Provided by: iptables_1.4.1.1-4ubuntu3_i386 bug

NAME

       iptables - administration tool for IPv4 packet filtering and NAT

SYNOPSIS

       iptables [-t table] -[AD] chain rule-specification [options]
       iptables [-t table] -I chain [rulenum] rule-specification [options]
       iptables [-t table] -R chain rulenum rule-specification [options]
       iptables [-t table] -D chain rulenum [options]
       iptables [-t table] -[LFZ] [chain] [options]
       iptables [-t table] -N chain
       iptables [-t table] -X [chain]
       iptables [-t table] -P chain target [options]
       iptables [-t table] -E old-chain-name new-chain-name

DESCRIPTION

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

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

TARGETS

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

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

TABLES

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

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

              The tables are as follows:

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

              nat:
                  This table is consulted when a packet  that  creates  a  new
                  connection  is encountered.  It consists of three built-ins:
                  PREROUTING (for altering packets as soon as they  come  in),
                  OUTPUT   (for   altering  locally-generated  packets  before
                  routing), and POSTROUTING (for altering packets as they  are
                  about to go out).

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

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

OPTIONS

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

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

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

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

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

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

       -L, --list [chain]
              List  all rules in the selected chain.  If no chain is selected,
              all chains are listed. Like every  other  iptables  command,  it
              applies  to  the specified table (filter is the default), so NAT
              rules get listed by
               iptables -t nat -n -L
              Please note that it is often used with the -n option,  in  order
              to  avoid  long reverse DNS lookups.  It is legal to specify the
              -Z (zero) option as well, in which case  the  chain(s)  will  be
              atomically  listed  and zeroed.  The exact output is affected by
              the other arguments given. The exact rules are suppressed  until
              you use
               iptables -L -v

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

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

       -Z, --zero [chain]
              Zero the packet and byte counters in all chains.  It is legal to
              specify  the  -L,  --list  (list)  option  as  well,  to see the
              counters immediately before they are cleared. (See above.)

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

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

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

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

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

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

       -p, --protocol [!] protocol
              The protocol of the  rule  or  of  the  packet  to  check.   The
              specified  protocol  can be one of tcp, udp, icmp, or all, or it
              can be a numeric value, representing one of these protocols or a
              different  one.   A  protocol  name  from /etc/protocols is also
              allowed.  A "!" argument before the protocol inverts  the  test.
              The  number  zero is equivalent to all.  Protocol all will match
              with all protocols and is taken as default when this  option  is
              omitted.

       -s, --source [!] address[/mask]
              Source  specification.   Address can be either a network name, a
              hostname (please note that specifying any name  to  be  resolved
              with a remote query such as DNS is a really bad idea), a network
              IP address (with /mask), or a plain IP address.  The mask can be
              either  a  network mask or a plain number, specifying the number
              of 1’s at the left side of the network mask.  Thus, a mask of 24
              is  equivalent  to  255.255.255.0.   A  "!"  argument before the
              address specification inverts the sense of the address. The flag
              --src is an alias for this option.

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

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

       -g, --goto chain
              This specifies that the processing should  continue  in  a  user
              specified  chain.  Unlike  the  --jump  option  return  will not
              continue processing in this chain but instead in the chain  that
              called us via --jump.

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

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

       [!]  -f, --fragment
              This  means  that  the  rule  only  refers to second and further
              fragments of fragmented packets.  Since there is no way to  tell
              the source or destination ports of such a packet (or ICMP type),
              such a packet will not match any rules which specify them.  When
              the  "!"  argument  precedes  the  "-f" flag, the rule will only
              match head fragments, or unfragmented packets.

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

   OTHER OPTIONS
       The following additional options can be specified:

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

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

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

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

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

MATCH EXTENSIONS

       iptables can use extended packet matching modules.  These are loaded in
       two  ways:  implicitly, when -p or --protocol is specified, or with the
       -m or --match options, followed by  the  matching  module  name;  after
       these,  various  extra command line options become available, depending
       on the specific  module.   You  can  specify  multiple  extended  match
       modules in one line, and you can use the -h or --help options after the
       module has been specified to receive help specific to that module.

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

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

       The following address types are possible:

       UNSPEC an unspecified address (i.e. 0.0.0.0)

       UNICAST
              an unicast address

       LOCAL  a local address

       BROADCAST
              a broadcast address

       ANYCAST
              an anycast packet

       MULTICAST
              a multicast address

       BLACKHOLE
              a blackhole address

       UNREACHABLE
              an unreachable address

       PROHIBIT
              a prohibited address

       THROW  FIXME

       NAT    FIXME

       XRESOLVE

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

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

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

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

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

       [!] --ahspi spi[:spi]

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

       --comment comment

       Example:
              iptables  -A  INPUT  -s  192.168.0.0/16  -m comment --comment "A
              privatized IP block"

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

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

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

       The  transferred  bytes  per  connection  can  also  be  viewed through
       /proc/net/ip_conntrack and accessed via ctnetlink

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

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

       --connbytes-mode {packets|bytes|avgpkt}
              whether  to  check  the  amount  of  packets,  number  of  bytes
              transferred or the  average  size  (in  bytes)  of  all  packets
              received  so  far.  Note  that when "both" is used together with
              "avgpkt", and data is going (mainly) only in one direction  (for
              example HTTP), the average packet size will be about half of the
              actual data packets.

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

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

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

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

       Examples:

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

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

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

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

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

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

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

       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
              according numeric value.

   ecn
       This allows you to match the ECN bits of the IPv4 and TCP header.   ECN
       is  the  Explicit  Congestion  Notification  mechanism  as specified in
       RFC3168

       [!] --ecn-tcp-cwr
              This matches if the TCP ECN CWR (Congestion Window Received) bit
              is set.

       [!] --ecn-tcp-ece
              This matches if the TCP ECN ECE (ECN Echo) bit is set.

       [!] --ecn-ip-ect num
              This  matches a particular IPv4 ECT (ECN-Capable Transport). You
              have to specify a number between ‘0’ and ‘3’.

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

       [!] --espspi spi[:spi]

   hashlimit
       hashlimit uses hash buckets to express a rate limiting match (like  the
       limit  match)  for a group of connections using a single iptables rule.
       Grouping can be done per-hostgroup (source and/or destination  address)
       and/or  per-port.  It  gives  you the ability to express "N packets per
       time quantum per group":

       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
       --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.

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

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

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

              Same rules apply for other conntrack-helpers.

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

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

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

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

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

   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,
              FORWARD or INPUT chains.

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

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

   multiport
       This  module  matches  a  set of source or destination ports.  Up to 15
       ports can be specified.  A port range (port:port) counts as two  ports.
       It can only be used in conjunction with -p tcp or -p udp.

       [!] --source-ports,--sport 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,--dport 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 it is yet unknown what
              the output device will be, then  the  packet  won’t  match  this
              option, unless ’!’ is used.

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

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

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

   pkttype
       This module matches the link-layer packet type.

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

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

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

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

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

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

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

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

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

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

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

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

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

       --quota bytes
              The quota in bytes.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       Examples:

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

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

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

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

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

       echo xx.xx.xx.xx > /proc/net/ipt_recent/DEFAULT
              to Add to the DEFAULT list

       echo -xx.xx.xx.xx > /proc/net/ipt_recent/DEFAULT
              to Remove from the DEFAULT list

       echo clear > /proc/net/ipt_recent/DEFAULT
              to empty the DEFAULT list.

       The module itself accepts parameters, defaults shown:

       ip_list_tot=100
              Number of addresses remembered per table

       ip_pkt_list_tot=20
              Number of packets per address remembered

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

       ip_list_perms=0644
              Permissions for /proc/net/ipt_recent/* files

       debug=0
              Set to 1 to get lots of debugging info

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

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

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

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

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

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

       Examples:

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

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

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

   set
       This modules macthes IP sets which can be defined by ipset(8).

       [!] --set setname flag[,flag]...
              where flags are src and/or dst and there can be no more than six
              of them. Hence the command
               iptables -A FORWARD -m set --set test src,dst
              will match packets, for which (depending on the type of the set)
              the  source address or port number of the packet can be found in
              the specified set. If there is a binding belonging to the mached
              set  element  or  there  is a default binding for the given set,
              then the  rule  will  match  the  packet  only  if  additionally
              (depending  on  the  type of the set) the destination address or
              port number of the packet can be found in the set  according  to
              the binding.

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

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

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

       Supported options:

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

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

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

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

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

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

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

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

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

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

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

       [!] --source-port,--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  port:port.  If the first port is
              omitted, "0" is assumed; if the  last  is  omitted,  "65535"  is
              assumed.  If the second port greater then the first they will be
              swapped.  The flag  --sport  is  a  convenient  alias  for  this
              option.

       [!] --destination-port,--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.

       --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,
              --timestart and --timestop to be UTC.

       --localtz

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

       EXAMPLES. To match on weekends, use:

              -m time --weekdays Sa,Su

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

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

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

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

       During lunch hour:

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

       The fourth Friday in the month:

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

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

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

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

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

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

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

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

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

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

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

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

              value := range | value "," range

              range := number | number ":" number

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

           location := number | location operator number

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

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

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

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

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

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

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

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

              B and C are unsigned 32 bit integers, initially zero

       The instructions are:

              number B = number;

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

              &number C = C & number

              << number C = C << number

              >> number C = C >> number

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

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

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

       Example:

              match IP packets with total length >= 256

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

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

              read bytes 0-3

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

       Example: (more realistic, hence more complicated)

              match ICMP packets with icmp type 0

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

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

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

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

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

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

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

       Example:

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

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

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

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

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

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

   udp
       These extensions can be used if  ‘--protocol  udp’  is  specified.   It
       provides the following options:

       [!] --source-port,--sport port[:port]
              Source port or port range specification.  See the description of
              the --source-port option of the TCP extension for details.

       [!] --destination-port,--dport port[:port]
              Destination  port  or  port  range   specification.    See   the
              description   of   the  --destination-port  option  of  the  TCP
              extension for details.

   unclean
       This module takes no options, but attempts to match packets which  seem
       malformed or unusual.  This is regarded as experimental.

TARGET EXTENSIONS

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

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

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

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

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

       --hashmode mode
              Specify  the hashing mode.  Has to be one of sourceip, sourceip-
              sourceport, sourceip-sourceport-destport

       --clustermac mac
              Specify the ClusterIP MAC  address.   Has  to  be  a  link-layer
              multicast address

       --total-nodes num
              Number of total nodes within this cluster.

       --local-node num
              Local node number within this cluster.

       --hash-init rnd
              Specify the random seed used for hash initialization.

   CONNMARK
       This module sets the netfilter mark value associated with a connection.

       --set-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  only
       valid in the mangle table.

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

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

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

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

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

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

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

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

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

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

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

   LOG
       Turn  on  kernel  logging of matching packets.  When this option is set
       for a rule, the  Linux  kernel  will  print  some  information  on  all
       matching packets (like most IP header fields) via the kernel log (where
       it can be read with dmesg or syslogd(8)).  This is  a  "non-terminating
       target",  i.e.  rule  traversal  continues at the next rule.  So if you
       want to LOG the packets you refuse, use two  separate  rules  with  the
       same matching criteria, first using target LOG then DROP (or REJECT).

       --log-level level
              Level of logging (numeric or see syslog.conf(5)).

       --log-prefix prefix
              Prefix  log messages with the specified prefix; up to 29 letters
              long, and useful for distinguishing messages in the logs.

       --log-tcp-sequence
              Log TCP sequence numbers. This is a security risk if the log  is
              readable by users.

       --log-tcp-options
              Log options from the TCP packet header.

       --log-ip-options
              Log options from the IP packet header.

       --log-uid
              Log the userid of the process which generated the packet.

   MARK
       This 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.)

   MASQUERADE
       This  target  is only valid in the nat table, in the POSTROUTING chain.
       It  should  only  be  used  with  dynamically  assigned   IP   (dialup)
       connections:  if  you have a static IP address, you should use the SNAT
       target.  Masquerading is equivalent to specifying a mapping to  the  IP
       address  of  the  interface  the  packet is going out, but also has the
       effect that connections are forgotten when  the  interface  goes  down.
       This  is  the correct behavior when the next dialup is unlikely to have
       the same interface address (and hence any established  connections  are
       lost anyway).  It takes one option:

       --to-ports port[-port]
              This  specifies  a  range of source ports to use, overriding the
              default SNAT source port-selection heuristics (see above).  This
              is only valid if the rule also specifies -p tcp or -p udp.

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

   MIRROR
       This is an experimental demonstration target which inverts  the  source
       and destination fields in the IP header and retransmits the packet.  It
       is only valid in the INPUT, FORWARD and PREROUTING  chains,  and  user-
       defined  chains which are only called from those chains.  Note that the
       outgoing  packets  are  NOT  seen  by  any  packet  filtering   chains,
       connection tracking or NAT, to avoid loops and other problems.

   NETMAP
       This  target  allows you to statically map a whole network of addresses
       onto another network of addresses.  It can only be used from  rules  in
       the nat table.

       --to address[/mask]
              Network  address  to  map  to.   The  resulting  address will be
              constructed in the following way: All ’one’ bits in the mask are
              filled in from the new ‘address’.  All bits that are zero in the
              mask are filled in from the original address.

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

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

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

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

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

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

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

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

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

       It can only be used in the
              raw table.

   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

   REDIRECT
       This  target  is  only  valid  in  the nat table, in the PREROUTING and
       OUTPUT chains, and user-defined chains which are only called from those
       chains.   It redirects the packet to the machine itself by changing the
       destination IP  to  the  primary  address  of  the  incoming  interface
       (locally-generated packets are mapped to the 127.0.0.1 address).

       --to-ports port[-port]
              This  specifies  a  destination  port  or range of ports to use:
              without this, the destination port is never  altered.   This  is
              only valid if the rule also specifies -p tcp or -p udp.

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

   REJECT
       This is used to send back an error packet in response  to  the  matched
       packet:  otherwise  it  is  equivalent  to  DROP so it is a terminating
       TARGET, ending rule traversal.  This target is only valid in the INPUT,
       FORWARD  and  OUTPUT  chains,  and  user-defined  chains which are only
       called from those chains.  The following option controls the nature  of
       the error packet returned:

       --reject-with type
              The type given can be
               icmp-net-unreachable
               icmp-host-unreachable
               icmp-port-unreachable
               icmp-proto-unreachable
               icmp-net-prohibited
               icmp-host-prohibited or
               icmp-admin-prohibited (*)
              which   return   the   appropriate  ICMP  error  message  (port-
              unreachable is the default).  The option tcp-reset can  be  used
              on  rules  which  only match the TCP protocol: this causes a TCP
              RST packet to be sent back.  This is mainly useful for  blocking
              ident  (113/tcp) probes which frequently occur when sending mail
              to broken mail hosts (which won’t accept your mail otherwise).

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

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

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

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

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

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

       --selctx security_context

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

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

       --del-set setname flag[,flag...]
              delete the address(es)/port(s) of  the  packet  from  the  sets,
              where flags are src and/or dst and there can be no more than six
              of them.

       The bindings to follow must previously be defined in order to use
              multilevel adding/deleting by the SET target.

   SNAT
       This target is only valid in the nat table, in the  POSTROUTING  chain.
       It  specifies  that the source address of the packet should be modified
       (and all future packets in this connection will also be  mangled),  and
       rules should cease being examined.  It takes one type of option:

       --to-source ipaddr[-ipaddr][:port[-port]]
              which  can  specify a single new source IP address, an inclusive
              range of IP addresses, and optionally, a port  range  (which  is
              only  valid if the rule also specifies -p tcp or -p udp).  If no
              port range is specified, then source ports  below  512  will  be
              mapped  to  other  ports  below  512: those between 512 and 1023
              inclusive will be mapped to ports below 1024,  and  other  ports
              will  be  mapped  to  1024  or  above.  Where  possible, no port
              alteration will

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

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

   TCPMSS
       This target allows to alter the  MSS  value  of  TCP  SYN  packets,  to
       control  the  maximum  size for that connection (usually limiting it to
       your outgoing interface’s MTU  minus  40  for  IPv4  or  60  for  IPv6,
       respectively).   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
       configuration like:
        iptables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN \
                    -j TCPMSS --clamp-mss-to-pmtu

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

       --clamp-mss-to-pmtu
              Automatically  clamp  MSS  value to (path_MTU - 40 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
       (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  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:chainname:type:rulenum " where type can be "rule"  for  plain
       rule, "return" for implicit rule at the end of a user defined chain and
       "policy" for the policy of the built in chains.
       It can only be used in the raw table.

   TTL
       This is used to modify the  IPv4  TTL  header  field.   The  TTL  field
       determines  how  many  hops  (routers) a packet can traverse until it’s
       time to live is exceeded.

       Setting  or  incrementing  the  TTL  field  can  potentially  be   very
       dangerous,
              so it should be avoided at any cost.

       Dont ever set or increment the value on packets that leave your  local
       network!
              mangle table.

       --ttl-set value
              Set the TTL value to ‘value’.

       --ttl-dec value
              Decrement the TTL value ‘value’ times.

       --ttl-inc value
              Increment the TTL value ‘value’ times.

   ULOG
       This target provides userspace logging of matching packets.  When  this
       target  is  set for a rule, the Linux kernel will multicast this packet
       through a netlink socket. One or  more  userspace  processes  may  then
       subscribe  to  various  multicast groups and receive the packets.  Like
       LOG, this is a "non-terminating target", i.e. rule traversal  continues
       at the next rule.

       --ulog-nlgroup nlgroup
              This  specifies  the netlink group (1-32) to which the packet is
              sent.  Default value is 1.

       --ulog-prefix prefix
              Prefix  log  messages  with  the  specified  prefix;  up  to  32
              characters  long,  and useful for distinguishing messages in the
              logs.

       --ulog-cprange size
              Number of bytes to be copied to userspace.  A value of 0  always
              copies the entire packet, regardless of its size.  Default is 0.

       --ulog-qthreshold size
              Number of packet to queue inside kernel.  Setting this value to,
              e.g.  10 accumulates ten packets inside the kernel and transmits
              them as one netlink multipart message to userspace.  Default  is
              1 (for backwards compatibility).

DIAGNOSTICS

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

BUGS

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

COMPATIBILITY WITH IPCHAINS

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

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

       iptables is a pure packet filter when using the default ‘filter’ table,
       with  optional  extension  modules.   This  should simplify much of the
       previous confusion over the combination of IP masquerading  and  packet
       filtering  seen  previously.   So  the  following  options  are handled
       differently:
        -j MASQ
        -M -S
        -M -L
       There are several other changes in iptables.

SEE ALSO

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

       The packet-filtering-HOWTO details iptables usage for packet filtering,
       the NAT-HOWTO details NAT, the netfilter-extensions-HOWTO  details  the
       extensions   that  are  not  in  the  standard  distribution,  and  the
       netfilter-hacking-HOWTO details the netfilter internals.
       See http://www.netfilter.org/.

AUTHORS

       Rusty Russell originally wrote iptables,  in  early  consultation  with
       Michael Neuling.

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

       James Morris wrote the TOS target, and tos match.

       Jozsef Kadlecsik wrote the REJECT target.

       Harald Welte wrote the ULOG and NFQUEUE target,  the  new  libiptc,  as
       well as the TTL, DSCP, ECN matches and targets.

       The  Netfilter  Core  Team is: Marc Boucher, Martin Josefsson, Yasuyuki
       Kozakai, Jozsef Kadlecsik, Patrick McHardy, James Morris,  Pablo  Neira
       Ayuso, Harald Welte and Rusty Russell.

       Man page originally written by Herve Eychenne <rv@wallfire.org>.

                                 Mar 09, 2002                      IPTABLES(8)