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IPTABLES(8)			iptables 1.4.14			   IPTABLES(8)

NAME
       iptables — administration tool for IPv4 packet filtering and NAT

SYNOPSIS
       iptables [-t table] {-A|-C|-D} chain rule-specification

       iptables [-t table] -I chain [rulenum] rule-specification

       iptables [-t table] -R chain rulenum rule-specification

       iptables [-t table] -D chain rulenum

       iptables [-t table] -S [chain [rulenum]]

       iptables [-t table] {-F|-L|-Z} [chain [rulenum]] [options...]

       iptables [-t table] -N chain

       iptables [-t table] -X [chain]

       iptables [-t table] -P chain target

       iptables [-t table] -E old-chain-name new-chain-name

       rule-specification = [matches...] [target]

       match = -m matchname [per-match-options]

       target = -j targetname [per-target-options]

DESCRIPTION
       Iptables	 is  used  to set up, maintain, and inspect the tables of IPv4
       packet filter rules in the Linux kernel.	 Several different tables  may
       be  defined.   Each  table contains a number of built-in chains and may
       also contain user-defined chains.

       Each chain is a list of rules which can match a set of  packets.	  Each
       rule specifies what to do with a packet that matches.  This is called a
       `target', which may be a jump to a user-defined chain in the  same  ta‐
       ble.

TARGETS
       A  firewall  rule specifies criteria for a packet and a target.	If the
       packet does not match, the next rule in the chain is the	 examined;  if
       it does match, then the next rule is specified by the value of the tar‐
       get, which can be the name of a user-defined chain or one of  the  spe‐
       cial values ACCEPT, DROP, QUEUE or RETURN.

       ACCEPT  means to let the packet through.	 DROP means to drop the packet
       on the floor.  QUEUE means to pass the packet to userspace.   (How  the
       packet can be received by a userspace process differs by the particular
       queue handler.  2.4.x and  2.6.x	 kernels  up  to  2.6.13  include  the
       ip_queue	 queue handler.	 Kernels 2.6.14 and later additionally include
       the nfnetlink_queue queue handler.  Packets with a target of QUEUE will
       be  sent	 to queue number '0' in this case. Please also see the NFQUEUE
       target as described  later  in  this  man  page.)   RETURN  means  stop
       traversing  this	 chain	and  resume  at	 the next rule in the previous
       (calling) chain.	 If the end of a built-in chain is reached or  a  rule
       in a built-in chain with target RETURN is matched, the target specified
       by the chain policy determines the fate of the packet.

TABLES
       There are currently three independent tables (which tables are  present
       at  any time depends on the kernel configuration options and which mod‐
       ules are present).

       -t, --table table
	      This option specifies the packet matching table which  the  com‐
	      mand  should operate on.	If the kernel is configured with auto‐
	      matic module loading, an attempt will be made to load the appro‐
	      priate module for that table if it is not already there.

	      The tables are as follows:

	      filter:
		  This	is  the	 default table (if no -t option is passed). It
		  contains the built-in chains INPUT (for packets destined  to
		  local	 sockets),  FORWARD  (for packets being routed through
		  the box), and OUTPUT (for locally-generated packets).

	      nat:
		  This table is consulted when a packet	 that  creates	a  new
		  connection  is encountered.  It consists of three built-ins:
		  PREROUTING (for altering packets as soon as they  come  in),
		  OUTPUT  (for altering locally-generated packets before rout‐
		  ing), and POSTROUTING (for  altering	packets	 as  they  are
		  about to go out).

	      mangle:
		  This table is used for specialized packet alteration.	 Until
		  kernel 2.4.17 it had two built-in  chains:  PREROUTING  (for
		  altering  incoming  packets  before routing) and OUTPUT (for
		  altering locally-generated packets before  routing).	 Since
		  kernel  2.4.18,  three  other	 built-in chains are also sup‐
		  ported: INPUT (for packets coming into the box itself), FOR‐
		  WARD	(for  altering	packets being routed through the box),
		  and POSTROUTING (for altering packets as they are  about  to
		  go out).

	      raw:
		  This	table  is  used mainly for configuring exemptions from
		  connection tracking in combination with the NOTRACK  target.
		  It registers at the netfilter hooks with higher priority and
		  is thus called before ip_conntrack, or any other IP  tables.
		  It  provides	the following built-in chains: PREROUTING (for
		  packets arriving via	any  network  interface)  OUTPUT  (for
		  packets generated by local processes)

	      security:
		  This	table  is used for Mandatory Access Control (MAC) net‐
		  working rules, such as those	enabled	 by  the  SECMARK  and
		  CONNSECMARK  targets.	  Mandatory  Access  Control is imple‐
		  mented by Linux Security Modules such as SELinux.  The secu‐
		  rity	table  is  called after the filter table, allowing any
		  Discretionary Access Control (DAC) rules in the filter table
		  to  take  effect  before MAC rules.  This table provides the
		  following built-in chains: INPUT (for	 packets  coming  into
		  the  box  itself),  OUTPUT  (for  altering locally-generated
		  packets before routing), and FORWARD (for  altering  packets
		  being routed through the box).

OPTIONS
       The options that are recognized by iptables can be divided into several
       different groups.

   COMMANDS
       These options specify the desired action to perform. Only one  of  them
       can be specified on the command line unless otherwise stated below. For
       long versions of the command and option names, you  need	 to  use  only
       enough  letters	to  ensure that iptables can differentiate it from all
       other options.

       -A, --append chain rule-specification
	      Append one or more rules to the end of the selected chain.  When
	      the  source  and/or  destination	names resolve to more than one
	      address, a rule will be added for each possible address combina‐
	      tion.

       -C, --check chain rule-specification
	      Check  whether  a	 rule matching the specification does exist in
	      the selected chain. This command uses the same logic  as	-D  to
	      find  a matching entry, but does not alter the existing iptables
	      configuration and uses its exit  code  to	 indicate  success  or
	      failure.

       -D, --delete chain rule-specification
       -D, --delete chain rulenum
	      Delete one or more rules from the selected chain.	 There are two
	      versions of this command: the rule can be specified as a	number
	      in  the  chain  (starting	 at 1 for the first rule) or a rule to
	      match.

       -I, --insert chain [rulenum] rule-specification
	      Insert one or more rules in the selected chain as the given rule
	      number.	So,  if	 the  rule  number is 1, the rule or rules are
	      inserted at the head of the chain.  This is also the default  if
	      no rule number is specified.

       -R, --replace chain rulenum rule-specification
	      Replace a rule in the selected chain.  If the source and/or des‐
	      tination names resolve to multiple addresses, the	 command  will
	      fail.  Rules are numbered starting at 1.

       -L, --list [chain]
	      List  all rules in the selected chain.  If no chain is selected,
	      all chains are listed. Like every	 other	iptables  command,  it
	      applies  to  the specified table (filter is the default), so NAT
	      rules get listed by
	       iptables -t nat -n -L
	      Please note that it is often used with the -n option,  in	 order
	      to  avoid	 long reverse DNS lookups.  It is legal to specify the
	      -Z (zero) option as well, in which case  the  chain(s)  will  be
	      atomically  listed  and zeroed.  The exact output is affected by
	      the other arguments given. The exact rules are suppressed	 until
	      you use
	       iptables -L -v

       -S, --list-rules [chain]
	      Print all rules in the selected chain.  If no chain is selected,
	      all chains are printed like iptables-save. Like every other ipt‐
	      ables  command, it applies to the specified table (filter is the
	      default).

       -F, --flush [chain]
	      Flush the selected chain (all the chains in the table if none is
	      given).	This  is  equivalent  to deleting all the rules one by
	      one.

       -Z, --zero [chain [rulenum]]
	      Zero the packet and byte counters in all	chains,	 or  only  the
	      given  chain,  or only the given rule in a chain. It is legal to
	      specify the -L, --list (list) option as well, to see  the	 coun‐
	      ters immediately before they are cleared. (See above.)

       -N, --new-chain chain
	      Create  a	 new user-defined chain by the given name.  There must
	      be no target of that name already.

       -X, --delete-chain [chain]
	      Delete the optional user-defined chain specified.	 There must be
	      no  references  to  the chain.  If there are, you must delete or
	      replace the referring rules before the  chain  can  be  deleted.
	      The  chain  must	be  empty,  i.e. not contain any rules.	 If no
	      argument is given, it will attempt to delete  every  non-builtin
	      chain in the table.

       -P, --policy chain target
	      Set  the policy for the chain to the given target.  See the sec‐
	      tion TARGETS for the legal targets.   Only  built-in  (non-user-
	      defined)	chains	can  have  policies,  and neither built-in nor
	      user-defined chains can be policy targets.

       -E, --rename-chain old-chain new-chain
	      Rename the user specified chain to the user supplied name.  This
	      is cosmetic, and has no effect on the structure of the table.

       -h     Help.   Give a (currently very brief) description of the command
	      syntax.

   PARAMETERS
       The following parameters make up a rule specification (as used  in  the
       add, delete, insert, replace and append commands).

       [!] -p, --protocol protocol
	      The  protocol of the rule or of the packet to check.  The speci‐
	      fied protocol can be one of tcp, udp, udplite,  icmp,  esp,  ah,
	      sctp or the special keyword "all", or it can be a numeric value,
	      representing one of these protocols or a different one.  A  pro‐
	      tocol  name from /etc/protocols is also allowed.	A "!" argument
	      before the protocol inverts the test.  The number zero is equiv‐
	      alent  to	 all. "all" will match with all protocols and is taken
	      as default when this option is omitted.

       [!] -s, --source address[/mask][,...]
	      Source specification. Address can be either a  network  name,  a
	      hostname,	 a  network  IP	 address  (with	 /mask), or a plain IP
	      address. Hostnames will be resolved once only, before  the  rule
	      is  submitted  to	 the  kernel.  Please note that specifying any
	      name to be resolved with a remote query such as DNS is a	really
	      bad idea.	 The mask can be either a network mask or a plain num‐
	      ber, specifying the number of 1's at the left side of  the  net‐
	      work  mask.   Thus, a mask of 24 is equivalent to 255.255.255.0.
	      A "!" argument before  the  address  specification  inverts  the
	      sense  of	 the  address.	The  flag  --src  is an alias for this
	      option.  Multiple addresses can  be  specified,  but  this  will
	      expand  to  multiple  rules (when adding with -A), or will cause
	      multiple rules to be deleted (with -D).

       [!] -d, --destination address[/mask][,...]
	      Destination  specification.   See	 the  description  of  the  -s
	      (source)	flag  for  a  detailed description of the syntax.  The
	      flag --dst is an alias for this option.

       -j, --jump target
	      This specifies the target of the rule; i.e., what to do  if  the
	      packet  matches  it.   The  target  can  be a user-defined chain
	      (other than the one this rule is in), one of the special builtin
	      targets  which  decide the fate of the packet immediately, or an
	      extension (see EXTENSIONS below).	 If this option is omitted  in
	      a rule (and -g is not used), then matching the rule will have no
	      effect on the packet's fate, but the counters on the  rule  will
	      be incremented.

       -g, --goto chain
	      This  specifies  that  the  processing should continue in a user
	      specified chain. Unlike the --jump option return will  not  con‐
	      tinue  processing	 in  this  chain but instead in the chain that
	      called us via --jump.

       [!] -i, --in-interface name
	      Name of an interface via which a packet was received  (only  for
	      packets  entering	 the  INPUT,  FORWARD  and PREROUTING chains).
	      When the "!" argument is used before  the	 interface  name,  the
	      sense  is	 inverted.   If the interface name ends in a "+", then
	      any interface which begins with this name will match.   If  this
	      option is omitted, any interface name will match.

       [!] -o, --out-interface name
	      Name of an interface via which a packet is going to be sent (for
	      packets entering the FORWARD, OUTPUT  and	 POSTROUTING  chains).
	      When  the	 "!"  argument	is used before the interface name, the
	      sense is inverted.  If the interface name ends in	 a  "+",  then
	      any  interface  which begins with this name will match.  If this
	      option is omitted, any interface name will match.

       [!] -f, --fragment
	      This means that the rule only refers to second and further frag‐
	      ments  of fragmented packets.  Since there is no way to tell the
	      source or destination ports of such a  packet  (or  ICMP	type),
	      such a packet will not match any rules which specify them.  When
	      the "!" argument precedes the "-f"  flag,	 the  rule  will  only
	      match head fragments, or unfragmented packets.

       -c, --set-counters packets bytes
	      This enables the administrator to initialize the packet and byte
	      counters of a rule (during INSERT, APPEND, REPLACE operations).

   OTHER OPTIONS
       The following additional options can be specified:

       -v, --verbose
	      Verbose output.  This option makes the  list  command  show  the
	      interface	 name,	the  rule options (if any), and the TOS masks.
	      The packet and byte counters are also listed,  with  the	suffix
	      'K',  'M' or 'G' for 1000, 1,000,000 and 1,000,000,000 multipli‐
	      ers respectively (but see the -x	flag  to  change  this).   For
	      appending,  insertion,  deletion	and  replacement,  this causes
	      detailed information on the rule or rules to be printed. -v  may
	      be specified multiple times to possibly emit more detailed debug
	      statements.

       -n, --numeric
	      Numeric output.  IP addresses and port numbers will  be  printed
	      in  numeric format.  By default, the program will try to display
	      them as host names, network names, or services (whenever	appli‐
	      cable).

       -x, --exact
	      Expand  numbers.	Display the exact value of the packet and byte
	      counters, instead of only the rounded number in  K's  (multiples
	      of  1000)	 M's (multiples of 1000K) or G's (multiples of 1000M).
	      This option is only relevant for the -L command.

       --line-numbers
	      When listing rules, add line numbers to the  beginning  of  each
	      rule, corresponding to that rule's position in the chain.

       --modprobe=command
	      When adding or inserting rules into a chain, use command to load
	      any necessary modules (targets, match extensions, etc).

MATCH EXTENSIONS
       iptables can use extended  packet  matching  modules  with  the	-m  or
       --match	options,  followed  by	the matching module name; after these,
       various extra command line options become available, depending  on  the
       specific	 module.   You	can specify multiple extended match modules in
       one line, and you can use the -h or --help options after the module has
       been specified to receive help specific to that module.

       If  the	-p  or	--protocol was specified and if and only if an unknown
       option is encountered, iptables will try load a	match  module  of  the
       same name as the protocol, to try making the option available.

   addrtype
       This module matches packets based on their address type.	 Address types
       are used within the kernel networking stack  and	 categorize  addresses
       into various groups.  The exact definition of that group depends on the
       specific layer three protocol.

       The following address types are possible:

       UNSPEC an unspecified address (i.e. 0.0.0.0)

       UNICAST
	      an unicast address

       LOCAL  a local address

       BROADCAST
	      a broadcast address

       ANYCAST
	      an anycast packet

       MULTICAST
	      a multicast address

       BLACKHOLE
	      a blackhole address

       UNREACHABLE
	      an unreachable address

       PROHIBIT
	      a prohibited address

       THROW  FIXME

       NAT    FIXME

       XRESOLVE

       [!] --src-type type
	      Matches if the source address is of given type

       [!] --dst-type type
	      Matches if the destination address is of given type

       --limit-iface-in
	      The address type checking can be limited to  the	interface  the
	      packet  is  coming in. This option is only valid in the PREROUT‐
	      ING, INPUT and FORWARD chains. It cannot be specified  with  the
	      --limit-iface-out option.

       --limit-iface-out
	      The  address  type  checking can be limited to the interface the
	      packet is going out. This option is only valid in the  POSTROUT‐
	      ING,  OUTPUT and FORWARD chains. It cannot be specified with the
	      --limit-iface-in option.

   ah
       This module matches the SPIs in Authentication header of IPsec packets.

       [!] --ahspi spi[:spi]

   cluster
       Allows you to deploy gateway and back-end load-sharing clusters without
       the need of load-balancers.

       This  match requires that all the nodes see the same packets. Thus, the
       cluster match decides if this node has to handle	 a  packet  given  the
       following options:

       --cluster-total-nodes num
	      Set number of total nodes in cluster.

       [!] --cluster-local-node num
	      Set the local node number ID.

       [!] --cluster-local-nodemask mask
	      Set  the	local  node  number  ID	 mask. You can use this option
	      instead of --cluster-local-node.

       --cluster-hash-seed value
	      Set seed value of the Jenkins hash.

       Example:

	      iptables -A PREROUTING -t mangle	-i  eth1  -m  cluster  --clus‐
	      ter-total-nodes  2  --cluster-local-node	1  --cluster-hash-seed
	      0xdeadbeef -j MARK --set-mark 0xffff

	      iptables -A PREROUTING -t mangle	-i  eth2  -m  cluster  --clus‐
	      ter-total-nodes  2  --cluster-local-node	1  --cluster-hash-seed
	      0xdeadbeef -j MARK --set-mark 0xffff

	      iptables -A PREROUTING -t mangle -i eth1 -m mark ! --mark 0xffff
	      -j DROP

	      iptables -A PREROUTING -t mangle -i eth2 -m mark ! --mark 0xffff
	      -j DROP

       And the following commands to make all nodes see the same packets:

	      ip maddr add 01:00:5e:00:01:01 dev eth1

	      ip maddr add 01:00:5e:00:01:02 dev eth2

	      arptables -A OUTPUT -o eth1 --h-length 6 -j mangle --mangle-mac-
	      s 01:00:5e:00:01:01

	      arptables	 -A  INPUT  -i	eth1  --h-length  6  --destination-mac
	      01:00:5e:00:01:01 -j mangle --mangle-mac-d 00:zz:yy:xx:5a:27

	      arptables -A OUTPUT  -o  eth2  --h-length	 6  -j	mangle	--man‐
	      gle-mac-s 01:00:5e:00:01:02

	      arptables	 -A  INPUT  -i	eth2  --h-length  6  --destination-mac
	      01:00:5e:00:01:02 -j mangle --mangle-mac-d 00:zz:yy:xx:5a:27

       In the case of TCP connections, pickup facility has to be  disabled  to
       avoid marking TCP ACK packets coming in the reply direction as valid.

	      echo 0 > /proc/sys/net/netfilter/nf_conntrack_tcp_loose

   comment
       Allows you to add comments (up to 256 characters) to any rule.

       --comment comment

       Example:
	      iptables -A INPUT -i eth1 -m comment --comment "my local LAN"

   connbytes
       Match  by  how  many  bytes  or packets a connection (or one of the two
       flows constituting the connection) has transferred so far, or by	 aver‐
       age bytes per packet.

       The counters are 64-bit and are thus not expected to overflow ;)

       The  primary  use is to detect long-lived downloads and mark them to be
       scheduled using a lower priority band in traffic control.

       The transferred bytes per connection can also be viewed	through	 `con‐
       ntrack -L` and accessed via ctnetlink.

       NOTE  that  for	connections  which have no accounting information, the
       match will always return false.	The  "net.netfilter.nf_conntrack_acct"
       sysctl  flag  controls  whether	new  connections  will	be byte/packet
       counted. Existing connection flows will	not  be	 gaining/losing	 a/the
       accounting structure when be sysctl flag is flipped.

       [!] --connbytes from[:to]
	      match  packets  from  a  connection  whose packets/bytes/average
	      packet size is more than FROM and less than TO bytes/packets. if
	      TO  is  omitted  only  FROM  check is done. "!" is used to match
	      packets not falling in the range.

       --connbytes-dir {original|reply|both}
	      which packets to consider

       --connbytes-mode {packets|bytes|avgpkt}
	      whether to check the amount of packets, number of	 bytes	trans‐
	      ferred or the average size (in bytes) of all packets received so
	      far. Note that when "both" is used together with	"avgpkt",  and
	      data is going (mainly) only in one direction (for example HTTP),
	      the average packet size will be about half of  the  actual  data
	      packets.

       Example:
	      iptables	  ..	-m    connbytes	   --connbytes	  10000:100000
	      --connbytes-dir both --connbytes-mode bytes ...

   connlimit
       Allows you to restrict the number of parallel connections to  a	server
       per client IP address (or client address block).

       --connlimit-upto n
	      Match if the number of existing connections is below or equal n.

       --connlimit-above n
	      Match if the number of existing connections is above n.

       --connlimit-mask prefix_length
	      Group  hosts  using  the prefix length. For IPv4, this must be a
	      number between (including) 0 and 32. For	IPv6,  between	0  and
	      128.  If not specified, the maximum prefix length for the appli‐
	      cable protocol is used.

       --connlimit-saddr
	      Apply the limit onto the source group. This is  the  default  if
	      --connlimit-daddr is not specified.

       --connlimit-daddr
	      Apply the limit onto the destination group.

       Examples:

       # allow 2 telnet connections per client host
	      iptables	 -A  INPUT  -p	tcp  --syn  --dport  23	 -m  connlimit
	      --connlimit-above 2 -j REJECT

       # you can also match the other way around:
	      iptables	-A  INPUT  -p  tcp  --syn  --dport  23	-m   connlimit
	      --connlimit-upto 2 -j ACCEPT

       #  limit	 the  number of parallel HTTP requests to 16 per class C sized
       source network (24 bit netmask)
	      iptables -p tcp --syn --dport 80 -m connlimit  --connlimit-above
	      16 --connlimit-mask 24 -j REJECT

       #  limit	 the number of parallel HTTP requests to 16 for the link local
       network
	      (ipv6) ip6tables	-p  tcp	 --syn	--dport	 80  -s	 fe80::/64  -m
	      connlimit --connlimit-above 16 --connlimit-mask 64 -j REJECT

       # Limit the number of connections to a particular host:
	      ip6tables	 -p  tcp  --syn	 --dport 49152:65535 -d 2001:db8::1 -m
	      connlimit --connlimit-above 100 -j REJECT

   connmark
       This module matches the netfilter mark field associated with a  connec‐
       tion (which can be set using the CONNMARK target below).

       [!] --mark value[/mask]
	      Matches  packets	in connections with the given mark value (if a
	      mask is specified, this is logically ANDed with the mark	before
	      the comparison).

   conntrack
       This  module,  when combined with connection tracking, allows access to
       the connection tracking state for this packet/connection.

       [!] --ctstate statelist
	      statelist is a comma separated list of the connection states  to
	      match.  Possible states are listed below.

       [!] --ctproto l4proto
	      Layer-4 protocol to match (by number or name)

       [!] --ctorigsrc address[/mask]

       [!] --ctorigdst address[/mask]

       [!] --ctreplsrc address[/mask]

       [!] --ctrepldst address[/mask]
	      Match against original/reply source/destination address

       [!] --ctorigsrcport port[:port]

       [!] --ctorigdstport port[:port]

       [!] --ctreplsrcport port[:port]

       [!] --ctrepldstport port[:port]
	      Match    against	  original/reply    source/destination	  port
	      (TCP/UDP/etc.) or GRE key.  Matching against port ranges is only
	      supported in kernel versions above 2.6.38.

       [!] --ctstatus statelist
	      statuslist  is a comma separated list of the connection statuses
	      to match.	 Possible statuses are listed below.

       [!] --ctexpire time[:time]
	      Match remaining lifetime in seconds against given value or range
	      of values (inclusive)

       --ctdir {ORIGINAL|REPLY}
	      Match  packets  that  are flowing in the specified direction. If
	      this flag is not specified  at  all,  matches  packets  in  both
	      directions.

       States for --ctstate:

       INVALID
	      meaning that the packet is associated with no known connection

       NEW    meaning  that the packet has started a new connection, or other‐
	      wise associated with a connection which has not seen packets  in
	      both directions, and

       ESTABLISHED
	      meaning  that  the  packet is associated with a connection which
	      has seen packets in both directions,

       RELATED
	      meaning that the packet is starting a  new  connection,  but  is
	      associated  with	an  existing  connection,  such as an FTP data
	      transfer, or an ICMP error.

       UNTRACKED
	      meaning that the packet is not tracked at all, which happens  if
	      you use the NOTRACK target in raw table.

       SNAT   A virtual state, matching if the original source address differs
	      from the reply destination.

       DNAT   A virtual state, matching if the	original  destination  differs
	      from the reply source.

       Statuses for --ctstatus:

       NONE   None of the below.

       EXPECTED
	      This  is	an expected connection (i.e. a conntrack helper set it
	      up)

       SEEN_REPLY
	      Conntrack has seen packets in both directions.

       ASSURED
	      Conntrack entry should never be early-expired.

       CONFIRMED
	      Connection is confirmed: originating packet has left box.

   cpu
       [!] --cpu number
	      Match cpu handling this packet. cpus  are	 numbered  from	 0  to
	      NR_CPUS-1	 Can  be  used	in combination with RPS (Remote Packet
	      Steering) or multiqueue NICs to spread network traffic  on  dif‐
	      ferent queues.

       Example:

       iptables -t nat -A PREROUTING -p tcp --dport 80 -m cpu --cpu 0 -j REDI‐
       RECT --to-port 8080

       iptables -t nat -A PREROUTING -p tcp --dport 80 -m cpu --cpu 1 -j REDI‐
       RECT --to-port 8081

       Available since Linux 2.6.36.

   dccp
       [!] --source-port,--sport port[:port]

       [!] --destination-port,--dport port[:port]

       [!] --dccp-types mask
	      Match  when  the	DCCP packet type is one of 'mask'. 'mask' is a
	      comma-separated list of packet types.  Packet types are: REQUEST
	      RESPONSE	DATA  ACK  DATAACK  CLOSEREQ  CLOSE RESET SYNC SYNCACK
	      INVALID.

       [!] --dccp-option number
	      Match if DCCP option set.

   dscp
       This module matches the 6 bit DSCP field within the TOS field in the IP
       header.	DSCP has superseded TOS within the IETF.

       [!] --dscp value
	      Match against a numeric (decimal or hex) value [0-63].

       [!] --dscp-class class
	      Match  the  DiffServ class. This value may be any of the BE, EF,
	      AFxx or CSx classes.  It will then be converted into its accord‐
	      ing numeric value.

   ecn
       This  allows you to match the ECN bits of the IPv4/IPv6 and TCP header.
       ECN is the Explicit Congestion Notification mechanism as	 specified  in
       RFC3168

       [!] --ecn-tcp-cwr
	      This matches if the TCP ECN CWR (Congestion Window Received) bit
	      is set.

       [!] --ecn-tcp-ece
	      This matches if the TCP ECN ECE (ECN Echo) bit is set.

       [!] --ecn-ip-ect num
	      This matches a particular IPv4/IPv6 ECT (ECN-Capable Transport).
	      You have to specify a number between `0' and `3'.

   esp
       This module matches the SPIs in ESP header of IPsec packets.

       [!] --espspi spi[:spi]

   hashlimit
       hashlimit  uses hash buckets to express a rate limiting match (like the
       limit match) for a group of connections using a single  iptables	 rule.
       Grouping	 can be done per-hostgroup (source and/or destination address)
       and/or per-port. It gives you the ability to  express  "N  packets  per
       time quantum per group" (see below for some examples).

       A  hash	limit option (--hashlimit-upto, --hashlimit-above) and --hash‐
       limit-name are required.

       --hashlimit-upto amount[/second|/minute|/hour|/day]
	      Match if the rate is below or equal  to  amount/quantum.	It  is
	      specified as a number, with an optional time quantum suffix; the
	      default is 3/hour.

       --hashlimit-above amount[/second|/minute|/hour|/day]
	      Match if the rate is above amount/quantum.

       --hashlimit-burst amount
	      Maximum initial number of packets to  match:  this  number  gets
	      recharged	 by  one  every	 time the limit specified above is not
	      reached, up to this number; the default is 5.

       --hashlimit-mode {srcip|srcport|dstip|dstport},...
	      A comma-separated list of objects to take into consideration. If
	      no  --hashlimit-mode option is given, hashlimit acts like limit,
	      but at the expensive of doing the hash housekeeping.

       --hashlimit-srcmask prefix
	      When  --hashlimit-mode  srcip  is	 used,	all  source  addresses
	      encountered will be grouped according to the given prefix length
	      and the so-created subnet will be subject to  hashlimit.	prefix
	      must be between (inclusive) 0 and 32. Note that --hashlimit-src‐
	      mask 0 is basically doing the same thing as not specifying srcip
	      for --hashlimit-mode, but is technically more expensive.

       --hashlimit-dstmask prefix
	      Like --hashlimit-srcmask, but for destination addresses.

       --hashlimit-name foo
	      The name for the /proc/net/ipt_hashlimit/foo entry.

       --hashlimit-htable-size buckets
	      The number of buckets of the hash table

       --hashlimit-htable-max entries
	      Maximum entries in the hash.

       --hashlimit-htable-expire msec
	      After how many milliseconds do hash entries expire.

       --hashlimit-htable-gcinterval msec
	      How many milliseconds between garbage collection intervals.

       Examples:

       matching on source host
	      "1000 packets per second for every host in 192.168.0.0/16" => -s
	      192.168.0.0/16 --hashlimit-mode srcip --hashlimit-upto 1000/sec

       matching on source port
	      "100 packets per second for every service of 192.168.1.1" =>  -s
	      192.168.1.1 --hashlimit-mode srcport --hashlimit-upto 100/sec

       matching on subnet
	      "10000  packets  per  minute  for	 every /28 subnet (groups of 8
	      addresses) in 10.0.0.0/8" =>  -s	10.0.0.8  --hashlimit-mask  28
	      --hashlimit-upto 10000/min

   helper
       This module matches packets related to a specific conntrack-helper.

       [!] --helper string
	      Matches packets related to the specified conntrack-helper.

	      string  can  be  "ftp"  for  packets related to a ftp-session on
	      default port.  For other ports append -portnr to the value,  ie.
	      "ftp-2121".

	      Same rules apply for other conntrack-helpers.

   icmp
       This  extension	can be used if `--protocol icmp' is specified. It pro‐
       vides the following option:

       [!] --icmp-type {type[/code]|typename}
	      This allows specification of the	ICMP  type,  which  can	 be  a
	      numeric ICMP type, type/code pair, or one of the ICMP type names
	      shown by the command
	       iptables -p icmp -h

   iprange
       This matches on a given arbitrary range of IP addresses.

       [!] --src-range from[-to]
	      Match source IP in the specified range.

       [!] --dst-range from[-to]
	      Match destination IP in the specified range.

   ipvs
       Match IPVS connection properties.

       [!] --ipvs
	      packet belongs to an IPVS connection

       Any of the following options implies --ipvs (even negated)

       [!] --vproto protocol
	      VIP protocol to match; by number or name, e.g. "tcp"

       [!] --vaddr address[/mask]
	      VIP address to match

       [!] --vport port
	      VIP port to match; by number or name, e.g. "http"

       --vdir {ORIGINAL|REPLY}
	      flow direction of packet

       [!] --vmethod {GATE|IPIP|MASQ}
	      IPVS forwarding method used

       [!] --vportctl port
	      VIP port of the controlling connection to match, e.g. 21 for FTP

   length
       This module matches the length of the  layer-3  payload	(e.g.  layer-4
       packet) of a packet against a specific value or range of values.

       [!] --length length[:length]

   limit
       This  module  matches at a limited rate using a token bucket filter.  A
       rule using this extension will match until this limit is	 reached.   It
       can be used in combination with the LOG target to give limited logging,
       for example.

       xt_limit has no negation support - you will have to use -m hashlimit  !
       --hashlimit rate in this case whilst omitting --hashlimit-mode.

       --limit rate[/second|/minute|/hour|/day]
	      Maximum  average	matching  rate: specified as a number, with an
	      optional `/second', `/minute', `/hour', or  `/day'  suffix;  the
	      default is 3/hour.

       --limit-burst number
	      Maximum  initial	number	of  packets to match: this number gets
	      recharged by one every time the limit  specified	above  is  not
	      reached, up to this number; the default is 5.

   mac
       [!] --mac-source address
	      Match   source   MAC   address.	 It   must   be	 of  the  form
	      XX:XX:XX:XX:XX:XX.  Note that this only makes sense for  packets
	      coming from an Ethernet device and entering the PREROUTING, FOR‐
	      WARD or INPUT chains.

   mark
       This module matches the netfilter mark field associated with  a	packet
       (which can be set using the MARK target below).

       [!] --mark value[/mask]
	      Matches packets with the given unsigned mark value (if a mask is
	      specified, this is logically ANDed with the mask before the com‐
	      parison).

   multiport
       This  module  matches  a	 set of source or destination ports.  Up to 15
       ports can be specified.	A port range (port:port) counts as two	ports.
       It can only be used in conjunction with -p tcp or -p udp.

       [!] --source-ports,--sports port[,port|,port:port]...
	      Match  if	 the  source port is one of the given ports.  The flag
	      --sports is a convenient alias for this option.  Multiple	 ports
	      or  port ranges are separated using a comma, and a port range is
	      specified using a colon.	53,1024:65535  would  therefore	 match
	      ports 53 and all from 1024 through 65535.

       [!] --destination-ports,--dports port[,port|,port:port]...
	      Match  if	 the  destination port is one of the given ports.  The
	      flag --dports is a convenient alias for this option.

       [!] --ports port[,port|,port:port]...
	      Match if either the source or destination ports are equal to one
	      of the given ports.

   nfacct
       The  nfacct  match  provides the extended accounting infrastructure for
       iptables.  You have to use this	match  together	 with  the  standalone
       user-space utility nfacct(8)

       The only option available for this match is the following:

       --nfacct-name name
	      This allows you to specify the existing object name that will be
	      use for accounting the traffic that this rule-set is matching.

       To use this extension, you have to create an accounting object:

	      nfacct add http-traffic

       Then, you have to attach it to the accounting object via iptables:

	      iptables -I INPUT -p tcp	--sport	 80  -m	 nfacct	 --nfacct-name
	      http-traffic

	      iptables	-I  OUTPUT  -p	tcp --dport 80 -m nfacct --nfacct-name
	      http-traffic

       Then, you can check for the amount of traffic that the rules match:

	      nfacct get http-traffic

	      { pkts = 00000000000000000156, bytes = 00000000000000151786 }  =
	      http-traffic;

       You  can	 obtain	 nfacct(8)  from http://www.netfilter.org or, alterna‐
       tively, from the git.netfilter.org repository.

   osf
       The osf module does passive operating system fingerprinting. This  mod‐
       ules  compares  some  data  (Window Size, MSS, options and their order,
       TTL, DF, and others) from packets with the SYN bit set.

       [!] --genre string
	      Match an operating system genre by using a passive  fingerprint‐
	      ing.

       --ttl level
	      Do  additional TTL checks on the packet to determine the operat‐
	      ing system.  level can be one of the following values:

       ·   0 - True IP address and fingerprint TTL comparison. This  generally
	   works for LANs.

       ·   1  - Check if the IP header's TTL is less than the fingerprint one.
	   Works for globally-routable addresses.

       ·   2 - Do not compare the TTL at all.

       --log level
	   Log determined genres into dmesg even if  they  do  not  match  the
	   desired one.	 level can be one of the following values:

       ·   0 - Log all matched or unknown signatures

       ·   1 - Log only the first one

       ·   2 - Log all known matched signatures

       You may find something like this in syslog:

       Windows	[2000:SP3:Windows  XP  Pro SP1, 2000 SP3]: 11.22.33.55:4024 ->
       11.22.33.44:139 hops=3 Linux [2.5-2.6:] : 1.2.3.4:42624	->  1.2.3.5:22
       hops=4

       OS  fingerprints	 are loadable using the nfnl_osf program. To load fin‐
       gerprints from a file, use:

       nfnl_osf -f /usr/share/xtables/pf.os

       To remove them again,

       nfnl_osf -f /usr/share/xtables/pf.os -d

       The  fingerprint	 database  can	be  downlaoded	from  http://www.open‐
       bsd.org/cgi-bin/cvsweb/src/etc/pf.os .

   owner
       This  module  attempts  to  match various characteristics of the packet
       creator, for locally generated packets. This match is only valid in the
       OUTPUT and POSTROUTING chains. Forwarded packets do not have any socket
       associated with them. Packets from kernel threads do have a socket, but
       usually no owner.

       [!] --uid-owner username

       [!] --uid-owner userid[-userid]
	      Matches if the packet socket's file structure (if it has one) is
	      owned by the given user. You may also specify a  numerical  UID,
	      or an UID range.

       [!] --gid-owner groupname

       [!] --gid-owner groupid[-groupid]
	      Matches  if  the	packet socket's file structure is owned by the
	      given group.  You may also specify a numerical  GID,  or	a  GID
	      range.

       [!] --socket-exists
	      Matches if the packet is associated with a socket.

   physdev
       This  module  matches  on  the  bridge  port  input  and output devices
       enslaved to a bridge device. This module is a part of  the  infrastruc‐
       ture that enables a transparent bridging IP firewall and is only useful
       for kernel versions above version 2.5.44.

       [!] --physdev-in name
	      Name of a bridge port via which a packet is received  (only  for
	      packets  entering	 the INPUT, FORWARD and PREROUTING chains). If
	      the interface name ends in  a  "+",  then	 any  interface	 which
	      begins  with  this  name will match. If the packet didn't arrive
	      through a bridge device, this packet won't  match	 this  option,
	      unless '!' is used.

       [!] --physdev-out name
	      Name  of	a  bridge  port via which a packet is going to be sent
	      (for  packets  entering  the  FORWARD,  OUTPUT  and  POSTROUTING
	      chains).	 If  the interface name ends in a "+", then any inter‐
	      face which begins with this name will match. Note	 that  in  the
	      nat and mangle OUTPUT chains one cannot match on the bridge out‐
	      put port, however one can in the filter  OUTPUT  chain.  If  the
	      packet  won't  leave  by a bridge device or if it is yet unknown
	      what the output device will be, then the packet won't match this
	      option, unless '!' is used.

       [!] --physdev-is-in
	      Matches if the packet has entered through a bridge interface.

       [!] --physdev-is-out
	      Matches if the packet will leave through a bridge interface.

       [!] --physdev-is-bridged
	      Matches  if  the	packet	is  being bridged and therefore is not
	      being routed.  This is only useful in the FORWARD and  POSTROUT‐
	      ING chains.

   pkttype
       This module matches the link-layer packet type.

       [!] --pkt-type {unicast|broadcast|multicast}

   policy
       This modules matches the policy used by IPsec for handling a packet.

       --dir {in|out}
	      Used  to	select whether to match the policy used for decapsula‐
	      tion or the policy that will be used for encapsulation.	in  is
	      valid  in the PREROUTING, INPUT and FORWARD chains, out is valid
	      in the POSTROUTING, OUTPUT and FORWARD chains.

       --pol {none|ipsec}
	      Matches if the packet is subject to IPsec processing. --pol none
	      cannot be combined with --strict.

       --strict
	      Selects  whether	to match the exact policy or match if any rule
	      of the policy matches the given policy.

       For each policy element that is to be described, one  can  use  one  or
       more of the following options. When --strict is in effect, at least one
       must be used per element.

       [!] --reqid id
	      Matches the reqid of the policy rule. The reqid can be specified
	      with setkey(8) using unique:id as level.

       [!] --spi spi
	      Matches the SPI of the SA.

       [!] --proto {ah|esp|ipcomp}
	      Matches the encapsulation protocol.

       [!] --mode {tunnel|transport}
	      Matches the encapsulation mode.

       [!] --tunnel-src addr[/mask]
	      Matches  the source end-point address of a tunnel mode SA.  Only
	      valid with --mode tunnel.

       [!] --tunnel-dst addr[/mask]
	      Matches the destination end-point address of a tunnel  mode  SA.
	      Only valid with --mode tunnel.

       --next Start  the next element in the policy specification. Can only be
	      used with --strict.

   quota
       Implements network quotas by decrementing  a  byte  counter  with  each
       packet.	The  condition	matches	 until	the byte counter reaches zero.
       Behavior is reversed with negation (i.e. the condition does  not	 match
       until the byte counter reaches zero).

       [!] --quota bytes
	      The quota in bytes.

   rateest
       The  rate  estimator  can  match on estimated rates as collected by the
       RATEEST target. It supports matching on absolute bps/pps	 values,  com‐
       paring  two  rate estimators and matching on the difference between two
       rate estimators.

       For a better understanding of the available options, these are all pos‐
       sible combinations:

       ·   rateest operator rateest-bps

       ·   rateest operator rateest-pps

       ·   (rateest minus rateest-bps1) operator rateest-bps2

       ·   (rateest minus rateest-pps1) operator rateest-pps2

       ·   rateest1 operator rateest2 rateest-bps(without rate!)

       ·   rateest1 operator rateest2 rateest-pps(without rate!)

       ·   (rateest1  minus  rateest-bps1)  operator  (rateest2 minus rateest-
	   bps2)

       ·   (rateest1 minus rateest-pps1)  operator  (rateest2  minus  rateest-
	   pps2)

       --rateest-delta
	   For	each  estimator	 (either absolute or relative mode), calculate
	   the difference between the estimator-determined flow rate  and  the
	   static  value  chosen with the BPS/PPS options. If the flow rate is
	   higher than the specified BPS/PPS, 0 will be used instead of a neg‐
	   ative value. In other words, "max(0, rateest#_rate - rateest#_bps)"
	   is used.

       [!] --rateest-lt
	   Match if rate is less than given rate/estimator.

       [!] --rateest-gt
	   Match if rate is greater than given rate/estimator.

       [!] --rateest-eq
	   Match if rate is equal to given rate/estimator.

       In the so-called "absolute mode", only one rate estimator is  used  and
       compared	 against  a  static  value, while in "relative mode", two rate
       estimators are compared against another.

       --rateest name
	      Name of the one rate estimator for absolute mode.

       --rateest1 name

       --rateest2 name
	      The names of the two rate estimators for relative mode.

       --rateest-bps [value]

       --rateest-pps [value]

       --rateest-bps1 [value]

       --rateest-bps2 [value]

       --rateest-pps1 [value]

       --rateest-pps2 [value]
	      Compare the estimator(s) by bytes or  packets  per  second,  and
	      compare  against the chosen value. See the above bullet list for
	      which option is to be used in which case. A unit suffix  may  be
	      used  -  available  ones	are:  bit, [kmgt]bit, [KMGT]ibit, Bps,
	      [KMGT]Bps, [KMGT]iBps.

       Example: This is what can be used to route  outgoing  data  connections
       from  an	 FTP server over two lines based on the available bandwidth at
       the time the data connection was started:

       # Estimate outgoing rates

       iptables -t mangle -A POSTROUTING -o  eth0  -j  RATEEST	--rateest-name
       eth0 --rateest-interval 250ms --rateest-ewma 0.5s

       iptables	 -t  mangle  -A	 POSTROUTING -o ppp0 -j RATEEST --rateest-name
       ppp0 --rateest-interval 250ms --rateest-ewma 0.5s

       # Mark based on available bandwidth

       iptables -t mangle -A balance -m	 conntrack  --ctstate  NEW  -m	helper
       --helper	 ftp -m rateest --rateest-delta --rateest1 eth0 --rateest-bps1
       2.5mbit --rateest-gt --rateest2 ppp0 --rateest-bps2 2mbit  -j  CONNMARK
       --set-mark 1

       iptables	 -t  mangle  -A	 balance  -m conntrack --ctstate NEW -m helper
       --helper ftp -m rateest --rateest-delta --rateest1 ppp0	--rateest-bps1
       2mbit  --rateest-gt  --rateest2 eth0 --rateest-bps2 2.5mbit -j CONNMARK
       --set-mark 2

       iptables -t mangle -A balance -j CONNMARK --restore-mark

   realm
       This matches the routing realm.	Routing realms	are  used  in  complex
       routing setups involving dynamic routing protocols like BGP.

       [!] --realm value[/mask]
	      Matches  a  given	 realm	number (and optionally mask). If not a
	      number, value can be a named realm from  /etc/iproute2/rt_realms
	      (mask can not be used in that case).

   recent
       Allows  you to dynamically create a list of IP addresses and then match
       against that list in a few different ways.

       For example, you can create a "badguy" list out of people attempting to
       connect	to  port 139 on your firewall and then DROP all future packets
       from them without considering them.

       --set, --rcheck, --update and --remove are mutually exclusive.

       --name name
	      Specify the list to use for the commands. If no  name  is	 given
	      then DEFAULT will be used.

       [!] --set
	      This  will  add the source address of the packet to the list. If
	      the source address is already in the list, this will update  the
	      existing entry. This will always return success (or failure if !
	      is passed in).

       --rsource
	      Match/save the source address of each packet in the recent  list
	      table. This is the default.

       --rdest
	      Match/save  the destination address of each packet in the recent
	      list table.

       [!] --rcheck
	      Check if the source address of the packet is  currently  in  the
	      list.

       [!] --update
	      Like  --rcheck,  except it will update the "last seen" timestamp
	      if it matches.

       [!] --remove
	      Check if the source address of the packet is  currently  in  the
	      list  and	 if  so that address will be removed from the list and
	      the rule will return true. If the address is not found, false is
	      returned.

       --seconds seconds
	      This  option must be used in conjunction with one of --rcheck or
	      --update. When used, this will narrow the match to  only	happen
	      when  the	 address  is  in the list and was seen within the last
	      given number of seconds.

       --reap This option can only be  used  in	 conjunction  with  --seconds.
	      When  used,  this	 will  cause entries older than the last given
	      number of seconds to be purged.

       --hitcount hits
	      This option must be used in conjunction with one of --rcheck  or
	      --update.	 When  used, this will narrow the match to only happen
	      when the address is in the list and packets  had	been  received
	      greater  than  or	 equal	to the given value. This option may be
	      used along with --seconds	 to  create  an	 even  narrower	 match
	      requiring a certain number of hits within a specific time frame.
	      The maximum value for the hitcount parameter  is	given  by  the
	      "ip_pkt_list_tot"	 parameter  of	the  xt_recent	kernel module.
	      Exceeding this value on the command line will cause the rule  to
	      be rejected.

       --rttl This option may only be used in conjunction with one of --rcheck
	      or --update. When used, this will narrow the match to only  hap‐
	      pen  when	 the address is in the list and the TTL of the current
	      packet matches that of the packet which hit the --set rule. This
	      may  be  useful  if  you	have problems with people faking their
	      source address in order to DoS you via this module by  disallow‐
	      ing others access to your site by sending bogus packets to you.

       Examples:

	      iptables	-A  FORWARD -m recent --name badguy --rcheck --seconds
	      60 -j DROP

	      iptables -A FORWARD -p tcp -i eth0 --dport 139 -m recent	--name
	      badguy --set -j DROP

       Steve's	ipt_recent  website  (http://snowman.net/projects/ipt_recent/)
       also has some examples of usage.

       /proc/net/xt_recent/* are the current lists of addresses	 and  informa‐
       tion about each entry of each list.

       Each  file  in /proc/net/xt_recent/ can be read from to see the current
       list or written two using the following commands to modify the list:

       echo +addr >/proc/net/xt_recent/DEFAULT
	      to add addr to the DEFAULT list

       echo -addr >/proc/net/xt_recent/DEFAULT
	      to remove addr from the DEFAULT list

       echo / >/proc/net/xt_recent/DEFAULT
	      to flush the DEFAULT list (remove all entries).

       The module itself accepts parameters, defaults shown:

       ip_list_tot=100
	      Number of addresses remembered per table.

       ip_pkt_list_tot=20
	      Number of packets per address remembered.

       ip_list_hash_size=0
	      Hash table size. 0 means to calculate it based  on  ip_list_tot,
	      default: 512.

       ip_list_perms=0644
	      Permissions for /proc/net/xt_recent/* files.

       ip_list_uid=0
	      Numerical UID for ownership of /proc/net/xt_recent/* files.

       ip_list_gid=0
	      Numerical GID for ownership of /proc/net/xt_recent/* files.

   rpfilter
       Performs	 a  reverse  path  filter test on a packet.  If a reply to the
       packet would be sent via the same interface that the packet arrived on,
       the  packet  will  match.   Note	 that, unlike the in-kernel rp_filter,
       packets protected by IPSec are not  treated  specially.	 Combine  this
       match  with  the policy match if you want this.	Also, packets arriving
       via the loopback interface are always permitted.	 This match  can  only
       be used in the PREROUTING chain of the raw or mangle table.

       --loose
	      Used  to specifiy that the reverse path filter test should match
	      even if the selected output device is not the expected one.

       --validmark
	      Also use the packets' nfmark value when performing  the  reverse
	      path route lookup.

       --accept-local
	      This will permit packets arriving from the network with a source
	      address that is also assigned to the  local  machine.   --invert
	      This  will  invert  the sense of the match.  Instead of matching
	      packets that passed the reverse path filter  test,  match	 those
	      that have failed it.

       Example to log and drop packets failing the reverse path filter test:

       iptables -t raw -N RPFILTER

       iptables -t raw -A RPFILTER -m rpfilter -j RETURN

       iptables	 -t  raw  -A  RPFILTER	-m  limit  --limit  10/minute -j NFLOG
       --nflog-prefix "rpfilter drop"

       iptables -t raw -A RPFILTER -j DROP

       iptables -t raw -A PREROUTING -j RPFILTER

       Example to drop failed packets, without logging:

       iptables -t raw -A RPFILTER -m rpfilter --invert -j DROP

   sctp
       [!] --source-port,--sport port[:port]

       [!] --destination-port,--dport port[:port]

       [!] --chunk-types {all|any|only} chunktype[:flags] [...]
	      The flag letter in upper case indicates  that  the  flag	is  to
	      match if set, in the lower case indicates to match if unset.

	      Chunk  types:  DATA  INIT	 INIT_ACK SACK HEARTBEAT HEARTBEAT_ACK
	      ABORT  SHUTDOWN  SHUTDOWN_ACK   ERROR   COOKIE_ECHO   COOKIE_ACK
	      ECN_ECNE ECN_CWR SHUTDOWN_COMPLETE ASCONF ASCONF_ACK FORWARD_TSN

	      chunk type	    available flags
	      DATA		    I U B E i u b e
	      ABORT		    T t
	      SHUTDOWN_COMPLETE	    T t

	      (lowercase means flag should be "off", uppercase means "on")

       Examples:

       iptables -A INPUT -p sctp --dport 80 -j DROP

       iptables -A INPUT -p sctp --chunk-types any DATA,INIT -j DROP

       iptables -A INPUT -p sctp --chunk-types any DATA:Be -j ACCEPT

   set
       This module matches IP sets which can be defined by ipset(8).

       [!] --match-set setname flag[,flag]...
	      where flags are the comma separated list of src and/or dst spec‐
	      ifications and there can be no more than six of them. Hence  the
	      command

	       iptables -A FORWARD -m set --match-set test src,dst

	      will match packets, for which (if the set type is ipportmap) the
	      source address and destination port pair can  be	found  in  the
	      specified	 set.  If  the set type of the specified set is single
	      dimension (for example ipmap), then the command will match pack‐
	      ets  for	which the source address can be found in the specified
	      set.

       The option --match-set can be replaced by --set if that does not	 clash
       with an option of other extensions.

       Use  of	-m  set requires that ipset kernel support is provided, which,
       for standard kernels, is the case since Linux 2.6.39.

   socket
       This matches if an open socket can be found by doing a socket lookup on
       the packet.

       --transparent
	      Ignore non-transparent sockets.

   state
       This  module,  when combined with connection tracking, allows access to
       the connection tracking state for this packet.

       [!] --state state
	      Where state is a comma separated list of the  connection	states
	      to  match.   Possible states are INVALID meaning that the packet
	      could not be identified for some reason which  includes  running
	      out  of  memory  and  ICMP  errors which don't correspond to any
	      known connection, ESTABLISHED meaning that the packet is associ‐
	      ated  with  a  connection	 which has seen packets in both direc‐
	      tions, NEW meaning that the packet has started a new connection,
	      or  otherwise  associated	 with  a connection which has not seen
	      packets in both directions, and RELATED meaning that the	packet
	      is starting a new connection, but is associated with an existing
	      connection, such as an FTP data  transfer,  or  an  ICMP	error.
	      UNTRACKED	 meaning  that the packet is not tracked at all, which
	      happens if you use the NOTRACK target in raw table.

   statistic
       This module matches packets based on some statistic condition.  It sup‐
       ports two distinct modes settable with the --mode option.

       Supported options:

       --mode mode
	      Set  the matching mode of the matching rule, supported modes are
	      random and nth.

       [!] --probability p
	      Set the probability for a packet to be randomly matched. It only
	      works  with  the	random mode. p must be within 0.0 and 1.0. The
	      supported granularity is in 1/2147483648th increments.

       [!] --every n
	      Match one packet every nth packet. It works only	with  the  nth
	      mode (see also the --packet option).

       --packet p
	      Set the initial counter value (0 <= p <= n-1, default 0) for the
	      nth mode.

   string
       This modules matches a given string  by	using  some  pattern  matching
       strategy. It requires a linux kernel >= 2.6.14.

       --algo {bm|kmp}
	      Select  the  pattern matching strategy. (bm = Boyer-Moore, kmp =
	      Knuth-Pratt-Morris)

       --from offset
	      Set the offset from which it starts looking for any matching. If
	      not passed, default is 0.

       --to offset
	      Set the offset up to which should be scanned. That is, byte off‐
	      set-1 (counting from 0) is the last one that is scanned.	If not
	      passed, default is the packet size.

       [!] --string pattern
	      Matches the given pattern.

       [!] --hex-string pattern
	      Matches the given pattern in hex notation.

   tcp
       These  extensions can be used if `--protocol tcp' is specified. It pro‐
       vides the following options:

       [!] --source-port,--sport port[:port]
	      Source port or port range specification. This can	 either	 be  a
	      service  name  or	 a port number. An inclusive range can also be
	      specified, using the format first:last.  If the  first  port  is
	      omitted,	"0"  is	 assumed;  if  the last is omitted, "65535" is
	      assumed.	If the first port is greater than the second one  they
	      will  be	swapped.   The	flag --sport is a convenient alias for
	      this option.

       [!] --destination-port,--dport port[:port]
	      Destination port or port range specification.  The flag  --dport
	      is a convenient alias for this option.

       [!] --tcp-flags mask comp
	      Match  when  the TCP flags are as specified.  The first argument
	      mask is the flags which we should examine, written as  a	comma-
	      separated	 list,	and  the second argument comp is a comma-sepa‐
	      rated list of flags which must be set.  Flags are: SYN  ACK  FIN
	      RST URG PSH ALL NONE.  Hence the command
	       iptables -A FORWARD -p tcp --tcp-flags SYN,ACK,FIN,RST SYN
	      will  only match packets with the SYN flag set, and the ACK, FIN
	      and RST flags unset.

       [!] --syn
	      Only match TCP packets with the SYN bit set and the ACK,RST  and
	      FIN  bits cleared.  Such packets are used to request TCP connec‐
	      tion initiation; for example, blocking such packets coming in an
	      interface	 will  prevent	incoming TCP connections, but outgoing
	      TCP  connections	will  be  unaffected.	It  is	equivalent  to
	      --tcp-flags  SYN,RST,ACK,FIN  SYN.  If the "!" flag precedes the
	      "--syn", the sense of the option is inverted.

       [!] --tcp-option number
	      Match if TCP option set.

   tcpmss
       This matches the TCP MSS	 (maximum  segment  size)  field  of  the  TCP
       header.	You can only use this on TCP SYN or SYN/ACK packets, since the
       MSS is only negotiated during the TCP handshake at  connection  startup
       time.

       [!] --mss value[:value]
	      Match a given TCP MSS value or range.

   time
       This  matches  if the packet arrival time/date is within a given range.
       All options are optional, but are ANDed when specified. All  times  are
       interpreted as UTC by default.

       --datestart YYYY[-MM[-DD[Thh[:mm[:ss]]]]]

       --datestop YYYY[-MM[-DD[Thh[:mm[:ss]]]]]
	      Only  match during the given time, which must be in ISO 8601 "T"
	      notation.	 The possible time  range  is  1970-01-01T00:00:00  to
	      2038-01-19T04:17:07.

	      If  --datestart or --datestop are not specified, it will default
	      to 1970-01-01 and 2038-01-19, respectively.

       --timestart hh:mm[:ss]

       --timestop hh:mm[:ss]
	      Only match during the given daytime. The possible time range  is
	      00:00:00	to 23:59:59. Leading zeroes are allowed (e.g. "06:03")
	      and correctly interpreted as base-10.

       [!] --monthdays day[,day...]
	      Only match on the given days of the month. Possible values are 1
	      to  31.  Note  that  specifying  31  will of course not match on
	      months which do not have a 31st day; the same goes  for  28-  or
	      29-day February.

       [!] --weekdays day[,day...]
	      Only  match on the given weekdays. Possible values are Mon, Tue,
	      Wed, Thu, Fri, Sat, Sun, or values from 1	 to  7,	 respectively.
	      You may also use two-character variants (Mo, Tu, etc.).

       --kerneltz
	      Use  the	kernel	timezone instead of UTC to determine whether a
	      packet meets the time regulations.

       About kernel timezones: Linux keeps the system time in UTC, and	always
       does  so.   On boot, system time is initialized from a referential time
       source. Where this time source has no timezone information, such as the
       x86 CMOS RTC, UTC will be assumed. If the time source is however not in
       UTC, userspace should provide the correct system time and  timezone  to
       the kernel once it has the information.

       Local  time  is	a  feature on top of the (timezone independent) system
       time. Each process has its own idea of local time, specified via the TZ
       environment variable. The kernel also has its own timezone offset vari‐
       able. The TZ userspace environment variable specifies how the UTC-based
       system time is displayed, e.g. when you run date(1), or what you see on
       your desktop clock.  The TZ string may resolve to different offsets  at
       different  dates,  which	 is what enables the automatic time-jumping in
       userspace. when DST changes. The kernel's timezone offset  variable  is
       used  when  it  has  to	convert	 between  non-UTC sources, such as FAT
       filesystems, to UTC (since the latter is what the rest  of  the	system
       uses).

       The  caveat  with  the  kernel timezone is that Linux distributions may
       ignore to set the kernel timezone, and  instead	only  set  the	system
       time.  Even if a particular distribution does set the timezone at boot,
       it is usually does not keep the kernel timezone offset - which is  what
       changes	on DST - up to date.  ntpd will not touch the kernel timezone,
       so running it will not resolve the issue. As such, one may encounter  a
       timezone that is always +0000, or one that is wrong half of the time of
       the year. As such, using --kerneltz is highly discouraged.

       EXAMPLES. To match on weekends, use:

	      -m time --weekdays Sa,Su

       Or, to match (once) on a national holiday block:

	      -m time --datestart 2007-12-24 --datestop 2007-12-27

       Since the stop time is actually inclusive, you would need the following
       stop time to not match the first second of the new day:

	      -m      time     --datestart     2007-01-01T17:00	    --datestop
	      2007-01-01T23:59:59

       During lunch hour:

	      -m time --timestart 12:30 --timestop 13:30

       The fourth Friday in the month:

	      -m time --weekdays Fr --monthdays 22,23,24,25,26,27,28

       (Note that this exploits a certain mathematical	property.  It  is  not
       possible	 to  say "fourth Thursday OR fourth Friday" in one rule. It is
       possible with multiple rules, though.)

   tos
       This module matches the 8-bit Type of Service field in the IPv4	header
       (i.e.   including  the  "Precedence" bits) or the (also 8-bit) Priority
       field in the IPv6 header.

       [!] --tos value[/mask]
	      Matches packets with the given TOS mark  value.  If  a  mask  is
	      specified,  it  is  logically ANDed with the TOS mark before the
	      comparison.

       [!] --tos symbol
	      You can specify a symbolic name when using  the  tos  match  for
	      IPv4.  The list of recognized TOS names can be obtained by call‐
	      ing iptables with -m tos -h.  Note that this implies a  mask  of
	      0x3F, i.e. all but the ECN bits.

   ttl
       This module matches the time to live field in the IP header.

       [!] --ttl-eq ttl
	      Matches the given TTL value.

       --ttl-gt ttl
	      Matches if TTL is greater than the given TTL value.

       --ttl-lt ttl
	      Matches if TTL is less than the given TTL value.

   u32
       U32  tests  whether quantities of up to 4 bytes extracted from a packet
       have specified values. The specification of what to extract is  general
       enough to find data at given offsets from tcp headers or payloads.

       [!] --u32 tests
	      The  argument amounts to a program in a small language described
	      below.

	      tests := location "=" value | tests "&&" location "=" value

	      value := range | value "," range

	      range := number | number ":" number

       a single number, n, is interpreted the same as n:n. n:m is  interpreted
       as the range of numbers >=n and <=m.

	   location := number | location operator number

	   operator := "&" | "<<" | ">>" | "@"

       The  operators &, <<, >> and && mean the same as in C.  The = is really
       a set membership operator and the value syntax describes a set.	The  @
       operator is what allows moving to the next header and is described fur‐
       ther below.

       There are currently some artificial implementation limits on  the  size
       of the tests:

	   *  no more than 10 of "=" (and 9 "&&"s) in the u32 argument

	   *  no more than 10 ranges (and 9 commas) per value

	   *  no more than 10 numbers (and 9 operators) per location

       To describe the meaning of location, imagine the following machine that
       interprets it. There are three registers:

	      A is of type char *, initially the address of the IP header

	      B and C are unsigned 32 bit integers, initially zero

       The instructions are:

	      number B = number;

	      C = (*(A+B)<<24) + (*(A+B+1)<<16) + (*(A+B+2)<<8) + *(A+B+3)

	      &number C = C & number

	      << number C = C << number

	      >> number C = C >> number

	      @number A = A + C; then do the instruction number

       Any access of memory outside [skb->data,skb->end] causes the  match  to
       fail.  Otherwise the result of the computation is the final value of C.

       Whitespace is allowed but not required in the tests. However, the char‐
       acters that do occur there are likely to require shell quoting,	so  it
       is a good idea to enclose the arguments in quotes.

       Example:

	      match IP packets with total length >= 256

	      The IP header contains a total length field in bytes 2-3.

	      --u32 "0 & 0xFFFF = 0x100:0xFFFF"

	      read bytes 0-3

	      AND  that	 with 0xFFFF (giving bytes 2-3), and test whether that
	      is in the range [0x100:0xFFFF]

       Example: (more realistic, hence more complicated)

	      match ICMP packets with icmp type 0

	      First test that it is an ICMP packet, true iff byte 9 (protocol)
	      = 1

	      --u32 "6 & 0xFF = 1 && ...

	      read  bytes  6-9,	 use & to throw away bytes 6-8 and compare the
	      result to 1. Next test that it is not a  fragment.  (If  so,  it
	      might be part of such a packet but we cannot always tell.) N.B.:
	      This test is generally needed if	you  want  to  match  anything
	      beyond  the IP header. The last 6 bits of byte 6 and all of byte
	      7 are 0 iff this is a complete packet (not a fragment). Alterna‐
	      tively, you can allow first fragments by only testing the last 5
	      bits of byte 6.

	       ... 4 & 0x3FFF = 0 && ...

	      Last test: the first byte past the IP header (the	 type)	is  0.
	      This  is	where we have to use the @syntax. The length of the IP
	      header (IHL) in 32 bit words is stored in the right half of byte
	      0 of the IP header itself.

	       ... 0 >> 22 & 0x3C @ 0 >> 24 = 0"

	      The  first 0 means read bytes 0-3, >>22 means shift that 22 bits
	      to the right. Shifting 24 bits would give	 the  first  byte,  so
	      only  22	bits is four times that plus a few more bits. &3C then
	      eliminates the two extra bits on the right and  the  first  four
	      bits  of	the  first  byte.  For instance, if IHL=5, then the IP
	      header is 20 (4 x 5) bytes long. In this case, bytes 0-1 are (in
	      binary)	xxxx0101   yyzzzzzz,  >>22  gives  the	10  bit	 value
	      xxxx0101yy and &3C gives 010100. @ means to use this number as a
	      new  offset  into	 the packet, and read four bytes starting from
	      there. This is the first 4 bytes of the ICMP payload,  of	 which
	      byte 0 is the ICMP type. Therefore, we simply shift the value 24
	      to the right to throw out all but the first byte and compare the
	      result with 0.

       Example:

	      TCP payload bytes 8-12 is any of 1, 2, 5 or 8

	      First we test that the packet is a tcp packet (similar to ICMP).

	      --u32 "6 & 0xFF = 6 && ...

	      Next, test that it is not a fragment (same as above).

	       ... 0 >> 22 & 0x3C @ 12 >> 26 & 0x3C @ 8 = 1,2,5,8"

	      0>>22&3C as above computes the number of bytes in the IP header.
	      @ makes this the new offset into the packet, which is the	 start
	      of the TCP header. The length of the TCP header (again in 32 bit
	      words) is the left half of  byte	12  of	the  TCP  header.  The
	      12>>26&3C	 computes  this	 length	 in  bytes  (similar to the IP
	      header before). "@" makes this the  new  offset,	which  is  the
	      start  of	 the  TCP  payload. Finally, 8 reads bytes 8-12 of the
	      payload and = checks whether the result is any of 1, 2, 5 or 8.

   udp
       These extensions can be used if `--protocol udp' is specified. It  pro‐
       vides the following options:

       [!] --source-port,--sport port[:port]
	      Source port or port range specification.	See the description of
	      the --source-port option of the TCP extension for details.

       [!] --destination-port,--dport port[:port]
	      Destination port or port range specification.  See the  descrip‐
	      tion  of	the --destination-port option of the TCP extension for
	      details.

   unclean
       This module takes no options, but attempts to match packets which  seem
       malformed or unusual.  This is regarded as experimental.

TARGET EXTENSIONS
       iptables can use extended target modules: the following are included in
       the standard distribution.

   AUDIT
       This target allows to create audit records for packets hitting the tar‐
       get.  It can be used to record accepted, dropped, and rejected packets.
       See auditd(8) for additional details.

       --type {accept|drop|reject}
	      Set type of audit record.

       Example:

	      iptables -N AUDIT_DROP

	      iptables -A AUDIT_DROP -j AUDIT --type drop

	      iptables -A AUDIT_DROP -j DROP

   CHECKSUM
       This target allows to selectively work around broken/old	 applications.
       It can only be used in the mangle table.

       --checksum-fill
	      Compute and fill in the checksum in a packet that lacks a check‐
	      sum.  This is particularly useful, if you need  to  work	around
	      old  applications	 such  as  dhcp clients, that do not work well
	      with checksum offloads, but don't want to disable checksum  off‐
	      load in your device.

   CLASSIFY
       This  module  allows you to set the skb->priority value (and thus clas‐
       sify the packet into a specific CBQ class).

       --set-class major:minor
	      Set the major and minor  class  value.  The  values  are	always
	      interpreted as hexadecimal even if no 0x prefix is given.

   CLUSTERIP
       This  module  allows  you  to  configure a simple cluster of nodes that
       share a certain IP and MAC address without an explicit load balancer in
       front  of  them.	  Connections  are  statically distributed between the
       nodes in this cluster.

       --new  Create a new ClusterIP.  You always have	to  set	 this  on  the
	      first rule for a given ClusterIP.

       --hashmode mode
	      Specify  the  hashing  mode.   Has  to be one of sourceip, sour‐
	      ceip-sourceport, sourceip-sourceport-destport.

       --clustermac mac
	      Specify the ClusterIP MAC address. Has to be a link-layer multi‐
	      cast address

       --total-nodes num
	      Number of total nodes within this cluster.

       --local-node num
	      Local node number within this cluster.

       --hash-init rnd
	      Specify the random seed used for hash initialization.

   CONNMARK
       This module sets the netfilter mark value associated with a connection.
       The mark is 32 bits wide.

       --set-xmark value[/mask]
	      Zero out the bits given by mask and XOR value into the ctmark.

       --save-mark [--nfmask nfmask] [--ctmask ctmask]
	      Copy the packet mark (nfmark) to the  connection	mark  (ctmark)
	      using  the  given	 masks.	 The new nfmark value is determined as
	      follows:

	      ctmark = (ctmark & ~ctmask) ^ (nfmark & nfmask)

	      i.e. ctmask defines what bits to clear and nfmask what  bits  of
	      the  nfmark to XOR into the ctmark. ctmask and nfmask default to
	      0xFFFFFFFF.

       --restore-mark [--nfmask nfmask] [--ctmask ctmask]
	      Copy the connection mark (ctmark) to the	packet	mark  (nfmark)
	      using  the  given	 masks.	 The new ctmark value is determined as
	      follows:

	      nfmark = (nfmark & ~nfmask) ^ (ctmark & ctmask);

	      i.e. nfmask defines what bits to clear and ctmask what  bits  of
	      the  ctmark to XOR into the nfmark. ctmask and nfmask default to
	      0xFFFFFFFF.

	      --restore-mark is only valid in the mangle table.

       The following mnemonics are available for --set-xmark:

       --and-mark bits
	      Binary AND the  ctmark  with  bits.  (Mnemonic  for  --set-xmark
	      0/invbits, where invbits is the binary negation of bits.)

       --or-mark bits
	      Binary  OR  the  ctmark  with  bits.  (Mnemonic  for --set-xmark
	      bits/bits.)

       --xor-mark bits
	      Binary XOR the  ctmark  with  bits.  (Mnemonic  for  --set-xmark
	      bits/0.)

       --set-mark value[/mask]
	      Set  the connection mark. If a mask is specified then only those
	      bits set in the mask are modified.

       --save-mark [--mask mask]
	      Copy the nfmark to the ctmark. If	 a  mask  is  specified,  only
	      those bits are copied.

       --restore-mark [--mask mask]
	      Copy  the	 ctmark	 to  the  nfmark. If a mask is specified, only
	      those bits are copied. This is only valid in the mangle table.

   CONNSECMARK
       This module copies security markings from packets  to  connections  (if
       unlabeled),  and	 from  connections back to packets (also only if unla‐
       beled).	Typically used in conjunction with SECMARK, it is valid in the
       security	 table	(for backwards compatibility with older kernels, it is
       also valid in the mangle table).

       --save If the packet has a security marking, copy it to the  connection
	      if the connection is not marked.

       --restore
	      If  the packet does not have a security marking, and the connec‐
	      tion does, copy the security marking from the connection to  the
	      packet.

   CT
       The  CT	target allows to set parameters for a packet or its associated
       connection. The target attaches a "template" connection tracking	 entry
       to the packet, which is then used by the conntrack core when initializ‐
       ing a new ct entry. This target is thus only valid in the "raw" table.

       --notrack
	      Disables connection tracking for this packet.

       --helper name
	      Use the helper identified by name for the	 connection.  This  is
	      more  flexible  than  loading  the conntrack helper modules with
	      preset ports.

       --ctevents event[,...]
	      Only generate the specified conntrack events  for	 this  connec‐
	      tion.  Possible  event  types are: new, related, destroy, reply,
	      assured, protoinfo, helper, mark (this refers to the ctmark, not
	      nfmark), natseqinfo, secmark (ctsecmark).

       --expevents event[,...]
	      Only  generate the specified expectation events for this connec‐
	      tion.  Possible event types are: new.

       --zone id
	      Assign this packet to zone id and only have lookups done in that
	      zone.  By default, packets have zone 0.

       --timeout name
	      Use  the	timeout	 policy identified by name for the connection.
	      This is provides more flexible timeout  policy  definition  than
	      global   timeout	 values	  available  at	 /proc/sys/net/netfil‐
	      ter/nf_conntrack_*_timeout_*.

   DNAT
       This target is only valid in the nat table, in the PREROUTING and  OUT‐
       PUT  chains,  and  user-defined chains which are only called from those
       chains.	It specifies that the destination address of the packet should
       be  modified  (and  all	future packets in this connection will also be
       mangled), and rules should cease being examined.	 It takes one type  of
       option:

       --to-destination [ipaddr[-ipaddr]][:port[-port]]
	      which can specify a single new destination IP address, an inclu‐
	      sive range of IP addresses, and optionally, a port range	(which
	      is  only valid if the rule also specifies -p tcp or -p udp).  If
	      no port range is specified, then the destination port will never
	      be  modified. If no IP address is specified then only the desti‐
	      nation port will be modified.

	      In Kernels up to 2.6.10 you  can	add  several  --to-destination
	      options.	For those kernels, if you specify more than one desti‐
	      nation  address,	either	via  an	 address  range	 or   multiple
	      --to-destination	 options,  a  simple  round-robin  (one	 after
	      another in cycle)	 load  balancing  takes	 place	between	 these
	      addresses.  Later Kernels (>= 2.6.11-rc1) don't have the ability
	      to NAT to multiple ranges anymore.

       --random
	      If option --random is used then port mapping will be  randomized
	      (kernel >= 2.6.22).

       --persistent
	      Gives  a	client	the  same source-/destination-address for each
	      connection.  This supersedes the SAME target. Support  for  per‐
	      sistent mappings is available from 2.6.29-rc2.

   DSCP
       This  target  allows to alter the value of the DSCP bits within the TOS
       header of the IPv4 packet.  As this manipulates a packet, it  can  only
       be used in the mangle table.

       --set-dscp value
	      Set the DSCP field to a numerical value (can be decimal or hex)

       --set-dscp-class class
	      Set the DSCP field to a DiffServ class.

   ECN
       This target allows to selectively work around known ECN blackholes.  It
       can only be used in the mangle table.

       --ecn-tcp-remove
	      Remove all ECN bits from the TCP header.	Of course, it can only
	      be used in conjunction with -p tcp.

   IDLETIMER
       This  target can be used to identify when interfaces have been idle for
       a certain period of time.  Timers are identified by labels and are cre‐
       ated  when a rule is set with a new label.  The rules also take a time‐
       out value (in seconds) as an option.  If more than one  rule  uses  the
       same timer label, the timer will be restarted whenever any of the rules
       get a hit.  One entry  for  each	 timer	is  created  in	 sysfs.	  This
       attribute  contains  the	 timer remaining for the timer to expire.  The
       attributes are located under the xt_idletimer class:

       /sys/class/xt_idletimer/timers/<label>

       When the timer expires, the target module sends a sysfs notification to
       the userspace, which can then decide what to do (eg. disconnect to save
       power).

       --timeout amount
	      This is the time in seconds that will trigger the notification.

       --label string
	      This is a unique identifier for the timer.  The  maximum	length
	      for the label string is 27 characters.

   LOG
       Turn  on	 kernel	 logging of matching packets.  When this option is set
       for a rule, the Linux kernel will print some information on all	match‐
       ing  packets  (like most IP header fields) via the kernel log (where it
       can be read with dmesg or syslogd(8)).  This is a "non-terminating tar‐
       get",  i.e.  rule traversal continues at the next rule.	So if you want
       to LOG the packets you refuse, use two separate	rules  with  the  same
       matching criteria, first using target LOG then DROP (or REJECT).

       --log-level level
	      Level of logging (numeric or see syslog.conf(5)).

       --log-prefix prefix
	      Prefix  log messages with the specified prefix; up to 29 letters
	      long, and useful for distinguishing messages in the logs.

       --log-tcp-sequence
	      Log TCP sequence numbers. This is a security risk if the log  is
	      readable by users.

       --log-tcp-options
	      Log options from the TCP packet header.

       --log-ip-options
	      Log options from the IP packet header.

       --log-uid
	      Log the userid of the process which generated the packet.

   MARK
       This target is used to set the Netfilter mark value associated with the
       packet.	It can, for example, be used in conjunction with routing based
       on fwmark (needs iproute2). If you plan on doing so, note that the mark
       needs to be set in the PREROUTING chain of the mangle table  to	affect
       routing.	 The mark field is 32 bits wide.

       --set-xmark value[/mask]
	      Zeroes out the bits given by mask and XORs value into the packet
	      mark ("nfmark"). If mask is omitted, 0xFFFFFFFF is assumed.

       --set-mark value[/mask]
	      Zeroes out the bits given by mask and ORs value into the	packet
	      mark. If mask is omitted, 0xFFFFFFFF is assumed.

       The following mnemonics are available:

       --and-mark bits
	      Binary  AND  the	nfmark	with  bits.  (Mnemonic for --set-xmark
	      0/invbits, where invbits is the binary negation of bits.)

       --or-mark bits
	      Binary OR	 the  nfmark  with  bits.  (Mnemonic  for  --set-xmark
	      bits/bits.)

       --xor-mark bits
	      Binary  XOR  the	nfmark	with  bits.  (Mnemonic for --set-xmark
	      bits/0.)

   MASQUERADE
       This target is only valid in the nat table, in the  POSTROUTING	chain.
       It  should  only	 be used with dynamically assigned IP (dialup) connec‐
       tions: if you have a static IP address, you should use the SNAT target.
       Masquerading is equivalent to specifying a mapping to the IP address of
       the interface the packet is going out, but also	has  the  effect  that
       connections  are	 forgotten  when the interface goes down.  This is the
       correct behavior when the next dialup is	 unlikely  to  have  the  same
       interface  address (and hence any established connections are lost any‐
       way).

       --to-ports port[-port]
	      This specifies a range of source ports to	 use,  overriding  the
	      default SNAT source port-selection heuristics (see above).  This
	      is only valid if the rule also specifies -p tcp or -p udp.

       --random
	      Randomize source port mapping If option --random	is  used  then
	      port mapping will be randomized (kernel >= 2.6.21).

   MIRROR
       This  is	 an experimental demonstration target which inverts the source
       and destination fields in the IP header and retransmits the packet.  It
       is  only	 valid	in the INPUT, FORWARD and PREROUTING chains, and user-
       defined chains which are only called from those chains.	Note that  the
       outgoing	 packets  are NOT seen by any packet filtering chains, connec‐
       tion tracking or NAT, to avoid loops and other problems.

   NETMAP
       This target allows you to statically map a whole network	 of  addresses
       onto  another  network of addresses.  It can only be used from rules in
       the nat table.

       --to address[/mask]
	      Network address to map to.  The resulting address will  be  con‐
	      structed	in  the	 following way: All 'one' bits in the mask are
	      filled in from the new `address'.	 All bits that are zero in the
	      mask are filled in from the original address.

   NFLOG
       This  target  provides logging of matching packets. When this target is
       set for a rule, the Linux kernel will pass the  packet  to  the	loaded
       logging	backend to log the packet. This is usually used in combination
       with nfnetlink_log as logging backend, which will multicast the	packet
       through	a netlink socket to the specified multicast group. One or more
       userspace processes may subscribe to the group to receive the  packets.
       Like LOG, this is a non-terminating target, i.e. rule traversal contin‐
       ues at the next rule.

       --nflog-group nlgroup
	      The netlink group (0 - 2^16-1) to which packets are (only appli‐
	      cable for nfnetlink_log). The default value is 0.

       --nflog-prefix prefix
	      A	 prefix string to include in the log message, up to 64 charac‐
	      ters long, useful for distinguishing messages in the logs.

       --nflog-range size
	      The number of bytes to be copied to userspace  (only  applicable
	      for  nfnetlink_log).  nfnetlink_log  instances may specify their
	      own range, this option overrides it.

       --nflog-threshold size
	      Number of packets to queue inside the kernel before sending them
	      to  userspace (only applicable for nfnetlink_log). Higher values
	      result in less overhead per packet, but increase delay until the
	      packets reach userspace. The default value is 1.

   NFQUEUE
       This  target  is an extension of the QUEUE target. As opposed to QUEUE,
       it allows you to put a packet into any specific	queue,	identified  by
       its  16-bit  queue  number.   It	 can only be used with Kernel versions
       2.6.14 or later, since it requires the nfnetlink_queue kernel  support.
       The  queue-balance  option  was	added in Linux 2.6.31, queue-bypass in
       2.6.39.

       --queue-num value
	      This specifies the QUEUE number to use. Valid queue numbers  are
	      0 to 65535. The default value is 0.

       --queue-balance value:value
	      This  specifies  a range of queues to use. Packets are then bal‐
	      anced across the given queues.  This  is	useful	for  multicore
	      systems:	start  multiple	 instances of the userspace program on
	      queues x, x+1, .. x+n and use "--queue-balance x:x+n".   Packets
	      belonging to the same connection are put into the same nfqueue.

       --queue-bypass
	      By  default, if no userspace program is listening on an NFQUEUE,
	      then all packets that are to be queued are dropped.   When  this
	      option  is  used, the NFQUEUE rule is silently bypassed instead.
	      The packet will move on to the next rule.

   NOTRACK
       This target disables connection tracking for all packets matching  that
       rule.

       It can only be used in the raw table.

   RATEEST
       The RATEEST target collects statistics, performs rate estimation calcu‐
       lation and saves the results for later  evaluation  using  the  rateest
       match.

       --rateest-name name
	      Count  matched  packets into the pool referred to by name, which
	      is freely choosable.

       --rateest-interval amount{s|ms|us}
	      Rate measurement interval, in seconds, milliseconds or microsec‐
	      onds.

       --rateest-ewmalog value
	      Rate measurement averaging time constant.

   REDIRECT
       This  target is only valid in the nat table, in the PREROUTING and OUT‐
       PUT chains, and user-defined chains which are only  called  from	 those
       chains.	 It redirects the packet to the machine itself by changing the
       destination IP  to  the	primary	 address  of  the  incoming  interface
       (locally-generated packets are mapped to the 127.0.0.1 address).

       --to-ports port[-port]
	      This  specifies  a  destination  port  or range of ports to use:
	      without this, the destination port is never  altered.   This  is
	      only valid if the rule also specifies -p tcp or -p udp.

       --random
	      If  option --random is used then port mapping will be randomized
	      (kernel >= 2.6.22).

   REJECT
       This is used to send back an error packet in response  to  the  matched
       packet:	otherwise it is equivalent to DROP so it is a terminating TAR‐
       GET, ending rule traversal.  This target is only valid  in  the	INPUT,
       FORWARD	and  OUTPUT  chains,  and  user-defined	 chains which are only
       called from those chains.  The following option controls the nature  of
       the error packet returned:

       --reject-with type
	      The  type	 given can be icmp-net-unreachable, icmp-host-unreach‐
	      able,	  icmp-port-unreachable,       icmp-proto-unreachable,
	      icmp-net-prohibited,  icmp-host-prohibited or icmp-admin-prohib‐
	      ited  (*)	 which	return	the  appropriate  ICMP	error  message
	      (port-unreachable	 is the default).  The option tcp-reset can be
	      used on rules which only match the TCP protocol: this  causes  a
	      TCP  RST	packet	to  be	sent  back.  This is mainly useful for
	      blocking ident (113/tcp)	probes	which  frequently  occur  when
	      sending  mail to broken mail hosts (which won't accept your mail
	      otherwise).

       (*) Using icmp-admin-prohibited with kernels that  do  not  support  it
       will result in a plain DROP instead of REJECT

   SAME
       Similar	to SNAT/DNAT depending on chain: it takes a range of addresses
       (`--to 1.2.3.4-1.2.3.7') and gives a client the	same  source-/destina‐
       tion-address for each connection.

       N.B.: The DNAT target's --persistent option replaced the SAME target.

       --to ipaddr[-ipaddr]
	      Addresses	 to map source to. May be specified more than once for
	      multiple ranges.

       --nodst
	      Don't use the destination-ip in the calculations when  selecting
	      the new source-ip

       --random
	      Port  mapping will be forcibly randomized to avoid attacks based
	      on port prediction (kernel >= 2.6.21).

   SECMARK
       This is used to set the security mark value associated with the	packet
       for  use	 by  security  subsystems such as SELinux.  It is valid in the
       security table (for backwards compatibility with older kernels,	it  is
       also valid in the mangle table). The mark is 32 bits wide.

       --selctx security_context

   SET
       This  modules  adds  and/or  deletes  entries from IP sets which can be
       defined by ipset(8).

       --add-set setname flag[,flag...]
	      add the address(es)/port(s) of the packet to the sets

       --del-set setname flag[,flag...]
	      delete the address(es)/port(s) of the packet from the sets

	      where flags are src and/or dst specifications and there  can  be
	      no more than six of them.

       --timeout value
	      when  adding  entry,  the	 timeout  value	 to use instead of the
	      default one from the set definition

       --exist
	      when adding entry if it already exists, reset the timeout	 value
	      to the specified one or to the default from the set definition

       Use  of	-j  SET requires that ipset kernel support is provided, which,
       for standard kernels, is the case since Linux 2.6.39.

   SNAT
       This target is only valid in the nat table, in the  POSTROUTING	chain.
       It  specifies  that the source address of the packet should be modified
       (and all future packets in this connection will also be	mangled),  and
       rules should cease being examined.  It takes one type of option:

       --to-source [ipaddr[-ipaddr]][:port[-port]]
	      which  can  specify a single new source IP address, an inclusive
	      range of IP addresses, and optionally, a port  range  (which  is
	      only  valid if the rule also specifies -p tcp or -p udp).	 If no
	      port range is specified, then source ports  below	 512  will  be
	      mapped  to  other	 ports	below  512: those between 512 and 1023
	      inclusive will be mapped to ports below 1024,  and  other	 ports
	      will  be mapped to 1024 or above. Where possible, no port alter‐
	      ation will occur.

	      In Kernels  up  to  2.6.10,  you	can  add  several  --to-source
	      options.	For those kernels, if you specify more than one source
	      address, either via an address  range  or	 multiple  --to-source
	      options, a simple round-robin (one after another in cycle) takes
	      place between these addresses.  Later  Kernels  (>=  2.6.11-rc1)
	      don't have the ability to NAT to multiple ranges anymore.

       --random
	      If  option --random is used then port mapping will be randomized
	      (kernel >= 2.6.21).

       --persistent
	      Gives a client the  same	source-/destination-address  for  each
	      connection.   This  supersedes the SAME target. Support for per‐
	      sistent mappings is available from 2.6.29-rc2.

   TCPMSS
       This target allows to alter the MSS value of TCP SYN packets,  to  con‐
       trol  the maximum size for that connection (usually limiting it to your
       outgoing interface's MTU minus 40 for IPv4  or  60  for	IPv6,  respec‐
       tively).	 Of course, it can only be used in conjunction with -p tcp.

       This  target  is	 used to overcome criminally braindead ISPs or servers
       which block "ICMP Fragmentation Needed"	or  "ICMPv6  Packet  Too  Big"
       packets.	  The  symptoms of this problem are that everything works fine
       from your Linux firewall/router,	 but  machines	behind	it  can	 never
       exchange large packets:

       1.  Web browsers connect, then hang with no data received.

       2.  Small mail works fine, but large emails hang.

       3.  ssh works fine, but scp hangs after initial handshaking.

       Workaround:  activate  this option and add a rule to your firewall con‐
       figuration like:

	       iptables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN
			   -j TCPMSS --clamp-mss-to-pmtu

       --set-mss value
	      Explicitly sets MSS option to specified value. If the MSS of the
	      packet  is  already  lower  than value, it will not be increased
	      (from Linux 2.6.25 onwards) to avoid more	 problems  with	 hosts
	      relying on a proper MSS.

       --clamp-mss-to-pmtu
	      Automatically  clamp  MSS	 value to (path_MTU - 40 for IPv4; -60
	      for IPv6).  This may not function as  desired  where  asymmetric
	      routes  with differing path MTU exist — the kernel uses the path
	      MTU which it would use to send packets from itself to the source
	      and  destination	IP  addresses. Prior to Linux 2.6.25, only the
	      path MTU to the destination IP address was  considered  by  this
	      option;  subsequent  kernels  also  consider the path MTU to the
	      source IP address.

       These options are mutually exclusive.

   TCPOPTSTRIP
       This target will strip TCP options off a TCP packet. (It will  actually
       replace	them  by  NO-OPs.)  As	such,  you will need to add the -p tcp
       parameters.

       --strip-options option[,option...]
	      Strip the given option(s). The options may be specified  by  TCP
	      option  number  or  by  symbolic	name.  The  list of recognized
	      options can be obtained by calling iptables with -j  TCPOPTSTRIP
	      -h.

   TEE
       The  TEE	 target will clone a packet and redirect this clone to another
       machine on the local network segment. In other words, the nexthop  must
       be  the target, or you will have to configure the nexthop to forward it
       further if so desired.

       --gateway ipaddr
	      Send the cloned packet to the host reachable  at	the  given  IP
	      address.	 Use  of  0.0.0.0  (for	 IPv4 packets) or :: (IPv6) is
	      invalid.

       To forward all incoming traffic on eth0 to  an  Network	Layer  logging
       box:

       -t mangle -A PREROUTING -i eth0 -j TEE --gateway 2001:db8::1

   TOS
       This  module sets the Type of Service field in the IPv4 header (includ‐
       ing the "precedence" bits) or the Priority field in  the	 IPv6  header.
       Note  that  TOS shares the same bits as DSCP and ECN. The TOS target is
       only valid in the mangle table.

       --set-tos value[/mask]
	      Zeroes out the bits given by mask	 (see  NOTE  below)  and  XORs
	      value  into  the TOS/Priority field. If mask is omitted, 0xFF is
	      assumed.

       --set-tos symbol
	      You can specify a symbolic name when using the  TOS  target  for
	      IPv4.  It	 implies  a mask of 0xFF (see NOTE below). The list of
	      recognized TOS names can be obtained by calling iptables with -j
	      TOS -h.

       The following mnemonics are available:

       --and-tos bits
	      Binary  AND  the	TOS  value  with bits. (Mnemonic for --set-tos
	      0/invbits, where invbits is the binary negation  of  bits.   See
	      NOTE below.)

       --or-tos bits
	      Binary  OR  the  TOS  value  with	 bits. (Mnemonic for --set-tos
	      bits/bits. See NOTE below.)

       --xor-tos bits
	      Binary XOR the TOS value	with  bits.  (Mnemonic	for  --set-tos
	      bits/0. See NOTE below.)

       NOTE:  In  Linux kernels up to and including 2.6.38, with the exception
       of  longterm  releases  2.6.32  (>=.42),	 2.6.33	 (>=.15),  and	2.6.35
       (>=.14),	 there	is  a bug whereby IPv6 TOS mangling does not behave as
       documented and differs from the IPv4 version. The  TOS  mask  indicates
       the  bits  one  wants  to  zero	out, so it needs to be inverted before
       applying it to the original TOS field. However, the aformentioned  ker‐
       nels forgo the inversion which breaks --set-tos and its mnemonics.

   TPROXY
       This  target is only valid in the mangle table, in the PREROUTING chain
       and user-defined chains which are only called from this chain. It redi‐
       rects  the  packet to a local socket without changing the packet header
       in any way. It can also change the mark value which can then be used in
       advanced routing rules.	It takes three options:

       --on-port port
	      This  specifies  a  destination  port  to	 use. It is a required
	      option, 0 means the new destination port	is  the	 same  as  the
	      original.	 This  is only valid if the rule also specifies -p tcp
	      or -p udp.

       --on-ip address
	      This specifies a destination address  to	use.  By  default  the
	      address  is  the	IP  address of the incoming interface. This is
	      only valid if the rule also specifies -p tcp or -p udp.

       --tproxy-mark value[/mask]
	      Marks packets with the given value/mask. The  fwmark  value  set
	      here  can be used by advanced routing. (Required for transparent
	      proxying to work: otherwise these packets	 will  get  forwarded,
	      which is probably not what you want.)

   TRACE
       This  target marks packets so that the kernel will log every rule which
       match the packets as those traverse the tables, chains, rules.

       A logging backend, such as ip(6)t_LOG or nfnetlink_log, must be	loaded
       for this to be visible.	The packets are logged with the string prefix:
       "TRACE: tablename:chainname:type:rulenum " where type can be "rule" for
       plain  rule,  "return"  for  implicit rule at the end of a user defined
       chain and "policy" for the policy of the built in chains.
       It can only be used in the raw table.

   TTL
       This is used to modify the IPv4 TTL header field.  The TTL field deter‐
       mines  how many hops (routers) a packet can traverse until it's time to
       live is exceeded.

       Setting or incrementing the TTL field can potentially be	 very  danger‐
       ous,  so it should be avoided at any cost. This target is only valid in
       mangle table.

       Don't ever set or increment the value on packets that leave your	 local
       network!

       --ttl-set value
	      Set the TTL value to `value'.

       --ttl-dec value
	      Decrement the TTL value `value' times.

       --ttl-inc value
	      Increment the TTL value `value' times.

   ULOG
       This  target provides userspace logging of matching packets.  When this
       target is set for a rule, the Linux kernel will multicast  this	packet
       through a netlink socket. One or more userspace processes may then sub‐
       scribe to various multicast groups and receive the packets.  Like  LOG,
       this  is	 a  "non-terminating target", i.e. rule traversal continues at
       the next rule.

       --ulog-nlgroup nlgroup
	      This specifies the netlink group (1-32) to which the  packet  is
	      sent.  Default value is 1.

       --ulog-prefix prefix
	      Prefix  log messages with the specified prefix; up to 32 charac‐
	      ters long, and useful for distinguishing messages in the logs.

       --ulog-cprange size
	      Number of bytes to be copied to userspace.  A value of 0	always
	      copies the entire packet, regardless of its size.	 Default is 0.

       --ulog-qthreshold size
	      Number of packet to queue inside kernel.	Setting this value to,
	      e.g. 10 accumulates ten packets inside the kernel and  transmits
	      them  as one netlink multipart message to userspace.  Default is
	      1 (for backwards compatibility).

DIAGNOSTICS
       Various error messages are printed to standard error.  The exit code is
       0 for correct functioning.  Errors which appear to be caused by invalid
       or abused command line parameters cause an exit code of	2,  and	 other
       errors cause an exit code of 1.

BUGS
       Bugs?   What's  this?  ;-)  Well,  you  might  want  to	have a look at
       http://bugzilla.netfilter.org/

COMPATIBILITY WITH IPCHAINS
       This iptables is very similar to ipchains by Rusty Russell.   The  main
       difference  is  that the chains INPUT and OUTPUT are only traversed for
       packets coming into the local host and originating from the local  host
       respectively.   Hence every packet only passes through one of the three
       chains (except loopback traffic, which involves both INPUT  and	OUTPUT
       chains); previously a forwarded packet would pass through all three.

       The  other main difference is that -i refers to the input interface; -o
       refers to the output interface, and  both  are  available  for  packets
       entering the FORWARD chain.

       The  various  forms  of NAT have been separated out; iptables is a pure
       packet filter when using the  default  `filter'	table,	with  optional
       extension modules.  This should simplify much of the previous confusion
       over the combination of IP masquerading and packet filtering seen  pre‐
       viously.	 So the following options are handled differently:
	-j MASQ
	-M -S
	-M -L
       There are several other changes in iptables.

SEE ALSO
       iptables-save(8), iptables-restore(8), ip6tables(8), ip6tables-save(8),
       ip6tables-restore(8), libipq(3).

       The packet-filtering-HOWTO details iptables usage for packet filtering,
       the  NAT-HOWTO  details NAT, the netfilter-extensions-HOWTO details the
       extensions that are not in the standard distribution, and  the  netfil‐
       ter-hacking-HOWTO details the netfilter internals.
       See http://www.netfilter.org/.

AUTHORS
       Rusty  Russell  originally  wrote  iptables, in early consultation with
       Michael Neuling.

       Marc Boucher made Rusty abandon ipnatctl	 by  lobbying  for  a  generic
       packet  selection  framework  in iptables, then wrote the mangle table,
       the owner match, the mark stuff, and ran around doing cool stuff every‐
       where.

       James Morris wrote the TOS target, and tos match.

       Jozsef Kadlecsik wrote the REJECT target.

       Harald  Welte  wrote  the  ULOG and NFQUEUE target, the new libiptc, as
       well as the TTL, DSCP, ECN matches and targets.

       The Netfilter Core Team is: Marc Boucher,  Martin  Josefsson,  Yasuyuki
       Kozakai,	 Jozsef	 Kadlecsik, Patrick McHardy, James Morris, Pablo Neira
       Ayuso, Harald Welte and Rusty Russell.

       Man page originally written by Herve Eychenne <rv@wallfire.org>.

VERSION
       This manual page applies to iptables @PACKAGE_VERSION@.

iptables 1.4.14							   IPTABLES(8)
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