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iptables



SYNOPSIS

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

       ip6tables [-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 and ip6tables are used to set up, maintain,  and  inspect  the
       tables  of IPv4 and IPv6 packet filter rules in the Linux kernel.  Sev-
       eral 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 specifies 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 ta-
       ble.


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 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, one of the targets
       described in iptables-extensions(8),  or  one  of  the  special  values
       ACCEPT, DROP or RETURN.

       ACCEPT  means to let the packet through.  DROP means to drop the packet
       on the floor.  RETURN means stop traversing this chain  and  resume  at
       the  next rule in the previous (calling) chain.  If the end of a built-

              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-generated 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 rout-
                  ing), and POSTROUTING (for  altering  packets  as  they  are
                  about  to go out).  IPv6 NAT support is available since ker-
                  nel 3.7.

              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  packets before routing).  Since
                  kernel 2.4.18, three other built-in  chains  are  also  sup-
                  ported: INPUT (for packets coming into the box itself), FOR-
                  WARD (for altering packets being routed  through  the  box),
                  and  POSTROUTING  (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_conntrack, or any other IP tables.
                  It provides the following built-in chains:  PREROUTING  (for
                  packets  arriving  via  any  network  interface) OUTPUT (for
                  packets generated by local processes)

              security:
                  This table is used for Mandatory Access Control  (MAC)  net-
                  working  rules,  such  as  those  enabled by the SECMARK and
                  CONNSECMARK targets.  Mandatory  Access  Control  is  imple-
                  mented by Linux Security Modules such as SELinux.  The secu-
                  rity table is called after the filter  table,  allowing  any
                  Discretionary Access Control (DAC) rules in the filter table
                  to take effect before MAC rules.  This  table  provides  the
                  following  built-in  chains:  INPUT (for packets coming into
                  the box  itself),  OUTPUT  (for  altering  locally-generated
                  packets  before  routing), and FORWARD (for altering packets
                  being routed through the box).


OPTIONS

              tion.

       -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 des-
              tination  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 suppressed 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 ipt-
              ables 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.

              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  sec-
              tion  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 targets.

       -E, --rename-chain old-chain new-chain
              Rename the user specified chain to the user supplied name.  This
              is cosmetic, 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).

       -4, --ipv4
              This option has no effect in iptables and iptables-restore.   If
              a  rule  using  the  -4  option is inserted with (and only with)
              ip6tables-restore, it will be silently ignored. Any  other  uses
              will  throw  an  error.  This option allows to put both IPv4 and
              IPv6 rules in a single rule file for  use  with  both  iptables-
              restore and ip6tables-restore.

       -6, --ipv6
              If  a  rule using the -6 option is inserted with (and only with)
              iptables-restore, it will be silently ignored.  Any  other  uses
              will  throw  an  error.  This option allows to put both IPv4 and
              IPv6 rules in a single rule file for  use  with  both  iptables-
              restore  and  ip6tables-restore.   This  option has no effect in
              ip6tables and ip6tables-restore.

       [!] -p, --protocol protocol
              The protocol of the rule or of the packet to check.  The  speci-
              fied protocol can be one of tcp, udp, udplite, icmp, icmpv6,esp,
              ah, sctp, mh or the special  keyword  "all",  or  it  can  be  a
              numeric  value, representing one of these protocols or a differ-
              ent 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. "all" will match with  all  protocols
              and is taken as default when this option is omitted.  Note that,
              in ip6tables, IPv6 extension headers except esp are not allowed.
              esp  and  ipv6-nonext  can be used with Kernel version 2.6.11 or
              later.  The number zero is equivalent to all, which  means  that
              you  cannot test the protocol field for the value 0 directly. To
              match on a HBH header, even if it were the last, you cannot  use
              -p 0, but always need -m hbh.
              -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.

       -m, --match match
              Specifies  a  match  to  use,  that is, an extension module that
              tests for a specific property. The set of matches  make  up  the
              condition under which a target is invoked. Matches are evaluated
              first to last as specified on  the  command  line  and  work  in
              short-circuit fashion, i.e. if one extension yields false, eval-
              uation will stop.

       -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 incremented.

       -g, --goto chain
              This  specifies  that  the  processing should continue in a user
              specified chain. Unlike the --jump option return will  not  con-
              tinue  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  IPv4
              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  packet  and  byte counters are also listed, with the suffix
              'K', 'M' or 'G' for 1000, 1,000,000 and 1,000,000,000  multipli-
              ers  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. -v may
              be specified multiple times to possibly emit more detailed debug
              statements.

       -w, --wait [seconds]
              Wait for the xtables lock.  To prevent multiple instances of the
              program from running concurrently, an attempt will  be  made  to
              obtain  an  exclusive  lock  at launch.  By default, the program
              will exit if the lock cannot be obtained.  This option will make
              the  program  wait  (indefinitely or for optional seconds) until
              the exclusive lock can be obtained.

       -W, --wait-interval microseconds
              Interval to wait per each iteration.  When running latency  sen-
              sitive  applications,  waiting for the xtables lock for extended
              durations may not be acceptable.  This  option  will  make  each
              iteration  take the amount of time specified. The default inter-
              val is 1 second. This option only works with -w.

       -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  appli-
              cable).

       -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, corresponding to that rule's position in the chain.

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


MATCH AND TARGET EXTENSIONS

       iptables can use extended packet matching and target modules.   A  list
       of these is available in the iptables-extensions(8) manpage.


DIAGNOSTICS

       Various error messages are printed to standard error.  The exit code is
       0 for correct 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.
       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 masquerading and packet filtering seen pre-
       viously.  So the following options are handled differently:
        -j MASQ
        -M -S
        -M -L
       There are several other changes in iptables.


SEE ALSO

       iptables-apply(8),   iptables-save(8),    iptables-restore(8),    ipta-
       bles-extensions(8),

       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 netfil-
       ter-hacking-HOWTO details the netfilter internals.
       See http://www.netfilter.org/.


AUTHORS

       Rusty Russell originally wrote iptables,  in  early  consultation  with
       Michael Neuling.

       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 every-
       where.

       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@wallfire.org>.


VERSION

       This manual page applies to iptables/ip6tables @PACKAGE_AND_VERSION@.


iptables 1.4.21 IPTABLES(8)



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