iptables <root
IPTABLES(8)                               iptables 1.6.0                              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 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 (call‐
       ing)  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 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-generated packets).

              nat:
                  This table is consulted when a packet that creates a new connection is  encoun‐
                  tered.   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 rout‐
                  ing) and OUTPUT (for altering locally-generated packets before routing).  Since
                  kernel 2.4.18, three other built-in chains are also supported: INPUT (for pack‐
                  ets 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 pro‐
                  cesses)

              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 dif‐
       ferent 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 differenti‐
       ate 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  (fil‐
              ter 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 built-in (non-user-defined) chain to the given target.  The
              policy target must be either ACCEPT or DROP.

       -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 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
              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, representing one of these protocols or a  dif‐
              ferent  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.

       [!] -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.  Mul‐
              tiple 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 omit‐
              ted, any interface name will match.

       [!] -f, --fragment
              This means that the rule only refers to second and further IPv4 fragments of  frag‐
              mented  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  mul‐
              tipliers  respectively (but see the -x flag to change this).  For appending, inser‐
              tion, 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  run‐
              ning  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.

       -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,  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 mod‐
              ules (targets, match extensions, etc).

MATCH AND TARGET EXTENSIONS
       iptables can use extended packet matching and target modules.  A list of these  is  avail‐
       able 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  parame‐
       ters 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.netfil‐
       ter.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  out‐
       put 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 filter‐
       ing seen previously.  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), iptables-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 netfilter-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 frame‐
       work  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: Jozsef Kadlecsik, Patrick McHardy, Pablo Neira Ayuso, Eric
       Leblond and Florian Westphal. Emeritus Core Team members are: Marc Boucher, Martin Josefs‐
       son, Yasuyuki Kozakai, James Morris, Harald Welte and Rusty Russell.

       Man page originally written by Herve Eychenne .

VERSION
       This manual page applies to iptables/ip6tables 1.6.0.

iptables 1.6.0                                                                        IPTABLES(8)

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