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IPTABLES(8)				 iptables 1.4.10			      IPTABLES(8)

NAME
       iptables -- administration tool for IPv4 packet filtering and NAT

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 [rulenum]] [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 num-
       ber 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  previ-
       ous  (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  encoun-
		  tered.   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 rout-
		  ing) and OUTPUT (for altering locally-generated packets before routing).  Since
		  kernel 2.4.18, three other built-in chains are also supported: INPUT (for pack-
		  ets  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 pro-
		  cesses)

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  differenti-
       ate it from all other options.

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

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

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

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

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

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

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

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

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

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

       -P, --policy chain target
	      Set  the policy for the chain to the given target.  See the section TARGETS for the
	      legal targets.  Only built-in (non-user-defined) chains can have policies, and nei-
	      ther 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, 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  protocol  inverts  the
	      test.  The number zero is equivalent to all.  Protocol all will match with all pro-
	      tocols 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,  a  network
	      IP  address  (with  /mask),  or a plain IP address. Hostnames will be resolved once
	      only, before the rule is submitted to the kernel.  Please note that specifying  any
	      name to be resolved with a remote query such as DNS is a really bad idea.  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.  Multiple addresses can be specified,
	      but this will expand to multiple rules (when adding with -A), or will cause  multi-
	      ple rules to be deleted (with -D).

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

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

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

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

       [!] -o, --out-interface name
	      Name  of	an interface via which a packet is going to be sent (for packets entering
	      the FORWARD, OUTPUT and POSTROUTING chains).  When the "!" argument is used  before
	      the  interface  name,  the sense is inverted.  If the interface name ends in a "+",
	      then any interface which begins with this name will match.  If this option is omit-
	      ted, 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  frag-
	      ments, 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  mul-
	      tipliers	respectively (but see the -x flag to change this).  For appending, inser-
	      tion, 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 mod-
	      ules (targets, match extensions, etc).

MATCH EXTENSIONS
       iptables  can use extended packet matching modules.  These are loaded in two ways: implic-
       itly, 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 avail-
       able, depending on the specific module.	You can specify multiple extended  match  modules
       in  one line, and you can use the -h or --help options after the module has been specified
       to receive help specific to that module.

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

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

       The following address types are possible:

       UNSPEC an unspecified address (i.e. 0.0.0.0)

       UNICAST
	      an unicast address

       LOCAL  a local address

       BROADCAST
	      a broadcast address

       ANYCAST
	      an anycast packet

       MULTICAST
	      a multicast address

       BLACKHOLE
	      a blackhole address

       UNREACHABLE
	      an unreachable address

       PROHIBIT
	      a prohibited address

       THROW  FIXME

       NAT    FIXME

       XRESOLVE

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

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

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

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

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

       [!] --ahspi spi[:spi]

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

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

       --cluster-total-nodes num
	      Set number of total nodes in cluster.

       [!] --cluster-local-node num
	      Set the local node number ID.

       [!] --cluster-local-nodemask mask
	      Set  the	local  node  number  ID  mask. You can use this option instead of --clus-
	      ter-local-node.

       --cluster-hash-seed value
	      Set seed value of the Jenkins hash.

       Example:

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

	      iptables -A PREROUTING -t mangle -i eth2 -m cluster --cluster-total-nodes 2 --clus-
	      ter-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 man-
	      gle --mangle-mac-d 00:zz:yy:xx:5a:27

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

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

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

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

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

       --comment comment

       Example:
	      iptables -A INPUT -i eth1 -m comment --comment "my local LAN"

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

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

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

       The  transferred  bytes	per  connection  can  also  be	viewed through `conntrack -L` and
       accessed via ctnetlink.

       NOTE that for connections which have no accounting  information,  the  match  will  always
       return  false. The "net.netfilter.nf_conntrack_acct" sysctl flag controls whether new con-
       nections will be byte/packet counted. Existing connection flows will not be gaining/losing
       a/the accounting structure when be sysctl flag is flipped.

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

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

       --connbytes-mode {packets|bytes|avgpkt}
	      whether  to check the amount of packets, number of bytes transferred or the average
	      size (in bytes) of all packets received so far.  Note  that  when  "both"  is  used
	      together with "avgpkt", and data is going (mainly) only in one direction (for exam-
	      ple 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 net-
       mask)
	      iptables -p tcp --syn --dport 80 -m connlimit --connlimit-above 16 --connlimit-mask
	      24 -j REJECT

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

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

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

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

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

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

       [!] --ctorigsrc address[/mask]

       [!] --ctorigdst address[/mask]

       [!] --ctreplsrc address[/mask]

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

       [!] --ctorigsrcport port

       [!] --ctorigdstport port

       [!] --ctreplsrcport port

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

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

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

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

       States for --ctstate:

       INVALID
	      meaning that the packet is associated with no known connection

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

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

       RELATED
	      meaning  that  the  packet  is starting a new connection, but is associated with an
	      existing connection, such as an FTP data transfer, or an ICMP error.

       UNTRACKED
	      meaning that the packet is not tracked at all, which happens if you use the NOTRACK
	      target in raw table.

       SNAT   A  virtual  state,  matching  if the original source address differs from the reply
	      destination.

       DNAT   A virtual state, matching if  the  original  destination	differs  from  the  reply
	      source.

       Statuses for --ctstatus:

       NONE   None of the below.

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

       SEEN_REPLY
	      Conntrack has seen packets in both directions.

       ASSURED
	      Conntrack entry should never be early-expired.

       CONFIRMED
	      Connection is confirmed: originating packet has left box.

   cpu
       [!] --cpu number
	      Match  cpu  handling this packet. cpus are numbered from 0 to NR_CPUS-1 Can be used
	      in combination with RPS (Remote Packet Steering) or multiqueue NICs to spread  net-
	      work traffic on different queues.

       Example:

       iptables -t nat -A PREROUTING -p tcp --dport 80 -m cpu --cpu 0 -j REDIRECT --to-port 8080

       iptables -t nat -A PREROUTING -p tcp --dport 80 -m cpu --cpu 1 -j REDIRECT --to-port 8081

       Available since Linux 2.6.36.

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

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

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

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

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

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

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

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

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

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

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

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

       [!] --espspi spi[:spi]

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

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

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

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

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

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

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

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

       --hashlimit-mode {srcip|srcport|dstip|dstport},...
	      A  comma-separated  list	of  objects  to  take  into  consideration. If no --hash-
	      limit-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 sub-
	      ject  to	hashlimit. prefix must be between (inclusive) 0 and 32. Note that --hash-
	      limit-srcmask 0 is basically doing the same  thing  as  not  specifying  srcip  for
	      --hashlimit-mode, but is technically more expensive.

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

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

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

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

       --hashlimit-htable-expire msec
	      After how many milliseconds do hash entries expire.

       --hashlimit-htable-gcinterval msec
	      How many milliseconds between garbage collection intervals.

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

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

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

	      Same rules apply for other conntrack-helpers.

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

       [!] --icmp-type {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.

   ipvs
       Match IPVS connection properties.

       [!] --ipvs
	      packet belongs to an IPVS connection

       Any of the following options implies --ipvs (even negated)

       [!] --vproto protocol
	      VIP protocol to match; by number or name, e.g. "tcp"

       [!] --vaddr address[/mask]
	      VIP address to match

       [!] --vport port
	      VIP port to match; by number or name, e.g. "http"

       --vdir {ORIGINAL|REPLY}
	      flow direction of packet

       [!] --vmethod {GATE|IPIP|MASQ}
	      IPVS forwarding method used

       [!] --vportctl port
	      VIP port of the controlling connection to match, e.g. 21 for FTP

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

       [!] --length length[:length]

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

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

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

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

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

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

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

       [!] --source-ports,--sports port[,port|,port:port]...
	      Match  if the source port is one of the given ports.  The flag --sports is a conve-
	      nient 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.

   osf
       The osf module does passive operating system fingerprinting. This  modules  compares  some
       data  (Window  Size,  MSS, options and their order, TTL, DF, and others) from packets with
       the SYN bit set.

       [!] --genre string
	      Match an operating system genre by using a passive fingerprinting.

       --ttl level
	      Do additional TTL checks on the packet to determine the  operating  system.   level
	      can be one of the following values:

       o   0 - True IP address and fingerprint TTL comparison. This generally works for LANs.

       o   1 - Check if the IP header's TTL is less than the fingerprint one. Works for globally-
	   routable addresses.

       o   2 - Do not compare the TTL at all.

       --log level
	   Log determined genres into dmesg even if they do not match the desired one.	level can
	   be one of the following values:

       o   0 - Log all matched or unknown signatures

       o   1 - Log only the first one

       o   2 - Log all known matched signatures

       You may find something like this in syslog:

       Windows	[2000:SP3:Windows  XP  Pro  SP1,  2000	SP3]: 11.22.33.55:4024 -> 11.22.33.44:139
       hops=3 Linux [2.5-2.6:] : 1.2.3.4:42624 -> 1.2.3.5:22 hops=4

       OS fingerprints are loadable using the nfnl_osf program. To load fingerprints from a file,
       use:

       nfnl_osf -f /usr/share/xtables/pf.os

       To remove them again,

       nfnl_osf -f /usr/share/xtables/pf.os -d

       The    fingerprint   database   can   be   downlaoded   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.  This  match  is only valid in the OUTPUT and POSTROUTING chains. For-
       warded packets do not have any socket associated with them. Packets from kernel threads do
       have a socket, but usually no owner.

       [!] --uid-owner username

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

       [!] --gid-owner groupname

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

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

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

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

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

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

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

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

   pkttype
       This module matches the link-layer packet type.

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

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

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

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

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

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

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

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

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

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

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

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

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

       [!] --quota bytes
	      The quota in bytes.

   rateest
       The  rate  estimator  can  match on estimated rates as collected by the RATEEST target. It
       supports matching on absolute bps/pps values, comparing 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 calculated).

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

       --rateest-bps1 value

       --rateest-bps2 value
	      Compare bytes per second.

       --rateest-pps1 value

       --rateest-pps2 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-inter-
       val 250ms --rateest-ewma 0.5s

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

       # Mark based on available bandwidth

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

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

       iptables -t mangle -A balance -j CONNMARK --restore-mark

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

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

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

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

       --set, --rcheck, --update and --remove are mutually exclusive.

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

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

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

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

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

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

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

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

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

       --hitcount hits
	      This  option  must  be  used  in conjunction with one of --rcheck or --update. When
	      used, this will narrow the match to only happen when the address is in the list and
	      packets had been received greater than or equal to the given value. This option may
	      be used along with --seconds to create an even narrower match requiring  a  certain
	      number  of  hits	within	a specific time frame. The maximum value for the hitcount
	      parameter is given by the "ip_pkt_list_tot" parameter of the xt_recent kernel  mod-
	      ule. Exceeding this value on the command line will cause the rule to be rejected.

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

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

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

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

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

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

       The module itself accepts parameters, defaults shown:

       ip_list_tot=100
	      Number of addresses remembered per table.

       ip_pkt_list_tot=20
	      Number of packets per address remembered.

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

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

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

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

   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 SHUT-
	      DOWN_ACK ERROR COOKIE_ECHO COOKIE_ACK  ECN_ECNE  ECN_CWR	SHUTDOWN_COMPLETE  ASCONF
	      ASCONF_ACK FORWARD_TSN

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

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

       Examples:

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

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

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

   set
       This module matches IP sets which can be defined by ipset(8).

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

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

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

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

       Use of -m set requires that ipset kernel support is provided. As standard kernels  do  not
       ship this currently, the ipset or Xtables-addons package needs to be installed.

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

   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 connec-
	      tion which has seen packets in both directions, NEW meaning  that  the  packet  has
	      started  a  new connection, or otherwise associated with a connection which has not
	      seen packets in both directions, and RELATED meaning that the packet is starting	a
	      new  connection, but is associated with an existing connection, such as an FTP data
	      transfer, or an ICMP error.  UNTRACKED meaning that the packet is  not  tracked  at
	      all, which happens if you use the NOTRACK target in raw table.

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

       Supported options:

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

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

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

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

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

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

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

       --to offset
	      Set the offset up to which should be scanned. That is, byte offset-1 (counting from
	      0) is the last one that is scanned.  If not passed, default is the packet size.

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

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

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

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

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

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

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

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

   tcpmss
       This matches the TCP MSS (maximum segment size) field of the TCP header.  You can only use
       this  on TCP SYN or SYN/ACK packets, since the MSS is only negotiated during the TCP hand-
       shake 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 pos-
	      sible time range is 1970-01-01T00:00:00 to 2038-01-19T04:17:07.

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

       --timestart hh:mm[:ss]

       --timestop hh:mm[:ss]

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

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

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

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

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

       --utc

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

       --localtz

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

       EXAMPLES. To match on weekends, use:

	      -m time --weekdays Sa,Su

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

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

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

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

       During lunch hour:

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

       The fourth Friday in the month:

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

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

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

       [!] --tos value[/mask]
	      Matches  packets with the given TOS mark value. If a mask is specified, it is logi-
	      cally 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 rec-
	      ognized  TOS  names  can be obtained by calling iptables with -m tos -h.	Note that
	      this implies a mask of 0x3F, i.e. all but the ECN bits.

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

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

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

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

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

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

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

	      value := range | value "," range

	      range := number | number ":" number

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

	   location := number | location operator number

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

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

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

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

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

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

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

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

	      B and C are unsigned 32 bit integers, initially zero

       The instructions are:

	      number B = number;

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

	      &number C = C & number

	      << number C = C << number

	      >> number C = C >> number

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

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

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

       Example:

	      match IP packets with total length >= 256

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

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

	      read bytes 0-3

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

       Example: (more realistic, hence more complicated)

	      match ICMP packets with icmp type 0

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

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

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

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

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

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

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

       Example:

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

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

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

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

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

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

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

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

       [!] --destination-port,--dport port[:port]
	      Destination  port or port range specification.  See the description of the --desti-
	      nation-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 dis-
       tribution.

   CHECKSUM
       This target allows to selectively work around broken/old applications.	It  can  only  be
       used in the mangle table.

       --checksum-fill
	      Compute  and  fill in the checksum in a packet that lacks a checksum.  This is par-
	      ticularly useful, if you need to work around old applications such as dhcp clients,
	      that  do	not  work well with checksum offloads, but don't want to disable checksum
	      offload in your device.

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

       --set-class major:minor
	      Set the major and minor class value. The values are always interpreted as hexadeci-
	      mal 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 stati-
       cally 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, sour-
	      ceip-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.	The  mark  is  32
       bits wide.

       --set-xmark value[/mask]
	      Zero out the bits given by mask and XOR value into the ctmark.

       --save-mark [--nfmask nfmask] [--ctmask ctmask]
	      Copy  the  packet  mark  (nfmark)  to  the connection mark (ctmark) using the given
	      masks. The new nfmark value is determined as follows:

	      ctmark = (ctmark & ~ctmask) ^ (nfmark & nfmask)

	      i.e. ctmask defines what bits to clear and nfmask what bits of the  nfmark  to  XOR
	      into the ctmark. ctmask and nfmask default to 0xFFFFFFFF.

       --restore-mark [--nfmask nfmask] [--ctmask ctmask]
	      Copy  the  connection  mark  (ctmark)  to  the packet mark (nfmark) using the given
	      masks. The new ctmark value is determined as follows:

	      nfmark = (nfmark & ~nfmask) ^ (ctmark & ctmask);

	      i.e. nfmask defines what bits to clear and ctmask what bits of the  ctmark  to  XOR
	      into the nfmark. ctmask and nfmask default to 0xFFFFFFFF.

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

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

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

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

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

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

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

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

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

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

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

   CT
       The CT target allows to set parameters for a packet or its associated connection. The tar-
       get  attaches  a "template" connection tracking entry to the packet, which is then used by
       the conntrack core when initializing a new ct entry. This target is thus only valid in the
       "raw" table.

       --notrack
	      Disables connection tracking for this packet.

       --helper name
	      Use  the	helper	identified by name for the connection. This is more flexible than
	      loading the conntrack helper modules with preset ports.

       --ctevents event[,...]
	      Only generate the specified conntrack events for this  connection.  Possible  event
	      types  are:  new,  related,  destroy, reply, assured, protoinfo, helper, mark (this
	      refers to the ctmark, not nfmark), natseqinfo, secmark (ctsecmark).

       --expevents event[,...]
	      Only generate the specified expectation events for this connection.  Possible event
	      types are: new.

       --zone id
	      Assign this packet to zone id and only have lookups done in that zone.  By default,
	      packets have zone 0.

   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 spec-
	      ifies  -p tcp or -p udp).  If no port range is specified, then the destination port
	      will never be modified. If no IP address is specified  then  only  the  destination
	      port will be modified.

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

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

       --persistent
	      Gives  a	client	the  same  source-/destination-address for each connection.  This
	      supersedes the SAME target. Support  for	persistent  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 con-
	      junction with -p tcp.

   IDLETIMER
       This target can be used to identify when interfaces have been idle for a certain period of
       time.   Timers  are  identified	by  labels  and are created when a rule is set with a new
       label.  The rules also take a timeout value (in seconds) as an option.  If more	than  one
       rule  uses the same timer label, the timer will be restarted whenever any of the rules get
       a hit.  One entry for each timer is created in sysfs.  This attribute contains  the  timer
       remaining  for  the  timer  to  expire.	The attributes are located under the xt_idletimer
       class:

       /sys/class/xt_idletimer/timers/<label>

       When the timer expires, the target module sends a sysfs	notification  to  the  userspace,
       which can then decide what to do (eg. disconnect to save power).

       --timeout amount
	      This is the time in seconds that will trigger the notification.

       --label string
	      This is a unique identifier for the timer.  The maximum length for the label string
	      is 27 characters.

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

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

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

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

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

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

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

   MARK
       This target is used to set the Netfilter mark value associated with the packet.	 It  can,
       for  example, be used in conjunction with routing based on fwmark (needs iproute2). If you
       plan on doing so, note that the mark needs to be set in the PREROUTING chain of the mangle
       table to affect routing.  The mark field is 32 bits wide.

       --set-xmark value[/mask]
	      Zeroes  out  the bits given by mask and XORs value into the packet mark ("nfmark").
	      If mask is omitted, 0xFFFFFFFF is assumed.

       --set-mark value[/mask]
	      Zeroes out the bits given by mask and ORs value into the packet mark.  If  mask  is
	      omitted, 0xFFFFFFFF is assumed.

       The following mnemonics are available:

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

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

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

   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 connec-
       tions 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 con-
       nections 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 speci-
	      fies -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,  FOR-
       WARD  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,  con-
       nection 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  fol-
	      lowing  way:  All 'one' bits in the mask are filled in from the new `address'.  All
	      bits that are zero in the mask are filled in from the original address.

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

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

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

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

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

   NFQUEUE
       This target is an extension of the QUEUE target. As opposed to QUEUE, it allows you to put
       a  packet  into any specific queue, identified by its 16-bit queue number.  It can only be
       used with Kernel versions 2.6.14 or later, since it requires  the  nfnetlink_queue  kernel
       support. The queue-balance option was added in Linux 2.6.31.

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

       --queue-balance value:value
	      This specifies a range of queues to use. Packets are then balanced across the given
	      queues.	This  is  useful  for  multicore systems: start multiple instances of the
	      userspace program on queues x, x+1, .. x+n and use "--queue-balance x:x+n".   Pack-
	      ets belonging to the same connection are put into the same nfqueue.

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

       It can only be used in the raw table.

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

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

       --rateest-interval amount{s|ms|us}
	      Rate measurement interval, in seconds, milliseconds or microseconds.

       --rateest-ewmalog value
	      Rate measurement averaging time constant.

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

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

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

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

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

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

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

       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 for use by security
       subsystems such as SELinux.  It is only valid in the mangle table. The  mark  is  32  bits
       wide.

       --selctx security_context

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

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

       --del-set setname flag[,flag...]
	      delete the address(es)/port(s) of the packet from the sets

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

       Use of -j SET requires that ipset kernel support is provided. As standard kernels  do  not
       ship this currently, the ipset or Xtables-addons package needs to be installed.

   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  con-
       nection	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 spec-
	      ifies -p tcp or -p udp).	If no port range is specified, then  source  ports  below
	      512  will  be mapped to other ports below 512: those between 512 and 1023 inclusive
	      will be mapped to ports below 1024, and other ports  will  be  mapped  to  1024  or
	      above. Where possible, no port alteration will

	      In  Kernels  up  to 2.6.10, you can add several --to-source options. For those ker-
	      nels, 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	persistent  mappings  is  available  from
	      2.6.29-rc2.

   TCPMSS
       This  target allows to alter the MSS value of TCP SYN packets, to control the maximum size
       for that connection (usually limiting it to your outgoing interface's  MTU  minus  40  for
       IPv4 or 60 for IPv6, respectively).  Of course, it can only be used in conjunction with -p
       tcp.

       This target is used to overcome criminally braindead ISPs or  servers  which  block  "ICMP
       Fragmentation  Needed"  or  "ICMPv6 Packet Too Big" packets.  The symptoms of this problem
       are that everything works fine from your Linux firewall/router, but machines behind it can
       never exchange large packets:
	1) Web browsers connect, then hang with no data received.
	2) Small mail works fine, but large emails hang.
	3) ssh works fine, but scp hangs after initial handshaking.
       Workaround: activate this option and add a rule to your firewall configuration like:

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

       --set-mss value
	      Explicitly  sets MSS option to specified value. If the MSS of the packet is already
	      lower than value, it will not be increased (from Linux  2.6.25  onwards)	to  avoid
	      more problems with hosts relying on a proper MSS.

       --clamp-mss-to-pmtu
	      Automatically  clamp MSS value to (path_MTU - 40 for IPv4; -60 for IPv6).  This may
	      not function as desired where asymmetric routes with differing path  MTU	exist  --
	      the  kernel uses the path MTU which it would use to send packets from itself to the
	      source and destination IP addresses. Prior to Linux 2.6.25, only the  path  MTU  to
	      the  destination	IP address was considered by this option; subsequent kernels also
	      consider the path MTU to the source IP address.

       These options are mutually exclusive.

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

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

   TEE
       The TEE target will clone a packet and redirect this clone to another machine on the local
       network segment. In other words, the nexthop must be the target, or you will have to  con-
       figure the nexthop to forward it further if so desired.

       --gateway ipaddr
	      Send  the  cloned  packet  to  the  host reachable at the given IP address.  Use of
	      0.0.0.0 (for IPv4 packets) or :: (IPv6) is invalid.

       To forward all incoming traffic on eth0 to an Network Layer logging box:

       -t mangle -A PREROUTING -i eth0 -j TEE --gateway 2001:db8::1

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

       --set-tos value[/mask]
	      Zeroes out the bits given by mask 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 redirects the packet to a local socket
       without changing the packet header in any way. It can also change the mark value which can
       then be used in advanced routing rules.	It takes three options:

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

       --on-ip address
	      This  specifies  a  destination  address	to  use. By default the address is the IP
	      address of the incoming interface. This is only valid if the rule also specifies -p
	      tcp or -p udp.

       --tproxy-mark value[/mask]
	      Marks  packets  with the given value/mask. The fwmark value set here can be used by
	      advanced routing. (Required for transparent proxying to work: otherwise these pack-
	      ets will get forwarded, which is probably not what you want.)

   TRACE
       This target marks packes so that the kernel will log every rule which match the packets as
       those traverse the tables, chains, rules. (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 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.

       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 subscribe to various multicast groups and receive  the  pack-
       ets.   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 accumu-
	      lates ten packets inside the kernel and transmits them  as  one  netlink	multipart
	      message to userspace.  Default is 1 (for backwards compatibility).

DIAGNOSTICS
       Various	error  messages  are  printed  to standard error.  The exit code is 0 for correct
       functioning.  Errors which appear to be caused by invalid or abused command  line  parame-
       ters 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.netfil-
       ter.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  out-
       put 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 filter-
       ing 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 frame-
       work in iptables, then wrote the mangle table, the owner match, the mark  stuff,  and  ran
       around doing cool stuff everywhere.

       James Morris wrote the TOS target, and tos match.

       Jozsef Kadlecsik wrote the REJECT target.

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

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

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

iptables 1.4.10 								      IPTABLES(8)
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