*BASH User Commands Ubuntu 10.04.4 LTS Server coreutils
GNU/Linux
IP6TABLES(8)                    iptables 1.4.4                    IP6TABLES(8)



NAME
       ip6tables - IPv6 packet filter administration

SYNOPSIS
       ip6tables [-t table] {-A|-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] [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  ta-
       ble.

TARGETS
       A  firewall  rule specifies criteria for a packet and a target.  If the
       packet does not match, the next rule in the chain is the  examined;  if
       it does match, then the next rule is specified by the value of the tar-
       get, which can be the name of a user-defined chain or one of  the  spe-
       cial values ACCEPT, DROP, QUEUE or RETURN.

       ACCEPT  means to let the packet through.  DROP means to drop the packet
       on the floor.  QUEUE means to pass the packet to userspace.   (How  the
       packet can be received by a userspace process differs by the particular
       queue handler.  2.4.x and  2.6.x  kernels  up  to  2.6.13  include  the
       ip_queue  queue handler.  Kernels 2.6.14 and later additionally include
       the nfnetlink_queue queue handler.  Packets with a target of QUEUE will
       be  sent  to queue number '0' in this case. Please also see the NFQUEUE
       target as described  later  in  this  man  page.)   RETURN  means  stop
       traversing  this  chain  and  resume  at  the next rule in the previous
       (calling) chain.  If the end of a built-in chain is reached or  a  rule
       in a built-in chain with target RETURN is matched, the target specified
       by the chain policy determines the fate of the packet.

TABLES
       There are currently three independent tables (which tables are  present
       at  any time depends on the kernel configuration options and which mod-
       ules are present).

       -t, --table table
              This option specifies the packet matching table which  the  com-
              mand  should operate on.  If the kernel is configured with auto-
              matic module loading, an attempt will be made to load the appro-
              priate module for that table if it is not already there.

              The tables are as follows:

              filter:
                  This  is  the  default table (if no -t option is passed). It
                  contains the built-in chains INPUT (for packets destined  to
                  local  sockets),  FORWARD  (for packets being routed through
                  the box), and OUTPUT (for locally-generated packets).

              mangle:
                  This table is used for specialized packet alteration.  Until
                  kernel  2.4.17  it  had two built-in chains: PREROUTING (for
                  altering incoming packets before routing)  and  OUTPUT  (for
                  altering  locally-generated  packets before routing).  Since
                  kernel 2.4.18, three other built-in  chains  are  also  sup-
                  ported: INPUT (for packets coming into the box itself), FOR-
                  WARD (for altering packets being routed  through  the  box),
                  and  POSTROUTING  (for altering packets as they are about to
                  go out).

              raw:
                  This table is used mainly for  configuring  exemptions  from
                  connection  tracking in combination with the NOTRACK target.
                  It registers at the netfilter hooks with higher priority and
                  is  thus called before ip_conntrack, or any other IP tables.
                  It provides the following built-in chains:  PREROUTING  (for
                  packets  arriving  via  any  network  interface) OUTPUT (for
                  packets generated by local processes)

OPTIONS
       The options that are recognized by ip6tables can be divided  into  sev-
       eral 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 combina-
              tion.

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

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

       -R, --replace chain rulenum rule-specification
              Replace a rule in the selected chain.  If the source and/or des-
              tination  names  resolve to multiple addresses, the command will
              fail.  Rules are numbered starting at 1.

       -L, --list [chain]
              List all rules in the selected chain.  If no chain is  selected,
              all  chains  are  listed. 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]
              Zero the packet and byte counters in all chains.  It is legal to
              specify  the  -L, --list (list) option as well, to see the coun-
              ters immediately before they are cleared. (See above.)

       -N, --new-chain chain
              Create a new user-defined chain by the given name.   There  must
              be no target of that name already.

       -X, --delete-chain [chain]
              Delete the optional user-defined chain specified.  There must be
              no references to the chain.  If there are, you  must  delete  or
              replace  the  referring  rules  before the chain can be deleted.
              The chain must be empty, i.e. not  contain  any  rules.   If  no
              argument  is  given, it will attempt to delete every non-builtin
              chain in the table.

       -P, --policy chain target
              Set the policy for the chain to the given target.  See the  sec-
              tion  TARGETS  for  the legal targets.  Only built-in (non-user-
              defined) chains can have  policies,  and  neither  built-in  nor
              user-defined chains can be policy targets.

       -E, --rename-chain old-chain new-chain
              Rename the user specified chain to the user supplied name.  This
              is cosmetic, and has no effect on the structure of the table.

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

       -h     Help.   Give a (currently very brief) description of the command
              syntax.

   PARAMETERS
       The following parameters make up a rule specification (as used  in  the
       add, delete, insert, replace and append commands).

       [!] -p, --protocol protocol
              The  protocol of the rule or of the packet to check.  The speci-
              fied protocol can be one of tcp, udp, udplite, icmpv6,  esp,  mh
              or  all, or it can be a numeric value, representing one of these
              protocols or a different one. A protocol name  from  /etc/proto-
              cols is also allowed.  But IPv6 extension headers except esp are
              not allowed.  esp and ipv6-nonext can be used with  Kernel  ver-
              sion  2.6.11  or  later.   A  "!"  argument  before the protocol
              inverts the test.  The number zero is equivalent to all.  Proto-
              col  all  will  match with all protocols and is taken as default
              when this option is omitted.

       [!] -s, --source address[/mask]
              Source specification.  Address can be either a hostname  (please
              note that specifying any name to be resolved with a remote query
              such as DNS is a really bad idea), a network IPv6 address  (with
              /mask),  or  a plain IPv6 address.  (the network name isn't sup-
              ported now).  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.

       [!] -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 con-
              tinue processing in this chain but instead  in  the  chain  that
              called us via --jump.

       [!] -i, --in-interface name
              Name  of  an interface via which a packet was received (only for
              packets entering the  INPUT,  FORWARD  and  PREROUTING  chains).
              When  the  "!"  argument  is used before the interface name, the
              sense is inverted.  If the interface name ends in  a  "+",  then
              any  interface  which begins with this name will match.  If this
              option is omitted, any interface name will match.

       [!] -o, --out-interface name
              Name of an interface via which a packet is going to be sent (for
              packets  entering  the  FORWARD, OUTPUT and POSTROUTING chains).
              When the "!" argument is used before  the  interface  name,  the
              sense  is  inverted.   If the interface name ends in a "+", then
              any interface which begins with this name will match.   If  this
              option is omitted, any interface name will match.

       -c, --set-counters packets bytes
              This enables the administrator to initialize the packet and byte
              counters of a rule (during INSERT, APPEND, REPLACE operations).

   OTHER OPTIONS
       The following additional options can be specified:

       -v, --verbose
              Verbose output.  This option makes the  list  command  show  the
              interface  name,  the  rule options (if any), and the TOS masks.
              The packet and byte counters are also listed,  with  the  suffix
              'K',  'M' or 'G' for 1000, 1,000,000 and 1,000,000,000 multipli-
              ers respectively (but see the -x  flag  to  change  this).   For
              appending,  insertion,  deletion  and  replacement,  this causes
              detailed information on the rule or rules to be printed.

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

       -x, --exact
              Expand  numbers.  Display the exact value of the packet and byte
              counters, instead of only the rounded number in  K's  (multiples
              of  1000)  M's (multiples of 1000K) or G's (multiples of 1000M).
              This option is only relevant for the -L command.

       --line-numbers
              When listing rules, add line numbers to the  beginning  of  each
              rule, corresponding to that rule's position in the chain.

       --modprobe=command
              When adding or inserting rules into a chain, use command to load
              any necessary modules (targets, match extensions, etc).

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

       The following are included in the base package, and most of  these  can
       be preceded by a "!" to invert the sense of the match.

   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  --clus-
              ter-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  --clus-
              ter-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  --man-
              gle-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 -s 192.168.0.0/16 -m comment --comment "A pri-
              vatized IP block"

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

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

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

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

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

       Examples:

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

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

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

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

   connmark
       This module matches the netfilter mark field associated with a  connec-
       tion (which can be set using the CONNMARK target below).

       [!] --mark value[/mask]
              Matches  packets  in connections with the given mark value (if a
              mask is specified, this is logically ANDed with the mark  before
              the comparison).

   conntrack
       This  module,  when combined with connection tracking, allows access to
       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

       [!] --ctorigdstport port

       [!] --ctreplsrcport port

       [!] --ctrepldstport port
              Match    against    original/reply    source/destination    port
              (TCP/UDP/etc.) or GRE key.

       [!] --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  other-
              wise  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.

       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.

   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 accord-
              ing 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 FOR-
       WARD 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":

       matching on source host
              "1000 packets per second for every host in 192.168.0.0/16"

       matching on source prot
              "100 packets per second for every service of 192.168.1.1"

       matching on subnet
              "10000 packets per minute for every /28 subnet in 10.0.0.0/8"

       A hash limit option (--hashlimit-upto, --hashlimit-above)  and  --hash-
       limit-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-src-
              mask 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.

   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.  Pos-
              sible 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.

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

       [!] --length length[:length]

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

       [!] --limit rate[/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, FOR-
              WARD or INPUT chains.

   mark
       This  module  matches the netfilter mark field associated with a packet
       (which can be set using the MARK target below).

       [!] --mark value[/mask]
              Matches packets with the given unsigned mark value (if a mask is
              specified, this is logically ANDed with the mask before the com-
              parison).

   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  infrastruc-
       ture that enables a transparent bridging IP firewall and is only useful
       for kernel versions above version 2.5.44.

       [!] --physdev-in name
              Name of a bridge port via which a packet is received  (only  for
              packets  entering  the INPUT, FORWARD and PREROUTING chains). If
              the interface name ends in  a  "+",  then  any  interface  which
              begins  with  this  name will match. If the packet 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 inter-
              face which begins with this name will match. Note  that  in  the
              nat and mangle OUTPUT chains one cannot match on the bridge out-
              put port, however one can in the filter  OUTPUT  chain.  If  the
              packet  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  POSTROUT-
              ING chains.

   pkttype
       This module matches the link-layer packet type.

       [!] --pkt-type {unicast|broadcast|multicast}

   policy
       This modules matches the policy used by IPsec for handling a packet.

       --dir {in|out}
              Used  to  select whether to match the policy used for decapsula-
              tion or the policy that will be used for encapsulation.   in  is
              valid  in the PREROUTING, INPUT and FORWARD chains, out is valid
              in the POSTROUTING, OUTPUT and FORWARD chains.

       --pol {none|ipsec}
              Matches if the packet is subject to IPsec processing.

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

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

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

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

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

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

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

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

   quota
       Implements  network  quotas  by  decrementing  a byte counter with each
       packet.

       --quota bytes
              The quota in bytes.

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

       --rateest1 name
              Name of the first rate estimator.

       --rateest2 name
              Name of the second rate estimator (if difference is to be calcu-
              lated).

       --rateest-delta
              Compare difference(s) to given rate(s)

       --rateest1-bps value

       --rateest2-bps value
              Compare bytes per second.

       --rateest1-pps value

       --rateest2-pps value
              Compare packets per second.

       [!] --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.

       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.

       --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  must  be  used in conjunction with --seconds. When
              used, this will remove entries with the  most  recent  timestamp
              older then --seconds since the last packet was received.

       [!] --hitcount hits
              This  option must be used in conjunction with one of --rcheck or
              --update. When used, this will narrow the match to  only  happen
              when  the  address  is in the list and packets had been received
              greater than or equal to the given value.  This  option  may  be
              used  along  with  --seconds  to  create  an even narrower match
              requiring a certain number of hits within a specific time frame.

       --rttl This option may only be used in conjunction with one of --rcheck
              or  --update. When used, this will narrow the match to only hap-
              pen when the address is in the list and the TTL of  the  current
              packet matches that of the packet which hit the --set rule. This
              may be useful if you have  problems  with  people  faking  their
              source  address in order to DoS you via this module by disallow-
              ing others access to your site by sending bogus packets to you.

       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 informa-
       tion 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

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

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

       Examples:

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

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

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

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

       [!] --state state
              Where state is a comma separated list of the  connection  states
              to  match.   Possible states are INVALID meaning that the packet
              could not be identified for some reason which  includes  running
              out  of  memory  and  ICMP  errors which don't correspond to any
              known connection, ESTABLISHED meaning that the packet is associ-
              ated  with  a  connection  which has seen packets in both direc-
              tions, NEW meaning that the packet has started a new connection,
              or  otherwise  associated  with  a connection which has not seen
              packets in both directions, and RELATED meaning that the  packet
              is starting a new connection, but is associated with an existing
              connection, such as an FTP data transfer, or an ICMP error.

   statistic
       This module matches packets based on some statistic condition.  It sup-
       ports two distinct modes settable with the --mode option.

       Supported options:

       --mode mode
              Set  the matching mode of the matching rule, supported modes are
              random and nth.

       --probability p
              Set the probability from 0 to 1 for  a  packet  to  be  randomly
              matched. It works only with the random mode.

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

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

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

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

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

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

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

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

   tcp
       These  extensions can be used if `--protocol tcp' is specified. It pro-
       vides 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-sepa-
              rated list of flags which must be set.  Flags are: SYN  ACK  FIN
              RST URG PSH ALL NONE.  Hence the command
               iptables -A FORWARD -p tcp --tcp-flags SYN,ACK,FIN,RST SYN
              will  only match packets with the SYN flag set, and the ACK, FIN
              and RST flags unset.

       [!] --syn
              Only match TCP packets with the SYN bit set and the ACK,RST  and
              FIN  bits cleared.  Such packets are used to request TCP connec-
              tion initiation; for example, blocking such packets coming in an
              interface  will  prevent  incoming TCP connections, but outgoing
              TCP  connections  will  be  unaffected.   It  is  equivalent  to
              --tcp-flags  SYN,RST,ACK,FIN  SYN.  If the "!" flag precedes the
              "--syn", the sense of the option is inverted.

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

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

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

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

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

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

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

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

       --timestart hh:mm[:ss]

       --timestop hh:mm[:ss]

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

       [!] --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.).

       --utc

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

       --localtz

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

       EXAMPLES. To match on weekends, use:

              -m time --weekdays Sa,Su

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

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

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

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

       During lunch hour:

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

       The fourth Friday in the month:

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

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

   tos
       This module matches the 8-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 call-
              ing 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 fur-
       ther 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 char-
       acters 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). Alterna-
              tively, 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  pro-
       vides 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  descrip-
              tion  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.

   CLASSIFY
       This  module  allows you to set the skb->priority value (and thus clas-
       sify the packet into a specific CBQ class).

       --set-class major:minor
              Set the major and minor  class  value.  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.

       --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  unla-
       beled).   Typically  used in conjunction with SECMARK, it is only valid
       in the mangle table.

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

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


   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  man-
       gle 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.

   LOG
       Turn on kernel logging of matching packets.  When this  option  is  set
       for  a rule, the Linux kernel will print some information on all match-
       ing packets (like most IPv6 IPv6-header  fields)  via  the  kernel  log
       (where it can be read with dmesg or syslogd(8)).  This is a "non-termi-
       nating 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.   The  target can only be used in the mangle table. It can, for
       example, be used in conjunction with routing  based  on  fwmark  (needs
       iproute2).

       --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 contin-
       ues at the next rule.

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

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

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

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

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

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

       It  can  only  be  used  with Kernel versions 2.6.14 or later, since it
       requires the nfnetlink_queue kernel support.

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

       It can only be used in the raw table.

   RATEEST
       The RATEEST target collects statistics, performs rate estimation calcu-
       lation 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 microsec-
              onds.

       --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  TAR-
       GET,  ending  rule  traversal.  This target is only valid in the INPUT,
       FORWARD and OUTPUT chains,  and  user-defined  chains  which  are  only
       called  from those chains.  The following option controls the nature of
       the error packet returned:

       --reject-with type
              The type given can be icmp6-no-route,  no-route,  icmp6-adm-pro-
              hibited,  adm-prohibited,  icmp6-addr-unreachable, addr-unreach,
              icmp6-port-unreachable or port-unreach which return  the  appro-
              priate  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  only  valid  in
       the mangle table.

       --selctx security_context

   TCPMSS
       This  target  allows to alter the MSS value of TCP SYN packets, to con-
       trol the maximum size for that connection (usually limiting it to  your
       outgoing  interface's  MTU  minus  40  for IPv4 or 60 for IPv6, respec-
       tively).  Of course, it can only be used in conjunction  with  -p  tcp.
       It is only valid in the mangle table.
       This  target  is  used to overcome criminally braindead ISPs or servers
       which block "ICMP Fragmentation Needed"  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 con-
       figuration like:

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

       --set-mss value
              Explicitly set MSS option to specified value.

       --clamp-mss-to-pmtu
              Automatically clamp MSS value to (path_MTU - 40  for  IPv4;  -60
              for IPv6).

       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.

   TOS
       This module sets the Type of Service field in the IPv4 header  (includ-
       ing  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  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. 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.)

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

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

   TRACE
       This  target  marks packes so that the kernel will log every rule which
       match the packets as those traverse the  tables,  chains,  rules.  (The
       ipt_LOG  or  ip6t_LOG  module is required for the logging.) The packets
       are  logged  with   the   string   prefix:   "TRACE:   tablename:chain-
       name: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 Neul-
       ing.

       Marc Boucher made Rusty abandon ipnatctl  by  lobbying  for  a  generic
       packet  selection  framework  in iptables, then wrote the mangle table,
       the owner match, the mark stuff, and ran around doing cool stuff every-
       where.

       James Morris wrote the TOS target, and tos match.

       Jozsef Kadlecsik wrote the REJECT target.

       Harald  Welte  wrote  the  ULOG and NFQUEUE target, the new libiptc, as
       well as 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>.



iptables 1.4.4                                                    IP6TABLES(8)