iptables-extensions(8)                     iptables-extensions(8)

     NAME
          iptables-extensions - list of extensions in the standard
          iptables distribution

     SYNOPSIS
          ip6tables [-m name [module-options...]]  [-j target-name
          [target-options...]

          iptables [-m name [module-options...]]  [-j target-name
          [target-options...]

     MATCH EXTENSIONS
          iptables can use extended packet matching modules with the
          -m or --match options, followed by the matching module name;
          after these, various extra command line options become
          available, depending on the specific module.  You can
          specify multiple extended match modules in one line, and you
          can use the -h or --help options after the module has been
          specified to receive help specific to that module.  The
          extended match modules are evaluated in the order they are
          specified in the rule.

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

        addrtype
          This module matches packets based on their address type.
          Address types are used within the kernel networking stack
          and 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

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     iptables-extensions(8)                     iptables-extensions(8)

          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 inter-
               face 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 inter-
               face the packet is going out. This option is only valid
               in the POSTROUTING, OUTPUT and FORWARD chains. It can-
               not be specified with the --limit-iface-in option.

        ah (IPv6-specific)
          This module matches the parameters in Authentication header
          of IPsec packets.

          [!] --ahspi spi[:spi]
               Matches SPI.

          [!] --ahlen length
               Total length of this header in octets.

          --ahres
               Matches if the reserved field is filled with zero.

        ah (IPv4-specific)
          This module matches the SPIs in Authentication header of

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          IPsec packets.

          [!] --ahspi spi[:spi]

        bpf
          Match using Linux Socket Filter. Expects a path to an eBPF
          object or a cBPF program in decimal format.

          --object-pinned path
               Pass a path to a pinned eBPF object.

          Applications load eBPF programs into the kernel with the
          bpf() system call and BPF_PROG_LOAD command and can pin them
          in a virtual filesystem with BPF_OBJ_PIN.  To use a pinned
          object in iptables, mount the bpf filesystem using

               mount -t bpf bpf ${BPF_MOUNT}

          then insert the filter in iptables by path:

               iptables -A OUTPUT -m bpf --object-pinned
               ${BPF_MOUNT}/{PINNED_PATH} -j ACCEPT

          --bytecode code
               Pass the BPF byte code format as generated by the
               nfbpf_compile utility.

          The code format is similar to the output of the tcpdump -ddd
          command: one line that stores the number of instructions,
          followed by one line for each instruction. Instruction lines
          follow the pattern 'u16 u8 u8 u32' in decimal notation.
          Fields encode the operation, jump offset if true, jump off-
          set if false and generic multiuse field 'K'. Comments are
          not supported.

          For example, to read only packets matching 'ip proto 6',
          insert the following, without the comments or trailing
          whitespace:

               4               # number of instructions
               48 0 0 9        # load byte  ip->proto
               21 0 1 6        # jump equal IPPROTO_TCP
               6 0 0 1         # return     pass (non-zero)
               6 0 0 0         # return     fail (zero)

          You can pass this filter to the bpf match with the following
          command:

               iptables -A OUTPUT -m bpf --bytecode '4,48 0 0 9,21 0 1
               6,6 0 0 1,6 0 0 0' -j ACCEPT

          Or instead, you can invoke the nfbpf_compile utility.

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               iptables -A OUTPUT -m bpf --bytecode "`nfbpf_compile
               RAW 'ip proto 6'`" -j ACCEPT

          Or use tcpdump -ddd. In that case, generate BPF targeting a
          device with the same data link type as the xtables match.
          Iptables passes packets from the network layer up, without
          mac layer. Select a device with data link type RAW, such as
          a tun device:

               ip tuntap add tun0 mode tun
               ip link set tun0 up
               tcpdump -ddd -i tun0 ip proto 6

          See tcpdump -L -i $dev for a list of known data link types
          for a given device.

          You may want to learn more about BPF from FreeBSD's bpf(4)
          manpage.

        cgroup
          [!] --path path
               Match cgroup2 membership.

               Each socket is associated with the v2 cgroup of the
               creating process.  This matches packets coming from or
               going to all sockets in the sub-hierarchy of the speci-
               fied path.  The path should be relative to the root of
               the cgroup2 hierarchy.

          [!] --cgroup classid
               Match cgroup net_cls classid.

               classid is the marker set through the cgroup net_cls
               controller.  This option and --path can't be used
               together.

          Example:

               iptables -A OUTPUT -p tcp --sport 80 -m cgroup ! --path
               service/http-server -j DROP

               iptables -A OUTPUT -p tcp --sport 80 -m cgroup !
               --cgroup 1 -j DROP

          IMPORTANT: when being used in the INPUT chain, the cgroup
          matcher is currently only of limited functionality, meaning
          it will only match on packets that are processed for local
          sockets through early socket demuxing. Therefore, general
          usage on the INPUT chain is not advised unless the implica-
          tions are well understood.

          Available since Linux 3.14.

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        cluster
          Allows you to deploy gateway and back-end load-sharing clus-
          ters 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

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     iptables-extensions(8)                     iptables-extensions(8)

               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

          NOTE: the arptables commands above use mainstream syntax. If
          you are using arptables-jf included in some RedHat, CentOS
          and Fedora versions, you will hit syntax errors. Therefore,
          you'll have to adapt these to the arptables-jf syntax to get
          them working.

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

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

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

          --comment comment

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

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

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

          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 informa-
          tion, the match will always return false. The
          "net.netfilter.nf_conntrack_acct" sysctl flag controls
          whether new connections will be byte/packet counted. Exist-
          ing connection flows will not be gaining/losing a/the
          accounting structure when be sysctl flag is flipped.

          [!] --connbytes from[:to]

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               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 pack-
               ets 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 ...

        connlabel
          Module matches or adds connlabels to a connection.  connla-
          bels are similar to connmarks, except labels are bit-based;
          i.e.  all labels may be attached to a flow at the same time.
          Up to 128 unique labels are currently supported.

          [!] --label name
               matches if label name has been set on a connection.
               Instead of a name (which will be translated to a num-
               ber, see EXAMPLE below), a number may be used instead.
               Using a number always overrides connlabel.conf.

          --set
               if the label has not been set on the connection, set
               it.  Note that setting a label can fail.  This is
               because the kernel allocates the conntrack label stor-
               age area when the connection is created, and it only
               reserves the amount of memory required by the ruleset
               that exists at the time the connection is created.  In
               this case, the match will fail (or succeed, in case
               --label option was negated).

          This match depends on libnetfilter_conntrack 1.0.4 or later.
          Label translation is done via the
          /etc/xtables/connlabel.conf configuration file.

          Example:

               0    eth0-in
               1    eth0-out
               2    ppp-in

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               3    ppp-out
               4    bulk-traffic
               5    interactive

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

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

          --connlimit-above n
               Match if the number of existing connections is above n.

          --connlimit-mask prefix_length
               Group hosts using the prefix length. For IPv4, this
               must be a number between (including) 0 and 32. For
               IPv6, between 0 and 128. If not specified, the maximum
               prefix length for the applicable protocol is used.

          --connlimit-saddr
               Apply the limit onto the source group. This is the
               default if --connlimit-daddr is not specified.

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

          Examples:

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

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

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

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

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

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     iptables-extensions(8)                     iptables-extensions(8)

               REJECT

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

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

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

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

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

          [!] --ctorigsrc address[/mask]

          [!] --ctorigdst address[/mask]

          [!] --ctreplsrc address[/mask]

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

          [!] --ctorigsrcport port[:port]

          [!] --ctorigdstport port[:port]

          [!] --ctreplsrcport port[:port]

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

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

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

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

          States for --ctstate:

          INVALID
               The packet is associated with no known connection.

          NEW  The packet has started a new connection or otherwise
               associated with a connection which has not seen packets
               in both directions.

          ESTABLISHED
               The packet is associated with a connection which has
               seen packets in both directions.

          RELATED
               The packet is starting a new connection, but is associ-
               ated with an existing connection, such as an FTP data
               transfer or an ICMP error.

          UNTRACKED
               The packet is not tracked at all, which happens if you
               explicitly untrack it by using -j CT --notrack in the
               raw table.

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

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

          Statuses for --ctstatus:

          NONE None of the below.

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

          SEEN_REPLY
               Conntrack has seen packets in both directions.

          ASSURED
               Conntrack entry should never be early-expired.

          CONFIRMED
               Connection is confirmed: originating packet has left
               box.

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

          Example:

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

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

          Available since Linux 2.6.36.

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

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

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

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

        devgroup
          Match device group of a packets incoming/outgoing interface.

          [!] --src-group name
               Match device group of incoming device

          [!] --dst-group name
               Match device group of outgoing device

        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.

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        dst (IPv6-specific)
          This module matches the parameters in Destination Options
          header

          [!] --dst-len length
               Total length of this header in octets.

          --dst-opts type[:length][,type[:length]...]
               numeric type of option and the length of the option
               data in octets.

        ecn
          This allows you to match the ECN bits of the IPv4/IPv6 and
          TCP header.  ECN is the Explicit Congestion Notification
          mechanism as specified in RFC3168

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

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

          [!] --ecn-ip-ect num
               This matches a particular IPv4/IPv6 ECT (ECN-Capable
               Transport). You have to specify a number between `0'
               and `3'.

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

          [!] --espspi spi[:spi]

        eui64 (IPv6-specific)
          This module matches the EUI-64 part of a stateless autocon-
          figured IPv6 address.  It compares the EUI-64 derived from
          the source MAC address in Ethernet frame with the lower 64
          bits of the IPv6 source address. But "Universal/Local" bit
          is not compared. This module doesn't match other link layer
          frame, and is only valid in the PREROUTING, INPUT and
          FORWARD chains.

        frag (IPv6-specific)
          This module matches the parameters in Fragment header.

          [!] --fragid id[:id]
               Matches the given Identification or range of it.

          [!] --fraglen length
               This option cannot be used with kernel version 2.6.10
               or later. The length of Fragment header is static and
               this option doesn't make sense.

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          --fragres
               Matches if the reserved fields are filled with zero.

          --fragfirst
               Matches on the first fragment.

          --fragmore
               Matches if there are more fragments.

          --fraglast
               Matches if this is the last fragment.

        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" or "N bytes per seconds" (see below for some
          examples).

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

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

          --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.  When byte-based rate matching is requested, this
               option specifies the amount of bytes that can exceed
               the given rate.  This option should be used with cau-
               tion -- if the entry expires, the burst value is reset
               too.

          --hashlimit-mode {srcip|srcport|dstip|dstport},...
               A comma-separated list of objects to take into consid-
               eration. If no --hashlimit-mode option is given, hash-
               limit 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

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               given prefix length and the so-created subnet will be
               subject to hashlimit. prefix must be between (inclu-
               sive) 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 expen-
               sive.

          --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 inter-
               vals.

          --hashlimit-rate-match
               Classify the flow instead of rate-limiting it. This
               acts like a true/false match on whether the rate is
               above/below a certain number

          --hashlimit-rate-interval sec
               Can be used with --hashlimit-rate-match to specify the
               interval at which the rate should be sampled

          Examples:

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

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

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

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          matching bytes per second
               "flows exceeding 512kbyte/s" => --hashlimit-mode
               srcip,dstip,srcport,dstport --hashlimit-above 512kb/s

          matching bytes per second
               "hosts that exceed 512kbyte/s, but permit up to 1Mega-
               bytes without matching" --hashlimit-mode dstip
               --hashlimit-above 512kb/s --hashlimit-burst 1mb

        hbh (IPv6-specific)
          This module matches the parameters in Hop-by-Hop Options
          header

          [!] --hbh-len length
               Total length of this header in octets.

          --hbh-opts type[:length][,type[:length]...]
               numeric type of option and the length of the option
               data in octets.

        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.

        hl (IPv6-specific)
          This module matches the Hop Limit field in the IPv6 header.

          [!] --hl-eq value
               Matches if Hop Limit equals value.

          --hl-lt value
               Matches if Hop Limit is less than value.

          --hl-gt value
               Matches if Hop Limit is greater than value.

        icmp (IPv4-specific)
          This extension can be used if `--protocol icmp' is speci-
          fied. It provides the following option:

          [!] --icmp-type {type[/code]|typename}
               This allows specification of the ICMP type, which can

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     iptables-extensions(8)                     iptables-extensions(8)

               be a numeric ICMP type, type/code pair, or one of the
               ICMP type names shown by the command
                iptables -p icmp -h

        icmp6 (IPv6-specific)
          This extension can be used if `--protocol ipv6-icmp' or
          `--protocol icmpv6' is specified. It provides the following
          option:

          [!] --icmpv6-type type[/code]|typename
               This allows specification of the ICMPv6 type, which can
               be a numeric ICMPv6 type, type and code, or one of the
               ICMPv6 type names shown by the command
                ip6tables -p ipv6-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.

        ipv6header (IPv6-specific)
          This module matches IPv6 extension headers and/or upper
          layer header.

          --soft
               Matches if the packet includes any of the headers spec-
               ified with --header.

          [!] --header header[,header...]
               Matches the packet which EXACTLY includes all specified
               headers. The headers encapsulated with ESP header are
               out of scope.  Possible header types can be:

          hop|hop-by-hop
               Hop-by-Hop Options header

          dst  Destination Options header

          route
               Routing header

          frag Fragment header

          auth Authentication header

          esp  Encapsulating Security Payload header

          none No Next header which matches 59 in the 'Next Header

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     iptables-extensions(8)                     iptables-extensions(8)

               field' of IPv6 header or any IPv6 extension headers

          prot which matches any upper layer protocol header. A proto-
               col name from /etc/protocols and numeric value also
               allowed. The number 255 is equivalent to prot.

        ipvs
          Match IPVS connection properties.

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

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

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

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

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

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

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

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

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

          [!] --length length[:length]

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

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

          --limit rate[/second|/minute|/hour|/day]
               Maximum average matching rate: specified as a number,

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     iptables-extensions(8)                     iptables-extensions(8)

               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).

        mh (IPv6-specific)
          This extension is loaded if `--protocol ipv6-mh' or `--pro-
          tocol mh' is specified. It provides the following option:

          [!] --mh-type type[:type]
               This allows specification of the Mobility Header(MH)
               type, which can be a numeric MH type, type or one of
               the MH type names shown by the command
                ip6tables -p mh -h

        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 one of the following protocols: tcp, udp, udplite, dccp
          and sctp.

          [!] --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

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     iptables-extensions(8)                     iptables-extensions(8)

               ports.  The flag --dports is a convenient alias for
               this option.

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

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

          The only option available for this match is the following:

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

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

               nfacct add http-traffic

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

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

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

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

               nfacct get http-traffic

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

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

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

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

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     iptables-extensions(8)                     iptables-extensions(8)

               fingerprinting.

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

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

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

          +o   2 - Do not compare the TTL at all.

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

          +o   0 - Log all matched or unknown signatures

          +o   1 - Log only the first one

          +o   2 - Log all known matched signatures

          You may find something like this in syslog:

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

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

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

          To remove them again,

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

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

        owner
          This module attempts to match various characteristics of the
          packet creator, for locally generated packets. This match is
          only valid in the OUTPUT and POSTROUTING chains. Forwarded
          packets do not have any socket associated with them. Packets
          from kernel threads do have a socket, but usually no owner.

          [!] --uid-owner username

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     iptables-extensions(8)                     iptables-extensions(8)

          [!] --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 spec-
               ify 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.

          --suppl-groups
               Causes group(s) specified with --gid-owner to be also
               checked in the supplementary groups of a process.

          [!] --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 ver-
          sion 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 bridged packets entering the FORWARD and
               POSTROUTING chains).  If the interface name ends in a
               "+", then any interface which begins with this name
               will match.

          [!] --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

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     iptables-extensions(8)                     iptables-extensions(8)

               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 module matches the policy used by IPsec for handling a
          packet.

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

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

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

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

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

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

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

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

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

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

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     iptables-extensions(8)                     iptables-extensions(8)

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

        quota
          Implements network quotas by decrementing a byte counter
          with each packet. The condition matches until the byte
          counter reaches zero. Behavior is reversed with negation
          (i.e. the condition does not match until the byte counter
          reaches zero).

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

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

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

          +o   rateest operator rateest-bps

          +o   rateest operator rateest-pps

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

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

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

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

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

          +o   (rateest1 minus rateest-pps1) operator (rateest2 minus
              rateest-pps2)

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

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

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     iptables-extensions(8)                     iptables-extensions(8)

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

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

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

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

          --rateest1 name

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

          --rateest-bps [value]

          --rateest-pps [value]

          --rateest-bps1 [value]

          --rateest-bps2 [value]

          --rateest-pps1 [value]

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

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

          # Estimate outgoing rates

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

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

          # Mark based on available bandwidth

     Page 24                  iptables 1.8.7         (printed 5/24/22)

     iptables-extensions(8)                     iptables-extensions(8)

          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 (IPv4-specific)
          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).  Both value and mask are four byte unsigned
               integers and may be specified in decimal, hex (by pre-
               fixing with "0x") or octal (if a leading zero is
               given).

        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 exclu-
          sive.

          --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

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     iptables-extensions(8)                     iptables-extensions(8)

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

          --mask netmask
               Netmask that will be applied to this recent list.

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

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

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

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

          --reap
               This option can only be used in conjunction with --sec-
               onds.  When used, this will cause entries older than
               the last given number of seconds to be purged.

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

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     iptables-extensions(8)                     iptables-extensions(8)

               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

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

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

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

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

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

          The module itself accepts parameters, defaults shown:

          ip_list_tot=100
               Number of addresses remembered per table.

          ip_pkt_list_tot=20
               Number of packets per address remembered.

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

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

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

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

        rpfilter
          Performs a reverse path filter test on a packet.  If a reply

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     iptables-extensions(8)                     iptables-extensions(8)

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

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

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

          --accept-local
               This will permit packets arriving from the network with
               a source address that is also assigned to the local
               machine.

          --invert
               This will invert the sense of the match.  Instead of
               matching packets that passed the reverse path filter
               test, match those that have failed it.

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

          iptables -t raw -N RPFILTER

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

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

          iptables -t raw -A RPFILTER -j DROP

          iptables -t raw -A PREROUTING -j RPFILTER

          Example to drop failed packets, without logging:

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

        rt (IPv6-specific)
          Match on IPv6 routing header

          [!] --rt-type type
               Match the type (numeric).

          [!] --rt-segsleft num[:num]

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     iptables-extensions(8)                     iptables-extensions(8)

               Match the `segments left' field (range).

          [!] --rt-len length
               Match the length of this header.

          --rt-0-res
               Match the reserved field, too (type=0)

          --rt-0-addrs addr[,addr...]
               Match type=0 addresses (list).

          --rt-0-not-strict
               List of type=0 addresses is not a strict list.

        sctp
          This module matches Stream Control Transmission Protocol
          headers.

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

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

          [!] --chunk-types {all|any|only} chunktype[:flags] [...]
               The flag letter in upper case indicates that the flag
               is to match if set, in the lower case indicates to
               match if unset.

               Chunk types: DATA INIT INIT_ACK SACK HEARTBEAT
               HEARTBEAT_ACK ABORT SHUTDOWN SHUTDOWN_ACK ERROR
               COOKIE_ECHO COOKIE_ACK ECN_ECNE ECN_CWR
               SHUTDOWN_COMPLETE ASCONF ASCONF_ACK FORWARD_TSN

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

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

          Examples:

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

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

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

        set
          This module matches IP sets which can be defined by

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     iptables-extensions(8)                     iptables-extensions(8)

          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.

          --return-nomatch
               If the --return-nomatch option is specified and the set
               type supports the nomatch flag, then the matching is
               reversed: a match with an element flagged with nomatch
               returns true, while a match with a plain element
               returns false.

          ! --update-counters
               If the --update-counters flag is negated, then the
               packet and byte counters of the matching element in the
               set won't be updated. Default the packet and byte coun-
               ters are updated.

          ! --update-subcounters
               If the --update-subcounters flag is negated, then the
               packet and byte counters of the matching element in the
               member set of a list type of set won't be updated.
               Default the packet and byte counters are updated.

          [!] --packets-eq value
               If the packet is matched an element in the set, match
               only if the packet counter of the element matches the
               given value too.

          --packets-lt value
               If the packet is matched an element in the set, match
               only if the packet counter of the element is less than
               the given value as well.

          --packets-gt value
               If the packet is matched an element in the set, match
               only if the packet counter of the element is greater
               than the given value as well.

          [!] --bytes-eq value
               If the packet is matched an element in the set, match

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               only if the byte counter of the element matches the
               given value too.

          --bytes-lt value
               If the packet is matched an element in the set, match
               only if the byte counter of the element is less than
               the given value as well.

          --bytes-gt value
               If the packet is matched an element in the set, match
               only if the byte counter of the element is greater than
               the given value as well.

          The packet and byte counters related options and flags are
          ignored when the set was defined without counter support.

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

        socket
          This matches if an open TCP/UDP socket can be found by doing
          a socket lookup on the packet. It matches if there is an
          established or non-zero bound listening socket (possibly
          with a non-local address). The lookup is performed using the
          packet tuple of TCP/UDP packets, or the original TCP/UDP
          header embedded in an ICMP/ICPMv6 error packet.

          --transparent
               Ignore non-transparent sockets.

          --nowildcard
               Do not ignore sockets bound to 'any' address.  The
               socket match won't accept zero-bound listeners by
               default, since then local services could intercept
               traffic that would otherwise be forwarded.  This option
               therefore has security implications when used to match
               traffic being forwarded to redirect such packets to
               local machine with policy routing.  When using the
               socket match to implement fully transparent proxies
               bound to non-local addresses it is recommended to use
               the --transparent option instead.

          Example (assuming packets with mark 1 are delivered
          locally):

               -t mangle -A PREROUTING -m socket --transparent -j MARK
               --set-mark 1

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          --restore-skmark
               Set the packet mark to the matching socket's mark. Can
               be combined with the --transparent and --nowildcard
               options to restrict the sockets to be matched when
               restoring the packet mark.

          Example: An application opens 2 transparent (IP_TRANSPARENT)
          sockets and sets a mark on them with SO_MARK socket option.
          We can filter matching packets:

               -t mangle -I PREROUTING -m socket --transparent
               --restore-skmark -j action

               -t mangle -A action -m mark --mark 10 -j action2

               -t mangle -A action -m mark --mark 11 -j action3

        state
          The "state" extension is a subset of the "conntrack" module.
          "state" 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. Only a subset of the states unterstood
               by "conntrack" are recognized: INVALID, ESTABLISHED,
               NEW, RELATED or UNTRACKED. For their description, see
               the "conntrack" heading in this manpage.

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

          Supported options:

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

          [!] --probability p
               Set the probability for a packet to be randomly
               matched. It only works with the random mode. p must be
               within 0.0 and 1.0. The supported granularity is in
               1/2147483648th increments.

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

          --packet p
               Set the initial counter value (0 <= p <= n-1, default

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               0) for the nth mode.

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

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

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

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

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

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

          --icase
               Ignore case when searching.

          Examples:

               # The string pattern can be used for simple text char-
               acters.
               iptables -A INPUT -p tcp --dport 80 -m string --algo bm
               --string 'GET /index.html' -j LOG

               # The hex string pattern can be used for non-printable
               characters, like |0D 0A| or |0D0A|.
               iptables -p udp --dport 53 -m string --algo bm --from
               40 --to 57 --hex-string
               '|03|www|09|netfilter|03|org|00|'

        tcp
          These extensions can be used if `--protocol tcp' is speci-
          fied. 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.
               The flag --sport is a convenient alias for this option.

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          [!] --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 argu-
               ment 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, block-
               ing 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. If a range is
               given, the second value must be greater than or equal
               to the first value.

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

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

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

               If --datestart or --datestop are not specified, it will

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     iptables-extensions(8)                     iptables-extensions(8)

               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 vari-
               ants (Mo, Tu, etc.).

          --contiguous
               When --timestop is smaller than --timestart value,
               match this as a single time period instead distinct
               intervals.  See EXAMPLES.

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

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

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

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

          EXAMPLES. To match on weekends, use:

               -m time --weekdays Sa,Su

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

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

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

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

          During lunch hour:

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

          The fourth Friday in the month:

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

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

          Matching across days might not do what is expected.  For
          instance,

               -m time --weekdays Mo --timestart 23:00  --timestop
               01:00 Will match Monday, for one hour from midnight to
               1 a.m., and then again for another hour from 23:00
               onwards.  If this is unwanted, e.g. if you would like
               'match for two hours from Montay 23:00 onwards' you
               need to also specify the --contiguous option in the
               example above.

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

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     iptables-extensions(8)                     iptables-extensions(8)

          (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 (IPv4-specific)
          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

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          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 argu-
               ment

              *
               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. How-
          ever, the characters that do occur there are likely to
          require shell quoting, so it is a good idea to enclose the
          arguments in quotes.

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     iptables-extensions(8)                     iptables-extensions(8)

          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 com-
               pare the result to 1. Next test that it is not a frag-
               ment. (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

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     iptables-extensions(8)                     iptables-extensions(8)

               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 speci-
          fied. 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.

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

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

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     iptables-extensions(8)                     iptables-extensions(8)

          --type {accept|drop|reject}
               Set type of audit record. Starting with linux-4.12,
               this option has no effect on generated audit messages
               anymore. It is still accepted by iptables for compati-
               bility reasons, but ignored.

          Example:

               iptables -N AUDIT_DROP

               iptables -A AUDIT_DROP -j AUDIT

               iptables -A AUDIT_DROP -j DROP

        CHECKSUM
          This target selectively works around broken/old applica-
          tions.  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 (IPv4-specific)
          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.

          Please note that CLUSTERIP target is considered deprecated
          in favour of cluster match which is more flexible and not
          limited to IPv4.

          --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.

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     iptables-extensions(8)                     iptables-extensions(8)

          --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.)

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     iptables-extensions(8)                     iptables-extensions(8)

          --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 connec-
          tions (if unlabeled), and from connections back to packets
          (also only if unlabeled).  Typically used in conjunction
          with SECMARK, it is valid in the security table (for back-
          wards compatibility with older kernels, it is also valid in
          the mangle table).

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

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

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

          --notrack
               Disables connection tracking for this packet.

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

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     iptables-extensions(8)                     iptables-extensions(8)

               modules with preset ports.

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

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

          --zone-orig {id|mark}
               For traffic coming from ORIGINAL direction, assign this
               packet to zone id and only have lookups done in that
               zone. If mark is used instead of id, the zone is
               derived from the packet nfmark.

          --zone-reply {id|mark}
               For traffic coming from REPLY direction, assign this
               packet to zone id and only have lookups done in that
               zone. If mark is used instead of id, the zone is
               derived from the packet nfmark.

          --zone {id|mark}
               Assign this packet to zone id and only have lookups
               done in that zone.  If mark is used instead of id, the
               zone is derived from the packet nfmark. By default,
               packets have zone 0. This option applies to both direc-
               tions.

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

        DNAT
          This target is only valid in the nat table, in the
          PREROUTING and OUTPUT chains, and user-defined chains which
          are only called from those chains.  It specifies that the
          destination address of the packet should be modified (and
          all future packets in this connection will also be mangled),
          and rules should cease being examined.  It takes the follow-
          ing options:

          --to-destination [ipaddr[-ipaddr]][:port[-port]]
               which can specify a single new destination IP address,
               an inclusive range of IP addresses. Optionally a port
               range, if the rule also specifies one of the following
               protocols: tcp, udp, dccp or sctp.  If no port range is

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               specified, then the destination port will never be mod-
               ified. If no IP address is specified then only the des-
               tination 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 desti-
               nation 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 any-
               more.

          --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. Sup-
               port for persistent mappings is available from 2.6.29-
               rc2.

          IPv6 support available since Linux kernels >= 3.7.

        DNPT (IPv6-specific)
          Provides stateless destination IPv6-to-IPv6 Network Prefix
          Translation (as described by RFC 6296).

          You have to use this target in the mangle table, not in the
          nat table. It takes the following options:

          --src-pfx [prefix/length]
               Set source prefix that you want to translate and length

          --dst-pfx [prefix/length]
               Set destination prefix that you want to use in the
               translation and length

          You have to use the SNPT target to undo the translation.
          Example:

               ip6tables -t mangle -I POSTROUTING -s fd00::/64  -o
               vboxnet0 -j SNPT --src-pfx fd00::/64 --dst-pfx
               2001:e20:2000:40f::/64

               ip6tables -t mangle -I PREROUTING -i wlan0 -d
               2001:e20:2000:40f::/64 -j DNPT --src-pfx
               2001:e20:2000:40f::/64 --dst-pfx fd00::/64

          You may need to enable IPv6 neighbor proxy:

               sysctl -w net.ipv6.conf.all.proxy_ndp=1

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          You also have to use the NOTRACK target to disable connec-
          tion tracking for translated flows.

        DSCP
          This target alters 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 (IPv4-specific)
          This target selectively works 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.

        HL (IPv6-specific)
          This is used to modify the Hop Limit field in IPv6 header.
          The Hop Limit field is similar to what is known as TTL value
          in IPv4.  Setting or incrementing the Hop Limit field can
          potentially be very dangerous, so it should be avoided at
          any cost. This target is only valid in mangle table.

          Don't ever set or increment the

          --hl-set value
               Set the Hop Limit to `value'.

          --hl-dec value
               Decrement the Hop Limit `value' times.

          --hl-inc value
               Increment the Hop Limit `value' times.

        HMARK
          Like MARK, i.e. set the fwmark, but the mark is calculated
          from hashing packet selector at choice. You have also to
          specify the mark range and, optionally, the offset to start
          from. ICMP error messages are inspected and used to calcu-
          late the hashing.

          Existing options are:

          --hmark-tuple tuple
               Possible tuple members are: src meaning source address

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               (IPv4, IPv6 address), dst meaning destination address
               (IPv4, IPv6 address), sport meaning source port (TCP,
               UDP, UDPlite, SCTP, DCCP), dport meaning destination
               port (TCP, UDP, UDPlite, SCTP, DCCP), spi meaning Secu-
               rity Parameter Index (AH, ESP), and ct meaning the
               usage of the conntrack tuple instead of the packet
               selectors.

          --hmark-mod value (must be > 0)
               Modulus for hash calculation (to limit the range of
               possible marks)

          --hmark-offset value
               Offset to start marks from.

     ify custom
          For advanced usage, instead of using --hmark-tuple, you can spec-
               prefixes and masks:

          --hmark-src-prefix cidr
               The source address mask in CIDR notation.

          --hmark-dst-prefix cidr
               The destination address mask in CIDR notation.

          --hmark-sport-mask value
               A 16 bit source port mask in hexadecimal.

          --hmark-dport-mask value
               A 16 bit destination port mask in hexadecimal.

          --hmark-spi-mask value
               A 32 bit field with spi mask.

          --hmark-proto-mask value
               An 8 bit field with layer 4 protocol number.

          --hmark-rnd value
               A 32 bit random custom value to feed hash calculation.

          Examples:

          iptables -t mangle -A PREROUTING -m conntrack --ctstate NEW
           -j HMARK --hmark-tuple ct,src,dst,proto --hmark-offset
          10000 --hmark-mod 10 --hmark-rnd 0xfeedcafe

          iptables -t mangle -A PREROUTING -j HMARK --hmark-offset
          10000 --hmark-tuple src,dst,proto --hmark-mod 10 --hmark-rnd
          0xdeafbeef

        IDLETIMER
          This target can be used to identify when interfaces have

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     iptables-extensions(8)                     iptables-extensions(8)

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

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

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

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

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

        LED
          This creates an LED-trigger that can then be attached to
          system indicator lights, to blink or illuminate them when
          certain packets pass through the system. One example might
          be to light up an LED for a few minutes every time an SSH
          connection is made to the local machine. The following
          options control the trigger behavior:

          --led-trigger-id name
               This is the name given to the LED trigger. The actual
               name of the trigger will be prefixed with "netfilter-".

          --led-delay ms
               This indicates how long (in milliseconds) the LED
               should be left illuminated when a packet arrives before
               being switched off again. The default is 0 (blink as
               fast as possible.) The special value inf can be given
               to leave the LED on permanently once activated. (In
               this case the trigger will need to be manually detached
               and reattached to the LED device to switch it off
               again.)

          --led-always-blink
               Always make the LED blink on packet arrival, even if
               the LED is already on.  This allows notification of new
               packets even with long delay values (which otherwise
               would result in a silent prolonging of the delay time.)

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          Example:

          Create an LED trigger for incoming SSH traffic:
               iptables -A INPUT -p tcp --dport 22 -j LED
               --led-trigger-id ssh

          Then attach the new trigger to an LED:
               echo netfilter-ssh >/sys/class/leds/ledname/trigger

        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/IPv6
          header fields) via the kernel log (where it can be read with
          dmesg(1) or read in the syslog).

          This is a "non-terminating target", i.e. rule traversal con-
          tinues 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, which can be (system-specific)
               numeric or a mnemonic.  Possible values are (in
               decreasing order of priority): emerg, alert, crit,
               error, warning, notice, info or debug.

          --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/IPv6 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 associ-
          ated with the packet.  It can, for example, be used in con-
          junction with routing based on fwmark (needs iproute2). If
          you plan on doing so, note that the mark needs to be set in
          either the PREROUTING or the OUTPUT chain of the mangle

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     iptables-extensions(8)                     iptables-extensions(8)

          table to affect routing.  The mark field is 32 bits wide.

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

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

          The following mnemonics are available:

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

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

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

        MASQUERADE
          This target is only valid in the nat table, in the
          POSTROUTING chain.  It should only be used with dynamically
          assigned IP (dialup) connections: if you have a static IP
          address, you should use the SNAT target.  Masquerading is
          equivalent to specifying a mapping to the IP address of the
          interface the packet is going out, but also has the effect
          that connections are forgotten when the interface goes down.
          This is the correct behavior when the next dialup is
          unlikely to have the same interface address (and hence any
          established connections are lost anyway).

          --to-ports port[-port]
               This specifies a range of source ports to use, overrid-
               ing the default SNAT source port-selection heuristics
               (see above).  This is only valid if the rule also spec-
               ifies one of the following protocols: tcp, udp, dccp or
               sctp.

          --random
               Randomize source port mapping If option --random is
               used then port mapping will be randomized (kernel >=
               2.6.21).  Since kernel 5.0, --random is identical to
               --random-fully.

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     iptables-extensions(8)                     iptables-extensions(8)

          --random-fully
               Full randomize source port mapping If option --random-
               fully is used then port mapping will be fully random-
               ized (kernel >= 3.13).

          IPv6 support available since Linux kernels >= 3.7.

        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.

          IPv6 support available since Linux kernels >= 3.7.

        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 user-
          space processes may subscribe to the group to receive the
          packets. Like LOG, this is a non-terminating target, i.e.
          rule traversal continues at the next rule.

          --nflog-group nlgroup
               The netlink group (0 - 2^16-1) to which packets are
               (only applicable for nfnetlink_log). The default value
               is 0.

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

          --nflog-range size
               This option has never worked, use --nflog-size instead

          --nflog-size 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

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     iptables-extensions(8)                     iptables-extensions(8)

               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 passes the packet to userspace using the
          nfnetlink_queue handler.  The packet is put into the queue
          identified by its 16-bit queue number.  Userspace can
          inspect and modify the packet if desired. Userspace must
          then drop or reinject the packet into the kernel.  Please
          see libnetfilter_queue for details.  nfnetlink_queue was
          added in Linux 2.6.14. The queue-balance option was added in
          Linux 2.6.31, queue-bypass in 2.6.39.

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

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

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

          --queue-cpu-fanout
               Available starting Linux kernel 3.10. When used
               together with --queue-balance this will use the CPU ID
               as an index to map packets to the queues. The idea is
               that you can improve performance if there's a queue per
               CPU. This requires --queue-balance to be specified.

        NOTRACK
          This extension disables connection tracking for all packets
          matching that rule.  It is equivalent with -j CT --notrack.
          Like CT, NOTRACK can only be used in the raw table.

        RATEEST
          The RATEEST target collects statistics, performs rate esti-
          mation calculation and saves the results for later evalua-
          tion using the rateest match.

          --rateest-name name

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     iptables-extensions(8)                     iptables-extensions(8)

               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 localhost address, 127.0.0.1 for
          IPv4 and ::1 for IPv6, and packets arriving on interfaces
          that don't have an IP address configured are dropped).

          --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
               one of the following protocols: tcp, udp, dccp or sctp.

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

          IPv6 support available starting Linux kernels >= 3.7.

        REJECT (IPv6-specific)
          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 icmp6-no-route, no-route,
               icmp6-adm-prohibited, adm-prohibited,
               icmp6-addr-unreachable, addr-unreach, or
               icmp6-port-unreachable, which return the appropriate
               ICMPv6 error message (icmp6-port-unreachable is the
               default). Finally, 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

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     iptables-extensions(8)                     iptables-extensions(8)

               won't accept your mail otherwise).  tcp-reset can only
               be used with kernel versions 2.6.14 or later.

          Warning: You should not indiscriminately apply the REJECT
          target to packets whose connection state is classified as
          INVALID; instead, you should only DROP these.

          Consider a source host transmitting a packet P, with P expe-
          riencing so much delay along its path that the source host
          issues a retransmission, P_2, with P_2 being successful in
          reaching its destination and advancing the connection state
          normally. It is conceivable that the late-arriving P may be
          considered not to be associated with any connection tracking
          entry. Generating a reject response for a packet so classed
          would then terminate the healthy connection.

          So, instead of:

          -A INPUT ... -j REJECT

          do consider using:

          -A INPUT ... -m conntrack --ctstate INVALID -j DROP -A INPUT
          ... -j REJECT

        REJECT (IPv4-specific)
          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
               (icmp-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 bro-
               ken mail hosts (which won't accept your mail other-
               wise).

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

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     iptables-extensions(8)                     iptables-extensions(8)

          Warning: You should not indiscriminately apply the REJECT
          target to packets whose connection state is classified as
          INVALID; instead, you should only DROP these.

          Consider a source host transmitting a packet P, with P expe-
          riencing so much delay along its path that the source host
          issues a retransmission, P_2, with P_2 being successful in
          reaching its destination and advancing the connection state
          normally. It is conceivable that the late-arriving P may be
          considered not to be associated with any connection tracking
          entry. Generating a reject response for a packet so classed
          would then terminate the healthy connection.

          So, instead of:

          -A INPUT ... -j REJECT

          do consider using:

          -A INPUT ... -m conntrack --ctstate INVALID -j DROP -A INPUT
          ... -j REJECT

        SECMARK
          This is used to set the security mark value associated with
          the packet for use by security subsystems such as SELinux.
          It is valid in the security table (for backwards compatibil-
          ity with older kernels, it is also valid in the mangle
          table). The mark is 32 bits wide.

          --selctx security_context

        SET
          This module 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 set

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

          --map-set setname flag[,flag...]
               [--map-mark] [--map-prio] [--map-queue] map packet
               properties (firewall mark, tc priority, hardware queue)

               where flag(s) are src and/or dst specifications and
               there can be no more than six of them.

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

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     iptables-extensions(8)                     iptables-extensions(8)

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

          --map-set set-name
               the set-name should be created with --skbinfo option
               --map-mark map firewall mark to packet by lookup of
               value in the set --map-prio map traffic control prior-
               ity to packet by lookup of value in the set --map-queue
               map hardware NIC queue to packet by lookup of value in
               the set

               The --map-set option can be used from the mangle table
               only. The --map-prio and --map-queue flags can be used
               in the OUTPUT, FORWARD and POSTROUTING chains.

          Use of -j SET requires that ipset kernel support is pro-
          vided, which, for standard kernels, is the case since Linux
          2.6.39.

        SNAT
          This target is only valid in the nat table, in the
          POSTROUTING and INPUT chains, and user-defined chains which
          are only called from those chains.  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 the following
          options:

          --to-source [ipaddr[-ipaddr]][:port[-port]]
               which can specify a single new source IP address, an
               inclusive range of IP addresses. Optionally a port
               range, if the rule also specifies one of the following
               protocols: tcp, udp, dccp or sctp.  If no port range is
               specified, then source ports below 512 will be mapped
               to other ports below 512: those between 512 and 1023
               inclusive will be mapped to ports below 1024, and other
               ports will be mapped to 1024 or above. Where possible,
               no port alteration will occur.  In Kernels up to
               2.6.10, you can add several --to-source options. For
               those kernels, if you specify more than one source
               address, either via an address range or multiple
               --to-source options, a simple round-robin (one after
               another in cycle) takes place between these addresses.
               Later Kernels (>= 2.6.11-rc1) don't have the ability to
               NAT to multiple ranges anymore.

          --random
               If option --random is used then port mapping will be
               randomized through a hash-based algorithm (kernel >=
               2.6.21).

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          --random-fully
               If option --random-fully is used then port mapping will
               be fully randomized through a PRNG (kernel >= 3.14).

          --persistent
               Gives a client the same source-/destination-address for
               each connection.  This supersedes the SAME target. Sup-
               port for persistent mappings is available from 2.6.29-
               rc2.

          Kernels prior to 2.6.36-rc1 don't have the ability to SNAT
          in the INPUT chain.

          IPv6 support available since Linux kernels >= 3.7.

        SNPT (IPv6-specific)
          Provides stateless source IPv6-to-IPv6 Network Prefix Trans-
          lation (as described by RFC 6296).

          You have to use this target in the mangle table, not in the
          nat table. It takes the following options:

          --src-pfx [prefix/length]
               Set source prefix that you want to translate and length

          --dst-pfx [prefix/length]
               Set destination prefix that you want to use in the
               translation and length

          You have to use the DNPT target to undo the translation.
          Example:

               ip6tables -t mangle -I POSTROUTING -s fd00::/64  -o
               vboxnet0 -j SNPT --src-pfx fd00::/64 --dst-pfx
               2001:e20:2000:40f::/64

               ip6tables -t mangle -I PREROUTING -i wlan0 -d
               2001:e20:2000:40f::/64 -j DNPT --src-pfx
               2001:e20:2000:40f::/64 --dst-pfx fd00::/64

          You may need to enable IPv6 neighbor proxy:

               sysctl -w net.ipv6.conf.all.proxy_ndp=1

          You also have to use the NOTRACK target to disable connec-
          tion tracking for translated flows.

        SYNPROXY
          This target will process TCP three-way-handshake parallel in
          netfilter context to protect either local or backend system.
          This target requires connection tracking because sequence
          numbers need to be translated.  The kernels ability to

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          absorb SYNFLOOD was greatly improved starting with Linux
          4.4, so this target should not be needed anymore to protect
          Linux servers.

          --mss maximum segment size
               Maximum segment size announced to clients. This must
               match the backend.

          --wscale window scale
               Window scale announced to clients. This must match the
               backend.

          --sack-perm
               Pass client selective acknowledgement option to backend
               (will be disabled if not present).

          --timestamps
               Pass client timestamp option to backend (will be dis-
               abled if not present, also needed for selective
               acknowledgement and window scaling).

          Example:

          Determine tcp options used by backend, from an external sys-
          tem

               tcpdump -pni eth0 -c 1 'tcp[tcpflags] == (tcp-syn|tcp-
               ack)'
                   port 80 &
               telnet 192.0.2.42 80
               18:57:24.693307 IP 192.0.2.42.80 > 192.0.2.43.48757:
                   Flags [S.], seq 360414582, ack 788841994, win
               14480,
                   options [mss 1460,sackOK,
                   TS val 1409056151 ecr 9690221,
                   nop,wscale 9],
                   length 0

          Switch tcp_loose mode off, so conntrack will mark
          out-of-flow packets as state INVALID.

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

          Make SYN packets untracked

               iptables -t raw -A PREROUTING -i eth0 -p tcp --dport 80
                   --syn -j CT --notrack

          Catch UNTRACKED (SYN packets) and INVALID (3WHS ACK packets)
          states and send them to SYNPROXY. This rule will respond to
          SYN packets with SYN+ACK syncookies, create ESTABLISHED for
          valid client response (3WHS ACK packets) and drop incorrect

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          cookies. Flags combinations not expected during 3WHS will
          not match and continue (e.g. SYN+FIN, SYN+ACK).

               iptables -A INPUT -i eth0 -p tcp --dport 80
                   -m state --state UNTRACKED,INVALID -j SYNPROXY
                   --sack-perm --timestamp --mss 1460 --wscale 9

          Drop invalid packets, this will be out-of-flow packets that
          were not matched by SYNPROXY.

               iptables -A INPUT -i eth0 -p tcp --dport 80 -m state
               --state INVALID -j DROP

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

          This target is used to overcome criminally braindead ISPs or
          servers which block "ICMP Fragmentation Needed" or "ICMPv6
          Packet Too Big" packets.  The symptoms of this problem are
          that everything works fine from your Linux firewall/router,
          but machines behind it can never exchange large packets:

          1.  Web browsers connect, then hang with no data received.

          2.  Small mail works fine, but large emails hang.

          3.  ssh works fine, but scp hangs after initial handshaking.

          Workaround: activate this option and add a rule to your
          firewall configuration like:

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

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

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

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               the destination IP address was considered by this
               option; subsequent kernels also consider the path MTU
               to the source IP address.

          These options are mutually exclusive.

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

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

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

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

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

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

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

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

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

          The following mnemonics are available:

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

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

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

          NOTE: In Linux kernels up to and including 2.6.38, with the
          exception of longterm releases 2.6.32 (>=.42), 2.6.33
          (>=.15), and 2.6.35 (>=.14), there is a bug whereby IPv6 TOS
          mangling does not behave as documented and differs from the
          IPv4 version. The TOS mask indicates the bits one wants to
          zero out, so it needs to be inverted before applying it to
          the original TOS field. However, the aformentioned kernels
          forgo the inversion which breaks --set-tos and its mnemon-
          ics.

        TPROXY
          This target is only valid in the mangle table, in the PRE-
          ROUTING 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 inter-
               face. 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 packets so that the kernel will log every

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          rule which match the packets as those traverse the tables,
          chains, rules. It can only be used in the raw table.

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

          With iptables-nft, the target is translated into nftables'
          meta nftrace expression. Hence the kernel sends trace events
          via netlink to userspace where they may be displayed using
          xtables-monitor --trace command. For details, refer to
          xtables-monitor(8).

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

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

          Don't ever set or increment the

          --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 (IPv4-specific)
          This is the deprecated ipv4-only predecessor of the NFLOG
          target.  It 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

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               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 mes-
               sage to userspace.  Default is 1 (for backwards compat-
               ibility).

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