Provided by: xtables-addons-common_2.3-1_amd64 bug


       Xtables-addons — additional extensions for iptables, ip6tables, etc.


       The  ACCOUNT  target  is a high performance accounting system for large local networks. It
       allows per-IP accounting in whole prefixes of IPv4 addresses with size of up to /8 without
       the need to add individual accouting rule for each IP address.

       The ACCOUNT is designed to be queried for data every second or at least every ten seconds.
       It is written as kernel module to handle high bandwidths without packet loss.

       The largest possible subnet size is  24  bit,  meaning  for  example  network.
       ACCOUNT uses fixed internal data structures which speeds up the processing of each packet.
       Furthermore, accounting data for one complete 192.168.1.X/24 network takes 4 KB of memory.
       Memory for 16 or 24 bit networks is only allocated when needed.

       To  optimize  the  kernel<->userspace  data  transfer  a  bit more, the kernel module only
       transfers information about IPs, where the src/dst packet counter is  not  0.  This  saves
       precious kernel time.

       There  is no /proc interface as it would be too slow for continuous access.  The read-and-
       flush query  operation  is  the  fastest,  as  no  internal  data  snapshot  needs  to  be
       created&copied  for  all  data.  Use the "read" operation without flush only for debugging


       ACCOUNT takes two mandatory parameters:

       --addr network/netmask
              where network/netmask is the subnet to account for, in CIDR syntax

       --tname NAME
              where NAME is the name of the table where  the  accounting  information  should  be

       The  subnet  is  a  special case: all data are then stored in the src_bytes and
       src_packets structure of slot "0". This is useful if  you  want  to  account  the  overall
       traffic to/from your internet provider.

       The data can be queried using the userspace libxt_ACCOUNT_cl library, and by the reference
       implementation to show usage of this library, the iptaccount(8) tool.

       Here is an example of use:

       iptables -A FORWARD -j ACCOUNT --addr --tname all_outgoing; iptables -A  FORWARD
       -j ACCOUNT --addr --tname sales;

       This  creates  two tables called "all_outgoing" and "sales" which can be queried using the
       userspace library/iptaccount tool.

       Note that this target is non-terminating  —  the  packet  destined  to  it  will  continue
       traversing the chain in which it has been used.

       Also  note  that once a table has been defined for specific CIDR address/netmask block, it
       can be referenced multiple times using -j ACCOUNT, provided that both the  original  table
       name and address/netmask block are specified.

       For more information go to

       Causes  confusion  on the other end by doing odd things with incoming packets.  CHAOS will
       randomly reply (or not) with one of its configurable subtargets:

              Use the REJECT and DELUDE targets as a base to do a sudden or  deferred  connection
              reset,   fooling  some  network  scanners  to  return  non-deterministic  (randomly
              open/closed)  results,  and  in  case  it  is   deemed   open,   it   is   actually

              Use  the  REJECT  and TARPIT target as a base to hold the connection until it times
              out. This consumes conntrack entries when  connection  tracking  is  loaded  (which
              usually  is  on most machines), and routers inbetween you and the Internet may fail
              to do their connection tracking if they have to handle more connections  than  they

       The  randomness  factor  of  not  replying vs. replying can be set during load-time of the
       xt_CHAOS module or during runtime in /sys/modules/xt_CHAOS/parameters.

       See for more  information  about  CHAOS,  DELUDE  and

       The  DELUDE  target will reply to a SYN packet with SYN-ACK, and to all other packets with
       an RST. This will terminate the connection much like REJECT, but  network  scanners  doing
       TCP  half-open  discovery  can be spoofed to make them belive the port is open rather than

       In conjunction with ebtables, DHCPMAC can be used to completely change all  MAC  addresses
       from  and  to a VMware-based virtual machine. This is needed because VMware does not allow
       to set a non-VMware MAC address before an operating system  is  booted  (and  the  MAC  be
       changed with `ip link set eth0 address aa:bb..`).

       --set-mac aa:bb:cc:dd:ee:ff[/mask]
              Replace  the  client  host MAC address field in the DHCP message with the given MAC
              address. This option is mandatory. The mask parameter specifies the  prefix  length
              of bits to change.

       EXAMPLE,  replacing  all  addresses  from  one  of VMware's assigned vendor IDs (00:50:56)
       addresses with something else:

       iptables -t mangle -A FORWARD -p udp --dport 67 -m physdev --physdev-in vmnet1 -m  dhcpmac
       --mac 00:50:56:00:00:00/24 -j DHCPMAC --set-mac ab:cd:ef:00:00:00/24

       iptables -t mangle -A FORWARD -p udp --dport 68 -m physdev --physdev-out vmnet1 -m dhcpmac
       --mac ab:cd:ef:00:00:00/24 -j DHCPMAC --set-mac 00:50:56:00:00:00/24

       (This assumes there is a bridge interface that has vmnet1 as a port. You will also need to
       add appropriate ebtables rules to change the MAC address of the Ethernet headers.)

       The  DNETMAP  target allows dynamic two-way 1:1 mapping of IPv4 subnets. A single rule can
       map a private subnet to a shorter public  subnet,  creating  and  maintaining  unambiguous
       private-public  IP  address  bindings.  The  second rule can be used to map new flows to a
       private subnet according to maintained bindings.  The target allows efficient public  IPv4
       space usage and unambiguous NAT at the same time.

       The target can be used only in the nat table in POSTROUTING or OUTPUT chains for SNAT, and
       in PREROUTING for DNAT. Only flows directed to bound addresses will be DNATed. The  packet
       continues chain traversal if there is no free postnat address to be assigned to the prenat
       address. The default binding TTL is 10 minutes and can be changed  using  the  default_ttl
       module option. The default address hash size is 256 and can be changed using the hash_size
       module option.

       --prefix addr/mask
              The network subnet to map to. If not specified, all existing prefixes are used.

              Reuse the entry for a given prenat address from any prefix even  if  the  binding's
              TTL is < 0.

              Set  the  prefix  to  be persistent. It will not be removed after deleting the last
              iptables rule. The option is effective only in the first rule for a  given  prefix.
              If  you  need  to  change persistency for an existing prefix, please use the procfs
              interface described below.

              Do not create dynamic mappings using this rule. Use static mappings only. Note that
              you  need to create static mappings via the procfs interface for this rule for this
              option to have any effect.

       --ttl seconds
              Reset the binding's TTL value to seconds. If a negative  value  is  specified,  the
              binding's  TTL is kept unchanged. If this option is not specified, then the default
              TTL value (600s) is used.

       * /proc interface

       The module creates the following entries for each new specified subnet:

              Contains the binding table for the given subnet/mask.  Each  line  contains  prenat
              address,  postnat  address,  ttl (seconds until the entry times out), lasthit (last
              hit to the entry in seconds relative to system boot time). Please note that the ttl
              and lasthit entries contain an

              Contains  statistics  for  a  given  subnet/mask.  The line contains four numerical
              values separated by spaces. The first one is the number of currently  used  dynamic
              addresses  (bindings  with  negative TTL excluded), the second one is the number of
              static assignments, the third one is the number of  all  usable  addresses  in  the
              subnet,  and  the  fourth  one is the mean TTL value for all active entries. If the
              prefix has the persistent flag set, it will be noted as fifth entry.

       The following write operations are supported via the procfs interface:

       echo "+prenat-address:postnat-address" >/proc/net/xt_DNETMAP/subnet_mask
              Adds a static binding between the prenat and postnap address. If postnat_address is
              already bound, any previous binding will be timed out immediately. A static binding
              is never timed out.

       echo "-address" >/proc/net/xt_DNETMAP/subnet_mask
              Removes the binding with address as prenat  or  postnat  address.  If  the  removed
              binding  is  currently  static,  it  will  make  the  entry  available  for dynamic

       echo "+persistent" >/proc/net/xt_DNETMAP/subnet_mask
              Sets the persistent flag for the prefix. It is useful if you do not  want  bindings
              to  get  flushed  when  the  firewall  is restarted. You can check if the prefix is
              persistent by printing the contents of /proc/net/xt_DNETMAP/subnet_mask_stat.

       echo "-persistent" >/proc/net/xt_DNETMAP/subnet_mask
              Unsets the persistent flag for the prefix. In this mode, the prefix will be deleted
              if the last iptables rule for that prefix is removed.

       echo "flush" >/proc/net/xt_DNETMAP/subnet_mask
              Flushes  all  bindings for the specific prefix. All static entries are also flushed
              and become available for dynamic bindings.

       Note! Entries are removed if the last iptables rule  for  a  specific  prefix  is  deleted
       unless the persistent flag is set.

       * Logging

       The  module  logs binding add/timeout events to klog. This behaviour can be disabled using
       the disable_log module parameter.

       * Examples

       1. Map subnet to subnets SNAT only:

       iptables -t nat -A POSTROUTING -s -j DNETMAP --prefix

       Active hosts from the subnet are mapped to If the packet  from
       a  not  yet  bound prenat address hits the rule and there are no free or timed-out (TTL<0)
       entries in prefix, then a  notice  is  logged  to  klog  and  chain  traversal
       continues. If packet from an already-bound prenat address hits the rule, the binding's TTL
       value is reset to default_ttl and SNAT is performed.

       2. Use of --reuse and --ttl switches, multiple rule interaction:

       iptables -t nat -A POSTROUTING -s -j DNETMAP --prefix  --reuse
       --ttl 200

       iptables -t nat -A POSTROUTING -s -j DNETMAP --prefix

       Active  hosts from subnet are mapped to with TTL = 200 seconds.
       If there are no free addresses in first prefix, the next one (  is  used  with
       the  default TTL. It is important to note that the first rule SNATs all flows whose source
       address is already actively bound (TTL>0) to ANY prefix. The --reuse parameter makes  this
       functionality work even for inactive (TTL<0) entries.

       If both subnets are exhausted, then chain traversal continues.

       3. Map to subnets in a bidirectional way:

       iptables -t nat -A POSTROUTING -s -j DNETMAP --prefix

       iptables -t nat -A PREROUTING -j DNETMAP

       If  the  host generates some traffic, it gets bound to first free address in
       the subnet — Now, any traffic directed to gets DNATed  to
       as  long  as  there  is  an  active  (TTL>0) binding. There is no need to specify --prefix
       parameter in a PREROUTING rule, because this way, it DNATs traffic to all active prefixes.
       You could specify the prefix you would like to make DNAT work for a specific prefix only.

       4. Map to subnets with static assignments only:

       iptables -t nat -A POSTROUTING -s -j DNETMAP --prefix --static

       echo "+" >/proc/net/xt_DNETMAP/
       echo "+" >/proc/net/xt_DNETMAP/
       echo "+" >/proc/net/xt_DNETMAP/

       This configuration will allow only preconfigured static bindings to work due to the static
       rule option. Without this  flag,  dynamic  bindings  would  be  created  using  non-static

       5. Persistent prefix:

       iptables  -t  nat  -A  POSTROUTING  -s  -j  DNETMAP  --prefix
       iptables -t nat -A POSTROUTING -s -j DNETMAP --prefix
       echo "+persistent" >/proc/net/xt_DNETMAP/

       Now, we can check the persistent flag of the prefix:
       cat /proc/net/xt_DNETMAP/
       0 0 64 0 persistent

       Flush the iptables nat table and see that prefix is still in existence:
       iptables -F -t nat
       ls -l /proc/net/xt_DNETMAP
       -rw-r--r-- 1 root root 0 06-10 09:01
       -rw-r--r-- 1 root root 0 06-10 09:01

       The ECHO target will send back all packets it received. It serves as an  examples  for  an
       Xtables target.

       ECHO takes no options.

       Allows  you  to  mark  a  received  packet basing on its IP address. This can replace many
       mangle/mark entries with only one, if you use firewall based classifier.

       This target is to be used inside the mangle table.

       --addr {src|dst}
              Select source or destination IP address as a basis for the mark.

       --and-mask mask
              Perform bitwise AND on the IP address and this bitmask.

       --or-mask mask
              Perform bitwise OR on the IP address and this bitmask.

       --shift value
              Shift addresses to the right by the given number of bits  before  taking  it  as  a
              mark.  (This  is  done  before ANDing or ORing it.) This option is needed to select
              part of an IPv6 address, because marks are only 32 bits in size.

       The order of IP address bytes is reversed to meet "human order of bytes":  is
       0xc0a80001. At first the "AND" operation is performed, then "OR".


       We  create  a  queue  for each user, the queue number is adequate to the IP address of the
       user,  e.g.:  all  packets  going  to/from  are  directed  to  1:0502  queue, -> 1:050c etc.

       We have one classifier rule:

              tc filter add dev eth3 parent 1:0 protocol ip fw

       Earlier we had many rules just like below:

              iptables -t mangle -A POSTROUTING -o eth3 -d -j MARK --set-mark 0x10502

              iptables -t mangle -A POSTROUTING -o eth3 -d -j MARK --set-mark 0x10503

       Using IPMARK target we can replace all the mangle/mark rules with only one:

              iptables  -t  mangle  -A POSTROUTING -o eth3 -j IPMARK --addr dst --and-mask 0xffff
              --or-mask 0x10000

       On the routers with hundreds of users there should  be  significant  load  decrease  (e.g.

       (IPv6  example) If the source address is of the form 2001:db8:45:1d:20d:93ff:fe9b:e443 and
       the resulting mark should be 0x93ff, then a right-shift of 16 is needed first:

              -t mangle -A PREROUTING -s 2001:db8::/32 -j IPMARK --addr src --shift 16 --and-mask

       The LOGMARK target will log packet and connection marks to syslog.

       --log-level level
              A logging level between 0 and 8 (inclusive).

       --log-prefix string
              Prefix  log messages with the specified prefix; up to 29 bytes long, and useful for
              distinguishing messages in the logs.

       The RAWDNAT target will rewrite the destination address in the IP header,  much  like  the
       NETMAP target.

       --to-destination addr[/mask]
              Network  address to map to. The resulting address will be constructed 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.

       See the RAWSNAT help entry for examples and constraints.

       The RAWSNAT and RAWDNAT targets provide stateless network address translation.

       The  RAWSNAT target will rewrite the source address in the IP header, much like the NETMAP
       target. RAWSNAT (and RAWDNAT) may only be used in the raw or rawpost tables,  but  can  be
       used  in  all chains, which makes it possible to change the source address either when the
       packet enters the machine or when it leaves it. The reason for this  table  constraint  is
       that RAWNAT must happen outside of connection tracking.

       --to-source addr[/mask]
              Network  address to map to. The resulting address will be constructed 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.

       As  an example, changing the destination for packets forwarded from an internal LAN to the

              -t raw -A  PREROUTING  -i  lan0  -d  -j  RAWDNAT  --to-destination
    ;  -t  rawpost  -A POSTROUTING -o lan0 -s -j RAWSNAT

       Note  that  changing  addresses  may  influence  the  route  selection!  Specifically,  it
       statically NATs packets, not connections, like the normal DNAT/SNAT targets would do. Also
       note that it can transform already-NATed connections — as said, it is completely  external
       to Netfilter's connection tracking/NAT.

       If  the  machine itself generates packets that are to be rawnat-ed, you need a rule in the
       OUTPUT chain instead, just like you would with the stateful NAT targets.

       It may be necessary that in doing so, you also need an extra RAWSNAT rule, to override the
       automatic  source  address  selection that the routing code does before passing packets to
       iptables. If the connecting socket has not been explicitly bound to an address, as is  the
       common  mode  of  operation, the address that will be chosen is the primary address of the
       device through which the packet would be routed with its initial destination address - the
       address as seen before any RAWNAT takes place.

       Like the DROP target, but does not throw an error like DROP when used in the OUTPUT chain.

       The  SYSRQ  target allows to remotely trigger sysrq on the local machine over the network.
       This can be useful when vital parts of  the  machine  hang,  for  example  an  oops  in  a
       filesystem  causing  locks  to be not released and processes to get stuck as a result — if
       still possible, use /proc/sysrq-trigger. Even when processes  are  stuck,  interrupts  are
       likely to be still processed, and as such, sysrq can be triggered through incoming network

       The xt_SYSRQ implementation uses a salted hash and a sequence number  to  prevent  network
       sniffers  from  either  guessing  the  password or replaying earlier requests. The initial
       sequence number comes  from  the  time  of  day  so  you  will  have  a  small  window  of
       vulnerability   should   time   go   backwards   at   a   reboot.    However,   the   file
       /sys/module/xt_SYSREQ/seqno can be used to both query  and  update  the  current  sequence
       number.  Also,  you  should limit as to who can issue commands using -s and/or -m mac, and
       also that the destination is correct using -d  (to  protect  against  potential  broadcast
       packets), noting that it is still short of MAC/IP spoofing:

              -A  INPUT  -s -m mac --mac-source aa:bb:cc:dd:ee:ff -d -p udp
              --dport 9 -j SYSRQ

              (with IPsec) -A INPUT -s -d -m policy --dir  in  --pol  ipsec
              --proto  esp  --tunnel-src  --tunnel-dst -p udp --dport 9 -j

       You should also limit the rate at which connections can be received to limit the CPU  time
       taken by illegal requests, for example:

              -A  INPUT  -s -m mac --mac-source aa:bb:cc:dd:ee:ff -d -p udp
              --dport 9 -m limit --limit 5/minute -j SYSRQ

       This extension does not take any options. The -p udp options are required.

       The SYSRQ password can be changed  through  /sys/module/xt_SYSRQ/parameters/password,  for

              echo -n "password" >/sys/module/xt_SYSRQ/parameters/password

       The module will not respond to sysrq requests until a password has been set.

       Alternatively,  the  password  may  be specified at modprobe time, but this is insecure as
       people  can  possible  see  it  through  ps(1).  You  can  use  an  option  line  in  e.g.
       /etc/modprobe.d/xt_sysrq if it is properly guarded, that is, only readable by root.

              options xt_SYSRQ password=cookies

       The  hash  algorithm can also be specified as a module option, for example, to use SHA-256
       instead of the default SHA-1:

              options xt_SYSRQ hash=sha256

       The xt_SYSRQ module is normally silent unless a successful request is  received,  but  the
       debug  module parameter can be used to find exactly why a seemingly correct request is not
       being processed.

       To trigger SYSRQ from a remote host, just use socat:

       sysrq_key="s"  # the SysRq key(s)
       seqno="$(date +%s)"
       salt="$(dd bs=12 count=1 if=/dev/urandom 2>/dev/null |
           openssl enc -base64)"
       req="$req,$(echo -n "$req,$ipaddr,$password" | sha1sum | cut -c1-40)"

       echo "$req" | socat stdin udp-sendto:$ipaddr:9

       See the Linux docs for possible sysrq keys.  Important  ones  are:  re(b)oot,  power(o)ff,
       (s)ync  filesystems, (u)mount and remount readonly. More than one sysrq key can be used at
       once, but bear in mind that, for example, a sync may  not  complete  before  a  subsequent
       reboot or poweroff.

       An  IPv4  address  should  have  no  leading  zeros, an IPv6 address should be in the full
       expanded form (as shown above). The debug option will cause output to be  emitted  in  the
       same form.

       The  hashing scheme should be enough to prevent mis-use of SYSRQ in many environments, but
       it is not perfect: take reasonable precautions to protect your machines.

       Captures and holds incoming TCP connections using no local per-connection resources.

       TARPIT only works at the TCP level, and is totally application agnostic. This module  will
       answer a TCP request and play along like a listening server, but aside from sending an ACK
       or RST, no data is sent. Incoming packets are  ignored  and  dropped.  The  attacker  will
       terminate  the  session eventually. This module allows the initial packets of an attack to
       be captured by other software  for  inspection.  In  most  cases  this  is  sufficient  to
       determine the nature of the attack.

       This  offers similar functionality to LaBrea <> but does
       not require dedicated hardware or IPs. Any TCP port that you would normally DROP or REJECT
       can instead become a tarpit.

              This mode completes a connection with the attacker but limits the window size to 0,
              thus keeping the attacker waiting long periods of time.  While  he  is  maintaining
              state  of the connection and trying to continue every 60-240 seconds, we keep none,
              so it is very lightweight. Attempts to close the connection  are  ignored,  forcing
              the  remote  side  to  time  out  the connection in 12-24 minutes. This mode is the

              This mode completes a connection with the attacker, but  signals  a  normal  window
              size, so that the remote side will attempt to send data, often with some very nasty
              exploit attempts. We can capture these packets for decoding and  further  analysis.
              The  module  does  not send any data, so if the remote expects an application level
              response, the game is up.

              This mode is handy because we can send an inline  RST  (reset).  It  has  no  other

       To tarpit connections to TCP port 80 destined for the current machine:

              -A INPUT -p tcp -m tcp --dport 80 -j TARPIT

       To  significantly  slow  down  Code Red/Nimda-style scans of unused address space, forward
       unused ip addresses to a Linux box not  acting  as  a  router  (e.g.  "ip  route" on a Cisco), enable IP forwarding on the Linux box, and add:

              -A FORWARD -p tcp -j TARPIT

              -A FORWARD -j DROP

       NOTE:  If  you  use  the  conntrack module while you are using TARPIT, you should also use
       unset tracking on the packet, or the kernel will unnecessarily allocate resources for each
       TARPITted  connection. To TARPIT incoming connections to the standard IRC port while using
       conntrack, you could:

              -t raw -A PREROUTING -p tcp --dport 6667 -j CT --notrack

              -A INPUT -p tcp --dport 6667 -j NFLOG

              -A INPUT -p tcp --dport 6667 -j TARPIT


       This matches if a specific condition variable is (un)set.

       [!] --condition name
              Match on boolean value stored in /proc/net/nf_condition/name.

       --mac aa:bb:cc:dd:ee:ff[/mask]
              Matches the DHCP "Client Host" address (a MAC address) in  a  DHCP  message.   mask
              specifies the prefix length of the initial portion to match.

       This module matches a rate limit based on a fuzzy logic controller (FLC).

       --lower-limit number
              Specifies the lower limit, in packets per second.

       --upper-limit number
              Specifies the upper limit, also in packets per second.

       Match a packet by its source or destination country.

       [!] --src-cc, --source-country country[,country...]
              Match packet coming from (one of) the specified country(ies)

       [!] --dst-cc, --destination-country country[,country...]
              Match packet going to (one of) the specified country(ies)

       NOTE:  The country is inputed by its ISO-3166 code.

       The  extra  files  you  will  need is the binary database files. They are generated from a
       country-subnet database with the tool that is shipped  with  the  source
       package,  and  which  should  be available in compiled packages in /usr/lib(exec)/xtables-
       addons/. The first command retrieves CSV files from MaxMind, while  the  other  two  build
       packed bisectable range files:

       mkdir -p /usr/share/xt_geoip; cd /tmp; $path/to/xt_geoip_dl;

       $path/to/xt_geoip_build -D /usr/share/xt_geoip GeoIP*.csv;

       The shared library is hardcoded to look in these paths, so use them.

       This module matches packets based on grsecurity RBAC status.

       [!] --enabled
              Matches packets if grsecurity RBAC is enabled.

       [!] --disabled
              Matches packets if grsecurity RBAC is disabled.

       Allows  you  to  check  interface  states.  First,  an  interface needs to be selected for
       comparison. Exactly one option of the following three must be specified:

       --iface name
              Check the states on the given interface.

              Check the states on the interface on which the packet came in. If the input  device
              is  not  set,  because for example you are using -m iface in the OUTPUT chain, this
              submatch returns false.

              Check the states on the interface on which the packet will go out.  If  the  output
              device  is  not set, because for example you are using -m iface in the INPUT chain,
              this submatch returns false.

       Following that, one can select the interface properties to check for:

       [!] --up, [!] --down
              Check the UP flag.

       [!] --broadcast
              Check the BROADCAST flag.

       [!] --loopback
              Check the LOOPBACK flag.

       [!] --pointtopoint
              Check the POINTTOPOINT flag.

       [!] --running
              Check the RUNNING flag. Do NOT rely on it!

       [!] --noarp, [!] --arp
              Check the NOARP flag.

       [!] --promisc
              Check the PROMISC flag.

       [!] --multicast
              Check the MULTICAST flag.

       [!] --dynamic
              Check the DYNAMIC flag.

       [!] --lower-up
              Check the LOWER_UP flag.

       [!] --dormant
              Check the DORMANT flag.

       This module matches certain packets in P2P flows. It is not designed to match all  packets
       belonging to a P2P connection — use IPP2P together with CONNMARK for this purpose.

       Use  it together with -p tcp or -p udp to search these protocols only or without -p switch
       to search packets of both protocols.

       IPP2P provides the following options, of which one or more may be specified on the command

       --edk  Matches as many eDonkey/eMule packets as possible.

              Matches as many KaZaA packets as possible.

       --gnu  Matches as many Gnutella packets as possible.

       --dc   Matches as many Direct Connect packets as possible.

       --bit  Matches BitTorrent packets.

              Matches AppleJuice packets.

       --soul Matches some SoulSeek packets. Considered as beta, use careful!

              Matches some WinMX packets. Considered as beta, use careful!

       --ares Matches Ares and AresLite packets. Use together with -j DROP only.

              Prints  some  information  about  each  hit  into  kernel logfile. May produce huge
              logfiles so beware!

       Note that ipp2p may not (and often, does not) identify all packets that are exchanged as a
       result of running filesharing programs.

       There  is  more  information  on  ,  but  it has not been updated since
       September 2006, and the syntax there is different from the ipp2p.c  provided  in  Xtables-
       addons;  most importantly, the --ipp2p flag was removed due to its ambiguity to match "all
       known" protocols.

       The "ipv4options" module allows to match against a set of IPv4 header options.

       --flags [!]symbol[,[!]symbol...]
              Specify the options that shall appear or not appear  in  the  header.  Each  symbol
              specification  is  delimited  by  a comma, and a '!' can be prefixed to a symbol to
              negate its presence. Symbols are either the name of an IPv4 option or  its  number.
              See examples below.

       --any  By  default,  all of the flags specified must be present/absent, that is, they form
              an AND condition. Use the --any flag instead to use an OR condition where  only  at
              least one symbol spec must be true.

       Known symbol names (and their number):

       1 — nop

       2 — security — RFC 1108

       3 — lsrr — Loose Source Routing, RFC 791

       4 — timestamp — RFC 781, 791

       7 — record-route — RFC 791

       9 — ssrr — Strict Source Routing, RFC 791

       11 — mtu-probe — RFC 1063

       12 — mtu-reply — RFC 1063

       18 — traceroute — RFC 1393

       20 — router-alert — RFC 2113


       Match packets that have both Timestamp and NOP: -m ipv4options --flags nop,timestamp

       ~ that have either of Timestamp or NOP, or both: --flags nop,timestamp --any

       ~ that have Timestamp and no NOP: --flags '!nop,timestamp'

       ~  that  have  either no NOP or a timestamp (or both conditions): --flags '!nop,timestamp'

       This module matches the length of a packet against a specific value or range of values.

       [!] --length length[:length]
              Match exact length or length range.

              Match the layer3 frame size (e.g. IPv4/v6 header plus payload).

              Match the layer4 frame size (e.g. TCP/UDP header plus payload).

              Match the layer5 frame size (e.g. TCP/UDP payload, often called layer7).

       If no --layer* option is given, --layer3 is assumed by default. Note that  using  --layer5
       may  not  match  a  packet  if  it is not one of the recognized types (currently TCP, UDP,
       UDPLite, ICMP, AH and ESP) or which has no 5th layer.

       Detects simple low-level scan  attempts  based  upon  the  packet's  contents.   (This  is
       different   from  other  implementations,  which  also  try  to  match  the  rate  of  new
       connections.) Note that an attempt is only discovered after it has been carried  out,  but
       this  information  can  be used in conjunction with other rules to block the remote host's
       future connections. So this match module will match on  the  (probably)  last  packet  the
       remote side will send to your machine.

              Match   if   the   packet   did   not   belong   to   any   known   TCP  connection
              (Stealth/FIN/XMAS/NULL scan).

              Match if the connection  was  a  TCP  half-open  discovery  (SYN  scan),  i.e.  the
              connection was torn down after the 2nd packet in the 3-way handshake.

              Match  if  the  connection  was  a TCP full open discovery (connect scan), i.e. the
              connection was torn down after completion of the 3-way handshake.

              Match if data in the connection only flew in the direction of the remote side, e.g.
              if  the  connection  was  terminated  after  a  locally  running  daemon  sent  its
              identification. (E.g. openssh, smtp, ftpd.) This may falsely trigger  on  warranted
              single-direction  data  flows,  usually  bulk  data  transfers  such  as  FTP  DATA
              connections or IRC DCC. Grab Scan Detection should only be used on  ports  where  a
              protocol runs that is guaranteed to do a bidirectional exchange of bytes.

       NOTE:  Some  clients  (Windows  XP  for  example) may do what looks like a SYN scan, so be
       advised to carefully use xt_lscan in conjunction with blocking rules, as it may  lock  out
       your very own internal network.

       Attempt  to  detect  TCP  and UDP port scans. This match was derived from Solar Designer's

       --psd-weight-threshold threshold
              Total weight of the latest TCP/UDP packets with different destination ports  coming
              from the same host to be treated as port scan sequence.

       --psd-delay-threshold delay
              Delay  (in  hundredths  of second) for the packets with different destination ports
              coming from the same host to be treated as possible port scan subsequence.

       --psd-lo-ports-weight weight
              Weight of the packet with privileged (<=1024) destination port.

       --psd-hi-ports-weight weight
              Weight of the packet with non-priviliged destination port.

       The "quota2" implements a named counter which can be increased or decreased on a per-match
       basis. Available modes are packet counting or byte counting.  The value of the counter can
       be read and reset through procfs, thereby making this match a minimalist accounting tool.

       When counting down from the initial quota, the counter will stop at 0 and the  match  will
       return  false, just like the original "quota" match. In growing (upcounting) mode, it will
       always return true.

       --grow Count upwards instead of downwards.

              Makes it so the counter or quota amount is never changed by packets  matching  this
              rule.  This  is  only  really  useful  in "quota" mode, as it will allow you to use
              complex prerouting rules in association with the quota system, without  counting  a
              packet twice.

       --name name
              Assign  the  counter a specific name. This option must be present, as an empty name
              is not allowed. Names  starting  with  a  dot  or  names  containing  a  slash  are

       [!] --quota iq
              Specify  the  initial  quota for this counter. If the counter already exists, it is
              not reset. An "!" may be used to invert the result of the match. The  negation  has
              no effect when --grow is used.

              Count packets instead of bytes that passed the quota2 match.

       Because  counters  in quota2 can be shared, you can combine them for various purposes, for
       example, a bytebucket filter that only lets as much traffic go out as has come in:

       -A INPUT -p tcp --dport 6881 -m quota --name bt --grow; -A OUTPUT -p tcp --sport  6881  -m
       quota --name bt;

       Pknock  match  implements  so-called  "port  knocking",  a  stealthy  system  for  network
       authentication: a client sends packets to selected ports in a specific sequence (=  simple
       mode,  see  example  1  below),  or  a  HMAC payload to a single port (= complex mode, see
       example 2 below), to a target machine  that  has  pknock  rule(s)  installed.  The  target
       machine  then  decides  whether  to unblock or block (again) the pknock-protected port(s).
       This can be used, for instance, to avoid brute force attacks on ssh or ftp services.

       Example prerequisites:

              modprobe cn

              modprobe xt_pknock

       Example 1 (TCP mode, manual closing of opened port not possible):

              iptables -P INPUT DROP

              iptables -A INPUT -p tcp -m pknock --knockports 4002,4001,4004 --strict --name  SSH
              --time 10 --autoclose 60 --dport 22 -j ACCEPT

       The  rule  will  allow  tcp  port  22  for  the attempting IP address after the successful
       reception of TCP SYN packets to ports 4002, 4001 and 4004, in  this  order  (a.k.a.  port-
       knocking).   Port  numbers in the connect sequence must follow the exact specification, no
       other ports may be "knocked" inbetween. The rule is named 'SSH' — a file of the same  name
       for  tracking  port  knocking  states will be created in /proc/net/xt_pknock .  Successive
       port knocks must occur with delay of at most 10 seconds. Port 22 (from the  example)  will
       be automatiaclly dropped after 60 minutes after it was previously allowed.

       Example  2  (UDP  mode  —  non-replayable and non-spoofable, manual closing of opened port
       possible, secure, also called "SPA" = Secure Port Authorization):

              iptables -A INPUT -p udp -m pknock --knockports 4000 --name  FTP  --opensecret  foo
              --closesecret bar --autoclose 240 -j DROP

              iptables -A INPUT -p tcp -m pknock --checkip --name FTP --dport 21 -j ACCEPT

       The  first  rule  will  create  an  "ALLOWED"  record in /proc/net/xt_pknock/FTP after the
       successful reception of an UDP packet to port 4000. The packet payload must be constructed
       as  a HMAC256 using "foo" as a key. The HMAC content is the particular client's IP address
       as a 32-bit network byteorder quantity, plus the number of minutes since the  Unix  epoch,
       also  as  a  32-bit  value.   (This  is  known as Simple Packet Authorization, also called
       "SPA".)  In such case, any subsequent attempt to connect to port 21 from the  client's  IP
       address will cause such packets to be accepted in the second rule.

       Similarly,  upon  reception  of  an  UDP packet constructed the same way, but with the key
       "bar", the first rule will remove a  previously  installed  "ALLOWED"  state  record  from
       /proc/net/xt_pknock/FTP,  which  means  that  the  second  rule  will  stop  matching  for
       subsequent connection attempts to port 21.  In case no  close-secret  packet  is  received
       within  4  hours, the first rule will remove "ALLOWED" record from /proc/net/xt_pknock/FTP

       Things worth noting:


       Specifying --autoclose 0 means that no automatic close will be performed at all.

       xt_pknock is capable of sending information about successful matches via a netlink  socket
       to  userspace,  should  you  need  to  implement  your  own  way of receiving and handling
       portknock notifications.  Be sure to read the documentation in the doc/pknock/  directory,
       or visit the original site — .

       TCP mode:

       This  mode  is  not immune against eavesdropping, spoofing and replaying of the port knock
       sequence by someone else (but its use may still be sufficient for  scenarios  where  these
       factors  are  not  necessarily this important, such as bare shielding of the SSH port from
       brute-force attacks).  However, if you need these features, you should use UDP mode.

       It is always wise to specify three or more ports that are not monotonically increasing  or
       decreasing  with  a  small stepsize (e.g. 1024,1025,1026) to avoid accidentally triggering
       the rule by a portscan.

       Specifying the inter-knock timeout  with  --time  is  mandatory  in  TCP  mode,  to  avoid
       permanent  denial  of  services  by  clogging  up the peer knock-state tracking table that
       xt_pknock internally keeps, should there be a DDoS on the  first-in-row  knock  port  from
       more  hostile IP addresses than what the actual size of this table is (defaults to 16, can
       be changed via the "peer_hasht_ents" module parameter).  It is also wise to use as short a
       time  as  possible  (1  second)  for  --time  for  this very reason. You may also consider
       increasing the size of the peer knock-state tracking table. Using --strict also helps,  as
       it  requires  the  knock sequence to be exact. This means that if the hostile client sends
       more knocks to the same port, xt_pknock will mark such attempt as  failed  knock  sequence
       and will forget it immediately.  To completely thwart this kind of DDoS, knock-ports would
       need to have an additional rate-limit protection. Or you may consider using UDP mode.

       UDP mode:

       This mode is immune against eavesdropping, replaying and spoofing  attacks.   It  is  also
       immune against DDoS attack on the knockport.

       For  this mode to work, the clock difference on the client and on the server must be below
       1 minute. Synchronizing time on both ends by means of NTP or rdate is strongly suggested.

       There is a rate limiter built into xt_pknock which blocks any subsequent open  attempt  in
       UDP  mode should the request arrive within less than one minute since the first successful
       open. This is intentional; it thwarts eventual spoofing attacks.

       Because the payload value of an UDP knock packet is influenced by client's IP address, UDP
       mode cannot be used across NAT.

       For  sending UDP "SPA" packets, you may use either or These may be
       found in doc/pknock/util.

See also

       iptables(8), ip6tables(8), iptables-extensions(8), iptaccount(8)

       For      developers,      the      book      "Writing      Netfilter      modules"      at  provides  detailed  information  on how to
       write such modules/extensions.

                                       African Heat Edition                     xtables-addons(8)