1iptables-extensions(8) iptables 1.4.21 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-
11 options...]
12 iptables [-m name [module-options...]] [-j target-name [target-
14 options...]
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
27 option is encountered, iptables will try load a match module of the
28 same 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 BPF program in decimal for‐
107 mat. This is the format generated by the nfbpf_compile utility.
108 --bytecode code
110 Pass the BPF byte code format (described in the example below).
111 The code format is similar to the output of the tcpdump -ddd command:
113 one line that stores the number of instructions, followed by one line
114 for each instruction. Instruction lines follow the pattern 'u16 u8 u8
115 u32' in decimal notation. Fields encode the operation, jump offset if
116 true, jump offset if false and generic multiuse field 'K'. Comments are
117 not supported.
118 For example, to read only packets matching 'ip proto 6', insert the
120 following, without the comments or trailing whitespace:
121 4 # number of instructions
123 48 0 0 9 # load byte ip->proto
124 21 0 1 6 # jump equal IPPROTO_TCP
125 6 0 0 1 # return pass (non-zero)
126 6 0 0 0 # return fail (zero)
127 You can pass this filter to the bpf match with the following command:
129 iptables -A OUTPUT -m bpf --bytecode '4,48 0 0 9,21 0 1 6,6 0 0
131 1,6 0 0 0' -j ACCEPT
132 Or instead, you can invoke the nfbpf_compile utility.
134 iptables -A OUTPUT -m bpf --bytecode "`nfbpf_compile RAW 'ip
136 proto 6'`" -j ACCEPT
137 You may want to learn more about BPF from FreeBSD's bpf(4) manpage.
139 cgroup
141 [!] --cgroup fwid
142 Match corresponding cgroup for this packet.
143 Can be used to assign particular firewall policies for aggre‐
145 gated task/jobs on the system. This allows for more fine-grained
146 firewall policies that only match for a subset of the system's
147 processes. fwid is the maker set through the net_cls cgroup's
148 id.
149 Example:
151 iptables -A OUTPUT -p tcp --sport 80 -m cgroup ! --cgroup 1 -j DROP
153 Available since Linux 3.14.
155 cluster
157 Allows you to deploy gateway and back-end load-sharing clusters without
158 the need of load-balancers.
159 This match requires that all the nodes see the same packets. Thus, the
161 cluster match decides if this node has to handle a packet given the
162 following options:
163 --cluster-total-nodes num
165 Set number of total nodes in cluster.
166 [!] --cluster-local-node num
168 Set the local node number ID.
169 [!] --cluster-local-nodemask mask
171 Set the local node number ID mask. You can use this option
172 instead of --cluster-local-node.
173 --cluster-hash-seed value
175 Set seed value of the Jenkins hash.
176 Example:
178 iptables -A PREROUTING -t mangle -i eth1 -m cluster --clus‐
180 ter-total-nodes 2 --cluster-local-node 1 --cluster-hash-seed
181 0xdeadbeef -j MARK --set-mark 0xffff
182 iptables -A PREROUTING -t mangle -i eth2 -m cluster --clus‐
184 ter-total-nodes 2 --cluster-local-node 1 --cluster-hash-seed
185 0xdeadbeef -j MARK --set-mark 0xffff
186 iptables -A PREROUTING -t mangle -i eth1 -m mark ! --mark 0xffff
188 -j DROP
189 iptables -A PREROUTING -t mangle -i eth2 -m mark ! --mark 0xffff
191 -j DROP
192 And the following commands to make all nodes see the same packets:
194 ip maddr add 01:00:5e:00:01:01 dev eth1
196 ip maddr add 01:00:5e:00:01:02 dev eth2
198 arptables -A OUTPUT -o eth1 --h-length 6 -j mangle --mangle-mac-
200 s 01:00:5e:00:01:01
201 arptables -A INPUT -i eth1 --h-length 6 --destination-mac
203 01:00:5e:00:01:01 -j mangle --mangle-mac-d 00:zz:yy:xx:5a:27
204 arptables -A OUTPUT -o eth2 --h-length 6 -j mangle --man‐
206 gle-mac-s 01:00:5e:00:01:02
207 arptables -A INPUT -i eth2 --h-length 6 --destination-mac
209 01:00:5e:00:01:02 -j mangle --mangle-mac-d 00:zz:yy:xx:5a:27
210 NOTE: the arptables commands above use mainstream syntax. If you are
212 using arptables-jf included in some RedHat, CentOS and Fedora versions,
213 you will hit syntax errors. Therefore, you'll have to adapt these to
214 the arptables-jf syntax to get them working.
215 In the case of TCP connections, pickup facility has to be disabled to
217 avoid marking TCP ACK packets coming in the reply direction as valid.
218 echo 0 > /proc/sys/net/netfilter/nf_conntrack_tcp_loose
220 comment
222 Allows you to add comments (up to 256 characters) to any rule.
223 --comment comment
225 Example:
227 iptables -A INPUT -i eth1 -m comment --comment "my local LAN"
228 connbytes
230 Match by how many bytes or packets a connection (or one of the two
231 flows constituting the connection) has transferred so far, or by aver‐
232 age bytes per packet.
233 The counters are 64-bit and are thus not expected to overflow ;)
235 The primary use is to detect long-lived downloads and mark them to be
237 scheduled using a lower priority band in traffic control.
238 The transferred bytes per connection can also be viewed through `con‐
240 ntrack -L` and accessed via ctnetlink.
241 NOTE that for connections which have no accounting information, the
243 match will always return false. The "net.netfilter.nf_conntrack_acct"
244 sysctl flag controls whether new connections will be byte/packet
245 counted. Existing connection flows will not be gaining/losing a/the
246 accounting structure when be sysctl flag is flipped.
247 [!] --connbytes from[:to]
249 match packets from a connection whose packets/bytes/average
250 packet size is more than FROM and less than TO bytes/packets. if
251 TO is omitted only FROM check is done. "!" is used to match
252 packets not falling in the range.
253 --connbytes-dir {original|reply|both}
255 which packets to consider
256 --connbytes-mode {packets|bytes|avgpkt}
258 whether to check the amount of packets, number of bytes trans‐
259 ferred or the average size (in bytes) of all packets received so
260 far. Note that when "both" is used together with "avgpkt", and
261 data is going (mainly) only in one direction (for example HTTP),
262 the average packet size will be about half of the actual data
263 packets.
264 Example:
266 iptables .. -m connbytes --connbytes 10000:100000
267 --connbytes-dir both --connbytes-mode bytes ...
268 connlabel
270 Module matches or adds connlabels to a connection. connlabels are sim‐
271 ilar to connmarks, except labels are bit-based; i.e. all labels may be
272 attached to a flow at the same time. Up to 128 unique labels are cur‐
273 rently supported.
274 [!] --label name
276 matches if label name has been set on a connection. Instead of
277 a name (which will be translated to a number, see EXAMPLE
278 below), a number may be used instead. Using a number always
279 overrides connlabel.conf.
280 --set if the label has not been set on the connection, set it. Note
282 that setting a label can fail. This is because the kernel allo‐
283 cates the conntrack label storage area when the connection is
284 created, and it only reserves the amount of memory required by
285 the ruleset that exists at the time the connection is created.
286 In this case, the match will fail (or succeed, in case --label
287 option was negated).
288 This match depends on libnetfilter_conntrack 1.0.4 or later. Label
290 translation is done via the /etc/xtables/connlabel.conf configuration
291 file.
292 Example:
294 0 eth0-in
296 1 eth0-out
297 2 ppp-in
298 3 ppp-out
299 4 bulk-traffic
300 5 interactive
301 connlimit
303 Allows you to restrict the number of parallel connections to a server
304 per client IP address (or client address block).
305 --connlimit-upto n
307 Match if the number of existing connections is below or equal n.
308 --connlimit-above n
310 Match if the number of existing connections is above n.
311 --connlimit-mask prefix_length
313 Group hosts using the prefix length. For IPv4, this must be a
314 number between (including) 0 and 32. For IPv6, between 0 and
315 128. If not specified, the maximum prefix length for the appli‐
316 cable protocol is used.
317 --connlimit-saddr
319 Apply the limit onto the source group. This is the default if
320 --connlimit-daddr is not specified.
321 --connlimit-daddr
323 Apply the limit onto the destination group.
324 Examples:
326 # allow 2 telnet connections per client host
328 iptables -A INPUT -p tcp --syn --dport 23 -m connlimit
329 --connlimit-above 2 -j REJECT
330 # you can also match the other way around:
332 iptables -A INPUT -p tcp --syn --dport 23 -m connlimit
333 --connlimit-upto 2 -j ACCEPT
334 # limit the number of parallel HTTP requests to 16 per class C sized
336 source network (24 bit netmask)
337 iptables -p tcp --syn --dport 80 -m connlimit --connlimit-above
338 16 --connlimit-mask 24 -j REJECT
339 # limit the number of parallel HTTP requests to 16 for the link local
341 network
342 (ipv6) ip6tables -p tcp --syn --dport 80 -s fe80::/64 -m
343 connlimit --connlimit-above 16 --connlimit-mask 64 -j REJECT
344 # Limit the number of connections to a particular host:
346 ip6tables -p tcp --syn --dport 49152:65535 -d 2001:db8::1 -m
347 connlimit --connlimit-above 100 -j REJECT
348 connmark
350 This module matches the netfilter mark field associated with a connec‐
351 tion (which can be set using the CONNMARK target below).
352 [!] --mark value[/mask]
354 Matches packets in connections with the given mark value (if a
355 mask is specified, this is logically ANDed with the mark before
356 the comparison).
357 conntrack
359 This module, when combined with connection tracking, allows access to
360 the connection tracking state for this packet/connection.
361 [!] --ctstate statelist
363 statelist is a comma separated list of the connection states to
364 match. Possible states are listed below.
365 [!] --ctproto l4proto
367 Layer-4 protocol to match (by number or name)
368 [!] --ctorigsrc address[/mask]
370 [!] --ctorigdst address[/mask]
372 [!] --ctreplsrc address[/mask]
374 [!] --ctrepldst address[/mask]
376 Match against original/reply source/destination address
377 [!] --ctorigsrcport port[:port]
379 [!] --ctorigdstport port[:port]
381 [!] --ctreplsrcport port[:port]
383 [!] --ctrepldstport port[:port]
385 Match against original/reply source/destination port
386 (TCP/UDP/etc.) or GRE key. Matching against port ranges is only
387 supported in kernel versions above 2.6.38.
388 [!] --ctstatus statelist
390 statuslist is a comma separated list of the connection statuses
391 to match. Possible statuses are listed below.
392 [!] --ctexpire time[:time]
394 Match remaining lifetime in seconds against given value or range
395 of values (inclusive)
396 --ctdir {ORIGINAL|REPLY}
398 Match packets that are flowing in the specified direction. If
399 this flag is not specified at all, matches packets in both
400 directions.
401 States for --ctstate:
403 INVALID
405 The packet is associated with no known connection.
406 NEW The packet has started a new connection or otherwise associated
408 with a connection which has not seen packets in both directions.
409 ESTABLISHED
411 The packet is associated with a connection which has seen pack‐
412 ets in both directions.
413 RELATED
415 The packet is starting a new connection, but is associated with
416 an existing connection, such as an FTP data transfer or an ICMP
417 error.
418 UNTRACKED
420 The packet is not tracked at all, which happens if you explic‐
421 itly untrack it by using -j CT --notrack in the raw table.
422 SNAT A virtual state, matching if the original source address differs
424 from the reply destination.
425 DNAT A virtual state, matching if the original destination differs
427 from the reply source.
428 Statuses for --ctstatus:
430 NONE None of the below.
432 EXPECTED
434 This is an expected connection (i.e. a conntrack helper set it
435 up).
436 SEEN_REPLY
438 Conntrack has seen packets in both directions.
439 ASSURED
441 Conntrack entry should never be early-expired.
442 CONFIRMED
444 Connection is confirmed: originating packet has left box.
445 cpu
447 [!] --cpu number
448 Match cpu handling this packet. cpus are numbered from 0 to
449 NR_CPUS-1 Can be used in combination with RPS (Remote Packet
450 Steering) or multiqueue NICs to spread network traffic on dif‐
451 ferent queues.
452 Example:
454 iptables -t nat -A PREROUTING -p tcp --dport 80 -m cpu --cpu 0 -j REDI‐
456 RECT --to-port 8080
457 iptables -t nat -A PREROUTING -p tcp --dport 80 -m cpu --cpu 1 -j REDI‐
459 RECT --to-port 8081
460 Available since Linux 2.6.36.
462 dccp
464 [!] --source-port,--sport port[:port]
465 [!] --destination-port,--dport port[:port]
467 [!] --dccp-types mask
469 Match when the DCCP packet type is one of 'mask'. 'mask' is a
470 comma-separated list of packet types. Packet types are: REQUEST
471 RESPONSE DATA ACK DATAACK CLOSEREQ CLOSE RESET SYNC SYNCACK
472 INVALID.
473 [!] --dccp-option number
475 Match if DCCP option set.
476 devgroup
478 Match device group of a packets incoming/outgoing interface.
479 [!] --src-group name
481 Match device group of incoming device
482 [!] --dst-group name
484 Match device group of outgoing device
485 dscp
487 This module matches the 6 bit DSCP field within the TOS field in the IP
488 header. DSCP has superseded TOS within the IETF.
489 [!] --dscp value
491 Match against a numeric (decimal or hex) value [0-63].
492 [!] --dscp-class class
494 Match the DiffServ class. This value may be any of the BE, EF,
495 AFxx or CSx classes. It will then be converted into its accord‐
496 ing numeric value.
497 dst (IPv6-specific)
499 This module matches the parameters in Destination Options header
500 [!] --dst-len length
502 Total length of this header in octets.
503 --dst-opts type[:length][,type[:length]...]
505 numeric type of option and the length of the option data in
506 octets.
507 ecn
509 This allows you to match the ECN bits of the IPv4/IPv6 and TCP header.
510 ECN is the Explicit Congestion Notification mechanism as specified in
511 RFC3168
512 [!] --ecn-tcp-cwr
514 This matches if the TCP ECN CWR (Congestion Window Received) bit
515 is set.
516 [!] --ecn-tcp-ece
518 This matches if the TCP ECN ECE (ECN Echo) bit is set.
519 [!] --ecn-ip-ect num
521 This matches a particular IPv4/IPv6 ECT (ECN-Capable Transport).
522 You have to specify a number between `0' and `3'.
523 esp
525 This module matches the SPIs in ESP header of IPsec packets.
526 [!] --espspi spi[:spi]
528 eui64 (IPv6-specific)
530 This module matches the EUI-64 part of a stateless autoconfigured IPv6
531 address. It compares the EUI-64 derived from the source MAC address in
532 Ethernet frame with the lower 64 bits of the IPv6 source address. But
533 "Universal/Local" bit is not compared. This module doesn't match other
534 link layer frame, and is only valid in the PREROUTING, INPUT and FOR‐
535 WARD chains.
536 frag (IPv6-specific)
538 This module matches the parameters in Fragment header.
539 [!] --fragid id[:id]
541 Matches the given Identification or range of it.
542 [!] --fraglen length
544 This option cannot be used with kernel version 2.6.10 or later.
545 The length of Fragment header is static and this option doesn't
546 make sense.
547 --fragres
549 Matches if the reserved fields are filled with zero.
550 --fragfirst
552 Matches on the first fragment.
553 --fragmore
555 Matches if there are more fragments.
556 --fraglast
558 Matches if this is the last fragment.
559 hashlimit
561 hashlimit uses hash buckets to express a rate limiting match (like the
562 limit match) for a group of connections using a single iptables rule.
563 Grouping can be done per-hostgroup (source and/or destination address)
564 and/or per-port. It gives you the ability to express "N packets per
565 time quantum per group" or "N bytes per seconds" (see below for some
566 examples).
567 A hash limit option (--hashlimit-upto, --hashlimit-above) and --hash‐
569 limit-name are required.
570 --hashlimit-upto amount[/second|/minute|/hour|/day]
572 Match if the rate is below or equal to amount/quantum. It is
573 specified either as a number, with an optional time quantum suf‐
574 fix (the default is 3/hour), or as amountb/second (number of
575 bytes per second).
576 --hashlimit-above amount[/second|/minute|/hour|/day]
578 Match if the rate is above amount/quantum.
579 --hashlimit-burst amount
581 Maximum initial number of packets to match: this number gets
582 recharged by one every time the limit specified above is not
583 reached, up to this number; the default is 5. When byte-based
584 rate matching is requested, this option specifies the amount of
585 bytes that can exceed the given rate. This option should be
586 used with caution -- if the entry expires, the burst value is
587 reset too.
588 --hashlimit-mode {srcip|srcport|dstip|dstport},...
590 A comma-separated list of objects to take into consideration. If
591 no --hashlimit-mode option is given, hashlimit acts like limit,
592 but at the expensive of doing the hash housekeeping.
593 --hashlimit-srcmask prefix
595 When --hashlimit-mode srcip is used, all source addresses
596 encountered will be grouped according to the given prefix length
597 and the so-created subnet will be subject to hashlimit. prefix
598 must be between (inclusive) 0 and 32. Note that --hashlimit-src‐
599 mask 0 is basically doing the same thing as not specifying srcip
600 for --hashlimit-mode, but is technically more expensive.
601 --hashlimit-dstmask prefix
603 Like --hashlimit-srcmask, but for destination addresses.
604 --hashlimit-name foo
606 The name for the /proc/net/ipt_hashlimit/foo entry.
607 --hashlimit-htable-size buckets
609 The number of buckets of the hash table
610 --hashlimit-htable-max entries
612 Maximum entries in the hash.
613 --hashlimit-htable-expire msec
615 After how many milliseconds do hash entries expire.
616 --hashlimit-htable-gcinterval msec
618 How many milliseconds between garbage collection intervals.
619 Examples:
621 matching on source host
623 "1000 packets per second for every host in 192.168.0.0/16" => -s
624 192.168.0.0/16 --hashlimit-mode srcip --hashlimit-upto 1000/sec
625 matching on source port
627 "100 packets per second for every service of 192.168.1.1" => -s
628 192.168.1.1 --hashlimit-mode srcport --hashlimit-upto 100/sec
629 matching on subnet
631 "10000 packets per minute for every /28 subnet (groups of 8
632 addresses) in 10.0.0.0/8" => -s 10.0.0.0/8 --hashlimit-mask 28
633 --hashlimit-upto 10000/min
634 matching bytes per second
636 "flows exceeding 512kbyte/s" => --hashlimit-mode
637 srcip,dstip,srcport,dstport --hashlimit-above 512kb/s
638 matching bytes per second
640 "hosts that exceed 512kbyte/s, but permit up to 1Megabytes with‐
641 out matching" --hashlimit-mode dstip --hashlimit-above 512kb/s
642 --hashlimit-burst 1mb
643 hbh (IPv6-specific)
645 This module matches the parameters in Hop-by-Hop Options header
646 [!] --hbh-len length
648 Total length of this header in octets.
649 --hbh-opts type[:length][,type[:length]...]
651 numeric type of option and the length of the option data in
652 octets.
653 helper
655 This module matches packets related to a specific conntrack-helper.
656 [!] --helper string
658 Matches packets related to the specified conntrack-helper.
659 string can be "ftp" for packets related to a ftp-session on
661 default port. For other ports append -portnr to the value, ie.
662 "ftp-2121".
663 Same rules apply for other conntrack-helpers.
665 hl (IPv6-specific)
667 This module matches the Hop Limit field in the IPv6 header.
668 [!] --hl-eq value
670 Matches if Hop Limit equals value.
671 --hl-lt value
673 Matches if Hop Limit is less than value.
674 --hl-gt value
676 Matches if Hop Limit is greater than value.
677 icmp (IPv4-specific)
679 This extension can be used if `--protocol icmp' is specified. It pro‐
680 vides the following option:
681 [!] --icmp-type {type[/code]|typename}
683 This allows specification of the ICMP type, which can be a
684 numeric ICMP type, type/code pair, or one of the ICMP type names
685 shown by the command
686 iptables -p icmp -h
687 icmp6 (IPv6-specific)
689 This extension can be used if `--protocol ipv6-icmp' or `--protocol
690 icmpv6' is specified. It provides the following option:
691 [!] --icmpv6-type type[/code]|typename
693 This allows specification of the ICMPv6 type, which can be a
694 numeric ICMPv6 type, type and code, or one of the ICMPv6 type
695 names shown by the command
696 ip6tables -p ipv6-icmp -h
697 iprange
699 This matches on a given arbitrary range of IP addresses.
700 [!] --src-range from[-to]
702 Match source IP in the specified range.
703 [!] --dst-range from[-to]
705 Match destination IP in the specified range.
706 ipv6header (IPv6-specific)
708 This module matches IPv6 extension headers and/or upper layer header.
709 --soft Matches if the packet includes any of the headers specified with
711 --header.
712 [!] --header header[,header...]
714 Matches the packet which EXACTLY includes all specified headers.
715 The headers encapsulated with ESP header are out of scope. Pos‐
716 sible header types can be:
717 hop|hop-by-hop
719 Hop-by-Hop Options header
720 dst Destination Options header
722 route Routing header
724 frag Fragment header
726 auth Authentication header
728 esp Encapsulating Security Payload header
730 none No Next header which matches 59 in the 'Next Header field' of
732 IPv6 header or any IPv6 extension headers
733 proto which matches any upper layer protocol header. A protocol name
735 from /etc/protocols and numeric value also allowed. The number
736 255 is equivalent to proto.
737 ipvs
739 Match IPVS connection properties.
740 [!] --ipvs
742 packet belongs to an IPVS connection
743 Any of the following options implies --ipvs (even negated)
745 [!] --vproto protocol
747 VIP protocol to match; by number or name, e.g. "tcp"
748 [!] --vaddr address[/mask]
750 VIP address to match
751 [!] --vport port
753 VIP port to match; by number or name, e.g. "http"
754 --vdir {ORIGINAL|REPLY}
756 flow direction of packet
757 [!] --vmethod {GATE|IPIP|MASQ}
759 IPVS forwarding method used
760 [!] --vportctl port
762 VIP port of the controlling connection to match, e.g. 21 for FTP
763 length
765 This module matches the length of the layer-3 payload (e.g. layer-4
766 packet) of a packet against a specific value or range of values.
767 [!] --length length[:length]
769 limit
771 This module matches at a limited rate using a token bucket filter. A
772 rule using this extension will match until this limit is reached. It
773 can be used in combination with the LOG target to give limited logging,
774 for example.
775 xt_limit has no negation support - you will have to use -m hashlimit !
777 --hashlimit rate in this case whilst omitting --hashlimit-mode.
778 --limit rate[/second|/minute|/hour|/day]
780 Maximum average matching rate: specified as a number, with an
781 optional `/second', `/minute', `/hour', or `/day' suffix; the
782 default is 3/hour.
783 --limit-burst number
785 Maximum initial number of packets to match: this number gets
786 recharged by one every time the limit specified above is not
787 reached, up to this number; the default is 5.
788 mac
790 [!] --mac-source address
791 Match source MAC address. It must be of the form
792 XX:XX:XX:XX:XX:XX. Note that this only makes sense for packets
793 coming from an Ethernet device and entering the PREROUTING, FOR‐
794 WARD or INPUT chains.
795 mark
797 This module matches the netfilter mark field associated with a packet
798 (which can be set using the MARK target below).
799 [!] --mark value[/mask]
801 Matches packets with the given unsigned mark value (if a mask is
802 specified, this is logically ANDed with the mask before the com‐
803 parison).
804 mh (IPv6-specific)
806 This extension is loaded if `--protocol ipv6-mh' or `--protocol mh' is
807 specified. It provides the following option:
808 [!] --mh-type type[:type]
810 This allows specification of the Mobility Header(MH) type, which
811 can be a numeric MH type, type or one of the MH type names shown
812 by the command
813 ip6tables -p mh -h
814 multiport
816 This module matches a set of source or destination ports. Up to 15
817 ports can be specified. A port range (port:port) counts as two ports.
818 It can only be used in conjunction with one of the following protocols:
819 tcp, udp, udplite, dccp and sctp.
820 [!] --source-ports,--sports port[,port|,port:port]...
822 Match if the source port is one of the given ports. The flag
823 --sports is a convenient alias for this option. Multiple ports
824 or port ranges are separated using a comma, and a port range is
825 specified using a colon. 53,1024:65535 would therefore match
826 ports 53 and all from 1024 through 65535.
827 [!] --destination-ports,--dports port[,port|,port:port]...
829 Match if the destination port is one of the given ports. The
830 flag --dports is a convenient alias for this option.
831 [!] --ports port[,port|,port:port]...
833 Match if either the source or destination ports are equal to one
834 of the given ports.
835 nfacct
837 The nfacct match provides the extended accounting infrastructure for
838 iptables. You have to use this match together with the standalone
839 user-space utility nfacct(8)
840 The only option available for this match is the following:
842 --nfacct-name name
844 This allows you to specify the existing object name that will be
845 use for accounting the traffic that this rule-set is matching.
846 To use this extension, you have to create an accounting object:
848 nfacct add http-traffic
850 Then, you have to attach it to the accounting object via iptables:
852 iptables -I INPUT -p tcp --sport 80 -m nfacct --nfacct-name
854 http-traffic
855 iptables -I OUTPUT -p tcp --dport 80 -m nfacct --nfacct-name
857 http-traffic
858 Then, you can check for the amount of traffic that the rules match:
860 nfacct get http-traffic
862 { pkts = 00000000000000000156, bytes = 00000000000000151786 } =
864 http-traffic;
865 You can obtain nfacct(8) from http://www.netfilter.org or, alterna‐
867 tively, from the git.netfilter.org repository.
868 osf
870 The osf module does passive operating system fingerprinting. This mod‐
871 ules compares some data (Window Size, MSS, options and their order,
872 TTL, DF, and others) from packets with the SYN bit set.
873 [!] --genre string
875 Match an operating system genre by using a passive fingerprint‐
876 ing.
877 --ttl level
879 Do additional TTL checks on the packet to determine the operat‐
880 ing system. level can be one of the following values:
881 · 0 - True IP address and fingerprint TTL comparison. This generally
883 works for LANs.
884 · 1 - Check if the IP header's TTL is less than the fingerprint one.
886 Works for globally-routable addresses.
887 · 2 - Do not compare the TTL at all.
889 --log level
891 Log determined genres into dmesg even if they do not match the
892 desired one. level can be one of the following values:
893 · 0 - Log all matched or unknown signatures
895 · 1 - Log only the first one
897 · 2 - Log all known matched signatures
899 You may find something like this in syslog:
901 Windows [2000:SP3:Windows XP Pro SP1, 2000 SP3]: 11.22.33.55:4024 ->
903 11.22.33.44:139 hops=3 Linux [2.5-2.6:] : 1.2.3.4:42624 -> 1.2.3.5:22
904 hops=4
905 OS fingerprints are loadable using the nfnl_osf program. To load fin‐
907 gerprints from a file, use:
908 nfnl_osf -f /usr/share/xtables/pf.os
910 To remove them again,
912 nfnl_osf -f /usr/share/xtables/pf.os -d
914 The fingerprint database can be downlaoded from http://www.open‐
916 bsd.org/cgi-bin/cvsweb/src/etc/pf.os .
917 owner
919 This module attempts to match various characteristics of the packet
920 creator, for locally generated packets. This match is only valid in the
921 OUTPUT and POSTROUTING chains. Forwarded packets do not have any socket
922 associated with them. Packets from kernel threads do have a socket, but
923 usually no owner.
924 [!] --uid-owner username
926 [!] --uid-owner userid[-userid]
928 Matches if the packet socket's file structure (if it has one) is
929 owned by the given user. You may also specify a numerical UID,
930 or an UID range.
931 [!] --gid-owner groupname
933 [!] --gid-owner groupid[-groupid]
935 Matches if the packet socket's file structure is owned by the
936 given group. You may also specify a numerical GID, or a GID
937 range.
938 [!] --socket-exists
940 Matches if the packet is associated with a socket.
941 physdev
943 This module matches on the bridge port input and output devices
944 enslaved to a bridge device. This module is a part of the infrastruc‐
945 ture that enables a transparent bridging IP firewall and is only useful
946 for kernel versions above version 2.5.44.
947 [!] --physdev-in name
949 Name of a bridge port via which a packet is received (only for
950 packets entering the INPUT, FORWARD and PREROUTING chains). If
951 the interface name ends in a "+", then any interface which
952 begins with this name will match. If the packet didn't arrive
953 through a bridge device, this packet won't match this option,
954 unless '!' is used.
955 [!] --physdev-out name
957 Name of a bridge port via which a packet is going to be sent
958 (for packets entering the FORWARD, OUTPUT and POSTROUTING
959 chains). If the interface name ends in a "+", then any inter‐
960 face which begins with this name will match. Note that in the
961 nat and mangle OUTPUT chains one cannot match on the bridge out‐
962 put port, however one can in the filter OUTPUT chain. If the
963 packet won't leave by a bridge device or if it is yet unknown
964 what the output device will be, then the packet won't match this
965 option, unless '!' is used.
966 [!] --physdev-is-in
968 Matches if the packet has entered through a bridge interface.
969 [!] --physdev-is-out
971 Matches if the packet will leave through a bridge interface.
972 [!] --physdev-is-bridged
974 Matches if the packet is being bridged and therefore is not
975 being routed. This is only useful in the FORWARD and POSTROUT‐
976 ING chains.
977 pkttype
979 This module matches the link-layer packet type.
980 [!] --pkt-type {unicast|broadcast|multicast}
982 policy
984 This modules matches the policy used by IPsec for handling a packet.
985 --dir {in|out}
987 Used to select whether to match the policy used for decapsula‐
988 tion or the policy that will be used for encapsulation. in is
989 valid in the PREROUTING, INPUT and FORWARD chains, out is valid
990 in the POSTROUTING, OUTPUT and FORWARD chains.
991 --pol {none|ipsec}
993 Matches if the packet is subject to IPsec processing. --pol none
994 cannot be combined with --strict.
995 --strict
997 Selects whether to match the exact policy or match if any rule
998 of the policy matches the given policy.
999 For each policy element that is to be described, one can use one or
1001 more of the following options. When --strict is in effect, at least one
1002 must be used per element.
1003 [!] --reqid id
1005 Matches the reqid of the policy rule. The reqid can be specified
1006 with setkey(8) using unique:id as level.
1007 [!] --spi spi
1009 Matches the SPI of the SA.
1010 [!] --proto {ah|esp|ipcomp}
1012 Matches the encapsulation protocol.
1013 [!] --mode {tunnel|transport}
1015 Matches the encapsulation mode.
1016 [!] --tunnel-src addr[/mask]
1018 Matches the source end-point address of a tunnel mode SA. Only
1019 valid with --mode tunnel.
1020 [!] --tunnel-dst addr[/mask]
1022 Matches the destination end-point address of a tunnel mode SA.
1023 Only valid with --mode tunnel.
1024 --next Start the next element in the policy specification. Can only be
1026 used with --strict.
1027 quota
1029 Implements network quotas by decrementing a byte counter with each
1030 packet. The condition matches until the byte counter reaches zero.
1031 Behavior is reversed with negation (i.e. the condition does not match
1032 until the byte counter reaches zero).
1033 [!] --quota bytes
1035 The quota in bytes.
1036 rateest
1038 The rate estimator can match on estimated rates as collected by the
1039 RATEEST target. It supports matching on absolute bps/pps values, com‐
1040 paring two rate estimators and matching on the difference between two
1041 rate estimators.
1042 For a better understanding of the available options, these are all pos‐
1044 sible combinations:
1045 · rateest operator rateest-bps
1047 · rateest operator rateest-pps
1049 · (rateest minus rateest-bps1) operator rateest-bps2
1051 · (rateest minus rateest-pps1) operator rateest-pps2
1053 · rateest1 operator rateest2 rateest-bps(without rate!)
1055 · rateest1 operator rateest2 rateest-pps(without rate!)
1057 · (rateest1 minus rateest-bps1) operator (rateest2 minus rateest-
1059 bps2)
1060 · (rateest1 minus rateest-pps1) operator (rateest2 minus rateest-
1062 pps2)
1063 --rateest-delta
1065 For each estimator (either absolute or relative mode), calculate
1066 the difference between the estimator-determined flow rate and the
1067 static value chosen with the BPS/PPS options. If the flow rate is
1068 higher than the specified BPS/PPS, 0 will be used instead of a neg‐
1069 ative value. In other words, "max(0, rateest#_rate - rateest#_bps)"
1070 is used.
1071 [!] --rateest-lt
1073 Match if rate is less than given rate/estimator.
1074 [!] --rateest-gt
1076 Match if rate is greater than given rate/estimator.
1077 [!] --rateest-eq
1079 Match if rate is equal to given rate/estimator.
1080 In the so-called "absolute mode", only one rate estimator is used and
1082 compared against a static value, while in "relative mode", two rate
1083 estimators are compared against another.
1084 --rateest name
1086 Name of the one rate estimator for absolute mode.
1087 --rateest1 name
1089 --rateest2 name
1091 The names of the two rate estimators for relative mode.
1092 --rateest-bps [value]
1094 --rateest-pps [value]
1096 --rateest-bps1 [value]
1098 --rateest-bps2 [value]
1100 --rateest-pps1 [value]
1102 --rateest-pps2 [value]
1104 Compare the estimator(s) by bytes or packets per second, and
1105 compare against the chosen value. See the above bullet list for
1106 which option is to be used in which case. A unit suffix may be
1107 used - available ones are: bit, [kmgt]bit, [KMGT]ibit, Bps,
1108 [KMGT]Bps, [KMGT]iBps.
1109 Example: This is what can be used to route outgoing data connections
1111 from an FTP server over two lines based on the available bandwidth at
1112 the time the data connection was started:
1113 # Estimate outgoing rates
1115 iptables -t mangle -A POSTROUTING -o eth0 -j RATEEST --rateest-name
1117 eth0 --rateest-interval 250ms --rateest-ewma 0.5s
1118 iptables -t mangle -A POSTROUTING -o ppp0 -j RATEEST --rateest-name
1120 ppp0 --rateest-interval 250ms --rateest-ewma 0.5s
1121 # Mark based on available bandwidth
1123 iptables -t mangle -A balance -m conntrack --ctstate NEW -m helper
1125 --helper ftp -m rateest --rateest-delta --rateest1 eth0 --rateest-bps1
1126 2.5mbit --rateest-gt --rateest2 ppp0 --rateest-bps2 2mbit -j CONNMARK
1127 --set-mark 1
1128 iptables -t mangle -A balance -m conntrack --ctstate NEW -m helper
1130 --helper ftp -m rateest --rateest-delta --rateest1 ppp0 --rateest-bps1
1131 2mbit --rateest-gt --rateest2 eth0 --rateest-bps2 2.5mbit -j CONNMARK
1132 --set-mark 2
1133 iptables -t mangle -A balance -j CONNMARK --restore-mark
1135 realm (IPv4-specific)
1137 This matches the routing realm. Routing realms are used in complex
1138 routing setups involving dynamic routing protocols like BGP.
1139 [!] --realm value[/mask]
1141 Matches a given realm number (and optionally mask). If not a
1142 number, value can be a named realm from /etc/iproute2/rt_realms
1143 (mask can not be used in that case).
1144 recent
1146 Allows you to dynamically create a list of IP addresses and then match
1147 against that list in a few different ways.
1148 For example, you can create a "badguy" list out of people attempting to
1150 connect to port 139 on your firewall and then DROP all future packets
1151 from them without considering them.
1152 --set, --rcheck, --update and --remove are mutually exclusive.
1154 --name name
1156 Specify the list to use for the commands. If no name is given
1157 then DEFAULT will be used.
1158 [!] --set
1160 This will add the source address of the packet to the list. If
1161 the source address is already in the list, this will update the
1162 existing entry. This will always return success (or failure if !
1163 is passed in).
1164 --rsource
1166 Match/save the source address of each packet in the recent list
1167 table. This is the default.
1168 --rdest
1170 Match/save the destination address of each packet in the recent
1171 list table.
1172 --mask netmask
1174 Netmask that will be applied to this recent list.
1175 [!] --rcheck
1177 Check if the source address of the packet is currently in the
1178 list.
1179 [!] --update
1181 Like --rcheck, except it will update the "last seen" timestamp
1182 if it matches.
1183 [!] --remove
1185 Check if the source address of the packet is currently in the
1186 list and if so that address will be removed from the list and
1187 the rule will return true. If the address is not found, false is
1188 returned.
1189 --seconds seconds
1191 This option must be used in conjunction with one of --rcheck or
1192 --update. When used, this will narrow the match to only happen
1193 when the address is in the list and was seen within the last
1194 given number of seconds.
1195 --reap This option can only be used in conjunction with --seconds.
1197 When used, this will cause entries older than the last given
1198 number of seconds to be purged.
1199 --hitcount hits
1201 This option must be used in conjunction with one of --rcheck or
1202 --update. When used, this will narrow the match to only happen
1203 when the address is in the list and packets had been received
1204 greater than or equal to the given value. This option may be
1205 used along with --seconds to create an even narrower match
1206 requiring a certain number of hits within a specific time frame.
1207 The maximum value for the hitcount parameter is given by the
1208 "ip_pkt_list_tot" parameter of the xt_recent kernel module.
1209 Exceeding this value on the command line will cause the rule to
1210 be rejected.
1211 --rttl This option may only be used in conjunction with one of --rcheck
1213 or --update. When used, this will narrow the match to only hap‐
1214 pen when the address is in the list and the TTL of the current
1215 packet matches that of the packet which hit the --set rule. This
1216 may be useful if you have problems with people faking their
1217 source address in order to DoS you via this module by disallow‐
1218 ing others access to your site by sending bogus packets to you.
1219 Examples:
1221 iptables -A FORWARD -m recent --name badguy --rcheck --seconds
1223 60 -j DROP
1224 iptables -A FORWARD -p tcp -i eth0 --dport 139 -m recent --name
1226 badguy --set -j DROP
1227 /proc/net/xt_recent/* are the current lists of addresses and informa‐
1229 tion about each entry of each list.
1230 Each file in /proc/net/xt_recent/ can be read from to see the current
1232 list or written two using the following commands to modify the list:
1233 echo +addr >/proc/net/xt_recent/DEFAULT
1235 to add addr to the DEFAULT list
1236 echo -addr >/proc/net/xt_recent/DEFAULT
1238 to remove addr from the DEFAULT list
1239 echo / >/proc/net/xt_recent/DEFAULT
1241 to flush the DEFAULT list (remove all entries).
1242 The module itself accepts parameters, defaults shown:
1244 ip_list_tot=100
1246 Number of addresses remembered per table.
1247 ip_pkt_list_tot=20
1249 Number of packets per address remembered.
1250 ip_list_hash_size=0
1252 Hash table size. 0 means to calculate it based on ip_list_tot,
1253 default: 512.
1254 ip_list_perms=0644
1256 Permissions for /proc/net/xt_recent/* files.
1257 ip_list_uid=0
1259 Numerical UID for ownership of /proc/net/xt_recent/* files.
1260 ip_list_gid=0
1262 Numerical GID for ownership of /proc/net/xt_recent/* files.
1263 rpfilter
1265 Performs a reverse path filter test on a packet. If a reply to the
1266 packet would be sent via the same interface that the packet arrived on,
1267 the packet will match. Note that, unlike the in-kernel rp_filter,
1268 packets protected by IPSec are not treated specially. Combine this
1269 match with the policy match if you want this. Also, packets arriving
1270 via the loopback interface are always permitted. This match can only
1271 be used in the PREROUTING chain of the raw or mangle table.
1272 --loose
1274 Used to specifiy that the reverse path filter test should match
1275 even if the selected output device is not the expected one.
1276 --validmark
1278 Also use the packets' nfmark value when performing the reverse
1279 path route lookup.
1280 --accept-local
1282 This will permit packets arriving from the network with a source
1283 address that is also assigned to the local machine.
1284 --invert
1286 This will invert the sense of the match. Instead of matching
1287 packets that passed the reverse path filter test, match those
1288 that have failed it.
1289 Example to log and drop packets failing the reverse path filter test:
1291 iptables -t raw -N RPFILTER
1293 iptables -t raw -A RPFILTER -m rpfilter -j RETURN
1295 iptables -t raw -A RPFILTER -m limit --limit 10/minute -j NFLOG
1297 --nflog-prefix "rpfilter drop"
1298 iptables -t raw -A RPFILTER -j DROP
1300 iptables -t raw -A PREROUTING -j RPFILTER
1302 Example to drop failed packets, without logging:
1304 iptables -t raw -A RPFILTER -m rpfilter --invert -j DROP
1306 rt (IPv6-specific)
1308 Match on IPv6 routing header
1309 [!] --rt-type type
1311 Match the type (numeric).
1312 [!] --rt-segsleft num[:num]
1314 Match the `segments left' field (range).
1315 [!] --rt-len length
1317 Match the length of this header.
1318 --rt-0-res
1320 Match the reserved field, too (type=0)
1321 --rt-0-addrs addr[,addr...]
1323 Match type=0 addresses (list).
1324 --rt-0-not-strict
1326 List of type=0 addresses is not a strict list.
1327 sctp
1329 [!] --source-port,--sport port[:port]
1330 [!] --destination-port,--dport port[:port]
1332 [!] --chunk-types {all|any|only} chunktype[:flags] [...]
1334 The flag letter in upper case indicates that the flag is to
1335 match if set, in the lower case indicates to match if unset.
1336 Chunk types: DATA INIT INIT_ACK SACK HEARTBEAT HEARTBEAT_ACK
1338 ABORT SHUTDOWN SHUTDOWN_ACK ERROR COOKIE_ECHO COOKIE_ACK
1339 ECN_ECNE ECN_CWR SHUTDOWN_COMPLETE ASCONF ASCONF_ACK FORWARD_TSN
1340 chunk type available flags
1342 DATA I U B E i u b e
1343 ABORT T t
1344 SHUTDOWN_COMPLETE T t
1345 (lowercase means flag should be "off", uppercase means "on")
1347 Examples:
1349 iptables -A INPUT -p sctp --dport 80 -j DROP
1351 iptables -A INPUT -p sctp --chunk-types any DATA,INIT -j DROP
1353 iptables -A INPUT -p sctp --chunk-types any DATA:Be -j ACCEPT
1355 set
1357 This module matches IP sets which can be defined by ipset(8).
1358 [!] --match-set setname flag[,flag]...
1360 where flags are the comma separated list of src and/or dst spec‐
1361 ifications and there can be no more than six of them. Hence the
1362 command
1363 iptables -A FORWARD -m set --match-set test src,dst
1365 will match packets, for which (if the set type is ipportmap) the
1367 source address and destination port pair can be found in the
1368 specified set. If the set type of the specified set is single
1369 dimension (for example ipmap), then the command will match pack‐
1370 ets for which the source address can be found in the specified
1371 set.
1372 --return-nomatch
1374 If the --return-nomatch option is specified and the set type
1375 supports the nomatch flag, then the matching is reversed: a
1376 match with an element flagged with nomatch returns true, while a
1377 match with a plain element returns false.
1378 ! --update-counters
1380 If the --update-counters flag is negated, then the packet and
1381 byte counters of the matching element in the set won't be
1382 updated. Default the packet and byte counters are updated.
1383 ! --update-subcounters
1385 If the --update-subcounters flag is negated, then the packet and
1386 byte counters of the matching element in the member set of a
1387 list type of set won't be updated. Default the packet and byte
1388 counters are updated.
1389 [!] --packets-eq value
1391 If the packet is matched an element in the set, match only if
1392 the packet counter of the element matches the given value too.
1393 --packets-lt value
1395 If the packet is matched an element in the set, match only if
1396 the packet counter of the element is less than the given value
1397 as well.
1398 --packets-gt value
1400 If the packet is matched an element in the set, match only if
1401 the packet counter of the element is greater than the given
1402 value as well.
1403 [!] -bytes-eq value
1405 If the packet is matched an element in the set, match only if
1406 the byte counter of the element matches the given value too.
1407 --bytes-lt value
1409 If the packet is matched an element in the set, match only if
1410 the byte counter of the element is less than the given value as
1411 well.
1412 --bytes-gt value
1414 If the packet is matched an element in the set, match only if
1415 the byte counter of the element is greater than the given value
1416 as well.
1417 The packet and byte counters related options and flags are ignored when
1419 the set was defined without counter support.
1420 The option --match-set can be replaced by --set if that does not clash
1422 with an option of other extensions.
1423 Use of -m set requires that ipset kernel support is provided, which,
1425 for standard kernels, is the case since Linux 2.6.39.
1426 socket
1428 This matches if an open TCP/UDP socket can be found by doing a socket
1429 lookup on the packet. It matches if there is an established or non-zero
1430 bound listening socket (possibly with a non-local address). The lookup
1431 is performed using the packet tuple of TCP/UDP packets, or the original
1432 TCP/UDP header embedded in an ICMP/ICPMv6 error packet.
1433 --transparent
1435 Ignore non-transparent sockets.
1436 --nowildcard
1438 Do not ignore sockets bound to 'any' address. The socket match
1439 won't accept zero-bound listeners by default, since then local
1440 services could intercept traffic that would otherwise be for‐
1441 warded. This option therefore has security implications when
1442 used to match traffic being forwarded to redirect such packets
1443 to local machine with policy routing. When using the socket
1444 match to implement fully transparent proxies bound to non-local
1445 addresses it is recommended to use the --transparent option
1446 instead.
1447 Example (assuming packets with mark 1 are delivered locally):
1449 -t mangle -A PREROUTING -m socket --transparent -j MARK
1451 --set-mark 1
1452 state
1454 The "state" extension is a subset of the "conntrack" module. "state"
1455 allows access to the connection tracking state for this packet.
1456 [!] --state state
1458 Where state is a comma separated list of the connection states
1459 to match. Only a subset of the states unterstood by "conntrack"
1460 are recognized: INVALID, ESTABLISHED, NEW, RELATED or UNTRACKED.
1461 For their description, see the "conntrack" heading in this man‐
1462 page.
1463 statistic
1465 This module matches packets based on some statistic condition. It sup‐
1466 ports two distinct modes settable with the --mode option.
1467 Supported options:
1469 --mode mode
1471 Set the matching mode of the matching rule, supported modes are
1472 random and nth.
1473 [!] --probability p
1475 Set the probability for a packet to be randomly matched. It only
1476 works with the random mode. p must be within 0.0 and 1.0. The
1477 supported granularity is in 1/2147483648th increments.
1478 [!] --every n
1480 Match one packet every nth packet. It works only with the nth
1481 mode (see also the --packet option).
1482 --packet p
1484 Set the initial counter value (0 <= p <= n-1, default 0) for the
1485 nth mode.
1486 string
1488 This modules matches a given string by using some pattern matching
1489 strategy. It requires a linux kernel >= 2.6.14.
1490 --algo {bm|kmp}
1492 Select the pattern matching strategy. (bm = Boyer-Moore, kmp =
1493 Knuth-Pratt-Morris)
1494 --from offset
1496 Set the offset from which it starts looking for any matching. If
1497 not passed, default is 0.
1498 --to offset
1500 Set the offset up to which should be scanned. That is, byte off‐
1501 set-1 (counting from 0) is the last one that is scanned. If not
1502 passed, default is the packet size.
1503 [!] --string pattern
1505 Matches the given pattern.
1506 [!] --hex-string pattern
1508 Matches the given pattern in hex notation.
1509 Examples:
1511 # The string pattern can be used for simple text characters.
1513 iptables -A INPUT -p tcp --dport 80 -m string --algo bm --string
1514 'GET /index.html' -j LOG
1515 # The hex string pattern can be used for non-printable charac‐
1517 ters, like |0D 0A| or |0D0A|.
1518 iptables -p udp --dport 53 -m string --algo bm --from 40 --to 57
1519 --hex-string '|03|www|09|netfilter|03|org|00|'
1520 tcp
1522 These extensions can be used if `--protocol tcp' is specified. It pro‐
1523 vides the following options:
1524 [!] --source-port,--sport port[:port]
1526 Source port or port range specification. This can either be a
1527 service name or a port number. An inclusive range can also be
1528 specified, using the format first:last. If the first port is
1529 omitted, "0" is assumed; if the last is omitted, "65535" is
1530 assumed. If the first port is greater than the second one they
1531 will be swapped. The flag --sport is a convenient alias for
1532 this option.
1533 [!] --destination-port,--dport port[:port]
1535 Destination port or port range specification. The flag --dport
1536 is a convenient alias for this option.
1537 [!] --tcp-flags mask comp
1539 Match when the TCP flags are as specified. The first argument
1540 mask is the flags which we should examine, written as a comma-
1541 separated list, and the second argument comp is a comma-sepa‐
1542 rated list of flags which must be set. Flags are: SYN ACK FIN
1543 RST URG PSH ALL NONE. Hence the command
1544 iptables -A FORWARD -p tcp --tcp-flags SYN,ACK,FIN,RST SYN
1545 will only match packets with the SYN flag set, and the ACK, FIN
1546 and RST flags unset.
1547 [!] --syn
1549 Only match TCP packets with the SYN bit set and the ACK,RST and
1550 FIN bits cleared. Such packets are used to request TCP connec‐
1551 tion initiation; for example, blocking such packets coming in an
1552 interface will prevent incoming TCP connections, but outgoing
1553 TCP connections will be unaffected. It is equivalent to
1554 --tcp-flags SYN,RST,ACK,FIN SYN. If the "!" flag precedes the
1555 "--syn", the sense of the option is inverted.
1556 [!] --tcp-option number
1558 Match if TCP option set.
1559 tcpmss
1561 This matches the TCP MSS (maximum segment size) field of the TCP
1562 header. You can only use this on TCP SYN or SYN/ACK packets, since the
1563 MSS is only negotiated during the TCP handshake at connection startup
1564 time.
1565 [!] --mss value[:value]
1567 Match a given TCP MSS value or range. If a range is given, the
1568 second value must be greater than or equal to the first value.
1569 time
1571 This matches if the packet arrival time/date is within a given range.
1572 All options are optional, but are ANDed when specified. All times are
1573 interpreted as UTC by default.
1574 --datestart YYYY[-MM[-DD[Thh[:mm[:ss]]]]]
1576 --datestop YYYY[-MM[-DD[Thh[:mm[:ss]]]]]
1578 Only match during the given time, which must be in ISO 8601 "T"
1579 notation. The possible time range is 1970-01-01T00:00:00 to
1580 2038-01-19T04:17:07.
1581 If --datestart or --datestop are not specified, it will default
1583 to 1970-01-01 and 2038-01-19, respectively.
1584 --timestart hh:mm[:ss]
1586 --timestop hh:mm[:ss]
1588 Only match during the given daytime. The possible time range is
1589 00:00:00 to 23:59:59. Leading zeroes are allowed (e.g. "06:03")
1590 and correctly interpreted as base-10.
1591 [!] --monthdays day[,day...]
1593 Only match on the given days of the month. Possible values are 1
1594 to 31. Note that specifying 31 will of course not match on
1595 months which do not have a 31st day; the same goes for 28- or
1596 29-day February.
1597 [!] --weekdays day[,day...]
1599 Only match on the given weekdays. Possible values are Mon, Tue,
1600 Wed, Thu, Fri, Sat, Sun, or values from 1 to 7, respectively.
1601 You may also use two-character variants (Mo, Tu, etc.).
1602 --contiguous
1604 When --timestop is smaller than --timestart value, match this as
1605 a single time period instead distinct intervals. See EXAMPLES.
1606 --kerneltz
1608 Use the kernel timezone instead of UTC to determine whether a
1609 packet meets the time regulations.
1610 About kernel timezones: Linux keeps the system time in UTC, and always
1612 does so. On boot, system time is initialized from a referential time
1613 source. Where this time source has no timezone information, such as the
1614 x86 CMOS RTC, UTC will be assumed. If the time source is however not in
1615 UTC, userspace should provide the correct system time and timezone to
1616 the kernel once it has the information.
1617 Local time is a feature on top of the (timezone independent) system
1619 time. Each process has its own idea of local time, specified via the TZ
1620 environment variable. The kernel also has its own timezone offset vari‐
1621 able. The TZ userspace environment variable specifies how the UTC-based
1622 system time is displayed, e.g. when you run date(1), or what you see on
1623 your desktop clock. The TZ string may resolve to different offsets at
1624 different dates, which is what enables the automatic time-jumping in
1625 userspace. when DST changes. The kernel's timezone offset variable is
1626 used when it has to convert between non-UTC sources, such as FAT
1627 filesystems, to UTC (since the latter is what the rest of the system
1628 uses).
1629 The caveat with the kernel timezone is that Linux distributions may
1631 ignore to set the kernel timezone, and instead only set the system
1632 time. Even if a particular distribution does set the timezone at boot,
1633 it is usually does not keep the kernel timezone offset - which is what
1634 changes on DST - up to date. ntpd will not touch the kernel timezone,
1635 so running it will not resolve the issue. As such, one may encounter a
1636 timezone that is always +0000, or one that is wrong half of the time of
1637 the year. As such, using --kerneltz is highly discouraged.
1638 EXAMPLES. To match on weekends, use:
1640 -m time --weekdays Sa,Su
1642 Or, to match (once) on a national holiday block:
1644 -m time --datestart 2007-12-24 --datestop 2007-12-27
1646 Since the stop time is actually inclusive, you would need the following
1648 stop time to not match the first second of the new day:
1649 -m time --datestart 2007-01-01T17:00 --datestop
1651 2007-01-01T23:59:59
1652 During lunch hour:
1654 -m time --timestart 12:30 --timestop 13:30
1656 The fourth Friday in the month:
1658 -m time --weekdays Fr --monthdays 22,23,24,25,26,27,28
1660 (Note that this exploits a certain mathematical property. It is not
1662 possible to say "fourth Thursday OR fourth Friday" in one rule. It is
1663 possible with multiple rules, though.)
1664 Matching across days might not do what is expected. For instance,
1666 -m time --weekdays Mo --timestart 23:00 --timestop 01:00 Will
1668 match Monday, for one hour from midnight to 1 a.m., and then
1669 again for another hour from 23:00 onwards. If this is unwanted,
1670 e.g. if you would like 'match for two hours from Montay 23:00
1671 onwards' you need to also specify the --contiguous option in the
1672 example above.
1673 tos
1675 This module matches the 8-bit Type of Service field in the IPv4 header
1676 (i.e. including the "Precedence" bits) or the (also 8-bit) Priority
1677 field in the IPv6 header.
1678 [!] --tos value[/mask]
1680 Matches packets with the given TOS mark value. If a mask is
1681 specified, it is logically ANDed with the TOS mark before the
1682 comparison.
1683 [!] --tos symbol
1685 You can specify a symbolic name when using the tos match for
1686 IPv4. The list of recognized TOS names can be obtained by call‐
1687 ing iptables with -m tos -h. Note that this implies a mask of
1688 0x3F, i.e. all but the ECN bits.
1689 ttl (IPv4-specific)
1691 This module matches the time to live field in the IP header.
1692 [!] --ttl-eq ttl
1694 Matches the given TTL value.
1695 --ttl-gt ttl
1697 Matches if TTL is greater than the given TTL value.
1698 --ttl-lt ttl
1700 Matches if TTL is less than the given TTL value.
1701 u32
1703 U32 tests whether quantities of up to 4 bytes extracted from a packet
1704 have specified values. The specification of what to extract is general
1705 enough to find data at given offsets from tcp headers or payloads.
1706 [!] --u32 tests
1708 The argument amounts to a program in a small language described
1709 below.
1710 tests := location "=" value | tests "&&" location "=" value
1712 value := range | value "," range
1714 range := number | number ":" number
1716 a single number, n, is interpreted the same as n:n. n:m is interpreted
1718 as the range of numbers >=n and <=m.
1719 location := number | location operator number
1721 operator := "&" | "<<" | ">>" | "@"
1723 The operators &, <<, >> and && mean the same as in C. The = is really
1725 a set membership operator and the value syntax describes a set. The @
1726 operator is what allows moving to the next header and is described fur‐
1727 ther below.
1728 There are currently some artificial implementation limits on the size
1730 of the tests:
1731 * no more than 10 of "=" (and 9 "&&"s) in the u32 argument
1733 * no more than 10 ranges (and 9 commas) per value
1735 * no more than 10 numbers (and 9 operators) per location
1737 To describe the meaning of location, imagine the following machine that
1739 interprets it. There are three registers:
1740 A is of type char *, initially the address of the IP header
1742 B and C are unsigned 32 bit integers, initially zero
1744 The instructions are:
1746 number B = number;
1748 C = (*(A+B)<<24) + (*(A+B+1)<<16) + (*(A+B+2)<<8) + *(A+B+3)
1750 &number C = C & number
1752 << number C = C << number
1754 >> number C = C >> number
1756 @number A = A + C; then do the instruction number
1758 Any access of memory outside [skb->data,skb->end] causes the match to
1760 fail. Otherwise the result of the computation is the final value of C.
1761 Whitespace is allowed but not required in the tests. However, the char‐
1763 acters that do occur there are likely to require shell quoting, so it
1764 is a good idea to enclose the arguments in quotes.
1765 Example:
1767 match IP packets with total length >= 256
1769 The IP header contains a total length field in bytes 2-3.
1771 --u32 "0 & 0xFFFF = 0x100:0xFFFF"
1773 read bytes 0-3
1775 AND that with 0xFFFF (giving bytes 2-3), and test whether that
1777 is in the range [0x100:0xFFFF]
1778 Example: (more realistic, hence more complicated)
1780 match ICMP packets with icmp type 0
1782 First test that it is an ICMP packet, true iff byte 9 (protocol)
1784 = 1
1785 --u32 "6 & 0xFF = 1 && ...
1787 read bytes 6-9, use & to throw away bytes 6-8 and compare the
1789 result to 1. Next test that it is not a fragment. (If so, it
1790 might be part of such a packet but we cannot always tell.) N.B.:
1791 This test is generally needed if you want to match anything
1792 beyond the IP header. The last 6 bits of byte 6 and all of byte
1793 7 are 0 iff this is a complete packet (not a fragment). Alterna‐
1794 tively, you can allow first fragments by only testing the last 5
1795 bits of byte 6.
1796 ... 4 & 0x3FFF = 0 && ...
1798 Last test: the first byte past the IP header (the type) is 0.
1800 This is where we have to use the @syntax. The length of the IP
1801 header (IHL) in 32 bit words is stored in the right half of byte
1802 0 of the IP header itself.
1803 ... 0 >> 22 & 0x3C @ 0 >> 24 = 0"
1805 The first 0 means read bytes 0-3, >>22 means shift that 22 bits
1807 to the right. Shifting 24 bits would give the first byte, so
1808 only 22 bits is four times that plus a few more bits. &3C then
1809 eliminates the two extra bits on the right and the first four
1810 bits of the first byte. For instance, if IHL=5, then the IP
1811 header is 20 (4 x 5) bytes long. In this case, bytes 0-1 are (in
1812 binary) xxxx0101 yyzzzzzz, >>22 gives the 10 bit value
1813 xxxx0101yy and &3C gives 010100. @ means to use this number as a
1814 new offset into the packet, and read four bytes starting from
1815 there. This is the first 4 bytes of the ICMP payload, of which
1816 byte 0 is the ICMP type. Therefore, we simply shift the value 24
1817 to the right to throw out all but the first byte and compare the
1818 result with 0.
1819 Example:
1821 TCP payload bytes 8-12 is any of 1, 2, 5 or 8
1823 First we test that the packet is a tcp packet (similar to ICMP).
1825 --u32 "6 & 0xFF = 6 && ...
1827 Next, test that it is not a fragment (same as above).
1829 ... 0 >> 22 & 0x3C @ 12 >> 26 & 0x3C @ 8 = 1,2,5,8"
1831 0>>22&3C as above computes the number of bytes in the IP header.
1833 @ makes this the new offset into the packet, which is the start
1834 of the TCP header. The length of the TCP header (again in 32 bit
1835 words) is the left half of byte 12 of the TCP header. The
1836 12>>26&3C computes this length in bytes (similar to the IP
1837 header before). "@" makes this the new offset, which is the
1838 start of the TCP payload. Finally, 8 reads bytes 8-12 of the
1839 payload and = checks whether the result is any of 1, 2, 5 or 8.
1840 udp
1842 These extensions can be used if `--protocol udp' is specified. It pro‐
1843 vides the following options:
1844 [!] --source-port,--sport port[:port]
1846 Source port or port range specification. See the description of
1847 the --source-port option of the TCP extension for details.
1848 [!] --destination-port,--dport port[:port]
1850 Destination port or port range specification. See the descrip‐
1851 tion of the --destination-port option of the TCP extension for
1852 details.
1853 unclean (IPv4-specific)
1855 This module takes no options, but attempts to match packets which seem
1856 malformed or unusual. This is regarded as experimental.
1857
1859 iptables can use extended target modules: the following are included in
1860 the standard distribution.
1861 AUDIT
1863 This target allows to create audit records for packets hitting the tar‐
1864 get. It can be used to record accepted, dropped, and rejected packets.
1865 See auditd(8) for additional details.
1866 --type {accept|drop|reject}
1868 Set type of audit record.
1869 Example:
1871 iptables -N AUDIT_DROP
1873 iptables -A AUDIT_DROP -j AUDIT --type drop
1875 iptables -A AUDIT_DROP -j DROP
1877 CHECKSUM
1879 This target allows to selectively work around broken/old applications.
1880 It can only be used in the mangle table.
1881 --checksum-fill
1883 Compute and fill in the checksum in a packet that lacks a check‐
1884 sum. This is particularly useful, if you need to work around
1885 old applications such as dhcp clients, that do not work well
1886 with checksum offloads, but don't want to disable checksum off‐
1887 load in your device.
1888 CLASSIFY
1890 This module allows you to set the skb->priority value (and thus clas‐
1891 sify the packet into a specific CBQ class).
1892 --set-class major:minor
1894 Set the major and minor class value. The values are always
1895 interpreted as hexadecimal even if no 0x prefix is given.
1896 CLUSTERIP (IPv4-specific)
1898 This module allows you to configure a simple cluster of nodes that
1899 share a certain IP and MAC address without an explicit load balancer in
1900 front of them. Connections are statically distributed between the
1901 nodes in this cluster.
1902 --new Create a new ClusterIP. You always have to set this on the
1904 first rule for a given ClusterIP.
1905 --hashmode mode
1907 Specify the hashing mode. Has to be one of sourceip, sour‐
1908 ceip-sourceport, sourceip-sourceport-destport.
1909 --clustermac mac
1911 Specify the ClusterIP MAC address. Has to be a link-layer multi‐
1912 cast address
1913 --total-nodes num
1915 Number of total nodes within this cluster.
1916 --local-node num
1918 Local node number within this cluster.
1919 --hash-init rnd
1921 Specify the random seed used for hash initialization.
1922 CONNMARK
1924 This module sets the netfilter mark value associated with a connection.
1925 The mark is 32 bits wide.
1926 --set-xmark value[/mask]
1928 Zero out the bits given by mask and XOR value into the ctmark.
1929 --save-mark [--nfmask nfmask] [--ctmask ctmask]
1931 Copy the packet mark (nfmark) to the connection mark (ctmark)
1932 using the given masks. The new nfmark value is determined as
1933 follows:
1934 ctmark = (ctmark & ~ctmask) ^ (nfmark & nfmask)
1936 i.e. ctmask defines what bits to clear and nfmask what bits of
1938 the nfmark to XOR into the ctmark. ctmask and nfmask default to
1939 0xFFFFFFFF.
1940 --restore-mark [--nfmask nfmask] [--ctmask ctmask]
1942 Copy the connection mark (ctmark) to the packet mark (nfmark)
1943 using the given masks. The new ctmark value is determined as
1944 follows:
1945 nfmark = (nfmark & ~nfmask) ^ (ctmark & ctmask);
1947 i.e. nfmask defines what bits to clear and ctmask what bits of
1949 the ctmark to XOR into the nfmark. ctmask and nfmask default to
1950 0xFFFFFFFF.
1951 --restore-mark is only valid in the mangle table.
1953 The following mnemonics are available for --set-xmark:
1955 --and-mark bits
1957 Binary AND the ctmark with bits. (Mnemonic for --set-xmark
1958 0/invbits, where invbits is the binary negation of bits.)
1959 --or-mark bits
1961 Binary OR the ctmark with bits. (Mnemonic for --set-xmark
1962 bits/bits.)
1963 --xor-mark bits
1965 Binary XOR the ctmark with bits. (Mnemonic for --set-xmark
1966 bits/0.)
1967 --set-mark value[/mask]
1969 Set the connection mark. If a mask is specified then only those
1970 bits set in the mask are modified.
1971 --save-mark [--mask mask]
1973 Copy the nfmark to the ctmark. If a mask is specified, only
1974 those bits are copied.
1975 --restore-mark [--mask mask]
1977 Copy the ctmark to the nfmark. If a mask is specified, only
1978 those bits are copied. This is only valid in the mangle table.
1979 CONNSECMARK
1981 This module copies security markings from packets to connections (if
1982 unlabeled), and from connections back to packets (also only if unla‐
1983 beled). Typically used in conjunction with SECMARK, it is valid in the
1984 security table (for backwards compatibility with older kernels, it is
1985 also valid in the mangle table).
1986 --save If the packet has a security marking, copy it to the connection
1988 if the connection is not marked.
1989 --restore
1991 If the packet does not have a security marking, and the connec‐
1992 tion does, copy the security marking from the connection to the
1993 packet.
1994 CT
1997 The CT target allows to set parameters for a packet or its associated
1998 connection. The target attaches a "template" connection tracking entry
1999 to the packet, which is then used by the conntrack core when initializ‐
2000 ing a new ct entry. This target is thus only valid in the "raw" table.
2001 --notrack
2003 Disables connection tracking for this packet.
2004 --helper name
2006 Use the helper identified by name for the connection. This is
2007 more flexible than loading the conntrack helper modules with
2008 preset ports.
2009 --ctevents event[,...]
2011 Only generate the specified conntrack events for this connec‐
2012 tion. Possible event types are: new, related, destroy, reply,
2013 assured, protoinfo, helper, mark (this refers to the ctmark, not
2014 nfmark), natseqinfo, secmark (ctsecmark).
2015 --expevents event[,...]
2017 Only generate the specified expectation events for this connec‐
2018 tion. Possible event types are: new.
2019 --zone id
2021 Assign this packet to zone id and only have lookups done in that
2022 zone. By default, packets have zone 0.
2023 --timeout name
2025 Use the timeout policy identified by name for the connection.
2026 This is provides more flexible timeout policy definition than
2027 global timeout values available at /proc/sys/net/netfil‐
2028 ter/nf_conntrack_*_timeout_*.
2029 DNAT
2031 This target is only valid in the nat table, in the PREROUTING and OUT‐
2032 PUT chains, and user-defined chains which are only called from those
2033 chains. It specifies that the destination address of the packet should
2034 be modified (and all future packets in this connection will also be
2035 mangled), and rules should cease being examined. It takes the follow‐
2036 ing options:
2037 --to-destination [ipaddr[-ipaddr]][:port[-port]]
2039 which can specify a single new destination IP address, an inclu‐
2040 sive range of IP addresses. Optionally a port range, if the rule
2041 also specifies one of the following protocols: tcp, udp, dccp or
2042 sctp. If no port range is specified, then the destination port
2043 will never be modified. If no IP address is specified then only
2044 the destination port will be modified. In Kernels up to 2.6.10
2045 you can add several --to-destination options. For those kernels,
2046 if you specify more than one destination address, either via an
2047 address range or multiple --to-destination options, a simple
2048 round-robin (one after another in cycle) load balancing takes
2049 place between these addresses. Later Kernels (>= 2.6.11-rc1)
2050 don't have the ability to NAT to multiple ranges anymore.
2051 --random
2053 If option --random is used then port mapping will be randomized
2054 (kernel >= 2.6.22).
2055 --persistent
2057 Gives a client the same source-/destination-address for each
2058 connection. This supersedes the SAME target. Support for per‐
2059 sistent mappings is available from 2.6.29-rc2.
2060 IPv6 support available since Linux kernels >= 3.7.
2062 DNPT (IPv6-specific)
2064 Provides stateless destination IPv6-to-IPv6 Network Prefix Translation
2065 (as described by RFC 6296).
2066 You have to use this target in the mangle table, not in the nat table.
2068 It takes the following options:
2069 --src-pfx [prefix/length]
2071 Set source prefix that you want to translate and length
2072 --dst-pfx [prefix/length]
2074 Set destination prefix that you want to use in the translation
2075 and length
2076 You have to use the SNPT target to undo the translation. Example:
2078 ip6tables -t mangle -I POSTROUTING -s fd00::/64 -o vboxnet0 -j
2080 SNPT --src-pfx fd00::/64 --dst-pfx 2001:e20:2000:40f::/64
2081 ip6tables -t mangle -I PREROUTING -i wlan0 -d
2083 2001:e20:2000:40f::/64 -j DNPT --src-pfx 2001:e20:2000:40f::/64
2084 --dst-pfx fd00::/64
2085 You may need to enable IPv6 neighbor proxy:
2087 sysctl -w net.ipv6.conf.all.proxy_ndp=1
2089 You also have to use the NOTRACK target to disable connection tracking
2091 for translated flows.
2092 DSCP
2094 This target allows to alter the value of the DSCP bits within the TOS
2095 header of the IPv4 packet. As this manipulates a packet, it can only
2096 be used in the mangle table.
2097 --set-dscp value
2099 Set the DSCP field to a numerical value (can be decimal or hex)
2100 --set-dscp-class class
2102 Set the DSCP field to a DiffServ class.
2103 ECN (IPv4-specific)
2105 This target allows to selectively work around known ECN blackholes. It
2106 can only be used in the mangle table.
2107 --ecn-tcp-remove
2109 Remove all ECN bits from the TCP header. Of course, it can only
2110 be used in conjunction with -p tcp.
2111 HL (IPv6-specific)
2113 This is used to modify the Hop Limit field in IPv6 header. The Hop
2114 Limit field is similar to what is known as TTL value in IPv4. Setting
2115 or incrementing the Hop Limit field can potentially be very dangerous,
2116 so it should be avoided at any cost. This target is only valid in man‐
2117 gle table.
2118 Don't ever set or increment the value on packets that leave your local
2120 network!
2121 --hl-set value
2123 Set the Hop Limit to `value'.
2124 --hl-dec value
2126 Decrement the Hop Limit `value' times.
2127 --hl-inc value
2129 Increment the Hop Limit `value' times.
2130 HMARK
2132 Like MARK, i.e. set the fwmark, but the mark is calculated from hashing
2133 packet selector at choice. You have also to specify the mark range and,
2134 optionally, the offset to start from. ICMP error messages are inspected
2135 and used to calculate the hashing.
2136 Existing options are:
2138 --hmark-tuple tuple
2140 Possible tuple members are: src meaning source address (IPv4,
2141 IPv6 address), dst meaning destination address (IPv4, IPv6
2142 address), sport meaning source port (TCP, UDP, UDPlite, SCTP,
2143 DCCP), dport meaning destination port (TCP, UDP, UDPlite, SCTP,
2144 DCCP), spi meaning Security Parameter Index (AH, ESP), and ct
2145 meaning the usage of the conntrack tuple instead of the packet
2146 selectors.
2147 --hmark-mod value (must be > 0)
2149 Modulus for hash calculation (to limit the range of possible
2150 marks)
2151 --hmark-offset value
2153 Offset to start marks from.
2154 For advanced usage, instead of using --hmark-tuple, you can specify
2156 custom
2157 prefixes and masks:
2158 --hmark-src-prefix cidr
2160 The source address mask in CIDR notation.
2161 --hmark-dst-prefix cidr
2163 The destination address mask in CIDR notation.
2164 --hmark-sport-mask value
2166 A 16 bit source port mask in hexadecimal.
2167 --hmark-dport-mask value
2169 A 16 bit destination port mask in hexadecimal.
2170 --hmark-spi-mask value
2172 A 32 bit field with spi mask.
2173 --hmark-proto-mask value
2175 An 8 bit field with layer 4 protocol number.
2176 --hmark-rnd value
2178 A 32 bit random custom value to feed hash calculation.
2179 Examples:
2181 iptables -t mangle -A PREROUTING -m conntrack --ctstate NEW
2183 -j HMARK --hmark-tuple ct,src,dst,proto --hmark-offset 10000
2184 --hmark-mod 10 --hmark-rnd 0xfeedcafe
2185 iptables -t mangle -A PREROUTING -j HMARK --hmark-offset 10000 --hmark-
2187 tuple src,dst,proto --hmark-mod 10 --hmark-rnd 0xdeafbeef
2188 IDLETIMER
2190 This target can be used to identify when interfaces have been idle for
2191 a certain period of time. Timers are identified by labels and are cre‐
2192 ated when a rule is set with a new label. The rules also take a time‐
2193 out value (in seconds) as an option. If more than one rule uses the
2194 same timer label, the timer will be restarted whenever any of the rules
2195 get a hit. One entry for each timer is created in sysfs. This
2196 attribute contains the timer remaining for the timer to expire. The
2197 attributes are located under the xt_idletimer class:
2198 /sys/class/xt_idletimer/timers/<label>
2200 When the timer expires, the target module sends a sysfs notification to
2202 the userspace, which can then decide what to do (eg. disconnect to save
2203 power).
2204 --timeout amount
2206 This is the time in seconds that will trigger the notification.
2207 --label string
2209 This is a unique identifier for the timer. The maximum length
2210 for the label string is 27 characters.
2211 LED
2213 This creates an LED-trigger that can then be attached to system indica‐
2214 tor lights, to blink or illuminate them when certain packets pass
2215 through the system. One example might be to light up an LED for a few
2216 minutes every time an SSH connection is made to the local machine. The
2217 following options control the trigger behavior:
2218 --led-trigger-id name
2220 This is the name given to the LED trigger. The actual name of
2221 the trigger will be prefixed with "netfilter-".
2222 --led-delay ms
2224 This indicates how long (in milliseconds) the LED should be left
2225 illuminated when a packet arrives before being switched off
2226 again. The default is 0 (blink as fast as possible.) The special
2227 value inf can be given to leave the LED on permanently once
2228 activated. (In this case the trigger will need to be manually
2229 detached and reattached to the LED device to switch it off
2230 again.)
2231 --led-always-blink
2233 Always make the LED blink on packet arrival, even if the LED is
2234 already on. This allows notification of new packets even with
2235 long delay values (which otherwise would result in a silent pro‐
2236 longing of the delay time.)
2237 Example:
2239 Create an LED trigger for incoming SSH traffic:
2241 iptables -A INPUT -p tcp --dport 22 -j LED --led-trigger-id ssh
2242 Then attach the new trigger to an LED:
2244 echo netfilter-ssh >/sys/class/leds/ledname/trigger
2245 LOG
2247 Turn on kernel logging of matching packets. When this option is set
2248 for a rule, the Linux kernel will print some information on all match‐
2249 ing packets (like most IP/IPv6 header fields) via the kernel log (where
2250 it can be read with dmesg(1) or read in the syslog).
2251 This is a "non-terminating target", i.e. rule traversal continues at
2253 the next rule. So if you want to LOG the packets you refuse, use two
2254 separate rules with the same matching criteria, first using target LOG
2255 then DROP (or REJECT).
2256 --log-level level
2258 Level of logging, which can be (system-specific) numeric or a
2259 mnemonic. Possible values are (in decreasing order of prior‐
2260 ity): emerg, alert, crit, error, warning, notice, info or debug.
2261 --log-prefix prefix
2263 Prefix log messages with the specified prefix; up to 29 letters
2264 long, and useful for distinguishing messages in the logs.
2265 --log-tcp-sequence
2267 Log TCP sequence numbers. This is a security risk if the log is
2268 readable by users.
2269 --log-tcp-options
2271 Log options from the TCP packet header.
2272 --log-ip-options
2274 Log options from the IP/IPv6 packet header.
2275 --log-uid
2277 Log the userid of the process which generated the packet.
2278 MARK
2280 This target is used to set the Netfilter mark value associated with the
2281 packet. It can, for example, be used in conjunction with routing based
2282 on fwmark (needs iproute2). If you plan on doing so, note that the mark
2283 needs to be set in the PREROUTING chain of the mangle table to affect
2284 routing. The mark field is 32 bits wide.
2285 --set-xmark value[/mask]
2287 Zeroes out the bits given by mask and XORs value into the packet
2288 mark ("nfmark"). If mask is omitted, 0xFFFFFFFF is assumed.
2289 --set-mark value[/mask]
2291 Zeroes out the bits given by mask and ORs value into the packet
2292 mark. If mask is omitted, 0xFFFFFFFF is assumed.
2293 The following mnemonics are available:
2295 --and-mark bits
2297 Binary AND the nfmark with bits. (Mnemonic for --set-xmark
2298 0/invbits, where invbits is the binary negation of bits.)
2299 --or-mark bits
2301 Binary OR the nfmark with bits. (Mnemonic for --set-xmark
2302 bits/bits.)
2303 --xor-mark bits
2305 Binary XOR the nfmark with bits. (Mnemonic for --set-xmark
2306 bits/0.)
2307 MASQUERADE
2309 This target is only valid in the nat table, in the POSTROUTING chain.
2310 It should only be used with dynamically assigned IP (dialup) connec‐
2311 tions: if you have a static IP address, you should use the SNAT target.
2312 Masquerading is equivalent to specifying a mapping to the IP address of
2313 the interface the packet is going out, but also has the effect that
2314 connections are forgotten when the interface goes down. This is the
2315 correct behavior when the next dialup is unlikely to have the same
2316 interface address (and hence any established connections are lost any‐
2317 way).
2318 --to-ports port[-port]
2320 This specifies a range of source ports to use, overriding the
2321 default SNAT source port-selection heuristics (see above). This
2322 is only valid if the rule also specifies one of the following
2323 protocols: tcp, udp, dccp or sctp.
2324 --random
2326 Randomize source port mapping If option --random is used then
2327 port mapping will be randomized (kernel >= 2.6.21).
2328 IPv6 support available since Linux kernels >= 3.7.
2330 MIRROR (IPv4-specific)
2332 This is an experimental demonstration target which inverts the source
2333 and destination fields in the IP header and retransmits the packet. It
2334 is only valid in the INPUT, FORWARD and PREROUTING chains, and user-
2335 defined chains which are only called from those chains. Note that the
2336 outgoing packets are NOT seen by any packet filtering chains, connec‐
2337 tion tracking or NAT, to avoid loops and other problems.
2338 NETMAP
2340 This target allows you to statically map a whole network of addresses
2341 onto another network of addresses. It can only be used from rules in
2342 the nat table.
2343 --to address[/mask]
2345 Network address to map to. The resulting address will be con‐
2346 structed in the following way: All 'one' bits in the mask are
2347 filled in from the new `address'. All bits that are zero in the
2348 mask are filled in from the original address.
2349 IPv6 support available since Linux kernels >= 3.7.
2351 NFLOG
2353 This target provides logging of matching packets. When this target is
2354 set for a rule, the Linux kernel will pass the packet to the loaded
2355 logging backend to log the packet. This is usually used in combination
2356 with nfnetlink_log as logging backend, which will multicast the packet
2357 through a netlink socket to the specified multicast group. One or more
2358 userspace processes may subscribe to the group to receive the packets.
2359 Like LOG, this is a non-terminating target, i.e. rule traversal contin‐
2360 ues at the next rule.
2361 --nflog-group nlgroup
2363 The netlink group (0 - 2^16-1) to which packets are (only appli‐
2364 cable for nfnetlink_log). The default value is 0.
2365 --nflog-prefix prefix
2367 A prefix string to include in the log message, up to 64 charac‐
2368 ters long, useful for distinguishing messages in the logs.
2369 --nflog-range size
2371 The number of bytes to be copied to userspace (only applicable
2372 for nfnetlink_log). nfnetlink_log instances may specify their
2373 own range, this option overrides it.
2374 --nflog-threshold size
2376 Number of packets to queue inside the kernel before sending them
2377 to userspace (only applicable for nfnetlink_log). Higher values
2378 result in less overhead per packet, but increase delay until the
2379 packets reach userspace. The default value is 1.
2380 NFQUEUE
2382 This target passes the packet to userspace using the nfnetlink_queue
2383 handler. The packet is put into the queue identified by its 16-bit
2384 queue number. Userspace can inspect and modify the packet if desired.
2385 Userspace must then drop or reinject the packet into the kernel.
2386 Please see libnetfilter_queue for details. nfnetlink_queue was added
2387 in Linux 2.6.14. The queue-balance option was added in Linux 2.6.31,
2388 queue-bypass in 2.6.39.
2389 --queue-num value
2391 This specifies the QUEUE number to use. Valid queue numbers are
2392 0 to 65535. The default value is 0.
2393 --queue-balance value:value
2395 This specifies a range of queues to use. Packets are then bal‐
2396 anced across the given queues. This is useful for multicore
2397 systems: start multiple instances of the userspace program on
2398 queues x, x+1, .. x+n and use "--queue-balance x:x+n". Packets
2399 belonging to the same connection are put into the same nfqueue.
2400 --queue-bypass
2402 By default, if no userspace program is listening on an NFQUEUE,
2403 then all packets that are to be queued are dropped. When this
2404 option is used, the NFQUEUE rule behaves like ACCEPT instead,
2405 and the packet will move on to the next table.
2406 --queue-cpu-fanout
2408 Available starting Linux kernel 3.10. When used together with
2409 --queue-balance this will use the CPU ID as an index to map
2410 packets to the queues. The idea is that you can improve perfor‐
2411 mance if there's a queue per CPU. This requires --queue-balance
2412 to be specified.
2413 NOTRACK
2415 This extension disables connection tracking for all packets matching
2416 that rule. It is equivalent with -j CT --notrack. Like CT, NOTRACK can
2417 only be used in the raw table.
2418 RATEEST
2420 The RATEEST target collects statistics, performs rate estimation calcu‐
2421 lation and saves the results for later evaluation using the rateest
2422 match.
2423 --rateest-name name
2425 Count matched packets into the pool referred to by name, which
2426 is freely choosable.
2427 --rateest-interval amount{s|ms|us}
2429 Rate measurement interval, in seconds, milliseconds or microsec‐
2430 onds.
2431 --rateest-ewmalog value
2433 Rate measurement averaging time constant.
2434 REDIRECT
2436 This target is only valid in the nat table, in the PREROUTING and OUT‐
2437 PUT chains, and user-defined chains which are only called from those
2438 chains. It redirects the packet to the machine itself by changing the
2439 destination IP to the primary address of the incoming interface
2440 (locally-generated packets are mapped to the localhost address,
2441 127.0.0.1 for IPv4 and ::1 for IPv6).
2442 --to-ports port[-port]
2444 This specifies a destination port or range of ports to use:
2445 without this, the destination port is never altered. This is
2446 only valid if the rule also specifies one of the following pro‐
2447 tocols: tcp, udp, dccp or sctp.
2448 --random
2450 If option --random is used then port mapping will be randomized
2451 (kernel >= 2.6.22).
2452 IPv6 support available starting Linux kernels >= 3.7.
2454 REJECT (IPv6-specific)
2456 This is used to send back an error packet in response to the matched
2457 packet: otherwise it is equivalent to DROP so it is a terminating TAR‐
2458 GET, ending rule traversal. This target is only valid in the INPUT,
2459 FORWARD and OUTPUT chains, and user-defined chains which are only
2460 called from those chains. The following option controls the nature of
2461 the error packet returned:
2462 --reject-with type
2464 The type given can be icmp6-no-route, no-route, icmp6-adm-pro‐
2465 hibited, adm-prohibited, icmp6-addr-unreachable, addr-unreach,
2466 or icmp6-port-unreachable, which return the appropriate ICMPv6
2467 error message (icmp6-port-unreachable is the default). Finally,
2468 the option tcp-reset can be used on rules which only match the
2469 TCP protocol: this causes a TCP RST packet to be sent back.
2470 This is mainly useful for blocking ident (113/tcp) probes which
2471 frequently occur when sending mail to broken mail hosts (which
2472 won't accept your mail otherwise). tcp-reset can only be used
2473 with kernel versions 2.6.14 or later.
2474 REJECT (IPv4-specific)
2476 This is used to send back an error packet in response to the matched
2477 packet: otherwise it is equivalent to DROP so it is a terminating TAR‐
2478 GET, ending rule traversal. This target is only valid in the INPUT,
2479 FORWARD and OUTPUT chains, and user-defined chains which are only
2480 called from those chains. The following option controls the nature of
2481 the error packet returned:
2482 --reject-with type
2484 The type given can be icmp-net-unreachable, icmp-host-unreach‐
2485 able, icmp-port-unreachable, icmp-proto-unreachable,
2486 icmp-net-prohibited, icmp-host-prohibited, or icmp-admin-prohib‐
2487 ited (*), which return the appropriate ICMP error message
2488 (icmp-port-unreachable is the default). The option tcp-reset
2489 can be used on rules which only match the TCP protocol: this
2490 causes a TCP RST packet to be sent back. This is mainly useful
2491 for blocking ident (113/tcp) probes which frequently occur when
2492 sending mail to broken mail hosts (which won't accept your mail
2493 otherwise).
2494 (*) Using icmp-admin-prohibited with kernels that do not support it
2496 will result in a plain DROP instead of REJECT
2497 SAME (IPv4-specific)
2499 Similar to SNAT/DNAT depending on chain: it takes a range of addresses
2500 (`--to 1.2.3.4-1.2.3.7') and gives a client the same source-/destina‐
2501 tion-address for each connection.
2502 N.B.: The DNAT target's --persistent option replaced the SAME target.
2504 --to ipaddr[-ipaddr]
2506 Addresses to map source to. May be specified more than once for
2507 multiple ranges.
2508 --nodst
2510 Don't use the destination-ip in the calculations when selecting
2511 the new source-ip
2512 --random
2514 Port mapping will be forcibly randomized to avoid attacks based
2515 on port prediction (kernel >= 2.6.21).
2516 SECMARK
2518 This is used to set the security mark value associated with the packet
2519 for use by security subsystems such as SELinux. It is valid in the
2520 security table (for backwards compatibility with older kernels, it is
2521 also valid in the mangle table). The mark is 32 bits wide.
2522 --selctx security_context
2524 SET
2526 This module adds and/or deletes entries from IP sets which can be
2527 defined by ipset(8).
2528 --add-set setname flag[,flag...]
2530 add the address(es)/port(s) of the packet to the set
2531 --del-set setname flag[,flag...]
2533 delete the address(es)/port(s) of the packet from the set
2534 where flag(s) are src and/or dst specifications and there can be
2536 no more than six of them.
2537 --timeout value
2539 when adding an entry, the timeout value to use instead of the
2540 default one from the set definition
2541 --exist
2543 when adding an entry if it already exists, reset the timeout
2544 value to the specified one or to the default from the set defi‐
2545 nition
2546 Use of -j SET requires that ipset kernel support is provided, which,
2548 for standard kernels, is the case since Linux 2.6.39.
2549 SNAT
2551 This target is only valid in the nat table, in the POSTROUTING and
2552 INPUT chains, and user-defined chains which are only called from those
2553 chains. It specifies that the source address of the packet should be
2554 modified (and all future packets in this connection will also be man‐
2555 gled), and rules should cease being examined. It takes the following
2556 options:
2557 --to-source [ipaddr[-ipaddr]][:port[-port]]
2559 which can specify a single new source IP address, an inclusive
2560 range of IP addresses. Optionally a port range, if the rule also
2561 specifies one of the following protocols: tcp, udp, dccp or
2562 sctp. If no port range is specified, then source ports below
2563 512 will be mapped to other ports below 512: those between 512
2564 and 1023 inclusive will be mapped to ports below 1024, and other
2565 ports will be mapped to 1024 or above. Where possible, no port
2566 alteration will occur. In Kernels up to 2.6.10, you can add
2567 several --to-source options. For those kernels, if you specify
2568 more than one source address, either via an address range or
2569 multiple --to-source options, a simple round-robin (one after
2570 another in cycle) takes place between these addresses. Later
2571 Kernels (>= 2.6.11-rc1) don't have the ability to NAT to multi‐
2572 ple ranges anymore.
2573 --random
2575 If option --random is used then port mapping will be randomized
2576 (kernel >= 2.6.21).
2577 --persistent
2579 Gives a client the same source-/destination-address for each
2580 connection. This supersedes the SAME target. Support for per‐
2581 sistent mappings is available from 2.6.29-rc2.
2582 Kernels prior to 2.6.36-rc1 don't have the ability to SNAT in the INPUT
2584 chain.
2585 IPv6 support available since Linux kernels >= 3.7.
2587 SNPT (IPv6-specific)
2589 Provides stateless source IPv6-to-IPv6 Network Prefix Translation (as
2590 described by RFC 6296).
2591 You have to use this target in the mangle table, not in the nat table.
2593 It takes the following options:
2594 --src-pfx [prefix/length]
2596 Set source prefix that you want to translate and length
2597 --dst-pfx [prefix/length]
2599 Set destination prefix that you want to use in the translation
2600 and length
2601 You have to use the DNPT target to undo the translation. Example:
2603 ip6tables -t mangle -I POSTROUTING -s fd00::/64 -o vboxnet0 -j
2605 SNPT --src-pfx fd00::/64 --dst-pfx 2001:e20:2000:40f::/64
2606 ip6tables -t mangle -I PREROUTING -i wlan0 -d
2608 2001:e20:2000:40f::/64 -j DNPT --src-pfx 2001:e20:2000:40f::/64
2609 --dst-pfx fd00::/64
2610 You may need to enable IPv6 neighbor proxy:
2612 sysctl -w net.ipv6.conf.all.proxy_ndp=1
2614 You also have to use the NOTRACK target to disable connection tracking
2616 for translated flows.
2617 TCPMSS
2619 This target allows to alter the MSS value of TCP SYN packets, to con‐
2620 trol the maximum size for that connection (usually limiting it to your
2621 outgoing interface's MTU minus 40 for IPv4 or 60 for IPv6, respec‐
2622 tively). Of course, it can only be used in conjunction with -p tcp.
2623 This target is used to overcome criminally braindead ISPs or servers
2625 which block "ICMP Fragmentation Needed" or "ICMPv6 Packet Too Big"
2626 packets. The symptoms of this problem are that everything works fine
2627 from your Linux firewall/router, but machines behind it can never
2628 exchange large packets:
2629 1. Web browsers connect, then hang with no data received.
2631 2. Small mail works fine, but large emails hang.
2633 3. ssh works fine, but scp hangs after initial handshaking.
2635 Workaround: activate this option and add a rule to your firewall con‐
2637 figuration like:
2638 iptables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN
2640 -j TCPMSS --clamp-mss-to-pmtu
2641 --set-mss value
2643 Explicitly sets MSS option to specified value. If the MSS of the
2644 packet is already lower than value, it will not be increased
2645 (from Linux 2.6.25 onwards) to avoid more problems with hosts
2646 relying on a proper MSS.
2647 --clamp-mss-to-pmtu
2649 Automatically clamp MSS value to (path_MTU - 40 for IPv4; -60
2650 for IPv6). This may not function as desired where asymmetric
2651 routes with differing path MTU exist — the kernel uses the path
2652 MTU which it would use to send packets from itself to the source
2653 and destination IP addresses. Prior to Linux 2.6.25, only the
2654 path MTU to the destination IP address was considered by this
2655 option; subsequent kernels also consider the path MTU to the
2656 source IP address.
2657 These options are mutually exclusive.
2659 TCPOPTSTRIP
2661 This target will strip TCP options off a TCP packet. (It will actually
2662 replace them by NO-OPs.) As such, you will need to add the -p tcp
2663 parameters.
2664 --strip-options option[,option...]
2666 Strip the given option(s). The options may be specified by TCP
2667 option number or by symbolic name. The list of recognized
2668 options can be obtained by calling iptables with -j TCPOPTSTRIP
2669 -h.
2670 TEE
2672 The TEE target will clone a packet and redirect this clone to another
2673 machine on the local network segment. In other words, the nexthop must
2674 be the target, or you will have to configure the nexthop to forward it
2675 further if so desired.
2676 --gateway ipaddr
2678 Send the cloned packet to the host reachable at the given IP
2679 address. Use of 0.0.0.0 (for IPv4 packets) or :: (IPv6) is
2680 invalid.
2681 To forward all incoming traffic on eth0 to an Network Layer logging
2683 box:
2684 -t mangle -A PREROUTING -i eth0 -j TEE --gateway 2001:db8::1
2686 TOS
2688 This module sets the Type of Service field in the IPv4 header (includ‐
2689 ing the "precedence" bits) or the Priority field in the IPv6 header.
2690 Note that TOS shares the same bits as DSCP and ECN. The TOS target is
2691 only valid in the mangle table.
2692 --set-tos value[/mask]
2694 Zeroes out the bits given by mask (see NOTE below) and XORs
2695 value into the TOS/Priority field. If mask is omitted, 0xFF is
2696 assumed.
2697 --set-tos symbol
2699 You can specify a symbolic name when using the TOS target for
2700 IPv4. It implies a mask of 0xFF (see NOTE below). The list of
2701 recognized TOS names can be obtained by calling iptables with -j
2702 TOS -h.
2703 The following mnemonics are available:
2705 --and-tos bits
2707 Binary AND the TOS value with bits. (Mnemonic for --set-tos
2708 0/invbits, where invbits is the binary negation of bits. See
2709 NOTE below.)
2710 --or-tos bits
2712 Binary OR the TOS value with bits. (Mnemonic for --set-tos
2713 bits/bits. See NOTE below.)
2714 --xor-tos bits
2716 Binary XOR the TOS value with bits. (Mnemonic for --set-tos
2717 bits/0. See NOTE below.)
2718 NOTE: In Linux kernels up to and including 2.6.38, with the exception
2720 of longterm releases 2.6.32 (>=.42), 2.6.33 (>=.15), and 2.6.35
2721 (>=.14), there is a bug whereby IPv6 TOS mangling does not behave as
2722 documented and differs from the IPv4 version. The TOS mask indicates
2723 the bits one wants to zero out, so it needs to be inverted before
2724 applying it to the original TOS field. However, the aformentioned ker‐
2725 nels forgo the inversion which breaks --set-tos and its mnemonics.
2726 TPROXY
2728 This target is only valid in the mangle table, in the PREROUTING chain
2729 and user-defined chains which are only called from this chain. It redi‐
2730 rects the packet to a local socket without changing the packet header
2731 in any way. It can also change the mark value which can then be used in
2732 advanced routing rules. It takes three options:
2733 --on-port port
2735 This specifies a destination port to use. It is a required
2736 option, 0 means the new destination port is the same as the
2737 original. This is only valid if the rule also specifies -p tcp
2738 or -p udp.
2739 --on-ip address
2741 This specifies a destination address to use. By default the
2742 address is the IP address of the incoming interface. This is
2743 only valid if the rule also specifies -p tcp or -p udp.
2744 --tproxy-mark value[/mask]
2746 Marks packets with the given value/mask. The fwmark value set
2747 here can be used by advanced routing. (Required for transparent
2748 proxying to work: otherwise these packets will get forwarded,
2749 which is probably not what you want.)
2750 TRACE
2752 This target marks packets so that the kernel will log every rule which
2753 match the packets as those traverse the tables, chains, rules.
2754 A logging backend, such as nf_log_ipv4(6) or nfnetlink_log, must be
2756 loaded for this to be visible. The packets are logged with the string
2757 prefix: "TRACE: tablename:chainname:type:rulenum " where type can be
2758 "rule" for plain rule, "return" for implicit rule at the end of a user
2759 defined chain and "policy" for the policy of the built in chains.
2760 It can only be used in the raw table.
2761 TTL (IPv4-specific)
2763 This is used to modify the IPv4 TTL header field. The TTL field deter‐
2764 mines how many hops (routers) a packet can traverse until it's time to
2765 live is exceeded.
2766 Setting or incrementing the TTL field can potentially be very danger‐
2768 ous, so it should be avoided at any cost. This target is only valid in
2769 mangle table.
2770 Don't ever set or increment the value on packets that leave your local
2772 network!
2773 --ttl-set value
2775 Set the TTL value to `value'.
2776 --ttl-dec value
2778 Decrement the TTL value `value' times.
2779 --ttl-inc value
2781 Increment the TTL value `value' times.
2782 ULOG (IPv4-specific)
2784 This is the deprecated ipv4-only predecessor of the NFLOG target. It
2785 provides userspace logging of matching packets. When this target is
2786 set for a rule, the Linux kernel will multicast this packet through a
2787 netlink socket. One or more userspace processes may then subscribe to
2788 various multicast groups and receive the packets. Like LOG, this is a
2789 "non-terminating target", i.e. rule traversal continues at the next
2790 rule.
2791 --ulog-nlgroup nlgroup
2793 This specifies the netlink group (1-32) to which the packet is
2794 sent. Default value is 1.
2795 --ulog-prefix prefix
2797 Prefix log messages with the specified prefix; up to 32 charac‐
2798 ters long, and useful for distinguishing messages in the logs.
2799 --ulog-cprange size
2801 Number of bytes to be copied to userspace. A value of 0 always
2802 copies the entire packet, regardless of its size. Default is 0.
2803 --ulog-qthreshold size
2805 Number of packet to queue inside kernel. Setting this value to,
2806 e.g. 10 accumulates ten packets inside the kernel and transmits
2807 them as one netlink multipart message to userspace. Default is
2808 1 (for backwards compatibility).
2809iptables 1.4.21 iptables-extensions(8)