<root
iptables-extensions(8)                    iptables 1.6.0                   iptables-extensions(8)

NAME
       iptables-extensions — list of extensions in the standard iptables distribution

SYNOPSIS
       ip6tables [-m name [module-options...]]  [-j target-name [target-options...]

       iptables [-m name [module-options...]]  [-j target-name [target-options...]

MATCH EXTENSIONS
       iptables can use extended packet matching modules with the -m or --match options, followed
       by the matching module name; after these, various extra command line options become avail‐
       able,  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 defi‐
       nition of that group depends on the specific layer three protocol.

       The following address types are possible:

       UNSPEC an unspecified address (i.e. 0.0.0.0)

       UNICAST
              an unicast address

       LOCAL  a local address

       BROADCAST
              a broadcast address

       ANYCAST
              an anycast packet

       MULTICAST
              a multicast address

       BLACKHOLE
              a blackhole address

       UNREACHABLE
              an unreachable address

       PROHIBIT
              a prohibited address

       THROW  FIXME

       NAT    FIXME

       XRESOLVE

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

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

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

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

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

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

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

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

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

       [!] --ahspi spi[:spi]

   bpf
       Match using Linux Socket Filter. Expects a BPF program in decimal format. This is the for‐
       mat 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 sup‐
       ported.

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

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

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

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

       Or instead, you can invoke the nfbpf_compile utility.

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

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

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

              Can  be  used in the OUTPUT chain to assign particular firewall policies for 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.

              IMPORTANT: when being used in the INPUT chain, the cgroup matcher is currently only
              of  limited functionality, meaning it will only match on packets that are processed
              for local sockets through early socket demuxing. Therefore, general  usage  on  the
              INPUT chain is disadviced unless the implications are well understood.

       Example:

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

       Available since Linux 3.14.

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

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

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

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

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

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

       Example:

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

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

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

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

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

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

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

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

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

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

              arptables -A INPUT -i eth2 --h-length 6 --destination-mac 01:00:5e:00:01:02 -j man‐
              gle --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. There‐
       fore, you'll have to adapt these to the arptables-jf syntax to get them working.

       In the case of TCP connections, pickup facility has to be disabled to  avoid  marking  TCP
       ACK packets coming in the reply direction as valid.

              echo 0 > /proc/sys/net/netfilter/nf_conntrack_tcp_loose

   comment
       Allows you to add comments (up to 256 characters) to any rule.

       --comment comment

       Example:
              iptables -A INPUT -i eth1 -m comment --comment "my local LAN"

   connbytes
       Match  by how many bytes or packets a connection (or one of the two flows constituting the
       connection) has transferred so far, or by average bytes per packet.

       The counters are 64-bit and are thus not expected to overflow ;)

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

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

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

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

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

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

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

   connlabel
       Module  matches  or adds connlabels to a connection.  connlabels are similar to connmarks,
       except labels are bit-based; i.e.  all labels may be attached to a flow at the same  time.
       Up to 128 unique labels are currently supported.

       [!] --label name
              matches  if label name has been set on a connection.  Instead of a name (which will
              be translated to a number, see EXAMPLE below), a number may be used instead.  Using
              a number always overrides connlabel.conf.

       --set  if the label has not been set on the connection, set it.  Note that setting a label
              can fail.  This is because the kernel allocates the conntrack  label  storage  area
              when  the connection is created, and it only reserves the amount of memory required
              by the ruleset that exists at the time the connection is created.   In  this  case,
              the match will fail (or succeed, in case --label option was negated).

       This  match  depends  on libnetfilter_conntrack 1.0.4 or later.  Label translation is done
       via the /etc/xtables/connlabel.conf configuration file.

       Example:

              0    eth0-in
              1    eth0-out
              2    ppp-in
              3    ppp-out
              4    bulk-traffic
              5    interactive

   connlimit
       Allows you to restrict the number of parallel  connections  to  a  server  per  client  IP
       address (or client address block).

       --connlimit-upto n
              Match if the number of existing connections is below or equal n.

       --connlimit-above n
              Match if the number of existing connections is above n.

       --connlimit-mask prefix_length
              Group  hosts  using  the  prefix  length.  For  IPv4, this must be a number between
              (including) 0 and 32. For IPv6, between 0 and 128. If not  specified,  the  maximum
              prefix length for the applicable protocol is used.

       --connlimit-saddr
              Apply  the limit onto the source group. This is the default if --connlimit-daddr is
              not specified.

       --connlimit-daddr
              Apply the limit onto the destination group.

       Examples:

       # allow 2 telnet connections per client host
              iptables -A INPUT -p tcp --syn --dport  23  -m  connlimit  --connlimit-above  2  -j
              REJECT

       # you can also match the other way around:
              iptables -A INPUT -p tcp --syn --dport 23 -m connlimit --connlimit-upto 2 -j ACCEPT

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

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

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

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

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

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

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

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

       [!] --ctorigsrc address[/mask]

       [!] --ctorigdst address[/mask]

       [!] --ctreplsrc address[/mask]

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

       [!] --ctorigsrcport port[:port]

       [!] --ctorigdstport port[:port]

       [!] --ctreplsrcport port[:port]

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

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

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

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

       States for --ctstate:

       INVALID
              The packet is associated with no known connection.

       NEW    The  packet  has started a new connection or otherwise associated with a connection
              which has not seen packets in both directions.

       ESTABLISHED
              The packet is associated with a connection which has seen packets  in  both  direc‐
              tions.

       RELATED
              The packet is starting a new connection, but is associated with an existing connec‐
              tion, such as an FTP data transfer or an ICMP error.

       UNTRACKED
              The packet is not tracked at all, which happens if you  explicitly  untrack  it  by
              using -j CT --notrack in the raw table.

       SNAT   A  virtual  state,  matching  if the original source address differs from the reply
              destination.

       DNAT   A virtual state, matching if  the  original  destination  differs  from  the  reply
              source.

       Statuses for --ctstatus:

       NONE   None of the below.

       EXPECTED
              This is an expected connection (i.e. a conntrack helper set it up).

       SEEN_REPLY
              Conntrack has seen packets in both directions.

       ASSURED
              Conntrack entry should never be early-expired.

       CONFIRMED
              Connection is confirmed: originating packet has left box.

   cpu
       [!] --cpu number
              Match  cpu  handling this packet. cpus are numbered from 0 to NR_CPUS-1 Can be used
              in combination with RPS (Remote Packet Steering) or multiqueue NICs to spread  net‐
              work traffic on different queues.

       Example:

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

       iptables -t nat -A PREROUTING -p tcp --dport 80 -m cpu --cpu 1 -j REDIRECT --to-port 8081

       Available since Linux 2.6.36.

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

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

       [!] --dccp-types mask
              Match  when the DCCP packet type is one of 'mask'. 'mask' is a comma-separated list
              of packet types.  Packet types are: REQUEST  RESPONSE  DATA  ACK  DATAACK  CLOSEREQ
              CLOSE RESET SYNC SYNCACK INVALID.

       [!] --dccp-option number
              Match if DCCP option set.

   devgroup
       Match device group of a packets incoming/outgoing interface.

       [!] --src-group name
              Match device group of incoming device

       [!] --dst-group name
              Match device group of outgoing device

   dscp
       This  module matches the 6 bit DSCP field within the TOS field in the IP header.  DSCP has
       superseded TOS within the IETF.

       [!] --dscp value
              Match against a numeric (decimal or hex) value [0-63].

       [!] --dscp-class class
              Match the DiffServ class. This value may be any of the BE, EF, AFxx or CSx classes.
              It will then be converted into its according numeric value.

   dst (IPv6-specific)
       This module matches the parameters in Destination Options header

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

       --dst-opts type[:length][,type[:length]...]
              numeric type of option and the length of the option data in octets.

   ecn
       This  allows  you  to  match  the  ECN  bits  of the IPv4/IPv6 and TCP header.  ECN is the
       Explicit Congestion Notification mechanism as specified in RFC3168

       [!] --ecn-tcp-cwr
              This matches if the TCP ECN CWR (Congestion Window Received) bit is set.

       [!] --ecn-tcp-ece
              This matches if the TCP ECN ECE (ECN Echo) bit is set.

       [!] --ecn-ip-ect num
              This matches a particular IPv4/IPv6 ECT (ECN-Capable Transport). You have to  spec‐
              ify a number between `0' and `3'.

   esp
       This module matches the SPIs in ESP header of IPsec packets.

       [!] --espspi spi[:spi]

   eui64 (IPv6-specific)
       This  module  matches the EUI-64 part of a stateless autoconfigured IPv6 address.  It com‐
       pares the EUI-64 derived from the source MAC address in Ethernet frame with the  lower  64
       bits  of  the  IPv6 source address. But "Universal/Local" bit is not compared. This module
       doesn't match other link layer frame, and is only valid in the PREROUTING, INPUT and  FOR‐
       WARD chains.

   frag (IPv6-specific)
       This module matches the parameters in Fragment header.

       [!] --fragid id[:id]
              Matches the given Identification or range of it.

       [!] --fraglen length
              This option cannot be used with kernel version 2.6.10 or later. The length of Frag‐
              ment 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 exam‐
       ples).

       A  hash  limit  option  (--hashlimit-upto,  --hashlimit-above)  and  --hashlimit-name  are
       required.

       --hashlimit-upto amount[/second|/minute|/hour|/day]
              Match  if the rate is below or equal to amount/quantum. It is specified either as a
              number, with an optional time  quantum  suffix  (the  default  is  3/hour),  or  as
              amountb/second (number of bytes per second).

       --hashlimit-above amount[/second|/minute|/hour|/day]
              Match if the rate is above amount/quantum.

       --hashlimit-burst amount
              Maximum initial number of packets to match: this number gets recharged by one every
              time the limit specified above is not reached, up to this number; the default is 5.
              When  byte-based  rate  matching  is requested, this option specifies the amount of
              bytes that can exceed the given rate.  This option should be used with  caution  --
              if the entry expires, the burst value is reset too.

       --hashlimit-mode {srcip|srcport|dstip|dstport},...
              A  comma-separated  list  of  objects  to  take  into  consideration. If no --hash‐
              limit-mode option is given, hashlimit acts like limit,  but  at  the  expensive  of
              doing the hash housekeeping.

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

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

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

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

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

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

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

       Examples:

       matching on source host
              "1000  packets  per  second  for every host in 192.168.0.0/16" => -s 192.168.0.0/16
              --hashlimit-mode srcip --hashlimit-upto 1000/sec

       matching on source port
              "100 packets per second for every service of 192.168.1.1" => -s 192.168.1.1 --hash‐
              limit-mode srcport --hashlimit-upto 100/sec

       matching on subnet
              "10000  packets  per  minute  for  every  /28  subnet  (groups  of  8 addresses) in
              10.0.0.0/8" => -s 10.0.0.0/8 --hashlimit-mask 28 --hashlimit-upto 10000/min

       matching bytes per second
              "flows  exceeding  512kbyte/s"  =>   --hashlimit-mode   srcip,dstip,srcport,dstport
              --hashlimit-above 512kb/s

       matching bytes per second
              "hosts  that  exceed  512kbyte/s,  but  permit  up  to 1Megabytes without matching"
              --hashlimit-mode dstip --hashlimit-above 512kb/s --hashlimit-burst 1mb

   hbh (IPv6-specific)
       This module matches the parameters in Hop-by-Hop Options header

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

       --hbh-opts type[:length][,type[:length]...]
              numeric type of option and the length of the option data in octets.

   helper
       This module matches packets related to a specific conntrack-helper.

       [!] --helper string
              Matches packets related to the specified conntrack-helper.

              string can be "ftp" for packets related to a  ftp-session  on  default  port.   For
              other ports append -portnr to the value, ie. "ftp-2121".

              Same rules apply for other conntrack-helpers.

   hl (IPv6-specific)
       This module matches the Hop Limit field in the IPv6 header.

       [!] --hl-eq value
              Matches if Hop Limit equals value.

       --hl-lt value
              Matches if Hop Limit is less than value.

       --hl-gt value
              Matches if Hop Limit is greater than value.

   icmp (IPv4-specific)
       This  extension  can  be used if `--protocol icmp' is specified. It provides the following
       option:

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

   icmp6 (IPv6-specific)
       This  extension can be used if `--protocol ipv6-icmp' or `--protocol icmpv6' is specified.
       It provides the following option:

       [!] --icmpv6-type type[/code]|typename
              This allows specification of the ICMPv6 type, which can be a numeric  ICMPv6  type,
              type and code, or one of the ICMPv6 type names shown by the command
               ip6tables -p ipv6-icmp -h

   iprange
       This matches on a given arbitrary range of IP addresses.

       [!] --src-range from[-to]
              Match source IP in the specified range.

       [!] --dst-range from[-to]
              Match destination IP in the specified range.

   ipv6header (IPv6-specific)
       This module matches IPv6 extension headers and/or upper layer header.

       --soft Matches if the packet includes any of the headers specified with --header.

       [!] --header header[,header...]
              Matches the packet which EXACTLY includes all specified headers. The headers encap‐
              sulated with ESP header are out of scope.  Possible header types can be:

       hop|hop-by-hop
              Hop-by-Hop Options header

       dst    Destination Options header

       route  Routing header

       frag   Fragment header

       auth   Authentication header

       esp    Encapsulating Security Payload header

       none   No Next header which matches 59 in the 'Next Header field' of IPv6  header  or  any
              IPv6 extension headers

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

   ipvs
       Match IPVS connection properties.

       [!] --ipvs
              packet belongs to an IPVS connection

       Any of the following options implies --ipvs (even negated)

       [!] --vproto protocol
              VIP protocol to match; by number or name, e.g. "tcp"

       [!] --vaddr address[/mask]
              VIP address to match

       [!] --vport port
              VIP port to match; by number or name, e.g. "http"

       --vdir {ORIGINAL|REPLY}
              flow direction of packet

       [!] --vmethod {GATE|IPIP|MASQ}
              IPVS forwarding method used

       [!] --vportctl port
              VIP port of the controlling connection to match, e.g. 21 for FTP

   length
       This module matches the length of the layer-3 payload (e.g. layer-4 packet)  of  a  packet
       against a specific value or range of values.

       [!] --length length[:length]

   limit
       This  module  matches  at  a  limited rate using a token bucket filter.  A rule using this
       extension will match until this limit is reached.  It can be used in combination with  the
       LOG target to give limited logging, for example.

       xt_limit  has  no negation support - you will have to use -m hashlimit !  --hashlimit rate
       in this case whilst omitting --hashlimit-mode.

       --limit rate[/second|/minute|/hour|/day]
              Maximum average matching rate: specified as a number, with an  optional  `/second',
              `/minute', `/hour', or `/day' suffix; the default is 3/hour.

       --limit-burst number
              Maximum initial number of packets to match: this number gets recharged by one every
              time the limit specified above is not reached, up to this number; the default is 5.

   mac
       [!] --mac-source address
              Match source MAC address.  It must be of the  form  XX:XX:XX:XX:XX:XX.   Note  that
              this  only  makes sense for packets coming from an Ethernet device and entering the
              PREROUTING, FORWARD or INPUT chains.

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

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

   mh (IPv6-specific)
       This extension is loaded if `--protocol ipv6-mh' or `--protocol mh' is specified. It  pro‐
       vides 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  speci‐
       fied.   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  conve‐
              nient  alias  for  this option. Multiple ports or port ranges are separated using a
              comma, and a port range is specified using a colon.  53,1024:65535 would  therefore
              match ports 53 and all from 1024 through 65535.

       [!] --destination-ports,--dports port[,port|,port:port]...
              Match  if  the  destination port is one of the given ports.  The flag --dports is a
              convenient alias for this option.

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

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

       The only option available for this match is the following:

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

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

              nfacct add http-traffic

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

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

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

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

              nfacct get http-traffic

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

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

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

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

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

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

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

       ·   2 - Do not compare the TTL at all.

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

       ·   0 - Log all matched or unknown signatures

       ·   1 - Log only the first one

       ·   2 - Log all known matched signatures

       You may find something like this in syslog:

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

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

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

       To remove them again,

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

       The    fingerprint   database   can   be   downlaoded   from   http://www.openbsd.org/cgi-
       bin/cvsweb/src/etc/pf.os .

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

       [!] --uid-owner username

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

       [!] --gid-owner groupname

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

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

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

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

       [!] --physdev-out name
              Name of a bridge port via which a packet is going to be sent (for  bridged  packets
              entering the FORWARD and POSTROUTING chains).  If the interface name ends in a "+",
              then any interface which begins with this name will match.

       [!] --physdev-is-in
              Matches if the packet has entered through a bridge interface.

       [!] --physdev-is-out
              Matches if the packet will leave through a bridge interface.

       [!] --physdev-is-bridged
              Matches if the packet is being bridged and therefore is not being routed.  This  is
              only useful in the FORWARD and POSTROUTING chains.

   pkttype
       This module matches the link-layer packet type.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       ·   rateest operator rateest-bps

       ·   rateest operator rateest-pps

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

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

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

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

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

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

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

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

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

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

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

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

       --rateest1 name

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

       --rateest-bps [value]

       --rateest-pps [value]

       --rateest-bps1 [value]

       --rateest-bps2 [value]

       --rateest-pps1 [value]

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

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

       # Estimate outgoing rates

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

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

       # Mark based on available bandwidth

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

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

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

   realm (IPv4-specific)
       This matches the routing realm.  Routing realms are used in complex routing setups involv‐
       ing dynamic routing protocols like BGP.

       [!] --realm value[/mask]
              Matches a given realm number (and optionally mask). If not a number, value can be a
              named realm from /etc/iproute2/rt_realms (mask can not be used in that case).

   recent
       Allows  you  to dynamically create a list of IP addresses and then match against that list
       in a few different ways.

       For example, you can create a "badguy" list out of people attempting to  connect  to  port
       139 on your firewall and then DROP all future packets from them without considering them.

       --set, --rcheck, --update and --remove are mutually exclusive.

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

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

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

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

       --mask netmask
              Netmask that will be applied to this recent list.

       [!] --rcheck
              Check if the source address of the packet is currently in the list.

       [!] --update
              Like --rcheck, except it will update the "last seen" timestamp if it matches.

       [!] --remove
              Check  if  the source address of the packet is currently in the list and if so that
              address will be removed from the list and the rule will return true. If the address
              is not found, false is returned.

       --seconds seconds
              This  option  must  be  used  in conjunction with one of --rcheck or --update. When
              used, this will narrow the match to only happen when the address is in the list and
              was seen within the last given number of seconds.

       --reap This  option  can only be used in conjunction with --seconds.  When used, this will
              cause entries older than the last given number of seconds to be purged.

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

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

       Examples:

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

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

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

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

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

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

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

       The module itself accepts parameters, defaults shown:

       ip_list_tot=100
              Number of addresses remembered per table.

       ip_pkt_list_tot=20
              Number of packets per address remembered.

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

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

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

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

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

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

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

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

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

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

       iptables -t raw -N RPFILTER

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

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

       iptables -t raw -A RPFILTER -j DROP

       iptables -t raw -A PREROUTING -j RPFILTER

       Example to drop failed packets, without logging:

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

   rt (IPv6-specific)
       Match on IPv6 routing header

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

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

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

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

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

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

   sctp
       This module matches Stream Control Transmission Protocol headers.

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

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

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

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

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

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

       Examples:

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

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

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

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

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

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

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

       --return-nomatch
              If the --return-nomatch option is specified and the set type supports  the  nomatch
              flag,  then  the matching is reversed: a match with an element flagged with nomatch
              returns true, while a match with a plain element returns false.

       ! --update-counters
              If the --update-counters flag is negated, then the packet and byte counters of  the
              matching  element in the set won't be updated. Default the packet and byte counters
              are updated.

       ! --update-subcounters
              If the --update-subcounters flag is negated, then the packet and byte  counters  of
              the  matching  element  in  the  member set of a list type of set won't be updated.
              Default the packet and byte counters are updated.

       [!] --packets-eq value
              If the packet is matched an element in the set, match only if the packet counter of
              the element matches the given value too.

       --packets-lt value
              If the packet is matched an element in the set, match only if the packet counter of
              the element is less than the given value as well.

       --packets-gt value
              If the packet is matched an element in the set, match only if the packet counter of
              the element is greater than the given value as well.

       [!] --bytes-eq value
              If  the  packet is matched an element in the set, match only if the byte counter of
              the element matches the given value too.

       --bytes-lt value
              If the packet is matched an element in the set, match only if the byte  counter  of
              the element is less than the given value as well.

       --bytes-gt value
              If  the  packet is matched an element in the set, match only if the byte counter of
              the element is greater than the given value as well.

       The packet and byte counters related options and  flags  are  ignored  when  the  set  was
       defined without counter support.

       The  option  --match-set can be replaced by --set if that does not clash with an option of
       other extensions.

       Use of -m set requires that ipset kernel support is provided, which, for standard kernels,
       is the case since Linux 2.6.39.

   socket
       This  matches  if  an  open  TCP/UDP  socket  can be found by doing a socket lookup on the
       packet. It matches if there is an established or non-zero bound listening socket (possibly
       with a non-local address). The lookup is performed using the packet tuple of TCP/UDP pack‐
       ets, or the original TCP/UDP header embedded in an ICMP/ICPMv6 error packet.

       --transparent
              Ignore non-transparent sockets.

       --nowildcard
              Do not ignore sockets bound to  'any'  address.   The  socket  match  won't  accept
              zero-bound  listeners by default, since then local services could intercept traffic
              that would otherwise be forwarded.  This option therefore has security implications
              when  used  to  match  traffic  being  forwarded  to redirect such packets to local
              machine with policy routing.  When using the socket match to implement fully trans‐
              parent  proxies  bound to non-local addresses it is recommended to use the --trans‐
              parent option instead.

       Example (assuming packets with mark 1 are delivered locally):

              -t mangle -A PREROUTING -m socket --transparent -j MARK --set-mark 1

       --restore-skmark
              Set the packet mark to the  matching  socket's  mark.  Can  be  combined  with  the
              --transparent  and  --nowildcard options to restrict the sockets to be matched when
              restoring the packet mark.

       Example: An application opens 2 transparent (IP_TRANSPARENT) sockets and sets  a  mark  on
       them with SO_MARK socket option. We can filter matching packets:

              -t mangle -I PREROUTING -m socket --transparent --restore-skmark -j action

              -t mangle -A action -m mark --mark 10 -j action2

              -t mangle -A action -m mark --mark 11 -j action3

   state
       The "state" extension is a subset of the "conntrack" module.  "state" allows access to the
       connection tracking state for this packet.

       [!] --state state
              Where state is a comma separated list of the connection states  to  match.  Only  a
              subset  of  the  states  unterstood  by "conntrack" are recognized: INVALID, ESTAB‐
              LISHED, NEW, RELATED or UNTRACKED. For their description, see the "conntrack" head‐
              ing in this manpage.

   statistic
       This  module  matches packets based on some statistic condition.  It supports two distinct
       modes settable with the --mode option.

       Supported options:

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

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

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

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

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

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

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

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

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

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

       --icase
              Ignore case when searching.

       Examples:

              # The string pattern can be used for simple text characters.
              iptables -A INPUT -p tcp --dport 80 -m string --algo bm --string 'GET  /index.html'
              -j LOG

              #  The hex string pattern can be used for non-printable characters, like |0D 0A| or
              |0D0A|.
              iptables -p udp --dport 53 -m string --algo  bm  --from  40  --to  57  --hex-string
              '|03|www|09|netfilter|03|org|00|'

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

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

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

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

       [!] --syn
              Only match TCP packets with the SYN bit set and the ACK,RST and FIN  bits  cleared.
              Such  packets  are used to request TCP connection initiation; for example, blocking
              such packets coming in an interface will prevent incoming TCP connections, but out‐
              going  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  hand‐
       shake at connection startup time.

       [!] --mss value[:value]
              Match a given TCP MSS value or range.

   time
       This  matches  if  the  packet  arrival time/date is within a given range. All options are
       optional, but are ANDed when specified. All times are interpreted as UTC by default.

       --datestart YYYY[-MM[-DD[Thh[:mm[:ss]]]]]

       --datestop YYYY[-MM[-DD[Thh[:mm[:ss]]]]]
              Only match during the given time, which must be in ISO 8601 "T" notation.  The pos‐
              sible time range is 1970-01-01T00:00:00 to 2038-01-19T04:17:07.

              If  --datestart  or --datestop are not specified, it will default to 1970-01-01 and
              2038-01-19, respectively.

       --timestart hh:mm[:ss]

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

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

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

       --contiguous
              When --timestop is smaller than --timestart value, match  this  as  a  single  time
              period instead distinct intervals.  See EXAMPLES.

       --kerneltz
              Use the kernel timezone instead of UTC to determine whether a packet meets the time
              regulations.

       About kernel timezones: Linux keeps the system time in UTC, and always does so.  On  boot,
       system  time  is initialized from a referential time source. Where this time source has no
       timezone information, such as the x86 CMOS RTC, UTC will be assumed. If the time source is
       however  not  in UTC, userspace should provide the correct system time and timezone to the
       kernel once it has the information.

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

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

       EXAMPLES. To match on weekends, use:

              -m time --weekdays Sa,Su

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

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

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

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

       During lunch hour:

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

       The fourth Friday in the month:

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

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

       Matching across days might not do what is expected.  For instance,

              -m time --weekdays Mo --timestart 23:00  --timestop 01:00 Will  match  Monday,  for
              one  hour  from  midnight  to  1  a.m.,  and then again for another hour from 23:00
              onwards.  If this is unwanted, e.g. if you would like 'match  for  two  hours  from
              Montay 23:00 onwards' you need to also specify the --contiguous option in the exam‐
              ple 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 logi‐
              cally 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 rec‐
              ognized  TOS  names  can be obtained by calling iptables with -m tos -h.  Note that
              this implies a mask of 0x3F, i.e. all but the ECN bits.

   ttl (IPv4-specific)
       This module matches the time to live field in the IP header.

       [!] --ttl-eq ttl
              Matches the given TTL value.

       --ttl-gt ttl
              Matches if TTL is greater than the given TTL value.

       --ttl-lt ttl
              Matches if TTL is less than the given TTL value.

   u32
       U32 tests whether quantities of up to 4 bytes extracted from a packet have specified  val‐
       ues.  The specification of what to extract is general enough to find data at given offsets
       from tcp headers or payloads.

       [!] --u32 tests
              The argument amounts to a program in a small language described below.

              tests := location "=" value | tests "&&" location "=" value

              value := range | value "," range

              range := number | number ":" number

       a single number, n, is interpreted the same as n:n. n:m is interpreted  as  the  range  of
       numbers >=n and <=m.

           location := number | location operator number

           operator := "&" | "<<" | ">>" | "@"

       The  operators  &,  <<, >> and && mean the same as in C.  The = is really a set membership
       operator and the value syntax describes a set. The @ operator is what allows moving to the
       next header and is described further below.

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

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

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

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

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

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

              B and C are unsigned 32 bit integers, initially zero

       The instructions are:

              number B = number;

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

              &number C = C & number

              << number C = C << number

              >> number C = C >> number

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

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

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

       Example:

              match IP packets with total length >= 256

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

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

              read bytes 0-3

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

       Example: (more realistic, hence more complicated)

              match ICMP packets with icmp type 0

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

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

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

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

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

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

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

       Example:

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

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

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

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

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

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

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

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

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

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

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

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

       Example:

              iptables -N AUDIT_DROP

              iptables -A AUDIT_DROP -j AUDIT --type drop

              iptables -A AUDIT_DROP -j DROP

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

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

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

       --set-class major:minor
              Set the major and minor class value. The values are always interpreted as hexadeci‐
              mal 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 stati‐
       cally distributed between the nodes in this cluster.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       --notrack
              Disables connection tracking for this packet.

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

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

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

       --zone-orig {id|mark}
              For traffic coming from ORIGINAL direction, assign this packet to zone id and  only
              have  lookups done in that zone. If mark is used instead of id, the zone is derived
              from the packet nfmark.

       --zone-reply {id|mark}
              For traffic coming from REPLY direction, assign this packet to  zone  id  and  only
              have  lookups done in that zone. If mark is used instead of id, the zone is derived
              from the packet nfmark.

       --zone {id|mark}
              Assign this packet to zone id and only have lookups done in that zone.  If mark  is
              used instead of id, the zone is derived from the packet nfmark. By default, packets
              have zone 0. This option applies to both directions.

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

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

       --to-destination [ipaddr[-ipaddr]][:port[-port]]
              which  can  specify  a  single new destination IP address, an inclusive range of IP
              addresses. Optionally a port range, if the rule also specifies one of the following
              protocols:  tcp, udp, dccp or sctp.  If no port range is specified, then the desti‐
              nation port will never be modified. If no IP address is  specified  then  only  the
              destination  port  will  be  modified.  In Kernels up to 2.6.10 you can add several
              --to-destination options. For those kernels, if you specify more than one  destina‐
              tion  address,  either via an address range or multiple --to-destination options, a
              simple round-robin (one after another in cycle) load balancing takes place  between
              these  addresses.   Later  Kernels (>= 2.6.11-rc1) don't have the ability to NAT to
              multiple ranges anymore.

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

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

       IPv6 support available since Linux kernels >= 3.7.

   DNPT (IPv6-specific)
       Provides stateless destination IPv6-to-IPv6 Network Prefix Translation  (as  described  by
       RFC 6296).

       You  have  to use this target in the mangle table, not in the nat table. It takes the fol‐
       lowing options:

       --src-pfx [prefix/length]
              Set source prefix that you want to translate and length

       --dst-pfx [prefix/length]
              Set destination prefix that you want to use in the translation and length

       You have to use the SNPT target to undo the translation. Example:

              ip6tables -t mangle -I POSTROUTING -s fd00::/64   -o  vboxnet0  -j  SNPT  --src-pfx
              fd00::/64 --dst-pfx 2001:e20:2000:40f::/64

              ip6tables -t mangle -I PREROUTING -i wlan0 -d 2001:e20:2000:40f::/64 -j DNPT --src-
              pfx 2001:e20:2000:40f::/64 --dst-pfx fd00::/64

       You may need to enable IPv6 neighbor proxy:

              sysctl -w net.ipv6.conf.all.proxy_ndp=1

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

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

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

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

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

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

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

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

       --hl-set value
              Set the Hop Limit to `value'.

       --hl-dec value
              Decrement the Hop Limit `value' times.

       --hl-inc value
              Increment the Hop Limit `value' times.

   HMARK
       Like MARK, i.e. set the fwmark, but the mark is calculated from hashing packet selector at
       choice. You have also to specify the mark range and, optionally, the offset to start from.
       ICMP error messages are inspected and used to calculate the hashing.

       Existing options are:

       --hmark-tuple tuple
              Possible  tuple  members  are: src meaning source address (IPv4, IPv6 address), dst
              meaning destination address (IPv4, IPv6 address), sport meaning source  port  (TCP,
              UDP, UDPlite, SCTP, DCCP), dport meaning destination port (TCP, UDP, UDPlite, SCTP,
              DCCP), spi meaning Security Parameter Index (AH, ESP), and ct meaning the usage  of
              the conntrack tuple instead of the packet selectors.

       --hmark-mod value (must be > 0)
              Modulus for hash calculation (to limit the range of possible marks)

       --hmark-offset value
              Offset to start marks from.

       For advanced usage, instead of using --hmark-tuple, you can specify custom
              prefixes and masks:

       --hmark-src-prefix cidr
              The source address mask in CIDR notation.

       --hmark-dst-prefix cidr
              The destination address mask in CIDR notation.

       --hmark-sport-mask value
              A 16 bit source port mask in hexadecimal.

       --hmark-dport-mask value
              A 16 bit destination port mask in hexadecimal.

       --hmark-spi-mask value
              A 32 bit field with spi mask.

       --hmark-proto-mask value
              An 8 bit field with layer 4 protocol number.

       --hmark-rnd value
              A 32 bit random custom value to feed hash calculation.

       Examples:

       iptables -t mangle -A PREROUTING -m conntrack --ctstate NEW
        -j  HMARK  --hmark-tuple ct,src,dst,proto --hmark-offset 10000 --hmark-mod 10 --hmark-rnd
       0xfeedcafe

       iptables -t mangle -A PREROUTING -j HMARK --hmark-offset 10000 --hmark-tuple src,dst,proto
       --hmark-mod 10 --hmark-rnd 0xdeafbeef

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

       /sys/class/xt_idletimer/timers/

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