bps1) operator (rateest2 minus rateest-
1110 bps2)
1111 • (rateest1 minus rateest-pps1) operator (rateest2 minus rateest-
1113 pps2)
1114 --rateest-delta
1116 For each estimator (either absolute or relative mode), calculate
1117 the difference between the estimator-determined flow rate and the
1118 static value chosen with the BPS/PPS options. If the flow rate is
1119 higher than the specified BPS/PPS, 0 will be used instead of a neg‐
1120 ative value. In other words, "max(0, rateest#_rate - rateest#_bps)"
1121 is used.
1122 [!] --rateest-lt
1124 Match if rate is less than given rate/estimator.
1125 [!] --rateest-gt
1127 Match if rate is greater than given rate/estimator.
1128 [!] --rateest-eq
1130 Match if rate is equal to given rate/estimator.
1131 In the so-called "absolute mode", only one rate estimator is used and
1133 compared against a static value, while in "relative mode", two rate es‐
1134 timators are compared against another.
1135 --rateest name
1137 Name of the one rate estimator for absolute mode.
1138 --rateest1 name
1140 --rateest2 name
1142 The names of the two rate estimators for relative mode.
1143 --rateest-bps [value]
1145 --rateest-pps [value]
1147 --rateest-bps1 [value]
1149 --rateest-bps2 [value]
1151 --rateest-pps1 [value]
1153 --rateest-pps2 [value]
1155 Compare the estimator(s) by bytes or packets per second, and
1156 compare against the chosen value. See the above bullet list for
1157 which option is to be used in which case. A unit suffix may be
1158 used - available ones are: bit, [kmgt]bit, [KMGT]ibit, Bps,
1159 [KMGT]Bps, [KMGT]iBps.
1160 Example: This is what can be used to route outgoing data connections
1162 from an FTP server over two lines based on the available bandwidth at
1163 the time the data connection was started:
1164 # Estimate outgoing rates
1166 iptables -t mangle -A POSTROUTING -o eth0 -j RATEEST --rateest-name
1168 eth0 --rateest-interval 250ms --rateest-ewma 0.5s
1169 iptables -t mangle -A POSTROUTING -o ppp0 -j RATEEST --rateest-name
1171 ppp0 --rateest-interval 250ms --rateest-ewma 0.5s
1172 # Mark based on available bandwidth
1174 iptables -t mangle -A balance -m conntrack --ctstate NEW -m helper
1176 --helper ftp -m rateest --rateest-delta --rateest1 eth0 --rateest-bps1
1177 2.5mbit --rateest-gt --rateest2 ppp0 --rateest-bps2 2mbit -j CONNMARK
1178 --set-mark 1
1179 iptables -t mangle -A balance -m conntrack --ctstate NEW -m helper
1181 --helper ftp -m rateest --rateest-delta --rateest1 ppp0 --rateest-bps1
1182 2mbit --rateest-gt --rateest2 eth0 --rateest-bps2 2.5mbit -j CONNMARK
1183 --set-mark 2
1184 iptables -t mangle -A balance -j CONNMARK --restore-mark
1186 realm (IPv4-specific)
1188 This matches the routing realm. Routing realms are used in complex
1189 routing setups involving dynamic routing protocols like BGP.
1190 [!] --realm value[/mask]
1192 Matches a given realm number (and optionally mask). If not a
1193 number, value can be a named realm from /etc/iproute2/rt_realms
1194 (mask can not be used in that case). Both value and mask are
1195 four byte unsigned integers and may be specified in decimal, hex
1196 (by prefixing with "0x") or octal (if a leading zero is given).
1197 recent
1199 Allows you to dynamically create a list of IP addresses and then match
1200 against that list in a few different ways.
1201 For example, you can create a "badguy" list out of people attempting to
1203 connect to port 139 on your firewall and then DROP all future packets
1204 from them without considering them.
1205 --set, --rcheck, --update and --remove are mutually exclusive.
1207 --name name
1209 Specify the list to use for the commands. If no name is given
1210 then DEFAULT will be used.
1211 [!] --set
1213 This will add the source address of the packet to the list. If
1214 the source address is already in the list, this will update the
1215 existing entry. This will always return success (or failure if !
1216 is passed in).
1217 --rsource
1219 Match/save the source address of each packet in the recent list
1220 table. This is the default.
1221 --rdest
1223 Match/save the destination address of each packet in the recent
1224 list table.
1225 --mask netmask
1227 Netmask that will be applied to this recent list.
1228 [!] --rcheck
1230 Check if the source address of the packet is currently in the
1231 list.
1232 [!] --update
1234 Like --rcheck, except it will update the "last seen" timestamp
1235 if it matches.
1236 [!] --remove
1238 Check if the source address of the packet is currently in the
1239 list and if so that address will be removed from the list and
1240 the rule will return true. If the address is not found, false is
1241 returned.
1242 --seconds seconds
1244 This option must be used in conjunction with one of --rcheck or
1245 --update. When used, this will narrow the match to only happen
1246 when the address is in the list and was seen within the last
1247 given number of seconds.
1248 --reap This option can only be used in conjunction with --seconds.
1250 When used, this will cause entries older than the last given
1251 number of seconds to be purged.
1252 --hitcount hits
1254 This option must be used in conjunction with one of --rcheck or
1255 --update. When used, this will narrow the match to only happen
1256 when the address is in the list and packets had been received
1257 greater than or equal to the given value. This option may be
1258 used along with --seconds to create an even narrower match re‐
1259 quiring a certain number of hits within a specific time frame.
1260 The maximum value for the hitcount parameter is given by the
1261 "ip_pkt_list_tot" parameter of the xt_recent kernel module. Ex‐
1262 ceeding this value on the command line will cause the rule to be
1263 rejected.
1264 --rttl This option may only be used in conjunction with one of --rcheck
1266 or --update. When used, this will narrow the match to only hap‐
1267 pen when the address is in the list and the TTL of the current
1268 packet matches that of the packet which hit the --set rule. This
1269 may be useful if you have problems with people faking their
1270 source address in order to DoS you via this module by disallow‐
1271 ing others access to your site by sending bogus packets to you.
1272 Examples:
1274 iptables -A FORWARD -m recent --name badguy --rcheck --seconds
1276 60 -j DROP
1277 iptables -A FORWARD -p tcp -i eth0 --dport 139 -m recent --name
1279 badguy --set -j DROP
1280 /proc/net/xt_recent/* are the current lists of addresses and informa‐
1282 tion about each entry of each list.
1283 Each file in /proc/net/xt_recent/ can be read from to see the current
1285 list or written two using the following commands to modify the list:
1286 echo +addr >/proc/net/xt_recent/DEFAULT
1288 to add addr to the DEFAULT list
1289 echo -addr >/proc/net/xt_recent/DEFAULT
1291 to remove addr from the DEFAULT list
1292 echo / >/proc/net/xt_recent/DEFAULT
1294 to flush the DEFAULT list (remove all entries).
1295 The module itself accepts parameters, defaults shown:
1297 ip_list_tot=100
1299 Number of addresses remembered per table.
1300 ip_pkt_list_tot=20
1302 Number of packets per address remembered.
1303 ip_list_hash_size=0
1305 Hash table size. 0 means to calculate it based on ip_list_tot,
1306 default: 512.
1307 ip_list_perms=0644
1309 Permissions for /proc/net/xt_recent/* files.
1310 ip_list_uid=0
1312 Numerical UID for ownership of /proc/net/xt_recent/* files.
1313 ip_list_gid=0
1315 Numerical GID for ownership of /proc/net/xt_recent/* files.
1316 rpfilter
1318 Performs a reverse path filter test on a packet. If a reply to the
1319 packet would be sent via the same interface that the packet arrived on,
1320 the packet will match. Note that, unlike the in-kernel rp_filter,
1321 packets protected by IPSec are not treated specially. Combine this
1322 match with the policy match if you want this. Also, packets arriving
1323 via the loopback interface are always permitted. This match can only
1324 be used in the PREROUTING chain of the raw or mangle table.
1325 --loose
1327 Used to specify that the reverse path filter test should match
1328 even if the selected output device is not the expected one.
1329 --validmark
1331 Also use the packets' nfmark value when performing the reverse
1332 path route lookup.
1333 --accept-local
1335 This will permit packets arriving from the network with a source
1336 address that is also assigned to the local machine.
1337 --invert
1339 This will invert the sense of the match. Instead of matching
1340 packets that passed the reverse path filter test, match those
1341 that have failed it.
1342 Example to log and drop packets failing the reverse path filter test:
1344 iptables -t raw -N RPFILTER
1346 iptables -t raw -A RPFILTER -m rpfilter -j RETURN
1348 iptables -t raw -A RPFILTER -m limit --limit 10/minute -j NFLOG
1350 --nflog-prefix "rpfilter drop"
1351 iptables -t raw -A RPFILTER -j DROP
1353 iptables -t raw -A PREROUTING -j RPFILTER
1355 Example to drop failed packets, without logging:
1357 iptables -t raw -A RPFILTER -m rpfilter --invert -j DROP
1359 rt (IPv6-specific)
1361 Match on IPv6 routing header
1362 [!] --rt-type type
1364 Match the type (numeric).
1365 [!] --rt-segsleft num[:num]
1367 Match the `segments left' field (range).
1368 [!] --rt-len length
1370 Match the length of this header.
1371 --rt-0-res
1373 Match the reserved field, too (type=0)
1374 --rt-0-addrs addr[,addr...]
1376 Match type=0 addresses (list).
1377 --rt-0-not-strict
1379 List of type=0 addresses is not a strict list.
1380 sctp
1382 This module matches Stream Control Transmission Protocol headers.
1383 [!] --source-port,--sport port[:port]
1385 [!] --destination-port,--dport port[:port]
1387 [!] --chunk-types {all|any|only} chunktype[:flags] [...]
1389 The flag letter in upper case indicates that the flag is to
1390 match if set, in the lower case indicates to match if unset.
1391 Chunk types: DATA INIT INIT_ACK SACK HEARTBEAT HEARTBEAT_ACK
1393 ABORT SHUTDOWN SHUTDOWN_ACK ERROR COOKIE_ECHO COOKIE_ACK
1394 ECN_ECNE ECN_CWR SHUTDOWN_COMPLETE ASCONF ASCONF_ACK FORWARD_TSN
1395 chunk type available flags
1397 DATA I U B E i u b e
1398 ABORT T t
1399 SHUTDOWN_COMPLETE T t
1400 (lowercase means flag should be "off", uppercase means "on")
1402 Examples:
1404 iptables -A INPUT -p sctp --dport 80 -j DROP
1406 iptables -A INPUT -p sctp --chunk-types any DATA,INIT -j DROP
1408 iptables -A INPUT -p sctp --chunk-types any DATA:Be -j ACCEPT
1410 set
1412 This module matches IP sets which can be defined by ipset(8).
1413 [!] --match-set setname flag[,flag]...
1415 where flags are the comma separated list of src and/or dst spec‐
1416 ifications and there can be no more than six of them. Hence the
1417 command
1418 iptables -A FORWARD -m set --match-set test src,dst
1420 will match packets, for which (if the set type is ipportmap) the
1422 source address and destination port pair can be found in the
1423 specified set. If the set type of the specified set is single
1424 dimension (for example ipmap), then the command will match pack‐
1425 ets for which the source address can be found in the specified
1426 set.
1427 --return-nomatch
1429 If the --return-nomatch option is specified and the set type
1430 supports the nomatch flag, then the matching is reversed: a
1431 match with an element flagged with nomatch returns true, while a
1432 match with a plain element returns false.
1433 ! --update-counters
1435 If the --update-counters flag is negated, then the packet and
1436 byte counters of the matching element in the set won't be up‐
1437 dated. Default the packet and byte counters are updated.
1438 ! --update-subcounters
1440 If the --update-subcounters flag is negated, then the packet and
1441 byte counters of the matching element in the member set of a
1442 list type of set won't be updated. Default the packet and byte
1443 counters are updated.
1444 [!] --packets-eq value
1446 If the packet is matched an element in the set, match only if
1447 the packet counter of the element matches the given value too.
1448 --packets-lt value
1450 If the packet is matched an element in the set, match only if
1451 the packet counter of the element is less than the given value
1452 as well.
1453 --packets-gt value
1455 If the packet is matched an element in the set, match only if
1456 the packet counter of the element is greater than the given
1457 value as well.
1458 [!] --bytes-eq value
1460 If the packet is matched an element in the set, match only if
1461 the byte counter of the element matches the given value too.
1462 --bytes-lt value
1464 If the packet is matched an element in the set, match only if
1465 the byte counter of the element is less than the given value as
1466 well.
1467 --bytes-gt value
1469 If the packet is matched an element in the set, match only if
1470 the byte counter of the element is greater than the given value
1471 as well.
1472 The packet and byte counters related options and flags are ignored when
1474 the set was defined without counter support.
1475 The option --match-set can be replaced by --set if that does not clash
1477 with an option of other extensions.
1478 Use of -m set requires that ipset kernel support is provided, which,
1480 for standard kernels, is the case since Linux 2.6.39.
1481 socket
1483 This matches if an open TCP/UDP socket can be found by doing a socket
1484 lookup on the packet. It matches if there is an established or non-zero
1485 bound listening socket (possibly with a non-local address). The lookup
1486 is performed using the packet tuple of TCP/UDP packets, or the original
1487 TCP/UDP header embedded in an ICMP/ICPMv6 error packet.
1488 --transparent
1490 Ignore non-transparent sockets.
1491 --nowildcard
1493 Do not ignore sockets bound to 'any' address. The socket match
1494 won't accept zero-bound listeners by default, since then local
1495 services could intercept traffic that would otherwise be for‐
1496 warded. This option therefore has security implications when
1497 used to match traffic being forwarded to redirect such packets
1498 to local machine with policy routing. When using the socket
1499 match to implement fully transparent proxies bound to non-local
1500 addresses it is recommended to use the --transparent option in‐
1501 stead.
1502 Example (assuming packets with mark 1 are delivered locally):
1504 -t mangle -A PREROUTING -m socket --transparent -j MARK
1506 --set-mark 1
1507 --restore-skmark
1509 Set the packet mark to the matching socket's mark. Can be com‐
1510 bined with the --transparent and --nowildcard options to re‐
1511 strict the sockets to be matched when restoring the packet mark.
1512 Example: An application opens 2 transparent (IP_TRANSPARENT) sockets
1514 and sets a mark on them with SO_MARK socket option. We can filter
1515 matching packets:
1516 -t mangle -I PREROUTING -m socket --transparent --restore-skmark
1518 -j action
1519 -t mangle -A action -m mark --mark 10 -j action2
1521 -t mangle -A action -m mark --mark 11 -j action3
1523 state
1525 The "state" extension is a subset of the "conntrack" module. "state"
1526 allows access to the connection tracking state for this packet.
1527 [!] --state state
1529 Where state is a comma separated list of the connection states
1530 to match. Only a subset of the states unterstood by "conntrack"
1531 are recognized: INVALID, ESTABLISHED, NEW, RELATED or UNTRACKED.
1532 For their description, see the "conntrack" heading in this man‐
1533 page.
1534 statistic
1536 This module matches packets based on some statistic condition. It sup‐
1537 ports two distinct modes settable with the --mode option.
1538 Supported options:
1540 --mode mode
1542 Set the matching mode of the matching rule, supported modes are
1543 random and nth.
1544 [!] --probability p
1546 Set the probability for a packet to be randomly matched. It only
1547 works with the random mode. p must be within 0.0 and 1.0. The
1548 supported granularity is in 1/2147483648th increments.
1549 [!] --every n
1551 Match one packet every nth packet. It works only with the nth
1552 mode (see also the --packet option).
1553 --packet p
1555 Set the initial counter value (0 <= p <= n-1, default 0) for the
1556 nth mode.
1557 string
1559 This module matches a given string by using some pattern matching
1560 strategy. It requires a linux kernel >= 2.6.14.
1561 --algo {bm|kmp}
1563 Select the pattern matching strategy. (bm = Boyer-Moore, kmp =
1564 Knuth-Pratt-Morris)
1565 --from offset
1567 Set the offset from which it starts looking for any matching. If
1568 not passed, default is 0.
1569 --to offset
1571 Set the offset up to which should be scanned. That is, byte off‐
1572 set-1 (counting from 0) is the last one that is scanned. If not
1573 passed, default is the packet size.
1574 [!] --string pattern
1576 Matches the given pattern.
1577 [!] --hex-string pattern
1579 Matches the given pattern in hex notation.
1580 --icase
1582 Ignore case when searching.
1583 Examples:
1585 # The string pattern can be used for simple text characters.
1587 iptables -A INPUT -p tcp --dport 80 -m string --algo bm --string
1588 'GET /index.html' -j LOG
1589 # The hex string pattern can be used for non-printable charac‐
1591 ters, like |0D 0A| or |0D0A|.
1592 iptables -p udp --dport 53 -m string --algo bm --from 40 --to 57
1593 --hex-string '|03|www|09|netfilter|03|org|00|'
1594 tcp
1596 These extensions can be used if `--protocol tcp' is specified. It pro‐
1597 vides the following options:
1598 [!] --source-port,--sport port[:port]
1600 Source port or port range specification. This can either be a
1601 service name or a port number. An inclusive range can also be
1602 specified, using the format first:last. If the first port is
1603 omitted, "0" is assumed; if the last is omitted, "65535" is as‐
1604 sumed. The flag --sport is a convenient alias for this option.
1605 [!] --destination-port,--dport port[:port]
1607 Destination port or port range specification. The flag --dport
1608 is a convenient alias for this option.
1609 [!] --tcp-flags mask comp
1611 Match when the TCP flags are as specified. The first argument
1612 mask is the flags which we should examine, written as a comma-
1613 separated list, and the second argument comp is a comma-sepa‐
1614 rated list of flags which must be set. Flags are: SYN ACK FIN
1615 RST URG PSH ALL NONE. Hence the command
1616 iptables -A FORWARD -p tcp --tcp-flags SYN,ACK,FIN,RST SYN
1617 will only match packets with the SYN flag set, and the ACK, FIN
1618 and RST flags unset.
1619 [!] --syn
1621 Only match TCP packets with the SYN bit set and the ACK,RST and
1622 FIN bits cleared. Such packets are used to request TCP connec‐
1623 tion initiation; for example, blocking such packets coming in an
1624 interface will prevent incoming TCP connections, but outgoing
1625 TCP connections will be unaffected. It is equivalent to
1626 --tcp-flags SYN,RST,ACK,FIN SYN. If the "!" flag precedes the
1627 "--syn", the sense of the option is inverted.
1628 [!] --tcp-option number
1630 Match if TCP option set.
1631 tcpmss
1633 This matches the TCP MSS (maximum segment size) field of the TCP
1634 header. You can only use this on TCP SYN or SYN/ACK packets, since the
1635 MSS is only negotiated during the TCP handshake at connection startup
1636 time.
1637 [!] --mss value[:value]
1639 Match a given TCP MSS value or range. If a range is given, the
1640 second value must be greater than or equal to the first value.
1641 time
1643 This matches if the packet arrival time/date is within a given range.
1644 All options are optional, but are ANDed when specified. All times are
1645 interpreted as UTC by default.
1646 --datestart YYYY[-MM[-DD[Thh[:mm[:ss]]]]]
1648 --datestop YYYY[-MM[-DD[Thh[:mm[:ss]]]]]
1650 Only match during the given time, which must be in ISO 8601 "T"
1651 notation. The possible time range is 1970-01-01T00:00:00 to
1652 2038-01-19T04:17:07.
1653 If --datestart or --datestop are not specified, it will default
1655 to 1970-01-01 and 2038-01-19, respectively.
1656 --timestart hh:mm[:ss]
1658 --timestop hh:mm[:ss]
1660 Only match during the given daytime. The possible time range is
1661 00:00:00 to 23:59:59. Leading zeroes are allowed (e.g. "06:03")
1662 and correctly interpreted as base-10.
1663 [!] --monthdays day[,day...]
1665 Only match on the given days of the month. Possible values are 1
1666 to 31. Note that specifying 31 will of course not match on
1667 months which do not have a 31st day; the same goes for 28- or
1668 29-day February.
1669 [!] --weekdays day[,day...]
1671 Only match on the given weekdays. Possible values are Mon, Tue,
1672 Wed, Thu, Fri, Sat, Sun, or values from 1 to 7, respectively.
1673 You may also use two-character variants (Mo, Tu, etc.).
1674 --contiguous
1676 When --timestop is smaller than --timestart value, match this as
1677 a single time period instead distinct intervals. See EXAMPLES.
1678 --kerneltz
1680 Use the kernel timezone instead of UTC to determine whether a
1681 packet meets the time regulations.
1682 About kernel timezones: Linux keeps the system time in UTC, and always
1684 does so. On boot, system time is initialized from a referential time
1685 source. Where this time source has no timezone information, such as the
1686 x86 CMOS RTC, UTC will be assumed. If the time source is however not in
1687 UTC, userspace should provide the correct system time and timezone to
1688 the kernel once it has the information.
1689 Local time is a feature on top of the (timezone independent) system
1691 time. Each process has its own idea of local time, specified via the TZ
1692 environment variable. The kernel also has its own timezone offset vari‐
1693 able. The TZ userspace environment variable specifies how the UTC-based
1694 system time is displayed, e.g. when you run date(1), or what you see on
1695 your desktop clock. The TZ string may resolve to different offsets at
1696 different dates, which is what enables the automatic time-jumping in
1697 userspace. when DST changes. The kernel's timezone offset variable is
1698 used when it has to convert between non-UTC sources, such as FAT
1699 filesystems, to UTC (since the latter is what the rest of the system
1700 uses).
1701 The caveat with the kernel timezone is that Linux distributions may ig‐
1703 nore to set the kernel timezone, and instead only set the system time.
1704 Even if a particular distribution does set the timezone at boot, it is
1705 usually does not keep the kernel timezone offset - which is what
1706 changes on DST - up to date. ntpd will not touch the kernel timezone,
1707 so running it will not resolve the issue. As such, one may encounter a
1708 timezone that is always +0000, or one that is wrong half of the time of
1709 the year. As such, using --kerneltz is highly discouraged.
1710 EXAMPLES. To match on weekends, use:
1712 -m time --weekdays Sa,Su
1714 Or, to match (once) on a national holiday block:
1716 -m time --datestart 2007-12-24 --datestop 2007-12-27
1718 Since the stop time is actually inclusive, you would need the following
1720 stop time to not match the first second of the new day:
1721 -m time --datestart 2007-01-01T17:00 --datestop
1723 2007-01-01T23:59:59
1724 During lunch hour:
1726 -m time --timestart 12:30 --timestop 13:30
1728 The fourth Friday in the month:
1730 -m time --weekdays Fr --monthdays 22,23,24,25,26,27,28
1732 (Note that this exploits a certain mathematical property. It is not
1734 possible to say "fourth Thursday OR fourth Friday" in one rule. It is
1735 possible with multiple rules, though.)
1736 Matching across days might not do what is expected. For instance,
1738 -m time --weekdays Mo --timestart 23:00 --timestop 01:00 Will
1740 match Monday, for one hour from midnight to 1 a.m., and then
1741 again for another hour from 23:00 onwards. If this is unwanted,
1742 e.g. if you would like 'match for two hours from Montay 23:00
1743 onwards' you need to also specify the --contiguous option in the
1744 example above.
1745 tos
1747 This module matches the 8-bit Type of Service field in the IPv4 header
1748 (i.e. including the "Precedence" bits) or the (also 8-bit) Priority
1749 field in the IPv6 header.
1750 [!] --tos value[/mask]
1752 Matches packets with the given TOS mark value. If a mask is
1753 specified, it is logically ANDed with the TOS mark before the
1754 comparison.
1755 [!] --tos symbol
1757 You can specify a symbolic name when using the tos match for
1758 IPv4. The list of recognized TOS names can be obtained by call‐
1759 ing iptables with -m tos -h. Note that this implies a mask of
1760 0x3F, i.e. all but the ECN bits.
1761 ttl (IPv4-specific)
1763 This module matches the time to live field in the IP header.
1764 [!] --ttl-eq ttl
1766 Matches the given TTL value.
1767 --ttl-gt ttl
1769 Matches if TTL is greater than the given TTL value.
1770 --ttl-lt ttl
1772 Matches if TTL is less than the given TTL value.
1773 u32
1775 U32 tests whether quantities of up to 4 bytes extracted from a packet
1776 have specified values. The specification of what to extract is general
1777 enough to find data at given offsets from tcp headers or payloads.
1778 [!] --u32 tests
1780 The argument amounts to a program in a small language described
1781 below.
1782 tests := location "=" value | tests "&&" location "=" value
1784 value := range | value "," range
1786 range := number | number ":" number
1788 a single number, n, is interpreted the same as n:n. n:m is interpreted
1790 as the range of numbers >=n and <=m.
1791 location := number | location operator number
1793 operator := "&" | "<<" | ">>" | "@"
1795 The operators &, <<, >> and && mean the same as in C. The = is really
1797 a set membership operator and the value syntax describes a set. The @
1798 operator is what allows moving to the next header and is described fur‐
1799 ther below.
1800 There are currently some artificial implementation limits on the size
1802 of the tests:
1803 * no more than 10 of "=" (and 9 "&&"s) in the u32 argument
1805 * no more than 10 ranges (and 9 commas) per value
1807 * no more than 10 numbers (and 9 operators) per location
1809 To describe the meaning of location, imagine the following machine that
1811 interprets it. There are three registers:
1812 A is of type char *, initially the address of the IP header
1814 B and C are unsigned 32 bit integers, initially zero
1816 The instructions are:
1818 number B = number;
1820 C = (*(A+B)<<24) + (*(A+B+1)<<16) + (*(A+B+2)<<8) + *(A+B+3)
1822 &number
1824 C = C & number
1825 << number
1827 C = C << number
1828 >> number
1830 C = C >> number
1831 @number
1833 A = A + C; then do the instruction number
1834 Any access of memory outside [skb->data,skb->end] causes the match to
1836 fail. Otherwise the result of the computation is the final value of C.
1837 Whitespace is allowed but not required in the tests. However, the char‐
1839 acters that do occur there are likely to require shell quoting, so it
1840 is a good idea to enclose the arguments in quotes.
1841 Example:
1843 match IP packets with total length >= 256
1845 The IP header contains a total length field in bytes 2-3.
1847 --u32 "0 & 0xFFFF = 0x100:0xFFFF"
1849 read bytes 0-3
1851 AND that with 0xFFFF (giving bytes 2-3), and test whether that
1853 is in the range [0x100:0xFFFF]
1854 Example: (more realistic, hence more complicated)
1856 match ICMP packets with icmp type 0
1858 First test that it is an ICMP packet, true iff byte 9 (protocol)
1860 = 1
1861 --u32 "6 & 0xFF = 1 && ...
1863 read bytes 6-9, use & to throw away bytes 6-8 and compare the
1865 result to 1. Next test that it is not a fragment. (If so, it
1866 might be part of such a packet but we cannot always tell.) N.B.:
1867 This test is generally needed if you want to match anything be‐
1868 yond the IP header. The last 6 bits of byte 6 and all of byte 7
1869 are 0 iff this is a complete packet (not a fragment). Alterna‐
1870 tively, you can allow first fragments by only testing the last 5
1871 bits of byte 6.
1872 ... 4 & 0x3FFF = 0 && ...
1874 Last test: the first byte past the IP header (the type) is 0.
1876 This is where we have to use the @syntax. The length of the IP
1877 header (IHL) in 32 bit words is stored in the right half of byte
1878 0 of the IP header itself.
1879 ... 0 >> 22 & 0x3C @ 0 >> 24 = 0"
1881 The first 0 means read bytes 0-3, >>22 means shift that 22 bits
1883 to the right. Shifting 24 bits would give the first byte, so
1884 only 22 bits is four times that plus a few more bits. &3C then
1885 eliminates the two extra bits on the right and the first four
1886 bits of the first byte. For instance, if IHL=5, then the IP
1887 header is 20 (4 x 5) bytes long. In this case, bytes 0-1 are (in
1888 binary) xxxx0101 yyzzzzzz, >>22 gives the 10 bit value
1889 xxxx0101yy and &3C gives 010100. @ means to use this number as a
1890 new offset into the packet, and read four bytes starting from
1891 there. This is the first 4 bytes of the ICMP payload, of which
1892 byte 0 is the ICMP type. Therefore, we simply shift the value 24
1893 to the right to throw out all but the first byte and compare the
1894 result with 0.
1895 Example:
1897 TCP payload bytes 8-12 is any of 1, 2, 5 or 8
1899 First we test that the packet is a tcp packet (similar to ICMP).
1901 --u32 "6 & 0xFF = 6 && ...
1903 Next, test that it is not a fragment (same as above).
1905 ... 0 >> 22 & 0x3C @ 12 >> 26 & 0x3C @ 8 = 1,2,5,8"
1907 0>>22&3C as above computes the number of bytes in the IP header.
1909 @ makes this the new offset into the packet, which is the start
1910 of the TCP header. The length of the TCP header (again in 32 bit
1911 words) is the left half of byte 12 of the TCP header. The
1912 12>>26&3C computes this length in bytes (similar to the IP
1913 header before). "@" makes this the new offset, which is the
1914 start of the TCP payload. Finally, 8 reads bytes 8-12 of the
1915 payload and = checks whether the result is any of 1, 2, 5 or 8.
1916 udp
1918 These extensions can be used if `--protocol udp' is specified. It pro‐
1919 vides the following options:
1920 [!] --source-port,--sport port[:port]
1922 Source port or port range specification. See the description of
1923 the --source-port option of the TCP extension for details.
1924 [!] --destination-port,--dport port[:port]
1926 Destination port or port range specification. See the descrip‐
1927 tion of the --destination-port option of the TCP extension for
1928 details.
1929
1931 iptables can use extended target modules: the following are included in
1932 the standard distribution.
1933 AUDIT
1935 This target creates audit records for packets hitting the target. It
1936 can be used to record accepted, dropped, and rejected packets. See au‐
1937 ditd(8) for additional details.
1938 --type {accept|drop|reject}
1940 Set type of audit record. Starting with linux-4.12, this option
1941 has no effect on generated audit messages anymore. It is still
1942 accepted by iptables for compatibility reasons, but ignored.
1943 Example:
1945 iptables -N AUDIT_DROP
1947 iptables -A AUDIT_DROP -j AUDIT
1949 iptables -A AUDIT_DROP -j DROP
1951 CHECKSUM
1953 This target selectively works around broken/old applications. It can
1954 only be used in the mangle table.
1955 --checksum-fill
1957 Compute and fill in the checksum in a packet that lacks a check‐
1958 sum. This is particularly useful, if you need to work around
1959 old applications such as dhcp clients, that do not work well
1960 with checksum offloads, but don't want to disable checksum off‐
1961 load in your device.
1962 CLASSIFY
1964 This module allows you to set the skb->priority value (and thus clas‐
1965 sify the packet into a specific CBQ class).
1966 --set-class major:minor
1968 Set the major and minor class value. The values are always in‐
1969 terpreted as hexadecimal even if no 0x prefix is given.
1970 CLUSTERIP (IPv4-specific)
1972 This module allows you to configure a simple cluster of nodes that
1973 share a certain IP and MAC address without an explicit load balancer in
1974 front of them. Connections are statically distributed between the
1975 nodes in this cluster.
1976 Please note that CLUSTERIP target is considered deprecated in favour of
1978 cluster match which is more flexible and not limited to IPv4.
1979 --new Create a new ClusterIP. You always have to set this on the
1981 first rule for a given ClusterIP.
1982 --hashmode mode
1984 Specify the hashing mode. Has to be one of sourceip, sour‐
1985 ceip-sourceport, sourceip-sourceport-destport.
1986 --clustermac mac
1988 Specify the ClusterIP MAC address. Has to be a link-layer multi‐
1989 cast address
1990 --total-nodes num
1992 Number of total nodes within this cluster.
1993 --local-node num
1995 Local node number within this cluster.
1996 --hash-init rnd
1998 Specify the random seed used for hash initialization.
1999 CONNMARK
2001 This module sets the netfilter mark value associated with a connection.
2002 The mark is 32 bits wide.
2003 --set-xmark value[/mask]
2005 Zero out the bits given by mask and XOR value into the ctmark.
2006 --save-mark [--nfmask nfmask] [--ctmask ctmask]
2008 Copy the packet mark (nfmark) to the connection mark (ctmark)
2009 using the given masks. The new nfmark value is determined as
2010 follows:
2011 ctmark = (ctmark & ~ctmask) ^ (nfmark & nfmask)
2013 i.e. ctmask defines what bits to clear and nfmask what bits of
2015 the nfmark to XOR into the ctmark. ctmask and nfmask default to
2016 0xFFFFFFFF.
2017 --restore-mark [--nfmask nfmask] [--ctmask ctmask]
2019 Copy the connection mark (ctmark) to the packet mark (nfmark)
2020 using the given masks. The new ctmark value is determined as
2021 follows:
2022 nfmark = (nfmark & ~nfmask) ^ (ctmark & ctmask);
2024 i.e. nfmask defines what bits to clear and ctmask what bits of
2026 the ctmark to XOR into the nfmark. ctmask and nfmask default to
2027 0xFFFFFFFF.
2028 --restore-mark is only valid in the mangle table.
2030 The following mnemonics are available for --set-xmark:
2032 --and-mark bits
2034 Binary AND the ctmark with bits. (Mnemonic for --set-xmark 0/in‐
2035 vbits, where invbits is the binary negation of bits.)
2036 --or-mark bits
2038 Binary OR the ctmark with bits. (Mnemonic for --set-xmark
2039 bits/bits.)
2040 --xor-mark bits
2042 Binary XOR the ctmark with bits. (Mnemonic for --set-xmark
2043 bits/0.)
2044 --set-mark value[/mask]
2046 Set the connection mark. If a mask is specified then only those
2047 bits set in the mask are modified.
2048 --save-mark [--mask mask]
2050 Copy the nfmark to the ctmark. If a mask is specified, only
2051 those bits are copied.
2052 --restore-mark [--mask mask]
2054 Copy the ctmark to the nfmark. If a mask is specified, only
2055 those bits are copied. This is only valid in the mangle table.
2056 CONNSECMARK
2058 This module copies security markings from packets to connections (if
2059 unlabeled), and from connections back to packets (also only if unla‐
2060 beled). Typically used in conjunction with SECMARK, it is valid in the
2061 security table (for backwards compatibility with older kernels, it is
2062 also valid in the mangle table).
2063 --save If the packet has a security marking, copy it to the connection
2065 if the connection is not marked.
2066 --restore
2068 If the packet does not have a security marking, and the connec‐
2069 tion does, copy the security marking from the connection to the
2070 packet.
2071 CT
2074 The CT target sets parameters for a packet or its associated connec‐
2075 tion. The target attaches a "template" connection tracking entry to the
2076 packet, which is then used by the conntrack core when initializing a
2077 new ct entry. This target is thus only valid in the "raw" table.
2078 --notrack
2080 Disables connection tracking for this packet.
2081 --helper name
2083 Use the helper identified by name for the connection. This is
2084 more flexible than loading the conntrack helper modules with
2085 preset ports.
2086 --ctevents event[,...]
2088 Only generate the specified conntrack events for this connec‐
2089 tion. Possible event types are: new, related, destroy, reply,
2090 assured, protoinfo, helper, mark (this refers to the ctmark, not
2091 nfmark), natseqinfo, secmark (ctsecmark).
2092 --expevents event[,...]
2094 Only generate the specified expectation events for this connec‐
2095 tion. Possible event types are: new.
2096 --zone-orig {id|mark}
2098 For traffic coming from ORIGINAL direction, assign this packet
2099 to zone id and only have lookups done in that zone. If mark is
2100 used instead of id, the zone is derived from the packet nfmark.
2101 --zone-reply {id|mark}
2103 For traffic coming from REPLY direction, assign this packet to
2104 zone id and only have lookups done in that zone. If mark is used
2105 instead of id, the zone is derived from the packet nfmark.
2106 --zone {id|mark}
2108 Assign this packet to zone id and only have lookups done in that
2109 zone. If mark is used instead of id, the zone is derived from
2110 the packet nfmark. By default, packets have zone 0. This option
2111 applies to both directions.
2112 --timeout name
2114 Use the timeout policy identified by name for the connection.
2115 This is provides more flexible timeout policy definition than
2116 global timeout values available at /proc/sys/net/netfil‐
2117 ter/nf_conntrack_*_timeout_*.
2118 DNAT
2120 This target is only valid in the nat table, in the PREROUTING and OUT‐
2121 PUT chains, and user-defined chains which are only called from those
2122 chains. It specifies that the destination address of the packet should
2123 be modified (and all future packets in this connection will also be
2124 mangled), and rules should cease being examined. It takes the follow‐
2125 ing options:
2126 --to-destination [ipaddr[-ipaddr]][:port[-port]]
2128 which can specify a single new destination IP address, an inclu‐
2129 sive range of IP addresses. Optionally a port range, if the rule
2130 also specifies one of the following protocols: tcp, udp, dccp or
2131 sctp. If no port range is specified, then the destination port
2132 will never be modified. If no IP address is specified then only
2133 the destination port will be modified. In Kernels up to 2.6.10
2134 you can add several --to-destination options. For those kernels,
2135 if you specify more than one destination address, either via an
2136 address range or multiple --to-destination options, a simple
2137 round-robin (one after another in cycle) load balancing takes
2138 place between these addresses. Later Kernels (>= 2.6.11-rc1)
2139 don't have the ability to NAT to multiple ranges anymore.
2140 --random
2142 If option --random is used then port mapping will be randomized
2143 (kernel >= 2.6.22).
2144 --persistent
2146 Gives a client the same source-/destination-address for each
2147 connection. This supersedes the SAME target. Support for per‐
2148 sistent mappings is available from 2.6.29-rc2.
2149 IPv6 support available since Linux kernels >= 3.7.
2151 DNPT (IPv6-specific)
2153 Provides stateless destination IPv6-to-IPv6 Network Prefix Translation
2154 (as described by RFC 6296).
2155 You have to use this target in the mangle table, not in the nat table.
2157 It takes the following options:
2158 --src-pfx [prefix/length]
2160 Set source prefix that you want to translate and length
2161 --dst-pfx [prefix/length]
2163 Set destination prefix that you want to use in the translation
2164 and length
2165 You have to use the SNPT target to undo the translation. Example:
2167 ip6tables -t mangle -I POSTROUTING -s fd00::/64 -o vboxnet0 -j
2169 SNPT --src-pfx fd00::/64 --dst-pfx 2001:e20:2000:40f::/64
2170 ip6tables -t mangle -I PREROUTING -i wlan0 -d
2172 2001:e20:2000:40f::/64 -j DNPT --src-pfx 2001:e20:2000:40f::/64
2173 --dst-pfx fd00::/64
2174 You may need to enable IPv6 neighbor proxy:
2176 sysctl -w net.ipv6.conf.all.proxy_ndp=1
2178 You also have to use the NOTRACK target to disable connection tracking
2180 for translated flows.
2181 DSCP
2183 This target alters the value of the DSCP bits within the TOS header of
2184 the IPv4 packet. As this manipulates a packet, it can only be used in
2185 the mangle table.
2186 --set-dscp value
2188 Set the DSCP field to a numerical value (can be decimal or hex)
2189 --set-dscp-class class
2191 Set the DSCP field to a DiffServ class.
2192 ECN (IPv4-specific)
2194 This target selectively works around known ECN blackholes. It can only
2195 be used in the mangle table.
2196 --ecn-tcp-remove
2198 Remove all ECN bits from the TCP header. Of course, it can only
2199 be used in conjunction with -p tcp.
2200 HL (IPv6-specific)
2202 This is used to modify the Hop Limit field in IPv6 header. The Hop
2203 Limit field is similar to what is known as TTL value in IPv4. Setting
2204 or incrementing the Hop Limit field can potentially be very dangerous,
2205 so it should be avoided at any cost. This target is only valid in man‐
2206 gle table.
2207 Don't ever set or increment the value on packets that leave your local
2209 network!
2210 --hl-set value
2212 Set the Hop Limit to `value'.
2213 --hl-dec value
2215 Decrement the Hop Limit `value' times.
2216 --hl-inc value
2218 Increment the Hop Limit `value' times.
2219 HMARK
2221 Like MARK, i.e. set the fwmark, but the mark is calculated from hashing
2222 packet selector at choice. You have also to specify the mark range and,
2223 optionally, the offset to start from. ICMP error messages are inspected
2224 and used to calculate the hashing.
2225 Existing options are:
2227 --hmark-tuple tuple
2229 Possible tuple members are: src meaning source address (IPv4,
2230 IPv6 address), dst meaning destination address (IPv4, IPv6 ad‐
2231 dress), sport meaning source port (TCP, UDP, UDPlite, SCTP,
2232 DCCP), dport meaning destination port (TCP, UDP, UDPlite, SCTP,
2233 DCCP), spi meaning Security Parameter Index (AH, ESP), and ct
2234 meaning the usage of the conntrack tuple instead of the packet
2235 selectors.
2236 --hmark-mod value (must be > 0)
2238 Modulus for hash calculation (to limit the range of possible
2239 marks)
2240 --hmark-offset value
2242 Offset to start marks from.
2243 For advanced usage, instead of using --hmark-tuple, you can specify
2245 custom
2246 prefixes and masks:
2247 --hmark-src-prefix cidr
2249 The source address mask in CIDR notation.
2250 --hmark-dst-prefix cidr
2252 The destination address mask in CIDR notation.
2253 --hmark-sport-mask value
2255 A 16 bit source port mask in hexadecimal.
2256 --hmark-dport-mask value
2258 A 16 bit destination port mask in hexadecimal.
2259 --hmark-spi-mask value
2261 A 32 bit field with spi mask.
2262 --hmark-proto-mask value
2264 An 8 bit field with layer 4 protocol number.
2265 --hmark-rnd value
2267 A 32 bit random custom value to feed hash calculation.
2268 Examples:
2270 iptables -t mangle -A PREROUTING -m conntrack --ctstate NEW
2272 -j HMARK --hmark-tuple ct,src,dst,proto --hmark-offset 10000
2273 --hmark-mod 10 --hmark-rnd 0xfeedcafe
2274 iptables -t mangle -A PREROUTING -j HMARK --hmark-offset 10000 --hmark-
2276 tuple src,dst,proto --hmark-mod 10 --hmark-rnd 0xdeafbeef
2277 IDLETIMER
2279 This target can be used to identify when interfaces have been idle for
2280 a certain period of time. Timers are identified by labels and are cre‐
2281 ated when a rule is set with a new label. The rules also take a time‐
2282 out value (in seconds) as an option. If more than one rule uses the
2283 same timer label, the timer will be restarted whenever any of the rules
2284 get a hit. One entry for each timer is created in sysfs. This attri‐
2285 bute contains the timer remaining for the timer to expire. The at‐
2286 tributes are located under the xt_idletimer class:
2287 /sys/class/xt_idletimer/timers/<label>
2289 When the timer expires, the target module sends a sysfs notification to
2291 the userspace, which can then decide what to do (eg. disconnect to save
2292 power).
2293 --timeout amount
2295 This is the time in seconds that will trigger the notification.
2296 --label string
2298 This is a unique identifier for the timer. The maximum length
2299 for the label string is 27 characters.
2300 LED
2302 This creates an LED-trigger that can then be attached to system indica‐
2303 tor lights, to blink or illuminate them when certain packets pass
2304 through the system. One example might be to light up an LED for a few
2305 minutes every time an SSH connection is made to the local machine. The
2306 following options control the trigger behavior:
2307 --led-trigger-id name
2309 This is the name given to the LED trigger. The actual name of
2310 the trigger will be prefixed with "netfilter-".
2311 --led-delay ms
2313 This indicates how long (in milliseconds) the LED should be left
2314 illuminated when a packet arrives before being switched off
2315 again. The default is 0 (blink as fast as possible.) The special
2316 value inf can be given to leave the LED on permanently once ac‐
2317 tivated. (In this case the trigger will need to be manually de‐
2318 tached and reattached to the LED device to switch it off again.)
2319 --led-always-blink
2321 Always make the LED blink on packet arrival, even if the LED is
2322 already on. This allows notification of new packets even with
2323 long delay values (which otherwise would result in a silent pro‐
2324 longing of the delay time.)
2325 Example:
2327 Create an LED trigger for incoming SSH traffic:
2329 iptables -A INPUT -p tcp --dport 22 -j LED --led-trigger-id ssh
2330 Then attach the new trigger to an LED:
2332 echo netfilter-ssh >/sys/class/leds/ledname/trigger
2333 LOG
2335 Turn on kernel logging of matching packets. When this option is set
2336 for a rule, the Linux kernel will print some information on all match‐
2337 ing packets (like most IP/IPv6 header fields) via the kernel log (where
2338 it can be read with dmesg(1) or read in the syslog).
2339 This is a "non-terminating target", i.e. rule traversal continues at
2341 the next rule. So if you want to LOG the packets you refuse, use two
2342 separate rules with the same matching criteria, first using target LOG
2343 then DROP (or REJECT).
2344 --log-level level
2346 Level of logging, which can be (system-specific) numeric or a
2347 mnemonic. Possible values are (in decreasing order of prior‐
2348 ity): emerg, alert, crit, error, warning, notice, info or debug.
2349 --log-prefix prefix
2351 Prefix log messages with the specified prefix; up to 29 letters
2352 long, and useful for distinguishing messages in the logs.
2353 --log-tcp-sequence
2355 Log TCP sequence numbers. This is a security risk if the log is
2356 readable by users.
2357 --log-tcp-options
2359 Log options from the TCP packet header.
2360 --log-ip-options
2362 Log options from the IP/IPv6 packet header.
2363 --log-uid
2365 Log the userid of the process which generated the packet.
2366 MARK
2368 This target is used to set the Netfilter mark value associated with the
2369 packet. It can, for example, be used in conjunction with routing based
2370 on fwmark (needs iproute2). If you plan on doing so, note that the mark
2371 needs to be set in either the PREROUTING or the OUTPUT chain of the
2372 mangle table to affect routing. The mark field is 32 bits wide.
2373 --set-xmark value[/mask]
2375 Zeroes out the bits given by mask and XORs value into the packet
2376 mark ("nfmark"). If mask is omitted, 0xFFFFFFFF is assumed.
2377 --set-mark value[/mask]
2379 Zeroes out the bits given by mask and ORs value into the packet
2380 mark. If mask is omitted, 0xFFFFFFFF is assumed.
2381 The following mnemonics are available:
2383 --and-mark bits
2385 Binary AND the nfmark with bits. (Mnemonic for --set-xmark 0/in‐
2386 vbits, where invbits is the binary negation of bits.)
2387 --or-mark bits
2389 Binary OR the nfmark with bits. (Mnemonic for --set-xmark
2390 bits/bits.)
2391 --xor-mark bits
2393 Binary XOR the nfmark with bits. (Mnemonic for --set-xmark
2394 bits/0.)
2395 MASQUERADE
2397 This target is only valid in the nat table, in the POSTROUTING chain.
2398 It should only be used with dynamically assigned IP (dialup) connec‐
2399 tions: if you have a static IP address, you should use the SNAT target.
2400 Masquerading is equivalent to specifying a mapping to the IP address of
2401 the interface the packet is going out, but also has the effect that
2402 connections are forgotten when the interface goes down. This is the
2403 correct behavior when the next dialup is unlikely to have the same in‐
2404 terface address (and hence any established connections are lost any‐
2405 way).
2406 --to-ports port[-port]
2408 This specifies a range of source ports to use, overriding the
2409 default SNAT source port-selection heuristics (see above). This
2410 is only valid if the rule also specifies one of the following
2411 protocols: tcp, udp, dccp or sctp.
2412 --random
2414 Randomize source port mapping If option --random is used then
2415 port mapping will be randomized (kernel >= 2.6.21). Since ker‐
2416 nel 5.0, --random is identical to --random-fully.
2417 --random-fully
2419 Full randomize source port mapping If option --random-fully is
2420 used then port mapping will be fully randomized (kernel >=
2421 3.13).
2422 IPv6 support available since Linux kernels >= 3.7.
2424 NETMAP
2426 This target allows you to statically map a whole network of addresses
2427 onto another network of addresses. It can only be used from rules in
2428 the nat table.
2429 --to address[/mask]
2431 Network address to map to. The resulting address will be con‐
2432 structed in the following way: All 'one' bits in the mask are
2433 filled in from the new `address'. All bits that are zero in the
2434 mask are filled in from the original address.
2435 IPv6 support available since Linux kernels >= 3.7.
2437 NFLOG
2439 This target provides logging of matching packets. When this target is
2440 set for a rule, the Linux kernel will pass the packet to the loaded
2441 logging backend to log the packet. This is usually used in combination
2442 with nfnetlink_log as logging backend, which will multicast the packet
2443 through a netlink socket to the specified multicast group. One or more
2444 userspace processes may subscribe to the group to receive the packets.
2445 Like LOG, this is a non-terminating target, i.e. rule traversal contin‐
2446 ues at the next rule.
2447 --nflog-group nlgroup
2449 The netlink group (0 - 2^16-1) to which packets are (only appli‐
2450 cable for nfnetlink_log). The default value is 0.
2451 --nflog-prefix prefix
2453 A prefix string to include in the log message, up to 64 charac‐
2454 ters long, useful for distinguishing messages in the logs.
2455 --nflog-range size
2457 This option has never worked, use --nflog-size instead
2458 --nflog-size size
2460 The number of bytes to be copied to userspace (only applicable
2461 for nfnetlink_log). nfnetlink_log instances may specify their
2462 own range, this option overrides it.
2463 --nflog-threshold size
2465 Number of packets to queue inside the kernel before sending them
2466 to userspace (only applicable for nfnetlink_log). Higher values
2467 result in less overhead per packet, but increase delay until the
2468 packets reach userspace. The default value is 1.
2469 NFQUEUE
2471 This target passes the packet to userspace using the nfnetlink_queue
2472 handler. The packet is put into the queue identified by its 16-bit
2473 queue number. Userspace can inspect and modify the packet if desired.
2474 Userspace must then drop or reinject the packet into the kernel.
2475 Please see libnetfilter_queue for details. nfnetlink_queue was added
2476 in Linux 2.6.14. The queue-balance option was added in Linux 2.6.31,
2477 queue-bypass in 2.6.39.
2478 --queue-num value
2480 This specifies the QUEUE number to use. Valid queue numbers are
2481 0 to 65535. The default value is 0.
2482 --queue-balance value:value
2484 This specifies a range of queues to use. Packets are then bal‐
2485 anced across the given queues. This is useful for multicore
2486 systems: start multiple instances of the userspace program on
2487 queues x, x+1, .. x+n and use "--queue-balance x:x+n". Packets
2488 belonging to the same connection are put into the same nfqueue.
2489 --queue-bypass
2491 By default, if no userspace program is listening on an NFQUEUE,
2492 then all packets that are to be queued are dropped. When this
2493 option is used, the NFQUEUE rule behaves like ACCEPT instead,
2494 and the packet will move on to the next table.
2495 --queue-cpu-fanout
2497 Available starting Linux kernel 3.10. When used together with
2498 --queue-balance this will use the CPU ID as an index to map
2499 packets to the queues. The idea is that you can improve perfor‐
2500 mance if there's a queue per CPU. This requires --queue-balance
2501 to be specified.
2502 NOTRACK
2504 This extension disables connection tracking for all packets matching
2505 that rule. It is equivalent with -j CT --notrack. Like CT, NOTRACK can
2506 only be used in the raw table.
2507 RATEEST
2509 The RATEEST target collects statistics, performs rate estimation calcu‐
2510 lation and saves the results for later evaluation using the rateest
2511 match.
2512 --rateest-name name
2514 Count matched packets into the pool referred to by name, which
2515 is freely choosable.
2516 --rateest-interval amount{s|ms|us}
2518 Rate measurement interval, in seconds, milliseconds or microsec‐
2519 onds.
2520 --rateest-ewmalog value
2522 Rate measurement averaging time constant.
2523 REDIRECT
2525 This target is only valid in the nat table, in the PREROUTING and OUT‐
2526 PUT chains, and user-defined chains which are only called from those
2527 chains. It redirects the packet to the machine itself by changing the
2528 destination IP to the primary address of the incoming interface (lo‐
2529 cally-generated packets are mapped to the localhost address, 127.0.0.1
2530 for IPv4 and ::1 for IPv6, and packets arriving on interfaces that
2531 don't have an IP address configured are dropped).
2532 --to-ports port[-port]
2534 This specifies a destination port or range of ports to use:
2535 without this, the destination port is never altered. This is
2536 only valid if the rule also specifies one of the following pro‐
2537 tocols: tcp, udp, dccp or sctp.
2538 --random
2540 If option --random is used then port mapping will be randomized
2541 (kernel >= 2.6.22).
2542 IPv6 support available starting Linux kernels >= 3.7.
2544 REJECT (IPv6-specific)
2546 This is used to send back an error packet in response to the matched
2547 packet: otherwise it is equivalent to DROP so it is a terminating TAR‐
2548 GET, ending rule traversal. This target is only valid in the INPUT,
2549 FORWARD and OUTPUT chains, and user-defined chains which are only
2550 called from those chains. The following option controls the nature of
2551 the error packet returned:
2552 --reject-with type
2554 The type given can be icmp6-no-route, no-route, icmp6-adm-pro‐
2555 hibited, adm-prohibited, icmp6-addr-unreachable, addr-unreach,
2556 or icmp6-port-unreachable, which return the appropriate ICMPv6
2557 error message (icmp6-port-unreachable is the default). Finally,
2558 the option tcp-reset can be used on rules which only match the
2559 TCP protocol: this causes a TCP RST packet to be sent back.
2560 This is mainly useful for blocking ident (113/tcp) probes which
2561 frequently occur when sending mail to broken mail hosts (which
2562 won't accept your mail otherwise). tcp-reset can only be used
2563 with kernel versions 2.6.14 or later.
2564 Warning: You should not indiscriminately apply the REJECT target to
2566 packets whose connection state is classified as INVALID; instead, you
2567 should only DROP these.
2568 Consider a source host transmitting a packet P, with P experiencing so
2570 much delay along its path that the source host issues a retransmission,
2571 P_2, with P_2 being successful in reaching its destination and advanc‐
2572 ing the connection state normally. It is conceivable that the late-ar‐
2573 riving P may be considered not to be associated with any connection
2574 tracking entry. Generating a reject response for a packet so classed
2575 would then terminate the healthy connection.
2576 So, instead of:
2578 -A INPUT ... -j REJECT
2580 do consider using:
2582 -A INPUT ... -m conntrack --ctstate INVALID -j DROP -A INPUT ... -j RE‐
2584 JECT
2585 REJECT (IPv4-specific)
2587 This is used to send back an error packet in response to the matched
2588 packet: otherwise it is equivalent to DROP so it is a terminating TAR‐
2589 GET, ending rule traversal. This target is only valid in the INPUT,
2590 FORWARD and OUTPUT chains, and user-defined chains which are only
2591 called from those chains. The following option controls the nature of
2592 the error packet returned:
2593 --reject-with type
2595 The type given can be icmp-net-unreachable, icmp-host-unreach‐
2596 able, icmp-port-unreachable, icmp-proto-unreachable,
2597 icmp-net-prohibited, icmp-host-prohibited, or icmp-admin-prohib‐
2598 ited (*), which return the appropriate ICMP error message
2599 (icmp-port-unreachable is the default). The option tcp-reset
2600 can be used on rules which only match the TCP protocol: this
2601 causes a TCP RST packet to be sent back. This is mainly useful
2602 for blocking ident (113/tcp) probes which frequently occur when
2603 sending mail to broken mail hosts (which won't accept your mail
2604 otherwise).
2605 (*) Using icmp-admin-prohibited with kernels that do not support
2607 it will result in a plain DROP instead of REJECT
2608 Warning: You should not indiscriminately apply the REJECT target to
2610 packets whose connection state is classified as INVALID; instead, you
2611 should only DROP these.
2612 Consider a source host transmitting a packet P, with P experiencing so
2614 much delay along its path that the source host issues a retransmission,
2615 P_2, with P_2 being successful in reaching its destination and advanc‐
2616 ing the connection state normally. It is conceivable that the late-ar‐
2617 riving P may be considered not to be associated with any connection
2618 tracking entry. Generating a reject response for a packet so classed
2619 would then terminate the healthy connection.
2620 So, instead of:
2622 -A INPUT ... -j REJECT
2624 do consider using:
2626 -A INPUT ... -m conntrack --ctstate INVALID -j DROP -A INPUT ... -j RE‐
2628 JECT
2629 SECMARK
2631 This is used to set the security mark value associated with the packet
2632 for use by security subsystems such as SELinux. It is valid in the se‐
2633 curity table (for backwards compatibility with older kernels, it is
2634 also valid in the mangle table). The mark is 32 bits wide.
2635 --selctx security_context
2637 SET
2639 This module adds and/or deletes entries from IP sets which can be de‐
2640 fined by ipset(8).
2641 --add-set setname flag[,flag...]
2643 add the address(es)/port(s) of the packet to the set
2644 --del-set setname flag[,flag...]
2646 delete the address(es)/port(s) of the packet from the set
2647 --map-set setname flag[,flag...]
2649 [--map-mark] [--map-prio] [--map-queue] map packet properties
2650 (firewall mark, tc priority, hardware queue)
2651 where flag(s) are src and/or dst specifications and there can be
2653 no more than six of them.
2654 --timeout value
2656 when adding an entry, the timeout value to use instead of the
2657 default one from the set definition
2658 --exist
2660 when adding an entry if it already exists, reset the timeout
2661 value to the specified one or to the default from the set defi‐
2662 nition
2663 --map-set set-name
2665 the set-name should be created with --skbinfo option --map-mark
2666 map firewall mark to packet by lookup of value in the set
2667 --map-prio map traffic control priority to packet by lookup of
2668 value in the set --map-queue map hardware NIC queue to packet by
2669 lookup of value in the set
2670 The --map-set option can be used from the mangle table only. The
2672 --map-prio and --map-queue flags can be used in the OUTPUT, FOR‐
2673 WARD and POSTROUTING chains.
2674 Use of -j SET requires that ipset kernel support is provided, which,
2676 for standard kernels, is the case since Linux 2.6.39.
2677 SNAT
2679 This target is only valid in the nat table, in the POSTROUTING and IN‐
2680 PUT chains, and user-defined chains which are only called from those
2681 chains. It specifies that the source address of the packet should be
2682 modified (and all future packets in this connection will also be man‐
2683 gled), and rules should cease being examined. It takes the following
2684 options:
2685 --to-source [ipaddr[-ipaddr]][:port[-port]]
2687 which can specify a single new source IP address, an inclusive
2688 range of IP addresses. Optionally a port range, if the rule also
2689 specifies one of the following protocols: tcp, udp, dccp or
2690 sctp. If no port range is specified, then source ports below
2691 512 will be mapped to other ports below 512: those between 512
2692 and 1023 inclusive will be mapped to ports below 1024, and other
2693 ports will be mapped to 1024 or above. Where possible, no port
2694 alteration will occur. In Kernels up to 2.6.10, you can add
2695 several --to-source options. For those kernels, if you specify
2696 more than one source address, either via an address range or
2697 multiple --to-source options, a simple round-robin (one after
2698 another in cycle) takes place between these addresses. Later
2699 Kernels (>= 2.6.11-rc1) don't have the ability to NAT to multi‐
2700 ple ranges anymore.
2701 --random
2703 If option --random is used then port mapping will be randomized
2704 through a hash-based algorithm (kernel >= 2.6.21).
2705 --random-fully
2707 If option --random-fully is used then port mapping will be fully
2708 randomized through a PRNG (kernel >= 3.14).
2709 --persistent
2711 Gives a client the same source-/destination-address for each
2712 connection. This supersedes the SAME target. Support for per‐
2713 sistent mappings is available from 2.6.29-rc2.
2714 Kernels prior to 2.6.36-rc1 don't have the ability to SNAT in the INPUT
2716 chain.
2717 IPv6 support available since Linux kernels >= 3.7.
2719 SNPT (IPv6-specific)
2721 Provides stateless source IPv6-to-IPv6 Network Prefix Translation (as
2722 described by RFC 6296).
2723 You have to use this target in the mangle table, not in the nat table.
2725 It takes the following options:
2726 --src-pfx [prefix/length]
2728 Set source prefix that you want to translate and length
2729 --dst-pfx [prefix/length]
2731 Set destination prefix that you want to use in the translation
2732 and length
2733 You have to use the DNPT target to undo the translation. Example:
2735 ip6tables -t mangle -I POSTROUTING -s fd00::/64 -o vboxnet0 -j
2737 SNPT --src-pfx fd00::/64 --dst-pfx 2001:e20:2000:40f::/64
2738 ip6tables -t mangle -I PREROUTING -i wlan0 -d
2740 2001:e20:2000:40f::/64 -j DNPT --src-pfx 2001:e20:2000:40f::/64
2741 --dst-pfx fd00::/64
2742 You may need to enable IPv6 neighbor proxy:
2744 sysctl -w net.ipv6.conf.all.proxy_ndp=1
2746 You also have to use the NOTRACK target to disable connection tracking
2748 for translated flows.
2749 SYNPROXY
2751 This target will process TCP three-way-handshake parallel in netfilter
2752 context to protect either local or backend system. This target requires
2753 connection tracking because sequence numbers need to be translated.
2754 The kernels ability to absorb SYNFLOOD was greatly improved starting
2755 with Linux 4.4, so this target should not be needed anymore to protect
2756 Linux servers.
2757 --mss maximum segment size
2759 Maximum segment size announced to clients. This must match the
2760 backend.
2761 --wscale window scale
2763 Window scale announced to clients. This must match the backend.
2764 --sack-perm
2766 Pass client selective acknowledgement option to backend (will be
2767 disabled if not present).
2768 --timestamps
2770 Pass client timestamp option to backend (will be disabled if not
2771 present, also needed for selective acknowledgement and window
2772 scaling).
2773 Example:
2775 Determine tcp options used by backend, from an external system
2777 tcpdump -pni eth0 -c 1 'tcp[tcpflags] == (tcp-syn|tcp-ack)'
2779 port 80 &
2780 telnet 192.0.2.42 80
2781 18:57:24.693307 IP 192.0.2.42.80 > 192.0.2.43.48757:
2782 Flags [S.], seq 360414582, ack 788841994, win 14480,
2783 options [mss 1460,sackOK,
2784 TS val 1409056151 ecr 9690221,
2785 nop,wscale 9],
2786 length 0
2787 Switch tcp_loose mode off, so conntrack will mark out-of-flow packets
2789 as state INVALID.
2790 echo 0 > /proc/sys/net/netfilter/nf_conntrack_tcp_loose
2792 Make SYN packets untracked
2794 iptables -t raw -A PREROUTING -i eth0 -p tcp --dport 80
2796 --syn -j CT --notrack
2797 Catch UNTRACKED (SYN packets) and INVALID (3WHS ACK packets) states and
2799 send them to SYNPROXY. This rule will respond to SYN packets with
2800 SYN+ACK syncookies, create ESTABLISHED for valid client response (3WHS
2801 ACK packets) and drop incorrect cookies. Flags combinations not ex‐
2802 pected during 3WHS will not match and continue (e.g. SYN+FIN, SYN+ACK).
2803 iptables -A INPUT -i eth0 -p tcp --dport 80
2805 -m state --state UNTRACKED,INVALID -j SYNPROXY
2806 --sack-perm --timestamp --mss 1460 --wscale 9
2807 Drop invalid packets, this will be out-of-flow packets that were not
2809 matched by SYNPROXY.
2810 iptables -A INPUT -i eth0 -p tcp --dport 80 -m state --state IN‐
2812 VALID -j DROP
2813 TCPMSS
2815 This target alters the MSS value of TCP SYN packets, to control the
2816 maximum size for that connection (usually limiting it to your outgoing
2817 interface's MTU minus 40 for IPv4 or 60 for IPv6, respectively). Of
2818 course, it can only be used in conjunction with -p tcp.
2819 This target is used to overcome criminally braindead ISPs or servers
2821 which block "ICMP Fragmentation Needed" or "ICMPv6 Packet Too Big"
2822 packets. The symptoms of this problem are that everything works fine
2823 from your Linux firewall/router, but machines behind it can never ex‐
2824 change large packets:
2825 1. Web browsers connect, then hang with no data received.
2827 2. Small mail works fine, but large emails hang.
2829 3. ssh works fine, but scp hangs after initial handshaking.
2831 Workaround: activate this option and add a rule to your firewall con‐
2833 figuration like:
2834 iptables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN
2836 -j TCPMSS --clamp-mss-to-pmtu
2837 --set-mss value
2839 Explicitly sets MSS option to specified value. If the MSS of the
2840 packet is already lower than value, it will not be increased
2841 (from Linux 2.6.25 onwards) to avoid more problems with hosts
2842 relying on a proper MSS.
2843 --clamp-mss-to-pmtu
2845 Automatically clamp MSS value to (path_MTU - 40 for IPv4; -60
2846 for IPv6). This may not function as desired where asymmetric
2847 routes with differing path MTU exist — the kernel uses the path
2848 MTU which it would use to send packets from itself to the source
2849 and destination IP addresses. Prior to Linux 2.6.25, only the
2850 path MTU to the destination IP address was considered by this
2851 option; subsequent kernels also consider the path MTU to the
2852 source IP address.
2853 These options are mutually exclusive.
2855 TCPOPTSTRIP
2857 This target will strip TCP options off a TCP packet. (It will actually
2858 replace them by NO-OPs.) As such, you will need to add the -p tcp pa‐
2859 rameters.
2860 --strip-options option[,option...]
2862 Strip the given option(s). The options may be specified by TCP
2863 option number or by symbolic name. The list of recognized op‐
2864 tions can be obtained by calling iptables with -j TCPOPTSTRIP
2865 -h.
2866 TEE
2868 The TEE target will clone a packet and redirect this clone to another
2869 machine on the local network segment. In other words, the nexthop must
2870 be the target, or you will have to configure the nexthop to forward it
2871 further if so desired.
2872 --gateway ipaddr
2874 Send the cloned packet to the host reachable at the given IP ad‐
2875 dress. Use of 0.0.0.0 (for IPv4 packets) or :: (IPv6) is in‐
2876 valid.
2877 To forward all incoming traffic on eth0 to an Network Layer logging
2879 box:
2880 -t mangle -A PREROUTING -i eth0 -j TEE --gateway 2001:db8::1
2882 TOS
2884 This module sets the Type of Service field in the IPv4 header (includ‐
2885 ing the "precedence" bits) or the Priority field in the IPv6 header.
2886 Note that TOS shares the same bits as DSCP and ECN. The TOS target is
2887 only valid in the mangle table.
2888 --set-tos value[/mask]
2890 Zeroes out the bits given by mask (see NOTE below) and XORs
2891 value into the TOS/Priority field. If mask is omitted, 0xFF is
2892 assumed.
2893 --set-tos symbol
2895 You can specify a symbolic name when using the TOS target for
2896 IPv4. It implies a mask of 0xFF (see NOTE below). The list of
2897 recognized TOS names can be obtained by calling iptables with -j
2898 TOS -h.
2899 The following mnemonics are available:
2901 --and-tos bits
2903 Binary AND the TOS value with bits. (Mnemonic for --set-tos
2904 0/invbits, where invbits is the binary negation of bits. See
2905 NOTE below.)
2906 --or-tos bits
2908 Binary OR the TOS value with bits. (Mnemonic for --set-tos
2909 bits/bits. See NOTE below.)
2910 --xor-tos bits
2912 Binary XOR the TOS value with bits. (Mnemonic for --set-tos
2913 bits/0. See NOTE below.)
2914 NOTE: In Linux kernels up to and including 2.6.38, with the exception
2916 of longterm releases 2.6.32 (>=.42), 2.6.33 (>=.15), and 2.6.35
2917 (>=.14), there is a bug whereby IPv6 TOS mangling does not behave as
2918 documented and differs from the IPv4 version. The TOS mask indicates
2919 the bits one wants to zero out, so it needs to be inverted before ap‐
2920 plying it to the original TOS field. However, the aformentioned kernels
2921 forgo the inversion which breaks --set-tos and its mnemonics.
2922 TPROXY
2924 This target is only valid in the mangle table, in the PREROUTING chain
2925 and user-defined chains which are only called from this chain. It redi‐
2926 rects the packet to a local socket without changing the packet header
2927 in any way. It can also change the mark value which can then be used in
2928 advanced routing rules. It takes three options:
2929 --on-port port
2931 This specifies a destination port to use. It is a required op‐
2932 tion, 0 means the new destination port is the same as the origi‐
2933 nal. This is only valid if the rule also specifies -p tcp or -p
2934 udp.
2935 --on-ip address
2937 This specifies a destination address to use. By default the ad‐
2938 dress is the IP address of the incoming interface. This is only
2939 valid if the rule also specifies -p tcp or -p udp.
2940 --tproxy-mark value[/mask]
2942 Marks packets with the given value/mask. The fwmark value set
2943 here can be used by advanced routing. (Required for transparent
2944 proxying to work: otherwise these packets will get forwarded,
2945 which is probably not what you want.)
2946 TRACE
2948 This target marks packets so that the kernel will log every rule which
2949 match the packets as those traverse the tables, chains, rules. It can
2950 only be used in the raw table.
2951 With iptables-legacy, a logging backend, such as ip(6)t_LOG or
2953 nfnetlink_log, must be loaded for this to be visible. The packets are
2954 logged with the string prefix: "TRACE: tablename:chainname:type:rulenum
2955 " where type can be "rule" for plain rule, "return" for implicit rule
2956 at the end of a user defined chain and "policy" for the policy of the
2957 built in chains.
2958 With iptables-nft, the target is translated into nftables' meta nftrace
2960 expression. Hence the kernel sends trace events via netlink to
2961 userspace where they may be displayed using xtables-monitor --trace
2962 command. For details, refer to xtables-monitor(8).
2963 TTL (IPv4-specific)
2965 This is used to modify the IPv4 TTL header field. The TTL field deter‐
2966 mines how many hops (routers) a packet can traverse until it's time to
2967 live is exceeded.
2968 Setting or incrementing the TTL field can potentially be very danger‐
2970 ous, so it should be avoided at any cost. This target is only valid in
2971 mangle table.
2972 Don't ever set or increment the value on packets that leave your local
2974 network!
2975 --ttl-set value
2977 Set the TTL value to `value'.
2978 --ttl-dec value
2980 Decrement the TTL value `value' times.
2981 --ttl-inc value
2983 Increment the TTL value `value' times.
2984 ULOG (IPv4-specific)
2986 This is the deprecated ipv4-only predecessor of the NFLOG target. It
2987 provides userspace logging of matching packets. When this target is
2988 set for a rule, the Linux kernel will multicast this packet through a
2989 netlink socket. One or more userspace processes may then subscribe to
2990 various multicast groups and receive the packets. Like LOG, this is a
2991 "non-terminating target", i.e. rule traversal continues at the next
2992 rule.
2993 --ulog-nlgroup nlgroup
2995 This specifies the netlink group (1-32) to which the packet is
2996 sent. Default value is 1.
2997 --ulog-prefix prefix
2999 Prefix log messages with the specified prefix; up to 32 charac‐
3000 ters long, and useful for distinguishing messages in the logs.
3001 --ulog-cprange size
3003 Number of bytes to be copied to userspace. A value of 0 always
3004 copies the entire packet, regardless of its size. Default is 0.
3005 --ulog-qthreshold size
3007 Number of packet to queue inside kernel. Setting this value to,
3008 e.g. 10 accumulates ten packets inside the kernel and transmits
3009 them as one netlink multipart message to userspace. Default is
3010 1 (for backwards compatibility).
3011iptables 1.8.7 iptables-extensions(8)