Provided by: iptables_1.6.0-2ubuntu3_i386 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).