Provided by: iptables_1.4.12-1ubuntu4_i386 bug

NAME

       iptables -- administration tool for IPv4 packet filtering and NAT

SYNOPSIS

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

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

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

       iptables [-t table] -D chain rulenum

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

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

       iptables [-t table] -N chain

       iptables [-t table] -X [chain]

       iptables [-t table] -P chain target

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

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

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

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

DESCRIPTION

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

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

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

OPTIONS

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

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

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

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

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

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

       -R, --replace chain rulenum rule-specification
              Replace  a  rule  in  the  selected chain.  If the source and/or
              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

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

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

       -Z, --zero [chain [rulenum]]
              Zero the packet and byte counters in all  chains,  or  only  the
              given  chain,  or only the given rule in a chain. It is legal to
              specify the -L,  --list  (list)  option  as  well,  to  see  the
              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, udplite,  icmp,  esp,
              ah,  sctp  or  the special keyword "all", or it can be a numeric
              value, representing one of these protocols or a  different  one.
              A  protocol  name  from  /etc/protocols  is also allowed.  A "!"
              argument before the protocol inverts the test.  The number  zero
              is equivalent to all. "all" will match with all protocols and is
              taken as default when this option is omitted.

       [!] -s, --source address[/mask][,...]
              Source specification. Address can be either a  network  name,  a
              hostname,  a  network  IP  address  (with  /mask), or a plain IP
              address. Hostnames will be resolved once only, before  the  rule
              is  submitted  to  the  kernel.  Please note that specifying any
              name to be resolved with a remote query such as DNS is a  really
              bad  idea.   The  mask  can  be either a network mask or a plain
              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.  Multiple addresses can be specified, but this will
              expand  to  multiple  rules (when adding with -A), or will cause
              multiple rules to be deleted (with -D).

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

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

       -g, --goto chain
              This  specifies  that  the  processing should continue in a user
              specified chain.  Unlike  the  --jump  option  return  will  not
              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 packets bytes
              This enables the administrator to initialize the packet and byte
              counters of a rule (during INSERT, APPEND, REPLACE operations).

   OTHER OPTIONS
       The following additional options can be specified:

       -v, --verbose
              Verbose output.  This option makes the  list  command  show  the
              interface  name,  the  rule options (if any), and the TOS masks.
              The packet and byte counters are also listed,  with  the  suffix
              'K',   'M'   or   'G'  for  1000,  1,000,000  and  1,000,000,000
              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. -v  may
              be specified multiple times to possibly emit more detailed debug
              statements.

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

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

       The following address types are possible:

       UNSPEC an unspecified address (i.e. 0.0.0.0)

       UNICAST
              an unicast address

       LOCAL  a local address

       BROADCAST
              a broadcast address

       ANYCAST
              an anycast packet

       MULTICAST
              a multicast address

       BLACKHOLE
              a blackhole address

       UNREACHABLE
              an unreachable address

       PROHIBIT
              a prohibited address

       THROW  FIXME

       NAT    FIXME

       XRESOLVE

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

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

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

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

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

       [!] --ahspi spi[:spi]

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

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

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

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

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

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

       Example:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       --comment comment

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

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

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

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

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

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

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

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

       --connbytes-mode {packets|bytes|avgpkt}
              whether  to  check  the  amount  of  packets,  number  of  bytes
              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-upto n
              Match if the number of existing connections is below or equal n.

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

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

       --connlimit-saddr
              Apply the limit onto the source group.

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

       Examples:

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

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

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

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

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

   connmark
       This  module  matches  the  netfilter  mark  field  associated  with  a
       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
       the connection tracking state for this packet/connection.

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

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

       [!] --ctorigsrc address[/mask]

       [!] --ctorigdst address[/mask]

       [!] --ctreplsrc address[/mask]

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

       [!] --ctorigsrcport port[:port]

       [!] --ctorigdstport port[:port]

       [!] --ctreplsrcport port[:port]

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

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

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

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

       States for --ctstate:

       INVALID
              meaning that the packet is associated with no known connection

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

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

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

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

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

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

       Statuses for --ctstatus:

       NONE   None of the below.

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

       SEEN_REPLY
              Conntrack has seen packets in both directions.

       ASSURED
              Conntrack entry should never be early-expired.

       CONFIRMED
              Connection is confirmed: originating packet has left box.

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

       Example:

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

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

       Available since Linux 2.6.36.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       Examples:

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

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

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

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

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

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

              Same rules apply for other conntrack-helpers.

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

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

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

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

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

   ipvs
       Match IPVS connection properties.

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

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

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

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

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

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

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

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

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

       [!] --length length[:length]

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

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

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

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

   mac
       [!] --mac-source address
              Match  source  MAC  address.    It   must   be   of   the   form
              XX:XX:XX:XX:XX:XX.   Note that this only makes sense for packets
              coming from an Ethernet  device  and  entering  the  PREROUTING,
              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,--sports port[,port|,port:port]...
              Match if the source port is one of the given  ports.   The  flag
              --sports  is  a convenient alias for this option. Multiple ports
              or port ranges are separated using a comma, and a port range  is
              specified  using  a  colon.  53,1024:65535 would therefore match
              ports 53 and all from 1024 through 65535.

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

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

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

       [!] --genre string
              Match  an  operating   system   genre   by   using   a   passive
              fingerprinting.

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

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

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

       o   2 - Do not compare the TTL at all.

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

       o   0 - Log all matched or unknown signatures

       o   1 - Log only the first one

       o   2 - Log all known matched signatures

       You may find something like this in syslog:

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

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

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

       To remove them again,

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

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

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

       [!] --uid-owner username

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

       [!] --gid-owner groupname

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

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

   physdev
       This  module  matches  on  the  bridge  port  input  and output devices
       enslaved  to  a  bridge  device.  This  module  is  a   part   of   the
       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 if it is yet unknown
              what the output device will be, then the packet won't match this
              option, unless '!' is used.

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

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

       [!] --physdev-is-bridged
              Matches  if  the  packet  is  being bridged and therefore is not
              being  routed.   This  is  only  useful  in  the   FORWARD   and
              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. --pol none
              cannot be combined with --strict.

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

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

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

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

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

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

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

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

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

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

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

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

       For a better understanding of the  available  options,  these  are  all
       possible combinations:

       o   rateest operator rateest-bps

       o   rateest operator rateest-pps

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

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

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

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

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

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

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

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

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

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

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

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

       --rateest1 name

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

       --rateest-bps [value]

       --rateest-pps [value]

       --rateest-bps1 [value]

       --rateest-bps2 [value]

       --rateest-pps1 [value]

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

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

       # Estimate outgoing rates

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

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

       # Mark based on available bandwidth

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       --reap reap
              This option can only be  used  in  conjunction  with  --seconds.
              When  used,  this  will cause entries older then 'seconds' to be
              purged.

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

       --rttl This option may only be used in conjunction with one of --rcheck
              or --update. When used, this  will  narrow  the  match  to  only
              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.

       Examples:

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

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

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

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

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

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

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

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

       The module itself accepts parameters, defaults shown:

       ip_list_tot=100
              Number of addresses remembered per table.

       ip_pkt_list_tot=20
              Number of packets per address remembered.

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

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

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

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

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

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

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

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

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

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

       Examples:

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

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

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

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

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

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

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

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

       Use  of  -m  set  requires  that  ipset  kernel support is provided. As
       standard kernels do not ship this  currently,  the  ipset  or  Xtables-
       addons package needs to be installed.

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

       --transparent
              Ignore non-transparent sockets.

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

       [!] --state state
              Where  state  is a comma separated list of the connection states
              to match.  Possible states are INVALID meaning that  the  packet
              could  not  be identified for some reason which includes running
              out of memory and ICMP errors  which  don't  correspond  to  any
              known   connection,  ESTABLISHED  meaning  that  the  packet  is
              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.  UNTRACKED meaning that the packet is not tracked at all,
              which happens if you use the NOTRACK target in raw table.

   statistic
       This  module  matches  packets  based  on some statistic condition.  It
       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 for a packet to be randomly matched. It only
              works with the random mode. p must be within 0.0  and  1.0.  The
              supported granularity is in 1/2147483648th increments.

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

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

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

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

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

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

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

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

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

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

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

       [!] --tcp-flags mask comp
              Match when the TCP flags are as specified.  The  first  argument
              mask  is  the flags which we should examine, written as a comma-
              separated list,  and  the  second  argument  comp  is  a  comma-
              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. All times are
       interpreted as UTC by default.

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

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

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

       --timestart hh:mm[:ss]

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

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

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

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

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

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

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

       EXAMPLES. To match on weekends, use:

              -m time --weekdays Sa,Su

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

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

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

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

       During lunch hour:

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

       The fourth Friday in the month:

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

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

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

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

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

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

       --ttl-eq ttl
              Matches the given TTL value.

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

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

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

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

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

              value := range | value "," range

              range := number | number ":" number

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

           location := number | location operator number

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

       The operators &, <<, >> and && mean the same as in C.  The = is  really
       a  set  membership operator and the value syntax describes a set. The @
       operator is what allows moving to the  next  header  and  is  described
       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,--sport port[:port]
              Source port or port range specification.  See the description of
              the --source-port option of the TCP extension for details.

       [!] --destination-port,--dport port[:port]
              Destination   port   or   port  range  specification.   See  the
              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.

TARGET EXTENSIONS

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

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

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

       Example:

              iptables -N AUDIT_DROP

              iptables -A AUDIT_DROP -j AUDIT --type drop

              iptables -A AUDIT_DROP -j DROP

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

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

   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. The values are always
              interpreted as hexadecimal even if no 0x prefix is given.

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

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

       --hashmode mode
              Specify  the  hashing  mode.   Has  to  be  one   of   sourceip,
              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.
       The mark is 32 bits wide.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       --notrack
              Disables connection tracking for this packet.

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

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

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

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

   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).

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

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

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

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

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

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

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

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

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

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

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

   LOG
       Turn on kernel logging of matching packets.  When this  option  is  set
       for  a  rule,  the  Linux  kernel  will  print  some information on all
       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 target is used to set the Netfilter mark value associated with the
       packet.  It can, for example, be used in conjunction with routing based
       on fwmark (needs iproute2). If you plan on doing so, note that the mark
       needs  to  be set in the PREROUTING chain of the mangle table to affect
       routing.  The mark field is 32 bits wide.

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

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

       The following mnemonics are available:

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

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

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

   MASQUERADE
       This  target  is only valid in the nat table, in the POSTROUTING chain.
       It  should  only  be  used  with  dynamically  assigned   IP   (dialup)
       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).

       --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  (0  -  2^16-1)  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.  It can only  be  used  with  Kernel  versions
       2.6.14  or later, since it requires the nfnetlink_queue kernel support.
       The queue-balance option was added in  Linux  2.6.31,  queue-bypass  in
       2.6.39.

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

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

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

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

       It can only be used in the raw table.

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

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

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

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

   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).

       --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.

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

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

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

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

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

       --selctx security_context

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

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

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

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

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

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

       Use of -j SET requires  that  ipset  kernel  support  is  provided.  As
       standard  kernels  do  not  ship  this currently, the ipset or Xtables-
       addons package needs to be installed.

   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 occur.

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

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

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

   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  for  IPv4  or  60  for  IPv6,
       respectively).   Of  course, it can only be used in conjunction with -p
       tcp.

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

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

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

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

       Workaround: activate this option  and  add  a  rule  to  your  firewall
       configuration like:

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

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

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

       These options are mutually exclusive.

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

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

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

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

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

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

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

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

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

       The following mnemonics are available:

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

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

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

       NOTE: In Linux kernels up to and including 2.6.38, with  the  exception
       of  longterm  releases  2.6.32.42  (or later) and 2.6.33.15 (or later),
       there is a bug whereby IPv6 TOS mangling does not behave as  documented
       and  differs from the IPv4 version. The TOS mask indicates the bits one
       wants to zero out, so it needs to be inverted before applying it to the
       original  TOS  field.  However,  the  aformentioned  kernels  forgo the
       inversion which breaks --set-tos and its mnemonics.

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

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

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

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

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

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

   TTL
       This  is  used  to  modify  the  IPv4  TTL header field.  The TTL field
       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.  This  target  is  only
       valid in mangle table.

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

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

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

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

   ULOG
       This target provides userspace logging of matching packets.  When  this
       target  is  set for a rule, the Linux kernel will multicast this packet
       through a netlink socket. One or  more  userspace  processes  may  then
       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).

DIAGNOSTICS

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

BUGS

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

COMPATIBILITY WITH IPCHAINS

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

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

       The  various  forms  of NAT have been separated out; iptables is a pure
       packet filter when using the  default  `filter'  table,  with  optional
       extension modules.  This should simplify much of the previous confusion
       over the combination of  IP  masquerading  and  packet  filtering  seen
       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>.

VERSION

       This manual page applies to iptables @PACKAGE_VERSION@.