iptables-extensions

iptables-extensions(8)          iptables 1.6.1          iptables-extensions(8)

NAME
       iptables-extensions -- list of extensions in the standard iptables dis-
       tribution

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 PREROUT-
              ING, 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  POSTROUT-
              ING,  OUTPUT and FORWARD chains. It cannot be specified with the
              --limit-iface-in option.

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

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

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

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

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

       [!] --ahspi spi[:spi]

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

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

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

              mount -t bpf bpf ${BPF_MOUNT}

       then insert the filter in iptables by path:

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

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

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

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

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

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

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

       Or instead, you can invoke the nfbpf_compile utility.

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

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

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

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

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

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

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

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

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

       Example:

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

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

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

       Available since Linux 3.14.

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

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

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

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

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

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

       Example:

              iptables  -A  PREROUTING  -t  mangle  -i eth1 -m cluster --clus-
              ter-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 --clus-
              ter-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 --man-
              gle-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  aver-
       age 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  `con-
       ntrack -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  trans-
              ferred 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 sim-
       ilar 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  cur-
       rently 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 allo-
              cates 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 appli-
              cable 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  connec-
       tion (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  pack-
              ets 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 explic-
              itly 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 dif-
              ferent queues.

       Example:

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

       iptables -t nat -A PREROUTING -p tcp --dport 80 -m cpu --cpu 1 -j REDI-
       RECT --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 accord-
              ing 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 FOR-
       WARD 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 --hash-
       limit-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 suf-
              fix (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-src-
              mask 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 with-
              out 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  pro-
       vides 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.  Pos-
              sible 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, FOR-
              WARD 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 com-
              parison).

   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, alterna-
       tively, from the git.netfilter.org repository.

   osf
       The osf module does passive operating system fingerprinting. This  mod-
       ules  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  fingerprint-
              ing.

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

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

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

       o   2 - Do not compare the TTL at all.

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

       o   0 - Log all matched or unknown signatures

       o   1 - Log only the first one

       o   2 - Log all known matched signatures

       You may find something like this in syslog:

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

       OS  fingerprints  are loadable using the nfnl_osf program. To load fin-
       gerprints 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.open-
       bsd.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  infrastruc-
       ture 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 inter-
              face 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 POSTROUT-
              ING 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  decapsula-
              tion  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, com-
       paring two rate estimators and matching on the difference  between  two
       rate estimators.

       For a better understanding of the available options, these are all pos-
       sible combinations:

       o   rateest operator rateest-bps

       o   rateest operator rateest-pps

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

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

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

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

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

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

       --rateest-delta
           For each estimator (either absolute or  relative  mode),  calculate
           the  difference  between the estimator-determined flow rate and the
           static value chosen with the BPS/PPS options. If the flow  rate  is
           higher than the specified BPS/PPS, 0 will be used instead of a neg-
           ative 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 hap-
              pen 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 disallow-
              ing 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  informa-
       tion about each entry of each list.

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

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

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

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

       The module itself accepts parameters, defaults shown:

       ip_list_tot=100
              Number of addresses remembered per table.

       ip_pkt_list_tot=20
              Number of packets per address remembered.

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

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

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

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

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

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

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

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

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

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

       iptables -t raw -N RPFILTER

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

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

       iptables -t raw -A RPFILTER -j DROP

       iptables -t raw -A PREROUTING -j RPFILTER

       Example to drop failed packets, without logging:

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

   rt (IPv6-specific)
       Match on IPv6 routing header

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

       [!] --rt-segsleft num[:num]
              Match the `segments left' field (range).

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

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

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

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

   sctp
       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 spec-
              ifications  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 pack-
              ets 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  for-
              warded.   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 com-
              bined  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 man-
              page.

   statistic
       This module matches packets based on some statistic condition.  It sup-
       ports 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 off-
              set-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  charac-
              ters, 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  pro-
       vides 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-sepa-
              rated 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 connec-
              tion 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 vari-
       able. 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 call-
              ing 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 fur-
       ther 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 char-
       acters 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). Alterna-
              tively, 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  pro-
       vides 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  descrip-
              tion  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 tar-
       get.  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 check-
              sum.   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 off-
              load in your device.

   CLASSIFY
       This module allows you to set the skb->priority value (and  thus  clas-
       sify 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,  sour-
              ceip-sourceport, sourceip-sourceport-destport.

       --clustermac mac
              Specify the ClusterIP MAC address. Has to be a link-layer multi-
              cast 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  unla-
       beled).  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  connec-
              tion  does, copy the security marking from the connection to the
              packet.

   CT
       The CT target sets parameters for a packet or  its  associated  connec-
       tion. 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 connec-
              tion. 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  connec-
              tion.  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/netfil-
              ter/nf_conntrack_*_timeout_*.

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

       --to-destination [ipaddr[-ipaddr]][:port[-port]]
              which can specify a single new destination IP address, an inclu-
              sive 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 per-
              sistent 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  man-
       gle 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 cre-
       ated  when a rule is set with a new label.  The rules also take a time-
       out 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 indica-
       tor 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 pro-
              longing 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  match-
       ing 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  prior-
              ity): 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) connec-
       tions: 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 any-
       way).

       --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  con-
              structed  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 contin-
       ues at the next rule.

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

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

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

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

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

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

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

       --queue-balance value:value
              This specifies a range of queues to use. Packets are  then  bal-
              anced  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 perfor-
              mance 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 calcu-
       lation 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 microsec-
              onds.

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

   REDIRECT
       This  target is only valid in the nat table, in the PREROUTING and OUT-
       PUT 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  pro-
              tocols: 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 TAR-
       GET, 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-pro-
              hibited, 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 TAR-
       GET, 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-unreach-
              able,       icmp-port-unreachable,       icmp-proto-unreachable,
              icmp-net-prohibited, icmp-host-prohibited, or icmp-admin-prohib-
              ited (*),  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 defi-
              nition

       --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, FOR-
              WARD 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  man-
       gled),  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  multi-
              ple 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  per-
              sistent 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  con-
       figuration 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  (includ-
       ing  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 ker-
       nels 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 redi-
       rects 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 deter-
       mines 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 danger-
       ous, 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 charac-
              ters long, and useful for distinguishing messages in the logs.

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

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

iptables 1.6.1                                          iptables-extensions(8)
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