iptables-extensions

iptables-extensions(8)          iptables 1.8.3          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

       MULTICAST
              a multicast address

       BLACKHOLE
              a blackhole address

       UNREACHABLE
              an unreachable address

       PROHIBIT
              a prohibited address

       THROW  FIXME

       NAT    FIXME

       XRESOLVE

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

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

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

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

   ah (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 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 offset 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.

              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 specified 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 implications are well understood.

       Available since Linux 3.14.

   cluster
       Allows you to deploy gateway and back-end load-sharing clusters without
       the need of load-balancers.

       This match requires that all the nodes see the same packets. Thus, the
       cluster match decides if this node has to handle a packet given the
       following options:

       --cluster-total-nodes num
              Set number of total nodes in cluster.

       [!] --cluster-local-node num
              Set the local node number ID.

       [!] --cluster-local-nodemask mask
              Set the local node number ID mask. You can use this option
              instead of --cluster-local-node.

       --cluster-hash-seed value
              Set seed value of the Jenkins hash.

       Example:

              iptables -A PREROUTING -t mangle -i eth1 -m cluster
              --cluster-total-nodes 2 --cluster-local-node 1
              --cluster-hash-seed 0xdeadbeef -j MARK --set-mark 0xffff

              iptables -A PREROUTING -t mangle -i eth2 -m cluster
              --cluster-total-nodes 2 --cluster-local-node 1
              --cluster-hash-seed 0xdeadbeef -j MARK --set-mark 0xffff

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

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

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

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

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

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

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

              arptables -A OUTPUT -o eth2 --h-length 6 -j mangle
              --mangle-mac-s 01:00:5e:00:01:02

              arptables -A INPUT -i eth2 --h-length 6 --destination-mac
              01:00:5e:00:01:02 -j mangle --mangle-mac-d 00:zz:yy:xx:5a:27

       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 overflow ;)

       The primary use is to detect long-lived downloads and mark them to be
       scheduled using a lower priority band in traffic control.

       The transferred bytes per connection can also be viewed through
       `conntrack -L` and accessed via ctnetlink.

       NOTE that for connections which have no accounting information, the
       match will always return false. The "net.netfilter.nf_conntrack_acct"
       sysctl flag controls whether new connections will be byte/packet
       counted. Existing connection flows will not be gaining/losing a/the
       accounting structure when be sysctl flag is flipped.

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

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

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

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

   connlabel
       Module matches or adds connlabels to a connection.  connlabels 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 number, 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 storage 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
              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

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

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

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

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

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

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

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

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

       [!] --ctorigsrc address[/mask]

       [!] --ctorigdst address[/mask]

       [!] --ctreplsrc address[/mask]

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

       [!] --ctorigsrcport port[:port]

       [!] --ctorigdstport port[:port]

       [!] --ctreplsrcport port[:port]

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

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

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

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

       States for --ctstate:

       INVALID
              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 associated 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.

   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.

   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 autoconfigured 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.

       --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 caution -- 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 consideration. If
              no --hashlimit-mode option is given, hashlimit acts like limit,
              but at the expensive of doing the hash housekeeping.

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

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

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

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

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

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

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

       --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

       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 1Megabytes
              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 specified. It
       provides the following option:

       [!] --icmp-type {type[/code]|typename}
              This allows specification of the ICMP type, which can be a
              numeric ICMP type, type/code pair, or one of the ICMP type names
              shown by the command
               iptables -p icmp -h

   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 specified 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 field' of
              IPv6 header or any IPv6 extension headers

       prot   which matches any upper layer protocol header. A protocol 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, 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 `--protocol 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 ports.  The
              flag --dports is a convenient alias for this option.

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

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

       The only option available for this match is the following:

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

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

              nfacct add http-traffic

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

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

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

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

              nfacct get http-traffic

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

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

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

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

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

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

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

       ·   2 - Do not compare the TTL at all.

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

       ·   0 - Log all matched or unknown signatures

       ·   1 - Log only the first one

       ·   2 - Log all known matched signatures

       You may find something like this in syslog:

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

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

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

       To remove them again,

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

       The fingerprint database can be 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

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

       [!] --gid-owner groupname

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

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

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

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

       [!] --physdev-out name
              Name of a bridge port via which a packet is going to be sent
              (for 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 not
              being routed.  This is only useful in the FORWARD and
              POSTROUTING chains.

   pkttype
       This module matches the link-layer packet type.

       [!] --pkt-type {unicast|broadcast|multicast}

   policy
       This modules matches the policy used by IPsec for handling a packet.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       ·   rateest operator rateest-bps

       ·   rateest operator rateest-pps

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

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

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

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

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

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

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

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

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

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

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

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

       --rateest1 name

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

       --rateest-bps [value]

       --rateest-pps [value]

       --rateest-bps1 [value]

       --rateest-bps2 [value]

       --rateest-pps1 [value]

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

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

       # Estimate outgoing rates

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

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

       # Mark based on available bandwidth

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

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

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

   realm (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 prefixing 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 exclusive.

       --name name
              Specify the list to use for the commands. If no name is given
              then DEFAULT will be used.

       [!] --set
              This will add the source address of the packet to the list. If
              the source address is already in the list, this will update the
              existing entry. This will always return success (or failure if !
              is passed in).

       --rsource
              Match/save the source address of each packet in the recent list
              table. This is the default.

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

       --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 --seconds.
              When used, this will cause entries older than the last given
              number of seconds to be purged.

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

       --rttl This option may only be used in conjunction with one of --rcheck
              or --update. When used, this will narrow the match to only
              happen when the address is in the list and the TTL of the
              current packet matches that of the packet which hit the --set
              rule. This may be useful if you have problems with people faking
              their source address in order to DoS you via this module by
              disallowing others access to your site by sending bogus packets
              to you.

       Examples:

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

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

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

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

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

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

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

       The module itself accepts parameters, defaults shown:

       ip_list_tot=100
              Number of addresses remembered per table.

       ip_pkt_list_tot=20
              Number of packets per address remembered.

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

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

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

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

   rpfilter
       Performs a reverse path filter test on a packet.  If a reply to the
       packet would be sent via the same interface that the packet arrived on,
       the packet will match.  Note that, unlike the in-kernel rp_filter,
       packets protected by IPSec are not treated 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]
              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
       [!] --source-port,--sport port[:port]

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

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

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

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

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

       Examples:

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

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

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

   set
       This module matches IP sets which can be defined by ipset(8).

       [!] --match-set setname flag[,flag]...
              where flags are the comma separated list of src and/or dst
              specifications and there can be no more than six of them. Hence
              the command

               iptables -A FORWARD -m set --match-set test src,dst

              will match packets, for which (if the set type is ipportmap) the
              source address and destination port pair can be found in the
              specified set. If the set type of the specified set is single
              dimension (for example ipmap), then the command will match
              packets for which the source address can be found in the
              specified set.

       --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 counters 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 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 provided, 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

       --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 condition.  It
       supports two distinct modes settable with the --mode option.

       Supported options:

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

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

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

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

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

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

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

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

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

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

       --icase
              Ignore case when searching.

       Examples:

              # The string pattern can be used for simple text characters.
              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 specified. It
       provides the following options:

       [!] --source-port,--sport port[:port]
              Source port or port range specification. This can either be a
              service name or a port number. An inclusive range can also be
              specified, using the format first:last.  If the first port is
              omitted, "0" is assumed; if the last is omitted, "65535" is
              assumed.  The flag --sport is a convenient alias for this
              option.

       [!] --destination-port,--dport port[:port]
              Destination port or port range specification.  The flag --dport
              is a convenient alias for this option.

       [!] --tcp-flags mask comp
              Match when the TCP flags are as specified.  The first argument
              mask is the flags which we should examine, written as a comma-
              separated list, and the second argument comp is a comma-
              separated list of flags which must be set.  Flags are: SYN ACK
              FIN RST URG PSH ALL NONE.  Hence the command
               iptables -A FORWARD -p tcp --tcp-flags SYN,ACK,FIN,RST SYN
              will only match packets with the SYN flag set, and the ACK, FIN
              and RST flags unset.

       [!] --syn
              Only match TCP packets with the SYN bit set and the ACK,RST and
              FIN bits cleared.  Such packets are used to request TCP
              connection initiation; for example, blocking such packets coming
              in an interface will prevent incoming TCP connections, but
              outgoing TCP connections will be unaffected.  It is equivalent
              to --tcp-flags SYN,RST,ACK,FIN SYN.  If the "!" flag precedes
              the "--syn", the sense of the option is inverted.

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

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

       [!] --mss value[:value]
              Match a given TCP MSS value or range. 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 default
              to 1970-01-01 and 2038-01-19, respectively.

       --timestart hh:mm[:ss]

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

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

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

       --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, userspace should provide the correct system time and timezone to
       the kernel once it has the information.

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

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

       EXAMPLES. To match on weekends, use:

              -m time --weekdays Sa,Su

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

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

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

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

       During lunch hour:

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

       The fourth Friday in the month:

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

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

       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 (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 next header and is described
       further below.

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

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

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

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

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

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

              B and C are unsigned 32 bit integers, initially zero

       The instructions are:

       number B = number;

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

       &number
              C = C & number

       << number
              C = C << number

       >> number
              C = C >> number

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

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

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

       Example:

              match IP packets with total length >= 256

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

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

              read bytes 0-3

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

       Example: (more realistic, hence more complicated)

              match ICMP packets with icmp type 0

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

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

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

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

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

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

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

       Example:

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

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

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

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

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

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

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

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

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

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

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

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

       Example:

              iptables -N AUDIT_DROP

              iptables -A AUDIT_DROP -j AUDIT

              iptables -A AUDIT_DROP -j DROP

   CHECKSUM
       This target allows to selectively work around broken/old applications.
       It can only be used in the mangle table.

       --checksum-fill
              Compute and fill in the checksum in a packet that lacks a
              checksum.  This is particularly useful, if you need to work
              around old applications such as dhcp clients, that do not work
              well with checksum offloads, but don't want to disable checksum
              offload in your device.

   CLASSIFY
       This module allows you to set the skb->priority value (and thus
       classify the packet into a specific CBQ class).

       --set-class major:minor
              Set the major and minor class value. The values are always
              interpreted as hexadecimal even if no 0x prefix is given.

   CLUSTERIP (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.

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

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

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

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

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

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

   CONNMARK
       This module sets the netfilter mark value associated with a connection.
       The mark is 32 bits wide.

       --set-xmark value[/mask]
              Zero out the bits given by mask and XOR value into the ctmark.

       --save-mark [--nfmask nfmask] [--ctmask ctmask]
              Copy the packet mark (nfmark) to the connection mark (ctmark)
              using the given masks. The new nfmark value is determined as
              follows:

              ctmark = (ctmark & ~ctmask) ^ (nfmark & nfmask)

              i.e. ctmask defines what bits to clear and nfmask what bits of
              the nfmark to XOR into the ctmark. ctmask and nfmask default to
              0xFFFFFFFF.

       --restore-mark [--nfmask nfmask] [--ctmask ctmask]
              Copy the connection mark (ctmark) to the packet mark (nfmark)
              using the given masks. The new ctmark value is determined as
              follows:

              nfmark = (nfmark & ~nfmask) ^ (ctmark & ctmask);

              i.e. nfmask defines what bits to clear and ctmask what bits of
              the ctmark to XOR into the nfmark. ctmask and nfmask default to
              0xFFFFFFFF.

              --restore-mark is only valid in the mangle table.

       The following mnemonics are available for --set-xmark:

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

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

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

       --set-mark value[/mask]
              Set the connection mark. If a mask is specified then only those
              bits set in the mask are modified.

       --save-mark [--mask mask]
              Copy the nfmark to the ctmark. If a mask is specified, only
              those bits are copied.

       --restore-mark [--mask mask]
              Copy the ctmark to the nfmark. If a mask is specified, only
              those bits are copied. This is only valid in the mangle table.

   CONNSECMARK
       This module copies security markings from packets to connections (if
       unlabeled), and from connections back to packets (also only if
       unlabeled).  Typically used in conjunction with SECMARK, it is valid in
       the security table (for backwards compatibility with older kernels, it
       is also valid in the mangle table).

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

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


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

       --notrack
              Disables connection tracking for this packet.

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

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

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

       --zone-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 directions.

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

   DNAT
       This target is only valid in the nat table, in the PREROUTING and
       OUTPUT chains, and user-defined chains which are only called from those
       chains.  It specifies that the destination address of the packet should
       be modified (and all future packets in this connection will also be
       mangled), and rules should cease being examined.  It takes the
       following 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 specified, then the
              destination port will never be modified. If no IP address is
              specified then only the destination port will be modified.  In
              Kernels up to 2.6.10 you can add several --to-destination
              options. For those kernels, if you specify more than one
              destination address, either via an address range or multiple
              --to-destination options, a simple round-robin (one after
              another in cycle) load balancing takes place between these
              addresses.  Later Kernels (>= 2.6.11-rc1) don't have the ability
              to NAT to multiple ranges anymore.

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

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

       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

       You also have to use the NOTRACK target to disable connection tracking
       for translated flows.

   DSCP
       This target allows to alter the value of the DSCP bits within the TOS
       header of the IPv4 packet.  As this manipulates a packet, it can only
       be used in the mangle table.

       --set-dscp value
              Set the DSCP field to a numerical value (can be decimal or hex)

       --set-dscp-class class
              Set the DSCP field to a DiffServ class.

   ECN (IPv4-specific)
       This target allows to selectively work around known ECN blackholes.  It
       can only be used in the mangle table.

       --ecn-tcp-remove
              Remove all ECN bits from the TCP header.  Of course, it can only
              be used in conjunction with -p tcp.

   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 value on packets that leave your local
       network!

       --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 calculate the hashing.

       Existing options are:

       --hmark-tuple tuple
              Possible tuple members are: src meaning source address (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 Security 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.

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

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

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

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

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

   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.)

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

       --log-level level
              Level of logging, 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 associated with the
       packet.  It can, for example, be used in conjunction with routing based
       on fwmark (needs iproute2). If you plan on doing so, note that the mark
       needs to be set in the PREROUTING chain of the mangle table to affect
       routing.  The mark field is 32 bits wide.

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

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

       The following mnemonics are available:

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

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

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

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

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

       --random-fully
              Full randomize source port mapping If option --random-fully is
              used then port mapping will be fully randomized (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
       userspace processes may subscribe to the group to receive the packets.
       Like LOG, this is a non-terminating target, i.e. rule traversal
       continues at the next rule.

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

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

       --nflog-range size
              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 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 estimation
       calculation and saves the results for later evaluation using the
       rateest match.

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

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

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

   REDIRECT
       This target is only valid in the nat table, in the PREROUTING and
       OUTPUT chains, and user-defined chains which are only called from those
       chains.  It redirects the packet to the machine itself by changing the
       destination IP to the primary address of the incoming interface
       (locally-generated packets are mapped to the localhost address,
       127.0.0.1 for IPv4 and ::1 for IPv6).

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

   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 broken mail hosts
              (which won't accept your mail otherwise).

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

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

       --selctx security_context

   SET
       This 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

       --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 priority 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 provided, 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).

       --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. Support 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 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 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 connection 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 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 disabled if not
              present, also needed for selective acknowledgement and window
              scaling).

       Example:

       Determine tcp options used by backend, from an external system

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

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

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

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

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

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

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

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

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

       These options are mutually exclusive.

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

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

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

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

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

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

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

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

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

       The following mnemonics are available:

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

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

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

       NOTE: In Linux kernels up to and including 2.6.38, with the exception
       of longterm releases 2.6.32 (>=.42), 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 mnemonics.

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

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

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

       --tproxy-mark value[/mask]
              Marks packets with the given value/mask. The fwmark value set
              here can be used by advanced routing. (Required for transparent
              proxying to work: otherwise these packets will get forwarded,
              which is probably not what you want.)

   TRACE
       This target marks packets so that the kernel will log every 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 traverse until it's
       time to live is exceeded.

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

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

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

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

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

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

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

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



iptables 1.8.3                                          iptables-extensions(8)