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IPTABLES(8)			iptables 1.4.18			   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 five 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).

       -4, --ipv4
	      This option has no effect in iptables and iptables-restore.

       -6, --ipv6
	      If  a  rule using the -6 option is inserted with (and only with)
	      iptables-restore, it will be silently ignored.  Any  other  uses
	      will  throw  an  error.  This option allows to put both IPv4 and
	      IPv6 rules in a single rule file for  use	 with  both  iptables-
	      restore and ip6tables-restore.

       [!] -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.

       -m, --match match
	      Specifies a match to use, that  is,  an  extension  module  that
	      tests  for  a  specific property. The set of matches make up the
	      condition under which a target is invoked. Matches are evaluated
	      first  to	 last  as  specified  on  the command line and work in
	      short-circuit fashion, i.e. if one extension yields false, eval-
	      uation will stop.

       -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 AND TARGET EXTENSIONS
       iptables	 can  use extended packet matching and target modules.	A list
       of these is available in the iptables-extensions(8) manpage.

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-apply(8),    iptables-save(8),	  iptables-restore(8),	 ipta-
       bles-extensions(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 1.4.18							   IPTABLES(8)