Provided by: iptables_1.6.0-2ubuntu3_amd64 bug

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 BPF program in  decimal  format.  This  is  the
       format generated by the nfbpf_compile utility.

       --bytecode code
              Pass the BPF byte code format (described in the example below).

       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

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

   cgroup
       [!] --cgroup fwid
              Match corresponding cgroup for this packet.

              Can  be  used  in  the  OUTPUT  chain  to  assign  particular firewall policies for
              aggregated task/jobs on the system. This  allows  for  more  fine-grained  firewall
              policies  that only match for a subset of the system's processes. fwid is the maker
              set through the net_cls cgroup's id.

              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 disadviced unless the implications are well understood.

       Example:

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

       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.

       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   downlaoded   from    http://www.openbsd.org/cgi-
       bin/cvsweb/src/etc/pf.os .

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

       [!] --uid-owner username

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

       [!] --gid-owner groupname

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

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

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

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

       [!] --physdev-out name
              Name  of  a bridge port via which a packet is going to be sent (for 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).

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

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

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

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

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

       iptables -t raw -N RPFILTER

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

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

       iptables -t raw -A RPFILTER -j DROP

       iptables -t raw -A PREROUTING -j RPFILTER

       Example to drop failed packets, without logging:

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

   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
       This module matches Stream Control Transmission Protocol headers.

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

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

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

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

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

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

       Examples:

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

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

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

   set
       This module matches IP sets which can be defined by 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.

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

       --type {accept|drop|reject}
              Set type of audit record.

       Example:

              iptables -N AUDIT_DROP

              iptables -A AUDIT_DROP -j AUDIT --type drop

              iptables -A AUDIT_DROP -j DROP

   CHECKSUM
       This target selectively works 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  sets  parameters  for  a  packet or its associated connection. The target
       attaches a "template" connection tracking entry to the packet, which is then used  by  the
       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  alters  the value of the DSCP bits within the TOS header of the IPv4 packet.
       As this manipulates a packet, it can only be used in the mangle table.

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

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

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

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

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

       Don't ever set or increment the 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).

       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
              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.

       --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 alters 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.

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

   TTL (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).