Provided by: iptables_1.4.12-1ubuntu4_i386 bug

NAME

       ip6tables -- IPv6 packet filter administration

SYNOPSIS

       ip6tables [-t table] {-A|-C|-D} chain rule-specification [options...]

       ip6tables [-t table] -I chain [rulenum] rule-specification [options...]

       ip6tables [-t table] -R chain rulenum rule-specification [options...]

       ip6tables [-t table] -D chain rulenum [options...]

       ip6tables [-t table] -S [chain [rulenum]]

       ip6tables [-t table] {-F|-L|-Z} [chain [rulenum]] [options...]

       ip6tables [-t table] -N chain

       ip6tables [-t table] -X [chain]

       ip6tables [-t table] -P chain target [options...]

       ip6tables [-t table] -E old-chain-name new-chain-name

DESCRIPTION

       Ip6tables  is  used to set up, maintain, and inspect the tables of IPv6
       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).

              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  ip6tables  can  be  divided  into
       several different groups.

   COMMANDS
       These options specify the specific action to perform.  Only one of them
       can be specified on the command line unless otherwise specified  below.
       For  all the long versions of the command and option names, you need to
       use only enough letters to ensure that ip6tables 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 ip6tables command, it
              applies to the specified table (filter is the default).

              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
               ip6tables -L -v

       -S, --list-rules [chain]
              Print all rules in the selected chain.  If no chain is selected,
              all chains are printed like  ip6tables-save.  Like  every  other
              ip6tables  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.

       -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.

       -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, icmpv6, esp,
              mh 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.   But  IPv6
              extension   headers   except  esp  are  not  allowed.   esp  and
              ipv6-nonext can be used with Kernel version 2.6.11 or later.   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 be a hostname, a
              network IP address (with /mask), or a plain IP  address.   Names
              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.
              (Resolving network names is not supported at  this  time.)   The
              mask is a plain number, specifying the number of 1's at the left
              side of the network mask.  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.

       -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

       ip6tables  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.

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

       [!] --ahspi spi[:spi]
              Matches SPI.

       [!] --ahlen length
              Total length of this header in octets.

       --ahres
              Matches if the reserved field is filled with zero.

   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.

   dst
       This module matches the parameters in Destination Options header

       [!] --dst-len length
              Total length of this header in octets.

       --dst-opts type[:length][,type[:length]...]
              numeric type of option and the length  of  the  option  data  in
              octets.

   esp
       This module matches the SPIs in ESP header of IPsec packets.

       [!] --espspi spi[:spi]

   eui64
       This  module matches the EUI-64 part of a stateless autoconfigured IPv6
       address.  It compares the EUI-64 derived from the source MAC address in
       Ethernet  frame  with the lower 64 bits of the IPv6 source address. But
       "Universal/Local" bit is not compared. This module doesn't match  other
       link  layer  frame,  and  is  only  valid  in the PREROUTING, INPUT and
       FORWARD chains.

   frag
       This module matches the parameters in Fragment header.

       [!] --fragid id[:id]
              Matches the given Identification or range of it.

       [!] --fraglen length
              This option cannot be used with kernel version 2.6.10 or  later.
              The  length of Fragment header is static and this option doesn't
              make sense.

       --fragres
              Matches if the reserved fields are filled with zero.

       --fragfirst
              Matches on the first fragment.

       --fragmore
              Matches if there are more fragments.

       --fraglast
              Matches if this is the last fragment.

   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

   hbh
       This module matches the parameters in Hop-by-Hop Options header

       [!] --hbh-len length
              Total length of this header in octets.

       --hbh-opts type[:length][,type[:length]...]
              numeric  type  of  option  and  the length of the option data in
              octets.

   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.

   hl
       This module matches the Hop Limit field in the IPv6 header.

       [!] --hl-eq value
              Matches if Hop Limit equals value.

       --hl-lt value
              Matches if Hop Limit is less than value.

       --hl-gt value
              Matches if Hop Limit is greater than value.

   icmp6
       This extension can be used if  `--protocol  ipv6-icmp'  or  `--protocol
       icmpv6' is specified. It provides the following option:

       [!] --icmpv6-type type[/code]|typename
              This  allows  specification  of  the ICMPv6 type, which can be a
              numeric ICMPv6 type, type and code, or one of  the  ICMPv6  type
              names shown by the command
               ip6tables -p ipv6-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.

   ipv6header
       This module matches IPv6 extension headers and/or upper layer header.

       --soft Matches if the packet includes any of the headers specified with
              --header.

       [!] --header header[,header...]
              Matches the packet which EXACTLY includes all specified headers.
              The  headers  encapsulated  with  ESP  header  are out of scope.
              Possible header types can be:

       hop|hop-by-hop
              Hop-by-Hop Options header

       dst    Destination Options header

       route  Routing header

       frag   Fragment header

       auth   Authentication header

       esp    Encapsulating Security Payload header

       none   No Next header which matches 59 in the 'Next  Header  field'  of
              IPv6 header or any IPv6 extension headers

       proto  which  matches  any upper layer protocol header. A protocol name
              from /etc/protocols and numeric value also allowed.  The  number
              255 is equivalent to proto.

   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).

   mh
       This extension is loaded if `--protocol ipv6-mh' or `--protocol mh'  is
       specified. It provides the following option:

       [!] --mh-type type[:type]
              This allows specification of the Mobility Header(MH) type, which
              can be a numeric MH type, type or one of the MH type names shown
              by the command
               ip6tables -p ipv6-mh -h

   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.

   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

   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.

   rt
       Match on IPv6 routing header

       [!] --rt-type type
              Match the type (numeric).

       [!] --rt-segsleft num[:num]
              Match the `segments left' field (range).

       [!] --rt-len length
              Match the length of this header.

       --rt-0-res
              Match the reserved field, too (type=0)

       --rt-0-addrs addr[,addr...]
              Match type=0 addresses (list).

       --rt-0-not-strict
              List of type=0 addresses is not a strict list.

   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.

   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.

TARGET EXTENSIONS

       ip6tables 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.

   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.

   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.

   HL
       This  is  used  to  modify  the Hop Limit field in IPv6 header. The Hop
       Limit field is similar to what is known as TTL value in IPv4.   Setting
       or  incrementing the Hop Limit 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!

       --hl-set value
              Set the Hop Limit to `value'.

       --hl-dec value
              Decrement the Hop Limit `value' times.

       --hl-inc value
              Increment the Hop Limit `value' times.

   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 IPv6 IPv6-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 IPv6 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.)

   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.

   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    icmp6-no-route,   no-route,
              icmp6-adm-prohibited,  adm-prohibited,   icmp6-addr-unreachable,
              addr-unreach,   icmp6-port-unreachable   or  port-unreach  which
              return the appropriate ICMPv6 error message (port-unreach is the
              default).  Finally,  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).
              tcp-reset can only be used with kernel versions 2.6.14 or later.

   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.

   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.

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...  the  counters  are not reliable on
       sparc64.

COMPATIBILITY WITH IPCHAINS

       This ip6tables 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.   There  are  several  other  changes in
       ip6tables.

SEE ALSO

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

       The packet-filtering-HOWTO details iptables usage for packet filtering,
       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  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 TTL match+target and libipulog.

       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.

       ip6tables  man  page created by Andras Kis-Szabo, based on iptables man
       page written by Herve Eychenne <rv@wallfire.org>.

VERSION

       This manual page applies to ip6tables @PACKAGE_VERSION@.