Provided by: iptables_1.3.3-2ubuntu4_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 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 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.  As  every  other  iptables  command,  it
              applies  to  the specified table (filter is the default), so NAT
              rules get listed by
               iptables -t nat -n -L
              Please note that it is often used with the -n option,  in  order
              to  avoid  long reverse DNS lookups.  It is legal to specify the
              -Z (zero) option as well, in which case  the  chain(s)  will  be
              atomically  listed  and zeroed.  The exact output is affected by
              the other arguments given. The exact rules are suppressed  until
              you use
               iptables -L -v

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

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

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

       -X, --delete-chain [chain]
              Delete the optional user-defined chain specified.  There must be
              no  references  to  the chain.  If there are, you must delete or
              replace the referring rules before the chain can be deleted.  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.

   account
       Account traffic for all hosts in defined network/netmask.

       Features:

       -   long  (one  counter  per  protocol  TCP/UDP/IMCP/Other)  and  short
       statistics

       - one iptables rule for all hosts in network/netmask

       - loading/saving counters (by reading/writting to procfs entries)

       --aaddr network/netmask
              defines network/netmask for which make statistics.

       --aname name
              defines name of list where statistics will be  kept.  If  no  is
              specified DEFAULT will be used.

       --ashort
              table  will  colect  only  short statistics (only total counters
              without splitting it into protocols.

       Example usage:

       account traffic for/to 192.168.0.0/24 network into table mynetwork:

       #  iptables  -A  FORWARD   -m   account   --aname   mynetwork   --aaddr
       192.168.0.0/24

       account traffic for/to WWW serwer for 192.168.0.0/24 network into table
       mywwwserver:

       # iptables -A INPUT -p tcp --dport 80
         -m account --aname mywwwserver --aaddr 192.168.0.0/24 --ashort

       # iptables -A OUTPUT -p tcp --sport 80
         -m account --aname mywwwserver --aaddr 192.168.0.0/24 --ashort

       read counters:

       #        cat        /proc/net/ipt_account/mynetwork        #        cat
       /proc/net/ipt_account/mywwwserver

       set counters:

       #     echo     "ip     =     192.168.0.1    packets_src    =    0"    >
       /proc/net/ipt_account/mywwserver

       Webpage:
         http://www.barbara.eu.org/~quaker/ipt_account/

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

       The following address types are possible:

       UNSPEC an unspecified address (i.e. 0.0.0.0) UNICAST an unicast address
              LOCAL a local address BROADCAST a broadcast address  ANYCAST  an
              anycast   packet  MULTICAST  a  multicast  address  BLACKHOLE  a
              blackhole address UNREACHABLE an unreachable address PROHIBIT  a
              prohibited address THROW FIXME NAT FIXME XRESOLVE FIXME

       --src-type type
              Matches if the source address is of given type

       --dst-type type
              Matches if the destination address is of given type

   ah
       This module matches the SPIs in AH header of IPSec packets.

       --ahspi [!] spi[:spi]

   childlevel
       This  is  an  experimental module.  It matches on whether the packet is
       part of a master connection or one of its children  (or  grandchildren,
       etc).   For  instance,  most packets are level 0.  FTP data transfer is
       level 1.

       --childlevel [!] level

   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"

   condition
       This matches if a specific /proc filename is ’0’ or ’1’.

       --condition [!] filename
              Match        on        boolean       value       stored       in
              /proc/net/ipt_condition/filename file

   connbytes
       Match by how many bytes or packets a connection  (or  one  of  the  two
       flows  constituting  the  connection)  have  tranferred  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  transfered  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 TCP connections to a
       server per client IP address (or address block).

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

       --connlimit-mask bits
              group hosts using mask

       Examples:

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

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

       #  limit  the  nr  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

   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).

   connrate
       This module matches the current transfer rate in a connection.

       --connrate [!] [from]:[to]
              Match  against the current connection transfer rate being within
              ’from’ and ’to’ bytes per second. When the "!" argument is  used
              before the range, the sense of the match is inverted.

   conntrack
       This  module,  when combined with connection tracking, allows access to
       more connection tracking information than  the  "state"  match.   (this
       module  is  present  only  if  iptables  was  compiled  under  a kernel
       supporting this feature)

       --ctstate state
              Where state is a comma separated list of the  connection  states
              to  match.   Possible states are INVALID meaning that the packet
              is associated with no known connection, ESTABLISHED meaning that
              the  packet  is  associated  with  a  connection  which has seen
              packets in both directions, NEW  meaning  that  the  packet  has
              started  a  new  connection,  or  otherwise  associated  with  a
              connection which has not seen packets in  both  directions,  and
              RELATED  meaning  that  the packet is starting a new connection,
              but is associated with an existing connection, such  as  an  FTP
              data transfer, or an ICMP error.  SNAT A virtual state, matching
              if  the  original  source  address  differs   from   the   reply
              destination.   DNAT  A  virtual  state, matching if the original
              destination differs from the reply source.

       --ctproto proto
              Protocol to match (by number or name)

       --ctorigsrc [!] address[/mask]
              Match against original source address

       --ctorigdst [!] address[/mask]
              Match against original destination address

       --ctreplsrc [!] address[/mask]
              Match against reply source address

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

       --ctstatus [NONE|EXPECTED|SEEN_REPLY|ASSURED][,...]
              Match against internal conntrack states

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

   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 [0-32].

       --dscp-class DiffServ Class
              Match the DiffServ class. This value may be any of the  BE,  EF,
              AFxx  or  CSx  classes.   It  will  then  be converted into it’s
              according numeric value.

   dstlimit
       This module allows you to limit the packet per second (pps) rate  on  a
       per  destination  IP  or  per destination port base.  As opposed to the
       ‘limit’ match, every destination ip / destination  port  has  it’s  own
       limit.

       --dstlimit avg
              Maximum  average  match rate (packets per second unless followed
              by /sec /minute /hour /day postfixes).

       --dstlimit-mode mode
              The limiting hashmode.  Is the specified limit per dstip, dstip-
              dstport  tuple,  srcip-dstip  tuple,  or  per srcipdstip-dstport
              tuple.

       --dstlimit-name name
              Name for /proc/net/ipt_dstlimit/* file entry

       [--dstlimit-burst burst]
              Number of packets to match in a burst.  Default: 5

       [--dstlimit-htable-size size]
              Number of buckets in the hashtable

       [--dstlimit-htable-max max]
              Maximum number of entries in the hashtable

       [--dstlimit-htable-gcinterval interval]
              Interval between garbage collection runs of  the  hashtable  (in
              miliseconds).  Default is 1000 (1 second).

       [--dstlimit-htable-expire time
              After  which  time  are  idle entries expired from hashtable (in
              miliseconds)?  Default is 10000 (10 seconds).

   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]

   fuzzy
       This module matches a rate limit based  on  a  fuzzy  logic  controller
       [FLC]

       --lower-limit  number"
              Specifies the lower limit (in packets per second).

       --upper-limit number
              Specifies the upper limit (in packets per second).

   geoip
       Match a packet by its source or destination country.

       [!] --src-cc, --source-country country[,country,country,...]
              Match packet coming from (one of) the specified country(ies)

       [!] --dst-cc, --destination-country country[,country,country,...]
              Match packet going to (one of) the specified country(ies)

       NOTE:  The country is inputed by its ISO3166 code.

       The  only extra files you need is a binary db (geoipdb.bin) & its index
       file (geoipdb.idx).  Both  files  are  generated  from  a  countries  &
       subnets    database    with    the    csv2bin    tool,   available   at
       www.cookinglinux.org/geoip/.  Both  files  MUST  also   be   moved   in
       /var/geoip/  as  the  shared  library  is  statically  looking for that
       pathname (ex.: /var/geoip/geoipdb.bin).

   hashlimit
       This patch adds a new match called ’hashlimit’.  The idea  is  to  have
       something   like   ’limit’,   but  either  per  destination-ip  or  per
       (destip,destport) tuple.

       It gives you the ability to express

               ’1000 packets per second for every host in 192.168.0.0/16’

               ’100 packets per second for every service of 192.168.1.1’

       with a single iptables rule.

       --hashlimit rate
              A rate just like the limit match

       --hashlimit-burst num
              Burst value, just like limit match

       --hashlimit-mode destip | destip-destport
              Limit per IP or per port

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

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

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

       --hashlimit-htable-expire num
              After how many miliseconds do hash entries expire

       --hashlimit-htable-gcinterval num
              How many miliseconds 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  is  loaded  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

   ipp2p
       This module matches certain packets in P2P flows. It is not designed to
       match all packets belonging to a P2P connection -  use  IPP2P  together
       with  CONNMARK  for  this  purpose. Also visit http://www.ipp2p.org for
       detailed information.

       Use it together with -p tcp or -p udp to search these protocols only or
       without -p switch to search packets of both protocols.

       IPP2P provides the following options:

       --edk  Matches as many eDonkey/eMule packets as possible.

       --kazaa
              Matches as many KaZaA packets as possible.

       --gnu  Matches as many Gnutella packets as possible.

       --dc   Matches as many Direct Connect packets as possible.

       --bit  Matches BitTorrent packets.

       --apple
              Matches AppleJuice packets.

       --soul Matches  some SoulSeek packets. Considered as beta, use careful!

       --winmx
              Matches some WinMX packets. Considered as beta, use careful!

       --ares Matches Ares and AresLite packets. Use  together  with  -j  DROP
              only.

       --ipp2p
              Short hand for: --edk --kazaa --gnu --dc

       --debug
              Prints  some information about each hit into kernel logfile. May
              produce huge logfiles so beware!

   iprange
       This matches on a given arbitrary range of IPv4 addresses

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

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

   ipv4options
       Match on  IPv4  header  options  like  source  routing,  record  route,
       timestamp and router-alert.

       --ssrr To match packets with the flag strict source routing.

       --lsrr To match packets with the flag loose source routing.

       --no-srr
              To match packets with no flag for source routing.

       [!] --rr
              To match packets with the RR flag.

       [!] --ts
              To match packets with the TS flag.

       [!] --ra
              To match packets with the router-alert option.

       [!] --any-opt
              To  match  a packet with at least one IP option, or no IP option
              at all if ! is chosen.

       Examples:

       $ iptables -A input -m ipv4options --rr -j DROP
              will drop packets with the record-route flag.

       $ iptables -A input -m ipv4options --ts -j DROP
              will drop packets with the timestamp flag.

   length
       This module matches the length of a packet against a specific value  or
       range of values.

       --length length[:length]

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

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

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

   mac
       --mac-source [!] address
              Match  source  MAC  address.    It   must   be   of   the   form
              XX:XX:XX:XX:XX:XX.   Note that this only makes sense for packets
              coming from an Ethernet  device  and  entering  the  PREROUTING,
              FORWARD or INPUT chains.

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

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

   mport
       This module matches a set of source or destination  ports.   Up  to  15
       ports can be specified.  It can only be used in conjunction with -p tcp
       or -p udp.

       --source-ports port[,port[,port...]]
              Match if the source port is one of the given  ports.   The  flag
              --sports is a convenient alias for this option.

       --destination-ports port[,port[,port...]]
              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...]]
              Match if the both the source and destination ports are equal  to
              each other and to one of the given ports.

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

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

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

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

   nth
       This module matches every ‘n’th packet

       --every value
              Match every ‘value’ packet

       [--counter num]
              Use internal counter number ‘num’.  Default is ‘0’.

       [--start num]
              Initialize the counter at the number ‘num’ insetad of ‘0’.  Most
              between ‘0’ and ‘value’-1.

       [--packet num]
              Match on ‘num’ packet.  Most be between ‘0’ and ‘value’-1.

   osf
       The  idea  of  passive  OS fingerprint matching exists for quite a long
       time, but was created as extension fo OpenBSD pf only some  weeks  ago.
       Original   idea  was  lurked  in  some  OpenBSD  mailing  list  (thanks
       grange@open...) and than adopted for Linux netfilter in  form  of  this
       code.

       Original   fingerprint   table   was   created   by   Michal   Zalewski
       <lcamtuf@coredump.cx>.

       This module compares some data(WS, MSS, options and it’s order, ttl, df
       and  others)  from first SYN packet (actually from packets with SYN bit
       set) with dynamically loaded OS fingerprints.

       --log 1/0
              If present, OSF will log determined genres even  if  they  don’t
              match  desired  one.    0 - log all determined entries, 1 - only
              first one.

              In syslog you find something like this:

              ipt_osf:  Windows  [2000:SP3:Windows  XP  Pro  SP1,  2000  SP3]:
              11.22.33.55:4024 -> 11.22.33.44:139

              ipt_osf:         Unknown:        16384:106:1:48:020405B401010402
              44.33.22.11:1239 -> 11.22.33.44:80

       --smart
              if present, OSF will use some smartness to determine remote  OS.
              OSF  will use initial TTL only if source of connection is in our
              local network.

       --netlink
              If present,  OSF  will  log  all  events  also  through  netlink
              NETLINK_NFLOG groupt 1.

       --genre [!] string
              Match a OS genre by passive fingerprinting

       Example:

       #iptables  -I  INPUT  -j  ACCEPT  -p  tcp  -m osf --genre Linux --log 1
       --smart

       NOTE: -p tcp is obviously required as it is a TCP match.

       Fingerprints can be  loaded  and  read  through  /proc/sys/net/ipv4/osf
       file.  One can flush all fingerprints with following command:

              echo -en FLUSH > /proc/sys/net/ipv4/osf

       Only one fingerprint per open/write/close.

       Fingerprints   can   be   downloaded  from  http://www.openbsd.org/cgi-
       bin/cvsweb/src/etc/pf.os

   owner
       This module attempts to match various  characteristics  of  the  packet
       creator,  for  locally-generated  packets.  It  is  valid in the INPUT,
       OUTPUT and POSTROUTING chains, however in the INPUT chain only TCP  and
       UDP  packets  can be matched. Also note that some packets (such as ICMP
       ping responses) may have no owner, and hence never match.

       --uid-owner userid
              Matches if the packet was created by a process  with  the  given
              effective user id.

       --gid-owner groupid
              Matches  if  the  packet was created by a process with the given
              effective group id.

       --pid-owner processid
              Matches if the packet was created by a process  with  the  given
              process id.

       --sid-owner sessionid
              Matches  if  the  packet  was  created by a process in the given
              session group.

       --cmd-owner name
              Matches if the packet was created by a process  with  the  given
              command  name.   (this  option  is  present only if iptables was
              compiled under a kernel supporting this feature)

       NOTE: pid, sid and command matching are broken on SMP

   physdev
       This module matches  on  the  bridge  port  input  and  output  devices
       enslaved   to   a   bridge  device.  This  module  is  a  part  of  the
       infrastructure that enables a transparent bridging IP firewall  and  is
       only useful for kernel versions above version 2.5.44.

       --physdev-in name
              Name  of  a bridge port via which a packet is received (only for
              packets entering the INPUT, FORWARD and PREROUTING  chains).  If
              the  interface  name  ends  in  a  "+", then any interface which
              begins with this name will match. If the  packet  didn’t  arrive
              through  a  bridge  device, this packet won’t match this option,
              unless ’!’ is used.

       --physdev-out name
              Name of a bridge port via which a packet is  going  to  be  sent
              (for  packets  entering  the  FORWARD,  OUTPUT  and  POSTROUTING
              chains).  If  the  interface  name  ends  in  a  "+",  then  any
              interface  which  begins with this name will match. Note that in
              the nat and mangle OUTPUT chains one cannot match on the  bridge
              output  port, however one can in the filter OUTPUT chain. If the
              packet won’t leave by a bridge device or it is yet unknown  what
              the  output  device  will  be,  then the packet won’t match this
              option, unless

       --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 address of a tunnel. Only valid with --mode
              tunnel.

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

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

   psd
       Attempt to detect TCP and UDP port scans. This match was  derived  from
       Solar Designer’s scanlogd.

       --psd-weight-threshold threshold
              Total  weight  of  the  latest  TCP/UDP  packets  with different
              destination ports coming from the same host  to  be  treated  as
              port scan sequence.

       --psd-delay-threshold delay
              Delay  (in  hundredths of second) for the packets with different
              destination ports coming from the same host  to  be  treated  as
              possible port scan subsequence.

       --psd-lo-ports-weight weight
              Weight  of the packet with privileged (<=1024) destination port.

       --psd-hi-ports-weight weight
              Weight of the packet with non-priviliged destination port.

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

       --quota bytes
              The quota in bytes.

       KNOWN BUGS: this does not work on SMP systems.

   random
       This module randomly matches a certain percentage of all packets.

       --average percent
              Matches  the given percentage.  If omitted, a probability of 50%
              is set.

   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).

   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.

       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.

   tcp
       These extensions are  loaded  if  ‘--protocol  tcp’  is  specified.  It
       provides the following options:

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

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

       --tcp-flags [!] mask comp
              Match when the TCP flags are as specified.  The  first  argument
              is  the  flags  which  we  should  examine,  written as a comma-
              separated list, and the second  argument  is  a  comma-separated
              list of flags which must be set.  Flags are: SYN ACK FIN RST URG
              PSH ALL NONE.  Hence the command
               iptables -A FORWARD -p tcp --tcp-flags SYN,ACK,FIN,RST SYN
              will only match packets with the SYN flag set, and the ACK,  FIN
              and RST flags unset.

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

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

       --mss value[:value]
              Match  TCP  SYN  or SYN/ACK packets with the specified MSS value
              (or range), which control  the  maximum  packet  size  for  that
              connection.

   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 facultative.

        --timestart value
              Match  only  if  it is after ‘value’ (Inclusive, format: HH:MM ;
              default 00:00).

       --timestop  value
              Match only if it is before ‘value’ (Inclusive, format:  HH:MM  ;
              default 23:59).

       --days listofdays
              Match  only  if  today  is  one  of  the  given  days.  (format:
              Mon,Tue,Wed,Thu,Fri,Sat,Sun ; default everyday)

       --datestart date
              Match  only  if  it  is   after   ‘date’   (Inclusive,   format:
              YYYY[:MM[:DD[:hh[:mm[:ss]]]]]  ; h,m,s start from 0 ; default to
              1970)

       --datestop date
              Match  only  if  it  is  before   ‘date’   (Inclusive,   format:
              YYYY[:MM[:DD[:hh[:mm[:ss]]]]]  ; h,m,s start from 0 ; default to
              2037)

   tos
       This module matches the 8 bits of Type  of  Service  field  in  the  IP
       header (ie. including the precedence bits).

       --tos tos
              The argument is either a standard name, (use
               iptables -m tos -h
              to see the list), or a numeric value to match.

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

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

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

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

   u32
       U32  allows  you  to extract quantities of up to 4 bytes from a packet,
       AND them with specified masks, shift them by specified amounts and test
       whether  the  results  are  in  any  of a set of specified ranges.  The
       specification of what to extract is general enough to skip over headers
       with lengths stored in the packet, as in IP or TCP header lengths.

       Details and examples are in the kernel module source.

   udp
       These  extensions  are  loaded  if  ‘--protocol  udp’ is specified.  It
       provides the following options:

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

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

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

TARGET EXTENSIONS

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

   BALANCE
       This  allows  you to DNAT connections in a round-robin way over a given
       range of destination addresses.

       --to-destination ipaddr-ipaddr
              Address range to round-robin over.

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

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

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

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

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

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

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

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

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

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

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

       --save-mark [--mask mask]
              Copy the netfilter packet mark value to the connection mark.  If
              a mask is specified then only those bits are copied.

       --restore-mark [--mask mask]
              Copy  the  connection  mark  value  to  the packet. If a mask is
              specified then only those bits are copied. This is only valid in
              the mangle table.

   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.

              You can add several --to-destination options.   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
              adresses.

   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.

   IPMARK
       Allows you to mark a received packet basing on its IP address. This can
       replace  many  mangle/mark  entries  with only one, if you use firewall
       based classifier.

       This target is to be used inside the mangle table, in  the  PREROUTING,
       POSTROUTING or FORWARD hooks.

       --addr src/dst
              Use source or destination IP address.

       --and-mask mask
              Perform bitwise ‘and’ on the IP address and this mask.

       --or-mask mask
              Perform bitwise ‘or’ on the IP address and this mask.

       The  order  of  IP  address  bytes  is reversed to meet "human order of
       bytes": 192.168.0.1 is 0xc0a80001. At  first  the  ‘and’  operation  is
       performed, then ‘or’.

       Examples:

       We create a queue for each user, the queue number is adequate to the IP
       address of the user, e.g.: all packets going  to/from  192.168.5.2  are
       directed to 1:0502 queue, 192.168.5.12 -> 1:050c etc.

       We have one classifier rule:

              tc filter add dev eth3 parent 1:0 protocol ip fw

       Earlier we had many rules just like below:

              iptables -t mangle -A POSTROUTING -o eth3 -d 192.168.5.2 -j MARK
              --set-mark 0x10502

              iptables -t mangle -A POSTROUTING -o eth3 -d 192.168.5.3 -j MARK
              --set-mark 0x10503

       Using  IPMARK target we can replace all the mangle/mark rules with only
       one:

              iptables -t mangle -A POSTROUTING -o eth3 -j  IPMARK  --addr=dst
              --and-mask=0xffff --or-mask=0x10000

       On  the routers with hundreds of users there should be significant load
       decrease (e.g. twice).

   IPV4OPTSSTRIP
       Strip all the IP options from a packet.

       The target doesn’t take any option, and therefore is extremly  easy  to
       use :

       # iptables -t mangle -A PREROUTING -j IPV4OPTSSTRIP

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

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

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

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

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

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

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

   MARK
       This  is  used  to  set  the  netfilter  mark value associated with the
       packet.  It is only valid in the mangle table.  It can for  example  be
       used in conjunction with iproute2.

       --set-mark mark

   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.

   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.

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

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

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

       It can only be used in the
              raw table.

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

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

   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

   ROUTE
       This  is  used  to explicitly override the core network stack’s routing
       decision.  mangle table.

       --oif ifname
              Route the packet through ‘ifname’ network interface

       --iif ifname
              Change the packet’s incoming interface to ‘ifname’

       --gw IP_address
              Route the packet via this gateway

       --continue
              Behave like a non-terminating target and continue traversing the
              rules.  Not valid in combination with ‘--iif’ or ‘--tee’

       --tee  Make  a  copy  of  the  packet, and route that copy to the given
              destination. For the original, uncopied packet,  behave  like  a
              non-terminating  target  and continue traversing the rules.  Not
              valid in combination with ‘--iif’ or ‘--continue’

   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

   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 occur.

              You  can  add  several --to-source options.  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 adresses.

   TARPIT
       Captures and  holds  incoming  TCP  connections  using  no  local  per-
       connection   resources.   Connections  are  accepted,  but  immediately
       switched to the persist state (0 byte window), in which the remote side
       stops sending data and asks to continue every 60-240 seconds.  Attempts
       to close the connection are ignored, forcing the remote  side  to  time
       out the connection in 12-24 minutes.

       This       offers       similar       functionality      to      LaBrea
       <http://www.hackbusters.net/LaBrea/>  but  doesn’t  require   dedicated
       hardware  or  IPs.  Any TCP port that you would normally DROP or REJECT
       can instead become a tarpit.

       To tarpit connections to TCP port 80 destined for the current machine:

              iptables -A INPUT -p tcp -m tcp --dport 80 -j TARPIT

       To significantly slow down Code Red/Nimda-style scans of unused address
       space,  forward  unused  ip  addresses  to  a Linux box not acting as a
       router (e.g. "ip route 10.0.0.0 255.0.0.0 ip.of.linux.box" on a Cisco),
       enable IP forwarding on the Linux box, and add:

              iptables -A FORWARD -p tcp -j TARPIT

              iptables -A FORWARD -j DROP

       NOTE:  If  you use the conntrack module while you are using TARPIT, you
              should  also  use  the  NOTRACK  target,  or  the  kernel   will
              unnecessarily  allocate resources for each TARPITted connection.
              To TARPIT incoming connections to the standard  IRC  port  while
              using conntrack, you could:

              iptables -t raw -A PREROUTING -p tcp --dport 6667 -j NOTRACK

              iptables -A INPUT -p tcp --dport 6667 -j TARPIT

   TCPMSS
       This  target  allows  to  alter  the  MSS  value of TCP SYN packets, to
       control the maximum size for that connection (usually  limiting  it  to
       your  outgoing  interface’s  MTU  minus 40).  Of course, it can only be
       used in conjunction with -p tcp.
       This target is used to overcome criminally braindead  ISPs  or  servers
       which  block  ICMP  Fragmentation Needed packets.  The symptoms of this
       problem are that everything works fine from your Linux firewall/router,
       but machines behind it can never exchange large packets:
        1) Web browsers connect, then hang with no data received.
        2) Small mail works fine, but large emails hang.
        3) ssh works fine, but scp hangs after initial handshaking.
       Workaround:  activate  this  option  and  add  a  rule to your firewall
       configuration like:
        iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN \
                    -j TCPMSS --clamp-mss-to-pmtu

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

       --clamp-mss-to-pmtu
              Automatically clamp MSS value to (path_MTU - 40).

       These options are mutually exclusive.

   TOS
       This is used to set the 8-bit Type of Service field in the  IP  header.
       It is only valid in the mangle table.

       --set-tos tos
              You can use a numeric TOS values, or use
               iptables -j TOS -h
              to see the list of valid TOS names.

   TRACE
       This  target  has  no options.  It just turns on packet tracing for all
       packets that match this rule.

   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).

   XOR
       Encrypt TCP and UDP traffic using a simple XOR encryption

       --key string
              Set key to "string"

       --block-size
              Set block size

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, Jozsef
       Kadlecsik, Patrick  McHardy,  James  Morris,  Harald  Welte  and  Rusty
       Russell.

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

                                 Mar 09, 2002                      IPTABLES(8)