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IPTABLES(8)                     iptables 1.4.21                    IPTABLES(8)



NAME
       iptables/ip6tables -- administration tool for IPv4/IPv6 packet filtering and NAT

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.  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 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 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 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 spe-
       cial 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-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 five independent tables (which tables are present at any time depends on the kernel config-
       uration 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-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 routing), and POSTROUTING (for altering packets as they are about
                  to go out).  IPv6 NAT support is available since kernel 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), FORWARD (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) networking rules, such as those enabled by the
                  SECMARK and CONNSECMARK targets.  Mandatory Access Control is implemented by Linux Security  Modules
                  such  as  SELinux.   The security 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
       The options that are recognized by iptables and ip6tables can be divided into several different groups.

   COMMANDS
       These  options  specify  the  desired  action to perform. Only one of them can be specified 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 iptables 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 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 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 references 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 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 specified 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, rep-
              resenting  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.
              "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 Ker-
              nel 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.

       [!] -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 an ipv4 network mask (for iptables) or a plain number, specifying  the
              number  of  1's  at  the  left  side of the network mask.  Thus, an iptables 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.

       -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,
              evaluation 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 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 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 "!" argument precedes the "-f" flag, the rule
              will only match head fragments, or unfragmented packets. This option is IPv4 specific, it is not  avail-
              able in ip6tables.

       -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. -v may be specified multiple times to possibly emit more detailed debug statements.

       -w, --wait
              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  until  the  exclusive  lock  can  be
              obtained.

       -n, --numeric
              Numeric  output.  IP addresses and port numbers will be printed in numeric format.  By default, the pro-
              gram 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, corresponding to that  rule's  posi-
              tion 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  ipta-
       bles-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.

BUGS
       Bugs?  What's this? ;-) Well, you might want to have a look at http://bugzilla.netfilter.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  respec-
       tively.   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 'fil-
       ter' table, with optional extension modules.  This should simplify much of the previous confusion over the com-
       bination of IP masquerading and packet filtering seen previously.  So the following options are handled differ-
       ently:
        -j MASQ
        -M -S
        -M -L
       There are several other changes in iptables.

SEE ALSO
       iptables-apply(8), iptables-save(8), iptables-restore(8), iptables-extensions(8),

       The packet-filtering-HOWTO details iptables usage for packet filtering, the NAT-HOWTO details NAT, the  netfil-
       ter-extensions-HOWTO  details the extensions that are not in the standard distribution, and the netfilter-hack-
       ing-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 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 tar-
       gets.

       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 <rvATwallfire.org>.

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



iptables 1.4.21                                                    IPTABLES(8)