iptables


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

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

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

       iptables [-t table] -D chain rulenum

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

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

       iptables [-t table] -N chain

       iptables [-t table] -X [chain]

       iptables [-t table] -P chain target

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

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

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

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

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

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

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

       ACCEPT  means to let the packet through.  DROP means to drop the packet
       on the floor.  QUEUE means to pass the packet to userspace.   (How  the
       packet can be received by a userspace process differs by the particular
       queue handler.  2.4.x and  2.6.x  kernels  up  to  2.6.13  include  the
       ip_queue  queue handler.  Kernels 2.6.14 and later additionally include
       the nfnetlink_queue queue handler.  Packets with a target of QUEUE will
       be  sent  to queue number '0' in this case. Please also see the NFQUEUE
       target as described  later  in  this  man  page.)   RETURN  means  stop
              mand  should operate on.  If the kernel is configured with auto-
              matic module loading, an attempt will be made to load the appro-
              priate module for that table if it is not already there.

              The tables are as follows:

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

              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 rout-
                  ing), 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 sup-
                  ported: INPUT (for packets coming into the box itself), FOR-
                  WARD  (for  altering  packets being routed through the box),
                  and POSTROUTING (for altering packets as they are  about  to
                  go out).

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

OPTIONS
       The options that are recognized by 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
              number.   So,  if  the  rule  number is 1, the rule or rules are
              inserted at the head of the chain.  This is also the default  if
              no rule number is specified.

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

       -L, --list [chain]
              List  all rules in the selected chain.  If no chain is selected,
              all chains are listed. Like every  other  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 ipt-
              ables  command, it applies to the specified table (filter is the
              default).

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

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

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

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

       -P, --policy chain target
              Set the policy for the chain to the given target.  See the  sec-
              tion  TARGETS  for  the legal targets.  Only built-in (non-user-

       add, delete, insert, replace and append commands).

       [!] -p, --protocol protocol
              The protocol of the rule or of the packet to check.  The  speci-
              fied  protocol  can  be one of tcp, udp, udplite, icmp, esp, ah,
              sctp 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  pro-
              tocol  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 con-
              tinue processing in this chain but instead  in  the  chain  that
              called us via --jump.

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

       [!] -o, --out-interface name
              Name of an interface via which a packet is going to be sent (for
              match head fragments, or unfragmented packets.

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

   OTHER OPTIONS
       The following additional options can be specified:

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

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

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

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

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

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

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

   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
              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  PREROUT-
              ING,  INPUT  and FORWARD chains. It cannot be specified with the
              --limit-iface-out option.

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

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

       [!] --ahspi spi[:spi]

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

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


       Example:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       --comment comment

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

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

       accounting structure when be sysctl flag is flipped.

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

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

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

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

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

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

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

       Examples:

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

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

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

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

       the connection tracking state for this packet/connection.

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

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

       [!] --ctorigsrc address[/mask]

       [!] --ctorigdst address[/mask]

       [!] --ctreplsrc address[/mask]

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

       [!] --ctorigsrcport port

       [!] --ctorigdstport port

       [!] --ctreplsrcport port

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

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

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

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

       States for --ctstate:

       INVALID
              meaning that the packet is associated with no known connection

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

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


       NONE   None of the below.

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

       SEEN_REPLY
              Conntrack has seen packets in both directions.

       ASSURED
              Conntrack entry should never be early-expired.

       CONFIRMED
              Connection is confirmed: originating packet has left box.

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

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

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

       [!] --dccp-option number
              Match if DCP option set.

   dscp
       This module matches the 6 bit DSCP field within the TOS field in the IP
       header.  DSCP has superseded TOS within the IETF.

       [!] --dscp value
              Match against a numeric (decimal or hex) value [0-63].

       [!] --dscp-class class
              Match  the  DiffServ class. This value may be any of the BE, EF,
              AFxx or CSx classes.  It will then be converted into its accord-
              ing numeric value.

   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.

       Grouping  can be done per-hostgroup (source and/or destination address)
       and/or per-port. It gives you the ability to  express  "N  packets  per
       time quantum per group":

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

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

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

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

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

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

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

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

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

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

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

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

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

              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 pro-
       vides the following option:

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

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

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

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

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

       [!] --length length[:length]

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

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

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

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

       It can only be used in conjunction with -p tcp or -p udp.

       [!] --source-ports,--sports port[,port|,port:port]...
              Match if the source port is one of the given  ports.   The  flag
              --sports  is  a convenient alias for this option. Multiple ports
              or port ranges are separated using a comma, and a port range  is
              specified  using  a  colon.  53,1024:65535 would therefore match
              ports 53 and all from 1024 through 65535.

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

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

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

       [!] --uid-owner username

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

       [!] --gid-owner groupname

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

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

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

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

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

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

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

   pkttype
       This module matches the link-layer packet type.

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

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

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

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

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

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

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

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

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

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

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

       --next Start  the next element in the policy specification. Can only be
       paring  two  rate estimators and matching on the difference between two
       rate estimators.

       --rateest1 name
              Name of the first rate estimator.

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

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

       --rateest1-bps value

       --rateest2-bps value
              Compare bytes per second.

       --rateest1-pps value

       --rateest2-pps value
              Compare packets per second.

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

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

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

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

       # Estimate outgoing rates

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

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

       # Mark based on available bandwidth

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

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

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

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

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

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

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

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

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

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

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

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

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

       [!] --hitcount hits
              This  option must be used in conjunction with one of --rcheck or
              ing others access to your site by sending bogus packets to you.

       Examples:

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

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

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

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

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

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

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

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

       The module itself accepts parameters, defaults shown:

       ip_list_tot=100
              Number of addresses remembered per table.

       ip_pkt_list_tot=20
              Number of packets per address remembered.

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

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

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

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

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

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


              (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).

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

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

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

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

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

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

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

   statistic
       This module matches packets based on some statistic condition.  It sup-
       --every n
              Match one packet every nth packet. It works only  with  the  nth
              mode (see also the --packet option).

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       --timestart hh:mm[:ss]

       --timestop hh:mm[:ss]

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

       [!] --monthdays day[,day...]

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

       [!] --weekdays day[,day...]

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

       --utc

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

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

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

       During lunch hour:

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

       The fourth Friday in the month:

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

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

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

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

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

   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.

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

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

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

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

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

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

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

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

              B and C are unsigned 32 bit integers, initially zero

       The instructions are:

              number B = number;

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

              &number C = C & number

              << number C = C << number

              >> number C = C >> number

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

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

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

       Example:

              match IP packets with total length >= 256

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

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

              read bytes 0-3

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

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

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

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

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

       Example:

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

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

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

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

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

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

   udp
   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 clas-
       sify the packet into a specific CBQ class).

       --set-class major:minor
              Set the major and minor  class  value.  The  values  are  always
              interpreted as hexadecimal even if no 0x prefix is given.

   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, sour-
              ceip-sourceport, sourceip-sourceport-destport.

       --clustermac mac
              Specify the ClusterIP MAC address. Has to be a link-layer multi-
              cast 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.  nfmask  defines what bits to clear and ctmask what bits of
              the ctmark to XOR into the nfmark. ctmask and nfmask default  to
              0xFFFFFFFF.

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

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

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

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

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

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

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

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

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

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

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


   DNAT
       This  target is only valid in the nat table, in the PREROUTING and OUT-
       PUT 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  options,  a  simple  round-robin  (one   after
              another  in  cycle)  load  balancing  takes  place between these
              addresses.  Later Kernels (>= 2.6.11-rc1) don't have the ability
              to NAT to multiple ranges anymore.

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

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

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

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

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

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

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

   LOG
       Turn on kernel logging of matching packets.  When this  option  is  set
       for  a rule, the Linux kernel will print some information on all match-
       ing packets (like most IP header fields) via the kernel log  (where  it
       can be read with dmesg or syslogd(8)).  This is a "non-terminating tar-
       get", 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
       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) connec-
       tions: 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 any-
       way).  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, connec-
       tion tracking or NAT, to avoid loops and other problems.

   NETMAP
       This target allows you to statically map a whole network  of  addresses
       logging  backend to log the packet. This is usually used in combination
       with nfnetlink_log as logging backend, which will multicast the  packet
       through  a netlink socket to the specified multicast group. One or more
       userspace processes may subscribe to the group to receive the  packets.
       Like LOG, this is a non-terminating target, i.e. rule traversal contin-
       ues at the next rule.

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

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

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

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

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

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

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

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

       It can only be used in the raw table.

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

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

       --rateest-interval amount{s|ms|us}

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

       --reject-with type
              The type given can be  icmp-net-unreachable,  icmp-host-unreach-
              able,       icmp-port-unreachable,       icmp-proto-unreachable,
              icmp-net-prohibited, icmp-host-prohibited or  icmp-admin-prohib-
              ited  (*)  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-/destina-
       tion-address for each connection.

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

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

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

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

   SECMARK
       This  is used to set the security mark value associated with the packet
       --del-set setname flag[,flag...]
              delete the address(es)/port(s) of the packet from the sets

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

   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  alter-
              ation 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).

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

   TCPMSS
       This  target  allows to alter the MSS value of TCP SYN packets, to con-
       trol the maximum size for that connection (usually limiting it to  your
       outgoing  interface's  MTU  minus  40  for IPv4 or 60 for IPv6, respec-
       tively).  Of course, it can only be used in conjunction  with  -p  tcp.
       It is only valid in the mangle table.
       This  target  is  used to overcome criminally braindead ISPs or servers
       which block "ICMP Fragmentation Needed"  or  "ICMPv6  Packet  Too  Big"
       packets.   The  symptoms of this problem are that everything works fine
       from your Linux firewall/router,  but  machines  behind  it  can  never
       exchange large packets:
        1) Web browsers connect, then hang with no data received.
        2) Small mail works fine, but large emails hang.
        3) ssh works fine, but scp hangs after initial handshaking.
       Workaround:  activate  this option and add a rule to your firewall con-
       figuration like:

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

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

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

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

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

       The following mnemonics are available:

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

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

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

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

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

       This  target  marks packes so that the kernel will log every rule which
       match the packets as those traverse the  tables,  chains,  rules.  (The
       ipt_LOG  or  ip6t_LOG  module is required for the logging.) The packets
       are  logged  with   the   string   prefix:   "TRACE:   tablename:chain-
       name:type:rulenum  "  where type can be "rule" for plain rule, "return"
       for implicit rule at the end of a user defined chain and  "policy"  for
       the policy of the built in chains.
       It can only be used in the raw table.

   TTL
       This is used to modify the IPv4 TTL header field.  The TTL field deter-
       mines 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 danger-
       ous, so it should be avoided at any cost.

       Don't 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 sub-
       scribe 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 charac-
              ters 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).

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

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

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

       James Morris wrote the TOS target, and tos match.

       Jozsef Kadlecsik wrote the REJECT target.

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