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IPTABLES(8)                     iptables 1.4.7                     IPTABLES(8)



NAME
       iptables -- administration tool for IPv4 packet filtering and NAT

SYNOPSIS
       iptables [-t table] {-A|-C|-D} chain rule-specification

       iptables [-t table] -I chain [rulenum] rule-specification

       iptables [-t table] -R chain rulenum rule-specification

       iptables [-t table] -D chain rulenum

       iptables [-t table] -S [chain [rulenum]]

       iptables [-t table] {-F|-L|-Z} [chain [rulenum]] [options...]

       iptables [-t table] -N chain

       iptables [-t table] -X [chain]

       iptables [-t table] -P chain target

       iptables [-t table] -E old-chain-name new-chain-name

       rule-specification = [matches...] [target]

       match = -m matchname [per-match-options]

       target = -j targetname [per-target-options]

DESCRIPTION
       Iptables  is used to set up, maintain, and inspect the tables of IPv4 packet filter
       rules in the Linux kernel.  Several different tables may be  defined.   Each  table
       contains a number of built-in chains and may also contain user-defined chains.

       Each  chain  is a list of rules which can match a set of packets.  Each rule speci-
       fies what to do with a packet that matches.  This is called a 'target',  which  may
       be a jump to a user-defined chain in the same table.

TARGETS
       A  firewall  rule specifies criteria for a packet and a target.  If the packet does
       not match, the next rule in the chain is the examined; if it does match,  then  the
       next rule is specified by the value of the target, which can be the name of a user-
       defined chain or one of the special values ACCEPT, DROP, QUEUE or RETURN.

       ACCEPT means to let the packet through.  DROP means  to  drop  the  packet  on  the
       floor.   QUEUE  means  to  pass  the  packet  to userspace.  (How the packet can be
       received by a userspace process differs by the particular queue handler.  2.4.x and
       2.6.x  kernels up to 2.6.13 include the ip_queue queue handler.  Kernels 2.6.14 and
       later additionally include the nfnetlink_queue queue handler.  Packets with a  tar-
       get  of  QUEUE  will  be sent to queue number '0' in this case. Please also see the
       NFQUEUE target as described later in this man page.)  RETURN means stop  traversing
       this chain and resume at the next rule in the previous (calling) chain.  If the end
       of a built-in chain is reached or a rule in a built-in chain with target RETURN  is
       matched,  the  target  specified  by  the  chain  policy determines the fate of the
       packet.

TABLES
       There are currently three independent tables (which tables are present at any  time
       depends on the kernel configuration options and which modules are present).

       -t, --table table
              This  option  specifies  the  packet matching table which the command should
              operate on.  If the kernel is configured with automatic module  loading,  an
              attempt  will be made to load the appropriate module for that table if it is
              not already there.

              The tables are as follows:

              filter:
                  This is the default table (if no -t option is passed). It  contains  the
                  built-in  chains  INPUT (for packets destined to local sockets), FORWARD
                  (for packets being routed through the box), and OUTPUT (for locally-gen-
                  erated packets).

              nat:
                  This  table  is consulted when a packet that creates a new connection is
                  encountered.  It consists of three built-ins: PREROUTING  (for  altering
                  packets as soon as they come in), OUTPUT (for altering locally-generated
                  packets before routing), and POSTROUTING (for altering packets  as  they
                  are about to go out).

              mangle:
                  This  table  is  used  for  specialized packet alteration.  Until kernel
                  2.4.17 it had two built-in chains:  PREROUTING  (for  altering  incoming
                  packets before routing) and OUTPUT (for altering locally-generated pack-
                  ets before routing).  Since kernel 2.4.18, three other  built-in  chains
                  are also supported: INPUT (for packets coming into the box itself), FOR-
                  WARD (for altering packets being routed through the box), and  POSTROUT-
                  ING (for altering packets as they are about to go out).

              raw:
                  This  table  is  used  mainly for configuring exemptions from connection
                  tracking in combination with the NOTRACK target.  It  registers  at  the
                  netfilter  hooks  with higher priority and is thus called before ip_con-
                  ntrack, or any other IP tables.   It  provides  the  following  built-in
                  chains: PREROUTING (for packets arriving via any network interface) OUT-
                  PUT (for packets generated by local processes)

OPTIONS
       The options that are recognized by iptables can be divided into  several  different
       groups.

   COMMANDS
       These options specify the desired action to perform. Only one of them can be speci-
       fied on the command line unless otherwise stated below. For long  versions  of  the
       command  and option names, you need to use only enough letters to ensure that ipta-
       bles can differentiate it from all other options.

       -A, --append chain rule-specification
              Append one or more rules to the end of the selected chain.  When the  source
              and/or  destination  names  resolve to more than one address, a rule will be
              added for each possible address combination.

       -C, --check chain rule-specification
              Check whether a rule matching the specification does exist in  the  selected
              chain.  This command uses the same logic as -D to find a matching entry, but
              does not alter the existing iptables configuration and uses its exit code to
              indicate success or failure.

       -D, --delete chain rule-specification
       -D, --delete chain rulenum
              Delete one or more rules from the selected chain.  There are two versions of
              this command: the rule can be specified as a number in the  chain  (starting
              at 1 for the first rule) or a rule to match.

       -I, --insert chain [rulenum] rule-specification
              Insert  one  or  more  rules in the selected chain as the given rule number.
              So, if the rule number is 1, the rule or rules are inserted at the  head  of
              the chain.  This is also the default if no rule number is specified.

       -R, --replace chain rulenum rule-specification
              Replace  a  rule  in  the  selected chain.  If the source and/or destination
              names resolve to multiple addresses,  the  command  will  fail.   Rules  are
              numbered starting at 1.

       -L, --list [chain]
              List  all  rules in the selected chain.  If no chain is selected, all chains
              are listed. Like every other iptables command, it applies to  the  specified
              table (filter is the default), so NAT rules get listed by
               iptables -t nat -n -L
              Please note that it is often used with the -n option, in order to avoid long
              reverse DNS lookups.  It is legal to specify the -Z (zero) option  as  well,
              in  which case the chain(s) will be atomically listed and zeroed.  The exact
              output is affected by the other arguments given. The exact  rules  are  sup-
              pressed until you use
               iptables -L -v

       -S, --list-rules [chain]
              Print  all rules in the selected chain.  If no chain is selected, all chains
              are printed like  iptables-save.  Like  every  other  iptables  command,  it
              applies to the specified table (filter is the default).

       -F, --flush [chain]
              Flush  the  selected  chain  (all the chains in the table if none is given).
              This is equivalent to deleting all the rules one by one.

       -Z, --zero [chain [rulenum]]
              Zero the packet and byte counters in all chains, or only the given chain, or
              only the given rule in a chain. It is legal to specify the -L, --list (list)
              option as well, to see the counters immediately  before  they  are  cleared.
              (See above.)

       -N, --new-chain chain
              Create  a new user-defined chain by the given name.  There must be no target
              of that name already.

       -X, --delete-chain [chain]
              Delete the optional user-defined chain specified.  There must be  no  refer-
              ences  to the chain.  If there are, you must delete or replace the referring
              rules before the chain can be deleted.  The chain must be  empty,  i.e.  not
              contain any rules.  If no argument is given, it will attempt to delete every
              non-builtin chain in the table.

       -P, --policy chain target
              Set the policy for the chain to the given target.  See the  section  TARGETS
              for  the  legal  targets.   Only built-in (non-user-defined) chains can have
              policies, and neither built-in nor user-defined chains can  be  policy  tar-
              gets.

       -E, --rename-chain old-chain new-chain
              Rename  the  user  specified  chain to the user supplied name.  This is cos-
              metic, and has no effect on the structure of the table.

       -h     Help.  Give a (currently very brief) description of the command syntax.

   PARAMETERS
       The following parameters make up a rule specification (as used in the add,  delete,
       insert, replace and append commands).

       [!] -p, --protocol protocol
              The  protocol of the rule or of the packet to check.  The specified protocol
              can be one of tcp, udp, udplite, icmp, esp, ah, sctp or all, or it can be  a
              numeric  value,  representing  one of these protocols or a different one.  A
              protocol name from /etc/protocols is also allowed.  A  "!"  argument  before
              the  protocol inverts the test.  The number zero is equivalent to all.  Pro-
              tocol all will match with all protocols and is taken as  default  when  this
              option is omitted.

       [!] -s, --source address[/mask][,...]
              Source  specification.  Address  can be either a network name, a hostname, a
              network IP address (with /mask), or a plain IP address.  Hostnames  will  be
              resolved once only, before the rule is submitted to the kernel.  Please note
              that specifying any name to be resolved with a remote query such as DNS is a
              really  bad  idea.  The mask can be either a network mask or a plain number,
              specifying the number of 1's at the left side of the network mask.  Thus,  a
              mask  of  24  is  equivalent  to  255.255.255.0.   A "!" argument before the
              address specification inverts the sense of the address. The flag --src is an
              alias  for  this option.  Multiple addresses can be specified, but this will
              expand to multiple rules (when adding with -A), or will cause multiple rules
              to be deleted (with -D).

       [!] -d, --destination address[/mask][,...]
              Destination  specification.  See the description of the -s (source) flag for
              a detailed description of the syntax.  The flag --dst is an alias  for  this
              option.

       -j, --jump target
              This  specifies  the  target  of  the  rule;  i.e., what to do if the packet
              matches it.  The target can be a user-defined chain (other than the one this
              rule is in), one of the special builtin targets which decide the fate of the
              packet immediately, or an extension (see EXTENSIONS below).  If this  option
              is  omitted in a rule (and -g is not used), then matching the rule will have
              no effect on the packet's fate, but the counters on the rule will be  incre-
              mented.

       -g, --goto chain
              This  specifies  that  the  processing  should  continue in a user specified
              chain. Unlike the --jump option return will not continue processing in  this
              chain but instead in the chain that called us via --jump.

       [!] -i, --in-interface name
              Name  of  an  interface  via  which  a packet was received (only for packets
              entering the INPUT, FORWARD and PREROUTING chains).  When the  "!"  argument
              is  used before the interface name, the sense is inverted.  If the interface
              name ends in a "+", then any interface which  begins  with  this  name  will
              match.  If this option is omitted, any interface name will match.

       [!] -o, --out-interface name
              Name  of  an  interface  via which a packet is going to be sent (for packets
              entering the FORWARD, OUTPUT and POSTROUTING chains).  When the "!" argument
              is  used before the interface name, the sense is inverted.  If the interface
              name ends in a "+", then any interface which  begins  with  this  name  will
              match.  If this option is omitted, any interface name will match.

       [!] -f, --fragment
              This  means  that  the  rule  only refers to second and further fragments of
              fragmented packets.  Since there is no way to tell the source or destination
              ports  of  such  a  packet  (or ICMP type), such a packet will not match any
              rules which specify them.  When the "!" argument precedes the "-f" flag, the
              rule will only match head fragments, or unfragmented packets.

       -c, --set-counters packets bytes
              This enables the administrator to initialize the packet and byte counters of
              a rule (during INSERT, APPEND, REPLACE operations).

   OTHER OPTIONS
       The following additional options can be specified:

       -v, --verbose
              Verbose output.  This option makes the list command show the interface name,
              the  rule options (if any), and the TOS masks.  The packet and byte counters
              are also listed, with the suffix 'K', 'M' or 'G'  for  1000,  1,000,000  and
              1,000,000,000 multipliers respectively (but see the -x flag to change this).
              For appending, insertion, deletion and  replacement,  this  causes  detailed
              information on the rule or rules to be printed.

       -n, --numeric
              Numeric  output.   IP  addresses and port numbers will be printed in numeric
              format.  By default, the program will try to display  them  as  host  names,
              network names, or services (whenever applicable).

       -x, --exact
              Expand  numbers.   Display  the exact value of the packet and byte counters,
              instead of only the rounded number in K's (multiples of 1000) M's (multiples
              of 1000K) or G's (multiples of 1000M).  This option is only relevant for the
              -L command.

       --line-numbers
              When listing rules, add line numbers to the beginning of each  rule,  corre-
              sponding to that rule's position in the chain.

       --modprobe=command
              When  adding or inserting rules into a chain, use command to load any neces-
              sary modules (targets, match extensions, etc).

MATCH EXTENSIONS
       iptables can use extended packet matching modules.  These are loaded in  two  ways:
       implicitly,  when -p or --protocol is specified, or with the -m or --match options,
       followed by the matching module name;  after  these,  various  extra  command  line
       options become available, depending on the specific module.  You can specify multi-
       ple 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  following  are included in the base package, and most of these can be preceded
       by a "!" to invert the sense of the match.

   addrtype
       This module matches packets based on their address type.  Address  types  are  used
       within  the  kernel  networking stack and categorize addresses into various groups.
       The exact definition of that group depends on the specific layer three protocol.

       The following address types are possible:

       UNSPEC an unspecified address (i.e. 0.0.0.0)

       UNICAST
              an unicast address

       LOCAL  a local address

       BROADCAST
              a broadcast address

       ANYCAST
              an anycast packet

       MULTICAST
              a multicast address

       BLACKHOLE
              a blackhole address

       UNREACHABLE
              an unreachable address

       PROHIBIT
              a prohibited address

       THROW  FIXME

       NAT    FIXME

       XRESOLVE

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

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

       --limit-iface-in
              The address type checking can be limited to the interface the packet is com-
              ing  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
       This module matches the SPIs in Authentication header of IPsec packets.

       [!] --ahspi spi[:spi]

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

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

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

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

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

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

       Example:

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

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

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

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

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

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

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

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

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

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

              arptables -A INPUT -i eth2 --h-length 6 --destination-mac  01:00:5e:00:01:02
              -j mangle --mangle-mac-d 00:zz:yy:xx:5a:27

       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 -s 192.168.0.0/16 -m comment --comment  "A  privatized  IP
              block"

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

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

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

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

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

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

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

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

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

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

       [!] --connlimit-above n
              Match if the number of existing connections is (not) 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.

       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-above 2
              -j ACCEPT

       # limit the number of parallel HTTP requests to 16 per class C  sized  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

   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 spec-
              ified, this is logically ANDed with the mark before the comparison).

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

       [!] --ctstate statelist
              statelist is a comma separated list of the connection states to match.  Pos-
              sible 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

       [!] --ctorigdstport port

       [!] --ctreplsrcport port

       [!] --ctrepldstport port
              Match against original/reply source/destination port (TCP/UDP/etc.)  or  GRE
              key.

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

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

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

       States for --ctstate:

       INVALID
              meaning that the packet is associated with no known connection

       NEW    meaning that the packet has started a new connection, or  otherwise  associ-
              ated with a connection which has not seen packets in both directions, and

       ESTABLISHED
              meaning that the packet is associated with a connection which has seen pack-
              ets in both directions,

       RELATED
              meaning that the packet is starting a new connection, but is associated with
              an existing connection, such as an FTP data transfer, or an ICMP error.

       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.

   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-sepa-
              rated list of packet types.  Packet types are:  REQUEST  RESPONSE  DATA  ACK
              DATAACK CLOSEREQ CLOSE RESET SYNC SYNCACK INVALID.

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

   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.

   ecn
       This  allows  you  to  match  the  ECN bits of the IPv4 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 ECT  (ECN-Capable  Transport).  You  have  to
              specify a number between '0' and '3'.

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

       [!] --espspi spi[:spi]

   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":

       matching on source host
              "1000 packets per second for every host in 192.168.0.0/16"

       matching on source prot
              "100 packets per second for every service of 192.168.1.1"

       matching on subnet
              "10000 packets per minute for every /28 subnet in 10.0.0.0/8"

       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 as a
              number, with an optional time quantum suffix; the default is 3/hour.

       --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.

       --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 subject to hashlimit. prefix must be between (inclusive) 0  and  32.
              Note  that  --hashlimit-srcmask  0  is basically doing the same thing as not
              specifying srcip for --hashlimit-mode, but is technically more expensive.

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

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

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

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

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

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

   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.

   icmp
       This  extension can be used if '--protocol icmp' is specified. It provides the fol-
       lowing 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

   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.

   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 (unless the '!' flag is
       used).  It can be used in combination with the LOG target to give limited  logging,
       for example.

       --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).

   multiport
       This module matches a set of source or destination ports.  Up to 15  ports  can  be
       specified.   A  port range (port:port) counts as two ports.  It can only be used in
       conjunction with -p tcp or -p udp.

       [!] --source-ports,--sports port[,port|,port:port]...
              Match if the source port is one of the given ports.  The flag --sports is  a
              convenient  alias  for  this option. Multiple ports or port ranges are sepa-
              rated 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.

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

       [!] --uid-owner username

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

       [!] --gid-owner groupname

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

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

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

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

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

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

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

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

   pkttype
       This module matches the link-layer packet type.

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

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

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

       --pol {none|ipsec}
              Matches if the packet is subject to IPsec processing.

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

       [!] --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.

       --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.

       --rateest1 name
              Name of the first rate estimator.

       --rateest2 name
              Name of the second rate estimator (if difference is to be calculated).

       --rateest-delta
              Compare difference(s) to given rate(s)

       --rateest1-bps value

       --rateest2-bps value
              Compare bytes per second.

       --rateest1-pps value

       --rateest2-pps value
              Compare packets per second.

       [!] --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.

       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 connec-
       tion was started:

       # Estimate outgoing rates

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

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

       # Mark based on available bandwidth

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

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

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

   realm
       This  matches the routing realm.  Routing realms are used in complex routing setups
       involving dynamic routing protocols like BGP.

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

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

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

       [!] --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.

       --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  nar-
              rower match requiring a certain number of hits within a specific time frame.
              The  maximum  value  for  the   hitcount   parameter   is   given   by   the
              "ip_pkt_list_tot"  parameter  of the xt_recent kernel module. Exceeding this
              value on the command line will cause the rule to be rejected.

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

       Examples:

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

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

       Steve's ipt_recent website (http://snowman.net/projects/ipt_recent/) also has  some
       examples of usage.

       /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 writ-
       ten 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.

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

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

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

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

              chunk type            available flags
              DATA                  U B E 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.

       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. As standard kernels
       do not ship this currently,  the  ipset  or  Xtables-addons  package  needs  to  be
       installed.

   socket
       This matches if an open socket can be found by doing a socket lookup on the packet.

       --transparent
              Ignore non-transparent sockets.

   state
       This module, when combined with connection tracking, allows access to  the  connec-
       tion tracking state for this packet.

       [!] --state state
              Where  state  is  a  comma separated list of the connection states to match.
              Possible states are INVALID meaning that the packet could not be  identified
              for  some  reason which includes running out of memory and ICMP errors which
              don't correspond to any  known  connection,  ESTABLISHED  meaning  that  the
              packet is associated with a connection which has seen packets in both direc-
              tions, NEW meaning that the packet has started a new connection,  or  other-
              wise  associated with a connection which has not seen packets in both direc-
              tions, and RELATED meaning that the packet is starting a new connection, but
              is  associated with an existing connection, such as an FTP data transfer, or
              an ICMP error.

   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 from 0 to 1 for a packet  to  be  randomly  matched.  It
              works only with the random mode.

       --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 from which it starts looking for any matching. If not passed,
              default is the packet size.

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

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

   tcp
       These extensions can be used if '--protocol tcp' is specified. It provides the fol-
       lowing 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.  If the first port is greater than  the  second
              one  they  will be swapped.  The flag --sport is a convenient alias for this
              option.

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

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

       [!] --syn
              Only  match  TCP  packets  with the SYN bit set and the ACK,RST and FIN bits
              cleared.  Such packets are used to request TCP  connection  initiation;  for
              example,  blocking such packets coming in an interface will prevent incoming
              TCP connections, but outgoing TCP connections will  be  unaffected.   It  is
              equivalent to --tcp-flags SYN,RST,ACK,FIN SYN.  If the "!" flag precedes the
              "--syn", the sense of the option is inverted.

       [!] --tcp-option number
              Match if TCP option set.

   tcpmss
       This matches the TCP MSS (maximum segment size) field of the TCP header.   You  can
       only  use this on TCP SYN or SYN/ACK packets, since the MSS is only negotiated dur-
       ing the TCP handshake at connection startup time.

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

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

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

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

              Only  match  during  the given time, which must be in ISO 8601 "T" notation.
              The possible time range is 1970-01-01T00:00:00 to 2038-01-19T04:17:07.

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

       --timestart hh:mm[:ss]

       --timestop hh:mm[:ss]

              Only  match during the given daytime. The possible time range is 00:00:00 to
              23:59:59. Leading zeroes are allowed (e.g.  "06:03")  and  correctly  inter-
              preted 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.).

       --utc

              Interpret  the  times  given  for  --datestart,  --datestop, --timestart and
              --timestop to be UTC.

       --localtz

              Interpret the times  given  for  --datestart,  --datestop,  --timestart  and
              --timestop to be local kernel time. (Default)

       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.)

   tos
       This module matches the 8-bit Type of  Service  field  in  the  IPv4  header  (i.e.
       including  the  "Precedence"  bits)  or the (also 8-bit) Priority field in the IPv6
       header.

       [!] --tos value[/mask]
              Matches packets with the given TOS mark value. If a mask is specified, it is
              logically ANDed with the TOS mark before the comparison.

       [!] --tos symbol
              You  can specify a symbolic name when using the tos match for IPv4. The list
              of recognized TOS names can be obtained by calling iptables with -m tos  -h.
              Note that this implies a mask of 0x3F, i.e. all but the ECN bits.

   ttl
       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 speci-
       fied values. The specification of what to extract is general enough to find data at
       given offsets from tcp headers or payloads.

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

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

              value := range | value "," range

              range := number | number ":" number

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

           location := number | location operator number

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

       The operators &, <<, >> and && mean the same as in C.  The = is really a  set  mem-
       bership  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.  Other-
       wise the result of the computation is the final value of C.

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

       Example:

              match IP packets with total length >= 256

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

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

              read bytes 0-3

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

       Example: (more realistic, hence more complicated)

              match ICMP packets with icmp type 0

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

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

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

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

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

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

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

       Example:

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

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

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

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

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

              0>>22&3C as above computes the number of bytes in the  IP  header.  @  makes
              this  the  new offset into the packet, which is the start of the TCP header.
              The length of the TCP header (again in 32 bit words) is  the  left  half  of
              byte 12 of the TCP header. The 12>>26&3C computes this length in bytes (sim-
              ilar 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 fol-
       lowing options:

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

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

   unclean
       This module takes no options, but attempts to match packets which seem malformed or
       unusual.  This is regarded as experimental.

TARGET EXTENSIONS
       iptables can use extended target modules: the following are included in  the  stan-
       dard distribution.

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

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

       Example:

              iptables -N AUDIT_DROP

              iptables -A AUDIT_DROP -j AUDIT --type drop

              iptables -A AUDIT_DROP -j DROP

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

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

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

       --set-class major:minor
              Set the major and minor class value. The values are  always  interpreted  as
              hexadecimal even if no 0x prefix is given.

   CLUSTERIP
       This  module allows you to configure a simple cluster of nodes that share a certain
       IP and MAC address without an explicit load balancer in front of them.  Connections
       are statically distributed between the nodes in this cluster.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       --save If the packet has a security marking, copy it to the connection if the  con-
              nection 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.


   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 one type of option:

       --to-destination [ipaddr][-ipaddr][:port[-port]]
              which can specify a single new destination IP address, an inclusive range of
              IP  addresses, and optionally, a port range (which is only valid if the rule
              also specifies -p tcp or -p udp).  If no port range is specified,  then  the
              destination  port will never be modified. If no IP address is specified then
              only the destination port will be modified.

              In Kernels up to 2.6.10 you can add several  --to-destination  options.  For
              those  kernels, if you specify more than one destination address, either via
              an address range or multiple --to-destination options, a simple  round-robin
              (one  after  another  in  cycle)  load  balancing  takes place between these
              addresses.  Later Kernels (>= 2.6.11-rc1) don't have the ability to  NAT  to
              multiple ranges anymore.

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

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

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

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

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

   LOG
       Turn on kernel logging of matching packets.  When this option is set  for  a  rule,
       the  Linux kernel will print some information on all matching packets (like most IP
       header fields) via the kernel log (where it can be read with dmesg or  syslogd(8)).
       This is a "non-terminating target", i.e. rule traversal continues at the next rule.
       So if you want to LOG the packets you refuse, use two separate rules with the  same
       matching criteria, first using target LOG then DROP (or REJECT).

       --log-level level
              Level of logging (numeric or see syslog.conf(5)).

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

       --log-tcp-sequence
              Log TCP sequence numbers. This is a security risk if the log is readable  by
              users.

       --log-tcp-options
              Log options from the TCP packet header.

       --log-ip-options
              Log options from the IP packet header.

       --log-uid
              Log the userid of the process which generated the packet.

   MARK
       This  target  is  used  to set the Netfilter mark value associated with the packet.
       The target can only be used in the mangle table. It can, for example,  be  used  in
       conjunction  with  routing  based  on fwmark (needs iproute2). The mark field is 32
       bits wide.

       --set-xmark value[/mask]
              Zeroes out the bits given by mask  and  XORs  value  into  the  packet  mark
              ("nfmark"). If mask is omitted, 0xFFFFFFFF is assumed.

       --set-mark value[/mask]
              Zeroes  out  the  bits  given by mask and ORs value into the packet mark. If
              mask is omitted, 0xFFFFFFFF is assumed.

       The following mnemonics are available:

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

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

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

   MASQUERADE
       This  target  is  only valid in the nat table, in the POSTROUTING chain.  It should
       only be used with dynamically assigned IP  (dialup)  connections:  if  you  have  a
       static  IP  address, you should use the SNAT target.  Masquerading is equivalent to
       specifying a mapping to the IP address of the interface the packet  is  going  out,
       but  also  has  the  effect  that connections are forgotten when the interface goes
       down.  This is the correct behavior when the next dialup is unlikely  to  have  the
       same interface address (and hence any established connections are lost anyway).  It
       takes one option:

       --to-ports port[-port]
              This specifies a range of source ports to use, overriding the  default  SNAT
              source  port-selection  heuristics  (see  above).  This is only valid if the
              rule also specifies -p tcp or -p udp.

       --random
              Randomize source port mapping If option --random is used then  port  mapping
              will be randomized (kernel >= 2.6.21).


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

   NETMAP
       This  target allows you to statically map a whole network of addresses onto another
       network of addresses.  It can only be used from rules in the nat table.

       --to address[/mask]
              Network address to map to.  The resulting address will be constructed in the
              following  way:  All  'one'  bits  in  the  mask  are filled in from the new
              'address'.  All bits that are zero in the mask are filled in from the origi-
              nal address.

   NFLOG
       This  target  provides  logging  of matching packets. When this target is set for a
       rule, the Linux kernel will pass the packet to the loaded logging  backend  to  log
       the packet. This is usually used in combination with nfnetlink_log as logging back-
       end, which will multicast the packet through a netlink socket to the specified mul-
       ticast group. One or more userspace processes may subscribe to the group to receive
       the packets. Like LOG, this is a non-terminating target, i.e. rule  traversal  con-
       tinues at the next rule.

       --nflog-group nlgroup
              The  netlink  group  (1  - 2^32-1) to which packets are (only applicable for
              nfnetlink_log). The default value is 0.

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

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

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

   NFQUEUE
       This target is an extension of the QUEUE target. As opposed to QUEUE, it allows you
       to put a packet into any specific queue, identified by its 16-bit queue number.  It
       can only be used with Kernel versions  2.6.14  or  later,  since  it  requires  the
       nfnetlink_queue kernel support. The queue-balance option was added in Linux 2.6.31,
       queue-bypass in 2.6.39.

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


       --queue-balance value:value
              This  specifies  a  range of queues to use. Packets are then balanced across
              the given queues.  This is useful  for  multicore  systems:  start  multiple
              instances  of  the  userspace  program  on  queues  x,  x+1,  .. x+n and use
              "--queue-balance x:x+n".  Packets belonging to the same connection  are  put
              into the same nfqueue.


       --queue-bypass
              By  default,  if  no  userspace program is listening on an NFQUEUE, then all
              packets that are to be queued are dropped.  When this option  is  used,  the
              NFQUEUE  rule  is  silently bypassed instead. The packet will move on to the
              next rule.

   NOTRACK
       This target disables connection tracking for all packets matching that rule.

       It can only be used in the raw table.

   RATEEST
       The RATEEST target collects statistics, performs rate  estimation  calculation  and
       saves the results for later evaluation using the rateest match.

       --rateest-name name
              Count  matched  packets  into  the pool referred to by name, which is freely
              choosable.

       --rateest-interval amount{s|ms|us}
              Rate measurement interval, in seconds, milliseconds or microseconds.

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

   REDIRECT
       This target is only valid in the nat table, in the PREROUTING  and  OUTPUT  chains,
       and  user-defined chains which are only called from those chains.  It redirects the
       packet to the machine itself by changing the destination IP to the primary  address
       of  the  incoming  interface (locally-generated packets are mapped to the 127.0.0.1
       address).

       --to-ports port[-port]
              This specifies a destination port or range of ports to  use:  without  this,
              the  destination port is never altered.  This is only valid if the rule also
              specifies -p tcp or -p udp.

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


   REJECT
       This is used to send back an error packet in response to the matched packet: other-
       wise it is equivalent to DROP so it is a terminating TARGET, ending rule traversal.
       This target is only valid in the INPUT, FORWARD and OUTPUT chains, and user-defined
       chains which are only called from those chains.  The following option controls  the
       nature of the error packet returned:

       --reject-with type
              The   type   given   can   be  icmp-net-unreachable,  icmp-host-unreachable,
              icmp-port-unreachable,     icmp-proto-unreachable,      icmp-net-prohibited,
              icmp-host-prohibited or icmp-admin-prohibited (*) which return the appropri-
              ate ICMP error  message  (port-unreachable  is  the  default).   The  option
              tcp-reset  can  be  used  on  rules  which only match the TCP protocol: this
              causes a TCP RST packet to be sent back.  This is mainly useful for blocking
              ident  (113/tcp)  probes  which frequently occur when sending mail to broken
              mail hosts (which won't accept your mail otherwise).

       (*) Using icmp-admin-prohibited with kernels that do not support it will result  in
       a plain DROP instead of REJECT

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

       N.B.: The DNAT target's --persistent option replaced the SAME target.

       --to ipaddr[-ipaddr]
              Addresses  to  map  source  to. May be specified more than once for multiple
              ranges.

       --nodst
              Don't use the destination-ip in the  calculations  when  selecting  the  new
              source-ip

       --random
              Port mapping will be forcibly randomized to avoid attacks based on port pre-
              diction (kernel >= 2.6.21).

   SECMARK
       This is used to set the security mark value associated with the packet for  use  by
       security  subsystems  such  as  SELinux.  It is only valid in the mangle table. The
       mark is 32 bits wide.

       --selctx security_context

   SET
       This modules adds and/or deletes entries from IP  sets  which  can  be  defined  by
       ipset(8).

       --add-set setname flag[,flag...]
              add the address(es)/port(s) of the packet to the sets

       --del-set setname flag[,flag...]
              delete the address(es)/port(s) of the packet from the sets

              where  flags are src and/or dst specifications and there can be no more than
              six of them.

       Use of -j SET requires that ipset kernel support is provided. As  standard  kernels
       do  not  ship  this  currently,  the  ipset  or  Xtables-addons package needs to be
       installed.

   SNAT
       This target is only valid in the nat table, in the POSTROUTING chain.  It specifies
       that the source address of the packet should be modified (and all future packets in
       this connection will also be mangled), and rules should cease being  examined.   It
       takes one type of option:

       --to-source ipaddr[-ipaddr][:port[-port]]
              which  can  specify a single new source IP address, an inclusive range of IP
              addresses, and optionally, a port range (which is only  valid  if  the  rule
              also  specifies  -p  tcp  or  -p  udp).  If no port range is specified, then
              source ports below 512 will be  mapped  to  other  ports  below  512:  those
              between 512 and 1023 inclusive will be mapped to ports below 1024, and other
              ports will be mapped to 1024 or above. Where possible,  no  port  alteration
              will

              In  Kernels up to 2.6.10, you can add several --to-source options. For those
              kernels, if you specify more than one source address, either via an  address
              range  or  multiple  --to-source  options,  a  simple round-robin (one after
              another in cycle) takes place between these addresses.   Later  Kernels  (>=
              2.6.11-rc1) don't have the ability to NAT to multiple ranges anymore.

       --random
              If  option  --random is used then port mapping will be randomized (kernel >=
              2.6.21).

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

   TCPMSS
       This target allows to alter the MSS value of TCP SYN packets, to control the  maxi-
       mum  size for that connection (usually limiting it to your outgoing interface's MTU
       minus 40 for IPv4 or 60 for IPv6, respectively).  Of course, it can only be used in
       conjunction with -p tcp.  It is only valid in the mangle table.
       This  target  is  used to overcome criminally braindead ISPs or servers which block
       "ICMP Fragmentation Needed" or "ICMPv6 Packet Too Big" packets.   The  symptoms  of
       this  problem  are  that everything works fine from your Linux firewall/router, but
       machines behind it can never exchange large packets:
        1) Web browsers connect, then hang with no data received.
        2) Small mail works fine, but large emails hang.
        3) ssh works fine, but scp hangs after initial handshaking.
       Workaround: activate this option and add a  rule  to  your  firewall  configuration
       like:

               iptables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN
                           -j TCPMSS --clamp-mss-to-pmtu

       --set-mss value
              Explicitly  sets  MSS option to specified value. If the MSS of the packet is
              already lower than value, it  will  not  be  increased  (from  Linux  2.6.25
              onwards) to avoid more problems with hosts relying on a proper MSS.

       --clamp-mss-to-pmtu
              Automatically  clamp  MSS  value  to (path_MTU - 40 for IPv4; -60 for IPv6).
              This may not function as desired where asymmetric routes with differing path
              MTU  exist -- the kernel uses the path MTU which it would use to send packets
              from itself to the source and  destination  IP  addresses.  Prior  to  Linux
              2.6.25,  only  the  path MTU to the destination IP address was considered by
              this option; subsequent kernels also consider the path MTU to the source  IP
              address.

       These options are mutually exclusive.

   TCPOPTSTRIP
       This target will strip TCP options off a TCP packet. (It will actually replace them
       by NO-OPs.) As such, you will need to add the -p tcp parameters.

       --strip-options option[,option...]
              Strip the given option(s). The options may be specified by TCP option number
              or by symbolic name. The list of recognized options can be obtained by call-
              ing iptables with -j TCPOPTSTRIP -h.

   TOS
       This module sets the Type of Service  field  in  the  IPv4  header  (including  the
       "precedence"  bits)  or the Priority field in the IPv6 header. Note that TOS shares
       the same bits as DSCP and ECN. The TOS target is only valid in the mangle table.

       --set-tos value[/mask]
              Zeroes out the bits given by mask  and  XORs  value  into  the  TOS/Priority
              field. If mask is omitted, 0xFF is assumed.

       --set-tos symbol
              You  can  specify  a  symbolic  name  when using the TOS target for IPv4. It
              implies a mask of 0xFF. The list of recognized TOS names can be obtained  by
              calling iptables with -j TOS -h.

       The following mnemonics are available:

       --and-tos bits
              Binary AND the TOS value with bits. (Mnemonic for --set-tos 0/invbits, where
              invbits is the binary negation of bits.)

       --or-tos bits
              Binary OR the TOS value with bits. (Mnemonic for --set-tos bits/bits.)

       --xor-tos bits
              Binary XOR the TOS value with bits. (Mnemonic for --set-tos bits/0.)

   TPROXY
       This target is only valid in the mangle table, in the PREROUTING  chain  and  user-
       defined  chains which are only called from this chain. It redirects the packet to a
       local socket without changing the packet header in any way. It can also change  the
       mark  value  which  can  then  be  used  in advanced routing rules.  It takes three
       options:

       --on-port port
              This specifies a destination port to use. It is a required option,  0  means
              the  new destination port is the same as the original. This is only valid if
              the rule also specifies -p tcp or -p udp.

       --on-ip address
              This specifies a destination address to use. By default the address  is  the
              IP  address  of  the incoming interface. This is only valid if the rule also
              specifies -p tcp or -p udp.

       --tproxy-mark value[/mask]
              Marks packets with the given value/mask. The fwmark value set  here  can  be
              used by advanced routing. (Required for transparent proxying to work: other-
              wise these packets will get forwarded, which is probably not what you want.)

   TRACE
       This  target  marks  packes  so that the kernel will log every rule which match the
       packets as those traverse the tables, chains, rules. (The ipt_LOG or ip6t_LOG  mod-
       ule  is  required  for the logging.) The packets are logged with the string prefix:
       "TRACE: tablename:chainname:type:rulenum " where type can be "rule" for plain rule,
       "return"  for implicit rule at the end of a user defined chain and "policy" for the
       policy of the built in chains.
       It can only be used in the raw table.

   TTL
       This is used to modify the IPv4 TTL header field.  The  TTL  field  determines  how
       many hops (routers) a packet can traverse until it's time to live is exceeded.

       Setting  or  incrementing  the  TTL  field can potentially be very dangerous, so it
       should be avoided at any cost.

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

       --ttl-set value
              Set the TTL value to 'value'.

       --ttl-dec value
              Decrement the TTL value 'value' times.

       --ttl-inc value
              Increment the TTL value 'value' times.

   ULOG
       This  target  provides  userspace logging of matching packets.  When this target is
       set for a rule, the Linux kernel will  multicast  this  packet  through  a  netlink
       socket.  One  or  more  userspace processes may then subscribe to various multicast
       groups and receive the packets.  Like LOG, this is a "non-terminating target", i.e.
       rule traversal continues at the next rule.

       --ulog-nlgroup nlgroup
              This  specifies  the  netlink  group  (1-32)  to  which  the packet is sent.
              Default value is 1.

       --ulog-prefix prefix
              Prefix log messages with the specified prefix; up to 32 characters long, and
              useful for distinguishing messages in the logs.

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

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

DIAGNOSTICS
       Various  error messages are printed to standard error.  The exit code is 0 for cor-
       rect functioning.  Errors which appear to be caused by invalid  or  abused  command
       line  parameters cause an exit code of 2, and other errors cause an exit code of 1.

BUGS
       Bugs?  What's this? ;-) Well, you might want to have a look at http://bugzilla.net-
       filter.org/

COMPATIBILITY WITH IPCHAINS
       This iptables is very similar to ipchains by Rusty Russell.  The main difference is
       that the chains INPUT and OUTPUT are only traversed for  packets  coming  into  the
       local  host  and  originating from the local host respectively.  Hence every packet
       only passes through one  of  the  three  chains  (except  loopback  traffic,  which
       involves  both  INPUT  and OUTPUT chains); previously a forwarded packet would pass
       through all three.

       The other main difference is that -i refers to the input interface;  -o  refers  to
       the  output  interface,  and  both  are  available for packets entering the FORWARD
       chain.

       The various forms of NAT have been separated out; iptables is a pure packet  filter
       when  using  the  default  'filter'  table,  with optional extension modules.  This
       should simplify much of the previous confusion over  the  combination  of  IP  mas-
       querading  and packet filtering seen previously.  So the following options are han-
       dled differently:
        -j MASQ
        -M -S
        -M -L
       There are several other changes in iptables.

SEE ALSO
       iptables-save(8),     iptables-restore(8),     ip6tables(8),     ip6tables-save(8),
       ip6tables-restore(8), libipq(3).

       The  packet-filtering-HOWTO  details  iptables usage for packet filtering, the NAT-
       HOWTO details NAT, the netfilter-extensions-HOWTO details the extensions  that  are
       not  in the standard distribution, and the netfilter-hacking-HOWTO details the net-
       filter internals.
       See http://www.netfilter.org/.

AUTHORS
       Rusty Russell originally wrote iptables, in early consultation with  Michael  Neul-
       ing.

       Marc Boucher made Rusty abandon ipnatctl by lobbying for a generic packet selection
       framework in iptables, then wrote the mangle  table,  the  owner  match,  the  mark
       stuff, and ran around doing cool stuff everywhere.

       James Morris wrote the TOS target, and tos match.

       Jozsef Kadlecsik wrote the REJECT target.

       Harald  Welte  wrote  the  ULOG and NFQUEUE target, the new libiptc, as well as the
       TTL, DSCP, ECN matches and targets.

       The Netfilter Core Team is:  Marc  Boucher,  Martin  Josefsson,  Yasuyuki  Kozakai,
       Jozsef  Kadlecsik,  Patrick  McHardy, James Morris, Pablo Neira Ayuso, Harald Welte
       and Rusty Russell.

       Man page originally written by Herve Eychenne <rv AT wallfire.org>.



iptables 1.4.7                                                     IPTABLES(8)

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