Provided by: iptables_1.4.0-4ubuntu2_i386 bug

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
       table.

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
       target, which can be the name of a user-defined chain  or  one  of  the
       special 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
       modules are present).

       -t, --table table
              This option  specifies  the  packet  matching  table  which  the
              command  should  operate  on.   If the kernel is configured with
              automatic module loading, an attempt will be made  to  load  the
              appropriate 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
                  routing), 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
                  supported: INPUT (for packets coming into the  box  itself),
                  FORWARD (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 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
              combination.

       -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
              destination 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

       -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
              counters 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
              section 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
              specified protocol can be one of tcp, udp, icmp, or all,  or  it
              can be a numeric value, representing one of these protocols or a
              different 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
              continue  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
              fragments  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
              multipliers  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
              applicable).

       -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
       modules in one line, and you can use the -h or --help options after the
       module has been specified to receive help specific to that module.

       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
              blackhole address UNREACHABLE an unreachable address PROHIBIT  a
              prohibited 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
              privatized IP block"

   connbytes
       Match  by  how  many  bytes  or packets a connection (or one of the two
       flows constituting the connection)  have  transferred  so  far,  or  by
       average 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 transferred  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
              transferred  or  the  average  size  (in  bytes)  of all packets
              received so far. Note that when "both"  is  used  together  with
              "avgpkt",  and data is going (mainly) only in one direction (for
              example HTTP), the average packet size will be about half of the
              actual data packets.

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

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

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

       --connlimit-mask prefix_length
              Group  hosts  using  the prefix length. For IPv4, this must be a
              number between (including) 0 and 32. For  IPv6,  between  0  and
              128.

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

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

   connmark
       This  module  matches  the  netfilter  mark  field  associated  with  a
       connection (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
       supporting 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
              packets  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 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.  SNAT A virtual state, matching
              if   the   original   source  address  differs  from  the  reply
              destination.  DNAT A virtual state,  matching  if  the  original
              destination differs from the reply source.

       --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 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
       (destip,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,srcip,dstport,srcport
              A comma-separated list of objects to take into consideration

       --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 milliseconds do hash entries expire

       --hashlimit-htable-gcinterval num
              How many milliseconds 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 can be used  if  ‘--protocol  icmp’  is  specified.   It
       provides 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.

   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,
              FORWARD 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
              comparison).

   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.

       --sid-owner sessionid
              Matches if the packet was created by  a  process  in  the  given
              session 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
              compiled 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
       infrastructure  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
              interface which begins with this name will match. Note  that  in
              the  nat and mangle OUTPUT chains one cannot match on the bridge
              output 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 ’!’ 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
              decapsulation 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.

   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
              disallowing others access to your site by sending bogus  packets
              to you.

       --name name
              Name of the recent list to be used.  DEFAULT used if none given.

       --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
       information 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

   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
              associated  with  a  connection  which  has seen packets 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  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
       supports 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  can  be  used  if  ‘--protocol tcp’ is specified. It
       provides 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-
              separated  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
              connection initiation; for example, blocking such packets coming
              in  an  interface  will  prevent  incoming  TCP connections, but
              outgoing TCP connections will be unaffected.  It  is  equivalent
              to  --tcp-flags  SYN,RST,ACK,FIN  SYN.  If the "!" flag precedes
              the "--syn", the sense of the option is inverted.

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

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

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

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

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

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

              Only match during the given time, which must be in ISO 8601  "T"
              notation.   The  possible  time  range is 1970-01-01T00:00:00 to
              2038-01-19T04:17:07.

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

       --timestart hh:mm[:ss]

       --timestop hh:mm[:ss]

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

       [!] --monthday day[,day...]

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

       [!] --weekdays day[,day...]

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

       --utc

              Interpret  the  times   given   for   --datestart,   --datestop,
              --timestart and --timestop to be UTC.

       --localtz

              Interpret   the   times   given   for  --datestart,  --datestop,
              --timestart and --timestop to be local kernel time. (Default)

       EXAMPLES. To match on weekends, use:

              -m time --weekdays Sa,Su

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

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

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

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

       During lunch hour:

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

       The fourth Friday in the month:

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

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

   tos
       This module matches the 8 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  tests  whether quantities of up to 4 bytes extracted from a packet
       have specified values. The specification of what to extract is  general
       enough to find data at given offsets from tcp headers or payloads.

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

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

              value := range | value "," range

              range := number | number ":" number

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

           location := number | location operator number

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

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

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

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

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

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

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

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

              B and C are unsigned 32 bit integers, initially zero

       The instructions are:

              number B = number;

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

              &number C = C & number

              << number C = C << number

              >> number C = C >> number

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

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

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

       Example:

              match IP packets with total length >= 256

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

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

              read bytes 0-3

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

       Example: (more realistic, hence more complicated)

              match ICMP packets with icmp type 0

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

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

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

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

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

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

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

       Example:

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

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

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

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

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

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

   udp
       These  extensions  can  be  used  if ‘--protocol udp’ is specified.  It
       provides 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
              description  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.

   ipv4options (not supported, see Patch-O-Matic)
       Match on  IPv4  header  options  like  source  routing,  record  route,
       timestamp 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.

   set (not supported, see Patch-O-Matic)
       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.

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
       classify 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
              multicast 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
              specified 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
       unlabeled).  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
              connection  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
       OUTPUT 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
              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 the destination  port
              will  never be modified. If no IP address is specified then only
              the destination 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
              destination address, either via an  address  range  or  multiple
              --to-destination   options,  a  simple  round-robin  (one  after
              another in cycle)  load  balancing  takes  place  between  these
              addresses.  Later Kernels (>= 2.6.11-rc1) don’t have the ability
              to NAT to multiple ranges anymore.

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

   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.

   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
       matching 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
       target",  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)
       connections:  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 anyway).  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.

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

   MIRROR
       This is an experimental demonstration target which inverts  the  source
       and destination fields in the IP header and retransmits the packet.  It
       is only valid in the INPUT, FORWARD and PREROUTING  chains,  and  user-
       defined  chains which are only called from those chains.  Note that the
       outgoing  packets  are  NOT  seen  by  any  packet  filtering   chains,
       connection 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
              constructed in the following way: All ’one’ bits in the mask are
              filled in from the new ‘address’.  All bits that are zero in the
              mask are filled in from the original address.

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

       --nflog-group nlgroup
              The  netlink  group  (1  -  2^32-1)  to  which packets are (only
              applicable for nfnetlink_log). The default value is 0.

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

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

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

   NFQUEUE
       This  target  is an extension of the QUEUE target. As opposed to QUEUE,
       it allows you to put a packet into any specific  queue,  identified  by
       its 16-bit queue number.

       --queue-num value
              This  specifies the QUEUE number to use. Valid 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
       OUTPUT 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.

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

   REJECT
       This  is  used  to send back an error packet in response to the matched
       packet: otherwise it is equivalent to  DROP  so  it  is  a  terminating
       TARGET, 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-
              unreachable  is  the default).  The option tcp-reset can be used
              on rules which only match the TCP protocol: this  causes  a  TCP
              RST  packet to be sent back.  This is mainly useful for blocking
              ident (113/tcp) probes which frequently occur when sending  mail
              to broken mail hosts (which won’t accept your mail otherwise).

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

   SAME
       Similar  to SNAT/DNAT depending on chain: it takes a range of addresses
       (‘--to   1.2.3.4-1.2.3.7’)   and    gives    a    client    the    same
       source-/destination-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

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

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

       --selctx security_context

   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
              alteration will

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

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

   TCPMSS
       This target allows to alter the  MSS  value  of  TCP  SYN  packets,  to
       control  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
       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  marks packes so that the kernel will log every rule which
       match the packets as those traverse the  tables,  chains,  rules.  (The
       ipt_LOG  module  is  required  for the logging.) The packets are logged
       with the  string  prefix:  "TRACE:  tablename:chainname:type:rulenum  "
       where  type can be "rule" for plain rule, "return" for implicit rule at
       the end of a user defined chain and "policy"  for  the  policy  of  the
       built in chains.
       It can only be used in the raw table.

   TTL
       This  is  used  to  modify  the  IPv4  TTL header field.  The TTL field
       determines 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
       dangerous,
              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
       subscribe 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
              characters 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).

   IPV4OPTSSTRIP (not supported, see Patch-O-Matic)
       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

   SET (not supported, see Patch-O-Matic)
       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.

   TARPIT (not supported, see Patch-O-Matic)
       Captures and  holds  incoming  TCP  connections  using  no  local  per-
       connection   resources.   Connections  are  accepted,  but  immediately
       switched to the persist state (0 byte window), in which the remote side
       stops sending 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.hackbusters.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
              unnecessarily  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

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
       previous confusion over the combination of IP masquerading  and  packet
       filtering  seen  previously.   So  the  following  options  are handled
       differently:
        -j MASQ
        -M -S
        -M -L
       There are several other changes in iptables.

SEE ALSO

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

       The packet-filtering-HOWTO details iptables usage for packet filtering,
       the NAT-HOWTO details NAT, the netfilter-extensions-HOWTO  details  the
       extensions   that  are  not  in  the  standard  distribution,  and  the
       netfilter-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
       everywhere.

       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>.

                                 Mar 09, 2002                      IPTABLES(8)