Provided by: iptables_1.4.12-1ubuntu4_amd64 bug

NAME

       iptables — administration tool for IPv4 packet filtering and NAT

SYNOPSIS

       iptables [-t table] {-A|-C|-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
       number of built-in chains and may also contain user-defined chains.

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

TARGETS

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

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

TABLES

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

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

              The tables are as follows:

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

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

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

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

              security:
                  This table is used for Mandatory Access Control (MAC) networking rules, such as
                  those enabled by the SECMARK and CONNSECMARK targets.  Mandatory Access Control
                  is implemented by Linux Security Modules such as SELinux.  The  security  table
                  is  called  after  the  filter table, allowing any Discretionary Access Control
                  (DAC) rules in the filter table to take effect before MAC  rules.   This  table
                  provides  the following built-in chains: INPUT (for packets coming into the box
                  itself), OUTPUT (for altering locally-generated packets  before  routing),  and
                  FORWARD (for altering packets being routed through the box).

OPTIONS

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

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

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

       -C, --check chain rule-specification
              Check whether a rule matching the specification does exist in the  selected  chain.
              This command uses the same logic as -D to find a matching entry, but does not alter
              the existing iptables configuration and uses its exit code to indicate  success  or
              failure.

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

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

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

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

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

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

       -Z, --zero [chain [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
              neither built-in nor user-defined chains can be policy targets.

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

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

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

       [!] -p, --protocol protocol
              The  protocol of the rule or of the packet to check.  The specified protocol can be
              one of tcp, udp, udplite, icmp, esp, ah, sctp or the special keyword "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. "all" will match
              with all protocols and is taken as default when this option is omitted.

       [!] -s, --source address[/mask][,...]
              Source specification. Address can be either a network name, a hostname,  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
              multiple 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
              omitted, any interface name will match.

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

       -c, --set-counters 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
              multipliers  respectively  (but  see  the  -x flag to change this).  For appending,
              insertion, deletion and replacement, this causes detailed information on  the  rule
              or  rules  to  be printed. -v may be specified multiple times to possibly emit more
              detailed debug statements.

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

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

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

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

MATCH EXTENSIONS

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

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

       The following address types are possible:

       UNSPEC an unspecified address (i.e. 0.0.0.0)

       UNICAST
              an unicast address

       LOCAL  a local address

       BROADCAST
              a broadcast address

       ANYCAST
              an anycast packet

       MULTICAST
              a multicast address

       BLACKHOLE
              a blackhole address

       UNREACHABLE
              an unreachable address

       PROHIBIT
              a prohibited address

       THROW  FIXME

       NAT    FIXME

       XRESOLVE

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

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

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

       --limit-iface-out
              The  address type 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
              --cluster-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
              --cluster-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
              --cluster-local-node 1 --cluster-hash-seed 0xdeadbeef -j MARK --set-mark 0xffff

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

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

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

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

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

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

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

              arptables -A OUTPUT -o eth2 --h-length 6 -j mangle --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
              mangle --mangle-mac-d 00:zz:yy:xx:5a:27

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

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

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

       --comment comment

       Example:
              iptables -A INPUT -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
       connections  will  be  byte/packet  counted.  Existing  connection  flows  will   not   be
       gaining/losing a/the accounting structure when be sysctl flag is flipped.

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

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

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

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

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

       --connlimit-upto n
              Match if the number of existing connections is below or equal n.

       --connlimit-above n
              Match if the number of existing connections is 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. If not  specified,  the  maximum
              prefix length for the applicable protocol is used.

       --connlimit-saddr
              Apply the limit onto the source group.

       --connlimit-daddr
              Apply the limit onto the destination group.

       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-upto 2 -j ACCEPT

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

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

       # Limit the number of connections to a particular host:
              ip6tables -p tcp --syn --dport 49152:65535 -d 2001:db8::1 -m connlimit --connlimit-
              above 100 -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[:port]

       [!] --ctorigdstport port[:port]

       [!] --ctreplsrcport port[:port]

       [!] --ctrepldstport port[:port]
              Match against original/reply source/destination port  (TCP/UDP/etc.)  or  GRE  key.
              Matching against port ranges is only supported in kernel versions above 2.6.38.

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

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

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

       States for --ctstate:

       INVALID
              meaning that the packet is associated with no known connection

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

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

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

       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
              network 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" (see below for some examples).

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

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

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

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

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

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

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

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

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

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

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

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

       Examples:

       matching on source host
              "1000 packets per second for every host in  192.168.0.0/16"  =>  -s  192.168.0.0/16
              --hashlimit-mode srcip --hashlimit-upto 1000/sec

       matching on source port
              "100  packets  per  second  for  every  service  of  192.168.1.1" => -s 192.168.1.1
              --hashlimit-mode srcport --hashlimit-upto 100/sec

       matching on subnet
              "10000 packets per  minute  for  every  /28  subnet  (groups  of  8  addresses)  in
              10.0.0.0/8" => -s 10.0.0.8 --hashlimit-mask 28 --hashlimit-upto 10000/min

   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.  It can be used in combination with  the
       LOG target to give limited logging, for example.

       xt_limit  has  no negation support - you will have to use -m hashlimit !  --hashlimit rate
       in this case whilst omitting --hashlimit-mode.

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

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

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

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

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

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

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

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

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

   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:

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

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

       ·   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:

       ·   0 - Log all matched or unknown signatures

       ·   1 - Log only the first one

       ·   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.
       Forwarded packets do not have any socket associated with them. Packets from kernel threads
       do have a socket, but usually no owner.

       [!] --uid-owner username

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

       [!] --gid-owner groupname

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

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

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

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

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

       --pol {none|ipsec}
              Matches if the packet is subject to IPsec processing. --pol none cannot be combined
              with --strict.

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

       For each policy element that is to be described, one can use one or more of the  following
       options. When --strict is in effect, at least one must be used per element.

       [!] --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.  The  condition
       matches  until the byte counter reaches zero. Behavior is reversed with negation (i.e. the
       condition does not match until the byte counter reaches zero).

       [!] --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.

       For a better understanding of the available options, these are all possible combinations:

       ·   rateest operator rateest-bps

       ·   rateest operator rateest-pps

       ·   (rateest minus rateest-bps1) operator rateest-bps2

       ·   (rateest minus rateest-pps1) operator rateest-pps2

       ·   rateest1 operator rateest2 rateest-bps(without rate!)

       ·   rateest1 operator rateest2 rateest-pps(without rate!)

       ·   (rateest1 minus rateest-bps1) operator (rateest2 minus rateest-bps2)

       ·   (rateest1 minus rateest-pps1) operator (rateest2 minus rateest-pps2)

       --rateest-delta
           For each estimator (either  absolute  or  relative  mode),  calculate  the  difference
           between  the  estimator-determined  flow  rate  and  the  static value chosen with the
           BPS/PPS options. If the flow rate is higher than the specified BPS/PPS, 0 will be used
           instead of a negative value. In other words, "max(0, rateest#_rate - rateest#_bps)" is
           used.

       [!] --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.

       In the so-called "absolute mode", only one rate estimator is used and compared  against  a
       static value, while in "relative mode", two rate estimators are compared against another.

       --rateest name
              Name of the one rate estimator for absolute mode.

       --rateest1 name

       --rateest2 name
              The names of the two rate estimators for relative mode.

       --rateest-bps [value]

       --rateest-pps [value]

       --rateest-bps1 [value]

       --rateest-bps2 [value]

       --rateest-pps1 [value]

       --rateest-pps2 [value]
              Compare  the  estimator(s)  by bytes or packets per second, and compare against the
              chosen value. See the above bullet list for which option is to  be  used  in  which
              case.  A  unit suffix may be used - available ones are: bit, [kmgt]bit, [KMGT]ibit,
              Bps, [KMGT]Bps, [KMGT]iBps.

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

       # Estimate outgoing rates

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

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

       # Mark based on available bandwidth

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

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

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

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

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

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

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

       --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 can only be used in conjunction with --seconds.  When used,  this  will
              cause entries older then 'seconds' to be purged.

       --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
              module.  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
              sending bogus packets to you.

       Examples:

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

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

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

       /proc/net/xt_recent/*  are the current lists of addresses and 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
              SHUTDOWN_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.

       --transparent
              Ignore non-transparent sockets.

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

       [!] --state state
              Where  state is a comma separated list of the connection states to match.  Possible
              states are INVALID meaning that the packet could not be identified for some  reason
              which  includes running out of memory and ICMP errors which don't correspond to any
              known connection,  ESTABLISHED  meaning  that  the  packet  is  associated  with  a
              connection  which  has seen packets in both directions, NEW meaning that the packet
              has started a new connection, or otherwise associated with a connection  which  has
              not  seen  packets  in  both  directions,  and  RELATED  meaning that the packet is
              starting a new connection, but is associated with an existing connection,  such  as
              an  FTP  data transfer, or an ICMP error.  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  for  a packet to be randomly matched. It only works with the
              random mode. p must be  within  0.0  and  1.0.  The  supported  granularity  is  in
              1/2147483648th increments.

       [!] --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
              outgoing TCP connections will be  unaffected.   It  is  equivalent  to  --tcp-flags
              SYN,RST,ACK,FIN SYN.  If the "!" flag precedes the "--syn", the sense of the option
              is inverted.

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

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

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

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

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

       --datestop YYYY[-MM[-DD[Thh[:mm[:ss]]]]]
              Only  match  during  the  given  time, which must be in ISO 8601 "T" notation.  The
              possible time range is 1970-01-01T00:00:00 to 2038-01-19T04:17:07.

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

       --timestart hh:mm[:ss]

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

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

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

       --kerneltz
              Use the kernel timezone instead of UTC to determine whether a packet meets the time
              regulations.

       About kernel timezones: Linux keeps the system time in UTC, and always does so.  On  boot,
       system  time  is initialized from a referential time source. Where this time source has no
       timezone information, such as the x86 CMOS RTC, UTC will be assumed. If the time source is
       however  not  in UTC, userspace should provide the correct system time and timezone to the
       kernel once it has the information.

       Local time is a feature on top of the (timezone independent) system time. Each process has
       its own idea of local time, specified via the TZ environment variable. The kernel also has
       its own timezone offset variable. The TZ userspace environment variable specifies how  the
       UTC-based  system  time  is  displayed, e.g. when you run date(1), or what you see on your
       desktop clock.  The TZ string may resolve to different offsets at different  dates,  which
       is  what  enables  the automatic time-jumping in userspace. when DST changes. The kernel's
       timezone offset variable is used when it has to convert between non-UTC sources,  such  as
       FAT filesystems, to UTC (since the latter is what the rest of the system uses).

       The  caveat  with  the  kernel  timezone is that Linux distributions may ignore to set the
       kernel timezone, and instead only set the system time. Even if a  particular  distribution
       does  set  the  timezone at boot, it is usually does not keep the kernel timezone offset -
       which is what changes on DST - up to date.  ntpd will not touch the  kernel  timezone,  so
       running  it  will  not  resolve  the  issue. As such, one may encounter a timezone that is
       always +0000, or one that is wrong half of the time of the year. As such, using --kerneltz
       is highly discouraged.

       EXAMPLES. To match on weekends, use:

              -m time --weekdays Sa,Su

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

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

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

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

       During lunch hour:

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

       The fourth Friday in the month:

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

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

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

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

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

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

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

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

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

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

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

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

              value := range | value "," range

              range := number | number ":" number

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

           location := number | location operator number

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

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

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

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

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

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

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

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

              B and C are unsigned 32 bit integers, initially zero

       The instructions are:

              number B = number;

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

              &number C = C & number

              << number C = C << number

              >> number C = C >> number

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

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

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

       Example:

              match IP packets with total length >= 256

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

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

              read bytes 0-3

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

       Example: (more realistic, hence more complicated)

              match ICMP packets with icmp type 0

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

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

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

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

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

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

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

       Example:

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

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

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

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

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

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

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

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

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

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

TARGET EXTENSIONS

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

   AUDIT
       This target allows to create audit records for packets hitting the target.  It can be used
       to record accepted, dropped, and rejected packets. See auditd(8) for additional details.

       --type {accept|drop|reject}
              Set type of audit record.

       Example:

              iptables -N AUDIT_DROP

              iptables -A AUDIT_DROP -j AUDIT --type drop

              iptables -A AUDIT_DROP -j DROP

   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
              particularly  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
              hexadecimal even if no 0x prefix is given.

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

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

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

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

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

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

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

   CONNMARK
       This  module  sets  the  netfilter mark value associated with a connection. 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  valid  in  the  security  table  (for backwards compatibility with older
       kernels, it is also 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
       target  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
              specifies  -p  tcp or -p udp).  If no port range is specified, then the destination
              port will never  be  modified.  If  no  IP  address  is  specified  then  only  the
              destination port will be modified.

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

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

       --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
              conjunction 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-
       terminating  target",  i.e.  rule traversal continues at the next rule.  So if you want to
       LOG the packets you refuse, use two separate rules with the same matching criteria,  first
       using target LOG then DROP (or REJECT).

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

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

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

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

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

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

   MARK
       This target is used to set the Netfilter mark value associated with the packet.   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
       connections are forgotten when the interface goes down.  This is the correct behavior when
       the  next dialup is unlikely to have the same interface address (and hence any established
       connections are lost anyway).

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

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

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

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

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

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

       --nflog-group nlgroup
              The  netlink  group  (0  -  2^16-1)  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-bypass in 2.6.39.

       --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".
              Packets belonging to the same connection are put into the same nfqueue.

       --queue-bypass
              By  default,  if  no userspace program is listening on an NFQUEUE, then all packets
              that are to be queued are dropped.  When this option is used, the NFQUEUE  rule  is
              silently bypassed instead. The packet will move on to the next rule.

   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
              destination port is never altered.  This is only valid if the rule  also  specifies
              -p tcp or -p udp.

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

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

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

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

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

       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  valid  in  the  security  table  (for  backwards
       compatibility with older kernels, it is also 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.

       --timeout value
              when adding entry, the timeout value to use instead of the default one from the set
              definition

       --exist
              when  adding  entry  if it already exists, reset the timeout value to the specified
              one or to the default from the set definition

       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
       connection  will  also  be  mangled), and rules should cease being examined.  It takes one
       type of option:

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

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

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

       --persistent
              Gives  a  client  the  same  source-/destination-address for each connection.  This
              supersedes the SAME target. Support  for  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
       configure 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  (see  NOTE  below)  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 (see NOTE below). 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.  See NOTE below.)

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

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

       NOTE: In Linux kernels up to and including 2.6.38, with the exception of longterm releases
       2.6.32.42  (or  later)  and 2.6.33.15 (or later), there is a bug whereby IPv6 TOS mangling
       does not behave as documented and differs from the IPv4 version. The  TOS  mask  indicates
       the  bits  one  wants  to  zero  out, so it needs to be inverted before applying it to the
       original TOS field. However, the aformentioned kernels forgo the  inversion  which  breaks
       --set-tos and its mnemonics.

   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
              packets 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.

       A  logging  backend,  such  as  ip(6)t_LOG or nfnetlink_log, must be loaded for this to be
       visible.    The    packets    are    logged    with    the    string    prefix:    "TRACE:
       tablename:chainname:type:rulenum  "  where type can be "rule" for plain rule, "return" for
       implicit rule at the end of a user defined chain and "policy" for the policy of the  built
       in chains.
       It can only be used in the raw table.

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

       Setting or incrementing the TTL field can potentially be very dangerous, so it  should  be
       avoided at any cost. This target is only valid in mangle table.

       Don't ever set or increment the value on packets that leave your local network!

       --ttl-set value
              Set the TTL value to `value'.

       --ttl-dec value
              Decrement the TTL value `value' times.

       --ttl-inc value
              Increment the TTL value `value' times.

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

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

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

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

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

DIAGNOSTICS

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

BUGS

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

COMPATIBILITY WITH IPCHAINS

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

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

       The various forms of NAT have been separated out; iptables is a pure  packet  filter  when
       using  the  default `filter' table, with optional extension modules.  This should simplify
       much of the previous  confusion  over  the  combination  of  IP  masquerading  and  packet
       filtering seen previously.  So the following options are handled differently:
        -j MASQ
        -M -S
        -M -L
       There are several other changes in iptables.

SEE ALSO

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

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

AUTHORS

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

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

       James Morris wrote the TOS target, and tos match.

       Jozsef Kadlecsik wrote the REJECT target.

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

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

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

VERSION

       This manual page applies to iptables @PACKAGE_VERSION@.