IPTABLES(8)                                                     iptables 1.4.12                                                    IPTABLES(8)

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@.
 

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