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iptables-extensions



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


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

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

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

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

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

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

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

       Example:

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

       Available since Linux 3.14.

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

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

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

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

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

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

       Example:

              iptables -A PREROUTING -t mangle  -i  eth1  -m  cluster  --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
              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}
       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.
              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
       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-
              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).

   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-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.


       [!] --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

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

   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

       [!] --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:
       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 .

       [!] --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  packets  entering  the  FORWARD,  OUTPUT  and  POSTROUTING
              chains).  If the interface name ends in a "+", then  any  inter-
              face  which  begins  with this name will match. Note that in the
              nat and mangle OUTPUT chains one cannot match on the bridge out-
              put  port,  however  one  can in the filter OUTPUT chain. If the
              packet won't leave by a bridge device or if it  is  yet  unknown
              what the output device will be, then the packet won't match this
              option, unless '!' is used.

       [!] --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
              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

       --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

       --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

       --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.

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

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

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

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

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

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

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

       iptables -t raw -N RPFILTER

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

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

       iptables -t raw -A RPFILTER -j DROP

       iptables -t raw -A PREROUTING -j RPFILTER

       Example to drop failed packets, without logging:

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

   rt (IPv6-specific)
       Match on IPv6 routing header

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

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

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

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

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

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

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

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

       Examples:

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

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

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

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

       [!] --match-set setname flag[,flag]...
              where flags are the comma separated list of src and/or dst 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
       --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
              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.

       Examples:

              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.   If the first port is greater than the second one they
              will be swapped.  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"
              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 --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.

       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
              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-


TARGET EXTENSIONS

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

   AUDIT
       This target allows to create audit records for packets hitting the 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 allows to selectively work around broken/old applications.
       It can only be used in the mangle table.

       --checksum-fill
              Compute and fill in the checksum in a packet that lacks a 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.

   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
              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 allows to set parameters for a packet or  its  associated
       connection.  The target attaches a "template" connection tracking entry
       to the packet, which is then used by the conntrack core when initializ-
       ing 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 id
              Assign this packet to zone id and only have lookups done in that
              zone.  By default, packets have zone 0.

       --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

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

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

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

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

       --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.

       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:
       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
       --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.

   MIRROR (IPv4-specific)
       This is an experimental demonstration target which inverts  the  source
       and destination fields in the IP header and retransmits the packet.  It
       is only valid in the INPUT, FORWARD and PREROUTING  chains,  and  user-
       defined  chains which are only called from those chains.  Note that the
       outgoing packets are NOT seen by any packet filtering  chains,  connec-
       tion tracking or NAT, to avoid loops and other problems.

   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
       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-
              (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

   SAME (IPv4-specific)
       Similar to SNAT/DNAT depending on chain: it takes a range of  addresses
       (`--to  1.2.3.4-1.2.3.7')  and gives a client the same source-/destina-
       tion-address for each connection.

   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

              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

       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

       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.

   TCPMSS
       This  target  allows to alter the MSS value of TCP SYN packets, to con-
       trol the maximum size for that connection (usually limiting it to  your
       outgoing  interface's  MTU  minus  40  for IPv4 or 60 for IPv6, respec-
       tively).  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.
              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

       --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 nf_log_ipv4(6) 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.

              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 1.4.21 iptables-extensions(8)



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