Quick ?s
Cheat Sheets
Man Pages
The Lynx
Software
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 1s 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 packets 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 Ks (multiples
	      of 1000) Ms (multiples of 1000K) or Gs (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 rules 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.

   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]

   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"

   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	-A  INPUT  -p  tcp  --syn  --dport  23	-m   connlimit
	      --connlimit-above 2 -j REJECT

       # you can also match the other way around:
	      iptables	-A  INPUT  -p  tcp  --syn  --dport  23	-m connlimit !
	      --connlimit-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).

   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 [0-32].

       --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 its
	      according numeric value.

   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]

   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 dstip | dstport | srcip | srcport
	      Limit per IP or per ip+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

       (Please	note:  This  match  requires  kernel support that might not be
       available in official Linux kernel sources or Debians  packaged	Linux
       kernel  sources.   And  if  support for this match is available for the
       specific Linux kernel source version, that support might not be enabled
       in the current Linux kernel binary.)


       [!]--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.

       (Please note: This match requires kernel  support  that	might  not  be
       available  in  official Linux kernel sources or Debians packaged Linux
       kernel sources.	And if support for this match  is  available  for  the
       specific Linux kernel source version, that support might not be enabled
       in the current Linux kernel binary.)


       --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).

   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.

   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.

	      (Please note: This option requires kernel support that might not
	      be  available in official Linux kernel sources or Debians pack
	      aged Linux kernel sources.  And if support for  this  option  is
	      available  for  the  specific  Linux kernel source version, that
	      support might  not  be  enabled  in  the	current  Linux	kernel
	      binary.)

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

	      (Please note: This option requires kernel support that might not
	      be  available in official Linux kernel sources or Debians pack
	      aged Linux kernel sources.  And if support for  this  option  is
	      available  for  the  specific  Linux kernel source version, that
	      support might  not  be  enabled  in  the	current  Linux	kernel
	      binary.)

       --cmd-owner name
	      Matches  if  the	packet was created by a process with the given
	      command name.

	      (Please note: This option requires kernel support that might not
	      be  available in official Linux kernel sources or Debians pack
	      aged Linux kernel sources.  And if support for  this  option  is
	      available  for  the  specific  Linux kernel source version, that
	      support might  not  be  enabled  in  the	current  Linux	kernel
	      binary.)

       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 didnt arrive
	      through a bridge device, this packet wont  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  wont leave by a bridge device or it is yet unknown what
	      the output device will be, then  the  packet  wont  match  this
	      option, unless ! is used.

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

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

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

   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.

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

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

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

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

       --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.

       --rsource
	      Match/Save  the source address of each packet in the recent list
	      table (default).

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

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

       (Please note: This match requires kernel  support  that	might  not  be
       available  in  official Linux kernel sources or Debians packaged Linux
       kernel sources.	And if support for this match  is  available  for  the
       specific Linux kernel source version, that support might not be enabled
       in the current Linux kernel binary.)


       --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  dont  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.

   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.

   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.

       (Please	note:  This  match  requires  kernel support that might not be
       available in official Linux kernel sources or Debians  packaged	Linux
       kernel  sources.   And  if  support for this match is available for the
       specific Linux kernel source version, that support might not be enabled
       in the current Linux kernel binary.)

       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.

   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.

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

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

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


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

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

	      In Kernels up to 2.6.10 you  can	add  several  --to-destination
	      options.	For those kernels, if you specify more than one desti
	      nation address, either via an address range  or  multiple  --to-
	      destination  options, a simple round-robin (one after another in
	      cycle) load  balancing  takes  place  between  these  addresses.
	      Later  Kernels  (>= 2.6.11-rc1) dont 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.

   IPV4OPTSSTRIP
       Strip all the IP options from a packet.

       (Please note: This target requires kernel support  that	might  not  be
       available  in  official Linux kernel sources or Debians packaged Linux
       kernel sources.	And if support for this target is  available  for  the
       specific Linux kernel source version, that support might not be enabled
       in the current Linux kernel binary.)

       The target doesnt 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 value
	      Set nfmark value

       --and-mark value
	      Binary AND the nfmark with value

       --or-mark value
	      Binary OR  the nfmark with value

   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 wont accept your mail otherwise).

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

   ROUTE
       This is used to explicitly override the core  network  stacks  routing
       decision.

       (Please	note:  This  target  requires kernel support that might not be
       available in official Linux kernel sources or Debians  packaged	Linux
       kernel  sources.   And  if support for this target is available for the
       specific Linux kernel source version, that support might not be enabled
       in the current Linux kernel binary.)

       mangle table.

       --oif ifname
	      Route the packet through ifname network interface

       --iif ifname
	      Change the packets incoming interface to ifname

       --gw IP_address
	      Route the packet via this gateway

       --continue
	      Behave like a non-terminating target and continue traversing the
	      rules.  Not valid in combination with --iif or --tee

       --tee  Make a copy of the packet, and route that copy to the given des
	      tination.  For the original, uncopied packet, behave like a non-
	      terminating target and continue traversing the rules.  Not valid
	      in combination with --iif or --continue

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

       --nodst
	      Dont use the destination-ip in the calculations when  selecting
	      the new source-ip

   SECMARK
       This  is used to set the security mark value associated with the packet
       for use by security subsystems such as SELinux.	It is  only  valid  in
       the mangle table.

       --selctx security_context

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

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

       --del-set setname flag[,flag...]
	      delete the address(es)/port(s) of  the  packet  from  the  sets,
	      where flags are src and/or dst 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)
	      dont 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.

       (Please note: This target requires kernel support  that	might  not  be
       available  in  official Linux kernel sources or Debians packaged Linux
       kernel sources.	And if support for this target is  available  for  the
       specific Linux kernel source version, that support might not be enabled
       in the current Linux kernel binary.)

       This  offers  similar   functionality   to   LaBrea    but doesnt 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 interfaces 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
       configuration 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 its 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.

       Dont  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).

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?  Whats 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 .



				 Mar 09, 2002			   IPTABLES(8)




Yals.net is © 1999-2009 Crescendo Communications
Sharing tech info on the web for more than a decade!
This page was generated Thu Apr 30 17:05:31 2009