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IPTABLES(8)							   IPTABLES(8)



NAME
       iptables - administration tool for IPv4 packet filtering and NAT

SYNOPSIS
       iptables [-t table] -[AD] chain rule-specification [options]
       iptables [-t table] -I chain [rulenum] rule-specification [options]
       iptables [-t table] -R chain rulenum rule-specification [options]
       iptables [-t table] -D chain rulenum [options]
       iptables [-t table] -[LFZ] [chain] [options]
       iptables [-t table] -N chain
       iptables [-t table] -X [chain]
       iptables [-t table] -P chain target [options]
       iptables [-t table] -E old-chain-name new-chain-name

DESCRIPTION
       Iptables	 is  used  to  set  up, maintain, and inspect the tables of IP
       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)

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

   COMMANDS
       These options specify the specific action to perform.  Only one of them
       can  be specified on the command line unless otherwise specified below.
       For all the 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.

       -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.  As  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

       -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]
	      Zero the packet and byte counters in all chains.	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, icmp, or all, or it can be
	      a	 numeric  value, representing one of these protocols or a dif-
	      ferent  one.   A	protocol  name	from  /etc/protocols  is  also
	      allowed.	 A  "!" argument before the protocol inverts the test.
	      The number zero is equivalent to all.  Protocol 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	(please	 note  that specifying any name to be resolved
	      with a remote query such as DNS is a really bad idea), a network
	      IP address (with /mask), or a plain IP address.  The mask can be
	      either a network mask or a plain number, specifying  the	number
	      of 1's at the left side of the network 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.

       -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 PKTS 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.

       -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.  These are loaded in
       two ways: implicitly, when -p or --protocol is specified, or  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 mod-
       ules 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.

       The  following  are included in the base package, and most of these can
       be preceded by a !  to invert the sense of the match.

   account
       Account traffic for all hosts in defined network/netmask.

       Features:

       - long (one counter per protocol TCP/UDP/IMCP/Other) and short  statis-
       tics

       - one iptables rule for all hosts in network/netmask

       - loading/saving counters (by reading/writting to procfs entries)


       --aaddr network/netmask
	      defines network/netmask for which make statistics.

       --aname name
	      defines  name  of	 list  where statistics will be kept. If no is
	      specified DEFAULT will be used.

       --ashort
	      table will colect only short  statistics	(only  total  counters
	      without splitting it into protocols.

       Example usage:

       account traffic for/to 192.168.0.0/24 network into table mynetwork:

       #   iptables   -A   FORWARD   -m	  account  --aname  mynetwork  --aaddr
       192.168.0.0/24

       account traffic for/to WWW serwer for 192.168.0.0/24 network into table
       mywwwserver:

       # iptables -A INPUT -p tcp --dport 80
	 -m account --aname mywwwserver --aaddr 192.168.0.0/24 --ashort

       # iptables -A OUTPUT -p tcp --sport 80
	 -m account --aname mywwwserver --aaddr 192.168.0.0/24 --ashort

       read counters:

       #	cat	   /proc/net/ipt_account/mynetwork	  #	   cat
       /proc/net/ipt_account/mywwwserver

       set counters:

       #    echo    "ip	   =	192.168.0.1	packets_src	=     0"     >
       /proc/net/ipt_account/mywwserver

       Webpage:
	 http://www.barbara.eu.org/~quaker/ipt_account/

   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	black-
	      hole  address UNREACHABLE an unreachable address PROHIBIT a pro-
	      hibited address THROW FIXME NAT FIXME XRESOLVE FIXME

       --src-type type
	      Matches if the source address is of given type

       --dst-type type
	      Matches if the destination address is of given type

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

       --ahspi [!] spi[:spi]

   childlevel
       This  is	 an  experimental module.  It matches on whether the packet is
       part of a master connection or one of its children  (or	grandchildren,
       etc).   For  instance,  most packets are level 0.  FTP data transfer is
       level 1.

       --childlevel [!] level

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

       --comment comment

       Example:
	      iptables -A INPUT -s 192.168.0.0/16 -m comment --comment "A pri-
	      vatized IP block"

   condition
       This matches if a specific /proc filename is '0' or '1'.

       --condition [!] filename
	      Match  on	 boolean value stored in /proc/net/ipt_condition/file-
	      name file

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

       The counters are 64bit 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  transfered	bytes  per  connection	can  also  be  viewed  through
       /proc/net/ip_conntrack and accessed via ctnetlink

       [!] --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 TCP connections to a
       server per client IP address (or address block).

       [!] --connlimit-above n
	      match if the number of existing tcp connections is (not) above n

       --connlimit-mask bits
	      group hosts using mask

       Examples:

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

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

       #  limit	 the nr of parallel http requests to 16 per class C sized net-
       work (24 bit netmask)
	      iptables	-p tcp --syn --dport 80 -m connlimit --connlimit-above
	      16 --connlimit-mask 24 -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).

   connrate
       This module matches the current transfer rate in a connection.

       --connrate [!] [from]:[to]
	      Match  against the current connection transfer rate being within
	      'from' and 'to' bytes per second. When the "!" argument is  used
	      before the range, the sense of the match is inverted.

   conntrack
       This  module,  when combined with connection tracking, allows access to
       more connection tracking information than  the  "state"	match.	 (this
       module is present only if iptables was compiled under a kernel support-
       ing this feature)

       --ctstate state
	      Where state is a comma separated list of the  connection	states
	      to  match.   Possible states are INVALID meaning that the packet
	      is associated with no known connection, ESTABLISHED meaning that
	      the  packet is associated with a connection which has seen pack-
	      ets in both directions, 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 mean-
	      ing that the packet is starting a new connection, but is associ-
	      ated with an existing connection, such as an FTP data  transfer,
	      or  an ICMP error.  SNAT A virtual state, matching if the origi-
	      nal source address differs from the reply destination.   DNAT  A
	      virtual state, matching if the original destination differs from
	      the reply source.

       --ctproto proto
	      Protocol to match (by number or name)

       --ctorigsrc [!] address[/mask]
	      Match against original source address

       --ctorigdst [!] address[/mask]
	      Match against original destination address

       --ctreplsrc [!] address[/mask]
	      Match against reply source address

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

       --ctstatus [NONE|EXPECTED|SEEN_REPLY|ASSURED][,...]
	      Match against internal conntrack states

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

   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 DCP 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 DiffServ Class
	      Match  the  DiffServ class. This value may be any of the BE, EF,
	      AFxx or CSx classes.   It	 will  then  be	 converted  into  it's
	      according numeric value.

   dstlimit
       This  module  allows you to limit the packet per second (pps) rate on a
       per destination IP or per destination port base.	  As  opposed  to  the
       'limit'	match,	every  destination  ip / destination port has it's own
       limit.

       THIS MODULE IS DEPRECATED AND HAS BEEN REPLACED BY ''hashlimit''

       --dstlimit avg
	      Maximum average match rate (packets per second  unless  followed
	      by /sec /minute /hour /day postfixes).

       --dstlimit-mode mode
	      The limiting hashmode.  Is the specified limit per dstip, dstip-
	      dstport tuple,  srcip-dstip  tuple,  or  per  srcipdstip-dstport
	      tuple.

       --dstlimit-name name
	      Name for /proc/net/ipt_dstlimit/* file entry

       [--dstlimit-burst burst]
	      Number of packets to match in a burst.  Default: 5

       [--dstlimit-htable-size size]
	      Number of buckets in the hashtable

       [--dstlimit-htable-max max]
	      Maximum number of entries in the hashtable

       [--dstlimit-htable-gcinterval interval]
	      Interval	between	 garbage  collection runs of the hashtable (in
	      miliseconds).  Default is 1000 (1 second).

       [--dstlimit-htable-expire time
	      After which time are idle entries	 expired  from	hashtable  (in
	      miliseconds)?  Default is 10000 (10 seconds).

   ecn
       This  allows you to match the ECN bits of the IPv4 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 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]

   fuzzy
       This  module  matches  a	 rate  limit based on a fuzzy logic controller
       [FLC]

       --lower-limit number
	      Specifies the lower limit (in packets per second).

       --upper-limit number
	      Specifies the upper limit (in packets per second).

   hashlimit
       This patch adds a new match called 'hashlimit'.	The idea  is  to  have
       something  like	'limit',  but  either  per destination-ip or per (des-
       tip,destport) tuple.

       It gives you the ability to express

	       '1000 packets per second for every host in 192.168.0.0/16'

	       '100 packets per second for every service of 192.168.1.1'

       with a single iptables rule.

       --hashlimit rate
	      A rate just like the limit match

       --hashlimit-burst num
	      Burst value, just like limit match

       --hashlimit-mode destip | destip-destport
	      Limit per IP or per port

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

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

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

       --hashlimit-htable-expire num
	      After how many miliseconds do hash entries expire

       --hashlimit-htable-gcinterval num
	      How many miliseconds between garbage collection intervals

   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 is loaded if '--protocol icmp' is	 specified.   It  pro-
       vides the following option:

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

   iprange
       This matches on a given arbitrary range of IPv4 addresses

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

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

   ipv4options
       Match  on IPv4 header options like source routing, record route, times-
       tamp and router-alert.

       --ssrr To match packets with the flag strict source routing.

       --lsrr To match packets with the flag loose source routing.

       --no-srr
	      To match packets with no flag for source routing.

       [!] --rr
	      To match packets with the RR flag.

       [!] --ts
	      To match packets with the TS flag.

       [!] --ra
	      To match packets with the router-alert option.

       [!] --any-opt
	      To match a packet with at least one IP option, or no  IP	option
	      at all if ! is chosen.

       Examples:

       $ iptables -A input -m ipv4options --rr -j DROP
	      will drop packets with the record-route flag.

       $ iptables -A input -m ipv4options --ts -j DROP
	      will drop packets with the timestamp flag.

   length
       This  module matches the length 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
       (unless the '!' flag is used).  It can be used in combination with  the
       LOG target to give limited logging, for example.

       --limit rate
	      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).

   mport
       This  module  matches  a	 set of source or destination ports.  Up to 15
       ports can be specified.	It can only be used in conjunction with -p tcp
       or -p udp.

       --source-ports port[,port[,port...]]
	      Match  if	 the  source port is one of the given ports.  The flag
	      --sports is a convenient alias for this option.

       --destination-ports 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...]]
	      Match  if the both the source and destination ports are equal to
	      each other and to one of the given ports.

   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 [!] 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.

       --destination-ports [!] 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.

   nth
       This module matches every 'n'th packet

       --every value
	      Match every 'value' packet

       [--counter num]
	      Use internal counter number 'num'.  Default is '0'.

       [--start num]
	      Initialize the counter at the number 'num' insetad of '0'.  Most
	      between '0' and 'value'-1.

       [--packet num]
	      Match on 'num' packet.  Most be between '0' and 'value'-1.

   osf
       The idea of passive OS fingerprint matching exists  for	quite  a  long
       time,  but  was created as extension fo OpenBSD pf only some weeks ago.
       Original	 idea  was  lurked  in	some  OpenBSD  mailing	list   (thanks
       grange@open...)	and  than  adopted for Linux netfilter in form of this
       code.

       Original	  fingerprint	table	was   created	by   Michal   Zalewski
       <lcamtuf@coredump.cx>.

       This module compares some data(WS, MSS, options and it's order, ttl, df
       and others) from first SYN packet (actually from packets with  SYN  bit
       set) with dynamically loaded OS fingerprints.

       --log 1/0
	      If  present,  OSF	 will log determined genres even if they don't
	      match desired one.    0 - log all determined entries, 1  -  only
	      first one.

	      In syslog you find something like this:

	      ipt_osf:	Windows	 [2000:SP3:Windows  XP	Pro  SP1,  2000	 SP3]:
	      11.22.33.55:4024 -> 11.22.33.44:139

	      ipt_osf:	      Unknown:	       16384:106:1:48:020405B401010402
	      44.33.22.11:1239 -> 11.22.33.44:80

       --smart
	      if  present, OSF will use some smartness to determine remote OS.
	      OSF will use initial TTL only if source of connection is in  our
	      local network.

       --netlink
	      If  present,  OSF	 will  log  all	 events	 also  through netlink
	      NETLINK_NFLOG groupt 1.

       --genre [!] string
	      Match a OS genre by passive fingerprinting

       Example:

       #iptables -I INPUT -j ACCEPT -p	tcp  -m	 osf  --genre  Linux  --log  1
       --smart

       NOTE: -p tcp is obviously required as it is a TCP match.

       Fingerprints  can  be  loaded  and  read through /proc/sys/net/ipv4/osf
       file.  One can flush all fingerprints with following command:

	      echo -en FLUSH > /proc/sys/net/ipv4/osf

       Only one fingerprint per open/write/close.

       Fingerprints  can  be   downloaded   from   http://www.openbsd.org/cgi-
       bin/cvsweb/src/etc/pf.os

   owner
       This  module  attempts  to  match various characteristics of the packet
       creator, for locally-generated packets.	It is only valid in the OUTPUT
       chain,  and  even  this	some packets (such as ICMP ping responses) may
       have no owner, and hence never match.

       --uid-owner userid
	      Matches if the packet was created by a process  with  the	 given
	      effective user id.

       --gid-owner groupid
	      Matches  if  the	packet was created by a process with the given
	      effective group id.

       --pid-owner processid
	      Matches if the packet was created by a process  with  the	 given
	      process id.

       --sid-owner sessionid
	      Matches if the packet was created by a process in the given ses-
	      sion group.

       --cmd-owner name
	      Matches if the packet was created by a process  with  the	 given
	      command name.  (this option is present only if iptables was com-
	      piled under a kernel supporting this feature)

       NOTE: pid, sid and command matching are broken on SMP

   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 it is yet unknown  what
	      the  output  device  will	 be,  then the packet won't match this
	      option, unless

       [!] --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.

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

       --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

   psd
       Attempt to detect TCP and UDP port scans. This match was	 derived  from
       Solar Designer's scanlogd.

       --psd-weight-threshold threshold
	      Total weight of the latest TCP/UDP packets with different desti-
	      nation ports coming from the same host to	 be  treated  as  port
	      scan sequence.

       --psd-delay-threshold delay
	      Delay  (in  hundredths of second) for the packets with different
	      destination ports coming from the same host  to  be  treated  as
	      possible port scan subsequence.

       --psd-lo-ports-weight weight
	      Weight  of the packet with privileged (<=1024) destination port.

       --psd-hi-ports-weight weight
	      Weight of the packet with non-priviliged destination port.

   quota
       Implements network quotas by decrementing  a  byte  counter  with  each
       packet.

       --quota bytes
	      The quota in bytes.

       KNOWN BUGS: this does not work on SMP systems.

   random
       This module randomly matches a certain percentage of all packets.

       --average percent
	      Matches  the given percentage.  If omitted, a probability of 50%
	      is set.

   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).

   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.

       --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).

       [!] --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.

       [!] --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.

       --rttl 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  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

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

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

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

       echo xx.xx.xx.xx > /proc/net/ipt_recent/DEFAULT
	      to Add to the DEFAULT list

       echo -xx.xx.xx.xx > /proc/net/ipt_recent/DEFAULT
	      to Remove from the DEFAULT list

       echo clear > /proc/net/ipt_recent/DEFAULT
	      to empty the DEFAULT list.

       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/ipt_recent/* files

       debug=0
	      Set to 1 to get lots of debugging info

   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

	      chunk type	    available flags
	      DATA		    U B E 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 modules macthes IP sets which can be defined by ipset(8).

       --set setname flag[,flag...]
	      where flags are src and/or dst and there can be no more than six
	      of them. Hence the command
	       iptables -A FORWARD -m set --set test src,dst
	      will match packets, for which (depending on the type of the set)
	      the source address or port number of the packet can be found  in
	      the specified set. If there is a binding belonging to the mached
	      set element or there is a default binding	 for  the  given  set,
	      then  the	 rule  will  match  the	 packet	 only  if additionally
	      (depending on the type of the set) the  destination  address  or
	      port  number  of the packet can be found in the set according to
	      the binding.

   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.

   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  from  0  to 1 for a packet to be randomly
	      matched. It works only with the random mode.

       --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 from which it starts looking for any matching. 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  are loaded if '--protocol tcp' is specified. It pro-
       vides the following options:

       --source-port [!] 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 port:port.  If  the  first  port  is
	      omitted,	"0"  is	 assumed;  if  the last is omitted, "65535" is
	      assumed.	If the second port greater then the first they will be
	      swapped.	 The  flag  --sport  is	 a  convenient	alias for this
	      option.

       --destination-port [!] 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
	      is the flags which we should examine, written as	a  comma-sepa-
	      rated list, and the second argument is a comma-separated 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.

       --mss value[:value]
	      Match TCP SYN or SYN/ACK packets with the	 specified  MSS	 value
	      (or  range), which control the maximum packet size for that con-
	      nection.

   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 facultative.

	--timestart value
	      Match only if it is after 'value' (Inclusive,  format:  HH:MM  ;
	      default 00:00).

       --timestop  value
	      Match  only  if it is before 'value' (Inclusive, format: HH:MM ;
	      default 23:59).

       --days listofdays
	      Match  only  if  today  is  one  of  the	given  days.  (format:
	      Mon,Tue,Wed,Thu,Fri,Sat,Sun ; default everyday)

       --datestart date
	      Match   only   if	  it   is  after  'date'  (Inclusive,  format:
	      YYYY[:MM[:DD[:hh[:mm[:ss]]]]] ; h,m,s start from 0 ; default  to
	      1970)

       --datestop date
	      Match   only   if	  it  is  before  'date'  (Inclusive,  format:
	      YYYY[:MM[:DD[:hh[:mm[:ss]]]]] ; h,m,s start from 0 ; default  to
	      2037)

   tos
       This  module  matches  the  8  bits  of Type of Service field in the IP
       header (ie. including the precedence bits).

       --tos tos
	      The argument is either a standard name, (use
	       iptables -m tos -h
	      to see the list), or a numeric value to match.

   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 allows you to extract quantities of up to 4 bytes  from  a  packet,
       AND them with specified masks, shift them by specified amounts and test
       whether the results are in any of a set of specified ranges.  The spec-
       ification  of  what  to	extract is general enough to skip over headers
       with lengths stored in the packet, as in IP or TCP header lengths.

       Details and examples are in the kernel module source.

   udp
       These extensions are loaded if '--protocol udp' is specified.  It  pro-
       vides the following options:

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

       --destination-port [!] 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.

   BALANCE
       This allows you to DNAT connections in a round-robin way over  a	 given
       range of destination addresses.

       --to-destination ipaddr-ipaddr
	      Address range to round-robin over.

   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.

   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,  sourceip-
	      sourceport, sourceip-sourceport-destport

       --clustermac mac
	      Specify  the ClusterIP MAC address.  Has to be a link-layer mul-
	      ticast 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

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

       --save-mark [--mask mask]
	      Copy  the netfilter packet mark value to the connection mark. If
	      a mask is specified then only those bits are copied.

       --restore-mark [--mask mask]
	      Copy the connection mark value to the packet. If a mask is spec-
	      ified then only those bits are copied. This is only valid in the
	      mangle table.

   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.

	      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.


   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.

   IPMARK
       Allows you to mark a received packet basing on its IP address. This can
       replace many mangle/mark entries with only one,	if  you	 use  firewall
       based classifier.

       This  target  is to be used inside the mangle table, in the PREROUTING,
       POSTROUTING or FORWARD hooks.

       --addr src/dst
	      Use source or destination IP address.

       --and-mask mask
	      Perform bitwise 'and' on the IP address and this mask.

       --or-mask mask
	      Perform bitwise 'or' on the IP address and this mask.

       The order of IP address bytes is	 reversed  to  meet  "human  order  of
       bytes": 192.168.0.1 is 0xc0a80001. At first the 'and' operation is per-
       formed, then 'or'.

       Examples:

       We create a queue for each user, the queue number is adequate to the IP
       address	of  the	 user, e.g.: all packets going to/from 192.168.5.2 are
       directed to 1:0502 queue, 192.168.5.12 -> 1:050c etc.

       We have one classifier rule:

	      tc filter add dev eth3 parent 1:0 protocol ip fw

       Earlier we had many rules just like below:

	      iptables -t mangle -A POSTROUTING -o eth3 -d 192.168.5.2 -j MARK
	      --set-mark 0x10502

	      iptables -t mangle -A POSTROUTING -o eth3 -d 192.168.5.3 -j MARK
	      --set-mark 0x10503

       Using IPMARK target we can replace all the mangle/mark rules with  only
       one:

	      iptables	-t  mangle -A POSTROUTING -o eth3 -j IPMARK --addr=dst
	      --and-mask=0xffff --or-mask=0x10000

       On the routers with hundreds of users there should be significant  load
       decrease (e.g. twice).

   IPV4OPTSSTRIP
       Strip all the IP options from a packet.

       The  target  doesn't take any option, and therefore is extremly easy to
       use :

       # iptables -t mangle -A PREROUTING -j IPV4OPTSSTRIP

   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 is used to set  the	 netfilter  mark  value	 associated  with  the
       packet.	 It  is only valid in the mangle table.	 It can for example be
       used in conjunction with iproute2.

       --set-mark mark

   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).  It takes one option:

       --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.

   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.

   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.

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

       It  can	only  be  used	with Kernel versions 2.6.14 or later, since it
       requires
	      the nfnetlink_queue kernel support.

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

       It can only be used in the
	      raw table.

   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).   It
       takes one option:

       --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.

   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-unreachable
	       icmp-port-unreachable
	       icmp-proto-unreachable
	       icmp-net-prohibited
	       icmp-host-prohibited or
	       icmp-admin-prohibited (*)
	      which return the appropriate ICMP error  message	(port-unreach-
	      able 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.

       --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

   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 and there can be no more than six
	      of them.

       The bindings to follow must previously be defined in order to use
	      multilevel adding/deleting by the SET target.

   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.

   TARPIT
       Captures	 and holds incoming TCP connections using no local per-connec-
       tion resources. Connections are accepted, but immediately  switched  to
       the persist state (0 byte window), in which the remote side stops send-
       ing data and asks to continue every 60-240 seconds.  Attempts to	 close
       the  connection	are  ignored,  forcing the remote side to time out the
       connection in 12-24 minutes.

       This  offers  similar   functionality   to   LaBrea   <http://www.hack-
       busters.net/LaBrea/> but doesn't require dedicated hardware or IPs. Any
       TCP port that you would normally DROP or REJECT can  instead  become  a
       tarpit.

       To tarpit connections to TCP port 80 destined for the current machine:

	      iptables -A INPUT -p tcp -m tcp --dport 80 -j TARPIT

       To significantly slow down Code Red/Nimda-style scans of unused address
       space, forward unused ip addresses to a	Linux  box  not	 acting	 as  a
       router (e.g. "ip route 10.0.0.0 255.0.0.0 ip.of.linux.box" on a Cisco),
       enable IP forwarding on the Linux box, and add:

	      iptables -A FORWARD -p tcp -j TARPIT

	      iptables -A FORWARD -j DROP

       NOTE:  If you use the conntrack module while you are using TARPIT,  you
	      should  also use the NOTRACK target, or the kernel will unneces-
	      sarily allocate resources	 for  each  TARPITted  connection.  To
	      TARPIT incoming connections to the standard IRC port while using
	      conntrack, you could:

	      iptables -t raw -A PREROUTING -p tcp --dport 6667 -j NOTRACK

	      iptables -A INPUT -p tcp --dport 6667 -j TARPIT

   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).  Of course, it can only be used  in
       conjunction with -p tcp.	 It is only valid in the mangle table.
       This  target  is	 used to overcome criminally braindead ISPs or servers
       which block ICMP Fragmentation Needed 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 set MSS option to specified value.

       --clamp-mss-to-pmtu
	      Automatically clamp MSS value to (path_MTU - 40).

       These options are mutually exclusive.

   TOS
       This  is	 used to set the 8-bit Type of Service field in the IP header.
       It is only valid in the mangle table.

       --set-tos tos
	      You can use a numeric TOS values, or use
	       iptables -j TOS -h
	      to see the list of valid TOS names.

   TRACE
       This target has no options.  It just turns on packet  tracing  for  all
       packets that match this rule.

   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.

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

       --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).

   XOR
       Encrypt TCP and UDP traffic using a simple XOR encryption

       --key string
	      Set key to "string"

       --block-size
	      Set block size

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.

       iptables is a pure packet filter when using the default 'filter' table,
       with optional extension modules.	 This should simplify much of the pre-
       vious confusion over the combination of IP masquerading and packet fil-
       tering  seen  previously.  So the following options are handled differ-
       ently:
	-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, Jozsef
       Kadlecsik, Patrick McHardy, James Morris, Harald Welte and  Rusty  Rus-
       sell.

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



				 Mar 09, 2002			   IPTABLES(8)
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