iptables

IPTABLES(8)                      iptables 1.4.7                      IPTABLES(8)



NAME
       iptables — administration tool for IPv4 packet filtering and NAT

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

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

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

       iptables [-t table] -D chain rulenum

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

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

       iptables [-t table] -N chain

       iptables [-t table] -X [chain]

       iptables [-t table] -P chain target

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

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

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

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

DESCRIPTION
       Iptables is used to set up, maintain, and inspect the tables of IPv4
       packet filter rules in the Linux kernel.  Several different tables may be
       defined.  Each table contains a 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)

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.

       -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
              all, or it can be a numeric value, representing one of these
              protocols or a different one.  A protocol name from /etc/protocols
              is also allowed.  A "!" argument before the protocol inverts the
              test.  The number zero is equivalent to all.  Protocol all will
              match with all 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.

       -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.

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

   addrtype
       This module matches packets based on their address type.  Address types
       are used within the kernel networking stack and categorize addresses into
       various groups.  The exact definition of that group depends on the
       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 -s 192.168.0.0/16 -m comment --comment "A
              privatized IP block"

   connbytes
       Match by how many bytes or packets a connection (or one of the two flows
       constituting the connection) has transferred so far, or by 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-above n
              Match if the number of existing connections is (not) above n.

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

       Examples:

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

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

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

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

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

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

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

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

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

       [!] --ctorigsrc address[/mask]

       [!] --ctorigdst address[/mask]

       [!] --ctreplsrc address[/mask]

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

       [!] --ctorigsrcport port

       [!] --ctorigdstport port

       [!] --ctreplsrcport port

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

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

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

       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.

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

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

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

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

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

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

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

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

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

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

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

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

       [!] --espspi spi[:spi]

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

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

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

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

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

   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.

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

       [!] --length length[:length]

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

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

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

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

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

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

   multiport
       This module matches a set of source or destination ports.  Up to 15 ports
       can be 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.

   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.

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

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

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

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

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

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

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

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

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

       --quota bytes
              The quota in bytes.

   rateest
       The rate estimator can match on estimated rates as collected by the
       RATEEST target. It supports matching on absolute bps/pps values,
       comparing two rate estimators and matching on the difference between two
       rate estimators.

       --rateest1 name
              Name of the first rate estimator.

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

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

       --rateest1-bps value

       --rateest2-bps value
              Compare bytes per second.

       --rateest1-pps value

       --rateest2-pps value
              Compare packets per second.

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

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

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

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

       # Estimate outgoing rates

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

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

       # Mark based on available bandwidth

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

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

       --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

              chunk type            available flags
              DATA                  U B E 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.

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

       Supported options:

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

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

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

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

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

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

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

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

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

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

   tcp
       These extensions can be used if `--protocol tcp' is specified. It
       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.

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

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

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

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

       --timestart hh:mm[:ss]

       --timestop hh:mm[:ss]

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

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

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

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

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

       --utc

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

       --localtz

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

       EXAMPLES. To match on weekends, use:

              -m time --weekdays Sa,Su

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

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

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

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

       During lunch hour:

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

       The fourth Friday in the month:

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

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

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

       [!] --tos value[/mask]
              Matches packets with the given TOS mark value. If a mask is
              specified, it is 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 only valid
       in the mangle table.

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

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


   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.

   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.  The target can only be used in the mangle table. It can, for
       example, be used in conjunction with routing based on fwmark (needs
       iproute2). 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).  It takes one option:

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

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

   MIRROR
       This is an experimental demonstration target which inverts the source and
       destination fields in the IP header and retransmits the packet.  It is
       only valid in the INPUT, FORWARD and PREROUTING chains, and user-defined
       chains which are only called from those chains.  Note that the outgoing
       packets are NOT seen by any packet filtering chains, 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 (1 - 2^32-1) to which packets are (only
              applicable for nfnetlink_log). The default value is 0.

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

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

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

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

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

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

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

       It can only be used in the raw table.

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

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

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

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

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

       --to-ports port[-port]
              This specifies a destination port or range of ports to use:
              without this, the 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 only valid in the
       mangle table. The mark is 32 bits wide.

       --selctx security_context

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

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

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

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

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

   SNAT
       This target is only valid in the nat table, in the POSTROUTING chain.  It
       specifies that the source address of the packet should be modified (and
       all future packets in this 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

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

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

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

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

       The following mnemonics are available:

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

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

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

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

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

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

       --tproxy-mark value[/mask]
              Marks packets with the given value/mask. The fwmark value set here
              can be used by advanced routing. (Required for transparent
              proxying to work: otherwise these 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. (The
       ipt_LOG or ip6t_LOG module is required for the logging.) 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.

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

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

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

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

   ULOG
       This target provides userspace logging of matching packets.  When this
       target is set for a rule, the Linux kernel will multicast this packet
       through a netlink socket. One or more userspace processes may then
       subscribe to various multicast groups and receive the 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>.



iptables 1.4.7                                                       IPTABLES(8)