iptables -- administration tool for IPv4 packet filtering and NAT

       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]

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 ker- nels 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 speci- fied 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 rout-
                  ing), and POSTROUTING (for altering packets as they are about to go out).

              mangle:
                  This table is used for specialized packet alteration.  Until kernel 2.4.17 it had two built-in chains: PREROUTING (for
                  altering incoming packets before routing) and OUTPUT (for altering locally-generated packets before  routing).   Since
                  kernel 2.4.18, three other built-in chains are also 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 suc-
              cess 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 num-
              ber 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 opera-
              tions).

   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 multi-
              pliers 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 (mul-
              tiples 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 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.

       If  the -p or --protocol was specified and if and only if an unknown option is encountered, iptables will try load a match module
       of the same name as the protocol, to try making the option available.

   addrtype
       This module matches packets based on their address type.  Address types are used within the kernel networking stack  and  catego-
       rize 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 PRE-
              ROUTING, 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_con-
       ntrack_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  exam-
              ple HTTP), the average packet size will be about half of the actual data packets.

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

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

       --connlimit-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. This is the default if --connlimit-daddr is not specified.

       --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 sup-
              ported 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 DCCP 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/IPv6 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/IPv6 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 --hash-
              limit-srcmask 0 is basically doing the same thing as not specifying srcip for --hashlimit-mode, but  is  technically  more
              expensive.

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

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

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

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

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

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

       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 val-
       ues.

       [!] --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  --hash-
       limit-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 there-
              fore 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.

   nfacct
       The nfacct match provides the extended accounting infrastructure for iptables.  You have to use  this  match  together  with  the
       standalone user-space utility nfacct(8)

       The only option available for this match is the following:

       --nfacct-name name
              This  allows  you  to  specify  the existing object name that will be use for accounting the traffic that this rule-set is
              matching.

       To use this extension, you have to create an accounting object:

              nfacct add http-traffic

       Then, you have to attach it to the accounting object via iptables:

              iptables -I INPUT -p tcp --sport 80 -m nfacct --nfacct-name http-traffic

              iptables -I OUTPUT -p tcp --dport 80 -m nfacct --nfacct-name http-traffic

       Then, you can check for the amount of traffic that the rules match:

              nfacct get http-traffic

              { pkts = 00000000000000000156, bytes = 00000000000000151786 } = http-traffic;

       You can obtain nfacct(8) from http://www.netfilter.org or, alternatively, from the git.netfilter.org repository.

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

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

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

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

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

       o   2 - Do not compare the TTL at all.

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

       o   0 - Log all matched or unknown signatures

       o   1 - Log only the first one

       o   2 - Log all known matched signatures

       You may find something like this in syslog:

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

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

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

       To remove them again,

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

       The fingerprint database can be downlaoded from http://www.openbsd.org/cgi-bin/cvsweb/src/etc/pf.os .

   owner
       This module attempts to match various characteristics of the packet creator, for locally generated packets. This  match  is  only
       valid  in  the  OUTPUT and POSTROUTING chains. 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  infra-
       structure 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 val-
       ues, 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:

       o   rateest operator rateest-bps

       o   rateest operator rateest-pps

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

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

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

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

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

       o   (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 This  option can only be used in conjunction with --seconds.  When used, this will cause entries older than the last given
              number of 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 ker-
              nel 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.

   rpfilter
       Performs a reverse path filter test on a packet.  If a reply to the packet would be sent via the same interface that  the  packet
       arrived  on,  the  packet will match.  Note that, unlike the in-kernel rp_filter, packets protected by IPSec are not treated spe-
       cially.  Combine this match with the policy match if you want this.  Also, packets arriving via the loopback interface are always
       permitted.  This match can only be used in the PREROUTING chain of the raw or mangle table.

       --loose
              Used  to  specifiy  that  the reverse path filter test should match even if the selected output device is not the expected
              one.

       --validmark
              Also use the packets' nfmark value when performing the reverse path route lookup.

       --accept-local
              This will permit packets arriving from the network with a source address that is  also  assigned  to  the  local  machine.
              --invert  This  will invert the sense of the match.  Instead of matching packets that passed the reverse path filter test,
              match those that have failed it.

       Example to log and drop packets failing the reverse path filter test:

       iptables -t raw -N RPFILTER

       iptables -t raw -A RPFILTER -m rpfilter -j RETURN

       iptables -t raw -A RPFILTER -m limit --limit 10/minute -j NFLOG --nflog-prefix "rpfilter drop"

       iptables -t raw -A RPFILTER -j DROP

       iptables -t raw -A PREROUTING -j RPFILTER

       Example to drop failed packets, without logging:

       iptables -t raw -A RPFILTER -m rpfilter --invert -j DROP

   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, which, for standard kernels, is the case since Linux 2.6.39.

   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  associ-
              ated  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, respec-
              tively. 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  ref-
       erential  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 filesys-
       tems, 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 any-
              thing beyond the IP header. The last 6 bits of byte 6 and all of byte 7 are 0 iff this is a complete packet (not  a  frag-
              ment). 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.

       --timeout name
              Use  the  timeout  policy  identified by name for the connection. This is provides more flexible timeout policy definition
              than global timeout values available at /proc/sys/net/netfilter/nf_conntrack_*_timeout_*.

   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 des-
              tination  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  abil-
              ity 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/
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 inter- nals. 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 . VERSION This manual page applies to iptables @PACKAGE_VERSION@.